Microbeam X-ray Diffraction Study of Granular Crystals Formed in Water-in-Oil Emulsion |
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Authors: | Leo Tanaka Kei Tanaka Shiho Yamato Satoru Ueno Kiyotaka Sato |
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Affiliation: | (1) Snow Brand Milk Products Co., Ltd., 1-2, Minamidai 1-chome, Kawagoe Saitama, 350-1165, Japan;(2) Graduate School of Biosphere Sciences, Hiroshima University, 1-4-4 Kagamiyama, Higashi-Hiroshima 739-8528, Japan; |
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Abstract: | Margarine and fat spread contain typical water-in-oil emulsions, including semi-solid fats, as continuous oil phases. The application of palm oil, one of the most promising trans-fat alternatives, for semi-solid fats is increasing. However, granular crystals often occur in palm-oil-based solid fats and cause deterioration. In this study, we carried out differential scanning calorimetry (DSC), optical microscopy, and X-ray diffraction (XRD) experiments on granular crystals in margarine. A conventional laboratory-scale technique was applied to examine thermal properties of high-melting fat fractions in granular crystals. In addition, microstructures of the granular crystal were precisely observed with a synchrotron radiation small-angle XRD (SR-μ-SAXD) technique by using a microbeam having a cross section of 5 × 5 μm2. The following results were obtained. (1) DSC indicated that granular crystals are composed of high-melting fractions having a melting temperature of 23 °C. (2) Conventional XRD of granular crystals indicated that β-fat crystals of a triple chain length structure (β-3) melted below the melting of β′-fat of a double chain length structure (β′-2). (3) SR-μ-SAXD indicated that the fat crystals in normal margarine were β′-2. However, the fat crystals of the double and triple chain length structures were simultaneously observed at the center region of a granular crystal, whereas only the fat crystals of β-3 were observed at the outer region of a granular crystal. We analyzed the microstructures and formation processes of granular crystals in relation to the fractional crystallization of the β form of 1,3-dipalmitoyl-2-oleoyl-sn-glycerol promoted by crystallization and transformation of tripalmitin and tristearin fractions. |
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