Study On Preparation Of Tilapia Muscle Hydrolysate And Its Antioxidant Activity

Tilapia, whose meat is highly nutritive, is one of the most vastly cultivated aquaticproducts in China, while the output of it in China has been the largest all over the worldthese years. Its processed products were mainly the frozen fish and tilapia fillet. It’s quitemeaningful to find a new way of utilization for promoting the cultivation and processing oftilapia. In this paper, as tilapia muscle the crude material, the separation effect of TCAprecipitation and ultrafiltration to hydrolysates were compared, and the hydrolysiscondition of tilapia muscle was optimized, and the nutritional evaluation, antioxidantactivity in vitro, antioxidant activity stability and functional properties of tilapia musclehydrolysate was studied in some extent. The main results were as follows:1. Various peptides of different molecular weight contained in1h,2h, and5h hydroltsatesof tilapia muscle by Alcalase2.4L were precipitated to varying degrees by1%,3%,5%,7%, and10%TCA, while47.86%⁵9.28%of the＞9.5kDa component,38.41%⁶5.49%of the2.5kDa¹.4kDa, and21.32%⁷8.89%of the about1.0kDa component was removed.The precipitating percentage mostly decreased with the increase of TCA concentrationwhiles it higher than5%. The content of component with the molecular weight lower thanactual MWCO increased in some different extent in ultrafiltrate after ultrafiltration ofMWCO5.0kDa compare to hydrolysate. In comparison to TCA precipitation, the MWCO5.0kDa ultrafiltration was better for removing the proteins in hydrolysate.2. As the peptide content the primary index, neutral protease was more suitable forpreparating peptide from tilapia muscle protein than pepsin, trpsin, alcalase2.4L andpapain. The optimum hydrolysis condition of neutral protease to tilapia muscle protein wasenzyme quantity1.38%, solid-liquid ratio1:3（g/mL）, temperature50℃, the inherent pHand the time7h.3. The nitrogen content of hydrolysate under optimum hydrolysis condition was0.60%±0.019%, while the nitrogen recovery ratio73.72%±0.237%. The nitrogen contentand nitrogen recovery ratio of ultrafiltrate was0.41%±0.014%and40.90%±0.136%afterMWCO5.0kDa ultrafiltration of hudrolysate respectively.The content of＜3.0kDa component in hydrolysate was59.15%, while the＜1.0kDa onewas19.79%. The counterparts in ultrafiltrate were5.53%and9.72%higher respectively.Hydrolysate and ultrafiltrate contained almost all the amino acid species. The content ofessential amino-acid was high, while it was41.05%in hydrolysate and62.10%in ultrafiltrate. The AAS of hydrolysate and ultrafiltrate was100points and6pointsrespectively. The FLAA and SLAA were Thr and Val in ultrafiltrate respectively.The hydrolysate and ultrafiltrate possessed reducing capacity in some extent, while thelatter was better and they all worse than GSH, the positive control. The IC50of scavengingOH, O^-₂· and DPPH· of hydrolysate and ultrafiltrate was12.47mg/mL,5.37mg/mL;16.23mg/mL,13.58mg/mL and3.28mg/mL,2.97mg/mL respectively, and the scavengingcapacity of them were all worse than that of GSH, the positive control. The antioxidantcapacity of hydrolysate and ultrafiltrate increased with the rise of its mass concentration inlinoleic acid system while the former increased slowly and the latter quickly. Theantioxidant capacity of ultrafiltrate was better than that of hydrolysate in linoleic acidsystem. The antioxidant capacity of10.00mg/ml ultrafiltrate was close to that of0.20mg/ml BHT solution with the inhibition rate being45.52%and45.58%respectively.4. In the range of assay, the O^-₂· inhibition rate of5.00mg/ml and10.00mg/ml tilapiamuscle hydrolysate solutions slightly decreased with the increase of sucrose mass fraction.The higher the concentration of hydrolysate, the weaker the effect of sucrose to itsO^-₂· inhibition activity in tilapia muscle hydrolysate solution. Citric acid has synergeticeffect on O^-₂· inhibition activity of tilapia fresh meat peptide. We found that citric acidaqueous solution exerted high O^-₂· scavenging activity.The O^-₂· inhibition activity of tilapia muscle hydrolysate was weakened by different heattreatment used in experiment, and the higher the hydrolysate concentration, the more theheat treatment stability of it. The stability of tilapia muscle hydrolysate in acidiccircumstances was good while bad in alkaline ones.The solubility of tilapia muscle hydrolysate were all higher than95%in the pH range of2.00¹2.00. The emulsibility and emulsion stability of tilapia muscle hydrolysate allincreased with the rise of pH value, while they were21.90m²/g±1.634m²/g and33.28min±3.264min at pH12.00respectively. The water absorbing ability of tilapia musclehydrolysate,1.22g water/g±0.019g water/g, was worse but the oil absorbing,3.44mL/g±0.509mL/g, was better.