Date of Award:

2012

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Nutrition, Dietetics, and Food Sciences

Advisor/Chair:

Dr. Silvana Martini

Abstract

Retention of lipid-soluble components can be increased in a curd matrix by using emulsions rather than the direct addition of fortified oil. The retention of vitamin D_3 was increased in a model system with fortified emulsions (emulsifier: dairy proteins) 96-97% compared to 62-72% control. Retention of fortified emulsions (78%) remained greater than the control (58%) in small-batch Cheddar cheese. Bilayer emulsions were evaluated to increase retention of lipid-soluble components even further. Physicochemical characteristics of the bilayer emulsions were evaluated prior to curd inclusion. Nonfat dry milk (NDM) was used as the primary emulsifier at 1wt% dairy proteins. Polysaccharides (iota-carrageenan, low-methoxyl [LMp] and high-methoxyl pectin) and gelatin were secondary layers. Secondary emulsions formulation was 2.5 wt% oil, 0.5 wt% protein, and 0.2 wt% secondary biopolymer. Emulsions were adjusted to pH 3, 5, and 7 after homogenization. Factors that influence stability are biopolymer concentration, droplet size/distribution/charge (zeta-potential), and viscosity. iota-Carrageenan was the most stable, independent of pH, of all the emulsions. This increased stability was a consequence of the affinity of the protein layer and iota-carrageenan through the additional homogenization step. LMp was also stable at pH 7 due to calcium bridging, which correlates with the increased viscosity. The microstructure of the emulsions was examined using scanning electron microscopy. A strong correlation was found between emulsion instability and the presence of thick webbing, due to excess biopolymer, as seen in the micrographs. Stable emulsions were likely to have distinct droplets without a thick web. The exception was gelatin (pH 3), which still had individual droplets but was unstable due to depletion flocculation.

The retention of lipid-soluble substances using secondary emulsion was evaluated in a model curd matrix between primary (50:50 fortified: non-fortified oil) and secondary (100% fortified oil) emulsions. There was no significant difference (α=0.05) in retention of “fortified” oil between primary and secondary emulsions; however, the same fortification level was obtained using secondary emulsions using half the oil. Curd made with 0.01M CaCl_2 had overall lower retention than curd with no additional calcium. Secondary emulsions could be used to fortify various gel matrices (e.g., curd, yogurt, and tofu). Marketing possibilities are endless after preliminary evaluation.

Comments

This work made publicly available electronically on April 12, 2012.

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