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theses

Recently, molecular gels have been studied with edible low molecular gelators and vegetable oils to respond to the increasing pressure to reduce the amount of saturated fat and trans fat in food products1. Molecular gels are a group of relatively new soft materials capable of numerous possible applications such as being an oil-spill recovery, drug carrier, cosmetic matrix, and fat substitute2. The gelators for forming molecular gel are low molecular weight molecules self-assembling into a three-dimensional network by means of supersaturation. The well-known 3-D network is self-assembly fibrillar networks (SAFiNs) capable of the entrapping high amount of liquid solvent (above 90 wt%) to provide the framework of molecular gels. It is widely accepted that supersaturation is the dynamic driving force for gelation kinetics; however, how the supersaturation affects the formation of a fiber network, particularly the creation of the junctions, remains poorly understood. But for a given gelling system, gelator concentration and gelation temperature can be described by supersaturation in solution. In addition, it has been studied that the force balance between gelator-gelator force and gelator-solvent force plays an important role in molecular gel formation even the mechanism behind it is still not clear. Thus, the aim of this study is to develop an alternative to fat by using a mixture of health promotional small lipid molecules to self-assemble into the three-dimensional network for entrapping several vegetable oils. Furthermore, the physical property of molecular gels is investigated by changing the mixing ratio of small molecules and changing the liquid solvent with 27 different vegetable oils. While choosing the edible gelators, -sitosterol got our attention because not only plant sterols are free of saturated fatty acids but also they have been found to lower blood cholesterol by interfering with cholesterol absorption in the intestine3. Thus, a two-component system, stearic acid + -sitosterol, with different concentrations and mass ratios was prepared with respect to their gelation ability, network structure, thermal property, and rheological properties in order to determine the optimum conditions under which canola oil gels. Results showed that stearic acid + -sitosterol was a promising structuring agent to entrap canola oil by means of forming a network consisting of needle- and platelet-like crystals through supersaturation. In addition, the ability of gel formation was tailored by manipulating the concentration and ratio of the two-component system. Based on the first stage of the study, stearic acid + -sitosterol was a successful system to structure canola oil. Thus this system was chosen to apply on various oils to test the effect of liquid environment on gelation. Twenty-five edible oils and two non-edible oils were tested and distinguished into three groups based on the gelation result, which were oleogels, partial oleogels, and non-oleogels. It was found that oil having more portions of unsaturated fatty acids than saturated fatty acids introduces the high chance of oleogel formation. It meant that an oil having more in linolenic acid with a low percentage of saturated fatty acids (<10%) was likely to form an oleogel according to the results of hierarchal clustering analysis. More potential oils enabling to be structured should be introduced by mixing the existed oils to match this high linolenic acid and low saturated fatty acid condition. In order to maximize the benefits of oleogels being fat substitutes, oil-soluble compounds such as carotenoids were considered to be added when preparing the oleogels due to the antioxidative ability and health benefits of carotenoids. Mango (Mangifera indica L.) is the second most important tropical fruit and has high amount of carotenoids, especially –carotene and zeaxanthin, which provides the color of yellow-orange of mango. Taking an advantage of oil solubility of carotenoids, canola oil was used to extract carotenoids out from fresh mango pulp via blending using an IKA ultra turrax Tube Drive control equipped with 30 stainless balls. Clear golden yellow canola oils were obtained after blending as a result of containing -carotene and zeaxanthin according to the results of visible spectrum. The specific max of 428, 450, and 480 nm were found as same as those from literature. Even though the changes made in solvents may break the force balance between gelator-gelator and gelator-solvent, the resulting oleogels were obtained using stearic acid + -sitosterol as structuring agent. Thus, it is a promising approach to include carotenoids in canola oil and to form an oleogel. However, carotenoids are susceptibility to heat, the effects of processing temperatures on carotenoids were investigated. As the result of the visible spectrum, hypsochromic shift showed in the visible spectrum of the sample under long time processing at the high temperature of 90°C or above. According to the numbers of max before and after long time heating, β-carotene and zeaxanthin converted to cis-violaxanthin. Thus, the processing temperature and time have definitely to be considered when the system is containing heat sensitive compounds. Overall, this final stage of study has illustrated even canola oil is modified by having carotenoid compounds, and it still can be structured, resulting in an oleogel.

ETD_8644

Ph.D.

Includes bibliographical references

by Tzu-Min Wang

doi:10.7282/T3988B7Z

ETD doctoral

The author owns the copyright to this work.