| China is rich in fishery resources, but the processing technology is undeveloped, most of the by-products produced during the processing of the freshwater fish, such as fish scales, fish skin, and fish bone, are discarded as by-products or waste, resulting in environmental pollution and a waste of resources.Fish scales are rich in collagen and calcium, which can be widely used in food industry. Although the nutritional value of these by-products is high, little attempt is being made to fully utilize this valuable freshwater fish resource.The aim of this work was to recover the collagen peptides and calcium from the fish scales efficiently, and evaluate their bioactivity using different models both in vitro and in vivo. The main results were shown as follows:1 Optimum conditions for recovering low molecular weight collagen peptides from grass carp scales and the basic characterization of the collagen peptidesThe best hydrolyzing conditions for recovering collagen peptides from grass carp scales by alcalase were optimized by single factor and orthogonal experiments, using degree of hydrolysis, peptide yield and hydroxyl radical scavenging effects as indicators. The best hydrolysis conditions were as follows:hydrolyzing temperature of 60℃, initial pH value 9.0, alcalase dosage of 3%, substrate concentration 10%(W/V), with a hydrolysis time of 5h, then inactive enzyme in boiling bath. Then hydrolysate was obtained after concentrated and freeze-dried. Under these conditions, the color of peptide was faint yellow, the content of crude protein, ash and moisture was 90.80%,0.89% and 9.97%, respectively, the peptides content was 63.23% measured by Biuret way. HPLC analysis showed that the molecular weight of components of the collagen peptides mainly ranged from 190 Da to 1000 Da (74.2%), indicating that GCSH obtained was mainly composed of low-molecular-weight peptides with two to six amino acid residues. Amino acid composition analysis revealed that the content of Pro, Glu, Gly, Ala, Hyp, Arg, Asp, Ser, Leu and Lys in the hydrolysate was relatively high, with the content of 12.28%,9.5%,20.84%,8.68%, 7.81%,6.88%,5.14%,3.38%,2.68%,3.22%, respectively. Isoelectric point of the peptide was 2.6, and the solubility was greater than 98% at different pH. The hydrolysate had a low viscosity; its viscosity was 0.58 mPaS and 0.87 mPaS at a concentration of 1% and 10%, respectively. In addition, the hydrolysate had good wettability and oil absorption ability.2 Antioxidant activities of the recovered hydrolysate both in vitro and in vivoIn the in vitro antioxidant models, the IC50 value of the hydrolysate on scavenging DPPH radical, hydroxyl radical, and superoxide anion was 5.44±0.25 mg/mL,0.15±0.02 mg/mL, and 78.03±4.31 mg/mL, respectively. It also showed high reducing power. Temperature and Na+ and K+ had no effect on its antioxidant activity in vitro but its antioxidant activity reduced significantly at alkaline pH value or coexisting with Cu2+ or Ca2+. Heating with glucose or sucrose could enhance its antioxidant activity. The antioxidant activity of the recovered hydrolysate could be preserved after treatment with either pepsin or trypsinase or the combining of the two gastrointestinal enzymes in vitro.In the in vivo antioxidant test, oral administered with grass carp scales hydrolysate could significantly reduced serum and liver MDA content of mice, improved the activities of T-AOC, GSH-Px and SOD of mice. In addition, it could significantly increase skin hydroxyproline content, which indicated that the hydrolysate had antioxidant activity both in in vitro and in vivo. Moreover, it exhibited calcium absorption promoting effect on normal mice 3 Recovering calcium from grass carp scales and its calcium supplements effectThe optimized conditions of recovering calcium from scales dregs were as follows: temperature of 60℃, substrate concentration 15%(W/V), and time of 2h, the yield of recovered calcium was 0.78g/g scales dregs, and the calcium element content of the revovered calcium was 19.56%. The animal experiments showed the recovered scales showed similar calcium supplements effect on calcium deficiency mice as calcium carbonate and calcium gluconate. It could improve the content of serum calcium and bone calcium, reduce serum phosphorus content, and reduce the activity of ALP in serum and liver, compared with the calcium deficiency mice.4 Development of chewable tablets rich in peptide and calcium recovered from grass carp scalesThe best formula of the chewable tablets was optimized by single factor and orthogonal experiments as follows:collagen hydrolysate 20%, full cream sweet milk powder 40%, sugar power 25%, starch 8.6%, citric acid 2%, essence 0.4%, grass carp scales calcium 4%, the product obtained under such conditions had a suitable hardness and a smooth and complete appearance, tasted sweet and sour. The product not only had a good nutrition effect but also had calcium supplement effect. |
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