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Agro-industrial wastes as sources of bioactive compounds for food and fermentation industries

Resíduos agroindustriais como fontes de compostos bioativos para as indústrias de alimentos e de fermentação

ABSTRACT:

Agro-industrial wastes are of great interest because they are important natural sources of bioactive compounds and can generate value-added byproducts. Recent studies have shown that byproducts generated by the food processing industry are rich in bioactive compounds, such as phenolic compounds, organic acids, and carotenoids, among others. The growing interest in replacing synthetic antioxidant and antimicrobial compounds with natural ones has stimulated a search for these bioactive compounds from plant sources, especially from fruit-processing wastes. The study aims to project the agro-industrial wastes as potential natural sources of antioxidants and antimicrobials and the feasible technological applications in food and fermentation industries, especially the bioethanol industry.

Key words:
phenolic compounds; antioxidant activity; antimicrobial activity; agro-industrial waste

RESUMO:

Resíduos agroindustriais são de grande interesse por serem importantes fontes naturais de compostos bioativos e assim gerar subprodutos de valor agregado. Estudos recentes mostraram que o processamento de alimentos gera subprodutos ricos em compostos bioativos tais como compostos fenólicos, ácidos orgânicos e carotenóides, entre outros. O crescente interesse em substituir compostos antioxidantes e antimicrobianos sintéticos por naturais tem estimulado a procura por esses compostos bioativos a partir de fontes vegetais, especialmente de resíduos de processamento de frutas. O objetivo desta revisão é destacar os resíduos agroindustriais como potenciais fontes naturais de antioxidantes e antimicrobianos assim como as possíveis aplicações tecnológicas nas indústrias de alimentos e de fermentação, especialmente a indústria do bioetanol.

Palavras-chave:
compostos fenólicos; atividade antioxidante; atividade antimicrobiana; resíduo agroindustrial

INTRODUCTION:

The production of primary and secondary metabolites is a characteristic property of living organisms that could be utilized for pharmacological and technological purposes. These chemical compounds are called “natural products.” Besides their pharmaceutical actions on humans, they also possess biological activity. Natural antimicrobials are secondary metabolites, which possess antimicrobial activity, and are extracted from different sources such as plants, animals, and microorganisms. Besides this, these secondary metabolites also contain the property of antioxidants, and therefore, are considered a prospective option for food preservation in contrast to synthetic preservatives (ARSHAD & BATOOL, 2017ARSHAD, M.S.; BATOOL, S.A. Natural antimicrobials, their sources and food safety. In: KARUNARATNE, D.N. Food additives. London: IntechOpen, 2017. p.87-102. Available from: <Available from: http://dx.doi.org/10.5772/intechopen.70197 >. Accessed: Oct. 31, 2019. doi: 10.5772/intechopen.70197.
http://dx.doi.org/10.5772/intechopen.701...
).

The valuable sources of these natural products with antimicrobial and antioxidant properties are the residues resulting from the agro-industrial processes, which may contribute to a significant pollution problem in lack of proper management. With no viable alternatives, they are often discarded directly into the surrounding environment. Apart from a considerable loss of valuable materials, the large amount of wastes produced by agro-industries also raises serious management problems, both from economic and environmental points of view (MIRABELLA et al., 2014MIRABELLA, N. et al. Current options for the valorization of food manufacturing waste: a review. Journal of Cleaner Production, v.65, p.28-41, 2014. Available from: <Available from: https://doi.org/10.1016/j.jclepro.2013.10.051 >. Accessed: Oct. 09, 2019. doi: 10.1016/j.jclepro.2013.10.051.
https://doi.org/10.1016/j.jclepro.2013.1...
). Many of these wastes, however, can potentially be used in other production systems, such as the production of natural food additives. Research on the composition and characterization of the generated wastes has been carried out with the objective that the waste residues can be put to value-added applications with possible technology (VIEIRA et al., 2009VIEIRA, P.A.F. et al. Caracterização química do resíduo do processamento agroindustrial da manga (Mangifera indica L.) var. Ubá. Alimentos e Nutrição, v.2, n.4, p.617-623, 2009. Available from: <Available from: http://serv-bib.fcfar.unesp.br/seer/index.php/alimentos/article/viewFile/1240/867&gt >. Accessed: Feb. 14, 2020.
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). Sustainable applications of the waste products (as alternatively called “byproducts”) include production of organic fertilizers, animal feeds, ethanol, enzymes, essential oils, and additives in various technological processes (FERRARI et al., 2004FERRARI, R.A. et al. Caracterização de subprodutos da industrialização do maracujá - aproveitamento das sementes. Revista Brasileira de Fruticultura , v.26, p.101-102-26, 2004. Available from: <Available from: http://dx.doi.org/10.1590/S0100-29452004000100027 >. Accessed: Oct. 09, 2019. doi: 10.1590/S0100-29452004000100027.
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). It is also observed that plant foods and their food processing byproducts are the potential source of phenolic bioactive compounds that have valuable health benefits (CAMARGO et al., 2018CAMARGO, A.C. et al. Opinion on the hurdles and potential health benefits in value-added use of plant food processing by-products as sources of phenolic compounds. International Journal of Molecular Sciences, v.19, n.11, 3498, 2018. Available from: <Available from: http://doi.org/10.3390/ijms19113498 >. Accessed: Oct. 31, 2019. doi: 10.3390/ijms19113498.
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).

Initially, interest was focused on the study of substances possessing antioxidant and antimicrobial activities that emerged from the search for new additives, which could be used in place of the synthetic ones already being used in technological processes. Synthetic additives alter enzymes and lipids in humans and animals and have a potential carcinogenic effect (ROCHA et al., 2007ROCHA, F.D. et al. Produtos naturais de algas marinhas e seu potencial antioxidante. Revista Brasileira de Farmacognisia, v.17, p.631-639, 2007. Available from: <Available from: http://dx.doi.org/10.1590/S0102-695X2007000400024 >. Accessed: Jul. 25, 2019. doi: 10.1590/S0102-695X2007000400024.
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). Thus, recent research has been conducted to replace chemical additives by non-synthetic ones that can be produced from agro-industrial wastes. The growing interest for natural antioxidant and antimicrobial compounds has led to research on plants as a source of such bioactive compounds (MOURE et al., 2001MOURE, A. et al. Natural antioxidants from residual sources. Food Chemistry, v.72, p.145-171, 2001. Available from: <Available from: https://doi.org/10.1016/S0308-8146(00)00223-5 >. Accessed: Oct. 01, 2019. doi: 10.1016/S0308-8146(00)00223-5.
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).

In this review, we aimed to project the agro-industrial wastes as potential natural sources of antioxidants and antimicrobials and explored their possible technological applications in the food and fermentation industry.

Bioactive compounds: application as antioxidants and antimicrobials

Bioactive compounds are defined as substances with biological activity and are able to modulate metabolic processes resulting in the promotion of better health conditions. The benefits exhibited by these compounds include antioxidant activity, inhibition or induction of enzymes, inhibition of receptor activities, and induction and inhibition of gene expression (CORREIA et al., 2012CORREIA, R.T. et al. Bioactive compounds and phenolic-linked functionality of powdered tropical fruit residues. Food Science and Technology International, v.18, n.6, p.539-547, 2012. Available from: <Available from: https://doi.org/10.1177/1082013211433077 >. Accessed: Oct. 31, 2019. doi: 10.1177/1082013211433077.
https://doi.org/10.1177/1082013211433077...
). Fruits, vegetables, and whole grains are good sources of bioactive compounds, which include a heterogeneous class of compounds mainly phenolics, carotenoids, tocopherols, phytosterols, and organosulfur compounds (CARBONELL-CAPELLA et al., 2013CARBONELL-CAPELLA, J.M. et al. Quality parameters, bioactive compounds and their correlation with antioxidant capacity of commercial fruit-based baby foods. Food Science and Technology International, v.20, n.7, p.479-487, 2013. Available from: <Available from: https://doi.org/10.1177/1082013213492523 >. Accessed: Oct. 03, 2019. doi: 10.1177/1082013213492523.
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; SERRANO-LEÓN et al., 2018SERRANO-LEÓN, D. et al. Chitosan active films containing agro-industrial residue extracts for shelf life extension of chicken restructured product. Food Research International, v.108, p.93-100, 2018. Available from: <Available from: https://doi.org/10.1016/j.foodres.2018.03.031 >. Accessed: Oct. 12, 2019. doi: 10.1016/j.foodres.2018.03.031.
https://doi.org/10.1016/j.foodres.2018.0...
) (Figure 1).

Figure 1
The main classes of bioactive compounds.

