The Effect of Pullulan on the Growth and Acidifying Activity of Selected Stool Microflora of Human

Pullulan is a microbial polysaccharide of low energy value, which can component of low-calorie foods and in dietary snacks for diabetics. The objective of the study was to determine the effect of pullulan on the growth and fermentation activity of selected human intestinal bacteria.

Commercial pullulan purchased from Focubase (China) of a molecular weight of 100,000 Da constituted as experimental material. Food grade pullulan 99% purity. Two control media were prepared: the first standard RCM composed of (g/100 ml): 0.5 glucose, 0.1 soluble starch, 1.0 peptone, 1.0 meat extract, 0.3 yeast extract, 0.3 sodium acetate, 0.05 cysteine hydrochloride, 0.5 NaCl, pH 6.8; and the second modified RCM, wherein the soluble starch was replaced by increased glucose concentration to 2.0% (RCM+G). Experimental medium was the modified RCM medium, wherein the soluble starch and glucose were replaced by pullulan at a concentration of 2.0% (RCM+P). Stool suspensions were prepared from fresh stool samples (1 g) in peptone water (9 g), which were previously homogenized. Then, suspensions at a volume of 300 μl were transferred to the media (RCM, RCM+G, and RCM+P). After mixing, flasks were placed in anaerobic tubes with AnaeroGenTM 2.5 l sachets. Incubation of samples was carried out at 37°C for 48 h.

The number of Bifidobacterium, Lactobacillus, and Escherichia coli bacteria, as well as pH and total acidity of the culture during 0, 24, and 48 h were measured. It was found that the numbers of bacteria of the Bifidobacterium and Lactobacillus genus in medium with pullulan were one logarithmic cycle lower in comparison to their numbers in the control media. Higher total acidity (1.48 g/100 ml) of pullulan culture in comparison to the control media was obtained (1.10 and 0.60 g/100 ml), and lower pH values than RCM medium, particularly 4.15 and 4.70, respectively. Pullulan exhibited selective effect on the natural microflora of the colon. Increase in the fermentation activity of bacteria in medium with pullulan favorably influenced modification of the composition of gut microbiota.

In summary, pullulan exhibited a selective effect on the natural microflora of the infants' colon. Although no stimulating effect of pullulan on the growth of Bifidobacterium and Lactobacillus was observed, their increased acidifying activity, which probably was the cause of reduction in the number of E. coli bacteria, was confirmed.