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

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. Fa t crystals are expected to contribute to the stability of margarine em ulsions if they are preferentially wetted by the oil phase (O degrees < theta < 90 degrees), but result in instability if they are preferent ially wetted by the water phase (90 degrees < theta < 180 degrees). In the absence of oil and water additives, fat crystals in alpha and bet a' 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 contac t angle for beta' crystals decreased with increasing temperature and w as slightly lower in butter oil than in soybean oil. Emulsifiers in th e oil phase (lecithins, monoglycerides and their esters, ethoxylated e mulsifiers) and surface-active proteins in the water phase (milk prote ins) made the crystals more polar (higher theta). Nonsurface-active pr oteins, sugar, and citric acid had no significant effect, although con centrations of salt lowered theta. Contact angle increased with temper ature for emulsifiers of limited solubility in the oil, e.g., saturate d monoglyceride.