Dry Matter, Starch Content, Reducing Sugar, Color and Crispiness Are Key Parameters of Potatoes Required for Chip Processing

: To make potato production more sustainable for smallholder farmers, product diversiﬁca-tion through processing is critical. On the other hand, the processing sector mandated some stringent standards in order to maintain product quality, hence potato quality evaluations are required for chip processing industries. Speciﬁc gravity, starch, reducing sugars, tuber dry matter, and chip color are all important characteristics to consider for processing. This study was designed to ﬁnd suitable potato varieties with satisfactory attributes for processing chips, in comparison with other processing potato varieties. Keeping this in mind, the study was performed during the winter season of 2019–2020 and 2020–2021 in Bangladesh. Six processing types of potato varieties viz. BARI Alu-25 (Asterix), BARI Alu-28 (Lady Rosetta), BARI Alu-29 (Courage), BARI Alu-68 (Atlantic), BARI Alu-70 (Destiny), and BARI Alu-71 (Dolly) were evaluated for different quality parameters (speciﬁc gravity, dry matter, starch content, reducing sugar, chip color, and crispiness). The result of the study showed an ample variation in the studied parameters among the potato varieties. Among the varieties, BARI Alu-28 (Lady Rosetta) and BARI Alu-29 (Courage) were found better for all the quality parameters, such as dry matter, starch, reducing sugar, chip color, and crispiness, and could be recommended for the processing industries.


Introduction
The potato (Solanum tuberosum L.) is the world's most vital non-cereal food crop and is ranked as the 4th most important harvested food crop following wheat, corn, and rice [1]. It has a momentous contribution to ensure food and nutritional security because of its yield potential and nutritional value. Considering the high yield potential, it can be a good alternative for cereal crops that have a high harvesting index above 75% [2,3]. Potato is high in starch content and low in sugar and fat. It is a good source of energy, with vitamins including vitamin B6, niacin, folate, vitamin C and minerals such as potassium, iron, phosphorus, and magnesium [4,5]. The potato is also a rich source of natural dietary antioxidants [6,7], which are advantageous to human beings because they defend against cardiovascular disease and reduce blood cholesterol levels [8].
the initial other soil properties are presented in Table 1. During the potato growing period (November-March) the sunshine hours, monthly mean maximum and minimum temperature, rainfall, and relative humidity were documented and are presented in Figure 1. In the first year, there was slight rainfall, and there was no rainfall during the growing season of the second year. longitude) of the Tuber Crops Research Centre (TCRC) of the Bangladesh Agricultural Research Institute (BARI), Gazipur, Bangladesh. The selected site is flat in topography and is at an elevation of 20 m above sea level. The experimental soil was silty clay and the initial other soil properties are presented in Table 1. During the potato growing period (November-March) the sunshine hours, monthly mean maximum and minimum temperature, rainfall, and relative humidity were documented and are presented in Figure 1. In the first year, there was slight rainfall, and there was no rainfall during the growing season of the second year.

Experimental Procedures and Management
In both years, well maintained and disease-free sprouted A grade (28-40 mm) whole seed tubers were planted in the last week of November. The recommended dose of manure and fertilizers were used in the form of Cow Dung, Urea, Muriate of Potash (MOP), Triple Super Phosphate (TSP), Boric Acid, Zinc Sulfate, and Gypsum [17], where half of the Urea and Muriate of Potash with a complete dose of other fertilizers were thoroughly mixed with the soil before planting. At 35 days after planting, the remaining Urea and Muriate of Potash were added as a side-dressing during earthing up. Necessary intercultural operations, for example, weeding, irrigation, earthing up, and plant preventive measures, were performed according to the recommendation of TCRC, BARI [18]. The crops were irrigated two times, at 30 and 60 days after planting (DAP). The first irrigation was given at 8-10 DAP to ensure appropriate tuber emergence; the second and third irrigations were applied at 30 and 45 DAP, respectively. Finally, light irrigation was applied at 60 days after planting. By spading in between the ridges and covering the ridges with loose soil, two hand weeding was done before the second (at 30 DAP) and last (at 60 DAP) irrigations. The haulm was removed 10 days before harvesting to harden the skin of the potato tubers, and they were left for ten days in the field.  Figure 1. Maximum and minimum mean monthly temperature, relative humidity (RH, %), monthly rainfall (Rf, mm), and sunshine (SS, hour) in 2019-20 and 2020-21.

