African Crop Science Journal African Crop Science Society ISSN: 1021-9730 EISSN: 2072-6589 Vol. 10, Num. 4, 2002, pp. 325-333

African Crop Science Journal, Vol. 10. No. 4, 2002, pp. 325-333

Processing quality of selected potato varieties for chip and french fry industries in Egypt

A. A. TAWFIK, S. A. MANSOUR, H. M. RAMADAN and  A. N. FAYAD

Department of Potato Research and Vegetatively Propagated Vegetable Crops,  Horticulture Research Institute,  Agricultural Research Centre, Giza, Egypt

(Received 21 October, 2001; accepted 16 July, 2002)

Code Number: cs02031

Abstract

The demand for potato varieties (Solanum tuberosum L.) with acceptable yield and processing characteristics of chip and French fry is increasing in Egypt. However, the productivity and processing characteristics of some recently introduced cultivars are largely unknown. This study sought to establish the productivity, chip and French fry processing attributes of six new potato varieties during two seasons. All varieties gave satisfactory tuber yields, with varieties, Bolesta, Diamant and Pamina exhibiting the highest  tuber yields. During spring, Diamant, Exquisa and Silvester varieties recorded the highest tuber specific gravity, dry matter and starch contents, whereas Diamant, Exquisa, Silvester and Spey emerged superior during fall. Varieties Bolesta, Diamant, Exquisa, and Silvester consistently exhibited the highest yield of chips during spring. While Diamant, Exquisa, Silvester and Spey  exhibited the greatest  chip net weight during fall. The same varieties plus Bolesta recorded the largest yield of French fry during spring and fall studies. A linear positive correlation was established between tuber specific gravity and dry matter (r= 0.98) and starch (r= 0.96). Similarly, a  linear positive relationship (r= 0.67) was obtained between the specific gravity and yield of potato chips after frying.

Key Words:  Characteristics, Solanum tuberosum, specific gravity, tuber yields

Résumé

La demande des variétés des patates (Solanum tuberosum L.) au rendement acceptable et présentant de bonnes caractéristiques de transformation en frites et la friture française a augmenté en Egypte. Cependant, la productivité et les caractéristiques de transformation de certaines variétés récemment introduites sont largement inconnues. Cette étude cherche a établir la productivité et les attributs des frites et autres fritures françaises de six nouvelles variétés de patates pendant deux saisons. Toutes les variétés ont donné un rendement satisfaisant en tubercules. Les variétés Bolesta, Diamant et Pamina ayant exhibé le rendement le plus élévé. Pendant, le printemps, les variétés diamant, exquisa, silvester ont enregistré le poids spécifique le plus élévé, la matière sèche et le contenu en fécule , tandis que les variétés diamant, exquisa, silvester et spey ont supérieurement émergé pendant l’automne. Les variétés Bolesta, diamant, exquisa et silvester ont exhibé de manière consistante le rendement le plus élévé pendant le printemps.  Les variétés diamant, exquisa, silvester et spey ont exhibé un poids net plus élévé pendant l’automne. Les mêmes variétés, en plus de Bolesta ont enregistré un rendement plus élévé de fritures françaises pendant les études du printemps et d’automne. Une corrélation linéaire positive était établie entre le poids spécifique des tubercules, la matière sèche (r=0.98), et la fécule (r=0.96). De façon similaire, une relation linéaire positive (r=0.67) était obtenue entre le poids spécifique et le rendement des frites des patates après friture.

Mots Clés: Caractéristiques, Solanum tuberosum, poids spécifique, rendement en tubercules

Introduction

In Egypt, the potato (Solanum tuberosum L.) processing industry is expanding to cater for the  requirements of local and export markets. Therefore, demand for new potato varieties with satisfactory yields and processing characteristics is on the increase. French fries and potato chips are the most important processed potato products for which suitable varieties need to be identified.

Several studies reported a wide range of variation in tuber yields (Coffin et al., 1989; Cipar et al., 1990; Reeves et al., 1990; Lynch et al., 1991), specific gravity (Foda, 1973; Chaudhry et al., 1987; Coffin et al., 1988; Reeves et al., 1990; Lynch et al., 1991; Sinha et al., 1992), dry matter percentage (Foda, 1973; Chaudhry, 1987) and starch content (Foda, 1973) among different potato varieties.

