Master of Science / Food Science Institute / Karen A. Schmidt / Radio frequency dielectric heating (RFDH) can provide rapid and uniform heating throughout the products' mass, and can be used to bake, dry, and defrost foods. Studies have shown that when RFDH induced a 5-log reduction of Salmonella spp. in nonfat dry milk (NDM), whey protein nitrogen index (WPNI) decreased, suggesting that functional properties of the NDM might be impacted. This research was conducted to determine if RFDH affected the functional properties of NDM [high-heat (HH) and low-heat (LH)]. Nonfat dry milk were treated to 75, 80 and 85°C in the RFDH unit, then were held for 125, 63 and 43 min for LH-NDM or 115, 52 and 43 min for HH-NDM, and cooled to ~23 ± 1°C. Powders were evaluated for WPNI , nitrogen solubility index, and color. Maillard browning and functional properties of NDM samples were evaluated after NDM was rehydrated to 3.5% protein with deionized water, and adjusted to pH 7.00. Glucono-delta-lactone was added in rehydrated NDM (3.5% protein; natural pH) as an acidifying agent to form milk gels, and the physical properties of the gels were determined. Two replications were conducted and data were analyzed with two-way ANOVA (RFDH and NDM) and Tukey mean differentiations (p ≤ 0.05). Results showed that LH-NDM (collapsed for RFDH treatments) had 5.7% less viscosity, 20.9% less overrun, 27.4% less foam stability, as well as 15% less water holding capacity compared with HH-NDM (collapsed for RFDH treatments). This can be explained by the natural whey protein denaturation differences in the HH-NDM and LH-NDM. Viscosity and surface tension were impacted by the RFDH treatment. NDM (HH and LH) treated to 85°C had 10% greater viscosity than the control, and the NDM treated to 75°C had less surface tension compared with samples treated to 80°C, 85°C and the control. Overall, RFDH decreased WPNI in LH-NDM, but not HH-NDM. The SDS-PAGE gel images provided supportive evidence to the WPNI results. RFDH is a processing technology that could change a few functional properties of NDM in this study, which makes it a promising method that may be further exploited for various food applications, such as emulsifiers, foaming agents, etc. However, potential negative impacts, such as color change caused by Maillard reaction, loss of WPNI in LH-NDM, cannot be neglected.

Two studies were conducted to evaluate the effects of milk solids on restructured and emulsified turkey rolls. the milk solids used were nonfat dry milk (NFDM), whey protein concentrate (WPC), and calcium caseinate (CC). Turkey rolls consisted of 100% breast meat or 90:10 or 70:30 breast-to-thigh, salt (1%), water (10%), internal or cluster fat (10%), and 3% of various milk solids (WPC, NFDM, CC). The objectives of these studies were to 1) determine which ratio between light and dark meat is preferred; 2) determine which of milk solids evaluated will permit the highest level of dark meat incorporation into evaluated products; 3) determine if there is a mechanism by which milk proteins lighten poultry meat; and 4) determine which milk protein produces the best bind between meat pieces. Panelists were used in the first study to evaluate cooked meat attributes of color intensity, color uniformity, cohesiveness, tenderness, roasted turkey flavor, juiciness, and overall acceptability. The attributes were rated on a seven-point scale. Rolls made with WPC or NFDM scored significantly higher for color uniformity, cohesiveness, roasted turkey flavor, and overall acceptability than rolls made with CC. No differences were noted among treatments for juiciness or toughness with rolls of the same light-to-dark meat ratio. However, the 90:10 rolls were rated significantly more tender than the rolls made with the 70:30 ratio. Rolls containing milk solids had significantly higher yields than the controls. In the second study, rolls were made using the preferred meat ratio (90:10 breast:thigh meat). NFDM and WPC were used as binders, but not CC, since in the first study it was an ineffective binding agent. The second study showed that no whitening or lightening occurred in turkey rolls. This researcher also found that both NFDM and WPC increased bind strength between meat pieces. Controls made without added milk solids had less bind strength between the meat particles. Meat particle size also affected bind strength in finished products, with finely chopped rolls having higher bind strength than coarsely ground rolls. Moreover, the second study had unexpected results indicating that NFDM will prevent development of pink discoloration during refrigerated storage. The penetrometer used for bind measurements is described.

