Inhibiton of browning by sulfur amino acids. 2. Fruit juices and protein-containing foods

Abstract

Enzymatic and nonenzymatic browning reactions may adversely affect the quality, nutritional value, and safety of foods. A need therefore exists to develop methods to control such reactions in a variety of foods. Reflectance measurements were used to compare the relative effectiveness of a series of compounds in inhibiting browning in freshly prepared and commercial fruit juices including apple, grape, grapefruit, orange, and pineapple juices. The potential inhibitors tested include ascorbic acid, a commercial formulation called Sporix, sodium sulfite, N-acetyl-L-cysteine, L-cysteine, and reduced glutathione. For comparison, related studies were also carried out with several protein-containing foods such as casein, barley flour, soy flour, nonfat dry milk, and the commercial infant formula Isomil. The results revealed that under certain conditions SH-containing N-acetyl-L-cysteine and the tripeptide reduced glutathione may be as effective as sodium sulfite in preventing both enzymatic and nonenzymatic browning. The unique electronic and nucleophilic properties of sulfhydryl compounds that enable them to act as inhibitors of both enzymatic and nonenzymatic browning are discussed. These sulfur amino acids merit further study to assess their potential for preventing long-term food browning under practical storage and processing conditions.