30C-5 |
Protein cross-linking in rice subjected to varying drying and tempering conditions |
S. Tang, N. S. HETTIARACHCHY, and A. Cnossen. Department of Food Science, University of Arkansas, Fayetteville, AR 72704 During drying and tempering of rough rice, high temperature and long heating time can cause rice protein denaturation and cross-linking that can affect milling quality of rice. We have shown that surface hydrophobicity of rice protein can be used as an index on the extent of protein denaturation. It is possible that varying temperature and tempering conditions during drying of rough rice can denature protein and increase polymer formation by cross-linking. However, literature information on protein cross-linking in rice under varying drying and tempering conditions is not available. The objective of this research was to evaluate protein cross-linking via formation of S-S bonds, and available lysine content under varying drying and tempering conditions of rough rice. Rough rice was dried at 25oC, and 19.5% RH as control. Rough rice was treated at 60oC for reduction of 4 or 5% of moisture with or without tempering at 19.5% RH. Protein, moisture, available lysine and disulfide contents were determined by Kjeldahl method, drying in oven, dye-binding and spectrophotometry, respectively. Rice flours of all treatments contained 10.7-11.8% moisture and 8.1-8.2% protein. Drying of 5% at 60oC and tempering for 3 h slightly increased the S-S content from 0.26 to 0.27g/100g protein, and decreased SH content from 0.15 to 0.13g/100g protein in comparison to the control (P>0.05). Available lysine content for all rice samples ranged from 3.1-3.4g/ 100g protein. Although the control had relatively higher available lysine (3.3g/100g protein) in comparison with 5% drying and tempered samples (3.1 g/100g), the available lysine content in control sample was not significantly different from those in any other rice dried with or without tempering at 60oC (P>0.05). These results suggest that rough rice drying at 60 oC with or without 3 h tempering does not significantly contribute to rice protein cross-linking via S-S bonds and available lysine.
Session 30C, Food Chemistry: Proteins
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