WETTING OF FAT CRYSTALS BY TRIGLYCERIDE OIL AND WATER .1. THE EFFECT OF ADDITIVES

摘要

Wetting of fat crystals has been extensively examined in this work by contact angle (theta) measurements of fat crystal, oil,, and water in th ree-phase contact. Contact angle was measured in oil. The crystals were nonpolar and wetted by oil for a contact angle equal to 0 degrees, and pol;lr and wetted by water for an angle equal to 180 degrees. Fat crystals are expected to contribute to the stability of margarine emulsions if they are preferentially wetted by the oil phase (O degrees < theta < 90 degrees), but result in instability if they are preferentially wetted by the water phase (90 degrees < theta < 180 degrees). In the absence of oil and water additives, fat crystals in alpha and beta' polymorphs were introduced to the oil/water interface from the oil side (contact angle theta similar to 30 degrees). beta Polymorphs were completely wetted by oil (theta approximate to O degrees), The contact angle for beta' crystals decreased with increasing temperature and was slightly lower in butter oil than in soybean oil. Emulsifiers in the oil phase (lecithins, monoglycerides and their esters, ethoxylated emulsifiers) and surface-active proteins in the water phase (milk proteins) made the crystals more polar (higher theta). Nonsurface-active proteins, sugar, and citric acid had no significant effect, although concentrations of salt lowered theta. Contact angle increased with temperature for emulsifiers of limited solubility in the oil, e.g., saturated monoglyceride. [References: 26]