Comparative Impact of Drying Techniques on Physicochemical, Proximate Compositions, and Antioxidant Properties of Roselle Calyces (Hibiscus sabdariffa L.) for Sustainable Agriculture

Abstract

This study evaluated the impact of different drying methods, freeze drying (-120°C), food dehydrator (65°C), and oven drying (65°C) on the quality of roselle calyces to extend their shelf life and availability, considering implications for sustainable agriculture. Key quality parameters assessed included physicochemical properties, proximate composition, and antioxidant activity. Freeze drying produced the highest quality results, closely resembling fresh roselle in several aspects. The colour analysis showed freeze-dried samples had the highest chroma values with L* (35.97), a* (31.86), and b* (17.3), indicating vibrant colour retention. The pH of freeze-dried roselle was the lowest at 2.74, indicating a desirable balance of acidity. In terms of proximate analysis, freeze-dried roselle had the lowest moisture content (7.55%) among dried samples, which is crucial for extended shelf life. It also had the highest ash content (8.06%), protein content (11.06%), and crude fat content (2.51%), highlighting its superior nutrient retention compared to other drying methods. Oven-dried roselle showed higher ash (8.69%) and fat (1.44%) contents but had a lower moisture content (6.36%) than dehydrator-dried roselle, which had the highest moisture content (8.30%) and the lowest ash (5.75%) and protein (5.86%) contents. Antioxidant analysis revealed that freeze drying preserved the highest levels of antioxidant activity (14.22% RSA), total phenolic content (12.3 mg GAE/mL), total flavonoid content (44.9 mg QE/mL), and ascorbic acid content (22.267 mg/100 g). These findings highlight the effectiveness of freeze-drying in maintaining the bioactive compounds and overall nutritional quality, which is crucial for sustainability agriculture practices aimed at preserving crop value and extending product availability.