NUTRITIVE AND SENSORY EVALUATION OF 20-YEAR-OLD NONFAT DRY MILK

A sample of instantized nonfat dry milk which was stored in well sealed tins for 20 yr was evaluated. The powder was light yellow in color and had a stale ordor. Flavor evaluation indicated that it was unsuitable for drinking and most cooking uses. Reconstituted nonfat dry milk containing as little as 5% of the old milk mixed with 95% fresh was characterized as stale, cooked, oxidized and old casein. Moisture content was 6.9%, approximately double that of the original powder. Vitamin analyses indicated losses ranging from 61% for thiamine to 2% for niacin. Microbiological testing showed bacterial content similar to fresh nonfat content was decreased by 30%, protein quality as measured by protein efficiency ratio was still high, 2.69 vs. 2.5 for casein. Additional feeding trials with rats indicated that the milk powder was health and growth promoting.