Reconstituted Nonfat Dry Milk

A 250-ml graduated cylinder was modified by attaching it to a blender base assembly. It was used to measure the foaming capacity of reconstituted nonfat dry milk. Measurements of foaming capacity with this device had a lower standard deviation (1.30-2.63) than those made with a conventional method (1.71-9.15). The device is easier to use and has fewer sources of error than conventional methods used to determine foaming capacity. Funct ional propert ies are important in selection of an ingredient to be used in a prepared food. A functional property is broadly defined as any physico-chemical property which affects the processing and behavior of protein in foods as judged by the quality attributes of the final product (2). These properties reflect complex interactions between composition, structure, conformation and physico-chemical properties of the protein. Of course, functional properties are also associated with other food constituents. Foaming capacity is an important functional property of some foods (3). During our studies on how this functional property of nonfat dry milk is affected by growth of psychrotrophic bacteria in skim milk before it is dried, we found that the conventional method to determine foaming capacity was not satisfactory. Consequently we devised an improved procedure which is described in this report. MATERIALS AND METHODS The device to determine foaming capacity consisted of a 250-ml graduated cylinder (Kimax), which was modified to fit an Eberbach blender base and semi-micro blender blade assembly (Eberbach Corporation, Ann Arbor, MI) (Fig. 1). General Electric silicon cement (General Electric, Schenectady, NY) and Teflon gaskets (Eberbach) were used to make the system leakproof. This apparatus fits a 2-speed commercial blender (Waring, New Hartford, CT). Milk or any other fluid to be foamed can be filled into the graduated cylinder to the 80-ml level and foamed without using a cover. If milk is to be filled about this level, a cover must be used. Another version of this device has been built with a water jacket surrounding the cylinder. This facilitates temperature control of the material to be foamed. It is particularly useful when extended mixing times are used with temperature-sensitive materials. Foaming capacity measurements are simple. A sample is placed in the apparatus to the 80-ml level, blended for the desired time and then maximum foam height is recorded. When the foam-liquid interface becomes apparent, height of the interface is recorded. Maximum foam height minus interface height is equal to the foam volume that is stable during the waiting period, which, in our hands, for nonfat dry milk was 2 min and 10 s. To obtain the percent foam volume one must divide the foam volume by the volume of milk in the cylinder (one must take into consideration the volume of liquid that the blade assembly displaces). Figure 2 is a schematic diagram showing use of the foaming apparatus in a test to determine foaming capacity of nonfat dry milk. A traditional method of measuring foamability involves foaming reconsituted nonfat dry milk in a blender or household-type electric beater, pouring the foam into a graduated beaker and noting the characteristics of the foam (1,4). We used a blender. This method has several sources of error: (a) not all of the material in the blender or beater may be transferred to the beaker in a reproducible fashion, and (b) moving the foamed material may increase or decrease the volume of that material. To compare a traditional test with our method, we measured the percent foam volume for three different brands of reconstituted nonfat dry milk. Nine hundred ml of water at 25°C was mixed with 100 g of low-heat nonfat dry milk. Reconstituted milk was blended for 30 s with a Waring 2-speed commercial blender. Maximum foam volume was recorded and interface height was measured 2 min and 10 s later. The same nonfat dry milk also was tested with the traditional method using a 2 min and 10 s waiting period. RESULTS AND DISCUSSION Foam volumes produced by the different brands of nonfat dry milk we tested were smaller when we used our device rather than the convention method (Table 1). The standard deviations of percent foam volume were smaller for brands A and C and slightly higher for brand B when our method rather than the conventional procedure was used (Table 1). This indicates that generally there was less variation in results obtained with our procedure than in those for the conventional method. In conclusion, our foaming apparatus simply, rapidly and reproducibly measures foam volume produced by reconstituted nonfat dry milk. JOURNAL OF FOOD PROTECTION, VOL. 47, FEBRUARY 1984 D ow naded rom hp://m eridianenpress.com /jfp/article-pdf/47/2468/0362-028x-47_2_140. pdf by gest on 29 Feruary 2020 DETERMINING FOAMING OF MILK 141 Figure 2. Procedure to measure foaming capacity using the new