High tuber yields and quality are important  determinants for the suitability of a given variety for large scale local production. Varieties with higher specific gravity and dry matter (Cunningham and Stevenson, 1963; Dearborn, 1975; Chaudhry et al., 1987; Jaswal, 1991; Rabie, 1996) tend  to have higher yields and better quality of finished chips and french fries. Moreover, colour of french fry and chip finished products depends on sugar content of tubers (Chaudhry, 1987; Coffin et al., 1989; Cipar et al., 1990; Reeves et al., 1990).

Several varieties have over the years been developed and released to farmers in Egypt.  Although, these varieties exhibit appreciable tuber characteristics, the processing quality of these varieties for chips and french fries is largely unknown. The objective of this study, therefore, was to  evaluate french fries and chips processing characteristics of selected potato varieties grown during spring and fall seasons in Egypt.

Materials and methods

Trials were carried out during spring and fall seasons of 1999 and 2000, at Gharbia province.  Six new potato varieties, namely,  Bolesta, Exquisa, Pamina, Platina, Silvester and Spey were used in the study to examine their productivity and suitability for french fries and chips processing. Diamant variety was the control (check). Table 1 presents the physical tuber characteristics of the potato varieties.Planting dates for spring and fall seasons, respectively, were January 17^th and October 11^th in 1999, and January 23^rd and October 19^th during 2000.

Imported seed tubers were used for planting during the spring, while seed used in fall trials were reserved from the spring crop of each year.  They were cold-stored at 4^o C during hot summer months.

Seed tubers were planted in rows at spacings of 0.70 m by 0.20 m. Cut and whole seed tubers were planted during the spring and fall seasons, respectively. The experimental unit area was 17.5 m^-2. A randomised complete block design, with three replicates, for each treatment (variety) was used for both seasons.

All cultural practices as well as disease and pest control were applied as recommended by the Egyptian Ministry of Agriculture. All experimental units received identical amounts of composted animal manure (8.4 ha^-1) and phosphorus (31.5 kg P₂O₅ ha^-1) using single super-phosphate (15% P₂O₅) banded on rows before planting and during soil preparation.  Nitrogen was applied at 50.4 kg ha^-1 (65% as ammonium sulphate  and 35% as ammonium nitrate). Total amount of potassium was appied at 40.32 kg K₂O  ha^-1, and sulphate of potash (48% K₂O) was the potassium (K) source.

Harvesting during spring and fall seasons was done at 111 and 121 days after planting (DAP), in 1999, and at 115 and 123 DAP, respectively, during 2000. Tuber yields were recorded at harvest for different varieties. Specific gravity (Murphy and Goven, 1959), percentage of dry matter (Dogras et al., 1991) and starch content (Burton, 1966) were determined starting two weeks after harvest.

Three tuber (45-60 mm diameter) samples, each of 500 g, from each variety were used to determine chips (crisps) and french fry qualities. Potato slices for crisps were prepared (Lulai and  Orr, 1980) and fried in 180^o C heated sunflower oil for 3 minutes. On the other hand, after being peeled and trimmed, tuber samples of french fries were cut into 6 mm strips.  Those of 30 mm and longer were fried in 170^o C heated sunflower oil for 6 minutes. Weight after frying (WAF) was recorded for both chips and french fries. Fried samples of chips were evaluated using a colour score scale of 1-9 where 1 = very dark; and  9 =  very light  basing on  the Netherlands colour charts. Similarly, the colour of french fry samples were evaluated using a colour scale of 1 - 6 where  1 = very light; and 6 = very dark.

A laboratory panel of 10 judges selected from staff of the potato research department evaluated the sensory qualities (colour, taste and crispiness) of chips and french fries.  Data were statistically analysed using a General Linear Model (GLM) procedure of SAS Institute (1989). Fishers protected Least Significant Difference (LSD) at P<0.05 was used to separate treatment means.

