Effect Of Frying On Water And Oil Distribution,Starch Physicochemical Properties And Digestibility In Glutinous Rice Cake

Fried glutinous rice cakes are one of the popular and traditional snacks in China;they are a kind of typical fried glutinous rice products.They are crispy on the outside and the waxy on the inside.But their research has not been reported on starch structure and digestibility of fried glutinous rice cakes.Therefore,this experiment was executed on homemade glutinous rice cakes,which were deep-fried for 6 minutes at 150,160,170,180 and 190 ℃,respectively.The parts of cakes were separated into crust,middle,central core,and whole cake,each part was analyzed for the distribution of the water and oil.The starch of each part was extracted and was studied for the particle,crystallization,thermodynamic and infrared properties.The in-vitro and in-vivo digestibility of fried glutinous rice cake and its separated parts were carried out.The purpose was to provide reference for the research of starch structure,quality evaluation,industrial production and healthy eating of the fried glutinous rice cake.The main results were as follows:1.The moisture content of glutinous rice was 14.4 %.The fat,starch,protein,and total ash were 0.59,90.88,7.82,and 0.39 %,respectively based on a dry weight of glutinous rice.2.In the order of the free water content measured by GB method was glutinous rice flour,core,whole cake,middle,and crust part.On the contrary,the oil content was crust,whole cake,middle,core,and glutinous rice flour.The bound water content by low field NMR was glutinous rice flour,core,whole cake,middle,and crust.Frying could affect the free water,bound water and oil content of glutinous rice cake.There was no significant difference in water content of different frying temperatures.However,the crust part was a trend that went up and down,and 170 ℃ was the maximum that was 17.63%.3.Results of scanning electron microscopy and X-diffraction showed that starch of each part of fried glutinous rice cakes were gelatinized and destroyed.The starch granules did not have the original smooth surface morphology and clear angle.Starch swelled and disintegrated to form aggregates,the glutinous rice starch and fat did not form the V-type complex.The different frying temperature had a similar effect on the starch of each part of fried glutinous rice cake.The results of differential scanning calorimetry indicated that in the order of the Δ H absorption of the starch structure after frying of the glutinous rice cake was as follows: core,middle,and crust.The Δ H decreased slightly with the frying temperature.The results of fourier transform infrared spectroscopy showed that there weretwo weak small peaks at 2854 cm-1and 1745 cm-1at 180 ℃ and 190 ℃,respectively.4.Results of in vitro digestion stated that the RDS content of native glutinous rice flour was 10.02 %,the RS content was as high as 67.16 %.While,the RDS content of different parts of glutinous rice cakes at different frying temperatures was high,the value among67.16 ~ 73.64 %.The SDS content of the native glutinous rice,fried and steamed glutinous rice cakes were all about 20 %.Each part of fried glutinous rice cakes and steamed cake had lower RS content that were below 10 %.RS of the crust region was slightly more than other parts but had no significant difference among them.RS of all the parts of fried cakes was significantly lower than that of steamed cake.The content of starch fragment in each part of fried glutinous rice cake at different temperatures had a similar trend.5.In the results of mice test,the average daily intake of each group were as follows,feed:6.85 g,glucose: 6.77 g,crust powder: 5.70 g,inner powder 6.71 g,whole cake powder:7.09 g,steamed cake powder: 6.87 g.The crust group’s intake and weight decreased significantly.In the simulation of BDI-GS system,there was no significant difference between fried and steamed glutinous rice cakes,the cumulative points were more than 8.They were basically beneficial to the overall nutrition and health of bodies.Crust,inner part of fried glutinous rice cakes,the whole cake and the steamed cake of GI were 62.48,60.47,61.54 and 59.93,they were all among 55 ~ 70.All samples belonged to the middle GI foods.The content of TC and LDL-C in the blood lipid of mice could be increased by feeding fried glutinous rice cake,and the content of TC,TG and LDL-C could be increased by feeding the crust part of fried glutinous rice cake.