MECHANISMS DRIVING EXTRACTABILITY AND AQUEOUS COLLOIDAL STABILITY OF 3-DEOXYANTHOCYANINS IN THE PRESENCE OF AMPHIPHILIC POLYSACCHARIDES
Abstract
Sorghum derived 3-deoxyanthocyanin (3-DXA) are of growing interest as natural food colors due to their unique stability compared to anthocyanins. The commercial use of 3-DXA is limited due to the poor extractability and reduced hydrophilicity of 3-DXA, causing self-association and precipitation in aqueous solutions.
Previous work from our group demonstrated that microwave-assisted extraction (MAE) improved extraction efficiency of 3-DXA from sorghum. Likewise, amphiphilic polysaccharides, such as gum arabic, were reported to improve aqueous stability of 3-DXA. The goal of this work was to determine mechanisms responsible for the enhanced efficiency of MAE and aqueous stability of 3-DXA in the presence of amphiphilic polysaccharides.
The increased extractability of 3-DXA by MAE was investigated by comparing pigment and copigment profile, of both non-tannin and tannin sorghum, after MAE to conventional extraction. The mechanisms of interaction between 3-DXA and amphiphilic polysaccharides was determined by investigating the effect of gum arabic and pectins of different degree of methylation (DE 38-86), 3-DXA profile, and pH on the aqueous stability of 3-DXA. Fluorescence quenching, zeta potential, and average particle size of 3-DXA polysaccharide complexes were measured.
The 3-DXA were structurally stable to microwave energy (1200 W/30 min); MAE induced sorghum cell wall degradation releasing ferulate esters. These two mechanisms were responsible for the increased extractability under MAE (2-3X) compared to conventional extraction.
Preliminary work showed that gum arabic stabilized more hydrophobic 3-DXA (apigeninidin) than hydrophilic 3-DXA (luteolinidin). Fluorescence quenching confirmed apigeninidin had a larger binding constant (19.2x103 M-1) with gum arabic compared to luteolinidin (1.72x103 M-1) and a stable 3-DXA-gum arabic complex was formed. Pectin (DE 54) was also more effective at stabilizing extracts with a higher proportion of apigeninidin compared to extracts higher in luteolinidin in aqueous solutions (38-86% vs 10-67%, respectively). Zeta potential was lower (-13 mV avg) in 3-DXA-pectin or -gum arabic solutions than without 3-DXA (-11 mV avg) suggesting that 3-DXA were encapsulated into hydrophobic regions of the polysaccharides. These results show that extracts with a greater proportion of apigeninidin than luteolinidin interact more efficiently with amphiphilic polysaccharides, suggesting hydrophobic interactions were a major interaction between the two components.
Subject
Sorghum3-deoxyanthocyanins
food color
microwave energy
amphiphilic polysaccharides
extraction
food color
natural food color
Citation
Brantsen, Julia F (2020). MECHANISMS DRIVING EXTRACTABILITY AND AQUEOUS COLLOIDAL STABILITY OF 3-DEOXYANTHOCYANINS IN THE PRESENCE OF AMPHIPHILIC POLYSACCHARIDES. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /192701.