| Tuber of Apios fortunei(A.fortunei)is a precious Chinese traditional medicine,which is rich in starch and other basic nutritional components,and has both medicinal and edible values.Its related reserch and industry began to develop since the large-scale cultivation in Shanxian in recent years.At present,A.fortunei is mainly sold as fresh products,showing the weaknessses of the simple product form and the low added value.Considering the characteristics of A.fortunei,applying it to the process of fermenting yellow wine with potential health care effect may be a suitable method of producing value-added products.However,in the traditional yellow wine brewing process,the traditional material pretreatment method of soaking and cooking is time-consuming,inefficient,and the discharge of organic wastewater will cause great environmental pressure.Enzymatic extrusion is a new processing technology emerging in recent years.The special environment of high pressure and high shear in the extrusion chamber endows enzymes with higher catalytic efficiency.In theory,enzymatic extrusion is more efficient and thorough for the gelatinization and saccharification of raw materials than traditional steam cooking,traditional extrusion,or enzyme liquefaction methods.In addition,enzymatic extrusion has the advantages of green and continuous operation,which meets the needs of pretreatment of yellow wine fermentation.This project planned to apply enzymatic extrusion to the pretreatment of A.fortunei and studied the changes of physicochemical properties of A.fortunei starch.Also,the quality and flavor of A.fortunei yellow wine was analyzed,to evaluate whether it could expand the category of yellow wine products.For fermentation,it is important to study the changes of physicochemical properties of raw materials during thermal pretreatments.Firstly,three different thermal pretreatments,steam cooking,traditional extrusion,and enzymatic extrusion,were set up to brew A.fortunei yellow wine.The results showed that under the synergistic effect of enzymolysis and extrusion,in enzymatically extruded A.fortunei,the viscosity was the lowest(<10 c P)and the water solubility index was the highest(66.06%),which made the fermentation broth have good fluidity.The degree of gelatinization was the highest(99.09%),the crystallinity of starch was the lowest,indicating the most available starch for ethanol fermentation.Small molecular sugar obtained from the degraded starch by enzymatic extrusion ensured rapid reproduction of yeast in early fermentation stage.These favorable conditions ensured successful fermentation and helped achieve the highest fermentation efficiency(73.47%).In order to further explore the effects of enzymatic extrusion on the physicochemical properties of A.fortunei,different amounts of α-amylase were set for enzymatic extrusion.The results showed that the degradation degree of starch increased with the increase of α-amylase concentration,mainly manifested as the increasing water solubility index,and reducing sugar content,decreasing starch relative crystallinity and average starch molecular weight.The degree of gelatinization reached 97.6% when the amylase concentration was 1‰.When the amylase concentration reached over 1‰,the effect of increasing amylase concentration on starch degradation was limited,because at high enzyme level,the contact between enzyme and cylinder and screw was increased,resulting in the increase of enzyme inactivation rate.The combination of the enzyme with polyphenols and fibers leads to the loss of enzymatic hydrolysis activity.Also,the rapid substrate accumulation can enhance the negative feedback effect in enzymatic hydrolysis reaction and limit the improvement of enzymatic hydrolysis effect.The results indicated the optimum amylase concentration is about 1‰(0.12 KUN/g,starch dry basis).The effect of amylase concentration on fermentation efficiency was similar to that of the former.In addition,enzymatic extrusion improved the antioxidant capacity of A.fortunei,which improve the antioxidant capacity of A.fortunei yellow wine.Finally,response surface experiment was designed to optimize the parameters of enzymatic extrusion,and the optimal parameters were obtained as follows: end zone temperature 104.9℃,water content 50.06%,screw rotation speed 96 rpm,enzyme concentration 1.40‰,under which the maximum degree of gelatinization and reducing sugar content were 98.89% and 20.69%,respectively.Then,yellow wine was fermented from A.fortunei with the optimal extrusion conditions,and compared with those pretreated by steam cooking and traditional extrusion,and three kinds of commercial yellow rice wine to assess the quality and flavor.The results showed that A.fortunei yellow wine had higher total acid and lower total sugar compared with commercial yellow rice wine.The contents of non-sugar soluble solid content,γ-aminobutyric acid,and the antioxidant capacity of A.fortunei yellow wine were significantly higher than those in three commercial yellow rice wines,indicating that A.fortunei yellow wine with good nutrients.Sensory evaluation experiment showed that A.fortunei yellow wine pretreated by enzymatic extrusion had the better overall evaluation than those pretreated by steam cooking and traditional extrusion,and found A.fortunei with the unique fragrance of flowers and plants.E-nose results showed that there was significant difference in flavor between A.fortunei yellow wine and commercial rice wine.A total of 142 flavor substances were detected in six kinds of yellow wine products by GC-MS,and OAV analysis showed that,in key aroma components(OAV>1,odor activity value),compared with commercial yellow rice wine,A.fortunei yellow wine lacked ethyl isovalerate,methyl disulfide,dimethyl trisulfide and other substances,but included linalool,myrcene and other key aroma components that commercial wine did not include.The difference of key aroma components in different yellow wine products might be the reason for the difference in overall flavor.Through the comparative analysis with commercial yellow wine products,it could be concluded that the A.fortunei yellow wine made by enzymatic extrusion had good quality and unique aroma,indicating it had the potential to expand the category of yellow wine products. |
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