Conservation advances on Physalis peruviana L. and Spondia purpurea: a review

Among fruits valued by their consumers due to their health benefits, Physalis peruviana L. and Spondia purpurea have special relevance due to their polyphenolic content, ascorbic acid, and carotenoids among others, which provide antioxidant properties. Through the years, fruit production and consumption have increased. A 4.2% annual growth was reported in South and Central America, while in Ecuador between 2013 and 2018, goldenberry farming showed a growth of 10%, with an increment of 160% in its exportation from 2015 to 2016 (Moreno-Miranda et al., 2019).


Introduction
Among fruits valued by their consumers due to their health benefits, Physalis peruviana L. and Spondia purpurea have special relevance due to their polyphenolic content, ascorbic acid, and carotenoids among others, which provide antioxidant properties. Through the years, fruit production and consumption have increased. A 4.2% annual growth was reported in South and Central America, while in Ecuador between 2013 and 2018, goldenberry farming showed a growth of 10%, with an increment of 160% in its exportation from 2015 to 2016 (Moreno-Miranda et al., 2019).
This behavior brings up the need for carrying out research on the conservation of the fruit's properties, so sensorial and functional characteristics of the fruits can compete in international market. This review collects the latest advances in research about characterization and fruit conservation of Physalis peruviana L. and Spondia purpurea, with emphasis in their functional and nutritional properties depending on their maturity and postharvest conservation technology. Health benefits and the chronology of the conservation method on fruit properties were also included.

Characterization
Among the most notorious factors that affect fruits physicochemical and functional properties are: farming zone, and edaphological and climate conditions to which the fruit is exposed. Many times, fruit properties are different even if they are of the same variety, as it is shown in this paper. Physalis peruviana L. from Argentina (Bazalar Pereda et al., 2019), Colombia (Bravo & Osorio, 2016), Peru (Maruenda et al., 2018), Brazil (Licodiedoff et al., 2016), South Africa (Carvalho et al., 2015), Egypt, South Africa, India, New Zeeland, Australia and Great Britain (Ramadan et al., 2015) have been reported. But among countries, the most advanced research is found in Colombia, where a normative (Norma Técnica Colombiana, 1999) to identify fruit maturity according to its color has been developed.
The research spectrum for Spondia purpurea is not extensive, and most observations are performed in Brazil (da Silva et al., 2016;Solorzano-Morán et al., 2015) and Mexico (Álvarez-Vargas et al., 2017), even when the farming region covers Venezuela, Colombia, Ecuador, Peru and Central America. Most studies have been focused on functional, nutritional and physicochemical characterization, and the application of conservation technology. Due to differences in data, the information on properties will be compared in tables for easier interpretation. Table 1 shows proximate analysis (g/100 g fresh weight) and physicochemical properties such as pH, acidity (%w/w citric acid), soluble solids (SS), humidity, and maturity indices (MI). Table 1 shows MI, they are different so are their properties, this factor is the most relevant to characterize a fruit. Table 2 shows mineral (mg/100 g fresh weight) and the functional content of Physalis peruviana L. as vitamin A, C, carotenoids, polyphenols, and antioxidant activity (aa). These last properties are widely studied, due to their relevance; aa is expressed as µmol Trolox/g fresh weight, vitamin A as mg equivalent retinol activity (ERA)/100 g fresh weight (fw), vitamin C as mg acid ascorbic/100 g fw and polyphenols as mg gallic acid equivalent (EGA)/100 g fw.
Mineral content depends on the farming zone, that is why a considerable variation on these parameters is expected. The wide range for functional properties could be attributed to different extraction and quantification methodologies, as it is known that extraction solution or quantification procedure can be modified from one author to another. This would affect data and so will the MI, climacteric fruits (as goldenberry) keep maturing and fluctuating functional components affecting aa.
There was characterization research on goldenberry either in juice or powder, where its functional properties were evaluated (Ordóñez-Santos et al., 2017), trying to maintain the original qualities, over different treatments (heat pasteurization or sonication). Table 3 shows properties of gooseberry juice without treatment.
Mexican plum (Spondia purpurea) does not have many studies but in Mexico and Brazil some of its physicochemical characteristics were described. It is known that among its functional properties has vitamin C, polyphenols, and carotenoids; the properties of the last ones are reflected on the epidermis. It possesses a high senescence rate, that is, in a few days it is no longer suitable for consumption. Research on conservation is increasing by trying to preserve its properties or studying new alternatives of consumption while, maintaining its sensorial, nutritional, and functional properties (Muñoz-López et al., 2018). Table 4 shows physicochemical and functional properties of Spondia purpurea.
Physalis peruviana L. and Spondia purpurea have benefits for health consumers due to their aa. The increase in cardiovascular diseases in recent decades (World Health Organization, 2017) has also boosted interest in foods that contain bioactive compounds with aa. These health problems are mostly caused by oxidative stress, due to oxygen reactive species (ORS) augmentation, produced by the oxidation of macromolecules with endothelial dysfunction, converting oxidative stress on a disbalance mediator between vasodilator and vasoconstrictor mechanism. It is also associated with chronic degenerative diseases such as cancer, diabetes, and premature aging. Functional components of goldenberry The difference in mineral content between Spondia purpurea (Table 5) and Physalis peruviana (Table 2) is not significant, but it is observed that the variety of these minerals contributes to the osmotic balance of the cell, as well as to the proper functioning of enzymes that require these micronutrients.

Storage methods comparation
Massive production brought new conservation technics without specialized equipment, that is why there is a special emphasis in chitosan (Bautista-Baños et al., 2006cited by Bautista-Baños et al., 2017. This is a semipermeable film which prolongs life of fruit and vegetable products with lower infection levels than any other technic, and this has been reported on Chitosan treated plums (2.0 and 2.5%) at 12 °C. Table 6 shows a variety of experiments in the last years, conservation elements are specified so as process characteristics and fruit exposure conditions. The use of plastics of different densities remains as the best preservation method, despite researchers' questions and the appearance of smart packaging. Due to the easy acquisition and lower production cost of polyethylene packages, considering that storage conditions play a fundamental role in obtaining the best storage effectiveness, research shows that food has been kept in perfect condition for 15 days when combined with temperatures ranging between 10 degrees Celsius, it is also necessary to mention that light conditions to which these packages are exposed interfere with the shelf life.

Conclusion
Technological developments have allowed to establish several preliminary tests to predict the physicochemical composition of the plum and goldenberry (in Mexico especially), which contributes significantly to the conservation methods used by making them more effective, optimizing the transfer times to the final consumer, and motivating the generation of new preservation alternatives; that through various research have shown better results of product storage at more favorable reproducibility conditions for the food industry, particularly those which work with large volumes of food worldwide.  Rezende et al. (2018)