Studies On Application Of Modified Starch In Frozen Dumpling

In this thesis, physicochemical properties of seven modified starches (three botanical sources:poatao,corn and tapioca; four modification method:acetylation, hydroxypropylation,acetylation and cross-linking, hydroxypropylation and cross-linking) was studied, and then systemically analyzed the effect of those modified starches on solvent retention capacity, pasting properties of wheat flour and property of frozen dumpling. Results indicated:1.The properties of food grade modified starches were determined both botanical sources and modified methods. Potato starch has low pasting temperature and tendency to retrogradation, high swelling power,transparency, viscosity and water holding-capacity. Corn starch has low swelling power, transparency and viscosity, but high pasting temperature and tendency to retrogradation. Those properties of tapioca starch were superior to potato starch but inferior to corn starch. The introduction of hydroxypropyl groups and acetyl groups into starch molecules by etherification and esterification leads to an increase in swelling power, solubility, transparency, water holding-capacity and an discrease in pasting temperature and tendency to retrogradation. while cross-linking has been observed to decrease the swelling power,solubility, transparency and breakdown value of starch, increase pasting temperature, tendency to retrogradation and temperature stability of starch pastes.2. Water retention capacity of flour were negatively correlated with water holding capacity of modified starches,wheat flour containing modified potato starches have higher water retention capacity. Modification methods of starch affected significantly the lactic acid solvent retention capacity(LASRC) of flour, flour containing modified tapioca starches have higher lactic acid retention capacity, and then modified corn starches, the modified potato starches was lowest.3. Pasting order of modified starches and whear flour determined the Brabender viscosity curve of mixtures of wheat flour and modified starches. When pasting end temperature of modified starches were close to whear flour,those two ingredient pasted to peak at the same time, then the viscositiy of mixtures was the sum of wheat flour and modified starches, and significantly inscreased pasting viscositiy of the mixtures. When pasting end temperature of modified starches were far lower than whear flour, the modified starches pasted firstly, and then disscreased pasting viscositiy of the mixtures.Flour substituted with acetylated corn starch and acetylated and cross-linked tapioca starch inscreased viscositiy of mixtures of wheat flour and modified starches.However, flour substituted with hydroxypropylated potato starch et al disscreased viscositiy of the mixtures.4. There was no a regular pattern on the effect of modified starches on frozen cracking rate of dumplings, but the frozen cracking rate of dumplings o inscreased with the increase of amount of modified starches. Cooking loss of dumplings wrapper was negatively correlated with hot paste viscositiy of flour. The dumplings wrapper substituted with acetylated corn starch and cross-linked starches has lower cooking loss. The dumplings wrapper substituted with seven modified starchrs increased lightness and discreased yellowness of dumplings wrapper. When dumplings wrapper substituted with high water holding-capacity modified starches(such as hydroxypropylated potato starch) discreased water loss of dumplings wrapper at seven day's storage time compard to the other samples. The sensorial test results indicated that frozen dumplings containing 5% hydroxypropylated potato starch was well accepted. The frozen cracking rate of dumplings and cooking loss of dumplings wrapper inscreased when addition of 10% or 15% modified starches.5.Scanning Electron Microscopy(SEM) showed dumplings wrapper containing 5% acetylated corn starchand hydroxypropylated potato starch and acetylated has a more continuous gluten matrix than the control dough. Differential Scanning Calorimetry(DSC) of dumplings wrapper showed that he glass transition of frozen dough occurs at the temperature around -30℃,and there was no difference between the control and modfied starch-substituted doughs. Dough substituted with 5% hydroxypropylated potato starch, acetylated tapioca starch and hydroxypropylated tapioca starch have a narrower ice melting range than the control, suggested a more homogeneous ice crystal structure in these products.