Productivity and quality of potato cultivars for processing as shoestrings and chips

Brazilian market of potato processing has presented expressive development in recent years. However, its expansion is constrained by raw material supply suitable for industrial processing. Selection of adequate cultivars contributes to final product cost reduction as well as its yield and quality improvement. The research aimed to study tuber yield and evaluate its frying potential for shoestrings and chips, of potato cultivars recently introduced in Brazil. Nine potato cultivars (Arizona, Caruso, Destiny, Excelence, Saviola, Agata, Almera, Fontane and Markies) were assessed in an experiment carried out between January and May, 2013, in South-West region of Minas Gerais State, Brazil. ‘Arizona’ and ‘Caruso’ cultivars exhibited superior productive potential and along with ‘Markies’ the highest production of marketable tubers. ‘Caruso’ and ‘Destiny’ produced more than 20% of dry matter and the lowest reducing sugar levels. ‘Caruso’ exhibited the highest frying yield in both processing shapes and absorbed less fat as shoestring. ‘Destiny’ absorbed less fat when processed as chips. ‘Excelence’ presented intermediary performance for every evaluated attribute. ‘Caruso’, ‘Destiny’, and ‘Excelence’ produced chips with appropriate color for market. Among the assessed cultivars, ‘Caruso’, ‘Destiny’, and ‘Excelence’ were the most promising. These cultivars demonstrated appropriate processing ability in the shape of shoestrings. ‘Destiny’ could also be indicated to be processed as chips.

Palavras-chave: Solanum tuberosum, massa seca, açúcares redutores, absorção de gordura, cor das fritas, rendimento industrial.To succeed in both field and processing, elevated yield potential cultivars should be employed and adequate to each form and processing (Pádua et al., 2012b).Aiming to obtain superior yield and final product enhanced quality, the cultivar choice should be based on its intended use (Fontes, 2005;Pádua et al., 2012b).Thus, for fries processing is necessary utilize cultivars that have, principally, uniform shape, elevated dry matter content, and low reducing sugars percentage (Popp, 2000).Fries industrial processing in both shoestrings and chips is similar and the requirement regarding quality characteristics of raw materials in terms of color, flavor, and texture are basically the same.
As this is an elevated aggregated value product, the raw material cost is an essential factor in every processing form.It is necessary to meet both the interests of producers and processors.Producers demand inferior cost and high yield.On the other hand, processors are also interested in raw material with reduced cost, but combined with the best quality in order to achieve quality minimum standards after processing (Popp, 2000;Pádua et al., 2016).However, the relation among price, raw material, and product's quality is often not considered (Popp, 2000).
Several smaller Brazilian industries employ tubers of Agata cultivar in frying processing due to its availability and raw materials price.This is the principal potato grown in the country due to several relevant factors, such as rapid seed potatoes sprouting, vigorous plants, early cycle, and eminent productive potential, besides producing a considerable percentage of substantial tubers with a satisfactory appearance.Nonetheless, this is a cultivar recommended for cooking, and demonstrates no aptitude for frying (Pádua et al., 2016).
Cultivars with frying aptitude represent a small portion of the entire volume produced in Brazil, limiting raw materials offer suitable for industries (Berbari, 2005).This fact occurs due to potato fresh market requirements for external appearance, shape and size of the tubers.Brazilian producers prefer precocious and productive varieties intending to achieve enhanced marked competitiveness.These selection criteria restrict the number of cultivars in use, even with several national and foreign cultivars registered for cultivation in the country, especially those suitable for frying, which usually present tubers with lower appearance, prolonged vegetative cycle and inferior productivity.
In this context, productivity performance of potato cultivars introduced in Brazil, and its quality attributes for industrial processing in the shapes of shoestrings and chips were assessed intending to recommend competitive cultivars with those designated for fresh market tubers.

