| Konjac glucomannan (KGM) has hydrophilic, gelling and thickening properties and physiological functions such as lowering blood pressure and blood sugar. However, its high water absorbability limits its application in flour based products. In order to decrease its water absorbency and increase the amount of its addition in flour based products, the optimum conditions of treatment on KGM by deacetylation, irradiation and enzymatic hydrolysis were determined respectively. The particle, physicochemical, structural and functional properties of these modified KGM were evaluated in this study. The effects of different amount of these modified KGM addition on flour farinograms index, bubble indicator and dough texture index were also investigated. Details are as following:(1) The importance sequence of influence factors impacting the degree of deacetylation of KGM were NaOH concentration, temperature, time and ethanol concentration, successively. The optimum parameters were 40% ethanol,0.12 mol/L alkali, temperature at 60℃ and time at 12 min. Under this optimal condition, acetyl group could be completely removed and water absorption rate of deacetyled KGM decreased to 9.32% compared to untreated sample.The water absorbency, whiteness and viscosity of KGM decreased after irradiated with 0-9 KGy60Coy-ray, while the transparency, swelling rate, viscosity stability and the content of -C=O groups increased after treatment. Meanwhile, the thermal decomposition temperature had only a little change, and the surface of particle lamellar became more loose, while the main chain of KGM was still remained its a-amorphous structure.The kinetics of P-mannanase hydrolysis on KGM were described and fitted with the Michaelis-Menten equation, and the kinetic parameters were calculated by ORIGIN nonlinear fitting. The Km and Vm were 3.4171 mg/mL and 0.7309mg/(mL·min) under the optimal conditions:pH 4.8 and 50℃. The enzymatic kinetic equation was applied for the temperature range of 303.15-328.15K, and the model-predicted values were consistent with the actually measured values.(2) The water absorption rate, L and AE of KGM decreasedand a value increased significantly after deacetylation, irradiation and enzymictreatment, while radiation treatment failed to decrease b value. Although irradiation and enzyme treatment caused an increase in acetyl content, the main chain structure didn’t show any changes. The moleculer, transformed from amellar structure into inseparable groove structure, and became denser and rougher and after deacetylation and irradiation.The crystal structure transformed from amorphous structure into a crystal structure, and the surface was inseparable and bumpy after enzymolysis processing. The deacelation process treatment could significantly improve the adsorption ability of saturated fatty acids and unsaturated fatty acids in KGM, and radiation treatment improved adsorption of sodium cholate, and also brought such effect on cholesterol.(3) Dough properties including water absorption rate, forming time, FQN, P value, P/L value and hardness significantly increased, while the weakening degree, L, G value and elasticity significantly decreased. The dough adhesion, elasticity and cohesiveness decreased after addition of deacetylated and radiated KGM. Nevertheless, the adhesion and chewing of dough increased, while the elasticity and cohesiveness remain unchanged after addition of enzymatic hydrolysised KGM. The hardness, shear work, stretching resistance ability, viscosity and adhesion capacity of noodles increased with increasing the amount of those modified KGM, while noodles elongation decreased after addition untreated, deacetylated and radiated KGM. It is conclude that addition of 4% enzymatic hydrolysised KGM improved noodles elongation, and processing quality. The variation of cooked noodles was similar to raw noodles. |
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