Effect Of Frying On Structure Of Gluten In Whole Wheat You-Tiao

You-tiao is traditional breakfast.However,the high oil content is not in conformity with modern health concept.The healthy whole wheat You-tiao is difficult to be accepted by consumers because of its poor quality.Gluten is an important component of flour.However,very little work has been done on the gluten aggregation and its relationship with the quality of the product during frying.In this paper,refined flour and whole wheat flour were used as material.Changes in physicochemical properties of gluten during frying process were explored in the complex food system and fried gluten system,respectively.In addition,to reveal the internal mechanism of poor-quailty of whole wheat You-tiao,the effect of arabinoxylan(AX)on physicochemical properties of gluten and its interaction with the gluten network have been studied during frying.Finally,the effects of xylanase on whole wheat You-tiao were investigated,which provided scientific basis for further improvement of the whole wheat fried products.The main research contents are as follows:First,the qualities of You-tiao and whole wheat You-tiao were analyzed.The total oil content of whole wheat You-tiao was 15.73%,which was significantly lower than the contrast(23.23%).Compared with the contrast,the specific volume of whole wheat You-tiao decreased from 5.69 cm~3/g to 3.16 cm~3/g.As function of frying temperature,the hydrogen bonds in the protein molecular chains of You-tiao were broken,resulting in the folding and helical structures unraveled.The percentage of?-helixes in the contrast was decreased from 32.45%to 27.53%,and the percentage of?-turn which is related to protein folding degree was reduced from 26.08%to 24.34%.While the percentage of?-helixes in whole wheat You-tiao was reduced from 32.65%to 29.14%,the percentage of?-turn was decreased from 26.65%to 24.03%.The unfolding protein chains have access to form inter-chain hydrogen bonds easily,resulting in the increases on the?-sheet content which is related to the degree of protein aggregation.The partial proteins aggregated into macromolecular proteins during frying,resulting in burial of the hydrophobic amino acids and the decrease in surface hydrophobicity.Gluten in the contrast You-tiao formed the higher molecular weight glutenin macropolymer(GMP,2.25%)through SS bonds,while gluten in whole wheat You-tiao aggregated the 55-72 kDa glutenins(3.69%)because of the present of bran.Secondly,gluten was extracted and studied in the pure system.There was no barrier from other flour components,so the increase of GMP in fried gluten(252.55%)was significantly higher than You-tiao(65%).The GMP in fried whole wheat gluten(45.11%)was significantly less than fried gluten(56.65%).The fried whole w heat gluten aggregated into more 55-72 kDa glutenins.The result indicated that a certain component expect wheat bran combines with gluten,which blocks gluten further thermal aggregation to GMP.Furthermore,the effects of AX to gluten during the frying process and its relationship between the quality of You-tiao were established.The low-molecular-weight water-soluble arabinoxylan(WEAX)bound to gluten protein through glycosylation,which reduced the surface hydrophobicity from 1987 to 1436,and increased the solubility of gluten protein.Due to the fact that gluten combined with WEAX,the steric hindrance between the low-molecular-weight proteins became larger,which makes it difficult to aggregate into GMP.As the increase of WEAX,the gluten protein was mainly maintained by non-covalent bonds instead of SS bonds,resulting in that the content of GMP decreased from 2.15%to 0.98%.WEAX bridged the gluten protein,expanding the gluten protein network,resulting in the less of the percentage of random coil(38.4%).The expansion of gluten network increased the specific volume of You-tiao from 5.69 cm~3/g to 8.44 cm~3/g,and increased the total oil content(28.30%).The high-molecular-weight water-insoluble arabinoxylan(WUAX)has a lower rate of glycosylation than WEAX.WUAX promoted thermal aggregation of gluten to form 55-72 kDa glutenins because of its high viscosity,which hindered further aggregation to form GMP.Meanwhile,the specific volume of You-tiao decreased from 5.69 cm~3/g to 4.05 cm~3/g,while the total oil content decreased from 23.23%to 19.87%.Finally,the effects of whole wheat You-tiao with 100?g/g xylanase were studied.The specific volume of whole wheat You-tiao increased from 3.16 cm~3/g to 4.01 cm~3/g,and its total oil content increased from 15.73%to 18.69%which was still lower than the contrast(23.23%).