Application Of Microwave Technology In Green And Efficient Preparation Of Gelatin

Due to the limitation of the gelatin production process,the industrial production of gelatin has the problems of long production cycle,large energy consumption,large amount of acid and alkali usage,huge wastewater discharge with high alkali,calcium,and COD,which seriously affect the production and living environment of local residents.The high pollution and high energy consumption of gelatin production coupled with the high cost of production waste disposal are not conducive to the green and sustainable development of gelatin enterprises.In order to solve the problems of large amount of acid and base used in gelatinization process and long heating extraction cycle in the traditional gelatin production,this study first explored the effect of microwave-assisted extraction to replace traditional water bath extraction,in order to shorten the time of thermal extraction of gelatin.At the same time,We innovatively proposed the method of microwave-rapid freezing-thawing-coupled gelatinization without acid or alkali,explored the key points of the production process of this method,characterized its gelatin properties,and finally conducted a preliminary exploration of the microwave-rapid freezing-thawing-coupled gelatinization mechanism,in order to realize the green and clean preparation of gelatin,and provide the theoretical basis for the healthy development of gelatin industry.The specific research results are as follows:(1)The microwave assisted extraction technology(MAE)of gelatin was studied.The results showed that Gelatin with higher gel strength could be obtained by short-term MAE(5~30 min),but its yield was lower than water bath extraction(WBE).With the prolongation of MAE,yield showed an increase and gel strength decreased due to degradation of high molecular weight subunits.Compared to WBE,gelatin obtained by short-term MAE formed gels at a slower rate,but more powerful triple helix-like structures could be obtained after a sufficiently long maturity(16~18 h).The reason was that microwave destroyed more hydrogen bonds during heating,but its large amount of high molecular weight subunits was the key to high gel strength.SEM showed that there were numerous holes on the surface of MAE gelatin but many fragments on the surface of WBE gelatin.(2)Microwave-rapid freezing-thawing-coupled gelatinization was used to extract fish skin gelatin,and the effect of key processing points on fish skin gelatin extraction was investigated.The results showed that microwave pretreatment was needed before freezing-thawing to achieve a better extraction yield.The gelatin extraction yield was positively correlated with the microwave pretreatment time,and the gel strength was higher in short-term microwave pretreatment(5~15 min).Microwave pretreatment temperature had little effect on the extraction yield,the best gel strength was obtained at the microwave pretreatment temperature of 55 °C or 75 ?.Increasing microwave pretreatment temperature was beneficial to the dissolution of high molecular weight subunits in gelatin.However,too high temperature may lead to the degradation of dissolved subunits during the heating extraction process.Rapid freezing-thawing had a great effect on gelatin extraction.After rapid freezing-thawing treatment,the gelatin extraction yield and gel strength increased significantly(P<0.05).The gel strength was 580.10 g after one rapid freezing-thawing cycle which increased the dissolution of ? subunits.The increase of freezing-thawing cycles could increase the extraction yield of gelatin,but led to the decrease of gel strength.The thawing temperature had no effect on gelatin extraction rate and gel strength.In summary,the optimal conditions for microwave-rapid freezing-thawing-coupled gelatinization were: microwave pretreatment at 55 ° C or 75 ° C for 15 min,one rapid freezing-thawing cycle.The yield of the obtained gelatin was 13.68%,and the gel strength was 565.11 g.(3)The properties of microwave-rapid freezing-thawing-coupled gelatinized fish skin gelatin were characterized.Different from type A and type B gelatins on the market,the microwave-rapid freezing-thawing-coupled gelatinized fish skin gelatin had an isoelectric point of pH = 7,the gel color was bluish,and the transmittance met the requirements of national standard.Compared with traditional acid gelatinization,microwave-rapid freezing-thawing-coupled gelatinization had more hydrogen bonds content,and the triple helix structure was more complete,but the less high molecular weight subunits contents led to lower gel strength than traditional method.After microwave-rapid freezing-thawing-coupled gelatinization,gelatin obtained by microwave-assisted extraction had slightly higher strength,and gelatin extracted by traditional water bath could form gel slightly faster.The way of gelatinization and heating extraction methods did not affect the amino acid composition of gelatin.Overall,the gel properties of gelatin were more related to gelatinization process,and the influence of thermal extraction methods were relatively small.(4)Preliminary Study on the mechanism of microwave-rapid freezing-thawing-coupled gelatinization was conducted.In general,microwave broke the collagen covalent bonds,and freezing-thawing treatment destroyed the non-covalent noncovalent interactions of collagen molecules,thus loosening the collagen triple helix structure and ultimately inducing collagen gelatinization.Different treatment conditions induced different changes in collagen gelatinization.The results showed that microwave pretreatment could promote the loosening of the triple helix structure of collagen.After 15 min of microwave pretreatment,the collagen could be moderately degraded and the collagen triple helix structure could be loosen to the greatest extent,and was more conducive to the retention of triple helix structure in gelatin.However,the long time of microwave treatment led to the degradation of collagen polymers and the aggregation and fragmentation of collagen molecular on the surface,which could increase the degradation of gelatin subunit components during heating extraction,resulting in decrease of gel strength Increasing the temperature of microwave pretreatment did not cause the degradation of collagen molecules.When the temperature was raised to 75?-95?,the backbone of collagen was effectively destroyed the exposure of collagen N-H groups,C=O of amide ?,and methyl and methylene of lipids increased significantly,which promoted the apparent dissolution of high molecular weight subunits of gelatin.However,the gel strength did not increase significantly as these subunit components would be more degraded,leading to an increase in small molecular components in gelatin during the extraction process.Rapid freezing-thawing after microwave pretreatment did not affect the molecular weight distribution of collagen.One freezing-thawing cycle was beneficial to the further loosening of collagen fiber and the dissolution of ? chains of gelatin.Two freezing-thawing cycles could increase the exposure of C-C bonds of collagen backbone,N-H bonds of collagen,C=O bonds of amide I,and methyl and methylene of lipids.Gelatin high molecular weight subunits chains were more easily degraded during thermal extraction,resulting in lower gel strength.After three freezing-thawing cycles,the collagen structure was severely damaged,collagen fiber surface was completely aggregated,gelatin chains were severely degraded during heating extraction,resulting in the lowest gel strength.