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Introduction
Potatoes, with a global production of about 380 million tons, are among the most consumed agricultural products worldwide, along with rice, barley and wheat (Food and Agriculture Organization of the United Nations [FAO], 2016). From a nutritional point of view, this tuber is an important source of carbohydrates, but it is also a source of protein, vitamins (C, B3 and B6), minerals (potassium, phosphorus and magnesium) and compounds with antioxidant characteristics of a phenolic nature that contribute to its functional quality (Andre et al., 2007; Burlingame, Mouillé, & Charrondière, 2009). Intake of these compounds helps prevent oxidative tissue damage, which is linked to the development of diseases such as cancer, diabetes, and neurodegenerative disorders (Ezekiel, Singh, Sharma, and Kaur, 2013). Although the presence of phenolic compounds is considered important from a functional point of view, some of them constitute the substrate of polyphenol oxidase (PPO) and peroxidase (POD) enzymes. These enzymes are responsible for enzymatic browning, the end product of which is melanins, dark high molecular weight pigments that degrade the quality of the final product (Yoruk & Marshall, 2003).
The potato has an important capacity for adaptation, being able to grow and develop in very diverse environments due to its great genetic variability, which influences agronomic traits, productivity and resistance to diseases and pests, among other aspects (Navarre, Goyer, & Shakya, 2009). In addition to these features, genetic variability also manifests itself in composition, affecting carbohydrates, proteins, vitamins, amount and type of phenolic compounds, and enzyme activity (Ezekiel et al., 2013).
It is very important to have genetic materials adapted to the place where they are grown; therefore, the development of local breeding programs becomes essential (Rodríguez-Galdón et al., 2012). In these programs, in addition to the agronomic traits of the potato, its composition must be considered, since the suitability for use of the different genetic materials, as well as the quality of the product obtained after processing, largely depend on it (Burlingame et al., 2009; Silveira, Oyarzún, Sepúlveda, & Escalona, 2017).
In the case of potato materials intended for frying, the attributes with the greatest impact are dry matter content and specific gravity, since they are indicative of the amount of starch in the potato, which will determine the quality of the frying process. In potato, the highest dry matter content (≥ 20 %), which corresponds to the highest specific gravity (≥ 1.080) and low levels of reducing sugars (≤ 250 mg·100 g-1 of fresh weight [FW]), result in chips with lower oil content, more crispness and no dark color (Gallego, Miguez, & de la Montaña, 2006; Morales-Fernández et al., 2015).
Considering the above, the objective of this paper was to characterize 24 genetic potato materials, selected for frying, and a commercial control, in terms of physical (dry matter, specific gravity and color) and chemical (total polyphenols, total antioxidant capacity and polyphenol oxidase activity) quality attributes.
Materials and methods
Plant material
In the work, 25 genetic materials, 24 from the National Agricultural Research Institute's (INIA, Las Brujas, Canelones, Uruguay) Genetic Improvement Program and a commercial variety (Challenger), were analyzed. The 24 materials were selected based on their good agronomic performance, mainly considering productivity and disease resistance, while ‘Challenger’, of Dutch origin, is suitable for frying and highly valued by the Uruguayan agroindustry. The materials were obtained from the spring cycle (southern hemisphere), for which they were sown in September and harvested in early December.
After harvest, the tubers were cured (18 °C, 85 % relative humidity, 12 days), a process by which harvest wounds heal, due to periderm formation, which reduces tuber dehydration and the entry of pathogens. After curing, the materials were characterized considering their shape and color of peel, pulp and chip (Figure 1); for this, three replications of 10 tubers each were used.
Potato frying
Three mm thick flakes were obtained with a kitchen mandoline (Tescoma®, Spain) and placed in water to avoid oxidation until frying, prior to which the flakes were removed from the water, centrifuged (Ilko®, Chile) and dried with a paper towel. Frying was done in a domestic fryer (model AF101932, Moulinex®, Spain), with sunflower oil (Optimo, Cousa, Uruguay), at 180 °C for 3 min.
