Preparation And Evaluation Of Zero-trans Fatty Acid Spread

Spread has been developed rapidly in China in recent years. However, due to the raw materials added hydrogenated oil, the system is generally contain about 10% trans fatty acids, and the product has the outstanding nutritional quality problem. Replacing hydrogenated oils with trans-free oil has obviously practical value. The problem of poor compatibility of the simple mixture can be resolved through enzymatic interesterification, using sunflower oil rich in essential oleic acid, linoleic acid and cheap palm stearin as materials. Meanwhile, new trans-free healthy spread can also be developed. A comprehensive analysis of the physical and chemical properties of six kinds of commercialized spreads was conducted. The results showed that the formulations differed greatly, but fatty acid composition, solid fat content and crystal morphology were very similar. Based on the comprehensive consideration of properties and composition, sunflower oil and palm stearin were selected as substrates for enzymatic interesterification.Enzymatic interesterification was catalyzed by Lipozyme RM IM. The single factor test results showed that the optimal conditions were as follows: stirring speed of 200 r/min, lipase amount of 8 %, reaction temperature of 70 oC and reaction time of 3 h. Furtherly, the reaction conditions were optimized through response surface methodology. And the effects of lipase amount, reaction temperature, reaction time on the interesterification reaction and their interactions were investigated. The optimal reaction conditions obtained were a lipase amount of 8.51 %, a reaction temperature of 74.3°C and a reaction time 3.36 h. Under the optium conditions the interesterification degree was 68.61%. The free fatty acids generated in the interesterification process were removed by short-range molecular distillation. After that, the acid value of the interesterification product dropped to 0.12 mgKOH/g.Through analysing and comparing the main triglyceride species of the oil before and after the interesterification, we found that the main triglyceride species did not change, but their relative content undergone great change. After interesterification, triglyceride composition was more balanced and more suitable for spread products. The crystal form of fats changed fromβtoβ' after interesterification. The crystallization rate slowed down, and the crystal morphology and recrystallization phenomenon of palm oil were improved.Water of 40 % and emulsifier of 0.7 % were added into the base oil of interesterification product. And the crystal form and physical analysis results were taken as the evaluation indicators for the evaluation and selection of the optimal emulsifier formulations. The optimal soybean emulsifier's formulation was: ecithin: monoglyceride and diglyceride: STS =2:1:1 or 1:2:1. The quality of thespreads produced using this formulation were the best. and did not differ significantly with the commercial ones. Moreover, they can inhibit the growth of fat crystals in the product as well as maintaining the stability of the crystal. Two commercial spreads were chosen to be melted, and then re-prepared according to the laboratory method. The product had little differences with original commercial spreads in the properities of crystal microstructure, spreadability and adhesiveness, so the properities in general were better.