Enzymatic Hydrolysis Of Tilapia And Deodorization Of Hydrolysates

Tilapia is a large breed fish in china, which is known as the fifth everybody fish and has a wide prospect for development and utilization. In this paper, hydrolysates of tilapia protein were prepared by enzymatic method and their unpleasant odor was removed respectively by adsorption (cation exchange resin and cativated charcoal) and fermentation. Sensory evaluation and Headspace-Solid phase microextraction (HS-SPME) coupled to gas chromatography-mass spectrometry (GC-MS) was used to analyze flavor and volatile compounds in tilapia enzymatic hydrolyzates. The main results were as follows:(1) Freezing pretreatment of tialapia increase the degree of hydrolysis (DH). The optimal hydrolysis technology was obtained:One part of tilapia protein was mixed with three parts of water (w/w), the mixture was added with 3000U/g of Alcalase(?) 2.4L FG (on basis of tilapia protein) with pH value adjusted to 8.0, and reactied at 60.0℃for 3.Oh. A highest DH value 18.23% was obtained under this condition. After debittering by Flavourzyme, hydrolyzates showed slight bitterness but strong fishy odor.(2) A PDMS/DVB coating fiber extractor, which contained 30%(w/v) of sodium chloride, was to extract the volatile compounds from tilapia enzymatic hydrolyzates (kept at 60℃for 40min under strring). The GC-MS detection showed that 69 kinds of volatile compounds were identified and the predominant flavor compounds were C6-C9 volatile carbonyl compounds, alcohols and nitrogenous, which molecular weights distribution were at a range of 80～200. All of those compounds showed synergistic effect on formation special flavor in tilapia enzymatic hydrolyzates.The predominant fishiness compounds were preliminary identified:Trimethylamine, (E,E)-2,4-Heptadienal, (E,E)-2,4-Decadienal, 1-Octen-3-ol, 1-penten-3-ol,2,5-Octanedione, (E,Z)-2,6-Nonadienal, (E,E)-2,4-Octadienal, (E)-2-Octenal, (E)-2-nonenal, (Z)-4-Heptenal.(3) The effect of deodorization by resin, active carbon and microorganisms fermentation was compared. It was evident that fermentation technology was the best option for deodorization of tialapia protein enzymatic hydrolyzates and basically without loss of protein. The optimal conditions for deodorization by fermentation were:0.87×109cfu/mL active dry yeast was inoculated and fermented for 1.5h, followed by inoculation of 5.6×107cfu/mL P.pertosaceus and continued fermentation for another 10.Oh, which was called fermentation with mixture microorganisms in this research. A clarified product with no fishiness, no bitterness was obtained after fermentation, and the protein recovery was 96.6% under the optimized conditions. The sensory quality of hydrolysates was improved obviously.