不同MA袋对鲜食核桃仁保鲜效果的比较

测定不同材质自发气调(modified atmosphere, MA)包装袋对鲜食核桃仁的保鲜效果。以‘香玲’鲜食核桃为试材，分别采用5种不同塑料复合包装袋包装：PA/PE袋-200 μm（处理1），PA/PE袋-180 μm（处理2），Al/PET袋-210 μm（处理3），PET/PE袋-160 μm（表面平滑）（处理4）和PET/PE袋-160 μm（表面网纹）（处理5），以地膜包装-6 μm（处理6）为对照，低温贮藏，定期测定其呼吸强度、脂肪含量、蛋白质含量、SOD酶活性、POD酶活性、酸价、过氧化值及碘价等指标的变化。结果表明：呼吸强度测试中，除处理3外，处理6和其他处理组在贮藏期前12天内呼吸强度从135 CO₂ mg/(kg·h)下降至60 CO₂ mg/(kg·h)以内，中后期几乎保持稳定状态；处理4和处理5核桃在贮藏15天后呼吸强度在30~40 CO₂ mg/(kg·h)之间；脂肪含量测试中，在贮藏30天内处理3的核桃脂肪含量为34.2 g/100 g；处理1、2、4、5的核桃在贮藏前期脂肪含量持续下降，60天时，处理4、5核桃脂肪含量分别为45.8 g/100 g和46.1g/100 g；在贮存60天时，蛋白质含量处理4、5核桃的蛋白质含量最高，达到17.6 g/100 g和17.1 g/100 g；酸价测试中，在贮藏期间处理6核桃仁的酸价从0.24 mg KOH/g增长到4.3 mg KOH/g，处理4、5核桃的酸价从0.24 mg KOH/g增加到2.7 mg KOH/g以内；SOD酶活性测试中，处理6对照组和处理1、2在贮藏30天时，SOD酶活性达到140.1 U/g和135.2 U/g；处理3、4、5的SOD活性在贮藏45天分别达到139.9、149.7 U/g和150.0 U/g；POD酶活性测试中，处理6对照组和处理3在贮藏30天时，POD活性达到最低值，分别为10.5 U/g和10.7 U/g，其他4组在45天时降至最小值，分别为：10.8、11.0、10.1、10.3 U/g；MDA含量测试中，整个贮藏期，鲜食核桃核仁的MDA含量持续上升，贮藏至60天时，处理4的MDA含量为6.25 mmol/g，处理5为6.08 mmol/g，均低于其他组数据，但差异不显著。上述6种包装材料中，PET/PE-160 μm包装保鲜效果最佳，可以推广使用。

Effects of Different Modified Atmosphere Packages on Preservation of Fresh Walnuts

The study aims to determine the fresh-keeping effects of modified atmosphere (MA) packages on fresh walnuts. With ‘Xiangling’ fresh walnuts as the test materials, five kinds of plastic composite packaging bags were used, including PA/PE bag -200 μm (T1), PA/PE bag -180 μm (T2), Al/PET bag -210μm (T3), PET/PE bag -160 μm (smooth surface) (T4) and PET/PE bag -160 μm (surface mesh) (T5), and plastic film packing -6 μm (T6) was used as the control. Fresh walnuts were stored at low temperature, and the changes of respiratory intensity, fat content, protein content, SOD activity, POD activity, acid value, peroxide value and iodine value were measured regularly. In the respiratory intensity test, except T3, the respiratory intensity of walnuts under T6 and other treatments decreased from 135 CO₂ mg/(kg·h) to less than 60 CO₂ mg/(kg·h) within 12 days from the beginning of the storage, then almost kept stable in the middle and late stages of the storage. The respiratory intensity under T4 and T5 was between 30-40 CO₂ mg/(kg·h) after 15 days of storage. The fat content of walnuts under T3 within 30 days of storage was 34.2 g/100 g; the fat content under T1, T2, T4 and T5 decreased continuously at the early stage of storage, and the fat content under T4 and T5 was 45.8 g/100 g and 46.1 g/100 g respectively on the 60th day of the storage. When fresh walnuts were stored for 60 days, the protein content under T4 and T5 was the highest, reaching 17.6 g/100 g and 17.1 g/100 g, respectively. During the storage period, the acid value of walnuts under T6 increased from 0.24 mg KOH/g to 4.3 mg KOH/g, and that under T4 and T5 increased from 0.24 mg KOH/g to less than 2.7 mg KOH/g. The SOD activity of walnuts under T6 reached 140.1 U/g and that under T1 and T2 reached 135.2 U/g on the 30th day of the storage. The walnut SOD activity under T3, T4 and T5 reached 139.9 U/g, 149.7 U/g and 150.0 U/g, respectively, on the 45th day of the storage. The POD activity of walnuts under T6 and T3 reached the lowest value on the 30th day of the storage, which was 10.5 U/g and 10.7 U/g, respectively, and the POD activity under the other 4 treatments dropped to the lowest value on the 45th day, which was 10.8 U/g, 11.0 U/g, 10.1 U/g, and 10.3 U/g, respectively. During the whole storage period, the MDA content of fresh walnuts continued to increase, and on the 60th day of the storage, the MDA content of T4 was 6.25 mmol/g and that of T5 was 6.08 mmol/g, both lower than that of other treatments, but the difference was not significant. Among the six tested packaging materials, PET/PE-160μm package has the best fresh-keeping effect and can be popularized.