降温方法对不同采收期鸭梨采后果心褐变和膜脂组分的影响

为了探讨缓慢降温抑制采后鸭梨果实褐变的机理，研究了不同降温方法对不同采收期鸭梨果心膜脂脂肪酸组分、含量、膜相变温度、脂氧合酶（LOX）活性以及果心褐变的影响。结果表明：鸭梨果心含有月桂酸、豆蔻酸、棕榈酸、棕榈油酸、珠光酸、硬脂酸、油酸、亚油酸、亚麻酸，其中含量较多的是亚油酸、棕榈酸和油酸。缓慢降温提高了早采鸭梨果心的亚麻酸和亚油酸相对含量及不饱和脂肪酸与饱和脂肪酸比值（U/S），降低了果心的膜相变温度，明显抑制了果心LOX活性和褐变。推迟采收提高了鸭梨果心的U/S值，降低了膜相变温度，但由于采收期晚，果实衰老较快，后期果心LOX活性快速升高，膜脂过氧化严重，导致晚采果更容易褐变。总之，适当早采结合缓慢降温可以提高鸭梨果心膜脂不饱和脂肪酸含量和U/S值，抑制果心褐变。

Effects of different cooling methods on core browning and membrane fatty acid components of postharvest Yali pears with different harvest periods

In order to investigate the mechanism that slow cooling inhibits the browning of Yali pears after harvest, the effect of different cooling methods on membrane fatty acid components, contents, phase transition temperature, lipoxygenase (LOX) activity and browning of core of Yali pears with different harvest period were studied. The results showed that fatty acid components of core contained lauric acid, tetradecanoic acid, palmitic acid, palmitoleic acid, perlatolic acid, stearic acid, oleic acid, linoleic acid, linolenic acid. And the contents of linoleic acid, palmitic acid and oleic acid were more. Slow cooling increased linolenic acid and linoleic acid relative contents and unsaturated-saturated fatty acid ratio (U/S) value, reduced the phase transition temperature, significantly inhibited LOX activity and browning of the core of early harvested Yali pears. Late harvest increased the U/S value, reduced the phase transition temperature of the core. But because the harvest period was later, fruits senesced more quickly, LOX activity rose quickly in the late period, and membrane lipid peroxidation got serious. All these changes mentioned above finally made the late harvested fruits much easier to get browning. In a word, early harvesting and slow cooling could increase the contents of unsaturated fatty acid and U/S value, restrain the core browning of Yali pear after harvest.