Regulation Mechanism Of Enzymatically Extruded Rice Quality And Its Application In Chinese Rice Wine

Enzymatic reactive extrusion(eREX)is a new technology combing thermomechanical extrusion with enzyme catalysis,which shows production characteristics of "green,high-efficiency,continuous treatment" for cereal process.Chinese rice wine(CRW)with a glorious history is a "gem" of the Chinese nation through millennium,however,there are many problems relating to its pretreatment of brewing including long-time for rice soaking,wastewater pollution,energy consumption,poor rice quality(half/over-cooked or retrograded rice),great loss of functional components,etc.Therefore,we used the eREX to treat rice for CRW brewing in this study,with the following objectives:to explore the mechanism and critical-factor control of rice modification,to build suitable models for engineering optimization and dynamic analysis,and to increase the utilization ratio and fermentation efficiency of rice for the improvement of CRW.Under these conditions,it is expected to promote the sustainable development of CRW industry.The changing regulations and threshold levels of different system parameters were studied by controlling the operating parameters in wide ranges.Results showed that,during extrusion,some real-time or simplify calculated system parameters(i.e.,product temperature,die pressure,torque and special mechanical energy(SME))were dramatically influenced by one or more operating parameters,that is,enzyme concentration(EC),barrel temperature(BT),moisture content(MC)and screw speed(SS).Among them,BT and MC are very special due they not only act on feed materials directly,but also affect them via enzyme indirectly.3D response analysis revealed that,given a fixed EC,a phenomenon of curvature increase occurred near the ranges of BT 86?/114?(i.e.,product temperature?90?/120?),indicating the activation/inhibition of enzyme.A similar phenomenon was observed when MC was higher than 48%,and it is mainly caused by the lubricating effect of water on extrudate.When a-amylase showed a high activity during extrusion,die pressure,torque and SME greatly decreased(<1.0 MPa?<6.7 Nm?<62 kJ/kg,respectively).Six-order response model was used to fit the data from the multiple target parameters of the eREX process(such as bulk density.WSI,WAI,viscosity,GE,total phenolics content(TPC)),based on the control of operating parameters in wide ranges.Among them,the key target parameters were:WSI(76.8%-90.1%),which was inceased as increasing EC and MC,and was increased followed by a slightly decrease as increasing BT;WAI(1.12 g/g-1.34 g/g),which was opposite to WSI for the changing rule,and the only different is that WAI was decreased followed by an increase as increasing MC;RVA peak viscosity(<41 cP),similar to that of WAI;GE(>99.57%),similar to that of WSI;TPC(71.1%-90.5%),which was increased as increasing EC,MC and SS while decreased as increasing BT.Under these conditions,the general ranges of system parameters(product temperature,86.8?-110.4?;die pressure,<0.9 MPa;torque,<3.6 Nm;SME,<45 kJ/kg)were obtained.The residence time distribution(RTD)and the flow pattern and mixing action of rice during eREX processing were investigated.Results showed that,the introduction of exogenous thermostable a-amylase induced the right shift of the peak of E(t)function curves where the peak became lower and wider with an obvious trailing.Furthermore,the mean residence time(MRT)was increased and the extent of mixing(represented by D/uL)was enhanced.When ?-amylase showed a high activity during extrusion,MRT(73.1 s-269.7 s)was increased as the increase of feed rate(FR)and SS that was fitted well by a double-reciprocal model of FR and SS;D/uL(0.059-0.097)was enhanced as the decrease of FR and the increase of SS that was fitted well by an exponentiated exponential model of special load ratio(i.e.,FR/SS).Standardized F(?)function curves exhibited that the trajectory of rice matrix during eREX processing tended to a perfect mixing flow.Besides,it was demonstrated that the Yeh-Jaw simplified model(or Wolf-Resnick model)with two changeable parameters could describe the flow pattern of eREX rice accurately(R2=0.9989,RSS=0.0040).The eREX method was compared to traditional steam-cooking,traditional extrusion and self-designed traditional/enzymatic autoclaving methods as the pretreatments of CRW brewing,which demonstrated a synergism of the extrusion fields and the action of exogenous thermostable a-amylase on starchy matrix.Results showed that,the properties of eREX rice(i.e.,high water solubility index(WSI);high extent of gelatinizaiton(GE);low water absorption index(WAI);low viscosity;low phenolics loss)were significantly different than those of other treated rice.The liquefaction and degradation of starch in eREX rice led to a higher ethanol yield(EY,36.72%),fermentation efficiency(FE,91.97%),total amino acid(6 g/L),soluble solid content(9.71%)and TPC(597.3 mg GAE/L)than those of traditional steam-cooked rice.Besides,eREX wine exhibited higher antioxidant capacities(DPPH?ABTS?RC?FRAP)in vitro.The dynamic analyses of enzyme-induced starch rapid gelatinization and phenolics slow destruction were determined.When the extrusion environment became more severe,the reaction constants of starch gelatinization(kG,9.08×10-3 s-1-2.08×10-2 s-1)and phenolics destruction(kp,4.74×10-3 s-1-1.54×10-2 s-1)exhibited a positive relationship during traditional extrusion processing,however,it turned to a negative relationship between the kG(2.92×10-2 s-1-7.69×10-2 s-1)and kp(1.58×10-3 s-1-5.26×10-3 s-1)of eREX.When a-amylase showed ahigh activity during extrusion,the activation energy(E)of starch gelatinization was decreased from 32.01 kJ/mol to 0.24 kJ/mol,while the E of total phenolics was increased from 37.49kJ/mol to 70.30 kJ/mol.Thermostable a-amylase not only attacks on starch substrate and increases the degradation rate of starch directly,but also decreases the destruction rate of phenolic compounds as non-substrates indirectly.In that sense,there are two reasons for the pehnomenon of "pheolics retention" in eREX:on one hand,a speical effect of cushioning and protection on phenolics may be obtained,probably due to the rapidly gelatinized starch macromolecules embedding the small molecules of phenolics softly;on the other hand,the milder extruison enviroment with extremely low torque,SME,pressure and shear stress can explain the slower degradation of phenolic compounds.The flavor composition of CRW fermented from eREX rice was studied via head space and solid phase microextraction(HS-SPME)and gas chromatography-mass spectrum(GC-MS).Due to the particularity of eREX wine,the operating conditions of HS-SPME were optimized as follows:alcohol degree,12%v/v;extraction temperature 50?;extraction time,45 min.Under these conditions,a total of 66 volatile compounds were identified in eREX wine.The formation and variation tendency of the volatiles in the fermentation processing of eREX rice were similar to that of traditional steam-cooked rice.However,their concentration levels were significantly different where there are more alcohols(especially higher alcohols),lactones and phenols but less acids,esters,ketones,aldehydes,aromatic compounds,furans,sulfides and nitrogen-containing compounds in eREX wine.Thus,the appearance,aroma,taste and style of eREX wine tend to be that of fresh type CRW.PCA analysis showed that eREX wine could be significantly distinguished from commercial wines due its characteristic flavor compounds that included(but not limited to)2-heptanol,1-octen-3-ol,ethyl 4-hydroxybenzoate,methylpentyl 2-propenoate,y-hexalactone,and 4-vinylguaiacol.