Studies On The Enzymatic Saccharification Of High Concentration Maltodextrin

In order to reduce the cost of starch sugar, one of the most effective ways was to reduceevaporation of water by improving the starch concentration. However, the reaction rate,product yield and purity of saccharification would be affected when increasing the substrateconcentration. As the intermediate produced by the hydrolysis of starch, maltodextrin wastaken as substrate. Therefore, saccharification process conditions were optimized firstly in theresearch and the effect of maltodextrin concentration on saccharification was studied. Thenthe saccharification of maltodextrin at high concentration was improved by ultrasoundpretreatment and compound enzyme method. In the end, the product purity were studied.The main research contents as follows:Firstly, the reaction system was established in high concentration saccharification. Thebetter saccharification process conditions could be as follows: maltodextrin solution (aboutDE15, pH4.5) was stired at60℃for48h and50U/g glucoamylase was added into thesolution.Secondly, effect of substrate concentration on saccharification was investigated. Theresults showed that the glucose concentration and yield of saccharification reaction bothincreased first and then decreased with the rising maltodextrin concentration. The glucoseconcentration in the saccharification solution reached the peak (531.3mg/mL) while theinitial maltodextrin concentration was50%. The maximum glucose yield reached91.4%when the initial maltodextrin concentration was30%. The main reasons were analyzed byNMR and water activity (Aw). The results showed that the molecular density of maltodextrinelevated with the rising concentration. Thus, the probability of collision between enzyme andsubstrate increased with the rising concentration, which resulted in the increase of glucoseconcentration and yield. However, as the further rising of the maltodextrin concentration, theviscosity of the system increased obviously, the water activity of the system reduced, themobility of water became poor and the free water became less, which might inhibited thesaccharification and resulted in decreasing glucose concentration and yield.Thirdly, the effects of ultrasound pretreatment on saccharification at high concentrationwere studied and its mechanism was discussed. It was shown that, the initial reaction rate andglucose yield were significantly enhanced by the ultrasound pretreatment. Compared withcontrol, the initial speed and glucose yield increased by31.5%and4.2%separately,meanwhile, the reaction time was shorten for24h. The effect of ultrasound on the substratestructure and reaction system was studied by SEM, NMR and Aw measurement. Themechanism might be that the reaction was accelerated by the holes and cracks generated byultrasound on the surface of maltodextrin. And Aw and relaxation time (T2) were alsoenhanced by ultrasound. The change of secondary structure of enzyme protein was studied by circular dichroism (CD) spectrum and enzyme activity was measured. Through the result, weconcluded that more outstretched and higher activity enzyme was achieved by ultrasoundpretreatment, which promoted saccharification.Fourthly, the effects of compound enzyme (glucoamylase and pullulanase) onsaccharification at high concentration were analyzed, and its mechanism was investigated. Itwas shown that the initial reaction rate and glucose yield were significantly enhanced by thecompound enzyme. Compared with control, the initial reaction rate and glucose yieldincreased by18.8%and4.5%separately, which was better than ultrasound pretreatment. Themain reasons might be expressed as below: the hydrolysis rate of α-1,6glycosidic bond bypullulanase was significantly higher than that of glucoamylase. In addition, maltodextrincould be throughly and rapidly hydrolyzed by the synergistic effect of glucoamylase andpullulanase.Finally, product purity of saccharification of high concentration maltodextrin wereanalyzed. The results showed that the product purity of saccharification increased firstly andthen decreased with the rising maltodextrin concentration. The glucose proportion reachedmaximum while the initial maltodextrin concentration reached20%. However, comparedwith the20%concentration, the glucose proportion only declined by3.32%while theconcentration was50%. The product purity was enhanced by ultrasound pretreatment. Higherproduct purity was also realized by the synergistic effect between glucoamylase andpullulanase.