Study On The Mechanism Of The Effect Of Frozen Storage On The Quality Of Dumpling Sheets

Dumpling is one of the traditional food loved by the people in our country, but dumpling’s edible quality will be decline after frozen storage because of frozen technical limitations. Therefore, study the mechanism of quality change in the process of frozen storage has important significance to improve the quality of dumpling. This topic has collected 13 different varieties of wheat, after milling,made into the dumpling sheet and wash out the gluten respectively and frozen storage treatment, research the change rule of dumpling sheets quality, gluten quality, gluten protein micro-structure and molecular weight during frozen storage, in order to explore the mechanism of dumpling quality changes during frozen storage. The main research and results are as follows:Make 13 kinds of wheat into the flour and determination the rheological properties of them, according to the quality of the gluten, it can be divided into three categories:gluten index≧65%, dough stability time≧8min, extension energy≧63cm-2, swelling volume≧15mL of wheat gluten quality is better; gluten index≦50%, stability time 4min, extension energy≦50cm-2, swelling volume≦11mL of wheat gluten quality is poorer; the gluten index between 50%-60%, stability time between 4min-8min,extension energy between50-2-63cm-2, swelling volume between 11mL-15 mL of wheat gluten medium samples.Using the texture analyzer determination the texture quality of dumpling sheet in the process of frozen storage, evaluate the sensory quality at the same time. The results showed that:frozen storage decrease the quality of dumpling sheet, specific performance as with the extension of freezing storage time, the firmness、toughness and the taste of dumpling sheet decreased. There was an obvious decline of different quality dumpling sheet in different time during the frozen storage, which made from different wheat flour with different gluten qualities. Samples made from wheat flour, which is of good gluten quality, gluten quality was significantly decreased at three months of frozen storage, but samples made from wheat flout, which is of poor quality before two months was significant decline during frozen storage. That is to say, samples made from powder with poor gluten quality, effect of frozen storage, quality decreased more serious.Using the texture analyzer measure the hardness of gluten during the frozen storage, observed the swelling volume of gluten in lactic acid solution at the same time. The result showed that:gluten quality deterioration caused by frozen storage and with prolonged frozen storage time, the hardness decreased more serious and the swelling volume of gluten reduced more serious. Samples of different gluten quality have obvious deterioration in about two months of frozen storage, but gluten sample with the poor quality than samples with the good quality, decreased the percentage of the hardness value and the swelling volume is bigger, the gluten samples of poor quality influence by frozen storage is more serious. Therefore,gluten index≧65%, stability time≧8min, stretch energy≧63cm-2, swelling volume≧15mL of wheat flour suitable for making the dumpling sheets as raw material, because of its quality has little effect on frozen storage. The gluten index≦50%, stability time≦4min, tensile energy≦50cm-2, swelling volume≦11mL of wheat flour is not suitable to be used as the raw material for making dumpling sheets, due to frozen storage has a great influence on its quality.Though different period of frozen storage gluten secondary structure of frozen storage were determined by FT-IR and using SEM to observe the micro-structure of gluten protein. The result showed that: the micro-structure of gluten protein was obviously changed by frozen storage, among them, the secondary structure of the β-fold turn into the β-sheet, and different gluten quality of gluten protein, the secondary structure changed significantly in different time, gluten protein samples with better gluten quality, the content of inter-molecular β-sheet increased most at three months in frozen storage, gluten protein sample with medium gluten quality, the content of inter-molecular β-sheet increased most at two months in frozen storage, the gluten protein samples of weak gluten quality, its structure changes in the early stage of frozen storage. Also, in the micro-structure of gluten protein the network becomes loose and the hole is enlarged, which leads to the weakening of the network structure. After 120 days of frozen storage, although the hole of the sample with better gluten quality becomes larger, the whole network structure still exists and no severe fracture, but the hole of the sample with poor quality of gluten increased and the network was broken completely.The molecular weight and distribution were measured by GPC(Gel Permeation Chromatography) during frozen storage. The result showed that:changes of molecular weight and distribution of gluten protein in frozen storage,regardless of gluten quality, there are a phenomenon that high molecular weight polymer depolymerization into new and small molecular protein. Samples with good gluten quality compared with samples of gluten quality is poorer, the time of the high molecular weight polymer depolymerization occurs late, the degree of depolymerization is lower.The change of the structure and molecular weight of gluten protein is the root of the change of the quality of dumpling sheet.