The Research Of Fat Crystallization Behavior And Macroscopic Physical Properties Of Palm Oil-based Margarine

As one of the most widely used plant oil, palm oil was used as base oil in margarine,shortening produced industry because of its good application characteristic. Different base oildirectly affects the quality of the plastic fat, leading to the different nature of the plastic fat.As consequence, to study crystallization behavior of palm oil and further understand thecrystallization characters of plastic fats production is significant. This study selected twotypes of fractionation of palm oil products (palm stearin and palm olein), and aimed toexplore crystallization behavior of margarine base oil as well as the macroscopic propertiesand microstructure. Contents and results are summarized as follows.(1) The triglyceride (TAG) composition, isothermal crystallization properties, isothermalcrystallization kinetics and non-isothermal crystallization process of two types of palm oils(Pos and POo) were compared. As shown, the composition of TAG influenced the crystalmorphology significantly. In the process of isothermal crystallization, the sample POs reachedthe end of crystallization rapidly, and their crystal morphologies were different. The Avramiindex of POs was pretty much the same as POo under the same isothermal condition,indicating the crystallization mechanism of the two samples based on super-cooled state wasdistinct. The Avrami exponent n for POs and POo increased with recreasing crystallizationtemperature. The value of n increased with the temperature rising, suggested that thetemperature changed the mechanism of nucleation and growth, from the high super-coolinginstantaneous nucleation to low super-cooling sporadic nucleation.(2) The binary system compatibility of POs-POo had also been studied, including theisothermal curve, basic properties, fatty acids composition and thermodynamic changes indifferent proportions of POs and POo. According to the results, the melting point was found tobe higher when iodine value was lower, and the content of saturated fatty acid increased andunsaturated fatty acid content decreased with the POs proportion components increased. Goodbinary system compatibility of POs-POo had been obtained, with ΔSFC of all the curveswithin±2.0. Partial crystal appeared at5℃and10℃, and also, when the temperature came to40℃and45℃, eutectic tendency appeared, respectively. The non-isothermal crystallizationcurves of the POs and POo determined by DSC revealed two peaks. With the POs contentincreased, the crystallization exothermics shifted to higher temperature at the same coolingrate, and the distribution of crystallization temperature broadened with increasing coolingrate. (3) The preparation of margarine in the laboratory was carried out according to theresults of the single factor experiment. The optimum treated condition was as follow: time ofchilling period was3min, temperature of chilling period was-5℃, stir speed of chillingperiod was300r/min, time of knead period was10min and stir speed of knead period was300r/min. With the of POs component increased, threshold value (γ0) of storage moduli (G’)increased, and the signal strength of β and β′polymorph became higher. When the componentproportion came to50%POs and50%POo, the signal strength of β’ was higher than thesignal strength of β. During the proportions of Pos and POo from1:9to5:5, hardnessincreased slowly. However, when the proportion came to60%POs and40%POo, thehardness increased rapidly. As shown from correlation analysis of properties, different baseoils all had a significant highly positive correlation between Palmitic acid, hardness and totalcrystallization strength; oleic acid and linoleic acid both showed highly significant negativelycorrelation with hardness and total crystallization strength; but the content of stearic acidshowed no significant correlation with product characteristics. Positive correlation was foundbetween hardness of the production and storage modili (G’), and loss moduli (G’’) was highlysignificant, suggesting the correlation of the product, G’ and G’’. The total crystallizationstrength was positively correlated with hardness.