Specific gravity
This variable was determined from the relationship between weight in air and weight in water, according to the methodology proposed by the International Potato Center (CIP, 2007). The determination was made in triplicate, with 10 tubers for each genetic material and replica. The formula used was as follows:
Dry matter content
To estimate the dry matter content, 20 g of pulp from a composite sample consisting of 10 tubers (this for each material) were weighed, placed in Petri dishes and kept in an oven (model GO 27, Blue M, USA) at 80 °C until constant weight (Silveira et al., 2017). The measurement was made in triplicate and the values were expressed as a percentage. The following formula was used for the calculation:
Color
Color was measured in 90 slices of each genetic material, both in raw and fried potatoes, with a colorimeter (model TCR 200, PCE Instruments, China). In the case of raw potato, the measurement was made before the frying of each genetic material. The parameters measured were L*, a*, b*, from the CIELab system, which were used to calculate the values of the hue angle [Hue = arctan b* x (a*)-1] and chroma (Chroma: Cab* = √ a*2 + b*2).
Polyphenol oxidase (PPO) enzyme activity
The activity of the enzyme was determined by spectrophotometry (Unico, S-2150, USA), as reported by Cabezas-Serrano, Amodio, Cornacchia, Rinaldi, and Colelli (2009), with some modifications. Four grams of pulp lyophilized with a freeze dryer (model LGJ 12, NanBei Instrument Equipment, China) were taken from a composite sample just like that of dry matter. Eight mL of cold acetone were added to this sample and homogenized for 2 min; the residue was recovered and treated again with acetone. Next, the acetone was volatilized using a vacuum pump. Once dry, it was homogenized for 30 min with the extraction buffer (0.1 M and pH 6.6), containing 20 mmol of ascorbic acid, 5 g·L-1 of Triton and 10 g·L-1 of polyvinylpyrrolidone, and then centrifuged at 8,000 g, 4 °C for 30 min. For the determination, 0.1 mL of the supernatant, 0.9 mL of sodium phosphate buffer (0.05 M, pH 7) and 0.1 mL of a 0.2 M catechol solution prepared in the same buffer were used. Absorbance at 420 nm was measured with readings every 5 s for 4 min. Total protein content was estimated by the Bradford test (Bradford, 1976), using bovine serum albumin as standard. Values were expressed as a unit of enzyme activity per gram of protein (U·gprotein -1 in dry weight [DW]).
Total polyphenol (TP) content and total antioxidant capacity (TAC)
TP and TAC was determined in an extract obtained by homogenizing 0.8 g of lyophilized pulp (also from a composite sample) with 5 mL of 70 % methanol. The sample was then centrifuged at 1050 g, at 4 °C for 20 min, and the supernatant used as extract was separated. TPs were obtained using the methodology proposed by Singleton and Rossi (1965), with slight modifications. Values were expressed as milligrams of gallic acid equivalent per gram in DW (mg GAE·g-1 in DW).
TAC was obtained using the ferric reducing antioxidant power (FRAP) methodology established by Silveira et al. (2017). First, 900 μL of reagent (10 mM 2,4,6-tris (2-pyridyl)-s-triazine in 40 mM HCl, 20 mM FeCl3 and 300 mM acetate buffer at a ratio of 1:1:10 v/v at pH 3.6) were mixed with 90 μL of distilled water and 30 μL of extract. After 1 h, absorbance was measured at 595 nm. Values were expressed as milligrams of Trolox equivalents per gram in DW (mg TE·g-1 in DW).
Statistical analysis
A randomized complete block design was established. When significant differences were found in the analysis of variance, the means were subjected to Tukey’s multiple comparison test (P ≤ 0.05). Additionally, the linear regression coefficient and Pearson’s correlation coefficient between the analyzed variables were calculated. Data processing was performed with Infostat statistical software version 2017.
Results and discussion
Dry matter content
Most of the genetic materials evaluated (21 clones), and the commercial variety Challenger, had a dry matter content of between 20.0 and 23.5 %, and in four materials analyzed this content was between 15.5 and 19.9 % (Table 1).
Table 1 Comparison of means of dry matter obtained in 25 genetic potato materials.
