| Canned freshwater fishes have good virtues in security, convenience and storagestability. However, under sterilization, the undesired softening of texture and severe damagein quality due to the tender and loose texture greatly limit the consumption of cannedfreshwater fishes, and impede its industrialization progress. In this research, with emphasis oneffects of pretreatment and sterilization technology on product quality, predictive model forthermophysical properties for canned freshwater fishes is established and sterilizationtechnology based on quality maintaining of canned freshwater fishes with minimum cookvalue is investigated to produce high-quality canned freshwater fish products. This research isof academic significance in enriching the theory of sterilization technology for canned food,and of great practical significance in creating innovation of sterilization technology forcanned food, promoting quality of canned food and facilitating the development of freshwaterfishes canning industry.In order to clarify the sterilization requirements of different canned fish products anddevelop different products as acidified canned fish product, solid-liquid mixing product andsolid product, the effect of product characteristics on sterilization condition and cook valuewere discussed by the analysis of the condition differences for achieving commercial sterilitysterilization. The results showed that acidified canned fish product could be treated withpasteurization or moderate temperature to sterilize, whose heat intensity was greatlydecreased. The solid-liquid mixing product exhibited quick heat transfer and its sterilizationtime as well as cook value was greatly shortened compared with solid products. Solid productshowed the highest heat intensity. Thus, the sterilization technologies are needed to reduce thecook value of solid product.In order to investigate the effect of pretreatment on the quality of fish, understand thechange in heat transfer characteristics, the pretreatment parameters was optimized byanalyzing the effect of curing and frying process parameters on mass transfer process,thermophysical properties and qualities of bighead carp, besides, the mass transfer model wasestablished by the analysis of the change in fish components under pretreatments withdifferent process parameters, and predictive model for thermophysical properties of fish afterpretreatment was also established. The results showed that the established model betweenmass transfer kinetic parameters and pretreatment parameters was well fitted, and the modelcan accurately control the content of each component after pretreatment and predict the effectof pretreatments on thermophysical properties of fish (thermal diffusivity, R2=0.97_) Theoptimal pretreatment process for sterilization and sensory quality of bighead carp weighing2.5kg was at NaCl concentration10-15g/g, curing time108-150min, frying temperature170-190oC, frying time180-250s. The optimum pretreatment process and thermal propertiesprediction model were beneficial in maintaining product quality and helpful in providing dataof heat transfer characteristics for the subsequent optimization of sterilization process.In order to explore sterilization technology of constant retort temperature (CRT) withlow cook value, the influence mechanism of thermal death force (F value) and product size on the optimal CRT process were studied. Besides, the influence mechanism of the cooling rateon the quality of the products were discussed and validated. The results showed that thesurface quality ratio (REGS) of product under optimal CRT process decreased with increasingF value and product size, and the optimal parameters varied from short time at hightemperature to long time at low temperature as the F value increased or the product sizedecreased. Compared with other sterilization conditions, the product under optimal CRTsterilization showed highest REGS, significantly improved textural properties and morecompact muscle fiber structure. Besides, the advantage of optimal CRT sterilization in qualityretention was also proved by the data of exudates properties, sensory attribute and flavorcomponents. The quality of large-size products could be improved by accelerating the coolingrate, and after sterilization, the product showed some increase in quality when applying icewater cooling under back-pressure condition. This treatment of optimal CRT sterilizationprocess and water ice cooling was one kind of low cook technology, which was of greatpractical significance in improving the quality of canned fish.A novel type of variable retort temperature (VRT) procedures with lower cook thanoptimal CRT sterilization was established. The VRT technology was optimized by numericalmethod. The effect of F value, product size, and sterilization time on optimal VRTsterilization technology was studied.By analyzing texture and flavor of product, the effect ofthe optimal VRT sterilization on product quality was investigated. The results show that,compared with optimum CRT sterilization, product of optimal VRT sterilization showedincreased REGS under different influencing factors and the increase rate of REGS of productfrom optimum VRT sterilization increased with increasing product size, F value andsterilization time. The novel VRT sterilization procedures fitted well with the temperaturecurves in retort (R2=0.978), which showed a good applicability for ordinary sterilizationequipments. Compared with optimum CRT sterilization, product of optimal VRT sterilizationachieved improved textural properties, more compact muscle fiber structure, and betterexudates properties, sensory attributes and flavor components. The research suggests that theVRT profiles showed decreased cook value compared with CRT sterilization, and had goodapplicability for ordinary sterilization equipment, which was of great academic and practicalsignificance in maximizing the quality of canned freshwater fish product.In this paper, sterilization requirements of canned freshwater fishes with differentcharacteristics and effect of pretreatment on the thermophysical properties, sterilization effectand product quality were investigated. CRT and VRT, which were characterized by qualityretention in low cook value, were established to improve the quality of canned freshwaterfishes, which was of practical significance in solving the problem concerning qualitymaintenance after sterilization of canned freshwater fishes. |
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