Experimental Procedures and Management
In both years, well maintained and disease-free sprouted A grade (28-40 mm) whole seed tubers were planted in the last week of November.

Experimental Procedures and Management
In both years, well maintained and disease-free sprouted A grade (28-40 mm) whole seed tubers were planted in the last week of November. The recommended dose of manure and fertilizers were used in the form of Cow Dung, Urea, Muriate of Potash (MOP), Triple Super Phosphate (TSP), Boric Acid, Zinc Sulfate, and Gypsum [17], where half of the Urea and Muriate of Potash with a complete dose of other fertilizers were thoroughly mixed with the soil before planting. At 35 days after planting, the remaining Urea and Muriate of Potash were added as a side-dressing during earthing up. Necessary intercultural operations, for example, weeding, irrigation, earthing up, and plant preventive measures, were performed according to the recommendation of TCRC, BARI [18]. The crops were irrigated two times, at 30 and 60 days after planting (DAP). The first

Experimental Procedures and Management
In both years, well maintained and disease-free sprouted A grade (28-40 mm) whole seed tubers were planted in the last week of November. The recommended dose of manure and fertilizers were used in the form of Cow Dung, Urea, Muriate of Potash (MOP), Triple Super Phosphate (TSP), Boric Acid, Zinc Sulfate, and Gypsum [17], where half of the Urea and Muriate of Potash with a complete dose of other fertilizers were thoroughly mixed with the soil before planting. At 35 days after planting, the remaining Urea and Muriate of Potash were added as a side-dressing during earthing up. Necessary intercultural operations, for example, weeding, irrigation, earthing up, and plant preventive measures, were performed according to the recommendation of TCRC, BARI [18]. The crops were irrigated two times, at 30 and 60 days after planting (DAP). The first irrigation was given at 8-10 DAP to ensure appropriate tuber emergence; the second and third irrigations were applied at 30

Experimental Procedures and Management
In both years, well maintained and disease-free sprouted A grade (28-40 mm) whole seed tubers were planted in the last week of November. The recommended dose of manure and fertilizers were used in the form of Cow Dung, Urea, Muriate of Potash (MOP), Triple Super Phosphate (TSP), Boric Acid, Zinc Sulfate, and Gypsum [17], where half of the Urea and Muriate of Potash with a complete dose of other fertilizers were thoroughly mixed with the soil before planting. At 35 days after planting, the remaining Urea and Muriate of Potash were added as a side-dressing during earthing up. Necessary intercultural operations, for example, weeding, irrigation, earthing up, and plant preventive measures, were performed according to the recommendation of TCRC, BARI [18]. The crops were irrigated two times, at 30 and 60 days after planting (DAP). The first irrigation was given at 8-10 DAP to ensure appropriate tuber emergence; the second and third irrigations were applied at 30 and 45 DAP, respectively. Finally, light irrigation was applied at 60 days after planting. By spading in between the ridges and covering the

Data Collection and Parameters Estimation
Data were recorded on different processing and biochemical parameters, specifically, specific gravity, starch content, reducing sugar, crispiness of chips, chip color, external appearance, and tuber dry matter content from randomly selected samples.

Specific Gravity
The method described by Kleinkopf et al. [19] was used to measure the specific gravity of potato. Five kg harvested tubers of various shapes and sizes were selected randomly from each plot were weighed in air and water using a Weltech digital hydrometer (Martin Lishman, Ltd., Bourne, UK, model: PW-2050) and the following formula was used to calculate specific gravity: Specific gravity = Weight of tuber in air Weight of tuber in air − Weight of tuber in water .