| Clone | Dry matter (%) | Clone | Dry matter (%) | |
|---|---|---|---|---|
| 17.6 | 21.36 ± 1.08 abz | 8035.2 | 21.85 ± 0.26 a | |
| 2083.6 | 21.82 ± 0.42 a | 9052.3 | 21.67 ± 0.27 ab | |
| 5012.3 | 20.83 ± 0.66 ab | 10007.1 | 21.01 ± 0.92 ab | |
| 6093.1 | 22.56 ± 0.97 a | 10011.1 | 23.04 ± 0.25 a | |
| 7032.3 | 17.19 ± 0.45 bcd | 10021.1 | 22.64 ± 0.63 a | |
| 7036.1 | 23.44 ± 0.49 a | 10021.2 | 23.01 ± 1.54 a | |
| 7046.2 | 22.04 ± 1.18 a | 10021.3 | 22.20 ± 0.92 a | |
| 7049.1 | 21.63 ± 1.06 a | 10025.1 | 16.31 ± 1.01 cd | |
| 7062.1 | 15.50 ± 0.62 d | 793101.3 | 22.24 ± 0.42 a | |
| 7065.3 | 23.53 ± 0.64 a | 93060.4 | 20.92 ± 0.79 ab | |
| 8025.1 | 21.62 ± 0.34 ab | Challenger | 20.72 ± 1.59 abc | |
| 8025.3 | 21.26 ± 0.29 ab | LSD1 | 4.14 | |
| 8026.2 | 19.95 ± 0.09 abc | CV (%) | 6.22 | |
| 8030.2 | 21.13 ± 0.84 ab |
LSD = least significant difference; CV = coefficient of variation. zMeans with the same letter within each column do not differ statistically (Tukey, P ≤ 0.05). The values are means (n = 90) ± standard error of the mean.
The percentage of dry matter is one of the most important quality parameters, as it defines the suitability of the potato for use. This is because higher dry matter content results in lower oil absorption during the frying process, and therefore allows for a better textured product. According to Cacace, Huarte, and Monti (1994), the materials with good suitability for frying are those with more than 20 % dry matter. Materials with average dry matter values (18 to 20 %) are more suitable for baking or mashing, and those with a lower content (15 to 17 %) are suitable for cooking. Considering the above, most of the materials analyzed (83.8 %), including the commercial variety, are suitable for frying, and a few (07032.3, 10025.1 and 07062.1) are suitable for cooking.
The materials were grown in the same season (spring), and in experimental plots with the same soil type and management; therefore, the differences in dry matter content are not due to an environmental effect, but rather to genetics, as stated by Martínez and Ligarreto (2005).
Specific gravity
Specific gravity, like dry matter content, is related to the suitability of the potato for use. This is due to the high and positive correlation between the two variables (Ochsenbein, Hoffmann, Escher, Kneubühler, & Keiser, 2010). No statistical differences were found between the measured specific gravity values, which were between 1.05 and 1.11 (data not shown), indicating that, with the exception of clones 7062.1 and 10025.1, all materials would be suitable for frying. According to CIP (2007), specific gravity values should be between 1.09 and 1.11, in order to have low oil absorption (considered to be 30 to 40 %).
A linear correlation was found between the percentage of dry matter and specific gravity (P ˂ 0.0001), with a value of R2 = 0.49, with the equation being as follows: dry matter (%) = -180.81 + 188.63 (specific gravity). Kumar, Ezekiel, Singh, and Ahmed (2005), who obtained a linear regression value of R2 = 0.93, report the following equation: dry matter (%) = -238.5 + 0.02 (specific gravity); these values can be considered from medium to low.
Specific gravity is a widely used parameter at the industrial level to define the frying suitability of a raw material. However, in this case, it has been shown that it is not as accurate as using dry matter content, although both parameters should be considered together, especially in breeding programs.
Color
According to the luminosity (L*) parameter of the raw pulp, the analyzed clones can be divided into two groups (P ˂ 0.0001): one of more luminous pulp with values from 66 to 67 and the other with values from 60 to 65 (Table 2). These values are lower than those recorded by Garcia, Lopes-do Carmo, Gonçalves-de Padua, and Leonel (2015), who report L* figures greater than 76. The pulp of the analyzed materials had yellow tones (P ˂ 0.0001), being lighter in materials 8026.2 and 10025.1, with Hue values of 79.62 and 83.08, respectively, and more yellow in the materials with Hue values ≥ 90. Regarding the intensity of the color (Chroma), the observed variation is greater (P ˂ 0.0001), finding materials with very low values, between 2.74 and 3.50, indicating a grayish and not very pure color, and materials with values between 9.26 and 10.10, indicating a more vivid color.
