Production of lactic acid in a medium based on food industry effluents using an immobilized mixed dairy culture

Abstract

Polylactic acid (PLA), the best-known bioplastic with the potential to substitute polymers derived from petroleum, is produced by lactic acid polymerization. The application of lactic acid in the production of polylactic acid has led to a substantial increase in the world consumption of this acid. However, the cost of the raw material represents a major obstacle in the economic production of lactic acid for this purpose. Thus, many materials have been considered as alternative substrates, including by-products from agricultural industries, food industries and natural biomasses. The present work evaluated the use of residues from the food industry as a nutritional supplement for the whey used in the production of lactic acid by an immobilized mixed culture of lactic acid bacteria (Lactobacillus acidophilus LA-5, Bifidobacterium BB-12 and Streptococcus thermophilus). Three pH conditions (6.0, 6.5 and 7.0) and three fermentation temperatures (30 ºC, 35 ºC and 40 ºC) were tested. Three levels of whey supplementation were also tested with each of the residues: corn maceration water - AMM (0%, 5% and 10%); vinasse (0%, 5% and 10%) and yeast extract (0%, 3% and 6%). At the end of the fermentations, it could be seen that the treatments with a temperature of 40 °C and an initial pH of 7.0 presented a lactic acid content 10% higher than the other treatments. All the residues were effective in increasing the lactic acid production when used to supplement the whey. The yeast extract presented the highest concentration of lactic acid, with 0.0307 mol.L-1, a result 20% higher than that obtained with corn maceration water and vinasse.