Abstract: Proteins isolated from the adductor muscle of of Chlamys farreri and common carp muscle (Cyprinus carpio) were glycosylated to improve their properties and the underlying mechanism was elucidated. A comparison of muscle proteins between marine invertebrates and vertebrates was carried out. The protein isolates were prepared in alkaline solution and then subjected to direct and indirect glycosylation. Direct glycosylation took place under drying conditions, while in indirect glycosylation the protein isolates were pretreated with?chymotrypsin before being reacted with glucose. Both glycosylation reactions were performed under identical conditions: protein-to-sugar ratio of 1:5 (m/m), 60 ℃, 65% relative humidity and 6 h. The glycosylation efficiency was evaluated by lysine reduction, fructosamine concentration, absorbance at a 420 nm (A420 nm) and SDS-PAGE analysis. Moreover, emulsifying properties and thermal stability of glycosylated products were determined. For both protein isolates glycosylation occurred after 6 h reaction, leading to a 59.89% and 30.94% reduction in lysine, fructosamine concentration of 3.04 and 2.99 mmol/L and A420 nm values of 0.000 and 0.084, respectively. Additionally, the electrophoretic bands of myosin heavy chain and actin were shifted upwards after glycosylation. The emulsifying activity index of the glycosylated proteins was 14.08 and 16.44 m2/g, respectively. Their thermal stability was improved, which decreased by 14% and 28% compared to 26% and 50% for the control counterparts, respectively. Chymotrypsin pretreatment could apparently increase the glycosylation efficiency of the protein isolate from scallop muscle. After glycosylation, the untreated and treated protein isolates showed a 30.94% and 67.64% reduction in lysine, a fructosamine concentration of 2.99 and 5.72 mmol/L, an upward shift of all protein bands, a 33.11% and 37.38% increase in emulsifying activity index and a 28% and 3% decrease in thermal stability, respectively. These results demonstrated that protein isolates from fish and scallop muscles had similar glycosylation characteristics. Chymotrypsin pretreatment evidently increased the glycosylation.

Key words: fish protein isolate, glycosylation, chymotrypsin, functional properties