Table 2 Comparison of means of raw potato pulp color parameters measured in 25 genetic materials.
| Clone | L* | Hue | Chroma |
|---|---|---|---|
| 17.6 | 66.31 ± 0.18 bcdefz | 90.19 ± 0.15 bcde | 9.72 ± 0.12 a |
| 2083.6 | 65.32 ± 0.25 fghij | 85.76 ± 0.56 l | 4.80 ± 0.10 ghi |
| 5012.3 | 64.87 ± 0.23 hijk | 90.97 ± 0.26 abc | 6.63 ± 0.13 bc |
| 6093.1 | 66.37 ± 0.2 abcdef | 89.56 ± 0.44 cdefgh | 2.74 ± 0.05 j |
| 7032.3 | 66.47 ± 0.15 abcde | 90.16 ± 0.26 bcdef | 5.92 ± 0.12 cde |
| 7036.1 | 67.50 ± 0.15 abc | 89.78 ± 0.38 bcdefgh | 10.1 ± 0.16 a |
| 7046.2 | 65.56 ± 0.24 defghi | 87.69 ± 0.41 ghijkl | 5.13 ± 0.13 efg |
| 7049.1 | 64.41 ± 0.24 jk | 87.45 ± 0.23 hijkl | 5.74 ± 0.20 cde |
| 7062.1 | 66.22 ± 0.20 cdefg | 87.82 ± 0.26 fghijkl | 4.19 ± 0.06 fghi |
| 7065.3 | 66.17 ± 0.22 cdefg | 89.79 ± 0.26 bcdefgh | 5.11 ± 0.15 efg |
| 8025.1 | 64.37 ± 0.20 jk | 88.59 ± 0.35 defghij | 3.07 ± 0.06 j |
| 8025.3 | 64.97 ± 0.19 k | 86.29 ± 0.75 jkl | 2.98 ± 0.05 j |
| 8026.2 | 67.46 ± 0.32 a | 79.62 ± 0.76 n | 3.52 ± 0.18 hij |
| 8030.2 | 66.56 ± 0.18 abcd | 92.84 ± 0.13 a | 9.26 ± 0.13 a |
| 8035.2 | 65.94 ± 0.21 defgh | 85.94 ± 0.32 l | 5.8 ± 0.11 ef |
| 9052.3 | 65.61 ± 0.2 deffghi | 86.17 ± 0.57 kl | 3.32 ± 0.05 ij |
| 10007.1 | 65.84 ± 0.21 defghi | 88.9 ± 0.24 cdefghi | 7.61 ± 0.13 b |
| 10011.1 | 65.36 ± 0.21 efghij | 89.97 ± 0.27 bcdefg | 6.33 ± 0.15 cd |
| 10021.1 | 64.80 ± 0.17 ijk | 88.01± 0.44 efghijkl | 3.14 ± 0.05 j |
| 10021.2 | 67.21 ± 0.17 abc | 90.34 ± 0.57 bcde | 9.64 ± 0.23 a |
| 10021.3 | 65.54 ± 0.27 defghi | 88.28 ± 0.35 defghijk | 5.16 ± 0.23 efg |
| 10025.1 | 65.13 ± 0.25 ghijk | 83.08 ± 0.57 m | 5.54 ± 0.11 de |
| 793101.3 | 67.35 ± 0.17 ab | 87.13 ± 0.50 ijkl | 6.08 ± 0.16 cde |
| 93060.4 | 62.32 ± 0.23 l | 90.59 ± 0.84 abcd | 4.51 ± 0.67 fgh |
| Challenger | 60.56 ± 0.30 m | 91.97 ± 0.41 ab | 9.76 ± 0.19 a |
| LSD | 1.12 | 2.34 | 0.99 |
| CV (%) | 3.14 | 4.85 | 31.33 |
LSD = least significant difference; CV = coefficient of variation. zMeans with the same letter within each column do not differ statistically (Tukey, P ≤ 0.05). The values are means (n = 90) ± standard error of the mean.
In potato chips, highly significant differences were also found. The lowest L* values (between 51 and 55) were measured in materials 10021.3, 7049.1, 93060.4, 5012.3 and 7065.3. The highest L* corresponded to materials 10021.2, 7062.1 and 8030.2, with values between 60 and 63 (Table 3). According to previous works, L* values ≥ 55 are considered acceptable (Wiberley-Bradford, Busse, & Bethke, 2016; Wiberley-Bradford & Bethke, 2017); therefore, those in the first group are not considered acceptable because they are darker. In this case, the tone values are very diverse, as shown in the same table (P ˂ 0.0001), since materials with more reddish-yellow tones (10025.1, 7049.1, 7036.1 and 7062.1) and materials with more yellowish tones, with values above 75, appear. The clones with the purest color were 7046.2, 8025.1, 7049.1, 17.6 and 7062.1, and the opposites in color were 7065.3, 5012.3, 100021.3 and 2083.6 (P ˂ 0.0001). On the other hand, no correlation was found between the color parameters measured, both in raw and fried potatoes, and the other variables evaluated (data not shown).