Nonfat dry milk (NOM) was evaluated to determine the effect of long term storage on its sensory quality, its solubility index and on the development of oxidative derivatives of sterols. Storage variables included the form of the milk, the atmosphere in the storage container, the type of package and the storage temperature. A trained taste panel evaluated the milk for the development of cooked, metallic, and oxidized/stale flavors, mouthfeel and overall acceptability. Gas chromatography was used to determine cholesterol content and the quantity of oxidative derivatives of cholesterol present in the samples. Although long term storage of NOM did not affect the solubility index of the milk, the sensory quality of the milk was affected. Over time storage temperature and type of package had the greatest effect on sensory quality. Milk stored for 30 months at 32 C developed an unacceptable oxidized/stale flavor and at 42 months of storage, milk stored in polybags at 21 C had also developed an oxidized/stale flavor. These results substantiate the importance of controlling storage conditions during long term storage of NOM. NOM stored for four years did not develop harmful quantities of oxidative derivatives of cholesterol. However, certain expected results did occur. NOM stored in polybags developed more oxidative derivatives than samples stored in cans. Samples stored at 32 C developed more oxidative derivatives of cholesterol than any other sample analyzed and 7S-hydroxycholesterol, the only known cytotoxic derivative of cholesterol identified, was present in the samples stored at 32 C. Fresh and control samples of NOM contained similar quantities of oxidative derivatives of cholesterol.

Two studies were conducted to determine the relative effect of various combinations of antioxidants on vitamin A oxidation and isomerization in nonfat dry milk (NDM). In the first study, one lot of pasteurized unfortified skim milk was divided, fortified with vitamins A and D and one of 11 antioxidant treatments, and spray dried. A control batch from the same lot was also fortified with vitamins A and D and spray dried. Samples were analyzed for total vitamin A bioactivity after zero, one, and two weeks of storage. After two weeks at 50°C, the only NDM samples that did not experience significant vitamin A loss were those treated with butylated hydroxytoluene, either alone at 0.57 ppm or at 0.29 ppm in combination with 250 ppm ascorbic acid. The control sample was significantly different from both of these treatments, and retained only 17% of its original retinol activity equivalents. Isomer composition changed over the two weeks of storage, with an increase of the 13-cis, 9,13-di-cis and the 9-cis isomers as well as a decrease in the all-trans isomer. In the second study, two lots of pasteurized, vitamin A & D fortified, condensed skim milk were divided into four batches, three of which were spiked with an antioxidant treatment: 250 ppm ascorbic acid + 1 ppm propyl gallate, 250 ppm ascorbic acid + 1 ppm butylated hydroxyanisole, or 2 ppm propyl gallate; the fourth batch was a control. Each of the eight batches was homogenized, spray dried and stored in the absence of light at 30°C for 3 months. Vitamin A and riboflavin were analyzed before spray drying, and after 0, 1, 2, 4, 6, 8, 10, and 12 weeks. Two treatments had significant higher vitamin A than the control, the 250 ppm ascorbic acid + 1 ppm butylated hydroxyanisole treatment and the 2 ppm propyl gallate treatment. Limited vitamin A degradation occurred in all samples during the study timeframe, although the overall degree of retinol isomerization began and remained high in all samples, with cis isomers accounting for approximately 23% of the total μg of retinol after 12 weeks. There were no significant differences in riboflavin content between any of the antioxidant treatments and no significant degradation in riboflavin over time. Antioxidants appear to be an effective means of reducing vitamin A oxidation and isomerization in nonfat dry milk. Butylated hydroxytoluene in combination with ascorbic acid was the most effective antioxidant blend observed. Antioxidants may be less effective at protecting against degradation of vitamin A if isomerization has already taken place.