40 MASS. EXPERIMENT STATION BULLETIN 347 



been grown in one plot during the summer of 1937. The data reported here were 

 drawn only from the first four samples, and the tentative conclusions may nec- 

 essarily be modified when the complete data are assembled. 



Starch and dry matter were found to be closely correlated with texture after 

 storage periods of three months and five months. This relationship was not 

 evident from samples analyzed before the storage periods. 



Previous workers have been unable to relate pectin fractions with texture of 

 cooked potatoes. It has been found that the usual methods of pectin analysis 

 and fractionation, originally devised for other types of plant material, could not 

 be applied to potato without modification. Modified methods were devised that 

 eliminated the protein and starch contaminants. These methods demonstrated 

 that all potato samples tested — raw, baked, and steamed — contained very 

 nearly 2 percent total pectin regardless of variety or texture. A fraction usualh 

 designated as calcium pectate ranged from 0.2 percent to 0.5 percent, with no 

 apparent relation to texture or variety. The so-called "proto pectin" (acid 

 soluble) could be completely extracted from potatoes in 12 hours bv water at 

 85° C. 



Additional data suggest that the larger part of the pectin in potato is so loosely 

 bound that it is hardly comparable to the "proto pectin" fraction in other types of 

 plant material. The total amount of this fraction, however, is not related to 

 texture. While small amounts of pectin can be obtained by exhaustively extract- 

 ing (mortar and pestle) fresh tissue with cold water, no pectin was extracted from 

 dried, finely ground samples by water at 37° C. 



Preliminary results indicated that the so-called "proto pectin" fraction was more 

 loosely bound in mealy potatoes than in waxy varieties. This allowed a means of 

 relating pectin to texture. Under certain conditions mealy varieties, cooked and 

 raw, gave two to three times as much pectin as waxy varieties. 



The usual method for drying potato samples did not increase the amount of 

 soluble pectin through enzyme hydrolysis. On the other hand, a boiling ethanol 

 dip, used presumably to halt this enzymatic hydrolysis, actually rendered water 

 soluble (37° C.) 20 percent of the total pectin. 



Cooking increased the water soluble (37° C.) pectin fraction from percent to 

 70 percent of the total pectin. Starch (including dextrin) decreased to some extent. 

 Reducing sugars increased slightly on cooking. Other data have been obtained, 

 and experiments are in progress concerning the effect of storage on these and other 

 relationships 



Possible changes in the potatoes due either to storage or to cooking or both are 

 also being followed by the "in vitro" methods suggested by Horwitt, Cowgill, 

 and Mendel. These methods were first used and reported on leafy material 

 (spinach). It is likely that some modification of the method will be necessary 

 since with potatoes (a starchy product) the crude fiber as determined is practi- 

 cally the equivalent of the total carbohydrate. Using the method with such a 

 sample as spinach, the carbohydrate (starch, etc.) would apparenth' be included 

 as part of the crude fiber. 



In addition to the work on the potato, possible changes in peas as a result 

 of storage and cooking are being studied. For this purpose samples were obtained 

 from the Birds Eye Frosted Foods Corporation during the past summer. The 

 control sample represented the fresh peas in the pod. These were shipped to 

 the laboratory where they were shelled and dried under suitable conditions. 

 Samples from the same field were canned and frozen and stored under these condi- 

 tions. These are being withdrawn from storage at definite intervals and prepared 

 for analysis. Comparisons are to be made on the basis of the "in vitro" analysis 

 mentioned above. Complete data are not available since storage periods are not 

 yet finished. 