Table 3 Comparison of means of potato chip pulp color parameters measured in 25 genetic materials.
| Clone | L* | Hue | Chroma |
|---|---|---|---|
| 17.6 | 57.87 ± 0.72 cdefgz | 70.67 ± 0.66 hi | 24.8 ± 0.47 ab |
| 2083.6 | 58.75 ± 1.25 bcdef | 77.29 ± 1.44 bcde | 16.45 ± 0.88 l |
| 5012.3 | 51.82 ± 1.58 k | 80.51 ± 1.16 a | 17.48 ± 0.57 kl |
| 6093.1 | 59.11 ± 0.75 bcde | 72.82 ± 0.80 fgh | 20.7 ± 0.53 fghi |
| 7032.3 | 58.16 ± 0.95 bcdef | 76.7 ± 0.76 cde | 21.54 ± 0.46 cdefg |
| 7036.1 | 59.36 ± 0.98 bcd | 61.98 ± 1.31 j | 21.77 ± 0.57 cdefg |
| 7046.2 | 59.42 ± 0.86 bcd | 70.77 ± 0.78 hi | 23.24 ± 0.46 bc |
| 7049.1 | 53.98 ± 0.86 ijk | 64.52 ± 1.16 j | 24.67 ± 0.49 ab |
| 7062.1 | 60.91 ± 0.8 ab | 57.22 ± 1.34 k | 26.07 ± 0.47 a |
| 7065.3 | 51.18 ± 1.02 k | 76.01 ± 1.55 cdef | 18.78 ± 0.55 jk |
| 8025.1 | 58.72 ± 0.86 bcdef | 71.84 ± 0.9 gh | 24.56 ± 0.52 ab |
| 8025.3 | 55.12 ± 0.85 ghij | 75.98 ± 0.85 def | 20.89 ± 0.58 efgh |
| 8026.2 | 57.73 ± 0.73 cdefgh | 71.54 ± 0.81 ghi | 22.34 ± 0.54 cdef |
| 8030.2 | 60.48 ± 1.04 abc | 80.26 ± 0.71 ab | 20.42 ± 0.53 ghij |
| 8035.2 | 57.27 ± 0.73 defgh | 72.17 ± 0.72 gh | 22.69 ± 0.46 cd |
| 9052.3 | 57.43 ± 0.93 defgh | 71.47 ± 0.83 ghi | 21.78 ± 0.45 cdefg |
| 10007.1 | 56.12 ± 0.79 fghi | 79.18 ± 0.96 abcd | 20.82 ± 0.68 efghi |
| 10011.1 | 57.50 ± 0.87 defgh | 79.15 ± 0.99 abcd | 21.48 ± 0.58 defg |
| 10021.1 | 56.25 ± 0.91 efghi | 75.59 ± 0.97 ef | 21.72 ± 0.59 cdefg |
| 10021.2 | 62.75 ± 1.10 a | 69.71 ± 1.27 hi | 22.09 ± 0.67 cdefg |
| 10021.3 | 54.89 ± 1.32 hij | 74.65 ± 1.64 efg | 16.96 ± 1.02 l |
| 10025.1 | 59.44 ± 0.96 bcd | 68.35 ± 1.02 i | 22.48 ± 0.53 cde |
| 793101.3 | 58.65 ± 0.78 bcdef | 79.21 ± 0.77 abc | 20.9 ± 0.58 efgh |
| 93060.4 | 53.53 ± 1.38 jk | 77.22 ± 1.22 bcde | 19.3 ± 0.63 hij |
| Challenger | 56.63 ± 1.13 defghi | 75.65 ± 1.23 ef | 19.09 ± 0.46 ijk |
| LSD | 2.97 | 3.20 | 1.75 |
| CV (%) | 9.47 | 4.01 | 15.05 |
LSD = least significant difference; CV = coefficient of variation. zMeans with the same letter within each column do not differ statistically (Tukey, P ≤ 0.05). The values are means (n = 90) ± standard error of the mean.
