Rheological measurements were conducted on samples of chocolate containing various lecithin fictions and lipid sources in order to find a replacement for PGPR, a yield value reducing synthetic emulsifier. Only the oats extract was found to provide the desired reduction in yield value. together with a reduction in plastic viscosity similar to lecithin. Synthetic surfactants bearing various structural characteristics were investigated for their ability to reduce the yield value of chocolate. The best performances were obtained for emulsifiers with long tail groups, such as polymerised fatty acids or long chain hydrocarbons. Polglycerol esters of fatty acids of low HLB provided an excellent yield value reducing ability. Strong interaction of the surfactant head group with the sugar surfaces (mostly by hydrogen bonding) was found to be crucial for effective yield value reduction. Visualisation of lecithin and P(1PR in a sugar in oil suspension (a model of chocolate) was achieved. Both emulsifiers were localised at the interface between sugar and oil, and lecithin was found to displace some of the PGPR from the interface. Solvent extraction experiments were conducted on sugar in oil suspensions containing lecithin, PGPR, an oats extract and a mixture of lecithin and PGPR. SAXS and SANS work conducted suggested that while free PGPR has no impact on the rheological properties of a sugar in oil suspension once a critical concentration corresponding to a yield value minimum had been reached, free lecithin contributed to the formation of loose multilayers between sugar particles, resulting in increased yield value. The influence of various emulsifiers on the rheological properties of cocoa suspensions was also investigated. Lecithin and PGPR showed a similar effects on the yield values to what was observed in the case of sugar in oil dispersions. However, the oats extract was found to have virtually no surface active effect, probably due to poor interactions of its surface active glycolipid with the cocoa particle surfaces
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:503471 |
| Date | January 1997 |
| Creators | Vernier, Frederic C. |
| Publisher | University of Reading |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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