Banana peels as substrate for lactic acid production: upstream fermentation bioprocess

Purpose Banana peels account for around 30–40% of the banana’s weight and represent an industrial waste. This biomass can be used as an eco-friendly solution for biotechnological bioprocesses. Still, due to the fibrous nature of banana peels, pretreatment becomes essential to enhance the effectiveness of enzymes on the hydrolysis of complex carbohydrates. This study aims to determine the best pretreatment and enzymatic hydrolysis conditions to produce a fermentation substrate suitable for producing lactic acid from the peels. Methods A diluted H2SO4 (0.5% and 0.25%) was used in an autoclave for 10 min at 121 °C. The pretreated material was subjected to several enzymatic hydrolysis tests in which two variables were evaluated for their influence: solid load (10, 15 and 20%), and H2SO4 concentration (0.5 and 0.25% v/v). Commercial enzymes (cellulolytic enzyme mixtures and pectinase) were used. Results All enzymatic hydrolysis yields of cellulose referring to glucose released in the hydrolysates surpassed 60% in all the conditions tested after pretreatment. After evaluating the pretreatment efficiency, the ideal parameters were defined as 0.25% H2SO4, and cellulolytic enzyme mixtures with 15 and 20% solid load. Subsequently, a screening was carried out in MRS+broth with the most suitable pH and temperature conditions for lactic acid production by Lacticaseibacillus rhamnosus. Conclusions The results showed the potential of BP medium for lactic acid production, with yields of 0.91 g/g sugar in sugarcontaining media from enzymatic hydrolysis at 15% solid load and 0.82 g/g sugar in media from 20% solid load assays.