The flow properties of milk, cream, and ice-cream mixes have been comparatively little studied. Bateman and Sharp (2) showed that, for ice-cream mixes over a limited range of stress, the rate of flow was linearly related, but not proportional, to the shearing stress; in another paper (3) they showed that the viscosity of various kinds of milk fell with increasing stress, and also that the viscosity, reduced by shearing, rose again on resting the sample. This last phenomenon ("false body") they ascribed to changes in the conditions of the fat clumps. These authors worked at 25°C., and they suggested that the fall in viscosity produced by shearing is more marked at low than at high temperatures.Mohr and Oldenburg (13) made a very thorough rheological study of milk and cream, using eonsistometers of various types (rotating cylinder, capillary, and falling cylinder). To interpret their data they used an equation of the Ostwald-de Waele type, in which the logarithm of the shearing stress is plotted against the logarithm of the rate of shear. Over a certain limited stress range, curves obtained in this way are linear, but the range of stresses used was so wide that many of the data fell outside the linear part of the curve.1 2 Mohr and Oldenburg also investigated the viscosityconcentration relation, which has recently received a very interesting treatment at the hands of Leighton and his coworkers (8,9,10,11,12), but this problem is not discussed in the present paper. In some of Leighton's papers, however, the authors do claim a linear relation between flow rate and shearing stress. A certain amount of other work has been done (20), but it was felt that the whole question of the nature of the flow of cream
It has been known for a long time that unblanched vegetables deteriorate in quality when held in frozen storage for extended periods of time. Rancidity of the lipid matter is one of the primary causes of off-flavor in unblanched peas which had been stored at 0°F. (-17.8"C.) (5). Large increases in acid numbers together with increases in peroxide numbers were observed in the lipids extracted from raw peas after several years of frozen storage. The main increase in acid number occurred during the first year of storage (8). Similar changes were noted in the lipids extracted from unblanched sweet corn, snap beans, and other vegetables after extended periods of storage at 0°F. (-17.8"C.) ( 4 ) .I n order to extend the knowledge of the changes which take place in such material, the present study was undertaken to determine the length of time that unblanched vegetables could be held in frozen storage before these undesirable changes could be detected, and to determine the course of the development of the acids and peroxides during the period of storage. MATERIALS AND METHODSThomas Laxton peas, Wade snap beans, and Golden Cross sweet corn were grown on the Experiment Station farm and were harvested, processed, and stored, as previously described (4, 5 ) .Quality changes were measured both chemically and by means of a taste panel. Samples from each lot were taken for immediate taste test a t the time of harvest, and at regular intervals during storage, until obvious deterioration in quality was definitely established. A t the same time, samples were dried by 1yophiIization and were extracted for 48 hours with peroxide-free anhydrous ethyl ether to obtain the crude lipid material, as described previously ( 5 ) . This work was started before it was determined that a 24-hour extraction period was sufficient to effect the extraction of the crude lipid (4), but was continued on the 48-hour basis to keep the conditions uniform. The chemical determinations were continued a t regular but lengthening intervals throughout the storage period. A final subjective and chemical examination of the 1952 samples was conducted after 2 years of storage. Chemical methods used were described previously (4, 5).
The influence of pH on the optical activity of purified and de-ashed calfskin gelatin has been determined at 0.5" and 40" C. It has been shown that calfskin gelatin exists in two different forms. The stable form at 40" C. (sol form) consists of a molecule in which the linkages between amino acids are probably of the chain type, while the stable form a t 0.5" C. (gel) consists of a molecule in which a t least a number of the linkages are of the ketopiperazine type. I t is shown that the grading of gelatin samples by the mutarotation method must be done a t a definite pH. A pH of 7.3 is satisfactory for calfskin and bone gelatins, and pH 5.0 is suitable for porkskin gelatins.A study of the influence of pH on the Bloom strength of purified de-ashed calfskin gelatin a t 0.7" and 10" C. showed a maximum gel strength to occur in a rather broad range, pH 5 to 7, a t both temperatures. In this region the gel strength was increased about 55 per cent by lowering the hardening temperature from 10" C. to 0.7OC.The influence of gelatin concentration on gel strength at low temperature follows the relation S = KCN for several gelatin samples of both calfskin and porkskin origin. The constants K and N appear to be different for each sample studied. Indications point toward the conclusion that the Bloom gelometer measures gel elasticity.The influence of hardening time and temperature on Bloom strength is considerable and the gain in gel strength is greater with the lower grade gelatin samples when the hardening time is lengthened and the temperature of hardening lowered. This is of more consequence with porkskin than with calfskin gelatins.The addition of ammonium sulfate increased the gel strength slightly. Insufficient amounts of this salt are contained in edible gelatin samples, however, to influence the grading by the Bloom gelometer. URIKG recent years several experimental methods have been described for the comparison and evalu-
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