Study On Composite Product Of Fish And Reversible Konjac Gel

China was abundant in freshwater fishes,and the production was 24.027 million tons in 2006.60%of them were low valued fishes such as silver carp,bighead,grass carp,and they contained massive protein.Konjac glucomannan(KGM) is a kind of water-soluble polysaccharide with good thickening,gelling,film forming properties and many physiological functions.KGM can be formed as thermo-irreversible gel and thermo-reversible gel in different conditions.The reversible KGM gel presents sol status at low temperature but gel status at room temperature or higher.According to this property,different types of composite product could be processed by mixxing fish, condiment and other ingredients with KGM sol at low temperature and then heating.In this article,the processing technology,product components and microstructure of composite product were studied based on optimized conditions for reversible KGM gel preparation.The gel mechanism between fish protein and reversible KGM gel was also explored through scanning electron microscopy observing,differential scanning calorimetry determination and so on.The main results were summarized as follows:(1) Effects of alkali types and concentration on properties of reversible KGM gel were studied,and the preparation conditions of reversible KGM gel were optimized through response surface analysis.Results showed that disodium hydrogen phosphate screened from four types of alkali reagents(sodium carbonate,sodium phosphate, calcium hydroxide and disodium hydrogen phosphate) was the best coagulator for preparation of reversible konjac gel under neutral or weak alkaline conditions.Properties of reversible KGM gel were significantly affected by KGM concentration,disodium hydrogen phosphate concentration and heating time.The optimum preparation conditions were that 2.82%KGM,1.00%disodium hydrogen phosphate and heating at 95℃for 3.00h.(2) Preparation technology of composite product based on fish protein and reversible KGM gel were investigated.Results showed that fish protein and salt had significant influence on qualities of composite product.The optimum technology for good textural characteristics and sensory valuation of composite product was that the proportion of surimi to reversible KGM gel,adding amount of water and adding amount of salts were 1:1,10%,1.5%respectively.There was no significant differences in qualities between the products prepared with one-step heating(90℃,20min) and that prepared with two steps heating(35℃,40min;90℃,20min),but the taste and holding water capacity in the former was better.The cooling methods had no significant effect on qualities of composite product.The qualities of composite product added reversible KGM gel were better than those added KGM sol and irreversible KGM gel.(3) Effects of the adding amount of native starches(potato starch,sweet potato starch, waxy maize starch,wheat starch,corn starch),calcium chloride and condiments(ginger juice,monosodium glutamate,pepper powder) on qualities of composite product were investigated.The composite product added potato starch had better textural characteristics, sensory evaluation and holding water capacity within five native starches and the suitable supplementation was 6%.0.4%-0.8%calcium chloride could improve the textural characteristics of product but decreased the sensory valuation,so calcium chloride was unsuitable.The flavor and taste could be improved by adding ginger juice,monosodium glutamate and pepper powder,and the optimum amount of these condiments was that ginger juice 2%,monosodium glutamate 0.05%,pepper powder 0.1%,salt 1.5%.(4) The microstructure of composite product was observed by H-E staining and scanning electron microscopy.The gel network formation of reversible konjac sol and protein was affected by salt adding sequence.The network of composite product prepared by first mixing reversible konjac sol with fish protein and then adding salt was more uniform and more compact than that by first mixing fish protein with salt and then homogenizing reversible konjac sol with the mixture.The gel skeleton of composite product added konjac sol and reversible konjac gel was gelatin of fish protein,and the konjac gel was dispersed in the protein gel.However,the gel skeleton of composte product added irreversible konjac gel was konjac gel,and the fish protein was dispersed or embedded in the konjac gel.(5) DSC analysis showed that transition temperature of the light meromyosin,heavy meromyosin of myofibrillar protein and actin filament increased 5.4℃,3.8℃and 0.6℃respectively by adding reversible konjac gel,so reversible konjac gel could enhance the fish protein thermostability.There was interaction between the fish protein and the reversible konjac gel,and the mixture gel of fish protein and reversible konjac gel was thermo-irreversible gel.