Factors influencing the occurrence of methanethiol in aqueous slurries of soy protein concentrates

Aqueous slurries of 6 commercial soy protein concentrate (SPC) contained from 9.8 to 21.7 ppb methanethiol, which corresponds to odor values (in water) of 49 to 108. Effects of temperature (5.5, 24, and 65°C), pH (4.8, 6.6, and 9.0), transition metals (FeCl₃, FeCl₂, and CuCl₂), lipoxygenase, and EDTA on methanethiol levels in SPC slurries were investigated. Higher temperature (65°C), basic pH (9.0), transition metals, lipoxygenase, and EDTA caused significant increases in methanethiol compared with the control. CuC1₂ caused greater increases in methanethiol than FeCl₃ and FeCl₂. In contrast, treatments with lower temperature (5.5°C) or acidic pH (4.8) resulted in lower levels of methanethiol in all commercial SPC sample examined.