Total polyphenols (TP) and total antioxidant capacity (TAC)
TP content was between 0.12 and 0.40 mg GAE·g-1 in DW, as shown in Table 4. The main differences (P ˂ 0.0244) were recorded between materials 7046.2 and 10021.2 (0.4 and 0.38 mg GAE·g-1 in DW, respectively), and materials 8025.3 and 8035.2 (with values of 0.13 and 0.12 mg GAE·g-1 in DW, respectively). The commercial Challenger variety had a low value, which would explain, in part, its low susceptibility to enzymatic browning and its suitability for frying.
Table 4 Comparison of means of total polyphenols, polyphenol oxidase activity and total antioxidant capacity in dry weight of 25 genetic potato materials.
| Clone | Total polyphenols (mg·g-1) | Polyphenol oxidase activity (U·gprotein -1) | Total antioxidant capacity (mg·g-1) |
|---|---|---|---|
| 17.6 | 0.26 ± 2.16 abz | 32.79 ± 1.29 defgh | 0.91 ± 0.16 abcd |
| 2083.6 | 0.30 ± 4.03 ab | 36.4 ± 2.79 cdefgh | 0.85 ± 0.1 bcde |
| 5012.3 | 0.20 ± 5.34 ab | 61.93 ± 4.51bc | 0.48 ± 0.1 de |
| 6093.1 | 0.28 ± 4.9 ab | 38.79 ± 4.89 cdefg | 0.71 ± 0.17 bcde |
| 7032.3 | 0.27 ± 4.64 ab | 11.25 ± 2.36 hij | 0.64 ± 0.13 bcde |
| 7036.1 | 0.22 ± 3.72 ab | 9.84 ± 3.67 hij | 0.44 ± 0.06 de |
| 7046.2 | 0.40 ± 4.86 ab | 45.80 ± 6.60 cdef | 1.02 ± 0.22 abcd |
| 7049.1 | 0.22 ± 5.85 ab | 85.68 ± 9.8 ab | 1.22 ± 0.15 abc |
| 7062.1 | 0.28 ± 1.21 ab | 54.28 ± 2.17 cde | 0.70 ± 0.03 bcde |
| 7065.3 | 0.28 ± 3.65 ab | 45.03 ± 6.06 cdefg | 0.77 ± 0.07 bcde |
| 8025.1 | 0.30 ± 3.51 ab | 101.43 ± 1.91 a | 0.80 ± 0.15 bcde |
| 8025.3 | 0.13 ± 4.38 b | 21.95 ± 0.81 fghij | 0.29 ± 0.05 e |
| 8026.2 | 0.23 ± 2.43 ab | 22.06 ± 1.68 fghij | 0.51 ± 0.05 cde |
| 8030.2 | 0.34 ± 9.44 ab | 30.27 ± 2.4 efghi | 1.06 ± 0.18 abc |
| 8035.2 | 0.12 ± 1.49 b | 18.4 ± 1.67 ghij | 0.37± 0.06 de |
| 9052.3 | 0.25 ± 6.79 ab | 2.10 ± 0.78 j | 0.74 ± 0.19 bcde |
| 10007.1 | 0.30 ±0.37 ab | 58.64 ± 5.70 cd | 0.57 ± 0.03 bcde |
| 10011.1 | 0.23 ± 4.24 ab | 57.94 ± 6.36 cd | 0.56 ± 0.09 bcde |
| 10021.1 | 0.30 ± 4.07 ab | 5.74 ± 1.08 ij | 0.67± 0.15 bcde |
| 10021.2 | 0.38 ± 4.11 a | 48.23 ± 6.32 cdef | 1.06 ± 0.08 abc |
| 10021.3 | 0.21 ± 5.5 ab | 26.90 ± 4.17 fghij | 1.63 ± 0.29 a |
| 10025.1 | 0.24 ± 1.02 ab | 41.43 ± 2.95 cdef | 1.24 ± 0.15 ab |
| 793101.3 | 0.17 ± 2.6 ab | 46.25 ± 3.54 cdef | 0.50 ± 0.05 de |
| 93060.4 | 0.22 ± 5.22 ab | 30.97 ± 6.78 efghi | 0.72 ± 0.1 bcde |
| Challenger | 0.12 ± 2.14 b | 2.73 ± 0.06 j | 0.46 ± 0.03 de |
| LSD | 24.23 | 27.33 | 0.73 |
| CV (%) | 30.98 | 23.18 | 30.67 |
LSD = least significant difference; CV = coefficient of variation. zMeans with the same letter within each column do not differ statistically (Tukey, P ≤ 0.05). The values are means (n = 90) ± standard error of the mean.
