Research And Application Of Heterogeneous Hygrothermal Degradation Of Konjac Glucomannan

The health benefits of Konjac Glucomannan(KGM)as water-soluble dietary fiber have received increasing attention in recent years.However,the native KGM couldn’t exert the its physiological activity when it was added to food products such as grain products in a small amount because of the large molecular weight and high viscosity.Therefore,the market demand for low-molecular weight and low-viscosity KGM is urgent.This study found that KGM powder with few moisture content can be rapidly degraded under highpressure hygrothermal sterilization treatment,which has great application prospects for the preparation of partial degraded KGM in the commercial.This subject studied the degradation law and degradation product characteristics of KGM in the heterogeneous hygrothermal environment with solid-liquid-vapor coexistence firstly.On this basis,the degradation products on wheat dough quality and wheat starch properties were investigated.It was confirmed that not only the quality of dough was improved by mildly degraded KGM,and the convenience of processing was not affected.The heterogeneous hygrothermal degradation of hydrocolloids was preliminary explored,and proving that the new method had practicality in the field of hydrocolloids.The full study research contents and results are as follows:1.The partially degraded KGM with weight-average molecular weight(Mw)in the range of 8.150×104 Da-4.205×105 Da was prepared by heterogeneous hygrothermal degradation,and the effects of treatment time and KGM initial moisture content on Mw,apparent viscosity,structure,and rheological properties,etc.of degraded KGM were studied.Hygrothermal treatment of KGM powder containing 5%moisture content in 121℃ for 20 min,the Mw decreased from 6.542×105 Da(non-degraded KGM)to 4.205 ×105 Da,and the apparent viscosity decreased from 39894.12 mPa·s(non-degraded KGM)to 3347.35 mPa·s.And lengthened treatment time to 120 min,the Mw and apparent viscosity were decreased to 8.150×104 Da and 28.02 mPa·s,respectively.The polydispersity index(PDI)of the degraded KGM was increased with the treatment time increased,but less than 2.00.The initial moisture content of KGM also was an important influence factor for degradation efficiency.Under the same processing conditions,the increase of KGM initial moisture content can reduce the Mw and PDI of the degradation products.But the konjac flour cannot maintain the powder form when the initial moisture content was too high.So the initial moisture content should be kept below 35%.From the analysis of degradation kinetics,it is known that the degradation system consistent with the first-order degradation kinetics reaction.The FT-IR and AFM analysis showed that the molecular chain of KGM was broken after degradation,but the main chain structure of KGM did not changed with degradation and no new groups were generated.The results of DSC and XRD analysis showed that the heterogeneous hygrothermal degradation improved the thermal stability and crystallinity of KGM.Rheological analysis shows that the increased of treatment time and the initial moisture content of KGM decreased the viscoelasticity of degraded KGM.2.The effects of partially degraded KGM on wheat dough properties and steamed bread quality were studied.The effect of slightly degraded KGM(KGM-1,Mw=4.205×105 Da)had significantly less than non-degraded KGM(Mw=6.542×105 Da)on the farinographical properties,tensile properties,rheological properties,and microstructure of dough.And slightly degraded KGM also had less impact on difficulty and efficiency of processing.The addition of KGM increased the specific volume of steamed bread.When the native KGM was added,the specific volume of steamed bread was the largest,which increased from 2.32 mL/g(Control)to 2.55 mL/g.KGM-1 had the greatest effect on the texture characteristics of steamed bread.The texture profile analysis showed that the addition of KGM-1 increased the springiness of steamed bread to 0.97.Meanwhile,the hardness and chewiness were reduced to 878.55 g and 660.33 respectively,which was significantly different(p<0.05)from compared with the control.Analysis of the change rate of hardness,chewiness and springiness of the samples showed that the inhibitory effect of KGM-1 on steamed bread retrogradation was significantly enhanced compared with the control group.To sum up,the slightly degraded KGM(4.205× 105 Da)was more conducive to improve the quality of bread and maintain the long-term storage stability,compare with the natural KGM(Mw=6.542×105 Da)and the relatively more degraded KGM(the Mw was 1.902×105 Da,1.039×105 Da,5.570×104 Da,respectively).3.The effects of partially degraded KGM on the properties of wheat starch were studied.The addition of KGM let the swelling of starch granules during the gelatinization process was inhibited,and the gelatinization temperature and gelatinization enthalpy of wheat starch was increased with the increase of KGM molecular weight,And the exudation of amylose in wheat starch,syneresis and retro gradation enthalpy was decrease with the decrease of KGM molecular weight,indicating that the retrogradation of starch was delayed.In addition,the shear-thinning behavior and viscoelasticity of the wheat starch paste were enhanced with KGM,and it was more obvious as the Mw of the increased of KGM.4.The heterogeneous hygrothermal degradation effects of guar gum,κ-carrageenan,sodium alginate,and locust bean gum were compared in order to popularize the degradation method to other hydrocolloids.The results show that the heterogeneous hygrothermal degradation method had good degradation effect on the above four hydrocolloids.After heterogeneous hygrothermal treatment for 120 min,the Mw of κ-carrageenan was decreased from 2.614×105 Da to 1.782×105 Da;the Mw of guar gum was decreased from 5.873×105 Da to 5.117×105 Da;the Mw of sodium alginate and locust bean gum also decreased by 1.152×105 Da and 1.449×105 Da,respectively.The Mw of degradation products were uniform and the apparent viscosity was also significantly decreased with the increased of treatment time.The degradation efficiency was related to the structure of hydrocolloids,that the highest degradation efficiency was KGM(87.54%)and the lowest was guar gum(12.87%).From the analysis of degradation kinetics,the degradation system of above hydrocolloids consistent with the first-order degradation kinetics reaction.