36 MASS. EXPERIMENT STATION BULLETIN 355 



same results. Reliable measurements of the oxidation potential of crude juice 

 could be obtained only in a nitrogen atmosphere after several hours; owing, 

 probably, to the reaction of some juice components with atmospheric oxygen. 

 After a partial clarification of the juice, oxidation potentials could be quickly 

 and easily determined. When rugose juice was so treated and adjusted to a low 

 oxidation potential by cysteine, its longevity in vitro was increased. 



Chemical Changes in Cooking of Vegetables. (Monroe E. Freeman and W. S. 

 Ritchie.) An important factor of cooking quality of potatoes and consumer 

 preference is the texture of the cooked tuber. Potatoes baked under uniform 

 conditions are mealy or waxy depending on variety and cultural conditions. The 

 cause of these differences in texture is not known. Two theories at least have 

 been proposed but not experimentally verified. This study will attempt to de- 

 termine the cause of differences in texture, because such knowledge should ma- 

 terially aid efforts to meet consumer demand. 



One characteristic of mealy potatoes is the separation of the cells in cooked 

 tissue. Since this may be caused by weakness of the intercellular binding material, 

 one theory suggests that there may be a relation between the pectic materials 

 and texture. The loss of pectin through enzymatic action during the preparation 

 of samples was minimized by steaming and by dipping raw slices in boiling 

 ethanol. However, it was noted that any heat treatment altered the distribution 

 of the pectin fractions. The analysis of 10 lots of potatoes for total pectin, 

 calcium pectate, proto pectin, and water soluble pectins did not reveal any rela- 

 tion between these fractions and texture. Nearly all the pectin was found in 

 the hot water fraction. Therefore, this fraction was, in turn, fractionated under 

 conditions designed to remove only a portion of the total pectin. If the theoretical 

 relation does exist, the mealy potatoes should yield a larger proportion of the total 

 pectin. Ten baked samples and two uncooked samples did not support this 

 idea. On the other hand, eight uncooked samples did. The evidence is not con- 

 clusive, but the experience with the eight raw samples seemed to warrant further 

 tests which are now in progress on twelve new samples. 



The storage of potatoes at higher temperatures may result in rapid changes 

 in the pectins accompanied by spoilage. The storage of four varieties for four 

 and six months just below 40° F. allowed little, if any, change in pectin and 

 maintained the tubers in good physical condition until late spring. Sugars, 

 however, accumulated to an undesirable extent. 



Baked mealy potatoes have a dry crumbly appearance, while waxy potatoes 

 look wet and soggy. The loss of water during baking, however, may be almost 

 the same. This observation has led to the theory that the particles in mealy 

 tissue have absorbed or bound the water naturally present to a greater extent 

 than in the waxy potatoes. The method for determining bound water proposed 

 by Dumanski seemed to be particularly suited for this type of material. Since 

 this is a relatively new method, preliminary tests were necessary and clearly 

 showed that extremely accurate measurements of refractive indices were nec- 

 essary in order to obtain only a fair degree of accuracy in the final results. When 

 ethanol was used instead of sucrose in this method negative values for bound 

 water resulted. Apparently, the ethanol was more readily absorbed by the 

 potato tissue than the water. Sucrose proved satisfactory after careful standardi- 

 zation of the refractometer. The amount of water bound by one gram of dry 

 potato seemed to be fairly constant over a wide range of sucrose concentrations. 



For the purpose of studying changes, if any, due to storage and cooking, peas 

 were preserved by canning and freezing in the fall of 1937. Peas obtained in the 

 pod from the same field producing those which were canned and frozen were 

 shelled and half of them dried at low temperatures without cooking. The other 



