Effect of moisture content and inoculum on the growth and conidia production by Beauveria bassiana on wheat bran

Abstract

The aim of the present work was to study the effect of moisture content and inoculum on the growth and conidia production by Beauveria bassiana on wheat bran (WB).The highest growth rate of B. bassiana 885.2 on WB media was obtained at aw=1.0, with no detected growth at aw < 0.97. Solid-state fermentation (SSF) using WB (66% moisture; aw=1.0) achieved a maximal yield of 1.18x1010 conidia per gram of dry substrate (gds). This yield decreased one order of magnitude with higher moisture contents or the addition of sugarcane bagasse (SCB) as a texturiser. In SSF using WB (66% humidity),the time to obtain a yield of 1x1010 conidia/gds, referred to as t10, could be predicted using a model considering common inoculum levels and maximal yields. For instance, t10 was 285 h with an inoculum of 1x106 conidia/gds; however, t10 was reduced to 232 h and 148 for inocula of 7x106 and 5x107 conidia/gds, respectively. The estimation of t10 values allowed both comparison between the cultures and prediction of harvesting times in production processes. Values for hydrophobicity were within 90 and 92%, whereas viability averages were around 70% for all the cultures.