Study On The Processing Technology Of Pike Eel Pickling

Cured fish is one of traditional foods with particular flavor , there are broad demands of cured fish in market . In order to satisfy consumption demands of food in safety, nutrition, flavor on modern life, it is necessary to innovate traditional processing technique of cured fish. In this paper, the effect factors, osmotic dehydration phenomena and biochemistry changes of protein of fish muscle during salting were systematically investigated; the techniques of improving flavor ripening and extending the preservation capability of cured fish were tried . The optimization pickling technique was set up.A novel, simple, rapid and reliable turbidity spectrophotometric method to determine sodium chloride in salted fish was developed and validated. The absorbance was measured at 385nm. The method was tested under various conditions: 2mL 1/4 (V/V) nitric acid, 2mL 1.5 g L-1 gelatin, 5mL 0.5% silver nitrate in a total volume of 50mL, mixed and heated at 60℃for 10 min. The accuracy and the results of this method comparing with GB/T12457~90 were not significantly different, this method is feasible to determination salt concentration and has low cost and is not time-consuming compare with GB/T12457~90.The effects of temperature, concentration, salt purity, fish fillet size, osmotic regulator and vacuum on salting process were evaluated through changes of salt concentration, moisture and weight using pike eel as material, the results showed that the higher the brine temperature was, the more fish muscle gain salt. The higher the brine concentration was, the more fish muscle gain salt , The effect of brine concentration on the weight change magnitude of pike eel muscle whether increase or decrease was crucial , the change ranged from 15% to 18%. Calcium and magnesium ion had negative effect on penetration of salt, so it is necessary to use pure salt in pickling. The effect of fillet size on osmotic rate was significant, the bigger the fillet size was, the less water loss and salt gain. When trehalose was added in brine solution, it could significantly accelerate salt gain and water loss, the higher trehalose concentration was, the more water loss and salt gain. Vacuum penetration at 22℃and 25% brine concentration could also accelerate salt gain and water loss, when vacuum degree increase, the effect also increased. So using vacuum and addition trehalose can accelerate salt penetration.The osmotic dehydration phenomena were investigated with salt gain and water loss, the results indicated that rate constant and salt penetration rate increased along with temperature and concentration increase. The salt diffusion coefficient was function of temperature and initial salt concentration. The magnitude of the activation energy was an indication of the temperature influence on the diffusion process. The values of activation energy decreased with initial salt concentration increase, When the salt concentration in muscle decreases, temperature starts to be an important factor for accelerating the process. The kinetics analysis showed that the fitting equations StG=0.193t/(3.20+t)①and WL=0.277t/(3.87+t)②of salt gain and water loss of pike eel muscle with time change were beneficial to guide production and ensure quality at definite brine temperature and concentration. Pickling with high salt concentration can accelerate water loss and salt gain and reduce drying time.The analysis biochemical changes of protein and its effect on quality of cured fish during salting using DSC, FT-IR, SDS-PAGE, fluorescence, etc were carried out, the results showed that along with increasing the salt concentration of pike eel muscle , actomyosin unfold gradually , the bond bridge of amino acids side chain of peptidic chain and hydrophobic region changes resulted in aggregation and denaturation of protein. The scanning electronic microscopy(SEM) showed that pike eel muscle became tight and hardness after salting at concentration of 12.7% and fresh pike eel muscle was loose. Texture profile analysis(TPA) indicated that the hardness and cohesiveness sharply increased with increasing salt penetration of cured fish, whereas the springiness decreased. Protein denaturation in fish not only resulted in toughness in fish fillets, which became inedible, but also impaired gelation properties. When trehalose content was 2.9% in salted pike eel muscle , the denaturation of protein could be inhibited and the quality of salted fish could be improved. The higher the temperature of salting solution was, the more amino acids dissolved in brine of pike eel muscle. The higher concentration of salting solution was, the less amino acids dissolved in brine of pike eel muscle. Whereas decompounding of protein in pike eel muscle was also affected with brine concentration and temperature and they had positive correlation .So it is better to pickle at 10℃and brine concentration at 20%The effect of methods by pickling and drying on quality of cured fish were evaluated with sensory evaluation, texture and principal composition. The results indicated that the quality of brine salting was better than pile salting. Vacuum drying was better than hot-air drying in decrease drying time, inhibition and slowing oxidation of fat, whereas hot-air drying was better in appearance and flavor accumulation of cured fish, so it is nice to combine vacuum drying with hot-air drying for cured fish quality. The quality of cured fish from chemical composition analysis, sensory evaluation and texture test could be analyzed ,the relativity between sensory, texture with chemical composition was significant, so the optimization of two indicators were put forward : salt concentration 6% and water activity 0.81.The methods to accelerate flavor ripening were tried through GC-MS analysis and sensory evaluation, the results indicated that adding flavourzyme and intermittent microwave were very effective. When the flavourzyme(0.4%) was added to brine solution for 2 hours and then deal with 1min by intermittent microwave, The flavor compounds were sharply increased from 36 at control to 61 of optimization technique condition, and carbonyl and ester compounds may be important compounds in cured fish flavor. The cured fish quality was largely improved compared with control in sensory evaluation.Modified atmosphere package (MAP) and ultra-high pressure(UHP) treatment were studied for preservation of cured fish with indicators of TVBN, TMAN, TVC & TBA etc. The results showed that MAP and UHP could extend shelf-life of cured fish ,but the increase magnitude was only for 3~4 days at 25℃. A new kind of additive—trehalose was found out using in preservation cured fish and could extend shelf-life more than 100 days compared with control at 4℃, this research results were foundation to industrialize for cured fish.