Comparative Analysis of Lactulose and Fructooligosaccharide on Growth Kinetics, Fermentation, and Antioxidant Activity of Common Probiotics

Abstract

Prebiotics are non-digestible oligosaccharides that selectively stimulate the growth of beneficial bacteria in the human gut. Fructooligosaccharide (FOS) is a common prebiotic found in food products and infant formula. Lactulose is primarily used as a pharmaceutical ingredient but also shows potential prebiotic activities. Our objectives were to determine and compare the effects of FOS and lactulose on: 1) growth kinetics of common probiotics in aerobic condition; 2) pH and titratable acidity after fermentation; and 3) antioxidant capacity of the probiotics. Ten probiotic and two non-probiotic strains, representing genera Lactobacillus, Bifidobacterium, Bacillus, and Escherichia were assembled. Media used for prebiotics experiment were modified to contain 2% FOS or lactulose as the sole or main carbohydrate source. All experiments were done in triplicate. In aerobic condition, most strains cultured with FOS or lactulose did not grow optimally compared to dextrose (a non-prebiotic), while all four Bifidobacterium spp. showed little growth regardless of the carbohydrate source. In anaerobic condition, lactulose and FOS fermentation of Bifidobacterium spp. yielded similar pH (p = 0.2723), but percent lactic acid, as determined by titratable acidity, was higher after lactulose fermentation (p = 0.0004). The non-probiotic strains were able to utilize both FOS and lactulose, but displayed weaker acid production and higher pH (p < 0.0001) relative to the probiotic strains. Antioxidant activity of spent medium was measured with Trolox as the reference standard. Overall, the antioxidant activity of probiotics was strain-dependent. FOS enhanced the antioxidant activity of Bifidobacterium spp. (p = 0.0002) and Lactobacillus spp. (p = 0.0447), but not probiotic E. coli and Bacillus spp. (p = 0.2599) or non-probiotics (p = 0.8816). In conclusion, lactulose supported growth activities of probiotics to a similar extent as FOS. Lactulose also stimulated higher acid production for Bifidobacterium spp. than FOS in anaerobic condition, thus it might be considered for incorporation into functional food products containing bifidobacteria.