Amino acids impact pasting properties of starch isolated from rice flour.

Proteins can affect starch gelatinization properties. Protein content negatively correlates with water absorption and positively correlates with cooking time. Removing proteins causes the gelatinization temperature of flour to decrease, indicating that rice protein can inhibit the swelling of starch granules.

The influence of individual amino acids on the pasting properties of isolated rice starch has not been extensively studied. The objective of scientists at Louisiana State University and elsewhere was to compare the impact of amino acid structure and the type of amino acid on the pasting properties of rice starch that had been isolated from flour. Their effort enhances the understanding of amino acid-starch interaction in rice flour, which may be the basis of starch modification and new ingredient development.

Researchers tested two acidic, two basic and two neutral amino acids on rice starch that was isolated from white rice flour. They then added amino acids at 2% and 6% of the starch, on a dry basis, for RVA analysis. Duplicate samples were analyzed. Flour was defatted and deproteinated using the alkaline protease digestion process.

Compared with the control, the presence of 6% arginine increased the peak viscosity (PV) by 31 RVU while other amino acids showed no influence on the PV of the rice starch. All amino acids except alanine showed an increase in breakdown, and aspartic acid showed the greatest increase in breakdown by 50 RVU. Aspartic and glutamic acids reduced total setback (TSB), but other amino acids had no influence on the TSB. At 6% concentrations, glutamic acid and arginine reduced the minimum viscosity (MV) of rice starch.

Leucine affected MV and breakdown. Alanine had no influence on pasting properties. Overall, the charged amino acids had more of an influence than neutral amino acids.

This research indicates that individual amino acids can influence the pasting properties of rice flour starch isolate in different ways. Adding individual amino acids may influence the functionality of starch-based products, including such properties as swelling, paste stability and retrogradation.

Further information. Joan King, Department of Food Science, Louisiana State University Agricultural Center, 111 Food Science Building, Louisiana State University, Baton Rouge, LA 70803; phone: [phone]; fax: [phone]; email: [e-mail].