Lactic acid production using free cells of bacteria and filamentous fungi and cells immobilized in polyvinyl alcohol cryogel: A comparative analysis of the characteristics of biocatalysts and processes

Abstract

The results from studies and a comparative analysis of process characteristics are presented for lactic acid (LA) production from glucose, performed under batch conditions of the long-duration use of different biocatalyst samples comprising cells of Lactobacillus сasei bacteria and Rhizopus oryzae filamentous fungi immobilized in polyvinyl alcohol (PVA) cryogel or applied as concentrated suspensions. It is established that for LA production, the bacteria and fungi must be used in the form of PVA-cryogel-immobilized cells because their half-life in this form is considerably longer than that of concentrated cell suspensions. After 200 h of the batch use of the same immobilized cell samples, the amounts of accumulated LA were similar for both fungal (920 ± 5 g) and bacterial (895 ± 5 g) biocatalysts. The fungal biocatalyst, however, was characterized by a twice higher rate of substrate conversion to product (0.92 g LA per 1 g glucose) than the bacterial biocatalyst. The half-life of the immobilized fungal biocatalyst was 80 days (96 working cycles), ten times longer than that of the bacterial biocatalyst. A comparison of our data and the literature data demonstrated the promise of using fungal cells immobilized in PVA cryogel to produce LA: the process based on their use is superior to all known processes in its main indicators, i.e., the rate of LA conversion to glucose and the maximum accumulated concentration of the product.