| Tuna is an important world economic fish.A lot of by-products,such as skin and bone,were produced during processing,which were usually discarded as waste,leading to significant loss of economic benefits.Fish bone is rich in calcium and phosphorus,which can improve the bioavailability of calcium after ultrafine pulverization.Bone bones and fish skins have abundant protein content.Collagen,gelatin,collagen peptides and polypeptide-calcium chelating complex could be produced by using fish bones and fish skins as raw materials.How to make use of these by-products is a hot issue in current research.In this study,ultra-fine fish bone powder was prepared by microwave-assisted method using fish bone,a by-product of tuna processing,as raw material,and the effects of different microwave conditions on fish bone powder were discussed,the microwave conditions were optimized by response surface analysis(RSM).Secondly,gelatin was extracted from tuna bone and fish skin by hydrothermal method.The effect temperature on gelatin yield and hydroxyproline content were compared.Moreover,antioxidant activity of peptide was analyzed.Finally,the effect of chelating conditions on the calcium binding ability of collagen peptides was studied by chelating collagen peptides with calcium chloride,from which the suitable chelating process was determined,and the peptide calcium chelate of tuna collagen polypeptide was prepared.The results can provide theoretical basis and technical reference for the utilization of tuna skin and bone.The main results are described as follows.In this experiment,the by-product of tuna processing,fish bone,was used as raw material,and the microwave-assisted method was used to study the preparation of tuna bone calcium powder.The microwave condition was optimized by Box-Behnken test design combined with response surface analysis method.The optimum parameter settings are as follows: sample quality 120 g,microwave powder 800 W,microwave time 90 min.The fish bone powder was enzymatically hydrolyzed and the contents of calcium and phosphorus were determined to be 192.3 mg/g and 149.8 mg/g,respectively.After scanning electron microscope(SEM)characterization and laser particle size analysis,the microwave fish bonepowder has a loose structure,micropores and cracks appear on the surface,and the average particle size can reach 16.6 ?m,which was close to the predicted value of the response surface.The bioavailability of fish bone meal was evaluated by zoological experiments.The results showed that the microwave fish bone powder group had a calcium absorption rate of59.62% and a calcium storage rate of 58.31%,which were higher than the common fish bone powder group and calcium carbonate group and low calcium control group(p < 0.05).Compared with other calcium preparations,microwave fish bone meal has higher absorption efficiency in vivo and is more conducive to promoting bone growth in rats.The gelatin and collagen peptides were prepared from tuna skin and fish bone.The effect temperature on the gelatin yield and hydroxyproline content was investigated.It was found that the highest yield of gelatin and hydroxyproline could be achieved at 100 °C,under which the yield of tuna skin gelatin was 70.22% with hydroxyproline 8.31% and the yield of bone gelatin was 28% with hydroxyproline 6.48%.There were four types of collagen peptides prepared by enzymatic hydrolysis of gelatin with alkaline protease and trypsin.The collagen polypeptide was analyzed by infrared.The infrared results showed the characteristics of the polypeptide.Determination of the peptide distribution of collagen polypeptides revealed that the content of oligopeptides was up to 87.67%.The results of SDS-PAGE indicated that the molecular weight of hydrothermally treated fish bone gelatin and fish skin gelatin protein was mainly concentrated below 20 kDa.Analysis of the antioxidant activity of collagen polypeptides revealed that the antioxidant properties of collagen polypeptides after enzymatic hydrolysis were improved.The scavenging effect of fish bone collagen peptides on hydroxyl radical(OH-),DPPH and hydrogen peroxide was higher than that of fish skin collagen peptides.The antioxidant capacity of fish bone collagen peptides was consistent with the content of oligopeptides.The preparation of peptide-calcium chelating complex on the basis of collagen peptides of tuna skin and bone was studied.The effect of chelating temperature,time,pH,and peptide calcium volume ratio on the calcium-binding ability of four types of collagen polypeptides hydrolysate was analyzed.The parameters were optimized to be chelation temperature 50 °C,time 60 min,pH 8,and a peptide calcium volume ratio of 1:2,under which the highest calcium binding capacity was determined to be 56.70%.Fourier transform infraredspectroscopy results showed that the amino terminus and the carboxyl terminus of the tuna collagen polypeptide were involved in chelation reaction.This study provides technical reference and theoretical support for the development of collagen polypeptide chelated calcium,a new calcium supplement preparation and the high value utilization of aquatic processing by-products. |
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