Determination of Dry Matter Content
Ten tubers from the harvested potatoes of each variety were randomly selected for tuber dry matter estimation. After that, the samples were weighted to 200 g two subsamples, then after washing, cutting, and mixing, the samples were dried in a drying oven (Memmert GmbH, UN-260, Schwabach, Germany) for 72 h at 72 • C. The dry matter was computed as a percentage based on the ratio of dry to fresh mass [20]. Additionally, the dry matter content was also estimated using the digital hydrometer method (Martin Lishman, Ltd., Bourne, UK, model: PW-2050).

Extraction of Sugar and Starch
To evaluate the reducing sugar and starch of each treatment, potato flesh was removed. At first, chopped potato of 1g was taken from the tuber samples and smashed properly with a motor. Then, 5 mL of 80% EtOH (Ethanol) was added and heated in a dry block heat bath for 30 min at 80 • C and the extracts were then centrifuged for 10 min at 5000 rpm. The supernatant was then decanted, and the process was repeated four to five times in total. All of the supernatants were combined and thoroughly mixed together, and 80% ethanol was used to make the final volume 25 mL, and sugar was extracted from this solution. The residues from this extraction process were collected for analysis of starch content.

Reducing Sugar Content Determination
The Somogyi method [21] with slight modifications was used to determine the reducing sugar of the tested potato varieties. At first, a small glass container was taken, and 3 mL of the extracted solution was added to it, and using an electric heater, dried properly. After that, 3 mL of distilled water was cojoined and mixed well with the help of a vortex. Second, the solution (0.5 mL) was taken from the glass container into a test tube and added 0.5 mL of copper solution in the test tube. Then the mixture was boiled for 10 min at 100 • C and cooled with running water immediately after boiling. After that, 0.5 mL Nelson reagent was added and diluted thoroughly. After 20 minutes, the final volume was made 9.5 mL by adding and mixing 8 mL of distilled water. Finally, the absorbance was quantified with a spectrophotometer at 660 nm wavelength (Abs) against a blank sample. Then, reducing sugar was enumerated from the absorbance value and stated as mg g −1 FW.

Starch Content Determination
The amount of starch in a potato was quantified following the Somogyi-Nelson method [21] with some adjustments. At first, 0.09 g Na 2 HPO 4 .12H 2 O and 0.74 g NaH 2 PO 4 .2H 2 O was added into double-distilled water of 100 mL and prepared a phosphate-buffered solution. Second, 0.1 g of Amyloglucosidase was mixed properly into the solution and kept at −20 • C. After the sugar extraction, the remaining residues were rinsed numerous times with distilled water to ensure that they were free of any soluble sugar. After that, the authors filled a beaker with distilled water up to 250 mL and stirred it with a magnetic stirrer. The solution (0.5 mL) was then transferred to a test tube and heated at 100 • C for 10 min while stirring, with 1 mL of stored solution added, then blended properly, and then heated for 120 min in a hot water at 50-60 • C. Then the mixture was cooled down and 0.5 mL of copper solution was mixed well with the mixture and boiled for 10 min at 100 • C. Again, the mixture was cooled down, then 0.5 mL Nelson solution was added, followed by 7 mL of distilled water, and it was carefully blended to make a final volume of 9.5 mL. Finally, the absorbance was measured against a blank sample using a spectrophotometer at a 660 nm wavelength (Abs). Using a glucose standard curve, the starch content was determined and expressed as mg g −1 FW.