 Results and discussion

Fresh weight of tubers. During spring studies, Diamant, Bolesta and Pamina varieties showed comparable and consistently higher fresh weight (FW) of tubers than the other varieties (Table 2). Bolesta yielded 5, 26, 41 and 28% more tubers than Exquisa, Platina, Silvester and Spey varieties during 1999 spring season, respectively. In 2000 spring trial, the respective yield increases for Bolesta variety were 27, 41, 13 and 12%, respectively. Moreover, Pamina out-yielded the same varieties by 13, 36, 52 and 38% during spring of 1999 and by 29, 43, 15 and 14% in 2000, respectively (Table 2). The lowest yielding varieties were Platina, Silvester and Spey during 1999 spring season, whereas Platina was in 2000.

During fall studies, Diamant yielded significant (P<0.05) and consistently more tubers than Bolesta, Platina, Silvester and Spey in 1999  than all varieties during 2000 (Table 3). Among the six new varieties, Exquisa showed fluctuating tuber yields, being high only during 1999. On the other hand, Pamina produced the highest and consistent tuber yields during both seasons as compared to the rest of new varieties. While Exquisa gave 15% higher tuber yields  than Pamina in 1999, the latter out-yielded the former by 55% during 2000 (Table 3). In 1999, Pamina variety out-yielded Bolesta, Platina, Silvester and Spey varieties by 9, 30, 2 and 10%, respectively. The respective yield increases during 2000 were 8, 17, 18 and 17%  (Table 3).

Platina consistently registered the lowest yields during both seasons. Differences of tuber yields  among varieties could be genotipic as pointed out in similar studies (Coffin et al., 1989; Cipar et al., 1990; Reeves et al., 1990; Lynch et al., 1991; Rabie, 1996).

Specific gravity, dry matter and starch content. In 1991 spring (Table 2), Exquisa and Diamant varieties produced tubers of higher specific gravity, dry matter percentage and starch content than the other varieties. Bolesta and Silvester, followed suit, while Platina gave  the lowest specific gravity, and starch percentage. On the contrary, tubers of Exquisa and Silvester exhibited the highest values during 2000 spring (Table 2), whereas Diamant tubers gave intermediate results. The lowest specific gravity, %DM  and starch content were observed in Pamina and Platina tubers.

Tubers of Diamant and Silvester varieties exhibited the highest specific gravity, %DM and starch content during 1999, whereas those of Silvester gave the highest values in 2000 (Table 3). Tubers of Pamina and Platina varieties exhibited  the lowest values of specific gravity, %DM and starch content in both years (Table 3). Differences among varieties for specific gravity have also been reported by previous workers (Foda, 1973; Chaudhry et al., 1987; Coffin et al., 1988; Reeves et al., 1990; Lynch et al., 1991; Sinha et al., 1992) and dry matter (Foda, 1973; Chaudhry et al., 1987) and are probably due to the genetic variability of different potato varieties (Burton, 1966). Positive linear correlations (Fig. 1) between tuber specific gravity and dry matter (r=0.99) as well as starch content (r=0.96) were observed. Similar results were previously reported (Burton, 1966; Schippers, 1976). Consequently, the observed differences in starch content among different varieties could be related to their differences in specific gravity.

Weight after frying. During the spring of 1999, chips weight after frying (WAF) of Bolesta variety was significantly (P<0.05) superior to Platina and Silvester (Table 4). In 2000, there were no significant differences in WAF for varieties, Exquisa and Silvester.  These varieties gave the highest WAF as compared to the other tested varieties. Platina variety consistently, gave the lowest  WAF during both years (Table  4).  Diamant  was significantly superior to the rest of varieties in french fry weight during spring of 1999 (Table 4). In 2000, Exquisa variety gave the highest french fry weight and did not significantly differ from Diamant and Spey varieties, but was significantly (P<0.05) higher than Bolesta, Pamina, Platina and Silvester varieties (Table 4). Pamina and Platina varieties gave the lowest french fry weight during 2000 spring.

