青花椒真空脉动干燥特性及干燥品质工艺优化

Drying characteristics and quality optimization of green prickly ashes during vacuum pulsed drying

为提升青花椒的干燥品质,减少其色泽褐变和风味物质流失等问题,该研究采用真空脉动干燥技术加工青花椒,并以热风干燥试验为对照组,研究了不同干燥温度、真空保持时间和常压保持时间对青花椒干燥特性及其品质的影响。在单因素试验基础上进行Box-Behnken中心组合试验设计,以青花椒的平均干燥速率、挥发油、酰胺含量、色差、开口率5个指标进行响应面优化分析。试验结果表明,Weibull模型可精确拟合青花椒真空脉动干燥曲线(R~2>0.99)。干燥温度升高可在一定程度上提高青花椒的干燥效率和开口率,减少褐变和挥发油损失,同时酰胺类含量随干燥温度上升而有所下降。根据响应面试验结果,各因素对青花椒干燥综合评分的影响效果由大到小顺序为:干燥温度、真空保持时间、常压保持时间。优化的工艺参数为真空脉动干燥温度61.4℃、真空保持时间5 min、常压保持时间5 min,综合评分值达8.06,验证试验结果偏差仅为2.6%。研究结果为青花椒真空脉动干燥应用提供参考。

Green prickly ash is one of the main flavoring spices in Chinese food,with a strong numb taste and medicinal effects,such as antipruritic,vasodilation,and lowering blood pressure.The initial moisture content of green prickly ash is up to 66%-70%(w.b.),easy to cause browning reaction and mildew during storage and transportation.Drying has also been a necessary step before deep processing of green prickly ash,in order to ensure the quality of products while prolonging the shelf life.A pulsed vacuum drying can keep the material in a circulating state of alternating vacuum and atmospheric pressure,where the microscopic pores inside the material are continuously squeezed or expanded to form micro-channels,which significantly improves the moisture migration rate for high drying efficiency.The vacuum environment is also beneficial to reducing the browning reaction and the loss of flavor components during drying.In this study,an investigation was made to clarify the effects of drying temperature(55,60,65 and 70℃),holding time of vacuum(5,10,15,and 20 min),and holding time of atmospheric pressure(1,3,5,7 min)on the drying characteristics and quality attributes of green prickly ash under a pulsed vacuum drying.The hot air drying was treated as the controlled group.A Weibull model was used to simulate the drying curves of green prickly ash.A single factor experiment was performed on the Box-Behnken platform.A response surface optimization was conducted,where five indicators were included of the average drying rate,color,aperture opening ratio,volatile oil and amide content of green pepper.The results showed that the Weibull model accurately simulated the vacuum pulsating drying.The pulsed vacuum drying of green prickly ash behaved a brief rise in the early stage,and then a slow-down drying stage.Both drying temperature and holding time of atmospheric pressure posed a significant effect on the drying rate of green prickly ash(P<0.05).Specifically,the drying rate was higher,as the holding time was shorter at atmospheric pressure.The drying rate,color and aperture opening ratio were improved,while the browning reaction and the loss of volatile oil content were reduced,as the drying temperature increased.Meanwhile,the amide content decreased with the rise of drying temperature.Once the temperature exceeded 70°C,a significant downward trend occurred in the quality indicators of green prickly ash.The influencing factors in green pepper drying were ranked as follows:drying temperature,vacuum holding time,atmospheric pressure holding time.The optimized processing parameters of pulsed vacuum drying were fixed at the drying temperature of 61.4℃,the vacuum holding time of 5 min,and the atmospheric pressure holding time of 5 min.The comprehensive score was up to the maximum of 8.06 in the response surface model under this condition.Three verification tests were carried out to take the average value.The relative deviation between the test and predicted value was only 2.6%in the response surface model,indicating that the optimization data was reliable.A verification test was determined as the average drying rate of 0.81 g/(g·min),ΔE value of 6.31,aperture opening ratio of 92.3%,volatile oil content of 0.72 mL/10 g,and amide content of 27.65 mg/g.The optimal processing parameters of green prickly ash can provide a sound reference for the practical application of similar materials under pulsed vacuum drying.