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1.Free Fatty Acid Value The FFA values were low (<1%) for all samplesthroughout the 72 h accelerated oxidation period at 60 C. There was no significant difference in the FFA content of safflower and soybean oils during the oxidation period, though coconut oil had the lowest value, and fish oil the highest (Data not shown). The high FFA value of fish oil is due to its higher concentration of polyunsaturated fatty acids, and therefore increased susceptibility to oxidation in comparison to the other oils. The SLs had higher FFA values than their starting materials, with SFO and SFOV having higher values than their counterparts (S1 and S1V) due to their fish oil content. However, the higher initial FFA values (>0.1%) of the SLs in comparison to the vegetable oils and oil blends may have been as a result of increased FFA production during the enzymatic interesterification process. The short-path distillation step resulted in a 0.3–0.4% residual FFA concentration in the SLs. Similar residual values were reported by Nielsen et al. where about 0.3% FFA remained after the distillation process. 2.Peroxide Value The PV of the oils are presented in Fig. 1. Coconut oil had the lowest initial (<0.1 mequiv/1,000 g) and final (\0.2 mequiv/1,000 g) values (Fig. 1). Coconut oil also had the lowest increase in PV throughout the accelerated oxidation period, which is due to its lower unsaturated fatty acid content in contrast to the other oils. The initial PV of fish oil was about 50% higher than that of the other oils. High initial PV value signifies a high production of primary oxidation products, which leads to faster progression of oxidation. Fish oil had the highest increase in PV because of high LCPUFAs and low antioxidant contents (Fig. 1). The SLs had a lower initial PV in comparison to the oil blends. This may be as a result of the enzyme reaction process, which increased the saturation of the lipids and also in part to the distillation process, which decreased the FFA, and other volatile contents of the SLs. Akoh and Moussata reported the stabilization of SLs to oxidative deterioration by incorporation of saturated medium chain fatty acid (caprylic). SFO had higher PV than S1 (Fig. 1) throughout the accelerated oxidation period because of its higher LCPUFAs content in comparison to S1. Comparison of SFO with SFOV shows significantly lower values for the SL with added tocopherol. A similar result was obtained when S1 and S1V were compared, whereby S1V has a lower PV than S1 (Fig. 1). The PV of S1V and SFOV in comparison to that of S1 and SFO shows the effect of tocopherol addition on the oxidative stability of the SLs. The PV were quite similar for the SLs with added tocopherols, irrespective of their LCPUFA content. |
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alvarohao
铁杆木虫 (著名写手)
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【答案】应助回帖
★ ★
爱与雨下(金币+2): 2011-11-04 19:41:31
momo198548(金币+50, 翻译EPI+1): 很强大，谢谢 2011-11-06 19:46:16
爱与雨下(金币+2): 2011-11-04 19:41:31
momo198548(金币+50, 翻译EPI+1): 很强大，谢谢 2011-11-06 19:46:16
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1. 游离脂肪酸（FFA）值 在整个60摄氏度72小时的加速氧化期间，所有样本的FFA值都比较低（<1%）。红花油和豆油在氧化期间的FFA含量没有显著的不同，尽管椰子油的含量最低，而鱼油的含量最高（未列出数据）。鱼油中的FFA值之所以最高，是因为含有较高浓度的多元不饱和脂肪酸，所以相对于其它油类更容易受到氧化的影响。根据它们的鱼油含量，SL要比其原材料含有更高的FFA值，SFO和SFOV也高于其相应的部分（S1和S1V）。但是，相对于植物油和调和油，SL含有较高初始FFA值（>0.1%）的原因很可能是在酶法酯交换过程中FFA产量增加的结果。短程蒸馏步骤导致在SL中产生FFA 0.3-0.4%的残余浓度。Nielsen等报道过类似的残余值，指出在蒸馏过程之后，大约有0.3%的FFA残余。 2. 过氧化值（PV） 图1显示了各种油的过氧化值。椰子油的初值（<0.1 mequiv/1,000 g）和终值（\0.2 mequiv/1,000 g）最低（图1）。而且在加速氧化时期，椰子油的PV增量也是最低的，这是因为它的不饱和脂肪酸含量比其它油要低。鱼油的初始过氧化值要比其它油高出约50%。较高的初始过氧化值意味着初级氧化产物的产量较高，这将导致氧化进程的加快。鱼油之所以拥有最高的PV增量，是因为含有较高的长链多不饱和脂肪酸（LCPUFA）和较低的抗氧化剂含量（图1）。SL的初始过氧化值低于调和油的原因是酶反应过程的结果，酶反应会增加油脂的饱和度，另外部分原因是由于蒸馏过程，这一过程会减小SL中FFA及其它挥发物的含量。Akoh和Moussata曾报道，通过中链饱和脂肪酸（羊脂酸）的加入，SL对氧化变质具有一定的稳定性。在整个加速氧化时期，SFO的过氧化值要高于S1（图1），这是因为，与S1相比，其长链多不饱和脂肪酸（LCPUFA）的含量较高。将SFO与SFOV比较之后，可以看出添加有生育酚的SL的过氧化值明显较低。比较S1和S1V之后，也有相似的结果，其中S1V的过氧化值要低于S1的（图1）。S1V和SFOV的PV与S1和SFO的PV的比较结果表明了生育酚的添加对SL氧化稳定性的效果。不论它们的LCPUFA含量如何，添加有生育酚的SL具有非常相似的过氧化值。 |
2楼2011-11-04 18:21:43
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