Preparation Of Polypeptide By Fermentation Of Cod Skin And Mechanism For Fishy Favor Removing

Collagen polypeptides are obtained by the enzymatic hydrolysis of collagen usingenzymatic or microbial fermentation. Compared with collagen, collagen peptides’physicaland chemical properties are much better. Cod skin is a kind of scraps from the aquaticproducts processing and has a good content of collagen, which make cod skin becomegood raw materials for the preparation of polypeptides. In this experiment, we chose codskin as raw material to prepare collagen peptide with good physical and chemicalproperties and no fishy flavor by fermentation with the microbial strains saved in thelaboratory.We used different microbial strains and different strain combinations to ferment thecod skin and selected the optimal combination of bacteria and yeast using sensoryevaluation and the degree of hydrolysis as indicators. The results showed thatJFTQ1+JQJM2had the highest degree of hydrolysis of cod skin by42.64%, and sensoryevaluation showed that the fermentation broth was almost no flavor,so we made this straincombination as fermentation strains.Then using the the degree of hydrolysis as the mainindicators,we chose orthogonal experimental method to optimize the three fermentationparameters of inoculum size, adding proportion of the two strains and fermentation time.Experimental results showed that the optimum conditions for fermentation of cod skin:inoculum size was8%, adding proportion of the two strains was1:1(bacteria: yeast)fermentation time was24h.In this condition, the fermentation liquor reached themaximum hydrolysis rate of43.94%, and the fermentation broth was almost no flavor.In this experiment Gas Chromatograph-Mass Spectrometer-computer (GC-MS) wasused to determin cod skin’s flavor components before and after fermentation. Throughsensory evaluation and the analysis of the flavor components,we made a preliminaryinquiry of the mechanism of the removing of fishy smell. Based on the determinationand the analysis, combined with the past related reports, we thought that the mainconstituent of cod skin fishy smell were nonanal, nitrogen-containing compounds (amines),benzene ringbased compounds and heterocyclic compound (thiazole, furan). The resultsshowed that: the disappearance of the nitrogen-containing compounds, the rich of the kinds of ketones, the reduction of the benzene ring compounds and types of changes, theemergence of the senior aldehyde and the disappearance of the nonanal were all good forthe fishy flavor’s elimination. In addition, the heterocyclic substances changing as well asthe detection of several epoxy alcohol may also affected the fishy flavor.Ethanol precipitation method was used to extract the collagen peptides in this paper.The process parameters for extraction collagen peptides were optimized by single factorand orthogonal experiments. The optimum extraction condition was: extraction system pHwas5.0, the ethanol additive amount was70%of the system,concentration offermentation broth was1/5of the original.