Adhesive solid-state fermentation producing Aspergillus niger conidia on stainless-steel dixon ring supports.

ABSTRACT

An adhesive solid-state fermentation (adSSF) mode was developed to produce Aspergillus niger conidia, which used a stainless-steel Dixon ring as the support and water-retaining adhesive to load nutritional media on its surface. To obtain high conidia yields, the components of the water-retaining adhesive were screened, optimized by single-factor optimization and response surface methodology, and the optimal dosages of the main components were wheat bran powder 0.023 g·cm-3bed, cassava starch 0.0022 g·cm-3bed, and xanthan gum 0.0083 g·cm-3bed. The experimentally tested conidia yield was 4.2-fold that without water-retaining adhesive but was 3.7% lower than the maximum yield predicted by the model. The observed double-side growth of A. niger on the Dixon ring supports improved space utilization of the fermentation bed, and the void fraction can increase with the shrinkage of the gel layer. In 1.6 L tray reactors with three-point online temperature monitoring, the inner-bed temperature of adSSF was at most 4 °C lower than the adsorbed carrier solid-state fermentation (ACSSF) mode, and the conidia yield was 1.68 × 108 conidia.cm-3bed, 61.5% higher than that of the ACSSF bed at the same time, but when the fermentation time was extended to 168 h, the conidia yield of the adSSF bed and ACSSF bed were close to each other. The results revealed that the high voidage of the adSSF bed was the main reason for low bed temperature, which can benefit the inner-bed natural convection and water evaporation.