Open Access
Killian, Lauren Bantz Ashworth
Graduate Program:
Food Science
Master of Science
Document Type:
Master Thesis
Date of Defense:
Committee Members:
  • John Neil Coupland, Thesis Advisor
  • water-in-oil
  • emulsions
  • chocolate
  • heat resistant
The sale and consumption of chocolate in warmer climates is limited because of the negative effects of heat on the desirable chocolate characteristics. The addition of a small amount of water to chocolate in a controlled manner provides the potential for increased heat resistance through the formation of an internal sugar skeleton that maintains the structural integrity of chocolate at higher temperatures. Water-in-oil emulsions are one way to deliver this water. The overall goal of this work was to determine if water-in-oil emulsions produced via a lab-scale cross flow membrane emulsification system are suitable for use in the production of heat resistant chocolate products. In order to accomplish this goal, 30% water-in-soybean oil emulsions were produced with different ingredients in the dispersed or continuous phases as well as under different processing conditions. The droplet size distributions of the resultant emulsions were examined both initially and over time. The results from this investigation were used to produce stable and unstable emulsions which were then added to dispersions of sugar crystals in oil which were then cooled to crystallize the fat and form a model chocolate. Samples prepared in this manner were compared to samples made with the direct addition of unemulsified water in order to determine the impact of different modes of water addition on the formation of a sugar skeleton and melt resistance in the product. Analysis of emulsion droplet size distributions showed that polyglycerol polyricinoleate (PGPR) was a more effective emulsifier than either soya lecithin or a 50:50 PGPR:lecithin blend at concentrations of 1 to 6 % (w/w; with respect to the continuous phase). At 2% emulsifier, PGPR-stabilized emulsions remained stable over a period of 4 weeks (d = 22 μm) while lecithin-stabilized emulsions nearly doubled in droplet size over 6 hours (d = 43 to 77 μm) and blend-stabilized emulsions completely destabilized within 3 hours (initially d = 68 μm). Water droplet size decreased with increasing concentration of the emulsifiers used. Emulsion droplet size and size distribution were also significantly affected by the use of different membranes. Decreasing the continuous phase flow rate (95.3 to 64.2 g/sec) resulted in larger droplets (d = 22 to 33 μm) and increasing the dispersed phase flow rate (0.6 to 1.1 g/sec) also resulted in larger droplets (d = 22 to 42μm). The addition of a gelling agent (2% κ-carrageenan) to the dispersed phase prior to emulsification made it more difficult to produce stable emulsions. A stable (2% PGPR-stabilized) and unstable (2% lecithin-stabilized) emulsion (30% water-in-soybean oil) were selected from the first portion of this work and 2 g were added to 120 g of a sugar-in-molten confectionery coating fat (CCF) dispersion (50% sucrose) and cooled to produce model chocolate samples. These samples were compared to samples with water added directly and control samples prepared without added water. Microscopy of sugar-in-oil dispersions in the presence of water-in-oil emulsions provided evidence for the formation of sugar aggregates formed by the adsorption of water at the capillaries between hydrophilic surfaces and resultant interparticle capillary forces. The effect of the presence of such structures was examined within the model chocolate samples. A quantitative test was developed in which samples on mesh stages were immersed in hexane. The hexane dissolved the solid fat component and any sugar not incorporated in the sugar skeleton fell through the mesh. Results showed that addition of water in any form to the samples produced a significant sugar skeleton (44 to 47% out of the total 49.2% sucrose in the original sample) while control samples prepared without added water had no skeleton and almost no sugar was retained on the mesh (0.4% out of the total 49.2% sucrose in the original sample). Since the presence of a sugar skeleton alone does not signify heat resistance, a meltability test was also developed. Samples were placed in an oven at 50 °C for 20 minutes and the change in height and the spread area were measured. Samples with water added via emulsions decreased in height by approximately 12% while samples with unemulsified water decreased by 41% and control samples decreased by 60%. Samples with stable emulsions added were able to contain the melted fat better than samples with unstable emulsions added resulting in areas of spread of 10.5 and 14.4 cm2 respectively. This study showed that water-in-oil emulsions produced by cross flow membrane emulsification and added to model chocolate are effective in producing samples with increased heat resistance conferred through the formation of a sugar skeleton.