On the relative effectiveness of varying steam sterilisation protocols on heat-resistant Trichoderma- and Bacillus-infected rye grain for mushroom spawn production

Abstract

The goal of this work is to investigate the efficacy of different sterilisation protocols as well as the possible impact of starting raw material contamination level and secondary contamination sources on grain spawn production. Several sterilisation protocols for Trichoderma- and Bacillus-infected rye grain were performed and monitored over a period of 17 weeks. These protocols are: standard, autoclave tyndallization (dual sterilisation), germination period and pasteurisation. It was found that the standard protocol is best although not perfect. Tyndallization worked well on Bacillus but had some potential issues with Trichoderma. Germination period and pasteurisation. were enough for Trichoderma but Bacillus showed a high rate of survival. There are indications that the main source of contamination for Bacillus is the substrate, while in the case of Trichoderma it could be due to manipulation. Bacillus exhibits very high levels of heat resistance and has the ability to survive 150 minutes at 121.4°C. It is recommended to investigate a complementary treatment to the standard consisting of a pH increase through the use of quicklime.