Comparison of drying methods on drying efficiency and physicochemical quality of okra (Abelmoschus esculentus) cultivated in China

Okra (Abelmoschus esculentus) is difficult to preserve after harvest. If not properly dried, because of its high moisture content, which will reduce the product value of okra and the value of nutrition. In this study, the effects of vacuum freeze-drying (VFD), ultrasonic pretreatment assisted vacuum drying (UPVD), and ultrasonic combined vacuum drying (UCVD) are compared and analyzed in terms of the drying characteristics effects and the physicochemical qualities of okra were studied. Compared with the drying curve and drying rate curve of okra dried by VFD, the drying time of okra dried by UCVD and UPVD was significantly reduced by 53.3% and 20.0%, respectively, and the total energy consumption of okra dried by UCVD and UPVD was saved by 21.8% and18.9%, respectively. The samples of UCVD had a higher b (yellowness), which keeps the original green color of Okra. The shrinkage ratio of samples dried by UPVD and UCVD had a significant difference (p < .05), and was 27.0% and 26.1%, respectively higher than that of samples dried by VFD. The rehydration curve of VFD sample was higher than that of other samples at 25 degrees C, and was the same as that of UCVD samples for 12 min at 100 degrees C. The total phenolic content of okra sample dried by UCVD was 7.7 +/- 0.14 mg/g, higher than others samples. Since polyphenols have good antioxidant activity, the ABTS radical-scavenging ability of UCVD samples was slightly higher than the other two samples, and the FRAP value of UCVD samples was significantly (p < .05) higher than the other two samples. SEM images of UCVD samples further confirmed the channeling effect caused by ultrasonic irradiation, which also confirmed the reliability of the above data in structure. Considering cost-effectiveness, practicability and scale-up, UCVD is a promising technology in the production of dried Okra. Practical application Ultrasonic combined vacuum drying (UCVD) is a novel technology for the food industry to reduce the energy consumption and improve food quality. Okra drying with UCVD can be successfully described by the Logarithmic model. The UCVD can significantly shorten the drying time and reduce the energy consumption of vegetables compared to the vacuum freeze drying. The products dried by UCVD retain various functional components of raw materials. Because of potential health, economic, and ecological benefits for the society, the UCVD is a promising technology in the production of Okra