Drying characteristics and quality attributes of kenaf leaves

Kenaf (Hibiscus cannabinus L.) is rich in bioactive components, natural antioxidants, total phenolic content, and structural properties, making it potentially valuable for the pharmaceutical and cosmeceutical sectors. The most common method for extending the shelf life of kenaf leaves is through drying treatment, which helps preserve their colour. However, there is a lack of specific studies addressing the preservation of kenaf leaves for further use and a scarcity of reliable references depicting the most effective mathematical model to describe kenaf behaviour. Therefore, this study aimed to analyse kenaf leaf drying characteristics, identify the best-fitting model, and assess the impact of drying temperature on their quality properties. The experiment was conducted using a hot air dryer, and the samples were dried at 30, 50, 70, and 90°C. The Folin-Ciocalteu reagent method was used to measure total phenolic content (TPC), and total antioxidant activity (TAA) was assessed using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) method. To identify the best-fitting model, five mathematical models were tested: Page, Henderson and Pabis, Newton (Lewis), Modified Page, and Two-term models. Among the models tested, the Two-term model best suited the drying characteristics of kenaf leaves. Besides, the findings showed that the best drying temperatures for maintaining the colour of kenaf leaves were found at 50 and 70°C. Finally, dried leaves showed an increment in TAA at 70°C (96.70±0.03%) and 90°C (96.43±0.27%), as well as an increment in TPC at 50°C (57.59±1.47 ppm), 70°C (55.78±4.74 ppm), and 90°C (62.49±6.39 ppm). For future studies, delving deeper into the mechanisms underlying the observed changes in TAA and TPC of kenaf leaves during the drying process would be beneficial. Investigating the specific compounds responsible for these changes and their potential health benefits could provide valuable insights for pharmaceutical and cosmeceutical applications.