91C-13 |
Effects of formulation and homogenization pressure on emulsion properties and on the stability of dried high-fat powders |
A. H. BARRETT1, P. Maguire, and W. L. Porter. (1) Combat Feeding Program, PEFST, US Army Natick Soldier Center, Kansas St., Natick, MA 01760-5018 The military seeks to increase the caloric density of some operational rations in order to provide more sustained energy to mobile troops. Caloric densification is achievable by increasing lipid content. However, there is a desire to use unsaturated oils in fortification, requiring physical stabilization. Our objectives were to determine effects of formulation/process parameters on emulsion quality, on the chemical stability of dried powders derived from the emulsions, and on the physical stability of performance bars containing different levels of the powders. Oil-in-water emulsion formulations stabilized by HiCap starch, lecithin, and calcium caseinate, and with viscosity adjusted by 3 levels of xanthan gum were produced using a Niro homogenizer operated between 20,000-100,000 kPa. Flow curves were evaluated using rotational viscometry; droplet size distribution was measured using light-scattering analysis. Emulsions were blast frozen, freeze-dried, sieved, and the powders incorporated into high-carbohydrate performance bars at 0, 5, 10, 15 and 20%. Bar texture was assessed by uniaxial compression; surface oil was evaluated by timed diffusion. Bars were also analyzed after 12 weeks storage at 30C. Oxidation volatiles from powders were evaluated by cobalt-catalyzed polyamide fluorescence. The finest emulsion (mean droplet size ~ 1 micron) was obtained using the lowest homogenizer pressure and the lowest viscosity formula. Droplet size increased with pressure and with addition of xanthan, and was directly correlated with amount of bar surface oil. Bar firmness increased with amount of fat-powder, and also with storage. Oxidation tendency was slightly higher for powders containing smaller droplets, and much higher for powders containing xanthan. Some emulsions can be “overprocessed” by high homogenization pressures, producing droplet coalescence. Increased viscosity can increase droplet size. Smallest droplet emulsions yield most physically stable fortified products, but when dried have a slightly higher tendency to oxidize due to increased lipid surface area.
Session 91C, Food Engineering: Food process engineering
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