1School of Science, RMIT University, Bundoora West Campus, Plenty Road, Melbourne, VIC, 3083, Australia
2Department of Chemical and Biological Engineering, Monash University, Clayton Campus, Alliance Lane, Melbourne, Vic, 3800, Australia
The inhibitory effects of dietary fibre on digestive enzyme kinetics are poorly understood, which limits the development of fortified foods and nutraceuticals. While inhibition is frequently attributed to viscosity effects, additional physicochemical interactions, including non-catalytic binding may also play a role1,2. To clarify these mechanisms, the present study isolated viscosity as the sole variable affecting alpha amylase activity, thus providing a framework for understanding how the physical properties of a food matrix can modulate digestive enzyme function3.
Gelatin solutions (0.01-0.2% w/v) were prepared from porcine gelatins of varying bloom strength (100, 175 and 300g) to determine the critical concentration range at which viscosity begins to significantly impact enzyme kinetics. Alpha amylase activity was measured using soluble starch as a substrate under controlled conditions (pH, enzyme concentration and viscosity). A clear inverse relationship was observed, indicating that the rate of substrate diffusion to the active site is limited in viscous media. To confirm that the inhibition was solely dependent on viscosity, complementary analyses were performed using fluorescence spectroscopy, confocal imaging and molecular dynamics simulations. These approaches revealed no significant binding interactions or structural alterations of alpha amylase in the presence of gelatin, thus supporting the conclusion that, in this system, reduced enzyme activity arises from rheological constraints imposed by increased viscosity rather than consequential molecular interactions.
This study demonstrates that viscosity alone can significantly inhibit alpha-amylase activity in the absence of binding, thereby identifying a key physical mechanism underlying dietary fibre-enzyme interactions. These findings provide the foundation for future work which aims to disentangle the impact of viscosity and non-catalytic binding both of which are suspected to be at play in systems containing dietary fibre. Success along these lines, would offer practical guidance for the development of fortified foods and nutraceuticals aimed at glycaemic control.
References
1Li, H., & Dhital, S. (2022). α-Amylase interaction with soluble fibre: Insights from diffusion experiment using fluorescence recovery after photobleaching (FRAP) and permeation experiment using ultrafiltration membrane. Bioactive Carbohydrates and Dietary Fibre ,28, 100319. https://doi.org/https://doi.org/10.1016/j.bcdf.2022.100319
2Qin, Y., Xiao, J., Wang, Y., Dong, Z., Woo, M. W., & Chen, X. D. (2020). Mechanistic exploration of glycemic lowering by soluble dietary fiber ingestion: Predictive modeling and simulation. Chemical Engineering Science , 228, 115965. https://doi.org/10.1016/j.ces.2020.115965
3Altug, C., Umut, M., Elif, K., Secil, K., & and Dinckaya, E. (2011). A Novel BiosensoBased on Glucose Oxidase for Activity Determination of α – Amylase. Artificial Cells, Blood Substitutes, and Biotechnology ,39(5), 298-303. https://doi.org/10.3109/10731199.2011.574635