During fall, Diamant produced the highest chips weight during both years, with the exception of Bolesta, Exquisa and Spey varieties in 2000 (Table 5). Pamina variety gave the lowest french fry weight during both fall seasons. Bolesta and Diamant varieties gave the highest  (P<0.05) french fry weight during 1999, followed by Spey variety (Table 5). On the contrary, differences among varieties were not significant during 2000 study.

The over all relationship between specific gravity and percentage of net weight of finished product of the varieties is illustrated in Figure 2. Exquisa, Silvester and Spey varieties gave the highest overall percentage of net chips weight  after frying, whereas Pamina and Platina gave the lowest values (Fig. 2A). Spey and Bolesta, in this respect, showed intermediate net weight. Overall, Diamant produced the highest french fry weight variety.   This was followed by Bolesta, Spey, Exquisa and Silvester (Fig. 2B). Again, Pamina and Platina varieties showed the lowest net weight. Differences among different varieties might be attributed to the differences in specific gravity and DM of the processed tubers (Cunningham and  Stevenson, 1963). In this study, Diamant, Exquisa and Silvester  showed high tuber specific gravity and DM content (Tables 2 and 3). This probably explains the increases in french fry quantities (Tables 4 and 5). The high french fry weight of low specific gravity and DM varieties could be due to the absorption by fried slices, of the frying oil (Cunningham and Stevenson, 1963; Dearborn, 1975; Chaudhry et al., 1987; Jaswal, 1991; Sinha et al., 1992). A positive relationship (R=0.67) between tuber specific gravity and WAF of chips was observed (Fig. 3A). On the contrary, a weak correlation (R=0.03) for WAF of chips (Fig. 3B) was recorded.

Sensory quality tests. The best chip colour (light) was displayed by Diamant and Spey varieties during 1999, whereas relatively darker colour was exhibited by Exquisa and Pamina (Table 4). In 2000, Silvester, Diamant, Exquisa and Spey had the lightest coloured chips, while Pamina gave darker coloured slices. Platina variety produced the darkest crisps during both spring studies (Table 4). As regards the taste and crispness, Bolesta, Diamant, Exquisa and Silvester were ranked the best in both seasons. The best colour of french fries was exhibited by varieties Bolesta, Diamant and Spey in 1999, whereas the rest of varieties produced darker coloured fries  (Table 4). In the 2000 study, Bolesta had the best  colour of fries, while Pamina and Platina produced darker strips. In this regard, Diamant, Exquisa, Silvester and Spey varieties showed intermediately acceptable colour of french fries (Table 4). The best french fry taste was presented by Diamant, Exquisa and Spey varieties in both years.

During both fall studies, Bolesta, Diamant and Silvester varieties showed the best colour of chips, whereas Exquisa, Pamina and Spey produced relatively darker colour (Table 5). Platina variety gave the worst colour in both years. Bolesta, Diamant, Exquisa and Silvester varieties showed the best taste and crispiness in both years, in addition to Spey in 2000 study. Varieties Diamant, Exquisa and Silvester showed the best light colour during both fall seasons, whereas Pamina and Platina varieties produced the darkest colour (Table 5). In both fall studies, all varieties produced french fries of acceptable taste except  Pamina and Platina varieties during 1999. Differences among potato cultivars in colour after frying have been reported by several researchers (Coffin et al., 1988,1989; Reeves et al., 1990; Lynch et al., 1991; Sinha et al., 1992; Rabie, 1996). Rabie (1996) reported that Diamant was superior in all sensory quality tests among other varieties. The dark colour associated with some varieties after  chip frying is a result of the browning reaction or Millard reaction (Chaudhry, 1987; Coffin et al., 1989; Cipar et al., 1990; Reeves et al., 1990). Although, reducing sugars participate in the browning reaction, other constituents of the potato such as amino acids, ascorbic acid and other organic compounds must be present before colour formation occurs (Smith, 1968).

It is concluded that the varieties Diamant, Bolesta, Silvester and Spey could be used for chip processing, in spite of the tuber shape of  the latter varieties.  Further studies may be required on the effect of baking and storage period on  different sensory quality tests.

References

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