The secondary metabolites produced by plants such as flavonoids, thiosulfinates, glucosinolates, organic acids, and saponins are antimicrobial agents used against a great variety of microorganisms. The most important group of compounds with antimicrobial activity is phenolics, which include terpenes, aliphatic alcohols, aldehydes, ketones, acids, anthocyanins, and isoflavonoids (SPANOS & WROLSTAD, 1992SPANOS, G.A.; WROLSTAD, R.E. Phenolic of apple, pear, and white grape juices and their changes with processing and storage - a review. Journal of Agricultural and Food Chemistry, v.40, p.1478-1487, 1992. Available from: <Available from: http://dx.doi.org/10.1021/jf00021a002 >. Accessed: Sep. 30, 2019. doi: 10.1021/jf00021a002.
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; BURT, 2004BURT, S. Essential oils: their antibacterial properties and potential applications in foods - a review. International Journal of Food Microbiology, v.94, n.3, p.223-53, 2004. Available from: <Available from: http://doi.org/10.1016/j.ijfoodmicro.2004.03.022 >. Accessed: Oct. 31 2019. doi: 10.1016/j.ijfoodmicro.2004.03.022.
http://doi.org/10.1016/j.ijfoodmicro.200...
; ARSHAD & BATOOL, 2017ARSHAD, M.S.; BATOOL, S.A. Natural antimicrobials, their sources and food safety. In: KARUNARATNE, D.N. Food additives. London: IntechOpen, 2017. p.87-102. Available from: <Available from: http://dx.doi.org/10.5772/intechopen.70197 >. Accessed: Oct. 31, 2019. doi: 10.5772/intechopen.70197.
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). Phenolic compounds are widely distributed in nature and are the most abundant secondary metabolites reported in plants (MAXCHEIX et al., 1990MAXCHEIX, J.J. et al. The main phenolic of fruits. In: _______. Fruit phenolics. Boca Raton : CRC Press, 1990. p.1-98.). The primary action of phenolics is related to the plant defense against biotic and abiotic stresses, pests, and pathogens (ATANASOVA-PENICHON et al., 2016ATANASOVA-PENICHON, V. et al. Antioxidant secondary metabolites in cereals: potential involvement in resistance to Fusarium and mycotoxin accumulation. Frontiers in Microbiology, v.7, 566, 2016. Available from: <Available from: https://doi.org/10.3389/fmicb.2016.00566 >. Accessed: Oct. 31, 2019. doi: 10.3389/fmicb.2016.00566.
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https://doi.org/10.1016/j.cofs.2016.02.0...
; CAMARGO et al., 2018CAMARGO, A.C. et al. Opinion on the hurdles and potential health benefits in value-added use of plant food processing by-products as sources of phenolic compounds. International Journal of Molecular Sciences, v.19, n.11, 3498, 2018. Available from: <Available from: http://doi.org/10.3390/ijms19113498 >. Accessed: Oct. 31, 2019. doi: 10.3390/ijms19113498.
http://doi.org/10.3390/ijms19113498...
).

Flavonoids are a large group of phenolic compounds reported in various fruits, vegetables, roots, etc. (MIDDLETON & KANDASWAMI, 1994MIDDLETON, E.; KANDASWAMI, C. Potential health-promoting properties of citrus flavonoids. Food Technology, v.48, p.115-119, 1994.; HOLLMAN & KATAN, 1997HOLLMAN, P.C.H., KATAN, M.B. Absorption, metabolism and health effects of dietary flavonoids in man. Biomedicine and Pharmacotherapy, v.51, p.305-310, 1997. Available from: <Available from: https://doi.org/10.1016/S0753-3322(97)88045-6 >. Accessed: Oct. 09, 2019. doi: 10.1016/S0753-3322(97)88045--6.
https://doi.org/10.1016/S0753-3322(97)88...
). The monomeric units of these compounds consist of two substituted benzene rings (A and B) and, in most cases, a heterocyclic ring (C) (HOLLMAN et al., 1996HOLLMAN, P.C.H. et al. Analysis and health effects of flavonoids. Food Chemistry, v.57, p.43-46, 1996. Available from: <Available from: https://doi.org/10.1016/0308-8146(96)00065-9 >. Accessed: Oct. 01, 2019. doi: 10.1016/0308-8146(96)00065-9.
https://doi.org/10.1016/0308-8146(96)000...
). More than 4,000 compounds of flavonoids have been identified (JAYAPRAKASHA et al., 2003JAYAPRAKASHA, G.K. et al. Antibacterial and antioxidant activities of grape (Vitis vinifera) seed extracts. Food Research International, v.36, n. 2, p.117-122, 2003. Available from: <Available from: https://doi.org/10.1016/S0963-9969(02)00116-3 >. Accessed: Sep. 09, 2019. doi: 10.1016/S0963-9969(02)00116-3.
https://doi.org/10.1016/S0963-9969(02)00...
). The different substitutions in rings A, B, and C, as well as the different ways in which ring B is bound to ring C, allow the formation of several types of flavonoids with different biological characteristics. Flavonoids consist of different subclasses as illustrated in Figure 1: flavanones, flavonols, flavones, flavanols (or flavan-3-ols), isoflavones and anthocyanidins (HE & GIUSTI, 2010HE, J.; GIUSTI, M.M. Anthocyanins: natural colorants with health-promoting properties. Annual Review of Food Science and Technology, v.1, p.163-187, 2010. Available from: <Available from: https://doi.org/10.1146/annurev.food.080708.100754 >. Accessed: Jan. 05, 2020. doi: 10.1146/annurev.food.080708.100754.
https://doi.org/10.1146/annurev.food.080...
; OLIVEIRA et al., 2014OLIVEIRA, L.L. et al. Health promoting and sensory properties of phenolic compounds in food. Revista Ceres, v.61, p.764-779, 2014. Available from: <Available from: http://dx.doi.org/10.1590/0034-737X201461000002 >. Accessed: Jan. 05, 2020. doi: 10.1590/S0100-40422009010.1590/0034-737X201461000002.
http://dx.doi.org/10.1590/0034-737X20146...
). They occur in various foods, such as anthocyanidins in grape, wine, cherries, and eggplant peel; flavonols in onion, broccoli, kale, apple peel, tea, and grape; flavones in sorghum, lemon, red pepper, and parsley; flavanols in apple skin, banana, berries, Camelia sinensis teas; isoflavonoids in soybean and soy products; and flavanones in citrus fruit and tomato skin, as some examples, many of them with antioxidant and antimicrobial activities (RICE-EVANS et al., 1996RICE-EVANS, C. et al. Structure-antioxidant activity relationships of flavonoids and phenolic acids. Free Radical Biology and Medicine, v.20, n.7, p.933-956, 1996. Available from: <Available from: https://doi.org/10.1016/0891-5849(95)02227-9 >. Accessed: August 05, 2019. doi: 10.1016/0891-5849(95)02227-9.
https://doi.org/10.1016/0891-5849(95)022...
; HOLLMAN & KATAN, 1997; OLIVEIRA et al., 2014; XU et al., 2017XU, D.P. et al. Natural antioxidants in foods and medicinal plants: extraction, assessment and resources. International Journal of Molecular Sciences , v.18, p.96, 2017. Available from: <Available from: https://doi.org/10.3390/ijms18010096 >. Accessed: Jan. 05, 2020. doi: 10.3390/ijms18010096.
https://doi.org/10.3390/ijms18010096...
). The highest activities are displayed by the class of flavanols, especially the procyanidin group and catechins, epicatechins, and their esterified derivatives.

Within the phenolics, non-flavonoids comprise phenolic acids, tannins, stilbenes and lignans. Phenolic acids are widely spread throughout the plant kingdom and their effects have been ascribed to their antioxidant, antimutagenic, anticarcinogenic, antimicrobial, and other biological properties (XU et al., 2008XU, G. et al. Composition and distribution of phenolic acids in Ponkan (Citrus poonensis Hort. Ex. Tanaka) and Huyou (Citrus paradise Macf. Changshanhuyou) during maturity. Journal of Food Compositions and Analysis, v.21, p.382-389, 2008. Available from: <Available from: https://doi.org/10.1016/j.jfca.2008.03.003 >. Accessed: Oct. 05, 2019. doi: 10.1016/j.jfca.2008.03.003.
https://doi.org/10.1016/j.jfca.2008.03.0...
). Substituted derivatives of hydroxybenzoic and hydroxycinnamic acids are the predominant phenolic acids. The most common hydroxycinnamic acids are caffeic, p-coumaric, and ferulic acids, which frequently occur in food as simple esters with quinic acid or glucose (SHAHIDI & AMBIGAIPALAN, 2015SHAHIDI, F.; AMBIGAIPALAN, P. Phenolics and polyphenolics in food, beverages and spices: antioxidant activity and health effects - A review. Journal of Functional Foods, v. 18, p.820-897, 2015. Available from: http://dx.doi.org/10.1016/j.jff.2015.06.018. Accessed: Oct. 01, 2019. doi: 10.1016/j.jff.2015.06.018.
https://doi.org/http://dx.doi.org/10.101...
), while the most common benzoic acid is gallic acid, occurring in red fruits, onions and black radish (XU et al., 2017).

Tannins are water-soluble polyphenols commonly presented as hydrolysable tannins or condensed tannins, the latter are the most common, consisting of two or more monomeric (+)-catechin or (-)-epicatechin units. Tannins are able to bind and precipitate proteins and other macromolecules in aqueous solutions, to bind metals and form blue to black complexes with iron salts, with molecular weight ranging from 500 to 3,000 daltons (SALMINEN & KARONEN, 2011SALMINEN, J.P.; KARONEN, M. Chemical ecology of tannins and other phenolics: we need a change in approach. Functional Ecology, v.25, p.325-338, 2011. Available from: <Available from: https://doi.org/10.1111/j.1365-2435.2010.01826 >. Accessed: Jan. 05, 2020. doi: 10.1111/j.1365-2435.2010.01826.
https://doi.org/10.1111/j.1365-2435.2010...
). The most known stilbene is resveratrol, which is reported in vine plant, peanut and berries, and extensively studied for its multiple bioactivities (XU et al., 2017XU, D.P. et al. Natural antioxidants in foods and medicinal plants: extraction, assessment and resources. International Journal of Molecular Sciences , v.18, p.96, 2017. Available from: <Available from: https://doi.org/10.3390/ijms18010096 >. Accessed: Jan. 05, 2020. doi: 10.3390/ijms18010096.
https://doi.org/10.3390/ijms18010096...
). Lignans are present in seeds, vegetable oils, cereals, legumes, fruits and vegetables, displaying an enormous structural diversity. The most common lignans are lariciresinol, pinoresinol, secoisolariciresinol, syringaresinol, matairesinol, 7-hydroxymatairesinol, sesamin, sesamolin and sesamol (GERSTENMEYER et al., 2013GERSTENMEYER, E. et al. Effect of thermal heating on some lignans in flax seeds, sesame seeds and rye. Food Chemistry, v.138, p.1847-1855, 2013. Available from: <Available from: http://doi.org/doi: 10.1016/j.foodchem.2012.11.117 >. Accessed: Jan. 05, 2020. doi: 10.1016/j.foodchem.2012.11.117.
http://doi.org/doi: 10.1016/j.foodchem.2...
).

