CHEMISTRY OF SULFUR COMPOUNDS IN CHEESE FLAVOR AND WHEY PROTEIN FUNCTIONALITY (THIOLATION, MICROENCAPSULATION, BREVIBACTERIUM LINENS, IMMOBILIZED CELLS)

Part 1. The potential for modifying functional properties of (beta)-lactoglobulin by thiolation with N-acetylhomocysteine thiolactone (N-AHTL) and S-acetylmercaptosuccinic anhydride (S-AMSA) was examined. Up to 18-22 sulfhydryl groups per dimer of (beta)-lactoglobulin were introduced. The isoionic point was lowered from 5.3 for (beta)-lactoglobulin to 4.7 for (beta)-lactoglobulin thiolated with N-AHTL and to 3.7 for (beta)-lactoglobulin thiolated with S-AMSA.;Part 2. Milkfat-coated microcapsules containing Brevibacterium linens, cysteine and methionine were used to produce sulfur compounds from methionine and cysteine. More than 80% of B. linens cells added to carrier were encapsulated in milkfat and more than 90% of cysteine and methionine were encapsulated and 90, 80, and 60% of the encapsulated amino acids were retained in the capsules after 24 h at 4, 12 and 26 C, respectively.;Partition coefficients of methionine and cysteine to milkfat were 0.117 and 0.275, respectively.;Optimum pH and temperature were 6 and 32 C for hydrogen sulfide synthesis from cysteine and 8 and 25 C for methanethiol production from methionine.;The endothermal response disappeared during differential scanning calorimetry of (beta)-lactoglobulin, in which 80% of the free amino groups were thiolated. When thiolated (beta)-lactoglobulin was treated with potassium iodate, polymers with molecular weights over 600,000 daltons, or strong and flexible gels were formed depending on the number of sulfhydryl groups and concentrations of the thiolated (beta)-lactoglobulin.;Rapid production of hydrogen sulfide from cysteine required anaerobic conditions.;Production of methanethiol from methionine occurred aerobically and anaerobically, but production was three times greater aerobically with most methanethiol being oxidized to dimethyl disulfide.;Either low temperatures, such as 4 - 12(DEGREES)C, or presence of hydrogen sulfide at high temperatures, such as 26(DEGREES)C, stabilized levels of methanethiol in microcapsules up to 11 days.