Abstract:

In the present study, wheat straw hydrolysate was fermented in a 500 mL shaking flask to prepare high-optical purity L-lactic acid for effectively elevating the utilization value of the agricultural waste. Considering metabolitic inhibition probably occurring during fermentation, the optimization of wheat straw hydrolysate concentration, amounts of added HN-Y13 type activated carbon and DM11 type macroporous resin as adsorbents to the fermentation inhibitors in wheat straw hydrolysate and shaking speed was carried out using orthogonal array design and back-propagation artificial neural network (BP-ANN). From the results of orthogonal array experiments, it was found that L-lactic acid production was remarkably influence by all the above four factors and reached up to 82.8 g/L under optimized conditions determined through range analysis. The optimal values of wheat straw hydrolysate concentration, amounts of added HN-Y13 type activated carbon and DM11 type macroporous resin and shaking speed were predicted with BP-ANN to be 126, 2.48 g/L and 1.6 g/L, and 234 r/min, respectively. The yield of L-lactic acid was 86.9 g/L under these conditions, much higher than before optimization.

Key words: wheat straw hydrolysate, Rhizopus oryzae, L-lactic acid, orthogonal array design, BP neural network