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, iV-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 IV-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.

Non-enzymatic browning in citrus juice: chemical markers, their detection and ways to improve product quality

“…The potential inhibitors tested include ascorbic acid, a commercial formulation called Sporix, sodium sulfite, N-acetyl-L-cysteine, L-cysteine, and reduced glutathione (Molnar-Perl and Friedman 1990).…”

“…Thus by retarding the accumulation of polyphenolics, there is a inhibition of browning of peel juice (Chu et al 2006;Chung et al 2007). Use of L-cysteine to inhibit NEB (Arnold 1969;Montgomery 1983) did not attract further research as cysteine is a flavor source in some foods which can be objectionable in fruit juice (Molnar-Perl and Friedman 1990;Roig et al 1999). Nevertheless, some thiol compounds are natural components of human diets and play significant physiological roles in vivo as nucleophiles and scavengers of free radicals.…”

Non-Enzymatic Degradation Pathways of Lactose and Their Significance in Dairy Products

“…However, paradoxically, in a mixed system containing lysine, tryptophan and cysteine, there was evidence that cysteine acted as an inhibitor of browning (Labuza and Massaro, 1990). Cysteine, N-acetyl-Lcysteine and reduced glutathione have been reported to inhibit non-enzymatic and enzymatic browning in both model and real food systems (Friedman and Molnar-Perl, 1990;Molner-Perl and Friedman, 1990). The strong nucleophilicity of such sulphur compounds probably contributes to their activity as browning inhibitors.…”

Medium-dependent cytotoxic effect of ascorbate

“…Serum albumin is able to decrease hydrogen peroxide and reperfusion injury in isolated rat hearts (4). Sulfhydryl-containing compounds are effective in preventing ascorbate browning in foods (11). The sulthydryl groups in our three culture systems were measured in our laboratory.…”

“…To further investigate the identity of the cell-killing agent in the culture system, the toxicity of ascorbate was examined in the presence of catalase, a hydrogen peroxide scavenger (4,11). The rates of degradation of ascorbate in the three media were also measured.…”