Studies On The Process Of Enzymatic Hydrolysis Of Tilapia Frame Proteins And Maillard Reaction

China is the largest tilapia producer and the largest tilapia exporter in the world. The mainlyprocessing products of tilapia are frozen whole fish, fresh or frozen fish fillets. In the processingof fish fillet, byproducts such as fish frames, fish heads, and fish skin, and so on, accounting for60%of the fish weight are produced. Most of the byproducts are discarded except that a smallpart of them are used to produce cheap feed stuff. The comprehensive utilization of theseby-products has become an important and urgent issue to be solved in tilapia processing industry.In this paper, the tilapia frames were hydrolyzed by proteases, and the enzymatic hydrolysisprocess had been optimized. Based on the optimized process, the Maillard enhancing aromareaction techniques and the spray drying process of the final products were studied. The resultsindicated here provide a technical support for processing and exploitation of tilapia byproducts.The main results are as follows:The degree of hydrolysis (DH) was used as the indicator to compare and analyse theenzymolysis effects of single enzyme and composed enzymes, and the surface analysismethodology (RSM) was used to optimize the enzymatic reaction parameters. Results showedthat the enzymatic effects of composed proteases, flavourzyme and papain, were good. The bestconditions for enzymatic hydrolysis were as follows: the total enzyme dosage was3.5%, theratio of flavourzyme and papain was2:1, the original pH value was7.2, and the enzymaticreaction temperature was53℃.The impact of different DH of the enzymatic hydrolyzate on the Maillard reaction wasdetermined through the Friedman test method. The results showed that the product’s flavor is thebest through Maillard reaction when the total time of enzymatic hydrolysis lasted for5hours,The optimum conditions for the Maillard reaction were as follows: the reaction time was57min,reaction temperature was111℃, the pH value was6.0. The dosage of reducing sugar (glucose:xylose=2:1) was2.0%. The addition of Glu, Ala and Arg was2.0%respectively, and theaddition of Gly, NaCl and VB1was1.0%,1.5%, and0.75%, respectively. The content of organicacid in the products after Maillard reaction was higher than before. The tartaric acid, malic acid,acetic acid, and succinic acid were detected. The nucleic acid related compounds such as GMPand Hx were detected, and the GMP (a flavour amino acid) was not found in the enzymatichydrolyzate before the Maillard reaction. The concentration of free amino acids reached15.11mg/mL. The extracts were analyzed by gas chromatograph-mass spectromrtry (GC-MS), and68 volatile compounds were identified.The spray drying process parameters of Maillard reaction products were optimizedaccording to sensory evaluation. The flavor of spray-dried product was the best when the solidcontent was40%, the inlet air temperature was190℃, and the compressed air flow rate was180ml/min. Under the optimized conditions, the spray-dried product was a kind of yellowish powderwith a unique flavor of the fish. The flavor is rich and has a lasting fragrance. The content ofprotein and fat were18.52%and0.82%respectively, and the content of moisture and ash were6.32%and4.11%respectively. The reducing sugar content was12.43%, and the concentration oftotal amino acids was123.20mg/g.