30 MASS. EXPERIMENT STATION BULLETIN 369 



Three methods for determining the water-binding properties of starch, raw pota- 

 toes, and baked potatoes have been tested. The Dumanski method, if carefully 

 followed, was found to be rapid and accurate for starch and other materials that 

 do not contain water-soluble solids. The method could not be applied to raw or 

 cooked potato tissue with much success. The dilatometric method was long and 

 tedious and quite unreliable unless the last traces of dissolved air were removed 

 from the sample by vacuum during a long process of intermittent freezing and 

 thawing. The calorimetric method proved to be rapid and reliable with all 

 types of potato material. The results of these methods agree very closely when 

 applied to starch and raw potato pulp. 



Starches from seven varieties of potatoes varying in mealiness all adsorbed 

 about .3 gram of bound water per gram of dry material. Analyses of a few varie- 

 ties of potatoes (raw) yielded a similar value. No significant differences were 

 found between mealy and waxy varieties. Studies are now being made on baked 

 potato tissue under these experimental conditions. 



Other methods are being applied that may give additional information regard- 

 ing the moisture relationship in raw and cooked potatoes. 



Continuing the work reported earlier with peas, spinach samples were obtained 

 to determine the changes, if any, due to storage and cooking after preservation 

 by canning and freezing. 



The fresh spinach was sent to the laboratory where it was dried at low tem- 

 peratures as a control sample. Additional spinach from the same field was 

 canned and frozen and so stored for three, six, nine, and twelve months. At the 

 end of each of these storage periods three cans of spinach were opened and drained. 

 Half the sample was dried without cooking. The other half was cooked in half 

 of the liquor from the cans and then filtered and dried. The unused half of the 

 liquor was kept as one sample and the filtrate from the cooking process was a 

 second sample. The same procedure was followed with the frozen samples. 

 Frozen spinach (one and one-half packages) was dried immediately after thawing. 

 A second sample of one and one-half packages was thawed and cooked with a 

 definite volume of distilled water after which it was dried. This cooking water 

 was saved for comparison with the liquor samples described above. These were 

 analyzed for total solids, ash and nitrogen. The samples of dried spinach were 

 subjected to methods of proximate analysis and the methods proposed by Horwitt, 

 Cowgill and Mendel. 



In general, results obtained by proximate analysis do not show any outstanding 

 changes. The ash in all stored samples was somewhat lower than in the original 

 sample. It has been suggested that perhaps the blanching process removed some 

 of the ash before the samples were processed. Long standing in the cans ap- 

 parently softened the tissue, with the result that ash was removed more easily 

 in cooking liquors. The protein was consistently higher in the cooked samples 

 and perhaps represents a real difference. The material soluble in ether increased 

 in the canned spinach while the frozen samples showed no change. Crude fiber 

 apparently did not change significantly in either canned or frozen samples when 

 stored. 



It appears that changes, if any, in the spinach, when stored either frozen or 

 canned, are not apparent by such a method of analysis. 



A second method of analysis has been suggested by Horwitt, Cowgill and 

 Mendel, which considers the solubility of food constituents using HgO, N/10 

 HCl, 0.50 percent NagCOg, N/10 HCl-f pepsin, and 0.50 percent Na2C03 + 

 trypsin as solvents. 



The water-soluble nitrogen showed no significant change as a result of storage. 

 The values for the frozen samples were higher than those for the canned samples, 

 indicating possibly a rupture of the cells and therefore greater extraction. Both 



