气体射流冲击干燥对脱盐海参理化特性和微观结构的影响

Effects of air impingement drying on the physicochemical characteristics and microstructure of desalted sea cucumber

为改善脱盐海参干燥时间长、干制品品质差的问题,该研究将气体射流冲击干燥(air impingement drying, AID)技术应用于脱盐海参干燥,研究了干燥温度(50、60和70℃)和气流速度(4、6和8 m/s)对脱盐海参干燥速率及干制品水分分布及状态、微观结构、硬度和皂苷含量的影响,并与热风干燥(hot air drying, HAD)进行对比。结果表明,随着干燥温度的增加,脱盐海参的干燥速率增加。AID不同干燥温度下脱盐海参的干燥时间比HAD 60℃的海参干燥时间缩短了6.67%~33.33%。温度为60℃时,风速对脱盐海参的干燥时间影响不显著(P>0.05)。微观结构分析表明,温度升高有利于增加物料表面的多孔结构,相同条件下AID海参样品的表面比HAD海参具有更多更大的多孔结构,使得AID海参干燥速率快于HAD。但随着风速的增加,脱盐海参表面因发生结壳现象阻止了形变,使得干海参孔洞结构变小,干燥速率降低。与HAD相比,AID海参的不易流动水弛豫时间向短弛豫时间移动更快,且峰幅度显著降低;干燥相同时间时(6 h),AID海参的质子密度信号比HAD减少更多,表明AID海参的水分迁移速率快于HAD的海参。随着AID温度和风速的升高,干海参的硬度呈先增加后减小的趋势。AID海参皂苷含量随着温度的升高而升高。AID海参的多孔结构不仅加速了水分迁移,而且利于营养成分渗出,提高了营养成分含量,相同条件下,AID海参的皂苷含量比HAD的海参增加了50.00%。综合考虑干燥效率和品质,温度为70℃,风速为6 m/s为脱盐海参AID的较好条件。研究结果有助于阐明AID提高脱盐海参干燥速率和营养成分保留率的机理,为生产高品质干海参提供理论依据和技术参考。

Here air impingement drying(AID)was introduced to dry the desalted sea cucumber for less drying time and better quality of dried products.A systematic investigation was implemented to clarify the impacts of AID temperature(50,60,and 70℃)and air velocity(4,6,and 8 m/s)on the moisture distribution,moisture state,microstructure,hardness,and saponin content of desalted sea cucumber.Conventional hot air drying(HAD)was also taken as a control.The results revealed that the drying rate of desalted sea cucumbers increased significantly,as the drying temperature increased.The drying time of desalted sea cucumber was also reduced by 6.67%-33.33%at 6 m/s air velocity and various AID temperatures,compared with the HAD at 60°C.The air velocity shared an insignificant effect on the drying time of desalted sea cucumbers(P>0.05)at the same temperature(60℃),particularly for the extended drying time(12-13 h)with the increased air velocity(4-8 m/s).The microstructure showed that the high AID temperature was beneficial to increase the porous structure of the material surface,leading to accelerated water migration.More and larger porous structures were observed on the surface of AID sea cucumber samples under the same conditions(the temperature was 60℃and the air velocity was 6 m/s),compared with the HAD ones.As such,the AID drying rate was accelerated as well.However,the high air velocity was used to prevent the surface deformation(such as crusting)of desalted sea cucumber,thus reducing the structure porosity,which hindered the water migration and lowered the drying rate.The relaxation time of immobilized water in the AID sea cucumbers moved faster toward the short relaxation time,and then the peak amplitude decreased significantly,compared with the HAD.The low freedom of water molecules also led to a decrease in drying rate,with the extension of drying time.There was a weaker signal of proton density in the AID sea cucumbers.The water content was lower under the same conditions(drying time was 6 h).The water migration rate of AID sea cucumbers was higher than that of HAD,indicating that the AID was beneficial in shortening the drying time.The hardness of dried sea cucumber increased first and then decreased,with the increase in AID temperature and air velocity.The maximum hardness(494.25 N)was recorded at an AID temperature of 60℃and 6 m/s air velocity.The saponin content(1.36-1.79μg/g dry matter)of AID sea cucumbers increased with the increase in temperature,while there was no significant change in the air velocity.The saponin content of AID sea cucumber samples increased by 50%under the same conditions,compared with HAD.The temperature of 70℃and the air velocity of 6 m/s were the better conditions for the AID sea cucumbers,in terms of drying efficiency and quality.The AID can be expected to improve the drying efficiency and ingredient retention rate of desalted sea cucumbers.The finding can provide theoretical reference and technical support for better drying quality.