| Kudzu root(the follows were abbreviated as KR)is the tuber one of the Pueraria montana var.lobata perennial grassy vine.KR,a medical and edible plant,riches in a variety of minerals,puerarin,soy glycosides and other nutritional and health components,has the effect of diastolic cardiovascular vessels,hypoglycemia,antioxidant,alcohol degradation and and liver protection,improve immunity,etc.It has great potential for development and.application.However,the status quo of the production of KR powder is that,the main nutritional and functional components contained in the KR go into the upper separation liquid,and the separation liquid is directly discarded in the process of KR starch separation and preparation.This mainstream production method not only causes the waste of the nutritional and functional components of the KR,but also has a negative impact on the environment.The emergence of a whole powder has largely solved the above-mentioned problems,but it brings new problems,namely,after retaining almost all the nutritional and functional components of KR,its reconstituability is greatly reduced,and it is not easy to disperse,and caking phenomenon is serious.Based on this background,this paper studied the cleaning and color protection process of KR(a cultivated category named as "Xiangge No.1")and a wild category of KR as the test materials,explored the effect of different drying methods on the quality of the dried products of the separation solution,investigated the best formulation of compound powder of KR,and analyzed and compared the difference in quality among the compound powder of KR,raw whole powder of KR(the follows were abbreviated as RWP-KR)and heat-treated whole powder of KR(the follows were abbreviated as HTWP-KR).The aim of this paper was to provide a reference for the production and processing of high-quality KR powder that takes into account the nutritional value,reconstituability,and sensory quality.The main research contents were as follows:1 The pretreatment technology of KR was studied.Firstly,the ultrasonic cleaning process of KR was studied.With cleanliness as the index,the ultrasonic treatment conditions were set at 40 KHz and 50 W.The study confirmed that ultrasonic cleaning has good effect,and ultrasonic cleaning could reach clean purpose in 12 min.Next,the color protection process of powdered KR was studied.Vc and EDTA-2Na were identified as the best color preservatives for KR through screening,using color and browning as indicators.The optimal process conditions for color protection of powdered KR determined by single-factor test combined with response surface method optimization also using color and browning degree as indicators were as follows:the concentration of compound color protector was EDTA-2Na 0.63 g/100mL+Vc 0.63 g/100mL,the cooking time was 15.50 min,and the thickness of slices was 4.50 mm.Under such conditions,the L value,a value,b value,and browning degree were 66.81,2.91,14.23,and 0.498,respectively.The color of KR was good and the browning was light after the color protection treatment.2 The drying process of the separated liquid produced by the processing of powdered KR was studied.The advantages and disadvantages of microwave,spray and vacuum freeze drying were compared in terms of powder collection rate,color,total isoflavone content and drying energy consumption.The powder collection rate of vacuum freeze drying was significantly higher than that of microwave drying and spray drying(P<0.05).The dried product of spray drying,showed white color,was the closest to the color of the separation liquid,and was significantly better than those of the other two drying methods(P<0.05).The difference in total isoflavone content between spray drying(inlet air temperature 180℃)and vacuum freeze drying was not significant(P>0.05).Taken the quality and energy consumption of the dried isolate into consideration,spray drying(inlet air temperature of 180℃)was a suitable drying method.3 The compounding ratio of KR compounding powder was studied.By combining the single-factor test with the response surface method optimization,it was found that the optimum ratio of starch powder of KR 68.30%to dried separation liquid 15.22%,and to whole powder of wild KR 16.28%.Under this condition,the reconstituability score and sensory score of compounding powder were 92.15 and 91.13 respectively.The powder was light yellow,homogeneous and fine,with the best brewing effect,harmonious flavor and the unique fragrance of KR.4 The differences in quality among the compound powder of KR,RWP-KR,and HTWP-KR were compared and analyzed.In terms of nutritional composition,the fat and protein contents of RWP-KR and HTWP-KR were significantly higher than those of the compounded powder of KR(P<0.05),but the contents of dietary fiber and total isoflavones were significantly lower than those of the compounded powder of KR(P<0.05).In terms of physical and chemical properties,the compound powder of KR had the characteristics of larger internal space gaps and loose,and its fluidity and filler properties were lower than those of the HTWP-KR,but significantly better than those of the RWP-KR(P<0.05).Higher content of dietary fiber and smaller particle size of the dried material increased the contact area among the particles and water and oil of the compound powder of KR,which made its water holding capacity,oil holding capacity,and freeze-thaw stability higher than those of the RWP-KR,and HTWP-KR(P<0.05).The dispersibility of HTWP-KR was higher than that of compound powder of KR,but the solubility and reconstituability were lower than that of the former(P<0.01).In terms of antioxidant activity,all three kinds of KR powder showed the scavenging ability against DPPH·,ABTS+·,and ·OH,also total reducing abillity.The compound powder of KR was exhibited the strongest antioxidant ability(P<0.05),while difference between the RWP-KR and the HTWP-KR was not significant(P>0.05).The overall quality of compound powder of KR was the best among the three kinds of powder. |
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