Prebiotic efficacy of natural gums and their partial hydrolysates: Linking fermentation dynamics with glycosyl hydrolase expression

Gums are naturally occurring heteropolysaccharides with hydrocolloidal properties. They are generally regarded as safe for consumption and are therefore used for food applications and other diverse industrial purposes. The structural complexity of natural gums resists their breakdown in the upper gastrointestinal tract. These soluble dietary fibre fractions with prebiotic characteristics have given this biopolymer the status of a functional food. The prebiotic capacity of four structurally diverse natural gums—guar (galactomannan), acacia (arabinogalactan), tamarind (glucan), and flaxseed (xylan)—and their corresponding partial hydrolysates were evaluated against six lactic acid bacterial strains. Further, in silico studies correlated the substrate specificity with species-specific profiles of glycosyl hydrolases (GHs) and the differential expression of their isozymes when provided with alternate substrates. Measured growth parameters showed that partial depolymerisation enhanced fermentability and substrate utilisation. Growth increased in acacia gum (from 7.72 ± 0.10 to 8.61 ± 0.10 log CFU/mL for L. lactis subsp. lactis 440), tamarind (8.74 ± 0.11 to 10.00 ± 0.02 for L. lactis subsp. lactis 3041), and flaxseed gum (9.75 ± 0.03 to 10.27 ± 0.04 for L. lactis subsp. lactis 3041), demonstrating that structural complexity limits their utilisation to varying degrees. However, all strains showed higher growth with native guar gum (GG) over partially hydrolysed guar gum (PHGG). A fold change of 18.43 ± 5.62 in one α-galactosidase isozyme in L. rhamnosus with GG provides insights into the superior utilisation of the gum, whereas the other two isozymes were overexpressed when provided with PHGG. Altogether, these results indicate the effectiveness of partial hydrolysates as prebiotic compounds and provide the basis for their use in functional foods to selectively support the growth of beneficial gut microflora.