Color Enhancement of Rambutan Peel Anthocyanins Extracts using Co-Pigmentation with Gallic Acid for pH-Sensitives Dye

Rambutan peels typically contain anthocyanins that can be utilized as pH-sensitive dye for intelligent food packaging. Therefore, this study aimed to isolate anthocyanins from rambutan peels and investigate their co-pigmentation with gallic acid (GA) to enhance color intensity while maintaining a pH sensitivity. Rambutan peel anthocyanins extracts (RPAE) were extracted using ultrasound-assisted extraction with 0.2 citric acid in 96 ethanol. The purification of RPAE was carried out using a chromatography column with Sephadex LH-20 as the stationary phase. Co-pigmentation was then performed using GA at various molar ratios of RPAE to GA (1:0, 1:100, 1:200, 1:300, 1:400 and 1:500). The results showed that the purification process with Sephadex LH-20 increased the anthocyanins content of RPAE to 157.50 mg CyE/100 g extract. After purification, RPAE was found to primarily consist of cyanidin 5-O-glucoside, delphinidin-3-O-glucoside, cyanidin 3-O-galactoside, delphinidin (aglycon), cyanidin-3-O-glucoside, pelargonidin 3-O-glucoside, and cyanidin (aglycon). Co-pigmentation with GA significantly reduced the degradation of total anthocyanin content compared to native RPAE during the 7-day observation period. Additionally, co-pigmentation with GA enhanced color intensity, as demonstrated by a decrease in the L* value across pH 1-10, an increase in the a* and b* values at low pH, and a decrease in the a* and b* values at high pH. However, compared to non-co-pigmentation, co-pigmentation with GA exhibited more pronounced color differences across varying pH levels, marked by higher a* at low pH and lower b* and L* at high pH. The interaction between GA and RPAE, presumably via hydrogen bonding comprising the carbonyl group of RPAE and GA, produced hyperchromic and bathochromic effects. These findings indicate that co-pigmentation with GA enhances the pH sensitivity of RPAE, making it a promising candidate for developing intelligent food packaging systems that can visually indicate changes in pH, such as monitoring food spoilage or freshness. © 2025, Walailak University. All rights reserved.