MATERIAL AND METHODS
Nine potato cultivars were evaluated: Agata, Almera, Arizona, and Saviola are not suitable for frying; Excelence, Fontane and Markies present dual aptitude, which signifies that those were recommended for both cooking and frying; lastly 'Caruso' and 'Destiny' are suggested for frying.Except for 'Caruso', originally from Germany, every other cultivars are of Dutch origin.
Agata, Almera, Arizona, Excelence, Saviola cultivars with early cycle, and 'Markies' with late maturation, presented elevated productivity, substantial tubers, elongated and oval shape, light yellow skin, uniform and great appearance.'Excelence' and 'Markies' showed tubers with high dry matter content.These cultivars demonstrated dual cooking aptitude (cooking and frying) and other with inferior dry matter content and cooking capacity were not appropriate for frying (Agrico, 2013).'Fontane', 'Destiny' and 'Caruso' demonstrated relevant productivity with oval tubers, yellow skin and tubers with elevated dry matter content.Moreover, these types are proper for frying wherein 'Fontane' has medium production cycle, great tubers and smooth skin, while 'Destiny' and 'Caruso' have early cycle, medium tubers and rough skin (Agrico 2013, Solana, 2013).
Experimental design was of randomized blocks with nine treatments and four replications.In field, the plot consisted of four furrows with 25 plants.The spacing was 0.80 m between furrows and 0.30 m between plants totaling an area of 24 m 2 per plot accounting 100 useful plants.Field phase was conducted at Prata Farm, in Nova Resende, Minas Gerais State, Brazil (21°07'30''S, 46°25'15"W, 1,250 m altitude), in the period between January and May, 2013.The experiment was performed during dry season in succession to corn crops in clayey soil, in which a preparation for planting consisted of plowing, harrowing and furrowing.Soil preparation, fertilization, and phytosanitary treatments were mechanically performed, while planting and furrows closures were manually made.Operations of ridging and topdressing were conducted in mechanized mode 30 days after planting.The harvest was accomplished 107 days after planting, when more than 80% of the plants were dead and dry.
The processing (Figure 1) and laboratorial evaluations were performed in Department of Agribusiness, Food, and Nutrition of Fruits and Vegetables Laboratory of ESALQ-USP.The dry matter content was determined gravimetrically according to AOAC (1995) and reducing sugar content was extracted by Yoshida (1972) method, quantified by Somogy method adapted by Nelson (1944) and expressed in wet basis percentage.Frying yield was defined according to a method cited by Paschoalino et al. (1975), adapted for potato processing for shoestring and chips shapes.The oil content was Productivity and quality of potato cultivars for processing as shoestrings and chips determined following AOAC (1995) method.Pulp mean color after frying was established by visual comparison method according to color scale and interpretation adopted by North Americans industries (USDA, 1988).The results were statistically analyzed using analysis of variance (ANOVA) and the means were compared by Tukey test at 5% of probability.Principal component analysis (PCA) was also carried out aiming to characterize cultivars and observe its correlations with analyzed attributes.

