Co-Pigmentation of Purple Sweet Potato and Red Cabbage Anthocyanins Using Gallic Acid and Green Tea

Lam, Li Zheng (2026) Co-Pigmentation of Purple Sweet Potato and Red Cabbage Anthocyanins Using Gallic Acid and Green Tea. Final Year Project (Bachelor), Tunku Abdul Rahman University of Management and Technology.

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Abstract

Anthocyanins are natural pigments found in fruits and vegetables and they are valued for their potential as natural food colorants due to antioxidant properties and health benefits. However, anthocyanins are highly unstable to heat, pH, and light, which ultimately limits their application in food systems. Therefore, this study aimed to investigate the effects of co-pigments, namely gallic acid (Ga) and green tea (Gt) on the color properties of anthocyanin extracts from purple sweet potato (Psp) and red cabbage (Rc). Anthocyanin extracts from purple sweet potato and red cabbage were prepared and standardised prior to mixing at different ratios with fixed pH. Green tea and Gallic acid were incorporated as Co-pigments. The effects of co-pigmentation were evaluated by examining several parameters including the absorbance at wavelengths (400-700 nm), hue angle, and CIELAB parameters. The results showed that both gallic acid and green tea act as effective co-pigments for anthocyanins, inducing a strong hyperchromic effect—an increase in absorbance (ranging from 65% to 165%) - which enhances the color intensity of anthocyanin pigments. A slight bathochromic shift (shift to a longer wavelength) was observed for most mixtures, causing the anthocyanin color to become a deeper bluish-red hue. The observations were attributed to intramolecular co-pigmentation (acylation) and intermolecular co-pigmentation via non-covalent interactions, including π–π stacking and hydrogen bonding, resulting in enhanced color intensity and stability of anthocyanins and supporting their potential use as natural food colorants and antioxidants.