Studies On Technology Of Drying Process For Tuna Skin

The meat of yellowfin tuna is nutritious,tender,delicate taste,and raw fish is always popular with consumers.However,it would produce a lot of by-product in the tuna process,such as the head,fish bones,skin,viscera,etc.,which accounting for about 50%of the total weight.Fish skin is rich of collagen and has high-value use.Because of the high fat content of yellowfin tuna,it is prone to lipid oxidation and yellowing during the drying process and storage.Therefore,the aimes of this thesis were to control the lipid oxidation and browing and maintain the stability of dried fish skin during storage,and provide raw materials or finished products for the process of water-swollen skin,snack food and pet food and so on by studying the technologies of enzymatic descaling,heat pump drying,oxidation control of the fish skin.The results of the study are shown as follows:(1)The basic components,collagen content,amino acid composition and volatile flavor compounds yellowfin tuna fish skin were analyzed.The results showed that yellowfin tuna skin was rich of crude protein,accounting for 32.29%of the skin total weight,and the collagen content was up to 30.08%of the skin total weight,skin total amino acid content is 271.46 mg/g,essential amino acid and half essential amino acid content were up to 36.51%;skin fat content was up to 10.45%of the skin total weight;skin contains 41 kinds of volatile compounds,mainly for alcohols,aldehydes and heterocyclic compounds,the most abundant trans-2-methyl-cyclopentanol,accounting for 16.24%of the total flavor compounds,olefine aldehyde accounted for the vast majority of aldehydes,it could give skin a special flavor.(2)The effect of neutral protease dosage,enzymolysis time,enzymolysis temperature and the solid-liquid ratio on skin collagen loss rate and descaling rate which contained the descaling degree,degree of surface color loss and thining degree was studied by sing single factor experiment.The results showed that the neutral protease dosage,enzymolysis time and enzymolysis temperature had a significant effect on the descaling rate,while the solid-liquid ratio had no significant effect,the optimum enzymolysis conditions ranges was 0.3?0.5%enzyme dosage,30?50 min enzymolysis time,45?55 ? enzymolysis temperature.On this basis,via orthogonal experiment was used to optimize the best enzyme descaling conditions,results showed that the priority impact of the three factors to skin enzyme descaling was enzymolysis temperature>enzymolysis time>enzyme dosage,the optimum enzymolysis process conditions was 50 ? enzymolysis temperature,30 min enzymolysis time,0.3%enzyme dosage,the lowest rate of skin collagen loss was 57.09 ?g/g,the descaling degree was greater than 90%,the degree of surface color loss and thining degree were less than 10%.(3)Effects of heat pump drying temperature(40?45?50?55?60 and 65 ?)and terminal moisture content of fish skin(8?10 and 13%)on the characteristics of yellowfin tuna skin were studied,including the rehydration rate,collagen protein,protein stability,fat oxidation,color and texture of the dried fish skin.Results showed that fish skin dried at 55 ? with the terminal moisture content of 10%displayed better color,lower lipid oxidation,higher collagen protein content and better protein stability.(4)The effect of different TBHQ(tert-Butylhydroquinone)concentration(0.02?0.14%)and soaking time(0.5?2.5 h)on the peroxide value,acid value,malondialdehyde content(TBA value),color and sensory evaluation of 65 ? forced oxidation skin were studied.Results showed that the degree of fish skin lipid oxidation significantly influenced by the concentration of TBHQ and immersion time,under the 1.0?2.0 h immersion time,the skin peroxide value,acid value and TBA value presented a trend of first increase than decrease with the increasing of TBHQ concentration(0.02?0.14%)and soaking time,and 0.1%TBHQ concentration and 1h soaking time could effectively inhibit the skin fat oxidative rancidity to minimum during storage,but it would cause red color skin during storage.On this basis,under the shorter immersion time(5-60 min),the influence of 0.1%TBHQ 9 0 alcohol solution and 9 ° alcohol solution(contrast)to skin color,smell and fat oxidation were studied.The results showed that TBHQ was the major cause of red changes of the skin color,shorten soaking time in 5?30 min was beneficial to inhibit skin color changes and control the degree of lipid oxidation.(5)On the base of the above study(4),the combined effect of TBHQ,tea polyphenols and D-sodium erythorbate on the lipid oxidation and color of dried fish skins in 37 ? accelerated storage for 7 d were were studied was studied by using response surface method.The result showed that the optimum condition for inhibiting lipid oxidation and maintain fisk skin color was 0.041%tea polyphenols,0.02%D-sodium erythorbate,0.053%TBHQ,with immersing 13.5min,where the skin color(AEab)and TBA value were the lowest,which were 2.00 and 0.184mgMDA/kg,respectively.