Effect of limited enzymatic hydrolysis on structure and emulsifying properties of rice glutelin

Abstract

27The influence of the degree of hydrolysis (DH) on the structure, solubility, 28 rheology, and emulsifying properties of rice glutelin was investigated. Structural 29 properties were characterized using analysis of molecular weight distribution, surface 30 hydrophobicity, intrinsic fluorescence, and Circular Dichroism (CD) spectra. Protein 31 hydrolysis changed molecular weight, increased flexibility, altered surface 32 hydrophobicity, and increased solubility. Oil-in-water emulsions were prepared from 33 rice glutelin with different DH (0.5%, 2%, and 6%) and their stability to storage, pH, 34 salt, and thermal processing was assessed. The storage, pH, salt, and temperature 35 stability of the emulsions increased with decreasing hydrolysis. Emulsions prepared 36 with 2% DH rice glutelin were stable over a range of environmental conditions: pH 7-9; 37 NaCl < 100mM (pH 7); temperatures < 90 ºC (pH 7, 0 mM NaCl) studied. These results 38 will facilitate the formulation and production of natural emulsion-based products using 39 rice glutelin as an emulsifier. 40 41 Keywords: rice glutelin; enzymatic hydrolysis; emulsion; stability; 42 43 44 45 46 47 48

Effect of enzyme types on the stability of oil‐in‐water emulsions formed with rice protein hydrolysates

“…31 In addition, during the analysis of the secondary structure, -sheets as protein structure ("trains") are relatively stable, whereas the -helix, -turn and random coils are relatively flexible and open. 16 In Table 1, enzymatic hydrolysis decreased the -sheet regions and increased the -helix, -turn and random coil regions, indicating that the secondary structure in the protein attains a more flexible and extended form after enzyme treatment. 32 These changes in surface hydrophobicity and secondary structure in the protein showed that the protein hydrolysates had more flexible structures than the native protein.…”

“…Nevertheless, the surface hydrophobicity index began to decrease with a higher DH, which might be a result of the decrease in peptide size in hydrolysates affecting the affinity of the ANS probe toward the protein . In addition, during the analysis of the secondary structure, β ‐sheets as protein structure (“trains”) are relatively stable, whereas the α ‐helix, β ‐turn and random coils are relatively flexible and open . In Table , enzymatic hydrolysis decreased the β ‐sheet regions and increased the α ‐helix, β ‐turn and random coil regions, indicating that the secondary structure in the protein attains a more flexible and extended form after enzyme treatment .…”

“…However, the thermal treatments obviously increased the size of neutrase hydrolysates, and droplet aggregation might be the result of a reduction in the electrostatic repulsion or a change in structures (e.g. non‐polar or sulfhydryl groups) …”

“…Tween 20 combined with rice protein hydrolysates systems can improve the storage stability and inhibit the lipid oxidation of a oil-in-water emulsion for long storage. 15 Furthermore, Xu et al 16 investigated the effect of limited trypsin hydrolysis on rice glutelin and found that rice glutelin hydrolysates at a degree of hydrolysis (DH) of 2% were most resistant to salt addition and thermal processing. Nevertheless, enzymes with specific cut sites led to a change in the exposed hydrophobic area in the protein, affecting their functional properties, especially the emulsifying property.…”

Gelation kinetics and characterization of enzymatically enhanced fish scale gelatin–pectin coacervate

“…Fluorescence measurements were performed using a fluorescence spectrophotometer (F‐7000, Hitachi, Japan) according to the method of Xu et al . A quartz cell with 1 cm path length was used for intrinsic fluorescence measurements.…”