Blanching and Potato Chip Preparation
Blanching is a crucial step in the frying of potatoes for improving the texture and color of the fried potatoes, as well as reducing oil uptake of surface starch through gela-  [22]. It also inactivates discoloration-related enzymes [23], reduces the sugar content [24], and makes them crispier. The chips were prepared after one month of harvesting with all the conditions of industrial processing. Ten healthy potato tubers were randomly picked from each replication and washed, peeled, and sliced using a handoperated chip cutter. The thickness of the slice was 1.5 mm thick, and after slicing, the slices were promptly washed in tap water for about 1 min. Then the slices were blanched at approximately 60 • C for 1 min and then cooled in normal water. Finally, the slices were covered with tissue paper to soak up excess surface water to make it dry. After drying the potato slices, they were fried according to Kita et al. [25] with slight modifications. Ten liters of refined soybean oil was heated in a deep fryer (Longer, LG-1000, ZhengZhou, China) to raise the temperature to 180 • C and checked with a thermometer. After that, 500 g of blanched potato slices were deep-fried in the frier for 3 min. The fried chips were drained for 5 min on a wire screen and cooled to room temperature, stored in plastic bags, and kept in the ambient environment for future experiments.

Assessment of Potato Chips Color
The method of Dervisi et al. [26] was used to measure the external color of the potato chips with a Chroma meter (Model CR-400, Minilta Corp., Japan). CIE L*a*b* coordinates were recorded using D65 illuminants and a 10 • standard observer was used as a reference system. Here, a*(-greenness to +redness) and b* (-blueness to +yellowness) are chromaticity coordinates, while L* is lightness. The chroma [C* = (a* 2 + b* 2 ) 1/2 ] and hue angle [H* = tan −1 (b*/a*)] were calculated by the converted value or a* and b*. The device was calibrated against a standard white tile before the measurement and the values of Lightness (L*), Hue angle (H*), and Chroma (C*) were then adjusted. Besides this, the chips were again scored using a color card on a 1-10 scale according to Ezekiel et al. [27], where 1 represents a light color and 10 represents a dark brown color.

Measurement of Chips Crispiness
The crispiness of the fried chips was evaluated through a TA. XT plus texture analyzer (Stable Micro Systems, Ltd., Surrey, Godalming, UK). The prove of the analyzer was inserted through the middle of the chips by the back extrusion technique. The operative characteristics of the instrument were determined using the test mode compression with a speed of 1 mm/s. After removing the chips from the frying oil, the texture measurements were completed two hours later. For each replication, three potato chips were analyzed, and the average data were recorded. The crispiness was determined by measuring the probe's travel distance (mm) prior to the first break, which was indicated by a sharp drop in force. If the amount of distance was lower, chips were assumed to be crispier.

Sensory Evaluation of Chips
The sensory quality attributes of the potato chips of different varieties were evaluated by a few panel tests after 15 days of frying. A judgment panel was formed comprised of 10 members from the Tuber Crops Research Center inter-divisional scientists to evaluate the appearance, aroma, taste, and overall acceptability of the chips based on a (0-9) hedonic scale [28].

Statistical Data Analysis
The collected data on different parameters were analyzed through analysis of variance (ANOVA) by statistical computer software R x 64-program v3.3.2 [29]. The treatment means were compared to find the significant variation among the treatments by the Least Significant Difference (LSD) test at a 5% level of probability. The Pearson correlation coefficients were also calculated among the quality parameters (specific gravity, starch, dry matter, reducing sugar, crispiness, and chip color) using the Metan package of R.

Specific Gravity and Dry Matter Content
Dry matter and specific gravity are the index of good processing quality for potatoes, which mostly controls the crispiness, color, oil absorption, flavor, and texture [30]. The results showed significant variation both in the case of specific gravity and dry matter content (Table 3). Among the varieties, BARI Alu-28 (1.085), BARI Alu-29 (1.084), and BARI Alu-71 (1.083) demonstrated maximum specific gravity than the other varieties. On the other hand, BARI Alu-28 (22.61%) exhibited maximum dry matter content followed by BARI Alu-29 (21.72%) in the oven-dry method, and BARI Alu-28 (21.42%) followed by BARI Alu-71 (21.11%), BARI Alu-68 (20.73%), and BARI Alu-29 (20.29%) in the digital Hydrometer method. The existing variation in dry matter and specific gravity may be because of genetic differences, as all the varieties were grown and evaluated providing similar management practices. Processing efficiency, i.e., the maximum recovery of processed produce, is greatly influenced by the dry matter content of the tuber [31].

