Font Size: a A A

Study On Controlled-enzymatic Hydrolysis Of Tuna(Katsuwonus Prlamis) Dark Muscle By-product And The Optimization Of Decolourization Of Hydrolysate

Posted on:2015-03-28Degree:MasterType:Thesis
Country:ChinaCandidate:B WangFull Text:PDF
GTID:2381330491959807Subject:Food Science
Abstract/Summary:PDF Full Text Request
Tuna dark muscle is a by-product of tuna and rich in protein.However,with the characteristics of deep color,easy oxidizing and perishable,tuna dark muscle is mostly used as fishmeal for animal feeding.Recently,some scholars have focused on the study of protein hydrolysis.The obtained polypeptides not only easily digested and absorbed,but also have many effectively functions like antioxidant,antiallergic,enhancing immune function,reducing blood pressure and cholesterol.Therefore,it is of great value to make researches on protein enzymatic hydrolysis and hydrolysates.This research was based on the present situation of tuna dark muscle and studied the controlled-enzymatic hydrolysis and the decolorizing technology of hydrolysates.These would open new possibilities in dark muscle application.The results were as follows.(1)Tuna dark muscle was high in protein(25.66%),low in fat(1.91%)and contained balanced portions of amino acids.In tuna dark muscle,the content of the essential amino acids was as high as 38.12%and the contents of metallic element like Ca,Mg,Fe,Zn were abundant.At the same time,heavy metal content complied with the standard of the state.(2)Through single-factor experiments,the determined optimum condition of trypsin was enzyme-to-substrate ratio 2000-2500U/g,hydrolysis time 4-6h,initial pH 7.5-8.5,temperature 45-55?,the optimum condition of flavourzyme was enzyme-to-substrate ratio 1000-1500U/g,initial pH 6.5-7.5,temperature 45-55 C.Trypsin contributed more to the recovery rate of nitrogen(RE)and flavourzyme contributed more to the degree of hydrolysis(DH).The molecular weight distribution was mainly in 0.5-3kDa when using trypsin and was below 0.5 kDa when using flavourzyme.(3)Through orthogonal test,the factors influencing the degree of hydrolysis(DH)and the optimal hydrolysis condition were investigated.The results showed that the priority impact of the four factors to DH was enzymolysis time>enzyme-to-substrate ratio>pH value>enzymolysis temperature.The highest degree of hydrolysis was obtained at following conditions:enzyme-to-substrate ratio 2400 U/g,temperature 55 ?,pH 8.0,and hydrolysis time 6 h.Under these conditions,the DH and RE of hydrolysate was 19.89±0.10%and 64.88±0.72%,respectively.(4)Amino nitrogen content(AN%)in hydrolysate increased with time,soluble nitrogen content(SN%)was stable after a certain period of time(4-6h),the nitrogen in the peptides(PN%)increased firstly,and then decreased.These illustrated that during a 12 hours' hydrolysis processing,the first half focused on the soluble of protein and then focused on the production of amino acids and peptides.As for the molecular weight distribution,the main distribution was in 1-3kDa after 1 hour and in 0.5-1kDa after 6 hours' hydrolysis.The hydrolysate was below 0.5kDa when hydrolyzing for 12 hours.According to the results of amino acid composition of hydrolysates,the ratio of bitter tasting amino acids decreased with time,which improved the flavor of hydrolysate;the ratio of hydrophobic amino acids increased with time.The antioxidant activity of hydrolysate was a little bit higher in 4-6h,which may be due to the peptides of molecular weight 0.5-1 kDa and composed of Glu,Asp,Cys,Ile,Ser,Pro.(5)According to the restrictive protease hydrolysis characteristics,kinetic model during the hydrolysis was setted up,which was DH=2.967 × In 1+(1104.4 ×E0/S0-3.9098)× 0.337 × t.At the same time,the relationship between the average molecular weight(Mw)and DH was Mw=541906 × DH-2.141.The experimental data of DH was well consistent with the theoretical prediction,which concluded that the model we setted up was of application value.We achieved the purpose of controlled-enzymatic hydrolysis preliminarily using this model.(6)The influence of activated carbon addition content,pH,temperature and time on the decoloration rate and protein loss rate were studied with single-factor experiments and orthogonal methodology.The results showed that the priority impact of the four factors to decoloration rate was activated carbon addition content>pH value>decoloration time>temperature.The optimal decoloration conditions were as follows:activated carbon addition content 3%,pH 3.0,temperature 70? and time 1 hour.Under these conditions,the decoloration rate and protein loss rate of the hydrolysate reached 89.77±0.77%and 13.47±0.72%,respectively.At the same time,the changes of fishy odour and metallic elements contents before and after activated carbon treatment were detected.The content of volatile compounds was reduced by 85.39%,and there was a considerable reduction in fishy odour content like trimethylamine,hexaldehyde and nonaldehyde et al.In addition,actived carbon had a high adsorption rate to Pb(93.2%)but not to other metallic elements.
Keywords/Search Tags:skipjack tuna(Katsuwonus pelamis) dark muscle by-product, trypsin, controlled-enzymatic hydrolysis, decolorization, activated carbon, orthogonal test
PDF Full Text Request
Related items