The great diversity of bioactive compounds reported in plant processing residues encourages the search for natural antioxidants for application in food and drug industries. According to the FDA (Food and Drug Administration), antioxidants are substances used to preserve food by retarding deterioration through rancidity or discoloration that is caused by the oxidation process (DZIEZAK, 1986DZIEZAK, J.D. Antioxidants - the ultimate answer to oxidation. Food Technology, v.40, p.94-102, 1986.). These are compounds present in small amounts with a primary function of preserving or retarding oil and fat oxidations (POKORNY, 1991POKORNY, J. Natural antioxidants for food use. Trends in Food Science and Technology, v.2, p.223-227, 1991. Available from: <Available from: https://doi.org/10.1016/0924-2244(91)90695-F >. Accessed: Oct. 08, 2019. doi: 10.1016/0924-2244(91)90695-F.
https://doi.org/10.1016/0924-2244(91)906...
). These substances may have originated from commercial sources and naturally isolated compounds from foods (ADEGOKE et al., 1998ADEGOKE, G.O. et al. Antioxidants, and lipid oxidation in foods - a critical appraisal. Journal of Food Science and Technology, v.35, n.4, p.283-298, 1998.). An essential requirement for the use of an antioxidant in food requires it to be efficient at low concentrations, compatible with the substrate, sensory acceptability, non-toxicity, and protection of the food from the deleterious effects of oxidation (SCHULER, 1990SCHULER, P. Natural antioxidants exploited commercially. In: HUDSON, B.J.F. Food antioxidants. Dordrecht : Elsevier Science Publishers, 1990. p.99-170. Available from: <Available from: https://link.springer.com/content/pdf/10.1007%2F978-94-009-0753-9_4.pdf >. Accessed: Feb. 14, 2020.
https://link.springer.com/content/pdf/10...
).

An antioxidant functions in various ways: competitively binding to oxygen, delaying the initiation step, and/or inhibiting the propagation step by destroying or binding free radicals or inhibiting the catalysts and stabilizing the hydroperoxides (ALLEN & HAMILTON, 1994ALLEN, J.C.; HAMILTON, R.J. Rancidity in foods. London: Blackie Academic, 1994. 290p.). The antioxidant may act on the cell membranes to protect food by: (1) sequestering free radicals and not starting the oxidation process; (2) inactivating metallic ions; (3) removing oxygen reactive species; (4) sequestering single oxygen; (5) destroying peroxides and preventing formation of radicals; and (6) removing and/or decreasing the local oxygen concentration (DZIEZAK, 1986DZIEZAK, J.D. Antioxidants - the ultimate answer to oxidation. Food Technology, v.40, p.94-102, 1986.).

Due to the potential risks of synthetic antioxidants to human health, much interest has been developed in natural sources of these compounds to reduce or delay oxidation processes on food in recent years (AHN et al., 1998AHN, D.U. et al. Packaging and irradiation effects on lipid oxidation and volatiles in pork patties. Journal of Food Science, v.63, n.1, p.15-19, 1998. Available from: <Available from: https://doi.org/10.1111/j.1365-2621.1998.tb15665x >. Accessed: Mar. 22, 2019. doi: 10.1111/j.1365-2621.1998.tb15665x.
https://doi.org/10.1111/j.1365-2621.1998...
; JAYAPRAKASHA et al., 2001JAYAPRAKASHA, G.K. et al. Antioxidant activity of grape seed (Vitis vinifera) extracts peroxidation models in vitro. Food Chemistry, v.73, p.285-290, 2001. Available from: <Available from: http://dx.doi.org/10.1016/S0308-8146(00)00298-3 >. Accessed: Oct. 01, 2019. doi: 10.1016/S0308-8146(00)00298-3.
http://dx.doi.org/10.1016/S0308-8146(00)...
; MOURE et al. 2001MOURE, A. et al. Natural antioxidants from residual sources. Food Chemistry, v.72, p.145-171, 2001. Available from: <Available from: https://doi.org/10.1016/S0308-8146(00)00223-5 >. Accessed: Oct. 01, 2019. doi: 10.1016/S0308-8146(00)00223-5.
https://doi.org/10.1016/S0308-8146(00)00...
; BREWER, 2011BREWER, M.S. Natural antioxidants: sources, compounds, mechanisms of action, and potential applications. Comprehensive Reviews in Food Science and Food Safety, v.10, p.221-247-10, 2011. Available from: <Available from: https://doi.org/10.1111/j.1541-4337.2011.00156.x >. Accessed: Oct. 03, 2019. doi: 10.1111/j.1541-4337.2011.00156.x.
https://doi.org/10.1111/j.1541-4337.2011...
). Natural antioxidants are molecules present in plants, in small amounts, which inhibit the oxidation process that produces free radicals. Natural antioxidants have the ability to reduce the rate of oxidation of the lipid compounds present in certain dietary products. These antioxidant compounds include flavonoids, phenolic acids, carotenoids, and tocopherols (KHANDUJA & BHARDWAJ, 2003KHANDUJA, K.L.; BHARDWAJ, A. Stable free radical scavenging and anti peroxidative properties of resveratrol in vitro compared with some others bioflavonoids. Indian Journal of Biochemistry and Biophysics, v.40, p.416-422, 2003. Available from: <Available from: https://pdfs.semanticscholar.org/c45e/5d3a15137b0c29e9d69409e7b823f35f0466.pdf >. Accessed: Feb. 14, 2020.
https://pdfs.semanticscholar.org/c45e/5d...
; OZSOY et al., 2009OZSOY, N. et al. Implications for degenerative disorder: antioxidant activity, total phenols, flavonoids, ascorbic acid, beta-carotene and beta-tocopherol in Aloe vera. Oxidative Medicine and Cell Longevity, v.2, n.2, p.99-106, 2009. Available from: <Available from: http://downloads.hindawi.com/journals/omcl/2009/315091.pdf >. Accessed: Feb. 14, 2020.
http://downloads.hindawi.com/journals/om...
).

The antioxidant potential of the bioactive compounds depends on the number and arrangement of the hydroxyl groups. These compounds can donate hydrogen atoms to lipid radicals and produce lipid derivatives and antioxidant radicals, which are more stable and less readily available to promote autoxidation (SHAHIDI & AMBIGAIPALAN, 2015SHAHIDI, F.; AMBIGAIPALAN, P. Phenolics and polyphenolics in food, beverages and spices: antioxidant activity and health effects - A review. Journal of Functional Foods, v. 18, p.820-897, 2015. Available from: http://dx.doi.org/10.1016/j.jff.2015.06.018. Accessed: Oct. 01, 2019. doi: 10.1016/j.jff.2015.06.018.
https://doi.org/http://dx.doi.org/10.101...
).

Plants are the main sources of natural antimicrobials, i.e., compounds capable of inhibiting the growth of microorganisms. They can be used along with older antibiotics to increase their potency to avoid the development of microbial resistance. The plant compounds that are extensively utilized for antimicrobial purposes comprise alkaloids, sulfur-containing compounds, terpenoids, and phenolic compounds (KHAMENEH et al., 2019KHAMENEH, B. et al. Review on plant antimicrobials: a mechanistic viewpoint. Antimicrobial Resistance & Infection Control, v.8, 118, 2019. Available from: <Available from: http://doi.org/10.1186/s13756-019-0559-6 >. Accessed: Oct. 31, 2019. doi:10.1186/s13756-019-0559-6.
http://doi.org/10.1186/s13756-019-0559-6...
). Thus far, more than 1,350 plants with antimicrobial activities and more than 30,000 antimicrobial substances extracted from plants have been reported (TAJKARIMI et al., 2010TAJKARIMI, M.M. et al. Antimicrobial herb and spice compounds in food. Food Control, v.21, p.1199-1218, 2010. Available from: <Available from: https://doi.org/10.1016/j.foodcont.2010.02.003 >. Accessed: Oct. 01, 2019. doi: 10.1016/j.foodcont.2010.02.003.
https://doi.org/10.1016/j.foodcont.2010....
). Plants are a big bet as sources of natural antimicrobials, and in this sense, the utilization of plant parts normally discarded as wastes arises as a sustainable and safe option in the search for novel antimicrobial agents.

