FACTORS ASSOCIATED WITH POTATO TEXTURE. I. SPECIFIC GRAVITY AND STARCH CONTENT^a

Abstract

Among the various problems of potato technology, the texture of the cooked product has been accorded a considerable proportion of research effort. It is well-recognized that some varieties, after cooking, are glistening in appearance and feel more or less dry and granular on the tongue. These are characterized as mealy. On the other hand, other varieties have a translucent appearance when cooked and feel wet and pasty on the tongue.These are characterized as soggy or waxy.There is often a considerable variation in texture within a given variety. I n fact, striking individual differences have been observed among potatoes taken from the same hill (9, 26) ; and different parts of a single potato will even vary in mealiness or sogginess (30). Texture or so-called "cooking quality'' has been shown in numerous investigations to be influenced by fertilizers (3, 23), by maturity, by growing conditions generally (such \as seasonal climate, region of growth, and physical condition of the soil), and by handling and storage conditions, etc. (8,9,10,29). Interest in the effect of these various growing and handling conditions, however, points up the fact that an understanding of textural differences must be based upon statistically established correlations between the chemical composition of a given sample and organoleptic and other aspects of texture. Thus, it has been found that a relatively high correlation exists between the degree of mealiness and the starch content of the raw tuber and between the degree of mealiness and specific gravityb (5, 11, 12, 20, 25, 26, 31). Bewell (2) has even stated categorically that potatoes with less than 20% dry material will be of poor quality ( i e . , soggy) and those with more than 26% dry material will always be mealy.Gilmore (8) and East (7) in attempting to explain the role of starch interpret mealiness as attendant upon the swelling and bursting of cells by the gelatinized starch within them. According to Whittenberger (29) and Whittenberger and Nutting (30), textural variatious are due to differences in internal pressure developed within cells by the swelling starch during cooking and to differences in the capacity of the individual cells to resist that pressure.The regression coefficient of the starch-texture relationship has been found to be of the order of 0.3-0.6. This suggests that the relatise amount of starch is not the sole factor in explaining texture and that an amplification of the concept is needed. Whittenberger (29) maintains that the relative amount of starch in individual cells has a greater influence on texture than Specific gravity is a good index of starch content and has been useful as a non-1, 1954. destructive measurement of potato ' 'quality." 71

TEXTURAL PROPERTIES OF COOKED TROPICAL YAM (DIOSCOREA SPP

“…In the potato industry, specific gravity determination is usually used as an index of the total solids or starch content in the tuber, and is a good indicator of the textural attribute of mealiness (Bettelheim andSterling 1955a. 1955b).…”

“…Potatoes, which have a composition similar to that of yam, have several factors that influence texture (Bettelheim andSterling 1955a, 1955b;Reeve 1954Reeve , 1977Hoff 1973;Linehan and Hughes 1969;Warren and Woodman 1974;Warren et al 1975). There is much evidence in the literature that differences in composition of potato cultivars, maturity, specific gravity, starch content or percent dry matter and mode of cooking affect the textural properties of the cooked potato tubers.…”

Factors Associated With Potato Texture.

“…When total calcium associated with pectic material and total calcium pectinate are considered as the pectic independent variables ( Table 4 ) , again a strong interrelationship is shown among the three independent variables (Table 5). However, in this case, although the calcium contenttexture coefficients are again negative, the total calcium pectinate-texture ' I n calculating partial coefficients, three assumptions have been made: (1) the gross correlatioiis hare linear regressions; (2) each independent variable has a n effect on the dependent variable (Le., the texture score) ; and ( 3 ) these effects are additive.…”

Factors Related to Potato Mealiness

“…Reeve (1977) has pointed out that, undoubtedly, both pectic materials and starches are significant to texture of potatoes. Bettelheim and Sterling (1955) were not able to correlate the amyIose and amylopectin content of the starch with mealiness of 10 different cultivars. Briant et al (1945) noted a high percentage of small starch granules (diameter: ~20 CL) was associated with lower mealiness scores.…”