The stabilization of food grade copper-chlorophyllin in low pH solutions through association with anionic polysaccharides
Graphical abstract
Introduction
The food industry is currently in a transitory period pressured by mounting concerns over the use of an array of synthetic or heavily processed ingredients that have been in ubiquitous use as modifiers, stabilizers, flavors, and colorants in most processed foods on the market. This is particularly so within the context of food colorants, as maintenance of vibrant and stable colors in products has been critical for food manufacturers aiming to deliver competitive and marketable products throughout the industrialization of the food industry over the past 100 years. The rising health awareness of modern consumers and disconcerting reports on safety related to the usage of vibrant and stable synthetic azo dyes (i.e. FD & C Blue 1, Red 40, and Yellow 5 in the US) in foods has pushed many manufacturers to seek out means to effectively use naturally available, yet often less stable, colorants(Houghton and Hendry, 2012) (Francis, 1995; Martins, Roriz, Morales, Barros, & Ferreira, 2016). This has pushed an influx of demand on researchers by manufacturers to provide novel, yet simple and safe, solutions to enable use of native pigments such as anthocyanins, betalains, carotenoids, phycocyanins, and chlorophylls in products. These efforts are often product specific and must approach color system development in a manner that creates lasting shelf-stable colors that are resistant to the chemical formulation and the processing requirements of a specific product (Wissgott & Bortlik, 1996).
Currently, in US markets green coloration in foods is either achieved by the natural state of the product or by the addition of artificial of FD&C Blue No. 1 and Yellow No. 5, and less often with the use of the triarylmethane food dye, Fast Green (FD&C Green No. 3). The most abundantly available natural pigments are the tetrapyrrole-based chlorophylls, although issues with color stability and water solubility prevent effective use in many food products. Currently, only sodium Cu-Chlorophyllin (Cu-ChP) produced from alfalfa extracted chlorophyll, via saponification and replacement of the Mg2+ with Cu2+ at the core, is the only approved form available for use as a food colorant (https://www.fda.gov/ForIndustry/ColorAdditives/ColorAdditiveInventories/ucm106626.htm) in the US. This modified chlorophyll derivative is more stable and water-soluble although only approved for use in citrus beverages (Tumolo & Lanfer-Marquez, 2012; Viera Alcaide, Pérez Gálvez, & Roca, 2019).
Despite improved stability, use of Cu-ChP as a colorant is still limited as this form, like other chlorophylls and natural pigments, is susceptible to range of degradation processes. The most common transformation being pheophytinization (replacement of the central metal ion with hydrogen) which readily occurs under acidic conditions and exposure to mild heat (Rodriguez-Amaya, 2019). High water activity and the presence of a number of structurally modifying enzymes also pose long term risk to the maintenance of robust green colors when chlorophyllin is used (Ngamwonglumlert, Devahastin, & Chiewchan, 2017). Furthermore, while generally water soluble, Cu-ChP is increasingly susceptible to hydrophobic aggregation at increasingly acidic pH as carboxylic acids on their structures become protonated, making it difficult to use in transparent acidic beverages (House & Schnitzer, 2008).
Herein, we explore the hypothesis that long-chain stabilizing anionic polysaccharides (xanthan gum or sodium alginate were tested) may interact through charge-charge relationships between the uronic acid constituents on the polysaccharides and the positive Cu-based chlorophyllin. We believe these small, but strong, electrostatic interactions may be enough to both stabilize the solubility of the pigments in acidic solutions as well as improve color stability by reducing local water activity, affecting access to degrading enzymes, and enhancing the stability of the color-improving copper ion in the pigment core. The general aim of this work was to assess this potential in the context of finding a simple means for the stabilization of Cu-ChP in acidic solutions to enable their use in translucent citrate buffered beverages; the study focuses on the effects of xanthan gum and alginate on dilute aqueous Cu-ChP solutions buffered with citric acid. Observed differences in zeta-potential, average particle size, L*a*b* color space data are used to elucidate beneficial mechanisms that may exist. Quartz crystal microbalance (QCM-D) with dissipation was used to observe physical associations that may occur between the Cu-ChPs and the polysaccharides and how such associations may be related to the colorant stability in solutions. The results presented herein should be of interest to researchers and industries working to develop more robust natural green coloration options for acidic beverages using chlorophyll-derived pigments.
Section snippets
Chlorophyllin & polysaccharides
Commercial sodium Cu-ChP used for all studies herein was sourced as concentrated “Liquid Chlorophyll” from Dynamic Health (Tulsa, Oklahoma). The reported Cu-ChP concentration of the processed alfalfa and mulberry leaf extract was 0.667% (w/w) in solution. Xanathan gum used for this study was C-type obtained as a sample from Colony Gums (Monroe, NC). The sodium alginate used herein was Manugel GHB provided by FMC Biopolymer (Philadelphia, PA, USA).
Chlorophyllin storage stability studies
All test Cu-ChP solutions were prepared at a
Results & discussion
During the initial phases of this work a range of polysaccharides not mentioned herein were assessed for their ability to maintain the solubility and color of the dispersed chlorophyllin. The focus on the alginate and xanthan gum tested is a response to their observed effectiveness during these screenings. To date, a few studies have investigated the potential for specific polysaccharides, such as maltodextrin, agave fructans, and sodium alginate, to improve the stability or delivery of
Declarations of interest
None.
This work has not previously been published and is not under consideration for publication elsewhere. The authors have read and agreed to the contents of the manuscript and have made substantial contributions to the overall body of work encompassed. There are no conflicts of interest regarding the publication of this work.
Acknowledgements
This work has been supported by resources within the Food Science Department. This work is partly based upon research conducted at the Cornell High Energy Synchrotron Source (CHESS), which is supported by the National Science Foundation under award DMR-1332208.
References (11)
- et al.
SERRS and visible extinction spectroscopy of copper chlorophyllin on silver colloids as a function of pH
Journal of Colloid and Interface Science
(2008) - et al.
Food colorants: Challenges, opportunities and current desires of agro-industries to ensure consumer expectations and regulatory practices
Trends in Food Science & Technology
(2016) - et al.
Molecular structure, stability and cytotoxicity of natural green colorants produced from Centella asiatica L. leaves treated by steaming and metal complexations
Food Chemistry
(2017) - et al.
Copper chlorophyllin: A food colorant with bioactive properties?
Food Research International
(2012) - et al.
Prospects for new natural food colorants
Trends in Food Science & Technology
(1996)
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