Agro-industrial wastes as sources of bioactive compounds

The agro-industrial products from food industries produce a large amount of vegetable and fruit wastes, which affect municipal landfills. Despite being highly biodegradable, these generate leachate and are responsible for methane emission (MISI & FORSTER, 2002MISI, S.N.; FORSTER, C.F. Semi-continuous anaerobic co-digestion of agro-waste. Environmental Technology, v.23, p.445-451, 2002. Available from: <Available from: http://dx.doi.org/10.1080/09593332508618405 >. Accessed: Oct. 06, 2019. doi: 10.1080/09593332508618405.
http://dx.doi.org/10.1080/09593332508618...
). These wastes are generated by different processes and contain an appreciable amount of bark, seeds, and other types of plant components. These waste components serve as a source of proteins, enzymes, essential oils, and other compounds with biological activity that can be recovered and used. The processing of food from vegetable origin results in production of byproducts that are rich sources of bioactive compounds (SCHIEBER et al., 2001SCHIEBER, A. et al. Byproducts of plant food processing as a source of functional compounds - recent developments. Trends in Food Science and Technology, v.12, p.401-413, 2001. Available from: <Available from: https://doi.org/10.1016/S0924-2244(02)00012-2 >. Accessed: Oct. 01, 2019. doi: 10.1016/S0924-2244(02)00012-2.
https://doi.org/10.1016/S0924-2244(02)00...
) (Figure 2). The availability of these compounds in the agroindustry residue will depend on the mode of extraction, type of solvent, and purification (SOQUETTA et al., 2018SOQUETTA, M.B. et al. Green technologies for the extraction of bioactive compounds in fruits and vegetables. CyTA - Journal of Food, v.16, n.1, p.400-412, 2018. Available from: <Available from: https://doi.org/10.1080/19476337.2017.1411978 >. Accessed: Nov. 01, 2019. doi: 10.1080/19476337.2017.1411978.
https://doi.org/10.1080/19476337.2017.14...
). A general scheme to obtain extracts from different parts of the plants is shown in figure 3.

Figure 2
Use of agro-industrial wastes as natural sources of bioactive compounds in food and fermentation industries.

Figure 3
A general scheme of the extraction method to obtain a bioactive compound-rich extract from agro-industrial wastes (stems, seeds, peels, leaves, etc.).

Antioxidant and antimicrobial activities have been reported in several agricultural products (BALASUNDRAM et al., 2006BALASUNDRAM, N. et al. Phenolic compounds in plants agri-industrial by products: antioxidant activity, occurrence, and potential uses. Food Chemistry, v.99, p.191-203, 2006. Available from: <Available from: https://doi.org/10.1016/j.foodchem.2005.07.042 >. Accessed: Oct. 02, 2019. doi: 10.1016/j.foodchem.2005.07.042.
https://doi.org/10.1016/j.foodchem.2005....
). DENG et al. (2012DENG, G.F. et al. Potential of fruit wastes as natural resources of bioactive compounds. International Journal of Molecular Sciences, v.13, p.8308-8323, 2012. Available from: <Available from: http://doi.org/10.3390/ijms13078308 >. Accessed: Jan. 05, 2020. doi: 10.3390/ijms13078308.
http://doi.org/10.3390/ijms13078308...
) evaluated the potential of wastes from 50 fruits (peel and seed) as resources of bioactive compounds and demonstrated that the antioxidant potential was higher in residues than in pulps. A large group of bioactive compounds was identified such as catechin, cyanidin 3-glucoside, epicatechin, galangin, gallic acid, homogentisic acid, kaempferol, and chlorogenic acid.

Tables 1,2,3 and 4 list the studies that used agro-industrial residues as natural sources of antioxidants and antimicrobials and summarize the main results and technological applications.

Table 1
Agro-industrial residues as natural sources of antioxidants and antimicrobials, the main results of the study, and the technological applications of the wastes - PART I.

Table 2
Agro-industrial residues as natural sources of antioxidants and antimicrobials, the main results of the study, and the technological applications of the wastes - PART II.

Table 3
Agro-industrial residues as natural sources of antioxidants and antimicrobials, the main results of the study, and the technological applications of the wastes - PART III.

Table 4
Agro-industrial residues as natural sources of antioxidants and antimicrobials, the main results of the study, and the technological applications of the wastes - PART IV.

Wastes from fruit processing: rich sources of bioactive compounds with technological applications

Grape

Grape (Vitis vinifera) seed extracts are obtained as the byproducts of wine-making or grape juice and are rich in proanthocyanidins (condensed tannins) and other phenolic compounds (RABABAH et al., 2004RABABAH, T.M. et al. Total phenolics and antioxidant activities of Fenugreek, Green Tea, Black Tea, Grape Seed, Ginger, Rosemary, Gotu Kola, and Ginkgo Extracts, Vitamin E and tert-Butylhydroquinone. Journal of Agricultural and Food Chemistry, v.52, p.5183-5186, 2004. Available from: <Available from: https://doi.org10.1021/jf049645z >. Accessed: Oct. 05, 2019. doi: 10.1021/jf049645z.
https://doi.org10.1021/jf049645z...
; MIELNIK et al., 2006MIELNIK, M.B. et al. Grape seed extract as antioxidant in cooked, cold stored turkey meat. LWT - Food Science and Technology, v.39, p.191-198, 2006. Available from: <Available from: http://dx.doi.org/10.1016/j.lwt.2005.02.003 >. Accessed: Oct. 06, 2019. doi: 10.1016/j.lwt.2005.02.003.
http://dx.doi.org/10.1016/j.lwt.2005.02....
; WEBER et al., 2007WEBER, H.A. et al. Comparison of proanthocyanidins in commercial antioxidants: grape seed and pine bark extracts. Journal of Agricultural Food and Chemistry, v.55, p.148-156, 2007. Available from: <Available from: https://doi.org/10.1021/jf063150n >. Accessed: Oct. 06, 2019. doi: 10.1021/jf063150n.
https://doi.org/10.1021/jf063150n...
). Phenolic compounds in grape and grape products can be divided into two groups, non-flavonoids and flavonoids. The most common phenolic acids found in grape include cinnamic acids (coumaric acid, caffeic acid, ferulic acid, chlorogenic acid, and neochlorogenic acid) and benzoic acids (p-hydroxybenzoic acid, vanillic acid, and gallic acid). Flavonoids include flavan-3-ols (catechin, epicatechin polymer and ester with galactic acid or glucose), flavonols (quercetin) and red and blue anthocyanins (SHI et al., 2003SHI, J. et al. Polyphenolics in grape seeds - biochemistry and functionality. Journal of Medicinal Food, v.6, p.291-299, 2003. Available from: <Available from: https://doi.org/10.1089/109662003772519831 >. Accessed: Oct. 02, 2019. doi: 10.1089/109662003772519831.
https://doi.org/10.1089/1096620037725198...
; SHAHIDI & AMBIGAIPALAN, 2015SHAHIDI, F.; AMBIGAIPALAN, P. Phenolics and polyphenolics in food, beverages and spices: antioxidant activity and health effects - A review. Journal of Functional Foods, v. 18, p.820-897, 2015. Available from: http://dx.doi.org/10.1016/j.jff.2015.06.018. Accessed: Oct. 01, 2019. doi: 10.1016/j.jff.2015.06.018.
https://doi.org/http://dx.doi.org/10.101...
). Studies have shown that grape seeds are rich sources of monomeric phenolics such as (+)-catechins, (-)-epicatechin, (+)-gallocatechins, (-)-epigallocatechin, and their dimeric, trimeric, and tetrameric proanthocyanidins (SHAHIDI & AMBIGAIPALAN, 2015).

The utilization of wastes produced from the wine industry as natural antioxidants has been extensively studied in various types of raw material, such as beef, chicken, pork, and turkey, by means of varied matrices such as hamburgers, meatballs, restructured, sausages, and marinated patties. The addition of grape seed and peel extracts (Isabel and Niagara varieties) as natural antioxidants delayed the lipid oxidation of chicken meat (processed, cooked and stored under refrigeration for 14 days), with results comparable to the synthetic antioxidant butylated hydroxytoluene (BHT). The addition of grape extracts combined with vacuum packaging proved to be a good technique to increase the lipid stability of cooked chicken meat (SHIRAHIGUE et al., 2010SHIRAHIGUE, L.D. et al. Wine industry residue as antioxidant in cooked chicken meat. International Journal of Food Science and Technology, v.45, p.863-870, 2010. Available from: <Available from: https://doi.org/10.1111/j.1365-2621.2010.02201.x >. Accessed: Oct. 04, 2019. doi: 10.1111/j.1365-2621.2010.02201.x.
https://doi.org/10.1111/j.1365-2621.2010...
).

Grape seed and peel extracts (Isabel and Niagara varieties) were as effective as the synthetic antioxidants (BHT and a commercial mixture of sodium erythorbate, citric acid, and sugar) in the prevention of lipid oxidation in the processed products of both raw and cooked chicken, which were stored under frozen conditions for nine months (SELANI et al., 2011SELANI, M.M. et al. Wine industry residues extracts as natural antioxidants in raw and cooked chicken meat during frozen storage. Meat Science, v.88, p.397-403, 2011. Available from: <Available from: https://doi.org/10.1016/j.meatsci.2011.01.017 >. Accessed: August 30, 2019. doi: 10.1016/j.meatsci.2011.01.017.
https://doi.org/10.1016/j.meatsci.2011.0...
). They also improved the oxidative stability of cooked beef (AHN et al., 2002AHN, J. et al. Antioxidant properties of natural plant extracts containing polyphenolic compounds in cooked ground beef. Journal of Food Science, v.67, p.1364-1369, 2002. Available from: <Available from: https://doi.org/10.1111/j.1365-2621.2002.tb10290.x >. Accessed: Sep. 14, 2019. doi: 10.1111/j.1365-2621.2002.tb10290.x.
https://doi.org/10.1111/j.1365-2621.2002...
), cooked chicken meat (SHIRAHIGUE et al., 2011SHIRAHIGUE, L.D. et al. Winery grape-residue extract: effects on quality and attributes of cooked chicken meat. Food Science and Biotechnology, v.20, p.1257-1264, 2011. Available from: <Available from: https://doi.org/10.1007/s10068-011-0173-8 >. Accessed: Oct. 04, 2019. doi: 10.1007/s10068-011-0173-8.
https://doi.org/10.1007/s10068-011-0173-...
), and parts of turkey (LAU & KING, 2003LAU, D.W.; KING, A.J. Pre-and post-mortem use of grape seed extract in dark poultry meat to inhibit development of thiobarbituric acid reactive substances. Journal of Agricultural and Food Chemistry, v.51, p.1602-1607-51, 2003. Available from: <Available from: https://doi.org/10.1021/jf020740m >. Accessed: Sep. 09, 2019. doi: 10.1021/jf020740m.
https://doi.org/10.1021/jf020740m...
).

