LECITHINS IN OIL-CONTINUOUS EMULSIONS - FAT CRYSTAL WETTING AND INTERFACIAL-TENSION

Lecithin is a powerful emulsifier widely used in foods, feeds and phar maceuticals. Several analytical methods have been proposed to characte rize lecithins, but they are often inadequate to determine the industr ial functionality. The purpose of this study was to find a relationshi p between the interfacial properties of lecithins (adsorption to oil/w ater and fat crystal/oil/water interfaces), phospholipid composition a nd functionality. Results show that all lecithins adsorb to fat crysta ls at the triglyceride oil/water interface, making their surface more polar (observed as an increase in the contact angle measured through t he oil at the interface: fat crystal/oil/water). This adsorption proce ss is quick (less than five minutes) for relatively polar lecithins, s uch as soybean phosphatidylcholine (PC), and results in highly polar s urfaces (contact angle approximate to 180 degrees). Less polar lecithi ns give slow adsorption (some hours) and less polar crystals (contact angle less than or equal to 90 degrees). The adsorption of different l ecithins to the oil/water interface, observed as a decrease in interfa cial tension, follows the adsorption pattern to the fat crystals. We f ound a relation between high-fat crystal polarity and poor lecithin fu nctionality in margarine (margarines spatters during frying), and also between high-fat crystal polarity and a high polar to nonpolar phosph olipids [Sigma(PI + PA + LPC)/Sigma PE; Pi, phosphatidylinositol; PA, phosphatidic acid; LPC, lysoPC; PE, phosphatidylethanolamine] ratio in lecithin. The correlations might be via aggregation properties of lec ithin in the oil. We found also that monoolein shifted the adsorption kinetics of lecithin (soybean PC) to fat crystals and the hydrophilici ty of adsorbed layers probably due to formation of mixed aggregates be tween monoolein and soybean PC.