Identification Of Volatile Flavor Compounds From Codfish And Study On Deodorization Methods

Codfish, with high protein and low fat, is of great nutritive value. Researches showed that, in enzymatic hydrolysate, there extensively existing functional peptides which could effectively reduce blood pressure, restrain oxidation, promote clotting, and et al. However, aquatic products generally have unpleasant fishy odors; moreover, as the enzymolysis process is hard to control, the hydrolysate, therefore, generally have unpleasant flavors, which have caused serious problems on its application in functional food processing.This study used codfish as raw material, and explored the optimum enzymolysis conditions to get codfish protein hydrolysate; extracted the volatile compounds from hydrolysate with a combination of sampling methods (simultaneous distillation extraction, SDE, and solid phase micro-extraction, SPME); separated and identified the volatile flavor compounds from the extracts with gas chromatography-mass spectrometry (GC-MS), and confirmed the identification results with Kovats indices (KI); applied macroporous resins and pulsed electric field (PEF) as the main methods for odor-removal, and explored the optimum deodorization conditions and mechanism. Research findings are listed as follows:Firstly, with index of degree of hydrolysis (DH) and peptide content, this study explored the optimum enzymolysis conditions. Results showed that the bacillus subtilis alkaline protease would be the most applicable protease for hydrolysis. The optimum conditions were:substrate concentration as 20%, protease amount as 0.15%, pH as 8.0, temperature as 55℃ and enzymolysis time as 4 h. Under the conditions above, DH could be as high as 19.30% and peptide content could reach 8.58 mg/mL, and these parameters could provide reference for the subsequent enzymolysis process.Secondly, SDE and multiple SPME were jointly applied for volatile compounds extraction, and GC-MS with Kovats indices were used for identification. Results showed that a total of 47 volatile compounds were extracted from codfish hydrolysate, with 39 kinds having specific flavors. These volatile compounds, including aldehydes, alcohols, esters, sulphur compounds, nitrogen compounds, ketones, carboxylic acids and alkanes, contributed to the flavor of codfish hydrolysate. Trimethylamine, bornyl isovaleriate and 3-mercapto-2-pentanone were found to be the main sources of fishy odors of codfish hydrolysate. Compared with previous studies, this study got more kinds of volatiles, indicating that the combination sampling method would fully extract volatiles than a single one. In addition, identification with MS and KJ would be more reliable and accurate than MS alone.Thirdly, three kinds of methods (resin adsorption under static state and dynamic state, and PEF processing) were studied on odor-removal from codfish hydrolysate. Single factor experiment and response surface methodology were carried out to determine the optimum deodorization conditions for each method. Results indicated that AB-8 adsorption resin was the most effective kind for deodorization of codfish hydrolysate; the optimum conditions for AB-8 static adsorption were:temperature as 25℃, resin amount as 13.23%, pH as 8.0, and under this condition, the sensory value and peptide loss ratio would be 2.0 and 17.89%, respectively; the optimum conditions for AB-8 dynamic adsorption were:temperature as 36 ℃, loading quantity as 20 BV, flow rate as 14.5 BV/h, and under this condition, the sensory value and peptide loss ratio would be 2.5 and 14.54%, respectively; the optimum conditions for PEF processing were:electric field intensity as 20 KV/cm, processing time as 200μs, and under this condition, the flavor turned out to be subtlest, and peptide loss ratio would be 15.28%.At last, this paper made comparisons between the volatiles before and after deodorization by the above-mentioned three methods respectively, and preliminarily discussed the mechanism of each method. Conclusions can be made like this:AB-8 sesin adsorption could remove some compounds of relatively high amount (i.e., pentanal,2-pentanol,2,3-pentadione, ethyl 3-methylbutanoate, etc.) and the main sources of fishy odors (i.e., trimethylamine,3-mercapto-pentanone, bornyl isovalerate, etc.). The deodorization mechanism of AB-8 resin adsorption based on its polarity and surface groups. After PEF processing,30 kinds of volatile flavor compounds (i.e., 1-penten-3-ol) were effectively removed or transformed. The deodorization mechanism of PEF lied in the function of electric field, for it prompting the the changes and transformations between organic molecules.