The efficacy of grape polyphenols in delaying the lipid oxidation of fish-based products when stored under frozen conditions was also demonstrated. PAZOS et al. (2005aPAZOS, M. et al. Preservation of the endogenous antioxidant system of fish muscle by grape polyphenols during frozen storage. European Food Research and Technology, v.220, n.5-6, p.514-519, 2005a. Available from: <Available from: https://doi.org/10.1007/s00217-004-1113-0 >. Accessed: August, 26, 2019. doi: 10.1007/s00217-004-1113-0.
https://doi.org/10.1007/s00217-004-1113-...
) verified the antioxidant activity of grape flavonoids obtained from the byproducts of the wine industry in systems containing fish oil and mackerel muscle (Scomber scombrus) and also observed that oligomeric flavonoids have a high potential in inhibiting oxidation in emulsions and in frozen fish muscle. Grape extract and its purified fractions were used in preserving fish meat among species that had high concentrations of polyunsaturated fatty acids (PAZOS et al., 2005bPAZOS, M. et al. Activity of grape polyphenol as inhibitors of the oxidation of fish lipids and frozen fish muscle. Food Chemistry, v.92, p.547-557, 2005b. Available from: <Available from: https://doi.org/10.1016/j.foodchem.2004.07.036 >. Accessed: August, 30, 2019. doi: 10.1016/j.foodchem.2004.07.036.
https://doi.org/10.1016/j.foodchem.2004....
).

The addition of fruit residues (grape seed, orange peel, and tomato paste) was an alternative source of natural antioxidants in enriching rice-based extruded foods (YAGCI & GOGUS, 2009YAGCI, S.; GOGUS, F. Effect of incorporation of various food byproducts on some nutritional properties of rice-based extruded foods. Food Science and Technology International, v.15, p.571-581, 2009. Available from: <Available from: https://doi.org/10.1177/1082013209353078 >. Accessed: Oct. 05, 2019. doi: 10.1177/1082013209353078.
https://doi.org/10.1177/1082013209353078...
). Bread formulated with a grape seed extract showed increased antioxidant activity and a decreased amount of carboxymethyl-lysine, a compound formed by the potentially toxic Maillard reaction. The only attribute imparted by the use of grape extract was the color of the bread (PENG et al., 2010PENG, X. et al. The effects of grape seed extract fortification on the antioxidant activity and quality attributes of bread. Food Chemistry, v.119, p.49-53, 2010. Available from: <Available from: http://dx.doi.org/10.1016/j.foodchem.2009.05.083 >. Accessed: August, 26, 2019. doi: 10.1016/j.foodchem.2009.05.083.
http://dx.doi.org/10.1016/j.foodchem.200...
). Grape extracts also increased the oxidative stability of the lipid in cheddar cheese (SHAN et al., 2011SHAN, B. et al. Potential application of spice and herbs extracts as natural preservatives in cheese. Journal of Medicinal Food, v.3, p.284-290, 2011. Available from: <Available from: http://dx.doi.org/10.1089/jmf.2010.0009 >. Accessed: Oct., 01 2019. doi: 10.1089/jmf.2010.0009.
http://dx.doi.org/10.1089/jmf.2010.0009...
) and the antioxidant activity in ice creams (HWANG et al., 2009HWANG, J.Y. et al. Grape wine lees improves the rheological and adds antioxidants properties to ice cream. LWT - Food Science and Technology, v.42, p.312-318, 2009. Available from: <Available from: http://dx.doi.org/10.1016/j.lwt.2008.03.008 >. Accessed: Oct. 01, 2019. doi: 10.1016/j.lwt.2008.03.008.
http://dx.doi.org/10.1016/j.lwt.2008.03....
).

The antimicrobial activity of grape extracts has been reported in the literature against a variety of microorganisms such as lactic acid bacteria, foodborne pathogens, and wine spoilage yeasts (JAYAPRAKASHA et al., 2003JAYAPRAKASHA, G.K. et al. Antibacterial and antioxidant activities of grape (Vitis vinifera) seed extracts. Food Research International, v.36, n. 2, p.117-122, 2003. Available from: <Available from: https://doi.org/10.1016/S0963-9969(02)00116-3 >. Accessed: Sep. 09, 2019. doi: 10.1016/S0963-9969(02)00116-3.
https://doi.org/10.1016/S0963-9969(02)00...
; BAYDAR et al., 2004BAYDAR, N.G. et al. Total phenolic contents and antibacterial activities of grape (Vitis vinifera L.) extracts. Food Control, v.15, n.5, p.335-339, 2004. Available from: <Available from: https://doi.org/10.1016/S0956-7135(03)00083-5 >. Accessed: Oct. 31, 2019. doi: 10.1016/S0956-7135(03)00083-5.
https://doi.org/10.1016/S0956-7135(03)00...
; BROWN et al., 2009BROWN, J.C. et al. Antibacterial effects of grape extracts on Helicobacter pylori. Applied and Environmental Microbiology, v.75, n.3, p.848-852, 2009. Available from: <Available from: https://doi.org/10.1128/AEM.01595-08 >. Accessed: Oct. 31, 2019. doi: 10.1128/AEM.01595-08.
https://doi.org/10.1128/AEM.01595-08...
; KATALINIC et al., 2010KATALINIC, V. et al. Polyphenolic profile, antioxidant properties and antimicrobial activity of grape skin extracts of 14 Vitis vinifera varieties grown in Dalmatia (Croatia). Food Chemistry, v.119, n.2, p.715-723, 2010. Available from: <Available from: https://doi.org/10.1016/j.foodchem.2009.07.019 >. Accessed: Sep. 30, 2019. doi: 10.1016/j.foodchem.2009.07.019.
https://doi.org/10.1016/j.foodchem.2009....
; PERUMALLA & HETTIARACHCHY, 2011PERUMALLA, A.S.; HETTIARACHCHY, N. Green tea and grape seed extracts - potential applications in food safety and quality. Food Research International, v.44, p.827-839, 2011. Available from: <Available from: http://dx.doi.org/10.1016/j.foodres.2011.01.022 > Accessed: Oct. 01, 2019. doi: 10.1016/j.foodres.2011.01.022.
http://dx.doi.org/10.1016/j.foodres.2011...
; PASTORKOVA et al., 2013PASTORKOVA, E. et al. Growth inhibitory effect of grape phenolic against wine spoilage yeasts and acetic acid bacteria. International Journal of Food Microbiology, v.161, p.209-213, 2013. Available from: <Available from: http://dx.doi.org/10.1016/j.ijfoodmicro.2012.12.018 > Accessed: Oct. 01, 2019. doi: 10.1016/j.ijfoodmicro.2012.12.018.
http://dx.doi.org/10.1016/j.ijfoodmicro....
). Growth of foodborne pathogens such as Staphylococcus aureus, Salmonella sp., Escherichia coli, Listeria monocytogenes, and Campylobacter sp. were inhibited by grape seed extracts (ROTAVA et al., 2009ROTAVA, R. et al. Atividade antibacteriana, antioxidante e tanante de subprodutos da uva. Ciência Rural, v.39, n.3, p.941-944, 2009. Available from: <Available from: http://dx.doi.org/10.1590/S10103-84782009000300051 >. Accessed: Oct. 01, 2019. doi: 10.1590/S10103-84782009000300051.
http://dx.doi.org/10.1590/S10103-8478200...
; SHAN et al., 2011SHAN, B. et al. Potential application of spice and herbs extracts as natural preservatives in cheese. Journal of Medicinal Food, v.3, p.284-290, 2011. Available from: <Available from: http://dx.doi.org/10.1089/jmf.2010.0009 >. Accessed: Oct., 01 2019. doi: 10.1089/jmf.2010.0009.
http://dx.doi.org/10.1089/jmf.2010.0009...
; SILVÁN et al., 2013SILVÁN, J.M. et al. Antibacterial activity of grape seed extract and its fractions against Campylobacter spp. Food Control, v.29, p.25-31, 2013. Available from: <Available from: https://doi.org/10.1016/j.foodcont.2012.05.063 >. Accessed: Oct. 01, 2019. doi: 10.1016/j.foodcont.2012.05.063.
https://doi.org/10.1016/j.foodcont.2012....
; FILOCAMO et al., 2015FILOCAMO, A. et al. In vitro antimicrobial activity and effect on biofilm production of a white grape juice (Vitis vinifera) extract. Evidence-Based Complementary and Alternative Medicine, v.2015, 856243, 2015. Available from: <Available from: https://doi.org/10.1155/2015/856243 >. Accessed: Oct. 13, 2019. doi: 10.1155/2015/856243.
https://doi.org/10.1155/2015/856243...
). A flavan-3-ol enriched grape seed extract inhibited the growth of lactic acid bacteria such as Lactobacillus fermentum and L. plantarum (TABASCO et al., 2011TABASCO, R. et al. Effect of grape polyphenols on lactic acid bacteria and bifidobacteria growth: resistance and metabolism. Food Microbiology, v.28, p.1345-1352, 2011. Available from: <Available from: https://doi.org/10.1016/j.fm.2011.06.005 >. Accessed: Oct. 01, 2019. doi: 10.1016/j.fm.2011.06.005.
https://doi.org/10.1016/j.fm.2011.06.005...
), which are the common contaminants of the bioethanol industry process (BASSO et al., 2014BASSO, T.O. et al. Homo-and heterofermentative lactobacilli differently affect sugarcane-based fuel ethanol fermentation. Antonie van Leeuwenhoek, v.105, p.169-177, 2014. Available from: <Available from: https://doi.org/10.1007/s10482-013-0063-6 >. Accessed: Oct. 31, 2019. doi: 10.1007/s10482-013-0063-6.
https://doi.org/10.1007/s10482-013-0063-...
). Grape extracts have been reported as more effective against bacteria than yeasts; and consequently, the results obtained with lactic acid bacteria are shown to be very promising for application in the ethanol fuel industry.

