The fermentation behavior of pectin by B. thetaiotaomicron and L. rhamnosus: insights into the changes in pectin structure and the metabolite profiles.

This study aims to investigate the utilization behavior of Bacteroides thetaiotaomicron (Bt78496) and Lactobacillus rhamnosus (Lr22825) toward pectin. Results show that Lr22825 can efficiently utilize galactose (Gal) (78.9%), but exhibits limited utilization of galacturonic acid (GalA), rhamnose (Rha), and arabinose (Ara). The utilization rate of Bt78496 for pectic monosaccharides is lower than that of Lr22825, except for Ara (18.9%). During fermentation, P3kDa and P10kDa (pectin with Mw of 3 kDa and 10 kDa) were degraded into smaller fragments (~0.8 kDa), while no new fragments were observed in the P1kDa group. Through monosaccharide composition analysis, it was found that Lr22825 preferentially utilizes the neutral side chains of pectin, while Bt78496 shows a fermentation selectivity for homogalacturonan. The utilization sequence of pectic domains by bacteria is simultaneously governed by the types of sugar units and their degree of exposure. On the other hand, different pectic monosaccharides tend to be metabolized into distinct acidic products, and such metabolic profiles are also strain-dependent. Overall, across different fermentation substrates, the total acids produced by Lr22825 (~4043 μg/mL) are commonly higher than those of Bt78496 (~2912 μg/mL), especially lactic acid (~2425 μg/mL). Malic acid (~1335 μg/mL) and succinic acid (~957 μg/mL) are the main acidic products of Bt78496. Notably, Bt78496 fermentation promotes a more diversified and balanced profile of acidic metabolites, while Lr22825 generates acetic acid (>95%) as the main short-chain fatty acid (SCFA). This work provides valuable information on the pectin fermentation behavior of gut bacteria.