Development of lactic acid production from coffee grounds hydrolysate by fermentation with Lacticaseibacillus rhamnosus

Spent coffee grounds (SCG) are commercial waste that are still rich in numerous valuable ingredients and can be further processed into useful products such as coffee oil, antioxidant extract, lactic acid, and lignin. The challenge and innovation is to develop the SCG processing technology, maximizing the use of raw material and minimizing the use of other resources within the sequential process. The presented research is focused on the aspect of biotechnological production of lactic acid from SCG by using the Lacticaseibacillus rhamnosus strain isolated from the environment. Thanks to the optimization of the processes of acid hydrolysis, neutralization, enzymatic hydrolysis of SCG, and fermentation, the obtained concentration of lactic acid was increased after 72 hr of culture from the initial 4.60 g/l to 48.6 g/l. In addition, the whole process has been improved, taking into account the dependence on other processes within the complete SCG biorefinery, economy, energy, and waste aspects. Costly enzymatic hydrolysis was completely eliminated, and it was proven that supplementation of SCG hydrolysate with expensive yeast extract can be replaced by cheap waste from the agri-food industry.One-Sentence Summary A process for efficient lactic acid production from spent coffee grounds using the Lacticaseibacillus rhamnosus strain was developed and optimized, including nutrient solution preparation, supplementation and fermentation. Graphical Abstract