Modification in physical properties of rice gel by microbial transglutaminase

• Main Authors: Chih-Fang Lin, 林志芳
• Other Authors: James Swi-Bea Wu
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/69133552267184197707

博士 === 國立臺灣大學 === 食品科技研究所 === 97 === Microbial transglutaminase (MTGase) may catalyze the cross-linking between a peptide-bound glutaminyl residue and an ε-amino group of lysine residue in protein. MTGase has been used to modify food protein for improving their functionality. Not pure MTGase could be supplied, so making it by myself. The commercial microbial transglutaminase was obtained from Ajinomoto Co.（Japan）. Added to water and followed by centrifugation. The supernatant was filtered to obtain the crude enzyme solution. The solution was precipitated with ammonium sulfate. In the obtained precipitates, 50~80% showed the better enzyme activity. Then the supernatant was purified by gel filtration through a CM- Sepharose CL-6B column and a Blue Sepharose Fast Flow column. Used SDS-PAGE profile could prove to get pure MTGase. Rice flour was treated with different concentrations of MTGase. The rheological properties, elastic (G'') and viscous (G") moduli of the rice gel increased at the addition of MTGase. However, high amount of the addition of MTGase at 0.3U/mg may reduce textural parameters. Therefore, rheological properties and textural parameters might be affected by the existing threshold number of connections for cross-links in rice protein. Differential scanning calorimetry (DSC) showed that MTGase treatment led to decrease the denaturation enthalpy. Sodium dodecyl sulfate- polyacrylamide gel electrophoresis (SDS-PAGE) confirmed that rice proteins were polymerized through the MTGase reaction. Scanning electron microscope (SEM) figure showed the more concentrations of MTGase added to rice flour, the better texture of rice flour gel. Therefore, those SEM photographs proved the added MTGase improved the rheological properties and textural parameters (hardness, and gumminess). Here another method was used to investigate the effects of MTGase to properties of rice protein. Rice protein was treated with different solvents and there were four kinds of extractions were obtained: water soluble (albumin), salt soluble (globulin), alkali soluble (glutelin) and alcohol soluble (prolamin) fractions. The amount obtained were in the order of alkali soluble protein＞salt soluble protein＞water soluble protein＞alcohol soluble protein. After SDS-PAGE analysis, alcohol soluble protein only one subunit. From Rheology test, water soluble protein (albumin) was proved has no contribution in strength of rice gel. Therefore it is suggested to remove it at the rice processing. Rice protein contain much cysteine, and affects the properties of the products. The rice contains much glutelin, from SDS-PAGE profile, the effects of MTGase addition to the linkages were observed.