Rhizopus oligosporus biomass, sporangiospore yield and viability as influenced by harvesting age and processing conditions

The objective of tempe starter preparation is to obtain the maximum viable sporangiospores that can be stored in dry conditions without significant loss of viability. The aim of this research was to establish relationships between spore-harvesting age, their numbers, yield, viability and survival of processing and storage conditions. Within 6 days of incubation on cooked rice substrate, about 8% w/w of fungal biomass was formed, containing 6·3×109 spores per gram. Of these spores, only 5–6% were viable. The remaining spores did not show damage to cytoplasmic membranes, and were probably dormant. Of the processing conditions, mild oven-drying had little negative effect on viability, unlike pulverization which caused mechanical damage and loss of viability. The age of spores at harvest influences their storage stability. This is evidenced by spores harvested after 3 days suffering bigger losses during 2 and 3 months storage compared to spores harvested after 4 or 5 days.