Flavor and Stability of Whole Milk Powder

Abstract

ABSTRACT

LLOYD, MICHELLE ANN. Flavor and Stability of Whole Milk Powder. (Under the direction of Dr. MaryAnne Drake.)

Flavor variability and stability of US-produced whole milk powder (WMP) are important parameters for maximizing quality and global competitiveness of this commodity. The US industry standard for shelf-life of whole milk powder (WMP) is 6-9 mo, although previous research has demonstrated flavor changes by 3 mo at ambient storage. Two studies were conducted using sensory and instrumental techniques to (1) characterize flavor and flavor stability of domestic WMP and (2) evaluate the influence of packaging atmosphere, storage temperature, and storage time on WMP shelf-life. Descriptive analysis was conducted using a 10-member trained panel. Selected volatiles were quantified using solid phase microextraction (SPME) with gas chromatography/mass-spectrometry: dimethyl sulfide, 2-methylbutanal, 3-methylbutanal, hexanal, 2-heptanone, heptanal, 1-octen-3-ol, octanal, 3-octen-2-one, and nonanal. For the first study, freshly produced (<1 mo) WMP was collected from 4 US production facilities 5 times over a 1 y period. Each sample was analyzed initially and every 2 mo for sensory profile, volatiles, color, water activity, and moisture through 12 mo storage. Multiple linear regression with backwards elimination was applied to generate equations to predict grassy and painty flavors based on selected volatiles. All WMP were between 2-3% moisture and 0.11-0.25 water activity initially. WMP varied in initial flavor profiles with varying levels of cooked, milkfat, and sweet aromatic flavors. During storage, grassy and painty flavors developed while sweet aromatic flavor intensities decreased. WMP developed painty flavor between 4 and 6 mo. Painty and grassy flavors were confirmed by increased levels (p<0.05) of lipid oxidation products such as hexanal, heptanal, and octanal. Hexanal, 2-heptanone, 1-octen-3-ol and nonanal concentrations were the best predictors of grassy flavor (r=0.62, R2=0.38, p<0.0001) while hexanal, 2-methylbutanal, 3-methylbutanal, octanal, and 3-octen-2-one concentrations were the best predictors of painty flavor (r=0.78, R2=0.61, p<0.0001). For the second study, two batches of WMP were repackaged in plastic laminate pouches with air or nitrogen and stored at 2 ˚C or 23 ˚C for one y. In addition to sensory and volatile compound analyses, consumer acceptance testing (n=75) was conducted every 3 mo with reconstituted WMP and white and milk chocolate made from each treatment. Data were analyzed using analysis of variance with Fisher’s LSD, Pearson’s correlation analysis, and principal component analysis with significance at p<0.05. Air stored WMP had higher peroxide values, lipid oxidation volatiles and grassy and painty flavors than nitrogen flushed WMP. Storage temperature did not impact levels of straight chain lipid oxidation volatiles; 23 ˚C storage resulted in higher cooked and milkfat flavors and lower levels of grassy flavor compared with 2 ˚C storage. Consumer acceptance was negatively correlated with lipid oxidation volatiles and painty flavor. Nitrogen flushing prevented the development of painty flavor in WMP stored up to 1 y at either temperature, resulting in chocolate with high consumer acceptance. Nitrogen flushing can be applied to extend the shelf life of WMP; refrigerated storage also plays a role, but to a lesser extent. These results provide baseline information to determine specific factors that can be controlled to optimize US WMP flavor and flavor stability.