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Color is the most important determinant of food quality perception by consumers; for this reason, the vast majority of manufactured foods contain added colors, mostly synthetic petroleum-based FD&C dyes. Consumer demand for clean label and natural colors has expanded rapidly out of concerns over potential adverse effect of artificial additives. Legislative mandates have further pushed the pursuit of natural colorants. The US accounts for 30% of global natural food colors market, valued at about $1.9 billion in 2017, with an expected annual growth of 8.5% between 2018-2026. Plant-derived anthocyanins are the most widely used water-soluble colorants in food and beverages. Unfortunately, anthocyanins have various drawbacks that limit their food use, primarily poor stability to food processing and handling conditions, and high cost. The anthocyanins tend to fade, brown, or change hue easily under various food processing conditions; they are also mostly commercially derived from bulky (high moisture) plant tissues with high enzyme activity that are expensive to store and process.Unlike other plants, sorghum exclusively accumulates unique and highly stable anthocyanin analogs, 3-deoxyanthocyanins (3DXA) with major potential as commercial food colorants. The pigments are located in sorghum grain pericarp, and other dry tissue that are easy to concentrate and store. The 3DXA pigments also have unique bioactive properties. Interest in these unique pigments has grown among food and ingredient companies. Unfortunately two major challenges stand in the way of commercial exploitation of these valuable pigments; i) the 3DXA are relatively difficult to extract using standard solvent systems, and ii) the 3DXA have high tendency to self-associate in aqueous systems, limiting use, especially in dairy and beverages.Our goal is to develop practical strategies that can enable the food industry to improve food quality and health promoting properties. Through this project we aim to address the two major challenges facing 3DXA commercial exploitation. We hypothesize that the poor extractability of the 3DXA is due to the sorghum pericarp cell wall structure (neutral polysaccharides with high levels of phenolate cross-linkages) and relatively high partition coefficient of the 3DXA that limits their affinity for anthocyanin-based solvents. Furthermore, we hypothesize that the self-association in aqueous systems is due to hydrophobic effect induced by the naked domain between C4 (C-ring) and C5´ (B-ring) in their structure (due to unsubstituted C3). We propose to use the widely available and practical microwave technology to effectively disrupt sorghum pericarp cell wall and enable efficient extraction of the sorghum 3DXA, and use encapsulation technology to prevent aqueous self-association of the pigments. Our preliminary data demonstrate that microwave energy, coupled with appropriate solvent system, can dramatically increase extractability of 3DXA from sorghum to achieve yields of 15 - 35 g/kg bran, compared to 0.5 - 1.8 g/kg typical for anthocyanins from fruits/vegetables. Furthermore, we found that, depending on the composition of the 3DXA and solution pH, very low levels of amphiphilic ionic polysaccharides (negligible impact on viscosity) can almost completely prevent self-association of these pigments in aqueous solution without affecting solution color (hue and chroma). This suggests specific and strong interactions of 3DXA with hydrophobic domains of the polysaccharides, perhaps stabilized via charge repulsion. Through this project, we aim to address three specific objectives:1) Establish effect of microwave-assisted extraction (MAE) conditions on the composition and yield of 3-deoxyanthocyanins and phenolic copigments from sorghum bran. In contrast to fruits and vegetables, sorghum bran cell wall structure is almost entirely composed of neutral sugars, with significant phenolic acid-ester cross linkages. These properties make the cell wall difficult to disrupt using traditional extraction systems. We expect that, when bran is tempered to the right moisture, high-energy microwave irradiation will generate instantaneous heat and steam pressure within the sorghum bran tissue cells to cause 'popcorn-type' cell wall rupture and allows the pigments to efficiently diffuse into the extracting medium. Even though MAE has been widely investigated for extracting anthocyanins (and other phenolics) from plant tissues, its overall application (and advantage) is limited by poor stability of these compounds to microwave energy and heat. The unique stability of 3DXA will likely overcome this problem, and thus lead to dramatic increase in pigment yield. A likely secondary benefit would be altered bran cell wall structure to increase soluble dietary fiber, and likely prebiotic properties of bran residue.2) Establish the effect of amphiphilic and ionic properties of polysaccharides on encapsulation efficiency of the sorghum 3-deoxyanthocyaninsm and their stability in aqueous systems. Self-aggregation in aqueous systems severely limits application of the sorghum 3DXA. We have evidence to suggest that the self-association is largely driven by hydrophobic attractions due to the naked domain between C4 and C5´ of 3DXA molecule. Interaction of the 3DXA with low levels of ionic polysaccharides with hydrophobic moieties appear to inhibit the self-aggregation. Here we propose to investigate precise the mechanisms that govern the 3DXA-polysaccharide interactions in aqueous systems to identify appropriate technologies to expand their use in food and beverages.3) Establish effect of ionic properties of solution on the stability of the 3DXA-polysaccharide complexes. We will use model beverage systems to evaluate stability and performance of the 3DXA-polysaccharide encapsulates under practically relevant processing and handling conditions, including thermal processing, presence of salts and mono/multivalent ions, reducing sugars, different pH, and different storage conditions typical to food beverages.

Awika, J.
Texas A&M University
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