The impact of dechlorophyllization (n-hexane: water partitioning, activated charcoal bleaching, and ChloroFiltr® decolorization) on major polyphenols of two herbal by-products (rosemary and thyme) was assessed. The aim was to produce decolorized extracts for food preservation and improve the quantification of their main phenolics. Activated charcoal bleaching and ChloroFiltr® decolorization effectively removed the chlorophyll a and b, whereas traces were detected after n-hexane: water partitioning. Dechlorophyllized thyme extracts prepared using activated charcoal and ChloroFiltr® had the lowest relative antioxidant capacity index (RACI) values based on 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS), ferric reducing antioxidant power (FRAP), and 2,2-diphenyl-1-picrylhydrazyl (DPPH) antioxidant assays. Conversely, rosemary extracts had positive RACI values following treatment with activated charcoal, whereas n-hexane led to a significant antioxidant loss. Chromatography-mass spectrometry analyses indicated that phenolic diterpenes (carnosol and carnosic acid), as well as rosmarinic acid were in general not significantly decreased (p ˃ .05) after activated charcoal treatment, while n-hexane maintained the flavonoids and phenolic acids with nonsignificant losses. PRACTICAL APPLICATIONS: Commercial exploitation of polyphenol-rich plant based extracts as natural antioxidant agents is impeded by their high chlorophyll content, which when incorporated in food products can result in products that do not meet the consumer expectations for appearance. This study has shown that the activated charcoal bleaching has potentials to remove chlorophyll and retain antioxidant polyphenols in particular diterpenes in fresh herb by-products. Moreover, the commonly used n-hexane was less effective in removing chlorophyll but retained the major flavonoids and phenolic acids. Thus, the choice of chlorophyll removal methods depend on retaining the class of antioxidant polyphenols abundant in the plant matrix.
Keywords: antioxidants; chlorophyll; polyphenols; rosemary; thyme.
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