Analysis In Physicochemical Properties And Crystallization Properties Of Lard-based 1,3-diacylglycerol

In this study,the physicochemical properties,thermal stability,oxidation resistance and crystallization properties of lard-based 1,3-diacylglycerol were tested to provide a theoretical basis for its application in China.(1)In this part,the changes in fatty acids composition during enzymatic preparation of the 1,3-diacylglycerols(DG)from lard and relevent indicators of lipid oxidation including acid value(AV),peroxide value(POV)and the amount of malondialdehyde(MDA)were measured based on the GB10146-2015 < national food safety standard of edible animal oil and fats > to reveal the characteristics of lipid oxidation in enzymatic preparation of 1,3-diacylglycerols from lard.The results showed that the 1,3-DG lard contained 20 fatty acids including 32.73% saturated fatty acids(SFA),40.82% monounsaturated fatty acids(MUFA),24.20% polyunsaturated fatty acids(PUFA).During the enzymatic preparation,the changes of fatty acids composition are not significanct(P>0.05);AV increased with increasing time and exceed the national standard after 2h(1.5 mg KOH/g);POV decreased smoothly and remained stable after 6h;the amount of MDA firstly increased then decreased and was finally tending towards stability.Both POV and the amount of MDA could meet the national standard requirement(0.10% and 0.25% respectively).Thus,the enzymatic process did not affect the fatty acids composition,and POV as well as the amount of MDA could meet the national standard requirement.AV degradation was significant,thus we should focus to the control of AV during enzymatic preparation of the 1,3-DG from lard.(2)In this part,the changes in fatty acids of lard-based 1,3-DG during heating process were analyzed by gas chromatography(GC)and relevant indicators of lipid oxidation including AV,POV,MDA and carbonyl group value(CGV)were measured to judge the quality of lard-based 1,3-DG oil during heating.The results showed that the amount of SFA,MUFA and TFAs of lard-based 1,3-DG oil increased with increasing heating temperature and time whereas those of PUFA decreased.When the heating temperature was 210 ?,the amount of MUFA increased in first and then decreased,showing its peaks on 4h.AV remains relatively stable while both POV and CGV values increased and the amount of CGV could not meet the national standard(50 meq/kg)after heating 6 h at 210 ?.After heating 4 h at 150,180 or 2 h at 210 ? ?,MDA began to slide.Heating of lard-based 1,3-DG oil at high temperature for a long time will lead to lower quality,therefore,the1,3-DG oil should not be heated at high temperature for a long time.(3)Crystallization and melting behaviors of the DG,TAG and TAG added with different proportions(25%,50%,750%)of DG were determinedby differential scanning calorimetry(DSC),pulsed-nuclear magnetic resonance(pNMR)and polarizedmicroscopy.The results showed that 1,3-DG promoted the crystallization of TAG,the solid fat content of the DG was higher than TAG.The results of X-ray diffraction indicated that the crystalline part of 1,3-DG was transformed into a more delicate ?'-crystal form.The polarized light microscopy revealed that the addition of 1,3-DG made the crystal more delicate.However,the 1,3-DG blended with TAG(mixed fat)was not significant to promote crystallization: adding 20% and 50% of 1,3-DG had lower solid fat content than lard.The SFC of the mixtures added with 75% 1,3-DG was closed to lard.The content of acicular crystals in the mixtures gradually improved with the increase of addition proportion of 1,3-DG.(4)Using Rancimat analysis the effects of three synthetic antioxidant BHA,BHT and TBHQ and three kinds of natural antioxidants: vitamin C,vitamin E and tea polyphenols on the lard-based 1,3-DG oil's oxidation stability,and their synergistic effect on the oxidative stability of the 1,3-DG oil.The oxidation induction time were determined by adding different mass concentrations of antioxidants in 1,3-DG oil samples.The results showed that the longest oxidation induction time 7.88 h was obtained by adding 0.1% of BHA in 1,3-DG oil,and oxidation induction time was 11.59 times higher than that of blank.In the complex combination of antioxidants,BHA 0.05% mixed with 0.05% VC had significant synergistic effect,the oxidation induction time was 5.14 times higher than that of blank.