Starch Content of Different Processing Varieties
Starch content (mg/g FW) among the potato varieties was found to vary significantly, ranging between 26.06 mg/g FW to 21.15 mg/g FW (Table 3). BARI Alu-28 (26.06 mg/g FW) showed maximum starch content followed by BARI Alu-29 (24.66 mg/g FW). The differences in starch content may be demonstrated because of genetic makeup and cultural practices at the time of growing, or due to the variation in dry matter of the tested processing potato varieties since starch content of potato tubers has a strong association with dry matter content [12,16,32]. The starch content of tubers is related to their dry matter content [33]. Tubers with higher levels of dry matter and starch have a crispier texture, provide more chips, and limit fat absorption during frying [34].

Reducing Sugar Content of Different Processing Varieties
Significant variation (0.591-0.809 mg/g FW) for reducing sugar was found among the processing varieties. Reducing sugar content was lowest in BARI Alu-28 (0.591 mg/g FW), followed by BARI Alu-29 and BARI Alu-71 (Table 3). The ability to have a high or low sugar content of a potato variety is a heritable feature and influenced by the genotype, environmental and cultural factors (temperature, moisture, nutrition, etc.), area, year, tuber maturity, and storage condition [16,35]. Sharker et al. [36] reported that to keep the light color of potato chips during frying, the reducing sugar content should be less than 2.5-3 mg per gram of potato. Tubers have low quantities of reducing sugars and yield light-colored chips immediately after harvest [37]. In this experiment, the higher reducing sugar content of the varieties could be attained by the different weather conditions than the original weather conditions, as these are exotic potato varieties. It has been reported that the reducing sugars of potatoes are regulated by variety, cultural, and environmental factors [38]. Acrylamide, a potentially carcinogenic substance found in potato chips, varies based on the chemical makeup of the tubers utilized, particularly the reducing sugar level [35].

Chips Crispiness and Color
The potato varieties differed significantly in the quality of crispiness ( Table 3). The potato varieties BARI Alu-28, BARI Alu-29, and BARI Alu-70 showed the lowest value for crispiness (0.723 mm, 0.731 mm, and 0.748 mm, respectively), which means that they were crispier than the other varieties. The crispiness of chips depends on the dry matter of the raw potato. Chips from the raw potato with a high dry matter content have a hard texture, resulting in crispy chips, whereas chips from a potato with low dry matter contained more oil, appeared greasy, and had sticky textures [39]. The crispiness is also directly associated with the amount of starch and reducing sugar of the potato [40].
There was a wide variation found in the Lightness (L*), Hue angle (H*), and Chroma (C*) parameters of the tested genotypes (Table 4). Light colored chips (L* > 50) were found from all the tested varieties, which indicates that there was no unnecessary dark color but chips produced from BARI Alu-28, BARI Alu-29, and BARI Alu-71 were lighter than the others ( Figure 2). This can be attributed to low reducing sugar levels exhibited by the varieties. The chroma and hue angle were also significantly affected by the varieties. A significantly similar chroma value (27.21 ± 1.78-28.96 ± 0.66) was found in BARI Alu-28, BARI Alu-29, BARI Alu-70, and BARI Alu-71. The hue angle (H*) value was also highest in BARI Alu-28 and BARI Alu-29. Similarly, in sensory evaluation scoring of chip color, BARI Alu-28 was noted for the lowest score (1.38 ± 0.07) and lightest color. The chip color for the other varieties was also in the acceptable range. The chip color variation could be the differences in composition within the varieties. Color is the first visual attribute that controls the consumers' choice for fried products, wherein a light color is acceptable compared to a brownish color. The result of this experiment conforms with the findings of Ooko and Kabira [41] and Rahman et al. [42]. Many factors influence the color and sensory qualities of potato chips, including cultivar, storage conditions prior to processing, slice thickness, frying duration, and temperature [43] There is a limitation of the present study that the nutritional quality of the chips after frying was not analyzed, and it should be analyzed in a future experiment.

