Solid-state Fermentation And Quality Changes During Maturation Process Of Surimi

In the present study,solid-state fermentation technology of low value sea surimi with Mucor XH-22 as starter was studied systematicly,based on the primiary study of pre-fermentation technology of surimi.The initial formula of surimi product used for fermentation was further optimized,the effect of water content on the pre-fermentation process was analyzed,the influences of curing conditions on surimi product during curing process were studied,and the dynamic changes of physico-chemical indexes during post-fermentation stage was analysed.Moreover,changes of flavor compounds in surimi products in different fermentation stage were studied.The main research results were as follows:1.Based on the research results of the pre-experiment,the existing formula of surimi product was optimized and the surimi products before and after optimization were used for fermentation under the same conditions.Changes of physico-chemical indexes and enzyme activities of surimi products during the pre-fermentation stage were measured.Results showed that compared to the existing formula,the activities of amylase and protease in the optimized surimi product were increased,while TC value and TVB-N content,which reflect the contamination degree of the surimi product were decreased,and this will benefit the flavor development and quality control of the fermentation product in the next fermentation stages.2.The initial water content of surimi products,which favored for the fermentation,was optimized.To conduct this,three experimental groups with different water content(65%.70%and 75%,respectively)were set,and the dynamic changes of surimi indexes during pre-fermention were studied.The results showed that the activities of amylase and protease increased with the increase of the intial water content of the surimi.After 48h fermentation,the protease and amylase activities of the surimi with 75%water content were 69.34 U/g and 57.44 U/g,which increased 23.41 U/g and 25.56 U/g,respectively,compared with that of the surimi with 65%water content.Higher water content also decreased the product of TVB-N during the fermentation significantly(p<0.05).The TVB-N content of surimi with 75%water content was 24.85 mg/100 g after 48 h fermentation,and this was 50%of that of the surimi with 65%water content,which was 58.85 mg/100 g.Higher water content of the surimi might be in favor of Mucor growth and inhibited the contamination of bacteria which could product TVB-N.So under the condition of without affecting the surimi forming,higher water content surimi food was preferably for the solid fermentation.3.The effects of the amount of salt added(16%,20%and 24%,v/v)and pickling temperature(20 ℃ and 4 ℃)on surimi product were studied.The results showed that,salt content in surimi increased with pickling time.Salt permeability and water diffusion in surimi were significant influenced by the salt amout added and pickling temperature(p<0.05).Higher NaCl supplementation increased the salt penetration rate of surimi fastly,and the salt content of surimi added with 24%NaCl reached 14%after 24 h curing,significantly higher than the group added with 16%NaCl(p<0.05).However,high salt addition also increase the the loss speed of water and nutrients.The salt penetration rate of surimi pickled at 4 0C was slower than that at 20 ℃,but lower pickling temperature inhibited the multiplication of microorganism during pickling.So,considering from safety of the products,4 ℃ was chosed as the pickling temperature.And three groups were selected for the further post-fermentation stage:20%NaCl,pickled for 24 h;24%NaCl,pickled for 24 h and 20%NaCl,pickled for 36 h.4.Dynamic variations of water content,salt content,texture,proteolysis,TVB-N content,biogenic amines content and aerobic plate count of post-fermentation products were analyzed,and antioxidative activity of salted pehtzes was also assayed preliminary.The results showed that:During the post-fermentation,the salt in salted pehtze diffused to the brine,while water in the birne filtrated to surimi.Textural properties of surimi gradually changed.Water soluble protein,amino nitrogen and free radical scavenging rate of the surimi product kept rising during the post-fermentation stage.All of these indexes tended to dynamic balance after 45 days fermentation.The surimi pehtze of the group pickled with 20%NaCl for 24 h showed poor texture tightness and easy to loose because of rapidly enzymolysis.While the surimi pehtze of the group pickled with higher salt addition and shorter salted time(24%24 h)showed tightness texture,due to the inhibition of the protease activity.5.The flavor compounds of surimi were analysed by amino acid composition,electronic nose analysis and headspace solid-phase microextraction(HS-SPME)combined with gas chromatography-mass spectrometry(GC-MS).The results showed that different flavor components were produced during different fermentation stages.The components of amino acid of surimi changed gradually,and varies of esters was synthesized during the post-fermentation stage.Although the types of the volatile aroma compounds were roughly the same for surimi with different pickling treatment,the respsctive contents of single flavor component in the surimi varied greatly among diffent groups.