Processing Optimization And Characterization Of Jelly From Grass Carp Fish Scales

It is known that fish scale contains numerous valuable organic andinorganic components. However, most of fish scales from different fishkinds have ralatively tough texture and they are unsuitable for direct eating.So fish scale is usually discarded as waste which results in resource wasteand environment pollution. Therefore, the development of food made fromfish scale has an important economic and social significance. Fish scalejelly is a kind of gelatin food which is produced after gelatin solutionabstracted from fish scale is cooled under low temperature. It is rich inwater soluble collagen and has the cosmetology, health care effects. As forfish scale jelly, there have been some articles about simple introduction ofprocessing while researches of systematic processing optimization andproperties have not been reported. Grass carp is a bulk of aquacultureproducts in our country, so fish scale resource from it is quite adequate.Furthermore, its collagen content is rich which is suitable for thepreparation of fish scale jelly. Consequently, processing optimization andproperties of fish scale jelly with grass carp fish scale as material wereinvestigated in this thesis, the main contents and results are as following： 1. Different pre-treatment methods of processing fish scale jelly forquality promotion were studied. Orthogonal tests were conducted toascertain separately the optimum conditions of acid pre-treatment, alkalipre-treatment and enzymatic pre-treatment which were verified afterwardswith collagen extraction rate and gel strength as dependent variables basedon single factor tests. The results showed that enzymatic pre-treatment wasthe optimum pre-treatment method and fish scale jelly processed with thismethod was with the highest collagen extraction rate and gel strength. Itsoptimum conditions were amount of protease A2G0.8%(w/w), hydrolysistemperature30℃and hydrolysis time5.5h. Acid pre-treatment was withlow cost and simple processing technology, so it was more cost effective.Fish scale jelly processed with acid pre-treatment was with higher collagenextraction rate and its gel strength had no significant difference comparedto enzyme pre-treatment method. Its optimum conditions were HClconcentration0.4mol/L, pickling time90min, the ratio of fish scale to HCl1:6(w/v). However, alkali pre-treatment with NaOH was not suitable forpre-treatment of processing fish scale jelly as fish scale jelly processed withthis method had much lower gel strength and a little higher collagenextraction rate.2. Orthogonal tests were conducted to ascertain separately theoptimum conditions of heat treatment of fish scale jelly processed by no pre-treatment, acid pre-treatment and enzymatic pre-treatment withcollagen extraction rate and gel strength as dependent variables based onthe research of processing optimization of pre-treatment of fish scale jelly.The results showed that the extraction temperatures were all100℃andthe extraction times were all2h, the ratios of fish scale to water were all1:4except the ratio of1:5for fish scale jelly processed by acidpre-treatment, and the pH of water was6for fish scale jelly processed byno pre-treatment. From these, the extraction temperature and extractiontime could be used for processing fish scale jelly from different fish kinds.However, the ratio of fish scale to water should be adjusted to meet therequirement of gel strength because of different collagen content ofdifferent fish scales.3. Physicochemical and texture properties of three different fish scalejellies processed under their respective optimum conditions were studied.Three different fish scale jellies had no significant differences in gelstrengh. They were all little higher than ordinary fruit jelly with fruit tasteand more lower than gelatin from fish scale in gel strength. They werealso more lower than gelatin from fish scale in viscosity. Enzymaticpre-treatment had a significant impact on gel strength and viscosity offishs scale jelly, while acid pre-treatment had a great effect on viscosity.The three fish scale jellies were all lower than gelatin from fish scale in gelling temperature and melting temperature. Among them, the fish scalejelly processed by no pre-treatment had the highest gelling temperatureand melting temperature which showed the best thermostability. Thegelling temperatures and melting temperatures showed that fish scalejellies should be cooled under10℃and below and preserved under20℃and below. All these physicochemical properties had something to do withthe collagen mass concentration and the structure of peptide chain of fishscale jelly. The three fish scale jellies were softer, more smooth and withmore springness in texture than ordinary fruit jelly with fruit taste and thetexture property of the fish scale jelly processed by no pre-treatment wasthe best among them.4. Fish scale jelly processed by no pre-treatment had good texture,simple production process and contained calcium and other mineralelements, but also had dificiencies that was low collagen massconcentration and low utilization of fish scale. Fish scale jelly processed byenzymatic pre-treatment had high collagen mass concentration and highutilization of fish scale, but also had dificiencies that is inferior texture,complicated production process and high cost. Fish scale jelly processed byacid pre-treatment had high yield because of the low ratio of fish scale towater and was cost effective but also had inferior texture.