ANNUAL REPORT, 1939 43 



the higher initial aging temperature was sought by studying properties of gelatin 

 which are likely to be influenced by the gel structure or which would serve as an 

 index to the colloidal behavior of the gelatin. In addition to studies of viscosity, 

 gel strength, optical rotation, and light scattering, which have been described 

 previously, studies were made during the past year of electrical conductance, 

 gold number, and effect of agitation. 



The higher initial aging temperature of 68° F. had no significant effect on the 

 velocity- of the hydrogen ion through the gelatin gel when compared with an aging 

 temperature of 38° F. for the entire period. However, the higher initial aging 

 temperature decreased the N'elocity of chromate ions through the gelatin gel when 

 compared with the lower temperature. The decreased rate of migration of 

 chromate ion through the higher initially aged solution suggests a more closely 

 knit structure. The rate of the hydrogen ion was not affected, probably because 

 of its smaller size. 



Gold number determinations must be made with very dilute gelatin solutions, 

 which may explain why the higher initial aging temperature did not increase the 

 protective action of the gelatin. 



Agitation of the gelatin solution while it was held at the higher initial aging 

 temperature was found to increase the gel structure. If an increase in viscosity 

 retards gel structure building, then it may be expected that agitation within 

 limits will facilitate gel structure formation in that more frequent collisions of 

 gelatin micelle may occur. 



Several other ice cream stabilizers were compared with gelatin with respect to 

 their response to high aging temperatures. Water solutions of karaya gum, oat 

 flour, sodium alginate, and agar-agar were initially aged at 68° F. for five hours. 

 Agar-agar was the only substance afifected by the higher initial aging temperature. 

 Both apparent and basic viscosity were increased when the high initially aged 

 solution was compared with a solution aged only at 38° F. However, the increase 

 was more pronounced for the apparent viscosity. 



The Use of Egg Solids in Ice Cream. (M. J. Mack.) Egg solids have been 

 used in ice cream since the very beginning of the business. The effect of egg yolk 

 on the properties of ice cream was studied here some years ago when only batch 

 freezers were used in the industry. Further work appeared necessary to see 

 whether egg yolk solids were desirable in ice cream made on a continuous freezer. 

 A study of the egg products known as egg powder "blends" also seemed desirable. 



The conclusions from the work done during the past year were summarized 

 in a recent article entitled "Egg Solids," by M. A. Widland and M. J. Mack, 

 published in the October 1939 issue of the Ice Cream Trade Journal. Egg yolk 

 solids improved the flavor, body, and texture of ice cream. Such defects as 

 coarse texture and weak or crumbly body are less likely to occur when the egg 

 solids are used. The product also causes the ice cream to appear creamy and 

 smooth when melting and helps to eliminate defects in melting appearance. 



The egg yolk blends, which are products containing dextrose, skim milk powder, 

 or egg albumin mixed with dehydrated egg yolk, are of value only to the extent 

 that they contain egg yolk. The use of these products instead of ordinary de- 

 hydrated egg yolk should be avoided. Methods of analysis which are suitable 

 for determining the percentage of yolk solids in a powdered egg product are dis- 

 cussed in the paper mentioned abov^e. 



Sodium Alginate as a Stabilizer for Ice Cream. (M. J. Mack.) In previous 

 annual reports, it has been shown that this stabilizer is satisfactory for use in ice 

 cream. Since each stabilizer has somewhat different characteristics, the ad- 

 visability of combining some of the common stabilizers for use in dairy products 

 should be of interest. Preliminary results indicate that certain combinations 



