Effects of temperature and relative humidity on growth and enzyme production by Actinomucor elegans and Rhizopus oligosporus during sufu pehtze preparation

Sufu is a Chinese soybean cheese obtained after maturation of solid-state mould-fermented tofu. Ambient temperatures of 30-35degreesC during the summer season prohibit the use of the usual starter Actinomucor elegans. We compared the properties of the latter with a potential alternative starter Rhizopus oligosporus that could be used at higher temperatures. The effects of temperature and relative humidity on growth rate of Actinomucor elegans and Rhizopus oligosporus were optimum at 25degreesC at RH 95-97%, and 35degreesC at RH 95-97%, respectively. Yields of protease (108 U/g pehtze), lipase (172 U/g) and glutaminase (176 U/g) by A. elegans were maximum after 48 h at 25degreesC and RH 95-97%, and for alpha-amylase (279 U/g pehtze) and alpha-galactosidase (227 U/g) at 30degreesC and RH 95-97% after 48 and 60 h of incubation. Highest protease (104 U/g pehtze), and lipase (187 U/g) activities of R. oligosporus were observed after 48 h at 35degreesC and RH 95-97%, while maximum alpha-amylase (288 U/g pehtze) and glutaminase (187 U/g) activities were obtained after 36 h at 35degreesC and RH 95-97%. Maximum alpha-galactosidase activity (226 U/g) by R. oligosporus was found after 36 h at 30degreesC and RH 95-97%. It is concluded that R. oligosporus is a potential alternative to A. elegans as sufu pehtze starter during hot seasons. (C) 2002 Elsevier Science Ltd. All rights reserved.