A carbohydrate-rich diet, namely starch-rich, is associated with type 2 diabetes due to its rapid digestion and absorption, generating an elevated glycaemic response. For this reason, different strategies have been proposed to modulate carbohydrate digestion, such as reducing available carbohydrates or decreasing carbohydrate digestion rate (Wee & Henry, 2020).
Starch is the main carbohydrate in foods, composed of two polymers: amylose (15–35%) and amylopectin (65–85%). Both consist of α-(1,4)-linked glucosyl chains, and with α-(1,6)-branched points in the case of amylopectin. Starch is used as a thickener, stabilizer, and gelling agent. A unique property of starch is its ability to gelatinize when heated in the presence of water, leading to the loss if its crystallinity structure (Schirmer, Jekle & Becker, 2015). From a digestion point of view, starch hydrolysis determines the postprandial glucose levels. The structural modification that starch undergoes during gelatinization increases the enzymes access to binding sites, favouring its hydrolysis by salivary and pancreatic α-amylases. According to the rate of starch hydrolysis, it is generally classified into three categories: rapidly digestible starch (RDS) associated with a fast increase in blood glucose level; slowly digestible starch (SDS) gradually hydrolyzed in the small intestine, related to moderate postprandial glycaemic response and with that, a beneficial effect in human health; and resistant starch (RS), starch that is not digested by the enzymes in the upper gastrointestinal tract, and which modulates the gut microbiota (Englyst, Kingman & Cummings, 1992).
This article was written by Maria Santamaria, PhD student at the Institute of Agrochemistry and Food Technology (IATA, CSIC, Spain), Dr Raquel Garzon (Research Assistant, Food Science Department, IATA) and Professor Cristina M. Rosell (Professor at IATA and Head of Department, Food and Human Nutritional Sciences, University of Manitoba, Canada).
The starch digestion process can be influenced by different food factors: nutritional composition, technological processing, or food matrix structure (Dupont, Le Feunteun, Marze & Souchon, 2018). Innovative strategies are currently being developed for slowing starch digestibility with the aim to reduce the effect on the glycaemic index. This physiological process is affected by starch characteristics (such as source, granule size, amylose–amylopectin ratio, or enzymatic/chemical modifications), but also the incorporation of functional ingredients (hydrocolloids, proteins, lipids, polyphenols) and processing (high hydrostatic pressures, shear, acidification, cold plasma) — which could modify starch digestibility (Pellegrini, Vittadini & Fogliano, 2020; Wang, Ral, Saulnier & Kansou, 2022; Wee & Henry, 2020).
The key to designing starchy foods with lower digestibility is to control the accessibility of the enzyme to its substrate. In food formulations, studies are generally based on the incorporation of hydrocolloids. Starch-hydrocolloid interactions can restrict enzyme accessibility. How? Several mechanisms have been described:
Association of hydrocolloids on the surface of starch granules;
Formation of hydrated networks that encapsulate starch granules;
Or Increasing the viscosity digest.
Viscosity has been associated with starch digestion rate, producing an impact on the glycaemic index. This property is defined as the thickness of the fluid, or as a measure of fluid resistance to flow. High-viscosity foods have been associated with slowing down eating and gastric emptying rates, affecting the enzymatic kinetics (Jin et al., 2022). Consequently, starch digestion can also be altered by the physical properties of the media, such as viscosity, providing an alternative way to modulate the rate of enzyme accessibility to starch substrates.
FSTA contains a wealth of reliable, interdisciplinary, food-focused information, making it a great tool for researching published science on viscosity and starch digestion. For example, FSTA content that investigates viscosity and starch digestion includes over 8,500 records across the whole database.
Is viscosity a relevant characteristic for digestion?
In our study, simple matrices were used to avoid interaction with other polymers (Santamaria, Garzon, Moreira & Rosell, 2021). Corn starch gels at various concentrations (1:04–1:08–1:16) were analyzed. The aim was to understand the impact of a starch gel’s viscosity and microstructure on their digestion. Starch gels showed different viscosities at 37˚C, with a progressive reduction as the starch content decreased (768, 112 and 48 mPa s, respectively). In addition, the microstructure of gels was different. As the dilution increased, the number of cavities decreased (226, 100 and 93 cavities/mm2, respectively), due to the presence of large cavities (Figure 1).
