Elsevier

Food Hydrocolloids

Volume 98, January 2020, 105255
Food Hydrocolloids

The stabilization of food grade copper-chlorophyllin in low pH solutions through association with anionic polysaccharides

https://doi.org/10.1016/j.foodhyd.2019.105255Get rights and content

Highlights

  • Sodium alginate and xanthan gum impart color stability to dilute copper chlorophyllin (Cu-ChP) solutions at acidic pH.

  • DLS analysis suggests complex formation between Cu-ChP and the polysaccharides does occur.

  • Xanthan gum showed the most promise during accelerated shelf stability tests at 40 °C.

  • CIE a* and b* color data indicate significant levels of green color can be preserved by the polysaccharides.

  • QCM-D monitoring provides additional insight into the mechanisms imparting the added stability.

  • Both polysaccharides are additionally effective mitigators aggregation in these solutions.

Abstract

This work investigates the potential for anionic polysaccharides, such as alginate and xanthan gum, to impart solution and color stability to dilute solutions of copper chlorophyllin (Cu-ChP) buffered at acidic pH. Under cold storage, both polysaccharides tested were shown with sufficient loading to mitigate Cu-ChP aggregation at pH 3.0 and 5.0; xanthan gum use required lower loadings than the sodium alginate tested. Analysis of polysaccharide stabilized Cu-ChP solutions by dynamic light scattering suggests complex formation does occur; this is likely driven by electrostatic interactions between copper cations coordinated at the pigment core and the heavily anionic surfaces of the polyccharide matrices created by the large number of uronic acid substituents on the hydrocolloids.. During accelerated stability testing at elevated temperature (40 °C), pure Cu-ChP controls readily aggregated and lost the solution color distribution, while both polysaccharides maintained both solution and color stability through the initial 5-day test; xanthan gum showed the best promise in this regard, maintaining solution stability and most of the original color through 14 days at both pH tested. CIE a* and b* color data further show more than half of the original green tones and nearly all of the original yellow tones are preserved during heating with either polysaccharide present. Despite this, the slight transition in overall color towards more olive-green tones suggest a level of pheophytinization (metal ion loss) occurs. Finally, quartz crystal microbalance with dissipation monitoring (QCM-D) provides initial insight into the stabilization of Cu-ChP solutions by these polysaccharides and suggests that the weaker, yet stable, association of the pigment source with xanthan gum compared to the sodium alginate tested may be key to its superiority as a stabilizer.

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)

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