Palatable Foods for a Methionine Restricted Diet

Abstract

Protein oxidation results in loss of tryptophan, oxidation of cysteine to cysteic acid, oxidation of methionine to methionine sulfoxide and ultimately to methionine sulfone. Methionine sulfoxide has been shown to be completely unavailable to mammalian cells and promote improved insulin sensitivity, lifespan extension, weight loss induction and reduce tumor growth in rat studies. Casein was oxidized with ozone or hydrogen peroxide to reduce the cysteine and methionine levels for use in sulfur amino acid restricted diets. Casein was isoelectrically precipitated from skim milk and oxidized with hydrogen peroxide at various pH levels, from 2.5–11. Two strong oxidizers were used: hydrogen peroxide (H2O2) and ozone (O3). Treatments with H2O2 were at 5, 10 and 20% concentration, heated to 90°C for 0.5, 1 and 2 hours to oxidize methionine. Hydrogen peroxide was removed by precipitation/washing or with catalase method. Ozone treatments were at 1, 3 and 12% concentration with a duration of 1-48 hours. Amino acid analysis was performed to determine extent of oxidation of methionine to methionine sulfone; cysteine to cysteic acid and tryptophan destruction. Hominex-2® a mixture of amino acids, has been used as a protein source to deliver sulfur amino acid restricted diets. Compliance has been difficult to maintain, because the mixture of amino acids is unpalatable. A sensory evaluation was conducted to assess the acceptability of the oxidized casein comparing it to Hominex-2®, methionine-free formula. An animal trial was performed with 45 week old male C57BL/6J mice to assess the metabolic and behavioral effects of oxidized casein to elemental methionine restricted supplementation. As a result of the oxidation treatments up to 91% of the methionine was oxidized by treatment at pH 2.5 for 2h at 10% H2O2. Treatments at alkaline pH were not successful in achieving desired levels of methionine oxidation in casein. Ozone treatments resulted in a partial oxidation (26%) of methionine to methionine sulfone. Sensory evaluation demonstrated that the panelists showed a significantly higher acceptance (p<0.05) for a drink prepared with oxidized casein over Hominex-2®. The animal trial demonstrated increased food consumption concomitant with weight loss in the group of rats fed with oxidized casein. Oxidized casein offers a new alternative to other methionine-restricted nutritional mixes prepared with blends of free amino acids, which have unpleasant taste. The development of methionine restricted food ingredients offers a low-methionine protein source to formulate MR diets which help restrict tumor growth in cancer patients and for weight loss therapy