Enzyme-assisted extraction and characterization of red roselle calyx (Hibiscus sabdariffa L.) bioactives and their application in ice cream matrices

Abstract

Roselle calyx (Hibiscus sabdariffa Linn.) is widely recognized for its rich phenolic and anthocyanin contents, which contribute to its antioxidant properties, colour, and health-promoting benefits. However, conventional extraction methods often result in low yields and compound degradation. Therefore, this study explored enzyme-assisted extraction using amylase, pectinase, and cellulase individually to enhance the recovery of bioactive compounds from roselle calyces under varying enzyme concentrations and temperatures. The optimized condition obtained from response surface methodology revealed that cellulase (10%, 60 °C) produced the highest total phenolic (55.34 mg GAE/100 g) and flavonoid (193.05 mg CE/100 g) contents, pectinase (15%, 50 °C) yielded the highest anthocyanin content (127.79 mg/100 g), and amylase (3%, 60 °C) achieved the highest antioxidant activity (39.14%). The incorporation of enzyme-optimized roselle extracts into ice cream formulations improved the colour intensity, texture, and overall sensory appeal. Cellulase provided the most vibrant colour and dense structure, resulting in a smoother and more aerated product with balanced sweetness and a moderately light texture. HPLC analysis of cellulase-assisted roselle calyx extract showed peaks corresponding to quercetin, with a high relative concentration of 52.87%, indicating the efficient enzymatic release of this key flavonoid without any structural degradation. FTIR spectroscopic analysis confirmed the retention of key phenolic and carbohydrate-based functional groups. SEM analysis revealed that fine roselle fragments were uniformly embedded within the ice cream matrix, supporting a smoother texture and reduced ice crystal formation. Overall, enzyme-assisted extraction emerges as a sustainable and effective approach for producing roselle-based natural colourants.