From Calyx to Colour: Drying, Extraction and Formulation as the Determinants of Anthocyanin Retention in Hibiscus sabdariffa

Hibiscus sabdariffa calyces are among the richest accessible sources of anthocyanins, carrying three times the pigment load of black grapes, and the clean-label retreat from synthetic reds has made them commercially attractive. The pigments themselves, however, are simple non-acylated sambubiosides, and almost everything that happens between the field and the finished product costs some of them. This review follows that chain — harvest, drying, milling, extraction, formulation, storage and reconstitution — and asks at each step how much pigment survives and what the operator controls. Four conclusions are drawn. First, drying temperature is not monotonic in its effect: 80 °C preserved phenolics better than 60 °C because exposure time fell faster than degradation rate rose, and 70 °C has been proposed as the best compromise across anthocyanins, phenolics and organic acids, so time multiplied by temperature is the variable to specify rather than temperature alone. Second, dehydration does far more than concentrate. Recalculating published figures on a dry-matter basis shows a concentration factor of 4.7 accompanied by a 15.5-fold rise in measured total phenolics and a 29-fold rise in measured anthocyanins, implying gains in extractability of roughly 3.3-fold and 6.1-fold beyond concentration alone — drying unlocks the matrix as much as it removes water. Third, water outperforms alcohol: an aqueous food-grade extract recovered 30.7% more total anthocyanins than a hydromethanolic control and 68.7% more than a hydroalcoholic one, which inverts the usual assumption that polyphenol recovery improves with organic solvent and favours the simplest and cheapest process. Fourth, more sugar is not more protection: in syrup formulations spanning 5% to 35% sucrose, the 5% formulation retained the highest anthocyanin concentration. Roselle is set throughout against butterfly pea, the other principal anthocyanin colourant of Southeast Asia, whose polyacylated pigments behave in the opposite way; between them the two species cover the acid and the neutral ends of the formulation range.