Abstract
In recent years, the consumption of red beetroots has increased significantly due to its good taste, high nutritional value and abundant active compounds. Red beetroot is prone to spoilage due to its high moisture content, making it perishable. Vacuum microwave drying is a gentle drying method by inducing fast water evaporation from food products at low temperature, which can improves the product quality. The objective of this study was to investigate the effects of vacuum microwave drying parameters, including microwave power (500, 1000, and 1500 W) and vacuum degree (50, 70, and 90 KPa), on the physicochemical properties (drying time, rehydration ratio, color change, and contents of betalain and total phenolic) of red beetroots. The results showed that microwave power and vacuum degree had significant effects on the physicochemical properties of red beetroots. All the red beetroots after vacuum microwave drying had higher lightness (L*), lower redness (a*) and yellowness (b*) than that of fresh red beetroots. The drying time, rehydration ratio, betacyanin content and betaxanthin content of red beetroots decreased significantly with the increase of microwave power (P < 0.05), while the rehydration ratio, color parameters (a*, b*, and chroma values), betacyanin content and betaxanthin content of red beetroots significantly increased with the increase of vacuum degree (P < 0.05). Compared with other microwave powers, the red beetroots dried at 500 W showed longer drying time, higher rehydration ratio, more yellowish hue, and higher contents of betacyanin and betaxanthin. The lowest values of total color difference (∆E) and hue angle (H°) of dried red beetroots were obtained at microwave power of 1500 W. The dried red beetroots obtained at 90 KPa had the shortest drying time, the highest rehydration ratio, the best color, and the highest contents of betacyanin and betaxanthin. Meanwhile, the red beetroots dried at 50 KPa had the highest total phenolic content (12.47 ± 0.09 mg GAE/g). Based on the physicochemical properties of red beetroots, vacuum microwave drying at low microwave powers and high vacuum degree appears to be a suitable method for drying red beetroots.
Highlights
Material and MethodsDrying is an effective method for preserving the quality of vegetables and fruits and works by applying heat to remove moisture (Madhava Naidu et al, 2016), which plays a vital role in prolonging shelf life of fresh perishable foods, reducing packaging costs as well as reducing the weight of transportation (Jin et al, 2018)
In order to determine the influence of microwave power on the physicochemical properties of red beetroots, fresh red beetroots were dried at slice thickness of 2 mm and vacuum degree of 80 KPa, and microwave power ranged 500, 1000, and 1500 W
This study analyzes the influence of microwave power and vacuum degree on the physicochemical properties of red beetroots
Summary
Drying is an effective method for preserving the quality of vegetables and fruits and works by applying heat to remove moisture (Madhava Naidu et al, 2016), which plays a vital role in prolonging shelf life of fresh perishable foods, reducing packaging costs as well as reducing the weight of transportation (Jin et al, 2018). Vacuum microwave drying has been widely used in drying vegetables and fruits, which confirming to preserve color, ascorbic acid, total phenolic, and total flavonoids (Hu et al, 2006; Tekgül & Baysal, 2019; Zienska & Zielinska, 2019). Due to the high moisture content, fresh red beetroot is exposed to spoilage and normally dried to prevent the microbial growth, maintain the desirable quality and reduce the storage volume. Dried red beetroots can be consumed directly in the form of chips as a substitute of traditional snacks that are rich in fatty acids, or after easy preparation as a component of instant food (Krejcova et al, 2007)
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