The advent of plastic fats, such as shortening and margarine, greatly meets the needs of consumers for different food processing, but plastic fats are usually prepared by hydrogenation, and this process often produces trans fatty acids. . Trans fatty acids can cause great damage to the human body, such as diabetes, obesity, and cardiovascular and cerebrovascular diseases. Triglycerides synthesized from medium-chain fatty acids (MCFA) can be quickly hydrolyzed in the human intestine and reduce accumulation. Therefore, shortening and margarine made from plastic fats rich in medium-chain fatty acids and zero trans fatty acids will have ideal physical properties Nutritional properties. Currently, enzymatic transesterification is an alternative method for producing such plastic fats.
This study is to use Lipozyme TL IM to combine high hydrogenated soybean oil (HSO) and camphor seed oil (with different mass ratios (60:40:100, 70:30:100, 80:20:100) at 65 ℃). CCSO) and perilla oil (PO) are mixed to catalyze the preparation of zero-trans fatty acid plastic fat rich in α-linolenic acid (ALA) for 8 hours. After the reaction, the physical and chemical properties of the transesterified product and the physical mixture were measured, including fatty acid composition, triglyceride composition, solid fat content, sliding melting point, tocopherol content, and solid fat crystal structure.
Results and analysis
1) The composition of triglycerides is extremely complex, and it is difficult to accurately determine the types of plastic fatty triglycerides. Gas-liquid chromatography was used to determine HSO, CCSO, PO, and the three according to the mass ratio of 60:40:100. The equivalent carbon number of the product of physical mixing and transesterification (Figure 1). The results found that the equivalent carbon number of the product after transesterification decreased, indicating that a certain amount of medium-chain triglycerides were produced by the reaction. Compared with the physical mixing method, the plastic fat prepared by the enzymatic transesterification method has LLL/POLn, PSP, PLL /LPL, SOO/OSO, LOO/OLO and POS content has increased.
2) Measure the solid fat content (SFC) by nuclear magnetic resonance (NMR) and determine the sliding melting point (SMP) according to AOCS. When the temperature rises to 40 ℃, the SFC of the transesterified product is significantly reduced, and compared to physical The hybrid SMP is lower (Figure 2). This is related to the change in fatty acid composition after transesterification.
3) Crystal structure is the most important functional characteristic index of shortening and margarine. The common crystal structures of solid fats are α, β, and β’. Among them, α-type fat has the worst thermal stability and the lowest melting point; β has the strongest thermal stability and the highest melting point; β’is between the two and has a medium melting point. It can give margarine a good taste, and it is not easy to grind and has a small graininess. X-ray diffraction (XRD) was used to determine the crystal structure of plastic fat prepared by physical mixing and enzymatic transesterification (Figure 3). The results show that the plastic fat prepared by the physical mixing method has a strong short pitch at 4.59? (β), 3.87? and 3.79? (β’), while the enzymatic transesterification products are at 3.83? and 4.21? (β’). ) Shows a stronger short pitch than at 4.59? (β). This is because during the enzymatic transesterification reaction, the fatty acids in the triglycerides are rearranged, and the symmetry of the newly formed triglycerides is reduced, resulting in a decrease in the β-type crystal structure, and a significant increase in the β’-type crystal structure, thereby increasing plasticity The palatability of fat.
4) When the mass ratio of HSO:CCSO:PO is 70:30:100, the crystal structure of the biological transesterification product and the physical mixture is obviously different. Microscopically, the physical mixture was observed to be spherical crystals (Figure 4(A)), while more minute crystals were observed in the transesterified product (Figure 4(B)). This indicates that the transesterified product contains a higher level of β’form, which can better meet the raw material requirements for preparing margarine.
Figure 1 The highest point is HSO, CCSO, PO, and physical mixing of the three according to 60:40:100 mass ratio And the equivalent carbon number of the product after the transesterification reaction
Figure 2 Different mass ratios of HSO, CCSO, and PO (60:40:100, 70:30:100, 80 ：20∶100) when using physical mixing method and enzymatic transesterification method to prepare the solid fat content of plastic fat
Figure 3 X-ray diffraction patterns of different mass ratio physical mixing methods and enzymatic transesterification products
Figure 4 HSO:CCSO:PO mass ratio of 70:30:100 physical blend (A) and The crystal structure of the transesterified product (B)
In this study, plastic fat was prepared by enzymatic transesterification with different mass ratios of 60:40:100, 70:30:100 and 80:20:100 from HSO, CCSO and PO. The product contains approximately 8.58-17.98%MCFA and 30%ALA. On the other hand, the product has ideal physical properties. The results show that the transesterified product is more suitable for preparing margarine, and the physical mixture is more suitable for the raw material of shortening. However, the cost of expensive enzyme preparations still limits their application in the food industry, so how to improve the efficiency of enzymes and reduce processing costs will become the focus of research.