Citrus

Citrus fruits, chiefly, oranges, mandarins, limes, and lemons, are the most produced and consumed fruits in the world (OLIVEIRA et al., 2009OLIVEIRA, A.C. et al. Fontes naturais de antioxidantes. Química Nova, v.32, p.689-702, 2009. Available from: <Available from: http://dx.doi.org/10.1590/S0100-40422009000300013 >. Accessed: Aug. 29, 2019. doi: 10.1590/S0100-40422009000300013.
http://dx.doi.org/10.1590/S0100-40422009...
). Different citrus fruits have a small edible portion and generate a large amount of residues such as peels and seeds during food processing (MIRABELLA et al., 2014MIRABELLA, N. et al. Current options for the valorization of food manufacturing waste: a review. Journal of Cleaner Production, v.65, p.28-41, 2014. Available from: <Available from: https://doi.org/10.1016/j.jclepro.2013.10.051 >. Accessed: Oct. 09, 2019. doi: 10.1016/j.jclepro.2013.10.051.
https://doi.org/10.1016/j.jclepro.2013.1...
). These residues are the sources of several compounds, mainly, water-soluble sugars, fibers, organic acids, amino acids and proteins, minerals, oils, and lipids. They also contain flavonoids and vitamins (FERNÁNDEZ-LOPEZ et al., 2004FERNÁNDEZ-LOPEZ, J. et al. Application of functional citrus byproducts to meat products. Trends in Food Science and Technology, v.15, p.176-185, 2004. Available from: <Available from: https://doi.org/10.1016/j.tifs.2003.08.007 >. Accessed: Oct. 05, 2019. doi: 10.1016/j.tifs.2003.08.007.
https://doi.org/10.1016/j.tifs.2003.08.0...
). Residues such as dry pulp and molasses, fiber, seeds, and bagasse are the sources of essential oils, pectin, ascorbic acid, and flavonoids (BRADDOCK, 1995BRADDOCK, R.J. Byproducts of citrus fruit. Food Technology, v.49, p.74-77, 1995.; OZAKI et al., 2000OZAKI, Y. et al. Limonoid glucosides of Satsuma mandarin (Citrus unshiu Marcov.) and its processing products. In: BERHOW, M.A. et al. Citrus limonoids: functional chemical in agriculture and food. Washington: ACS Symposium Series, 2000. p.107-119. Avaiable from: < Avaiable from: https://doi.org/10.1021/bk-2000-0758.ch008 >. Accessed: Aug. 23, 2019. doi: 10.1021/bk-2000-0758.ch008.
https://doi.org/10.1021/bk-2000-0758.ch0...
; SCHIEBER et al., 2001SCHIEBER, A. et al. Byproducts of plant food processing as a source of functional compounds - recent developments. Trends in Food Science and Technology, v.12, p.401-413, 2001. Available from: <Available from: https://doi.org/10.1016/S0924-2244(02)00012-2 >. Accessed: Oct. 01, 2019. doi: 10.1016/S0924-2244(02)00012-2.
https://doi.org/10.1016/S0924-2244(02)00...
).

Citrus peels are rich in various nutrients that act as functional and beneficial components, which have wide applications, depending on their composition. These byproducts have several secondary metabolites, such as terpenoids, carotenoids, coumarins, furanocoumarins, and flavonoids, especially flavonones and polyethoxylated flavones, which are rarely reported in other plants. These compounds protect plants against several biotic and abiotic stresses (AHMAD et al., 2006AHMAD, M.M. et al. Genetic variability to essential oil composition in four citrus fruit species. Pakistan Journal of Botany, v.38, n.2, p.319-324, 2006. Available from: <Available from: https://naturalingredient.org/wp/wp-content/uploads/PJB382319.pdf >. Accessed: Feb. 14, 2020.
https://naturalingredient.org/wp/wp-cont...
). They are present in the citrus extracts and citrus oils, and due to their antimicrobial and antioxidant activities, there is a growing interest in their application in several areas of food technology (CHOI et al., 2000CHOI, H. et al. Radical-scavenging activities of Citrus essential oils and their components: detection using 1,1-diphenyl-2-picrylhydrazyl. Journal of Agricultural and Food Chemistry, v.48, p.4156-4161, 2000. Available from: <Available from: https://doi.org/10.1021/jf000227d >. Accessed: Oct. 03, 2019. doi: 10.1021/jf000227d.
https://doi.org/10.1021/jf000227d...
; FRIEDMANN et al., 2004FRIEDMANN, M. et al. Antibacterial activities of plant essential oils and their components against Escherichia coli O157:H7 and Salmonella enterica in apple juice. Journal of Agricultural and Food Chemistry, v.52, p.6042-6048, 2004. Available from: <Available from: https://doi.org/10.1021/jf0495340 >. Accessed: Sep. 30, 2019. doi: 10.1021/jf0495340.
https://doi.org/10.1021/jf0495340...
; PATIL et al., 2009PATIL, J.R. et al. Bioactive compounds from Mexican lime (Citrus aurantifolia) juice induce apoptosis in human pancreatic cells. Journal of Agricultural and Food Chemistry, v.57, p.10933-10942, 2009. Available from: <Available from: https://doi.org/10.1021/jf901718u >. Accessed: August, 25, 2019. doi: 10.1021/jf901718u.
https://doi.org/10.1021/jf901718u...
; ASHOK KUMAR et al., 2011ASHOK KUMAR, K. et al. Antimicrobial activity and phytochemical analysis of citrus fruit peels - utilization of fruit waste. International Journal of Engineering Science and Technology, v.3, n.6, p.5414-5421, 2011. Available from: <Available from: https://pdfs.semanticscholar.org/0d23/d42295d3f4abd7cd9b121817a06b63a34588.pdf >. Accessed: Feb. 14, 2020.
https://pdfs.semanticscholar.org/0d23/d4...
; LIU et al., 2012LIU, L. et al. Structure-activity relationship of Citrus polymethoxylated flavones and their inhibitory effects on Aspergillus niger. Journal of Agricultural and Food Chemistry, v.60, p.4336-4341, 2012. Available from: <Available from: http://dx doi.org/10.1021/jf3012163 >. Accessed: Oct. 06, 2019. doi: 10.1021/jf3012163.
http://dx doi.org/10.1021/jf3012163...
).

The term ‘Essential Oil’ is utilized to designate complex mixtures of natural compounds of polar and non-polar natures (MASANGO, 2005MASANGO, P. Cleaner production of essential oils by steam distillation. Journal of Cleaner Production, v.13, p.833-839, 2005. Available from: <Available from: https://doi.org/10.1016/j.jclepro.2004.02.039 >. Acessed: Oct. 05, 2019. doi: 10.1016/j.jclepro.2004.02.039.
https://doi.org/10.1016/j.jclepro.2004.0...
). It is a product obtained by the distillation of natural materials, consisting of liquid, volatile, limpid, and colored mixtures of aromatic compounds extracted from herbs, spices, and from food and vegetable wastes (WU et al., 2017WU, F. et al. Electrofluidic pretreatment for enhancing essential oil extraction from citrus fruit peel waste. Journal of Cleaner Production, v.159, p.85-94, 2017. Available from: <Available from: https://doi.org/10.1016/j.jclepro.2017.05.010 >. Accessed: Oct. 05, 2019. doi: 10.1016/j.jclepro.2017.05.010.
https://doi.org/10.1016/j.jclepro.2017.0...
). Essential oils originate from the secondary metabolism of plants and consist of a mixture of compounds, mainly monoterpenes, sesquiterpenes, and oxygenated derivatives (alcohols, aldehydes, ester, ethers, ketones, phenols, and oxides). They also contain other volatile compounds, such as phenylpropanoids and substances containing sulfur or nitrogen (BAJPAI et al., 2008BAJPAI, V.K. et al. Chemical composition and inhibitory parameters of essential oil and extracts of Nandina domestica Thunb. to control food-borne pathogenic and spoilage. International Journal of Food Microbiology, v.125, n.2, p.117-122, 2008. Available from: <Available from: https://doi.org/10.1016/j.ijfoodmicro.2008.03.011 >. Accessed: Oct. 02, 2019. doi: 10.1016/j.ijfoodmicro.2008.03.011.
https://doi.org/10.1016/j.ijfoodmicro.20...
; VALERIANO et al., 2012VALERIANO, C. Atividade antimicrobiana de óleos essenciais em bactérias patogênicas de origem alimentar. Revista Brasileira de Plantas Medicinais, v.14, n.1, p.57-67, 2012. Available from: <Available from: http://dx.doi.org/10.1590/S1516-05722012000100009 >. Accessed: Sep., 14, 2019. doi: 10.1590/S1516-05722012000100009.
http://dx.doi.org/10.1590/S1516-05722012...
).

