Rice protein and starch digestibility in extruded rice
What it found
In lab tests, adding rice protein, soy protein isolate or whey protein concentrate to extruded rice starch reduced how quickly the starch was broken down.
Rice protein had the strongest effect.
What they found
Animal and lab studies
Starch digestibility
Adding any of the three proteins to extruded rice starch reduced rapidly digestible starch and increased slowly digestible and resistant starch. Rice protein had the lowest digestibility.
Protein barrier effect
When pepsin was left out, slowly digestible starch went up, showing that intact protein acts as a physical barrier that keeps amylase from reaching starch.
Enzyme inhibition
Soy and whey proteins inhibited amyloglucosidase, but rice protein did not. After breaking the proteins down with pepsin, all three inhibited the enzyme more strongly.
Protein-starch bonds
Rice and soy proteins interacted with starch mainly through hydrogen bonds and hydrophobic interactions. Whey protein also showed electrostatic interactions.
Swelling and amylose
All three proteins reduced the swelling power of the extrudates and lowered the amount of amylose that leaked out. Rice protein had the lowest swelling at every temperature.
Structure changes
Extrusion destroyed the crystalline structure of rice starch and formed a V-type structure. Adding proteins increased the relative crystallinity and short-range ordered structure.
What the authors conclude
- They conclude that adding rice protein, soy protein isolate or whey protein concentrate during extrusion reduces the digestibility of rice starch.
- They say the reduction is mainly due to the barrier effect of proteins and non-covalent bonding between proteins and starch.
- They suggest this lays a foundation for using exogenous proteins to make low glycemic index staple foods by extrusion.
How it was done
The authors wanted to understand how different proteins affect starch digestibility during extrusion, since slow-digesting starches may help control blood sugar.
They mixed rice starch with 10% rice protein, soy protein isolate or whey protein concentrate, extruded the mixtures, and measured starch digestibility, enzyme activity, structure and pasting properties in the lab.
What it can’t tell you
- These are lab tests, not studies in people. They cannot show what happens to blood sugar in someone who eats these extruded products.
- The digestion was simulated in test tubes, so the results may not match real digestion in the human gut.
Who paid
- Funding
- Funded by Special Support for Post-doc Creative Funding in Shandong Province; Jiangsu Agricultural Science and Technology Innovation Fund; Science & Technology Pillar Program of Jiangsu Province; Jiangsu Key Laboratory of Advanced Food Manufacturing Equipment & Technology (from the PubMed record).
- Authors work at
- Jiangnan University, China; The Affiliated Wuxi Children's Hospital of Nanjing Medical University, China
The paper
- Title
- Effects of rice protein, soy isolate protein, and whey concentrate protein on the digestibility and physicochemical properties of extruded rice starch
- Type
- Study
- Evidence
- Animals and lab studies
- Summarised from
- Full text
- Cite
- Bao H, Liu Q, Yang Y, et al (2023). Effects of rice protein, soy isolate protein, and whey concentrate protein on the digestibility and physicochemical properties of extruded rice starch. Journal of food science. doi:10.1111/1750-3841.16458Free full textPubMed 36704898DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error