Study On The Variation Of The Quality Of Wheat Flour Under Different Storage Conditions

The wheat flour was stored under the treatment combination of six levels of temperature (10,15,20,25,30,35℃) and three levels of relative humidity (55%,70%,85%). Various quality parameters of wheat flour samples were determined at a certain frequency. The wheat flour was stored for 180d, 165d and 90d under 55%RH, 70%RH and 85%RH, respectively .In this paper, the quality of wheat flour was studied during the storage. The changes of the main components of flour(enzyme activity, starch characteristic, dough rheological properties and cooking quality)were analysed. The relationship between the storage temperature and relative humidity with quality was discussed.The results can be concluded as:(1) the change of componentsThe moisture of wheat flour became stable as the storage progressed, reaching equilibrium in the end. At the same relative humidity, there was a negative correlation between storage temperature (X) and equilibrium moisture content (Y) (Y = a + bX, b <0). At the same temperature, the higher the relative humidity was, the higher the equilibrium moisture content the samples had.The crude protein content kept constant during the storage. Wet gluten content, water-holding rate of gluten and sedimentation value were decreased.Reducing sugar content, fatty acid value and acid value increased with different degree when the wheat flour was stored below 75% RH. There was a positive linear correlation between the storage time (X) and fatty acid value (Y) (Y = a + bX) under 55% RH,70% RH and85%RH,10¹5℃. For the condition of 85%RH and 20³5℃, those value increased first, then decreased. The relationship of the storage time (X) and fatty acid value (Y) followed one element cubic equation (Y = a+ bX+ cX2+ dX3).The low temperature can keep the amylase activity . When RH was below 75%, amylase activity was stable for a long time, then decreased. At high RH, amylase activity was increased by moisture of wheat flour and environmental temperature.(2) the change of RVA characteristicsUnder 55% RH and 70% RH, the peak viscosity, setback, breakdown viscosity and final viscosity increased during the storage.Under the condition of 85%RH and 20³5℃, the peak viscosity and final viscosity increasd ,while breakdown viscosity and setback viscosity decreased.(3) the change of rheology characteristicsUnder 55% RH and 70% RH, water absorption and stability time increased first and decreased afterwards. The degree of dough softening decreased first and increased afterwards, which indicated that the cooking quality of wheat flour deteriorates after stored for a certain of time. Under the condition of 85%RH and 20³5℃, after 20 days, the stability time was decreased and the degree of softening was increased. Therefore, high temperature and high relative humidity should not be utilized for flour storage.Under the condition of 55%RH and 70%RH, the relationship of the wet gluten content, water-holding rate of gluten, sedimentation value, water absorption , stability time and the degree of softening (Y) were binary linear correlated with temperature(X₁) and time(X₂) (Y =a+bX₁+cX₂), so were the reducing sugar content, peak viscosity, breakdown viscosity and final viscosity under the condition of 55%RH,70%RH and 85%RH.(4) the change of cooking quality characteristicsWith the increased storage time, the sensory score for the specific votume, color, luster, odor, stickiness and toughness of steamed bread decreased.