Saroat Rawdkuen

Chicken plasma protein affects gelation of surimi from bigeye snapper (Priacanthus tayenus)

Effect of chicken plasma protein (CPP) at different concentrations on gel properties of grade SA and A bigeye snapper surimi was investigated. Addition of 0.5% CPP in combination with setting at 40 °C for 30 min prior to heating at 90 °C for 20 min resulted in the highest breaking force and deformation (P<0.05). However, whiteness decreased to some extent. CPP was able to prevent the degradation of surimi proteins as indicated by the decrease in TCA-soluble peptides (P<0.05). Electrophoretic studies revealed that myosin heavy chain underwent polymerization to a lower extent as CPP concentration increased. Therefore, CPP worked as protease inhibitor rather than protein cross-linker. Microstructure of kamaboko gels, added with 0.5% CPP, had less linkage between protein strands with a coarser fibrillar structure, indicating the interfering effect of CPP on cross-linking of myofibrillar proteins. Thus, at an appropriate amount, CPP possibly worked as a filler in the surimi gel matrix, resulting in gel strengthening.

Trypsin Inhibitor from 3 Legume Seeds: Fractionation and Proteolytic Inhibition Study

The trypsin inhibitor from navy beans (Phaseoulus vulgaris), red kidney beans (Phaseoulus vulgaris L.), and adzuki beans (Vigna angularis) provided by the Royal Project Foundation in Thailand was isolated by heat and ammonium sulfate (AS) precipitation. Incubation at 70 degrees C for 10 min produced the highest trypsin inhibitor recovery for all legumes. The AS precipitation with 60% to 80% saturation (precipitate IV) resulted in 41-, 88-, and 34-fold of the purity and (-)26%, 126%, and (-)47% of percentage of activity increase for navy beans, red kidney beans, and adzuki beans, respectively. The trypsin inhibitors had a molecular weight of 132 kDa for navy beans, 118 kDa for red kidney beans, and 13 kDa for adzuki beans under nonreducing conditions. The obtained precipitate IV fraction from each legume effectively prevented the degradation of the tilapia muscle with concentration dependent. The myosin heavy chain increased as the concentration of the inhibitor fraction increased, especially at the highest level of addition. The result indicated that the precipitate IV from these legumes have potential for use as a protease inhibitor in fishery related products.

Discoloration and Lipid Deterioration of Farmed Giant Catfish (Pangasianodon gigas) Muscle during Refrigerated Storage

Discoloration and lipid deterioration of farmed giant catfish (Pangasianodon gigas) muscle during 14 d refrigerated storage were investigated. Lipid deterioration, lipolysis, and lipid oxidation in both dorsal and ventral muscles increased as storage time increased. A progressive formation of primary lipid oxidation products monitored by the increase in conjugated dienes (CD) was observed (P < 0.05) and the increase in thiobarbituric reactive substances (TBARS), an index of secondary lipid oxidation products, was noticeable throughout the storage (P < 0.05). The pH of both dorsal and ventral muscles tended to increase as storage time continued (P < 0.05). A gradual increase in free fatty acid (FFA) formation was found within the first 10 d of refrigerated storage (P < 0.05), suggesting hydrolysis induced by lipases and phospholipases. However, a sharp decrease in FFA content was observed at the end of storage. Refrigerated storage also resulted in changes in redness index of both dorsal and ventral muscles. These changes were coincidental with the changes in metmyoglobin content. Therefore, the discoloration and lipid changes in giant catfish muscle during refrigerated storage depended on the muscle type and might be related to the difference in composition between dorsal and ventral muscles.