| In this study,gelatin was prepared from bigeye tuna skin.First,the extraction of tuna skin gelatin was optimized.Then,the physical and chemical properties of gelatin and the mechanism of collagen gelatinization were analyzed.Finally,the gel properties of gelatin / ?-carrageenan compound gel were studied.This study aims at to provide a theoretical basis for the industrial production and application of tuna skin gelatin.The main contents of this research are as follows:The effects of alkali treatment concentration,alkali treatment time,acid treatment concentration and acid treatment time on gelatin preparation were studied by using extraction yield and gel strength of gelatin as the evaluation index.On the basis of the single factor and orthogonal test,the optimum extraction conditions was as follows:NaOH concentration 0.8%(w/v),alkali treatment time 1h,acetic acid concentration2.2%(w/v),acid treatment time 2h.Under this condition,the yield and gel strength of gelatin were(22.15±0.35)% and(426±11)g respectively.In this part,the basic physical and chemical properties and structure of tuna skin gelatin were analyzed.The results showed that the basic properties such as moisture,ash content,gel strength and transmission ratio of tuna skin gelatin reached the requirement of the gelatin standard(GB 6783-2013).Tuna skin gelatin was light yellow,odorless and transparent.The gelling and melting temperatures of tuna skin gelatin were21.5 ? and 28.8 ?,respectively,which were lower than those(25.3 ? and 33.4 ?)of porcine gelatin.The infrared characteristic vibration mode and the UV absorption spectrum of the tuna skin gelatin were similar to those of porcine gelatin.SDS-PAGE indicated that the content of small molecular weight component of tuna skin gelatin was6.67%.The amino acid composition analysis demonstrated that the content of sub-amino acid(Pro and Hyp)in tuna skin gelaitn was 19.09%.The low content of small molecular component and higher sub-amino acid content than cold water fish gelatin made the gel properties of tuna skin gelatin better than most of the cold water fish gelatin.Besides,tuna skin gelatin has smaller restrict in religion and epidemic disease.Therefore,tuna skin gelatin can be considered as a good alternative to mammalian gelatin.The effect of acid concentration and alkali concentration on the gelatinizationprocess of collagen was studied by FTIR infrared spectroscopy,scanning electron microscopy(SEC)and SDS-PAGE.The results of FTIR analysis showed that the intermolecular hydrogen bonds of the collagen were destroyed,while the intramolecular hydrogen bond enhanced after the alkali treatment.The breakage of the original hydrogen bond changed the structure of the collagen,and the triple helix structure stretched.This made the subunit easily released during the gelatin extraction process.When the alkali concentration was 0.3%-1.8%,most of the ?-turn in collagen gradually changed to ?-helix and ?-sheet.When the alkali concentration increased to2.3%,the ?-helix and ?-sheet changed to ?-turn and random coil,and disorder structure of collagen increased.The acid treatment with different concentration made the original structure of collagen destroyed and the triple helix structure stretched.The content of random coil increased.The results of scanning electron microscopy showed that the alkali treatment could only cause slight degradation of collagen structure.After the acid treatment,gelatinized collagen degradated obviously,and gradually become irregular curl.It was found that the apparent damage of collagen was more obvious when the concentration of alkali treatment was 0.8% and the concentration of acid treatment was2.0%.The SDS-PAGE result showed that when concentration of alkali treatment was low,the content of high molecular weight components was lower while the content of small molecular weight was higher than other groups.Increasing the concentration of alkali treatment gradually,the high molecular weight components increasd.When the concentration of alkali treatment was increased to 2.3%,the content of ?-chain in gelatin increased and the content of ?-chain decreased,which reduced the necessary crosslinking when gel was formed,resulting in a decrease in gel strength.When the acid concentration is 0.5%-1.5%,especially when the concentration of acid treatment was1.5%,the content of high molecular weight components was high,thus resulting in high gel strength.When the acid concentration was higher than 2.0%,the content of small weight molecule components in the gelatin was gradually increased.After the acid treatment concentration reached to 2.5%,the intensity of the small molecule weight components of gelatin was significantly enhanced.And thus the gel strength is gradually reduced.Gelatin gel and the ?-carrageenan gel as control,the gel strength,rheological properties,gel water holding capacity and TPA texture of the compound gel with different ratio were studied.It was found that the gel strength,viscosity,storage modulus and loss modulus of the compound gel increased with the increase of theproportion of ?-carrageenan.The gel gel water holding capacity and TPA texture of the compound were lower than that of gelatin when the ratio of gelatin / kappa-carrageenan was 7: 3.Continue to increase the proportion of ?-carrageenan,gel water holding capacity and texture characteristics increased significantly.The results of FTIR infrared spectroscopy showed that the absorption peak of amide A band of compound gel shifted to lower wave number,indicating that there is a certain interaction between?-carrageenan and gelatin and formed intermolecular hydrogen bonds.The interaction between ?-carrageenan and gelatin decreased with the increase of the propotion of?-carrageenan.?-carrageenan and gelatin interacted most at the ratio of 7: 3.The results of the scanning electron microscopy showed that bothe of gelatin and ?-carrageenan had dense structure and a smooth surface.But when mixed the gelatin with?-carrageenan,the suface of compound gel was wrinkled and gathered.It also showed that the combination of ?-carrageenan and gelatin were not simply mixed together.Therefore,in the actual production applications,different compound ratio can be chosen to meet the different needs of different products. |
PDF Full Text Request