Studies have reported the application of natural antimicrobials obtained from citrus essential oils (FISHER & PHILLIPS, 2008FISHER, K.; PHILLIPS, C. Potential antimicrobial uses of essential oils in food: is citrus an answer? Trends in Food Science and Technology, v.19, p.156-164, 2008. Available from: <Available from: https://doi.org/10.1016/j.tifs.2007.11.006 >. Accessed: Oct. 13, 2019. doi: 10.1016/j.tifs.2007.11.006.
https://doi.org/10.1016/j.tifs.2007.11.0...
). These products have reported their use in the development of several pharmaceutical preparations due to their antiseptic properties (BISIGNANO & SAIJA, 2002BISIGNANO, G.; SAIJA, A. The biological activity of citrus oils. In: DUGO, G.; DI GIACOMO, A. Citrus: the genus Citrus. Boca Raton: CRC Press, 2002. p.602-630.). GERHARDT et al. (2012GERHARDT, C. et al. Aproveitamento da casca de citros na perspectiva de alimentos: prospecção da atividade antibacteriana. Brazilian Journal of Food Technology, v.15, p.11-17, 2012. Available from: <Available from: http://dx.doi.org/10.1590/S1981-67232012005000033 >. Accessed: Sep. 03, 2019. doi: 10.1590/S1981-67232012005000033.
http://dx.doi.org/10.1590/S1981-67232012...
) evaluated the varieties of bergamot-pokan (Citrus reticulata Blanco), grapefruit (Citrus maxima (Burm.) Merr.), and lemon-bergamot (or lemon-clove, Citrus limonia Osbeck) in the growth inhibition of certain microorganisms, such as E. coli, Enterococcus faecalis, S. aureus, Salmonella enteritidis, and Pseudomonas aeruginosa, and observed that all extracts from these different citrus varieties were able to inhibit the growth and/or inactivate the bacterial action.

The control of certain lactic acid-producing spoilage bacteria in apple and orange juices was effective when citrus essential oils were added in combination with mild heat treatment process (PEDROSA et al., 2019PEDROSA, G.T.S. et al. Control of autochthonous spoilage lactic acid bacteria in apple and orange juices by sensorially accepted doses of Citrus spp. essential oils combined with mild heat treatments. Journal of Food Science, v.84, n.4, p.848-858, 2019. Available from: <Available from: https://doi.org/10.1111/1750-3841-14474 >. Accessed: August, 26, 2019. doi: 10.1111/1750-3841-14474.
https://doi.org/10.1111/1750-3841-14474...
). The lemon essential oil showed a considerable inhibitory effect on food spoilage yeasts, such as Geotrichum candidum, Pichia anomala, Saccharomyces cerevisiae, and Schizosaccharomyces pombe, as an alternative to synthetic preservatives in fruit-or-milk-based acidic products (TSERENNADMID et al., 2011TSERENNADMID, R. et al. Anti yeast activities of some essencial oils in growth medium, fruit juice and milk. International Journal ofFood Microbiology , v.144, p.480-486, 2011. Available from: <Available from: https://doi.org/ DOI: 10.1016/j.ijfoodmicro.2010.11.004 >. Accessed: Oct. 01, 2019. doi: 10.1016/j.ijfoodmicro.2010.11.004.
https://doi.org/ DOI: 10.1016/j.ijfoodmi...
). As indicated for grape extracts, citrus essential oil would be a prospective antimicrobial to be used in the bioethanol industry to control the growth of lactic acid bacteria and spoilage yeasts.

The cytotoxic activity of essential oils is attributed to the presence of phenolic compounds like aldehydes, terpenes, aliphatic alcohols, ketones, acids, and isoflavonoids. The phenolic compounds are thought to be the main compound of these oils responsible for the antibacterial properties, but there are reports of non-phenolic compounds, such as allyl isothiocyanate, that are more effective against Gram-negative bacteria (TURINA et al., 2006TURINA, A.V. et al. Natural terpenes: self-assembly and membrane partitioning. Biophysical Chemistry, v.101, p.113-122, 2006. Available from: <Available from: https://doi.org/10.1016/j.bpc.2006.02.007 >. Accessed: Oct. 01, 2019. doi: 10.1016/j.bpc.2006.02.007.
https://doi.org/10.1016/j.bpc.2006.02.00...
). The main characteristic feature of the essential oils is the property of hydrophobicity, which gives them the ability to alter the permeability of the mitochondrial cell membrane, thereby making it more permeable with consequent losses of ions and molecules (CARSON et al., 2002CARSON, C.F. et al. Mechanism of action of Melaleuca alternifolia (tea tree) oil on Staphylococcus aureus determined by time-kill, lysis, leakage and salt tolerance assays and electron microscopy. Antimicrobial Agents and Chemotherapy, v.46, p.1914:1920, 2002. Available from: <Available from: https://doi.org/10.1128/AAC.46.6.1914-1920.2002 >. Acessed: Sep. 27, 2019. doi: 10.1128/AAC.46.6.1914-1920.2002.
https://doi.org/10.1128/AAC.46.6.1914-19...
).

Mango

Mango (Mangifera indica L.) is an important tropical fruit in the world, which is extensively marketed because of vast production, wide distribution, and owing to its health benefits to humans (TORRES-LEON et al., 2016TORRES-LEON, C. et al. Mango seed: functional and nutritional properties. Trends in Food Science and Technology, v.55, p.109-117, 2016. Available from: <Available from: https://doi.org/10.1016/j.tifs.2016.06.009 >. Accessed: Oct. 01, 2019. doi: 10.1016/j.tifs.2016.06.009.
https://doi.org/10.1016/j.tifs.2016.06.0...
). Besides the excellent texture and flavor, it has a high nutritional value, being a source of vitamin A and C and rich in phenolic compounds (THARANATHAN et al., 2006THARANATHAN, R.N. et al. Mango (Mangifera indica L.), “The King of Fruits” - an overview. Food Reviews International, v.22, p.95-123, 2006. Available from: <Available from: https://doi.org/10.1080/87559120600574493 >. Accessed: Oct. 01, 2019. doi: 10.1080/87559120600574493.
https://doi.org/10.1080/8755912060057449...
).

Mango wastes, such as the seed kernel and peel, have high functional and nutritional potential. It is estimated that 35-60% of the fruit is discarded as wastes after processing (O’SHEA et al., 2012O’SHEA, N. et al. Dietary fibre and phytochemical characteristics of fruit and vegetable byproducts and their recent applications as novel ingredients in food products. Innovative Food Science & Emerging Technologies, v.16, p.1-10, 2012. Available from: <Available from: https://doi.org/10.1016/j.ifset.2012.06.002 >. Accessed: Aug. 29, 2019. doi: 10.1016/j.ifset.2012.06.002.
https://doi.org/10.1016/j.ifset.2012.06....
). The mango seed has been reported as a biowaste with a high content of bioactive compounds such as phenolic compounds, carotenoids, and vitamin C (JAHURUL et al., 2015JAHURUL, M.H.A. et al. Mango (Mangifera indica L.) by-products and their valuable components: a review. Food Chemistry, v.183, p.173-180, 2015. Available from: <Available from: https://doi.org/10.1016/j.bjp.2018.06.008 >. Accessed: Oct. 31, 2019. doi: 10.1016/j.bjp.2018.06.008.
https://doi.org/10.1016/j.bjp.2018.06.00...
; TORRES-LEON et al., 2016TORRES-LEON, C. et al. Mango seed: functional and nutritional properties. Trends in Food Science and Technology, v.55, p.109-117, 2016. Available from: <Available from: https://doi.org/10.1016/j.tifs.2016.06.009 >. Accessed: Oct. 01, 2019. doi: 10.1016/j.tifs.2016.06.009.
https://doi.org/10.1016/j.tifs.2016.06.0...
). The major phenolic compounds present in mango are gallic acid, ellagic acid, gallates, gallotannins, condensed tannins, mangiferins, catechin, epicatechin, and benzoic acid. Such compounds present in the seed and bark show greater antioxidant activity than the fruit as such (SOONG & BARLOW, 2004SOONG, Y.Y.; BARLOW, P.J. Antioxidant activity and phenolic content of select fruit seeds. Food Chemistry, v.88, p.411-417, 2004. Available from: <Available from: http://dx.doi.org/10.1016/j.foodchem.2004.02.003 >. Accessed: Sep. 08, 2019. doi: 10.1016/j.foodchem.2004.02.003.
http://dx.doi.org/10.1016/j.foodchem.200...
; RIBEIRO et al., 2008RIBEIRO, S.M.R. et al. Phenolic compounds and antioxidant capacity of Brazilian mango (Mangifera indica L.) varieties. Food Chemistry, v.110, p.620-626, 2008. Available from: <Available from: http://dx.doi.org/10.1016/j.foodchem.2008.02.067 >. Accessed: Aug. 20, 2019. doi: 10.1016/j.foodchem.2008.02.067.
http://dx.doi.org/10.1016/j.foodchem.200...
). This antioxidant activity is mainly due to their reducing properties, which play an important role in the neutralization or sequestration of free radicals or chelation of transition metals acting both in the initiation stage as well as in propagation of the oxidative process (SOARES, 2002SOARES, S.E. Ácidos fenólicos como antioxidantes. Revista de Nutrição, v.15, p.71-81, 2002. Available from: <Available from: http://dx.doi.org/10.1590/S1415-52732002000100008 >. Accessed: Oct., 01 2019. doi: 10.1590/S1415-52732002000100008.
http://dx.doi.org/10.1590/S1415-52732002...
).