Figure 1: Corn starch gels pictures by scanning electron micrograph (SEM)
After the gels were prepared at different viscosities, their hydrolysis was studied using porcine pancreatic α-amylase. Results indicated that less viscous gels (1:16) digested faster so the hydrolysis rate (k) was higher. Consequently, SDS, starch fraction hydrolyzed within 20–120 minutes was reduced.
Both parameters could be related to a higher postprandial glycaemic peak. Gel with higher viscosity (1:04) displayed a slower hydrolysis rate (k) and a higher content of SDS (Figure 2). These results confirm the viscosity impact during starch hydrolysis. Enzyme diffusion into the gel could be hindered due to high starch content and by the resistance associated with the mass transfer related to gel viscosity.
Figure 2: Hydrolysis parameters of corn starch gels digestion. Kinetic constant (k) is the hydrolysis rate; Slowly digestible starch (SDS) starch fraction hydrolyzed within 20–120 min
What would happen with other cereals?
The rheological properties and digestibility of corn, rice and wheat gels were also studied. The research was carried out at constant or variable viscosities of the starch gels. Constant viscosity samples displayed comparable hydrolysis parameters. Moreover, a positive correlation was obtained between viscosity and slowly digested starch, and a negative correlation among viscosity and kinetic constant was observed (Santamaria, Montes, Garzon, Moreira & Rosell, 2022).
Finally, exploring and understanding starch gel characteristics could be used as a predictor of a starch gel’s digestion performance. This is an opportunity to apply reverse engineering for the design of starch-based systems to reduce postprandial glucose levels and provide consumers with healthy foods.
- Dupont, D., Le Feunteun, S., Marze, S. & Souchon, I. (2018). Structuring food to control its disintegration in the gastrointestinal tract and optimize nutrient bioavailability. Innovative Food Science & Emerging Technologies, 46, 83–90. https://doi.org/10.1016/j.ifset.2017.10.005.
- Englyst, H.N., Kingman, S.M. & Cummings, J.H. (1992). Classification and measurement of nutritionally important starch fractions. European Journal of Clinical Nutrition, 46 Suppl 2, S33–50.
- Jin, Y., Wilde, P.J., Hou, Y., Wang, Y., Han, J. & Liu, W. (2022). An evolving view on food viscosity regulating gastric emptying. Critical Reviews in Food Science and Nutrition, 1-17. https://doi.org/10.1080/10408398.2021.2024132.
- Pellegrini, N., Vittadini, E. & Fogliano, V. (2020). Designing food structure to slow down digestion in starch-rich products. Current Opinion in Food Science, 32, 50–57. https://doi.org/10.1016/j.cofs.2020.01.010.
- Santamaria, M., Garzon, R., Moreira, R. & Rosell, C.M. (2021). Estimation of viscosity and hydrolysis kinetics of corn starch gels based on microstructural features using a simplified model. Carbohydrate Polymers, 273, 118549. https://doi.org/10.1016/j.carbpol.2021.118549.
- Santamaria, M., Montes, L., Garzon, R., Moreira, R. & Rosell, C.M. (2022). Unraveling the impact of viscosity and starch type on the in vitro starch digestibility of different gels. Food & Function. https://doi.org/10.1039/D2FO00697A.
- Schirmer, M., Jekle, M. & Becker, T. (2015). Starch gelatinization and its complexity for analysis. Starch - Stärke, 67(1–2), 30–41. https://doi.org/10.1002/star.201400071.
- Wang, Y., Ral, J.-P., Saulnier, L. & Kansou, K. (2022). How Does Starch Structure Impact Amylolysis? Review of Current Strategies for Starch Digestibility Study. Foods, 11(9), 1223. https://doi.org/10.3390/foods11091223.
- Wee, M.S.M., & Henry, C.J. (2020). Reducing the glycemic impact of carbohydrates on foods and meals: Strategies for the food industry and consumers with special focus on Asia. Comprehensive Reviews in Food Science and Food Safety, 19(2), 670–702. https://doi.org/10.1111/1541-4337.12525.
Researching Viscosity and Starch Digestion in FSTA
FSTA is quality-checked by experts in food-related sciences and contains a wealth of interdisciplinary, food-focused information that you can trust. This makes it a great tool for researching published science on food lipid oxidation and so many other topics.
FSTA content investigating viscosity and starch digestions includes >8,500 records across the whole database. Some key titles include Preparation and characterization of non-crystalline granular starch with low processing viscosity, Unraveling the impact of viscosity and starch type on the in vitro starch digestibility of different gels.