چكيده به لاتين
Microbial production of lactic acid has attracted researchers due to its high potential in recent years. The highest cost of lactic acid production in fermentation method belongs to the cost of the substrate. Therefore, the optimal production condition for lactic acid is essential with the use of cheap substrate. In this study, for the first time, lactic acid production was investigated by Lactobacillus delbruckii bacteria (PTCC 1333) by semi-solid fermentation at 73% (w/w) of initial moisture content of the mixture of wet spent grain and the extract from the hydrolysis of the same spent grain as a substrate. First of all, four hydrolysis methods including acidic, alkaline, acidic-alkaline and alkaline-acidic methods were studied to obtain the highest total sugar extract. Acid hydrolysis method with 370 grams total sugar extraction per gram of initial dried spent grain was chosen to hydrolyze the substrate. Effect of four variables of the percentage of hydrolyzed liquid composition with a hydrolyzed wet solid substrate, total glucose concentration, yeast extract concentration as a nitrogen source in 3 levels (4, 7 and 10 g / l), and calcium carbonate concentration as a neutralizing agent at levels of 0.5, 1, 1.5 and 2 g /l were investigated. The acid production were carried out at 37 ° C and pH = 6 ± 0.2 of the substrate in 50 mL-falcons during four days. Based on the analysis results, the highest amount of lactic acid was obtained 31.22 g/l for 1.35 grams of initial dry malt at 40 g/l initial total sugar, 7 g/l yeast extract, 1.5 g/l calcium carbonate in 96 hours.
