红肉火龙果粉的发泡微波冷冻干燥制备与质量评价

    Preparation and quality evaluation of red dragon fruit (Hylocereus polyrhizus) powder by foam-mat microwave freeze-drying

    • 摘要: 制备浆果粉末产品是延长其货架期的有效手段。为降低干燥过程能耗和保留产品营养成分,该研究以平均含水率(87.03±1.26)%的新鲜红肉火龙果果浆为原料,采用冷冻干燥和喷雾干燥两种方法制备了火龙果粉末。以残余湿含量、色泽和典型生物活性成分甜菜红素、芦丁和总酚保留率为指标对产品质量进行了评价。用质量比为3%(w/w)的分离乳清蛋白和2.5%(w/w)的果胶为添加剂制备了未发泡和发泡2种样品,进行了传统和微波冷冻干燥试验。结果表明,使用石英底盘,在30 ˚C、20 Pa下,发泡样品比未发泡样品冷冻干燥时间缩短了39.06%;施加1 W微波功率时,未发泡和发泡样品微波冷冻干燥时间比无微波时分别缩短了18.75%和12.82%。用碳化硅底盘替代石英底盘,在30 ˚C、20 Pa和1 W下,发泡样品微波冷冻干燥时间比未发泡和发泡样品传统无微波冷冻干燥分别缩短了65.62%和43.59%。分别以5.5%(w/w)的分离乳清蛋白和15.6 %(w/w)的麦芽糊精为添加剂,进行了喷雾干燥试验。工艺参数为进风温度150 ˚C、出风温度85 ˚C、进料速度28 mL/min。冷冻干燥产品的甜菜红素、芦丁和总酚保留率分别在72%、84%和75%以上,而喷雾干燥产品的保留率显著降低。该研究采用的冷冻干燥方法能够大幅缩短干燥时间、提高产品质量,为浆果类粉末产品的制备提供工业解决方案。

       

      Abstract: Red dragon fruit (Hylocereus polyrhizus) is one type of berry fruit rich in nutrients and trace elements, particularly with the high food, health and medicine values. However, the dragon fruit can easily dewater and soften during transportation, resulting in quality degradation, or even decay and spoilage. Fresh dragon fruit can often be processed into dried cakes or powders, in order to extend the shelf life. Freeze-drying (FD) and Spray drying (SD) are commonly used to process berry fruits into powder products. This study aims to reduce the energy consumption of drying and retain the nutrients of the product. Fresh red dragon fruit pulp was taken as the raw material with (87.03±1.26) % of mean moisture content. Red dragon fruit powder was prepared using FD and SD. Product qualities were also evaluated, including residual moisture content, color, betacyanin content , rutin content , and total phenolic content retentions. With 3%(w/w) (mass ratio, the same below) of whey protein isolate (WPI) and 2.5%(w/w) of pectin (P) as the additives, the unfoamed and foamed frozen samples were prepared with the same initial mass and moisture content. Quartz and silicon carbide (SiC) were utilized as the supporting pads of samples for comparison. Traditional and microwave FD experiments of dragon fruit pulp were conducted in a lab-scale microwave FD apparatus. Results showed that the foamed sample was reduced by 39.06% of drying time, compared with the unfoamed one at 30 ˚C of radiation temperature and 20 Pa of chamber pressure with the quartz pad. When 1 W of microwave power was applied under the same operating conditions, drying times of unfoamed and foamed samples decreased by 18.75% and 12.82%, respectively, compared with the traditional FD without microwave heating. With the SiC pad instead of the quartz pad under 30 ˚C, 20 Pa and 1 W, the microwave FD time of the foamed sample was shortened by 65.62% and 43.59%, respectively, compared with traditional FD. SiC-assisted microwave FD of foamed material was achieved the simultaneous enhancement of mass and heat transfers. With 5.5%(w/w) of WPI or 15.6%(w/w) of maltodextrin (MD) as the carrier agent, SD experiments were conducted in a pilot-scale SD apparatus. Operating conditions were 150 ˚C of inlet air temperature, 85 ˚C of outlet air temperature and 28 mL/min of feed speed. The quality evaluation revealed that the FD products basically had no significant color differences, except for the product from microwave FD of the unfoamed material with the quartz pad. SD products exhibited light colors, compared with FD products. Betacyanin, rutin and total phenolic content retentions of FD products were all above 72%, 83% and 75%, but those of SD products were much lower. SEM images showed that the porous and tenuous skeletons were observed in the FD products from the foamed materials, which was beneficial to the vapor migration and bound water desorption. There was no impact of microwave heating on the pore structure of both unfoamed and foamed materials. SD products appeared as spherical particles with smooth surfaces. The drying time was significantly reduced to produce high-quality products. The FD can provide an industrial solution to prepare berry powders.

       

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