Dynamic Effect Of Multiple Film Picking On The Quality Of Soybean Film

Soybean film,also known as tofu skin,is a kind of traditional non-fermented soy products in China,which is produced by the following procedure:soybean milk preparation,thermal insulation and film picking.Soybean film quality did not have an evaluation standard,because traditional production of soybean film is mainly guided by experience,the process parameters cannot be determined.In order to improve the quality of soybean film,we should know effects of dynamic changes of physicochemical properties of soymilk on the quality of soybean film during the formation of film.In this paper,the physicochemical properties of soymilk and soybean film were analyzed from the dynamic changes of the formation of putrefaction quality,and the changes of Maillard and flavor substances in soybean milk mother milk under long-term heating preservation were explored.The film-forming rate,boiling resistance,rehydration and mechanical properties of soybean film were determined.The sensory evaluation results of soybean film were compared with those of soybean film,and a method for evaluating the quality of putrefied peel was established.The quality of the soybean film was graded to distinguish the quality of them.Provide new ideas and methods for establishing the quality evaluation standard of soybean film.The main research contents and results are as follows:(1)Studied the dynamic physicochemical properties of soymilk and soybean film during multiple film picking.The results show that the protein content in soybean milk decreased from(43.63 ± 0.04)%to(42.13± 0.10)%,the fat content increased from(17.13 ± 0.15)%to(29.45 ±0.04)%,and the total sugar content remained unchanged.With the increase of film picking times,soymilk becomes sticky,and the particle size and viscosity of soymilk increased significantly,protein aggregation occurred in soymilk.The 11S/7S ratio of SDS-PAGE electrophoresis increased.The protein content in soybean film decreased from(47.27 ± 0.21)%to(46.35 ± 0.09)%,the fat content(26.80 ± 0.22)%to(20.39:± 0.04)%,and the sugar content reached the maximum of 4.16%at the sixth film.There were white globules(<100 nm)on the surface of soybean film.With the increase of film picking times,the more black-gray holes(<500 nm)which were oil body or evaporated by water vapor were distributed on the surface of soybean film.The secondary structure of protein of soymilk and soybean film mainly exists in the form of ?-sheet and ?-turn,but the relationship between them was not significant.(2)The changes of changes of flavor components,Maillard reaction products and color of the soybean film and soybean milk during film picking process at same interval were studied,in order to find the corresponding relationship between the degree of Maillard reaction and the change of flavor and color of soybean film.In this study,gas chromatography-mass spectrometry(GC-MS),high performance liquid chromatography(HPLC)were used to determine the corresponding relationship between soybean film flavor and color change.With the increase of film picking times,the browning index(BI)of soymilk increased significantly,melanoid substances produced by Maillard reaction accumulated in soymilk.The small molecule of the intermediate products of maillard reaction decreased,maillard reaction entered the advanced stage,and the soybean film became dark,yellow and brown.There were more than 60 main volatile components in the soymilk samples(matching degree>80%),among which the fragrant components were mainly ketones,alcohols,aldehydes,hydrocarbons,furans and aromatic compounds.The highest proportions of flavor components were aldehydes,and the content of which reached the maximum value in the 7th soybean film;the furan content gradually increased from the 1st to 10th soybean film.(3)The correlation between the sensory index,main nutrient composition,rehydration,mechanical properties and other quality indexes of soybean film was analyzed,and the soybean films were classified.Rehydration of soybean film reached its maximum at the 5th film,and its boiling resistance increased at first and then tended to be stable.The film forming rate increased continuously,but the mechanical properties decreased from 2.7 g/cm2 to 1.5 g/cm2.The sensory indexes(color,smell,taste and acceptance)of the soybean film showed that the sensory quality of the fifth film was the best,and the weighted average was 6.58 ± 0.35.There was a significant positive correlation between protein and the four sensory indexes(0.809**,0.816**,0.671*,0.760*),fat and color(0.985*),sugar and four sensory indexes were not significantly related.Film forming rate was negatively correlated with protein and fat(-0.681*,-0.935*)and positively correlated with sugar content(0.641*);rehydration was positively correlated with protein content(0.673*);breaking elongation(AE)and tensile strength(TS)were positively correlated with protein and fat content.There is a significant positive correlation(p<0.01).On the basis of correlation analysis,a comprehensive evaluation function is established:F = 0.53481 + 0.4651f2,this is an objective evaluation of the quality of soybean film.After principal component analysis and cluster analysis,the soybean films were divided into three grades:the first grade(fourth,fifth,sixth pieces of putrefied skin);the second grade(seventh,eighth,ninth pieces of putrefied skin);the second grade(first,second,third,tenth pieces of putrefied skin).