Blue Color Production from Huito and Watermelon Juice and Their Potential as Naturally-Derived Blue Colorants for Food Applications

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With consumer demand to transition away from synthetic coloring of food, companies are seeking new sources of natural color that are comparable alternatives to FD&C Blue No.1 and No. 2 [1]. Genipa americana L., also known as "Jagua" or "Huito"[2] , is a promising source of blue color that can serve as a naturally derived alternative to synthetic blue colorants for food applications. Natural blue color is particularly of interest to companies due to its scarcity in nature, providing limited options for food colorants [3]. In addition, most natural blue sources express blue only at a basic pH (most food products are at an acidic pH), while huito can produce blue at low pHs, making it stand out from the others [4]. Huito, a fruit native to the Amazon [5], is naturally colorless, but can turn blue when exposed to oxygen or amino acids [2]. It contains genipin, a color-producing iridoid, that can bind with primary amine groups on amino acids to produce colored monomers, dimers, or polymers [2]. Depending on the source of the primary-amine group, different colors can be expressed [6]. Watermelon juice – rich in amino acids [7] - has been shown to express a particularly favorable and stable blue color when combined with huito through its synthesis of iridoid blue based pigments [6]. Although promising, there has been limited research conducted on huito's coloring capabilities for food applications [4]. The objectives of this study were to investigate the conditions that impact the blue color expressed from interacting huito fruit powder with watermelon juice, as well as to determine which amino acids, or combination of amino acids, in watermelon juice are most ideal for the blue color reaction. Specifically, ratio of huito to watermelon juice, incubation time, and pH were investigated to determine their impact on blue color development. Dehydrated jagua powder was mixed with watermelon juice and distilled water at specific chosen ratios (1:5-1:40 huito:watermelon, pH ~ 5), and changes were monitored over 60hr in the dark at 25℃. Incubation at moderate temperature is recommended to induce blue color formation through the binding of genipin with the primary amine groups on the amino acids [8]. After incubation of each sample, absorbance was determined using a spectrophotometer, and converted to CIE values L* (lightness), a* (red/green), b* (blue (-)/yellow (+)), Cab* (chroma), hab (hue). ANOVA and TukeyHSD were conducted using RStudio. Additionally, watermelon juice was analyzed for its amino acid composition, and pure amino acids were individually mixed with huito and analyzed using spectrophotometry for absorbance and color after incubation. Blue color developed in all treatments and was stable at pHs 2-7. Ratios 1:10-1:20 H:WMJ had the highest absorbances at the λmax (594nm) with no statistical differences. Overall, ratios 1:10-1:20 developed the darkest, bluest colors that were the "best" ratios of the ratios tested. As incubation time increased, absorbance increased, expressing darker and more vivid blue color. Absorbance at the λmax (594nm) increased significantly until 36hr incubation, where absorbance increase significantly slowed with time beyond 36hr, peaking at 60hr. Glutamine and citrulline strongly contributed to the blue color produced from huito and watermelon juice. These results suggest that ratio of huito to watermelon juice and time of incubation impacts absorbance at the lambda max and the vividness of the blue color produced, while pH does not. Vivid, blue colors at acidic pHs were produced from huito and watermelon juices in a relatively short time period. Understanding how these conditions impact the blue color produced from huito and watermelon, as well as understanding which amino acids in particular are the most favorable for the reaction, will allow for a better understanding of its potential food applications. Utilizing the ideal conditions for blue color formation with huito and watermelon can help shape the color to a similar hue, lightness, and blueness as FD&C Blue No. 1 or Blue No. 2.


Food, Agricultural, and Environmental Sciences (FAES): 2nd Place (The Ohio State University Edward F. Hayes Graduate Research Forum)


huito, jagua, Genipa americana L., watermelon juice, naturally-derived blue color, blue color formation