| Barley-beer brewing is a new green,energy-saving and low-polluting brewing technology,which avoids the time-and energy-consuming malting process in the traditional brewing.However,the unmalted barley has hard tissues,compact cells and limited leach of soluble sugar,which greatly reduces the utilization rate of raw materials.Enzyme-extrusion technology has unique advantages in gelatinization and liquefaction of starch-based materials,which can effectively improve the utilization rate of raw materials,shorten the fermentation time and endue the fermented products with unique flavor.In this project,enzyme-extrusion is used as a pretreatment method for gelatinization and liquefaction of barley flour,and its performance in the saccharification process is inferred by the thermal modification effect,and the reason why enzyme-extrusion exacerbates filtration blocking is investigated and verified.It provides a theoretical basis for the application of enzyme-extruded barley flour in barley beer brewing.Firstly,the process design and optimization of enzymatic extrusion of barley flour were carried out,and the gelatinization degree and reducing sugar content were regarded as response indicators.The enzymatic extrusion parameters were optimized by the single factor experiment and response surface methodology(RSM),and the optimized conditions were determined as follows: the barrel temperature,96?;the screw speed,150 r/min;the moisture content,55%;enzyme content,0.096%.Under the condition,the gelatinization degree and reducing sugar content of enzymatic extrudates could reach 96.78% and 15.98%,respectively.Secondly,the effects of enzyme-extrusion and steam-cooking on the physicochemical properties of barley flour were studied.The enzyme-extrudates(EES)had the lowest swelling power(173.62%),the highest water-solubility index(58.25%)and bulk density(1.28 g/m L).The gelatinization degree of EES was the highest,and the enthalpy of gelatinization was not detected by the differential scanning calorimeter(DSC).The rapid visco analyzer(RVA)showed that heat-treatments significantly reduced the viscosity of barley flour,and the steamcooking reduced the peak viscosity by 57.14%,and the enzyme-extrusion reduced by 95.88%,which indicated that enzymatic extrusion resulted in almost complete gelatinization of barley starch.X-ray diffraction(XRD)and Fourier transform infrared spectroscopy(FTIR)showed that destruction of the long-and short-range order of EES was the highest.The results of high phase liquid chromatography(HPLC)showed that the enzyme-extrusion caused the highest degradation of starch,and a large number of small molecular components were formed.Scanning electron microscopy(SEM)showed that the structure of EES was destroyed,and the surface was rough with a lot of holes and pits.The results of laser confocal microscopy(CLSM)showed that the starch and protein were aggregated after heat treatments,and the effect of enzyme extrusion was the most significant.Then,the saccharification operation of barley flour with different heat treatments was carried out,and the reason of the filtration blocking in the mashing process aggravated by enzyme-extrusion was investigated.Compared with steam-cooking,the filter paper residue of the mashing derived from EES was compact plate,and the filter hole was completely blocked.After centrifugation,the precipitation of EES appeared obvious stratification,the upper layer was white sticky gel-like aggregates(WS),and the lower layer was black loose lumps(LS).The dry and wet particle sizes of WS and LS were measured by Laser particle size analyzer.The results showed that the value of D90 of WS was significantly reduced after dissolved in water,and nearly 90% of WS would disperse into fine particles,which could easily cause blocking.SEM images of WS and LS showed that WS was tighter,which was similar to the state of filter paper residue of mashing derived from EES.The determination of chemical composition of WS and LS was showed that the contents of ?-glucan,starch and protein in WS were significantly higher than that in LS.The optimized results of filtration blockage showed that the filtering performance of the EES was improved more significantly by the removal of blockage factors by the specific addition of enzymes.The wort obtained the highest leaching rate and fermentable sugar,and the amino acid composition of wort was more advantageous.Finally,the physicochemical parameters and flavor characteristics of the final beer were determined.The results showed that the beer obtained from enzymatic extrudate(EES-beer)had the highest alcohol content(5.08%vol),mass fraction of original wort(10.92 °P)and fermentation degree(69.53%).The volatile flavor compounds were determined by headspace solid-phase microextraction(HS-SPEM)and gas chromatography-mass spectrometry(GCMS).A total of 77 volatile compounds were detected in the four kinds of beers.Among them,40 volatile flavor compounds were detected in the commercial beer,including 6 alcohols,4acids,24 esters,3 olefins and 3 other compounds.43 kinds of volatile flavor compounds were detected in RAW-beer(fermented from raw barley flour),including 7 alcohols,4 acids,25 esters,4 olefins and 3 other compounds.47 kinds of volatile flavor compounds were detected in EESbeer,including 8 alcohols,5 acids,27 esters,4 olefins and 5 other compounds;42 volatile flavor compounds were detected in SCS-beer(fermented from steam-cooked barley flour),including5 alcohols,2 acids,27 esters,6 olefins and 2 other compounds.The results of rapid gas phase electronic nose(GC-O)and sensory evaluation showed that EES-beer had a more similar flavor to commercial beer,and the overall acceptability was higher.In summary,by comparing the results of thermal modification of barley flour by enzymeextrusion and steam-cooking,the advantages of enzyme-extrusion technology in improving the leaching rate of mashing were clarified,and explored the reasons why the enzyme-extrusion exacerbated the filtration blocking.Through targeted to remove blocking factor to improve the defects,the quality of EES-beer was higher.This study could provide a new solution and theoretical support for the prominent problems existing in barley-beer brewing. |
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