The influence of environmental temperature and substrate initial moisture content on Aspergillus niger growth and phytase production in solid-state cultivation

Aspergillus niger is being used commercially for phytase production utilizing solid-state cultivation; however, no studies have been published that investigated the optimal environmental temperature and initial substrate water content to maximize fungal growth and/or phytase production. Solid-state cultivations of Aspergillus niger on wheat bran and soybean meal were conducted at three temperatures (25°C, 30°C, and 35°C) and three initial moisture contents (50%, 55%, and 60% wet basis) in a split-plot full-factorial experimental design. Fermentations were conducted for 0, 24, 48, 72, and 120 h. The containers were sampled destructively and assayed for phytase activity and glucosamine concentration as an estimate of fungal biomass. Temperature affected phytase activity production, but substrate initial moisture content did not. The highest phytase activity was found at 30°C, 50% to 60% initial moisture content, and 72 h of fermentation. Initial substrate moisture content affected glucosamine production after 72 and 120 h of fermentation. The maximum glucosamine was produced at 35°C, either 50% or 60% initial moisture content, and 120 h of fermentation. The results show that the optimal biomass growth conditions are not the same as the optimal phytase production conditions, suggesting that phytase production is not entirely correlated with fungal growth.