TAC values were between 0.29 and 1.63 mg TE·g-1 in DW (Table 4), and in this case two groups were also identified (P ˂ 0.0001). The group with the highest values consists of materials with values between 1.06 and 1.63 mg TE·g-1 in DW, where 10021.3 stands out. The group with the lowest values includes the materials 5012.3, 7036.1, 7055.1, 8025.3, 8035.2 and Challenger, with contents between 0.29 and 0.48 mg TE·g-1 in DW. These values represent between 33 and 40 % less TAC compared to the materials in the first group, so they would have a lower functional quality.
The variability observed in both components may be due to factors such as degree of maturity, environmental conditions and genotype (Hu, Tsao, Liu, Sullivan, & McDonald, 2012; Ezekiel et al., 2013). In this case, as in dry matter, the differences may correspond to the genetic component. The fact that phenolic compounds are substrates for PPO indicates, a priori, that materials with lower content are less susceptible to enzymatic browning. In this regard, materials 8025.3 and 8035.2, which did not differ from the commercial control, are recommended.
A linear correlation was found between TAC and TP (P ˂ 0.0001), with a Pearson's correlation coefficient of 0.67, and by adjusting the equation it would be as follows: TAC = 0.1802 + 0.0205 (TP), with a value of R2 = 0.44. Although TP is one of the components of TAC, the materials with the highest TP content are not in all cases those with the highest TAC. The TP content includes flavonoids, other phenolic acids, and all compounds with phenolic features, but the specific composition of these phenolic compounds can vary among genetic materials, thus contributing differently to antioxidant activity (Pinhero et al., 2016). The values measured in the analyzed materials and the correlation between the variables confirm this situation.
TAC indicates that there are materials that make a greater potential contribution of beneficial compounds to the health of consumers, although it should be considered that their components, especially vitamins, are affected during cooking.
Polyphenol oxidase (PPO) activity
PPO activity was the variable with the largest range of variation (P ˂ 0.0001). The measured values were found between 101.43 and 2.00 U·gprotein -1 in DW. In the materials analyzed, 8025.1 and 7049.1 stood out, with the highest values (101.43 and 85.68 U·gprotein -1 in DW, respectively), and 7032.3, 7036.1, 10021.1 and 9052.3, with the lowest values (between 2 and 11 U·gprotein -1 in DW) (Table 4). The commercial variety Challenger exhibited an activity of 2.73 U·gprotein -1 in DW, placing it in the group with the least activity, this being the other factor that would explain its low susceptibility to enzymatic browning and its suitability for frying.
The measured values are within the range reported by other authors, but at the lower end. In this regard, Cabezas-Serrano et al. (2009), in assessing the suitability for minimum processing of five commercial potato varieties, found an activity of between 10 and 14 U·gprotein -1 in FW, which according to the dry matter content reported by the authors corresponds to 52 and 105 U·gprotein -1, respectively. Dario-Vitti, Fumi-Sasaki, Miguel, Kluge, and Moretti (2011) report an activity of between 12 and 22 U·gprotein -1 in FW for the Agata, Monalisa and Asterix varieties. These values would correspond to those measured in the low activity group of the present study.
Differences between materials were also reported by the authors mentioned above and by others in previous works. In this regard, Thygesen, Dry, and Robison (1995) conducted a comprehensive study linked to potato PPO. Among other aspects, these authors report the existence of variation in PPO activity in different genetic materials, where the tubers of the Saturna variety had between 3 and 4 times more activity than those of the Atlantic variety.
In general, the higher activity of the PPO enzyme indicates that materials 8025.1 and 7049.1 materials are more susceptible to enzymatic browning.
Conclusions
Ten genetic potato materials were identified as promising for frying, and should thus continue within the breeding program. However, materials 5012.3 and 7049.1 (due to their high PPO activity and dark brown flake color defects), 7062.1 and 10025.1 (due to low dry matter content and unfavorable frying color), 7036.1, 7065.1 and 7065.3 (due to flake color problems), and 7032.3 (due to low dry matter) would not be suitable and should be considered for withdrawal from the program. However, since the results are for one year, it would be appropriate to consider at least two more years of evaluation.
