Effects of Storage Conditions on Nutritional Qualities of Semipurified (AIN-76) and Natural Ingredient (NIH-07) Diets

Abstract

The effects of storage condition on the shelf life of the AIN-76 diet were investigated. Samples of the diet were stored at -70°, 4°, 20° and 20–30° under atmospheric air and at 4° and 20° under argon. Levels of vitamin A, thiamine, rancidity, bacteria and mold were monitored during 168 days of storage. A 41.3% loss of vitamin A occurred in samples stored at 23–30°. A marked decline in thiamine was observed in all samples stored at 20° or above. Loss of thiamine was significantly greater in samples stored at 20° than in those stored at 4°, and greater in samples stored under air than those stored under argon. Rancidity reached a level previously shown to be associated with a disagreeable odor and taste (peroxide value > 140) within 30, 50 and 90 days when the diet was stored at 23–30° or 20° under air and 20° under argon, respectively. Peroxide values remained well below 140 in samples stored at 4° or colder. None of the nutritional parameters tested reached unacceptable levels in any of the samples stored at 4° or colder during the 168 days. These results indicate that to achieve maximum shelf life, the AIN-76 diet should be stored at 4° or colder. Although less effective than low temperature, an argon atmosphere extended the shelf life and was additive with lower temperatures.