This project is seeking a better understanding of the physical properties of rice starch and rice protein, as well as mechanisms for successfully extracting those fractions from rice in order to produce high-value products. Rice protein is of special interest in this work for its potential heart-healthy benefits.

Working at both UC Davis and at the USDA laboratory in Albany, researchers analyzed different enzymes for their ability to isolate and extract rice protein and peptides from starch in M-202 rice. A commercial enzyme, Alcalase, was identified as the best choice for protein removal from milled rice.

 

The Potential for Lower Cholesterol by Peptides
	cholesterol lower effect (%)
Rice peptide from Alcalase treatment	82.6
Rice peptide from Protex 6L treatment	85.0
Soy peptide from Alcalase treatment	76.3
Dietary proteins have influenced serum cholesterol level in many studies using soy and milk peptides. Experiments conducted by food scientists with peptides derived from rice are encouraging. Results show very good potential for a cholesterol-lowering effect of rice peptides compared to soy peptides.

The pasting properties of rice starch prepared with Alcalase were found similar to those of rice flour, suggesting that enzymatic removal of protein from rice flour does not affect the properties of rice starch. Pasting properties of rice flours and starches describe the nature of the cooked, swollen form of the starch. The temperature at which it swells, the degree of swelling, its stability, and the thickening power of cooked starch are all part of the pasting properties. This is an important consideration for commercial markets if the starch is to be sold as a byproduct after protein isolation. This form of starch may be more acceptable to the food industry because of its lower protein content.

 

Microscopic examination of rice flours with scanning electrode microscopy shows starch granules prepared with Alcalase (top left) to be least affected by the separation process.

Researchers also compared these results with two chemical processes of protein removal from flour. Protein removal by detergent, strong alkali solution or Alcalase was similar. Upon examination with an electron microscope, they concluded that the enzymatic process leaves the starch granules more intact. Rice starch powder prepared through the enzymatic process is also finer and less coarse than other starch powders.

The enzymatic preparation results in a protein byproduct that has potential marketability as a healthy food ingredient. This byproduct, a peptide, showed the potential for lowering blood pressure and cholesterol levels, similar to soy peptides that have been extensively studied. Blood pressure can be lowered when an enzyme called “angiotensin converting enzyme” (ACE) is inhibited. The results of this research showed that peptides from hydrolyzed rice proteins can inhibit ACE and also produces a superior starch byproduct.