Obtaining lactic acid from oat husks
Polylactides are increasingly being used as biodegradable polymers in the production of packaging materials. It has been recently proposed to obtain a polylactide precursor - lactic acid - from inexpensive cellulose-containing raw materials. For the first time, the authors of the present work used oat husks for this purpose. Preliminary chemical treatment of oat husks was carried out in two stages using dilute solutions of nitric acid and sodium hydroxide to obtain technical cellulose, which was further subject to enzymatic hydrolysis. The asobtained glucose enzymatic hydrolysate was fermented by the producer Lactobacillus delbrueckii subsp. bulgaricus. The effect of the active acidity of the medium, activation of the starter culture and dosage of the yeast extract on the efficiency of lactic acid fermentation was investigated. According to the obtained results, the active acidity of the culture should be maintained at a pH level of 6.5 during the entire fermentation process, which allows the yield of lactic acid to be increased by 1.7 times compared to the process without adjusting the pH. It was shown that the activation of the starter culture using a glucose medium instead of a milk medium, which switches the fermentation process from lactose conversion to glucose conversion, increases the rate of lactic acid fermentation by 2.2 times and the fermentation constant by 2.7 times. It was established that the introduction of yeast extract into the medium in an amount of 1% intensifies lactic acid fermentation: the process of lactic acid fermentation accelerates by 1.8 times; the fermentation constant increases by 1.4 times; the yield of lactic acid increases by 9.6% compared to the control thus reaching 76.7%.