| Trans-fatty acid (TFA) is a group of unsaturated fatty acids which have trans-configuration or double bond. Its adversely affect human health by impacting digestion andabsorption of essential fatty acids, leading to cardiovascular disease. Declining the cerebralfunction to cause Alzheimer's disease and affecting body growth, etc.Domestic and overseasresearchers have attached great importance to the trans-fatty and its effection.Natural TFA exists in dairy products and adipose tissue of ruminant animals. There is4%-11%of TFA account for total fatty acid in adipose tissue and3%-5%in cow's milk&goat's milk.Generally, natural TFA is not harmful for health.The fat in Cow's milk existseveral kinds of unsaturated fatty acid in a single key at least; the position of the doublelinkage bond is between the Δ6and Δ16, and the trans bonds are all among in11-18carbonbonds. Inappropriate heat treatment processing may cause TFA content increases, or evenharmful for human health.There is a lot of research about TFA in various foods but for dairy products it is verylimited. Particularly, the hazards of TFA in cattle products by different processing technologyhave no relevant literature and evaluation.The trans-fatty acids was extracted by ethanol&petroleum ether and methyl-esterificated then analyzed with GC. This paper aims to investigate the variation of the TFA inpure milk processing with different heat treatment to provide the basic technologicalparameters.1.The comparison about three methyl-esterification methods for detection of C16T inmilk fat content.The results show that: for the same sample, the content of C16T in potassiumhydroxide-methanol method under normal temperature was (0.050mg/mL), which is lower ascompare to heating reflux method (0.052mg/mL) and boron trifluoride methanol refluxingmethod (0.060mg/mL). The efficiency of boron trifluoride method reluxing method issignificantly different (P<0.05). And is optimal.2.The optimization of the GC condition to detect the methyl esterification of fatty acid:Chromatographic column: Rtx-1701capillary column (30m×0.25mm×0.25μm); The carrier: N2, column flow0.8mL/min, constant flow mode; Diversion ratio30:1;Sample:1μL; Injectortemperature250℃; Detector temperature:280℃; Warming program:180℃keep5min,4℃/min rose to200℃, again with1℃/min rose to210℃,20℃/min last with rose to230℃.3.TFA content variation at different sterilization conditions shows that heating timesignificantly affect its content (P<0.05). For Pasteurization (85℃), prolong heating time,theC16T and C18T in milk are increased. C16T (0.15±0.01mg/mL) and C18T (1.82±0.04mg/mL) content reached to their peak when increased the heating time to90s. Under ultrahigh temperature (T>133℃) with constant time (4s), the content of C16T (0.056±0.002mg/mL-0.066±0.005mg/mL) and C18T (0.8±0.04mg/mL-0.95±0.08mg/mL)fluctuated with raising temperature, but both of them have no obvious difference. For hightemperature (130℃), the TFA content increasedsignificantly (P<0.05) with extendedsterilization time. The C18T content is high up to2.11±0.2mg/mL when heated to300s.4. The TFA content are varied in different product ion seasons. The results show that inJuly, August, April and October, the TFA content in the milk was significantly different(P<0.05), but other months of the year, have no significantly difference (P>0.05). The TFAcontent in October (C16T=0.056±0.002mg/mL, and C18T=0.82±0.04mg/mL), was lowerbut in July C16T=0.068+0.002mg/mL was in peak and in August (C18T=0.95±0.03mg/mL)was high. |
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