Effect Of Pretreatments On The Hot Air Drying Characteristics And Quality Of Star Anise

Fresh star anise has high moisture content and is prone to mold growth during storage,requiring timely drying to extend its storage period.The traditional drying method of star anise is usually dried after hot scalding,which has a long drying cycle and excessive dependence on weather.Although mechanical drying can improve the drying rate,the product quality is difficult to control and the loss of flavor substance is serious.Therefore,innovating the drying method of star anise is of great significance to improve the quality of star anise products.In this paper,three methods of freeze-thaw,lye and ultra-high pressure were used to pretreat raw materials before anise drying,study its influence on the drying characteristics and quality of anise,and optimize the drying process parameters of anise.The main research results are as follows:(1)Single factor tests were carried out on freeze-thaw,lye and ultra-high pressure pretreatment respectively.Using the drying time,color,shrinkage rate and volatile oil content of anise as indexes,the optimized process parameters were frozen at-8℃for 12 h,4%Na OH for 60 s,and 100 MPa for 300 s under ultra-high pressure respectively.The drying time of the untreated group was reduced by 25%,21.43%and 21.43%.Compared with the traditional scalding treatment,the three kinds of pretreatment could improve the product shrinkage and increase the content of volatile oil.Compared with the other two pretreatment methods,the product with freeze-thaw pretreatment had a brighter color,and the content of volatile oil was19.34%higher than that of the traditional hot treatment(control),and all the indexes were better than other pretreatment methods.(2)The volatile oil components of different pretreatment groups and scalding groups were analyzed.There were 14 volatile components in scalding group,18 in lye group,14 in ultra-high pressure treatment group,19 in untreated group and freeze-thaw group.The content of trans anisole in lye group and untreated group was 90.36%and 94.96%and96.16%in the freeze-thaw group.As a supplement to GC-MS,the electronic nose showed the highest response values in the W1W(sulfide and terpene compounds)and W2W(organic sulfide and aromatic compounds)sensors in the freeze-thaw group.Finally,freeze-thaw treatment was selected for constant temperature drying process.(3)Single factor and response surface method were used to optimize the freeze-constant temperature drying anise process.With-8℃freeze pretreatment time(8～14 h),drying temperature(65～85℃)and loading capacity(3.2～6.4 kg/m~2)as factors,energy consumption and volatile oil content as the main response,the optimal freeze-constant temperature drying process of anise was determined as follows:Under the conditions of-8℃,freezing time 13 h,drying temperature 76℃and loading capacity 4.8 kg/m~2,the energy consumption is 4.07k W·h/kg,and the volatile oil content is 9.22%.