Comparative studies of the degradation of grass fructan and inulin by strains of Lactobacillus paracasei subsp. paracasei and Lactobacillus plantarum

Abstract

Four strains of Lactobacillus paracasei subsp. paracasei and Lact. plantarum are investigated within 16 d in order to determine the formation of metabolites during the degradation of grass fructan and inulin as well as the subsequent fermentation to lactic acid. The decrease of the total content of fructans throughout the entire time of investigation shows differences specific for strains as for either fructan substrate. The strain Lact. plantarum V 54/6 completely degrades the grass fructan and inulin within no longer than 13 d. The utilization of fructan by the other strains is temporally delayed, and in a smaller degree of degradation, especially remarkable for inulin cleavage. The structural modifications of decomposed fructans are characterized by a noticeable shift of the mean DP from approximately 80 to the oligomeric range analysed by anion exchange chromatography. Additionally, a newly formed series of peaks of oligomeric saccharides was detected during the degradation of grass fructan and inulin. Part of the fructose that is derived from cleavage of fructans is fermented immediately by the LAB strains into differently high amounts of lactic acid. The abundance of formed fructose is enriched in the medium to a varying extent, depending on the strain as well as the substrate used. From these results a number of fructan degradative enzymes in lactobacilli have been concluded to possibly vary their modes of regulation: strain specific exo‐ and endohydrolases with different activities against β‐2,1 and β‐2,6 linked fructan.