RESULTS AND DISCUSSION
Classification of harvested tubers aims to standardize these by size (larger diameter), reduce losses and provide competitive prices (Ceasaminas, 2015).Table 1 presents results referring to tubers production of the nine evaluated cultivars.Concerning total production, 'Arizona' and 'Caruso' were the most productive.Total production reflects the varieties productive potential on tested environment.Considering the productive means over 24 t/ha, it can be considered that vast majority of tested cultivars have productive potential in Brazilian agro ecological conditions, as the national production average is 28.4 t/ha (IBGE, 2015).
On the other hand, marketable tubers production that brings together grades with highest market value, 'Arizona', 'Caruso', and 'Markies' were the most productive.On production grades, cv.Saviola stood out due to large tubers production not differing from 'Arizona', 'Excelence', 'Markies' and 'Agata' (Table 1).The tubers size is a characteristic tightly linked with cultivar genetic constitution, however, this can be influenced by environmental conditions and, principally, by crops management (Pádua et al., 2012b).These characteristics could be an explanation for observed variation on tubers size among the tested cultivars, wherein each cultivar concentrated the production in a determined grade size.Although majority of cultivars exhibit superior tubers concentration in large grades, Caruso cultivar staged a production concentrated on tubers of medium grade according to this cultivar standardize characteristic as stated by Solana (2013).'Excelence' and 'Saviola' were the varieties that presented lower production of tiny tubers.Large tubers grade is the most prized in fresh tubers market due to peeling facilitation on domestic processing.For chips frying process, the round or ovalround form is preferable besides larger size, to enable obtaining elevated yield of slices within commercial standards (Pádua et al., 2012b).Cultivar Destiny was the one that best approaches these requirements.
For shoestring potato production, the tubers size is not the most important characteristic, but the uniformity within the batch, which aims to provide improved efficiency in peeling and cutting process.Therefore, this is essential to obtain equal sized fillets that will result in a better and uniform frying (Pádua et al., 2012b).Thus, cvs.Caruso, Destiny and Fontane reveal themselves suitable for shoestrings production due to the presence of oval tubers, elevated concentration of average-sized tubers, and considerable size uniformity.
Overall mean for dry matter content obtained in this work was 17.43% (Table 2), which is in accordance with Brazilian Food Composition Table (TACO).This table describes that planted cultivars in Brazilian conditions achieve, in average, 17.1% of dry matter (Unicamp, 2006).Cultivars Caruso, Destiny, Excelence, Fontane, and Markies presented dry matter content over 17% (Table 2), which is close to the demands required for shoestring production that according to Gomes et al. (2005) should be superior to 18%.Vendrusco & Zorzella (2002) also pointed out that even with inferior dry matter content, several cultivars can be employed in fries industry with the condition that meets other frying quality attributes, which are color, oil residual content, taste, crispness and yield after processing.It is worth highlight Caruso and Destiny cultivars that presented dry matter content higher than 20% and comply, therefore, the requirements for the production of chips potato (Pádua et al., 2012b).
Dry matter content and reducing sugars can be considered, among others, the most limiting processing factors, considering that they are essential in fat absorption, final product appearance and texture.Reducing sugars in tubers react with proteins and free amino acids in cytoplasm, through Maillard reaction, during frying process producing brown colored pigments with bitter taste that depreciate the final product (Pádua et al., 2012b).Therefore, potato cultivars indicated to frying form processing should present reducing sugars content inferior to 0.035% of fresh matter (Stark et al., 2003).
'Caruso' and 'Markies' exhibit inferior content of reducing sugars, which is a notable factor to be considered in recommendation of these cvs.for frying, knowing that lower contents will permit a lighter color and a more pleasant flavor on final product.On the other hand, 'Destiny', 'Excelence',  'Fontane', and 'Agata' have shown intermediary content.Considering that 'Agata' presented inferior dry matter content, 'Destiny', 'Excelence', and 'Fontane' could be a more appropriated option to substitute Agata in frying process for industries that use them.'Saviola', 'Arizona' and 'Almera' displayed superior reducing sugars content, therefore, should not be utilized in frying process due to both darkening and bitter taste of final product (Table 2).
The fat absorption in potato frying process is of about 35% including that present on the surface, which penetrates into pulp after processes completion (Pedreschi et al., 2008).Dry matter content is inversely proportional to potato water content.This affects absorbed fat quantity due superior water absorption during heating and water evaporation.Besides dry matter content, this absorption is related to the type of potato cut.In this case, shoestring potato presents greater absorption than chips due to superior exposed surface.
According to TACO, average fat absorption of potatoes is 41% for shoestring and 36% for chips (Unicamp, 2006).Absorbed fat quantity is extremely trivial for final products.Elevated fat contents lead to drenched fries conferring inferior crispness, taste alteration, quality and appearance damaging as well as increasing production cost (Grizotto, 2005).Caruso and Destiny cvs.demonstrated inferior fat absorption when fried as shoestring, and chips respectively (Table 2).Comparing TACO (Unicamp, 2006) with obtained values of 'Caruso', 'Destiny', 'Fontane', and 'Markies' (Table 2) it can be observed that these cultivars could be recommended for chips, and of those, only Caruso would be indicated for shoestrings.
'Caruso' provided the best frying yield in both shapes.In contrast, 'Almera' presented the lowest yield in both frying forms (Table 2) highlighting that this cultivar was not suitable for this processing type.
Besides the attributes already evaluated, processed potato acceptance depends on, principally, final product coloration.This attribute is considered the most important in fried potato quality.Moreover, this characteristic is essential for consumer's acceptance.According to Tocchini & Mercadante (2001), in food evaluation, the visual impact caused by its color overlaps other attributes, highlighting that this feature is one of the most important for products commercialization being the first criterion for production acceptance and rejection.Therefore, its evaluation is extremely important for industrial processing.Grizotto (2005) pointed out that ideal fries color varies from light yellow to golden yellow without achieving brown tonality and absence of dark spots or lines.
Fried potato coloration varied from extremely light yellow and predominantly brown (Table 2; Figure 2).Destiny, Excelence, Fontane and Markies cvs.exhibit light color after fried as shoestrings and chips, which lead to a notable appearance final product.The other cultivars presented yellow coloration with brown parts varying from brow dots to predominantly brown, being unsuited for both processing forms.
Through principal components analysis (Figure 3), a relation among analysed attributes can be precisely assessed.Attributes reference lines reveal that total and marketable

Table 1 .
Total and marketable yield of potatoes, and tuber size grades (t/ha) {produtividade total e comercial de batata e classificação dos tubérculos por tamanho (t/ha)}.Piracicaba, ESALQ, 2013.Means followed by the same letter in each column do not differ by Tukey test at 5% level of probability (medias seguidas por letras iguais na coluna não diferem pelo teste de Tukey,5%).