Mango seeds can also be used as a source of natural antimicrobials. Ethanolic extracts of mango seeds exhibited a spectrum of antimicrobial activities and were effective against Gram-negative bacteria (KABUKI et al., 2000KABUKI, T. et al. Characterization of novel antimicrobial compounds from mango (Mangifera indica L.) kernel seeds. Food Chemistry, v.71, p.61-66, 2000. Available from: <Available from: https://doi.org/10.1016/S0308-8146(00)00126-6 >. Accessed: Sep. 09, 2019. doi: 10.1016/S0308-8146(00)00126-6.
https://doi.org/10.1016/S0308-8146(00)00...
). The structure of its active component confirmed it to be a phenolic compound. The antibacterial activity of different mango peel extracts against Gram-positive S. aureus and Gram-negative Pseudomonas fluorescens was investigated. Extracts showed varying degrees of antibacterial activities against both organisms. Generally, Gram-positive bacteria are susceptible to natural compounds, while Gram-negative organisms exhibit less sensitivity. The peel from Langra mango variety extracted with 70% ethanol and 80% acetone exhibited maximum zone of inhibition against both organisms. The difference in the antimicrobial effects between Gram-positive and Gram-negative bacteria is due to the presence of different cell wall structures. Compounds that can effectively diffuse the lipid bilayer and increase membrane fluidity may be considered as more effective antibacterial agents (KANATT & CHAWLA, 2017KANATT, S.R.; CHAWLA, S.P. Shelf life extension of chicken packed in active film developed with mango peel extract. Journal of Food Safety, v.38, n.1, e12385, 2017. Available from: < Available from: https://doi.org/10.1111/jfs.12385 >. Accessed: Sep. 30, 2019. doi: 10.1111/jfs.12385.
https://doi.org/10.1111/jfs.12385...
).

Avocado

Avocado (Persea americana Mill.) is a dicotyledonous plant belonging to the Lauraceae family, a native of Central America and Mexico, and cultivated in almost all tropical and subtropical regions worldwide. The fruits have high nutritional quality; contain high levels of vitamin, minerals, proteins, fibers, and unsaturated fatty acids, which are beneficial to health (TREMOCOLDI et al., 2018TREMOCOLDI, R. et al. Exploration of avocado by-products as natural sources of bioative compounds. PLoS ONE, v.13, e0192577, 2018. Available from: https://doi.org/10.1371/journal.pone.0192577. Accessed: Oct. 01, 2019. doi: 10.1371/journal.pone.0192577.
https://doi.org/https://doi.org/10.1371/...
). Avocado peels and seeds have high contents of bioactive compounds, such as phenolic acids, condensed tannins, flavonoids (including procyanidins and flavonols), hydroxybenzoic and hydroxycinnamic acids (HURTADO-FERNÁNDEZ et al., 2011HURTADO-FERNÁNDEZ, E. et al. Profiling LC-DAD-ESI-TOF MS method for the determination of phenolic metabolites from avocado (Persea americana). Journal of Agricultural and Food Chemistry, v.9, p.2255-2267, 2011. Available from: <Available from: https://doi.org/10.1021/jf104276a >. Accessed: Oct. 09, 2019. doi: 10.1021/jf104276a.
https://doi.org/10.1021/jf104276a...
; DAIUTO et al., 2014DAIUTO, E.R. et al. Composição química e atividade antioxidante da polpa e resíduos de abacate ‘HASS’. Revista Brasileira de Fruticultura, v.36, n.2, p.417-424, 2014. Available from: <Available from: http://dx.doi.org/10.1590/0100-2945-102/13 >. Accessed: Oct. 31, 2019. doi: 10.1590/0100-2945-102/13.
http://dx.doi.org/10.1590/0100-2945-102/...
; FIGUEROA et al., 2018aFIGUEROA, J.G. et al. Comprehensive characterization of phenolic and other polar compounds in the seed and seed coat of avocado by HPLC-DAD-ESIQTOF- MS. Food Research International, v.105, p.752-763, 2018a. Available from: <Available from: https://doi.org/10.1016/j.foodres.2017.11.082 >. Accessed: Oct. 16, 2019. doi: 10.1016/j.foodres.2017.11.082.
https://doi.org/10.1016/j.foodres.2017.1...
, b).

Industrial processing of avocado generates large quantities of agro-industrial byproducts (peel and seed), ranging from 18% to 23% of fruit dry weight (WANG et al. 2010WANG, W. et al. Antioxidant capacities, procyanidins and pigments in avocados of different strains and cultivars. Food Chemistry, v.122, p.1193-1198, 2010. Available from: <Available from: https://doi.org/10.1016/j.foodchem.2010.03.114 >. Accessed: Oct. 01, 2019. doi: 10.1016/j.foodchem.2010.03.114.
https://doi.org/10.1016/j.foodchem.2010....
). The individual phenolic profiles of hydroethanolic extracts of peels and kernels of avocado variety Hass showed correlation with their antioxidant, antimicrobial, and cytotoxic activities. Avocado byproducts presented a very distinct phenolic profile, with a higher concentration in peels (227.9 mg g-1 of total phenolic content), mainly of (epi)catechin derivatives (175 mg g-1), followed by chlorogenic derivatives (42.9 mg g-1) (MELGAR et al., 2018MELGAR, B. et al. Bioactive characterization of Persea americana Mill. by-products: a rich source of inherent antioxidants. Industrial Crops & Products, v.111, p.212:218, 2018. Available from: <Available from: http://dx.doi.org/10.1016/j.indcrop.2017.10.024 >. Accessed: Oct. 06, 2019. doi: 10.1016/j.indcrop.2017.10.024.
http://dx.doi.org/10.1016/j.indcrop.2017...
). The bioactive compounds can also be reported in seeds, such as catechin, protocatechin, epicatechin, and also p-coumaric, caffeic, ferulic, synaptic, p-hydroxybenzoic, vanillic, syringic, and gallic acids (RODRIGUEZ-CARPENA et al., 2011RODRIGUEZ-CARPENA, J.G. et al. Avocado (Persea americana Mill.) phenolic, in vitro antioxidant and antimicrobial activities, and inhibition of lipid and protein oxidation in porcine patties. Journal of Agricultural and Food Chemistry, v.59, p.5625-5635, 2011. Available from: <Available from: https://doi.org/10.1021/jf1048832 >. Accessed: Oct. 01, 2019. doi:10.1021/jf1048832.
https://doi.org/10.1021/jf1048832...
).

Studies have shown the antimicrobial effect of the compounds extracted from avocado seed extract on microorganisms. SALINAS-SALAZAR et al. (2017SALINAS-SALAZAR, C. et al. Inhibitory activity of avocado seed fatty acid derivates (acetogenins) against Listeria monocytogenes. Journal of Food Science, v.82, p.134-144, 2017. Available from: <Available from: http://dx.doi.org/10.1111/1750-3841.13553 > Accessed: Oct. 01, 2019. doi:10.1111/1750-3841.13553.
http://dx.doi.org/10.1111/1750-3841.1355...
) have shown a biocidal effect of avocado seed extracts (7.8-15 mg L-1) on L. monocytogenes, suggesting that the effect was due to the increase in permeability of cell membrane. The ethanolic extract of avocado seed had antimicrobial action against L. monocytogenes (375.0 µg L-1), Staphylococcus epidermidis (354.2 µg L-1) and Zygosaccharomyces bailii (500 µg L-1) (CHIA & DIKES, 2010CHIA, T.W.R.; DIKES, G.A. Antimicrobial activity of crude epicarp and seed extracts from mature avocado fruit (Persea americana) of three cultivars. Pharmaceutical Biology, v.48, n.7, p.753-756, 2010. Available from: <Available from: https://doi.org/10.3109/13880200903273922 >. Acessed: Oct. 31, 2019. doi: 10.3109/13880200903273922.
https://doi.org/10.3109/1388020090327392...
).

CONCLUSION:

Several low-cost raw materials are available as agro-industrial wastes that are valuable sources of bioactive compounds. The huge variety of compounds produced by plants as secondary metabolites may act as antioxidants and antimicrobials with applications in the food and fermentation industries. Fruit wastes, in particular citrus, avocado, grape, and mango wastes, have been used for the extraction of compounds with biological activities similar to the synthetic compounds that are commonly used. These compounds offer a more natural and safer option to the food industry. The fermentation process involved in the bioethanol production deals with bacterial contaminants that could be combated with these natural antimicrobials; however, their utilization in the context of this industry has not received due attention. A promising field of application emerges from these investigative reports that could relieve the unsustainable use of hazardous chemicals in the bioethanol industry to fight bacterial contamination.

ACKNOWLEDGMENTS

This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Brasil - finance code 001, including a grant for the first author (PNPD no.33001014051P7), and by Fundação de Amparo a Pesquisa do Estado de São Paulo (FAPESP), Brasil (research support no 2018/19139-2).

REFERENCES

  • CR-2019-0857.R1

Publication Dates

  • Publication in this collection
    06 Apr 2020
  • Date of issue
    2020

History

  • Received
    01 Nov 2019
  • Accepted
    26 Jan 2020
  • Reviewed
    02 Mar 2020
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