Quality of hermetically packaged nonfat dry milk in long-term storage
M. A. LLOYD1, L. V. Ogden, and O. A. Pike. (1) Department of Nutrition, Dietetics and Food Science, Brigham Young University, S221 Eyring Science Center, Provo, UT 84602
Over the past few decades, nonfat dry milk (NFDM) has been retail-packaged for long-term storage in No. 10 cans under reduced oxygen concentrations for use in emergency situations. Little information is available concerning the quality of NFDM held in such conditions for prolonged storage periods.
The objective of this research was to evaluate the quality attributes of NFDM in hermetically sealed cans with reduced oxygen levels held in long-term storage.
Twenty samples of regular and instant NFDM (representing 9 brands) stored up to 29 years at ambient conditions were obtained from 14 sources. Samples were evaluated for headspace oxygen, can seam quality, water activity, solubility index, sensory quality (50-member consumer panel using a 9-point hedonic score), and nutritional value.
Headspace oxygen ranged from 0.05%-20.9%, which was related to the efficacy of the oxygen removal treatment (nitrogen, carbon dioxide, or oxygen absorbers). Only 6 samples had <2% headspace oxygen. The sample with 20.9% oxygen had poor can seams, while all others had acceptable seams. Water activity ranged from 0.13-0.25 which is typical for NFDM. The solubility index was well below the typical 1 ml maximum for extra grade NFDM. Stepwise regression indicated that age and oxygen level explained 78% of the variation in flavor (2.8-6.2) and overall acceptability (2.9-6.2) scores. However, a 23-year old sample with low oxygen was not significantly different from fresh samples. Comparison of instant and regular NFDM showed no significant differences, indicating both types were suitable for storage. Available lysine varied from 1.22-2.28 g/100g NFDM and did not have a strong correlation with sample age.
Though there is some decline in quality over time, it appears possible to retain palatability and nutritional value in NFDM during long-term storage by using adequate packaging and storage conditions. Manufacturers need to ensure proper packaging of their products to optimize shelf-life.
Session 14A, Dairy Foods: General developments in dairy technology I