Physical properties of feeds for novel bioactives - encapsulating bead formation

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Hansen, Mackenzie M.
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University College Cork
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Encapsulation involves the entrapment of sensitive bioactive compounds with structure- forming food components to enhance protection and delivery. Blends of proteins and glass- forming carbohydrates are often used as encapsulation matrices and for structure formation. When bioactives intended for encapsulation are mixed with structuring proteins under acidic and neutral pH conditions and ambient temperatures, weak, non-covalent protein-bioactive interactions have been reported to occur. Complex formation may influence the physical properties of dispersions as well as dried products formed by feed mixtures. We hypothesized that: (i) Processes forming concentrated protein-carbohydrate feed dispersions into dry, solid beads could be developed, and (ii) formulation composition changes such as varied total solids, protein-carbohydrate ratios, protein isolates with different purities and structures, carbohydrate types, bioactives contents, and bioactives sources with diverse structures and sizes of predominant compounds would result in changes to the physico-chemical properties and drop formation abilities of dispersions, as well as the physical characteristics of dry beads formed. Key objectives of the present study were: (i) the development of two different simple, continuous processes forming feed dispersions into dried, novel bead structures, and (ii) characterization of the effects of changes in formulation compositions on the physical properties of liquid feeds and resulting dry beads. A full process design for simple solidification of concentrated liquid dispersions and a structure-forming formulation used for subsequent vitrification are reported, producing solid bead structures suitable for inclusion of bioactives in protein-carbohydrate matrices. Increasing total solids contents generally resulted in enhanced dispersion viscosities, altering surface tensions as well. Altering protein:carbohydrate ratios in dispersions generally did not strongly affect surface tension or particle sizes, increasing ratios often resulted in slightly increased viscosities. In comparing the effects of protein isolate types on the physical properties of dispersions with WPI, SPI, and PPI, WPI feeds had the highest surface tensions, lowest viscosities, and smallest particle sizes, while PPI had the lowest surface tensions, highest viscosities, and largest particle sizes. Upon altering the carbohydrate type used in dispersions between sucrose, maltitol, and trehalose, the physical properties of dispersions were not notably affected. Addition of bioactives to protein-carbohydrate dispersions resulted in slightly reduced pH values and increasing bioactives concentrations resulted in slightly increased surface tensions of dispersions under some conditions. Viscosities of dispersions with varying bioactives concentrations were generally not strongly affected, except for decreases in viscosities of PPI dispersions and increases in SPI dispersion viscosities with increasing polyphenols concentrations under few conditions. Particle sizes of remaining unhydrated/insoluble protein particles and aggregates in WPI dispersions were slightly reduced, SPI dispersions slightly increased, and PPI dispersions generally decreased with increasing Aronia polyphenols concentrations. Particle sizes of WPI-sucrose dispersions increased when cranberry extract and gallotannin polyphenols concentrations increased. Dispersions with cranberry extract had significantly higher surface tensions than those with Aronia and beet extracts, but not gallotannin. Beet extract affected particle sizes of dispersions the least, and cranberry extract resulted in the largest particle sizes detected. Dispersions with cranberry extract also had the highest viscosities. Dried beads containing sucrose were found to have lower hardness upon texture analysis (smaller compression forces required to compress beads 3 mm) than those with only WPI but did not undergo shrinkage upon drying. Beads formed by freeze granulation had water contents in the same range as those from the drop formation method involving gelation in hot oil and subsequent drying but lower water activities, potentially due to the lack of a gel network structure within beads entrapping water available for reactions after drying. Formulating with trehalose resulted in beads with the highest Tg and maltitol the lowest Tg. 1% Aronia PP did not strongly impact Tg of beads. Beads formed without WPI were harder than those formed with proteins. A strong, continuous glassy phase formed in the absence of proteins, but the glassy phase of beads containing WPI was interrupted by proteins dispersed throughout, weakening the continuous glassy structure. Aronia extract did not strongly affect the hardness of beads, and those formulated with maltitol tended to be softest, while those with trehalose were hardest. A modified method for bead formation by freeze granulation was also presented, forming structures under different conditions than the heated oil drop formation method. Results of this study provide insight into physical behaviors of high solids-concentrated protein-carbohydrate dispersions and effects of bioactives and protein-bioactives interactions in the aqueous blends and in dried materials formed from mixtures. These findings advance formulating high protein products with bioactives to obtain desired textural attributes and natural color preservation. Two processes for making foods with high physical stabilities and potential for the entrapment of flavors, emulsion droplets, colors, or bioactives are presented, which may serve as novel alternatives to drying or extrusion.
Protein , Bioactives , Encapsulation , Physico-chemical properties , Freeze granulation
Hansen, M. M. 2021. Physical properties of feeds for novel bioactives - encapsulating bead formation. PhD Thesis, University College Cork.
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