Evaluation of microbial transglutaminase and ribose cross-linked soy protein isolate-based microcapsules containing fish oil

Soy protein isolate (SPI)-based microcapsules containing fish oil were prepared using a modified coacervation method followed by cross-linking treatments. The procedure yielded 95-98% microcapsules containing 0.5-0.6 g fish oil/g capsule with a volume mean diameter ranged from similar to 260 to similar to 280 mu m. Four types of microcapsules produced were SPI with sucrose (MC-C/S), SPI with ribose (MC-C/R), SPI with sucrose and microbial transglutaminase (MC-MTG/S) and SPI with ribose and MTGase (MC-MTG/R). Protein cross-linking due to epsilon-(gamma-glutamyl)lysine bonds and "Maillard cross-linking" were evidenced in the SDS-PAGE profiles of MC-C/R, MC-MTG/S and MC-MTG/R. Even though the microcapsules prepared with cross-linking treatments had significantly (P < 0.05) lower protein solubility as compared to that of the control, the results of fish oil release in pepsin solution at 37 degrees C indicated that the core release of all microcapsules prepared with ribose (MC-C/R and MC-MTG/R) was significantly (P < 0.05) lower than other microcapsules. During storage, microcapsules prepared with ribose had longer shelf life as compared to other microcapsules. This may be due to the release of antioxidative Maillard reaction products during heating and storage and a slower rate of gas permeability through the capsules. industrial relevance: The use of protein-based wall materials in the food industry for sensitive ingredients is limited because proteins are generally unstable with heating and damaged by organic solvents and the cross-linking agent is usually harmful. Therefore a novel method of combining two familiar cross-linking agents such as the microbial transglutaminase and ribose can convert SPI microcapsules into a stable form. The application of SPI in industry would be increased. (c) 2008 Elsevier Ltd. All rights reserved.