Abstract
The utilisation of roselle (Hibiscus sabdariffa L.) calyx as a source of anthocyanins has been explored through intensive investigations. Due to its perishable property, the transformation of roselle calyces into dried extract without reducing their quality is highly challenging. The aim of this work was to study the effect of air temperatures and relative humidity on the kinetics and product quality during drying of roselle extract foamed with ovalbumin and glycerol monostearate (GMS). The results showed that foam mat drying increased the drying rate significantly and retained the antioxidant activity and colour of roselle calyces extract. Shorter drying time was achieved when higher air temperature and/or lower relative humidity was used. Foam mat drying produced dried brilliant red roselle calyces extract with better antioxidant activity and colour qualities when compared with nonfoam mat drying. The results showed the potential for retaining the roselle calyces extract quality under suggested drying conditions.
Highlights
Roselle (Hibiscus sabdariffa L.) is commercially cultivated in some countries like India, Indonesia, Malaysia, Sudan, Egypt, and Mexico [1]
This study aimed to study the effect of air temperatures and relative humidity on the kinetics and product quality during foam drying of roselle extract
The roselle extract was dried with foaming agent and without foaming agent at 40∘C and 60∘C
Summary
Roselle (Hibiscus sabdariffa L.) is commercially cultivated in some countries like India, Indonesia, Malaysia, Sudan, Egypt, and Mexico [1]. The roselle calyx is brilliant red in colour due to the existence of anthocyanins, such as cyanidin3-sambubioside, cyanidin-3-glucoside, and delphinidin-3glucoside [2]. The relationship between antioxidant activity and anthocyanin of roselle calyx has been reported in the literatures [5, 6]. The total anthocyanin content of roselle calyces is 2.52 g/100 g expressed as delphinidin-3-glucoside [7]. Wang et al observed that anthocyanins have many times more antioxidant activity than ascorbic acid [8]. The antioxidant activity of roselle extract is predominantly contributed by anthocyanins. Mazza and Miniati observed that thermal degradation of anthocyanin of roselle extract was fast at temperatures above 100∘C [10]
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