Color and antioxidant stability of foam-mat and conventional-dried red and purple roselle ( Hibiscus sabdariffa L.) calyces’ powder at different temperatures

This study aims to compare the phytochemicals of red and purple roselle calyces after foam-mat and conventional (cabinet) dried at different temperatures (60, 100, 121, 140, and 180°C after heating for 30 min) which represent processing temperatures of pasteurization, boiling/steaming, sterilization, frying, and baking. The results show that methanolic extracts of fresh red and purple roselle calyces and their corresponding foam-mat-dried powders contain phytochemicals comprising anthocyanins, proanthocyanidins, flavonoids, phenolics, alkaloids, essential oils, sterols and steroids, sugars, organic acids, and others, with flavonoids as the predominant. Purple roselle calyces contain a higher number and variability of phytochemicals. The typical anthocyanins for red roselle calyces are cyanidins, malvidins, and peonidin. Purple roselle calyces’ anthocyanins comprise cyanidins, delphinidins, petunidin, and pelargonidins. Foam-mat-dried powder matrix protects color and phytochemicals better than conventional-dried powder. The TPC retention of foam-mat-dried powder of red and purple roselle is 87.31–34.37% and 96.93–85.69% at temperatures of 60–180°C. Meanwhile, the TAC retention of foam-mat-dried powder of red and purple roselle is 96.10–7.57% and 94.42% to undetected. DPPH scavenging activity of the foam-mat-dried powder decreases from 19.48% to 9.61% for red roselle and 45.10–37.15% for the purple. Meanwhile, the decrease in ABTS scavenging is 51.17–35.40% for foam-mat-dried red roselle powder and 68.57–59.80% for the purple. At high temperature of 180°C, foam-mat-dried powder matrix retains antioxidant activity better. Foam-mat-dried powder is suggested for products with heating <180°C.