Estimation of Extra‐Cellular Starch of Dehydrated Potatoes

SUMMARY Extra-cellular starch is isolated from dehydrated mashed potatoes by rehydration of 0.5-g samples with 100 ml water at 150°F. The suspension is poured over a standard 150-mesh sieve, and the water containing the freed starch gel collected and filtered. Starch so collected on 7-cm hardened and extremely retentive filter paper is stained with iodine, and its reflection density (Rd) and color characteristics measured on a color-difference meter. Transmission values may also be determined. In addition, extra-cellular starch, so collected from l-g samples, may be dried and weighed. Rd values are a linear function of the amount of starch. The temperature of the sample suspension also has a linear effect on reflection density. Since added stearates do not interfere with reflection density values, the effects of added emulsifiers on iodine color of the collected starch gel are measurable by color-difference procedures. Color difference also provides a means of characterizing other starch changes, such as retrogradation, induced by processing treatments. An insignificant number of the smallest intact cells pass through the screen to be collected on the filter paper. The intact, separated cells of cooked potato range from less than 40 to nearly 400 μ in diameter. They average about 180 μ, and over 90% have diameters between 100 and 250 μ.