Sensory Evaluation of Chips
To evaluate the processing quality of a variety, it is very important to check the appearance, taste, aroma and overall acceptability of fried potatoes. Acceptance of potato chips is a critical requirement for the potato processing sector, and it is based entirely on consumer perception. There was a variation in appearance, aroma, taste and overall acceptability among the tested varieties. In appearance BARI Alu-29 (Courage) showed better (8.70) which were very close in scoring to BARI Alu-28 (Lady Rosetta). BARI Alu-28 (Lady Rosetta) obtained the highest score in taste (8.97), aroma (7.47) and overall acceptability (8.40) which was very close to BARI Alu-29 (Courage) ( Table 5). The most essential sensory elements on which customers base their evaluation of potato chips are flavor, aroma, color, and texture [44]. Aroma is an important quality of a product and some authors from the previous studies reported that consumers did not appear willing to negotiate on a product's flavor, regardless of its health advantages or other good consequences. [45]. Besides this, the taste is also controlled consumer acceptance of a food product [46].

Sensory Evaluation of Chips
To evaluate the processing quality of a variety, it is very important to check the appearance, taste, aroma and overall acceptability of fried potatoes. Acceptance of potato chips is a critical requirement for the potato processing sector, and it is based entirely on consumer perception. There was a variation in appearance, aroma, taste and overall acceptability among the tested varieties. In appearance BARI Alu-29 (Courage) showed better (8.70) which were very close in scoring to BARI Alu-28 (Lady Rosetta). BARI Alu-28 (Lady Rosetta) obtained the highest score in taste (8.97), aroma (7.47) and overall acceptability (8.40) which was very close to BARI Alu-29 (Courage) ( Table 5). The most essential sensory elements on which customers base their evaluation of potato chips are flavor, aroma, color, and texture [44]. Aroma is an important quality of a product and some authors from the previous studies reported that consumers did not appear willing to negotiate on a product's flavor, regardless of its health advantages or other good consequences. [45]. Besides this, the taste is also controlled consumer acceptance of a food product [46]. Table 5. Different sensory attributes (appearance, taste, aroma, overall acceptability) of potato chips.

Varieties
Sensory Attributes Appearance Taste

Correlations
Correlation studies among different processing parameters found a significant relationship of tested potato varieties (Table 6). Varieties with high specific gravity displayed a positive correlation with dry matter (r = 0.67 **) and starch (r = 0.687 **); in contrast, specific gravity exhibited a negative correlation with reducing sugars (r = −0.69 **). The amount of reducing sugar in the chips demonstrated a substantial and positive relationship with the color of the chips (r = 0.83 ***). Tuber specific gravity is frequently used in the processing industry to estimate dry matter quickly and in this study, these two parameters are passively correlated, which conforms with the result of Killick and Simmonds [47] and Grewal et al. [48]. Table 6. Correlation studies among specific gravity, dry matter, starch, reducing sugar, chip color, and crispiness of potato varieties.

Conclusions
Potatoes are potential food for the creation of unique food products (chips) with health advantages. However, myriads of factors influence the quality of potato chips, including varietal performance, agronomic techniques, management, environment, blanching time, and drying kinetics as well as dry matter, starch content, reducing sugar, color, and crispiness. To recapitulate from the two-year study, potato variety should be selected for potato chip processing with combined characteristics of high starch and dry matter content, a low amount of reducing sugars, and a satisfactory light color. Based on these parameters, BARI Alu-28 (Lady Rosetta) and BARI Alu-29 (Courage) demonstrated exceptional chip processing qualities and these varieties could be recommended for making chips for potato processing industries. The nutritional quality of the chips after storage and the individual role of each factor needs to determine in future research.