3.2. Effect of the concentrations of protease and cottonseed meal on DLA
production
Conventionally, protein hydrolysis and fermentation are separated,
which not only increases the additional treatment steps,
but also might destroy or remove the nutritional components
(Wang et al., 2011). In order to overcome these deficiencies, simultaneous
enzymatic hydrolysis and fermentation strategy was carried
out. To determine the optimum amount of protease
required, different concentrations of neutral protease were added.
As shown in Fig. 2a, the concentration of D-LA dramatically
increased in proportion with the dose of neutral protease. Maximum
D-LA production (120.3 g/L) was obtained with the neutral
protease concentration of 810 U/g cottonseed meal, which was
57.3% higher than that without protease supplementation. Further
protease addition resulted in a decrease in D-LA production, which
was consistent with many previous reports (Wang et al., 2011; Li
et al., 2013). The yield also presented a similar trend with the maximum
value of 0.88 g/g glucose when protease was added at a concentration
of 810 U/g cottonseed meal.