Liquid to Semisolid Rheological Transitions of Normal and High-oleic Peanut Oils upon Cooling to Refrigeration Temperatures

摘要

Rheological transitions of peanut oils cooled from 20 to 3 °C at 0.5 °C/min were monitored via small strain oscillatory measurements at 0.1 Hz and 1 Pa.Oils were from nine different cultivars of peanut,and three oils were classified as high-oleic (approximately 80% oleic acid).High-oleic oils maintained an overall liquid-like character at 3 °C for 2 h.In contrast,several normal (non high-oleic) peanut oils displayed a predominantly elastic (solid-like) response after 2 h at 3 °C.Increases in visco-elasticity were associated with lipid crystallization events as confirmed by DSC.The higher (p < 0.001) liquid viscosities and increased (p < 0.001) contents of oleic acid,which has a more non-linear structure as compared to other fatty acids typical in these oils,were hypothesized to hinder crystallization in high-oleic oils.Changes in visco-elasticity at 3 °C were greatest for three normal oils that had the significantly (p < 0.001) highest content of C20:0 and/or C22:0 fatty acids,and these long,saturated hydrocarbon chains are hypothesized to promote crystallization.No peanut oil maintained clarity after 5.5 h at 0 °C (modified cold test used to screen salad oils);however,these data as a whole suggest strategies for breeding and/or processing peanut oils for enhanced resistance to crystallization.