Abstract
Radio frequency (RF) drying is a rapid dehydration technique that reduces water activity and extends the shelf life of agricultural products. In this study, the drying characteristics of jujube during HARF and hot air (HA) were investigated, and quality analyses, such as color, vitamin C (VC) and total flavonoid content (TFC), of jujube were performed. The drying curves revealed that the drying time used to reduce the moisture content from 81.7 to 6.0% on a dry basis was 360 and 1320 min using HARF drying and hot air (HA) drying, respectively. The logarithmic model was the best to describe the HARF drying process with R 2, RMSE and SSE values of 0.998, 0.00508 and 0.000306, respectively. Quality analysis demonstrated significant differences in color, VC content and total flavonoid content between the HARF and HA treatments during the drying process and storage periods (P > 0.5), and the HARF-dried jujube product performed much better than that dried by HA. Compared with HA drying, HARF drying showed a shorter drying time, higher drying efficiency and better product quality, indicating that HARF drying was a more promising drying method for jujube with acceptable product quality.
Highlights
As a member of the Rhamnaceae family, Chinese jujube (Zizyphus jujube Mill.) is widely distributed in the subtropical and tropical regions of southern Asia, and China is the world's largest producer and exporter of jujubes (Song et al, 2020)
When hot air (50 °C) was applied, an electrode of 20 cm was demonstrated to be suitable for jujube drying based on the desirable hearting rate and acceptable product quality and stable sample temperatures
This study found that HARF treatments could significantly reduce the drying process of jujube compared to hot air (HA)-only drying
Summary
As a member of the Rhamnaceae family, Chinese jujube (Zizyphus jujube Mill.) is widely distributed in the subtropical and tropical regions of southern Asia, and China is the world's largest producer and exporter of jujubes (Song et al, 2020). Given its richness in various nutrients, such as sugars, polysaccharides, phenolics, proteins, organic acids, polyphenols and vitamin C (Wang et al, 2021), jujube is widely loved worldwide. As freshly harvested jujube has a high moisture content and high sugar content, it cannot be stored for more than ten days under ambient conditions (Song et al, 2020). After harvesting, the moisture content (MC) of fresh jujube must be dried to 6.0% for long-term storage (Moradinezhad & Dorostkar, 2021). It is necessary and important to explore new jujube preservation methods to extend its shelf life
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