Instituto de Agroquímica y Tecnología de Alimentos, Paterna, Spain.
J Agric Food Chem. 2011 Jul 27;59(14):7832-40. doi: 10.1021/jf201246g. Epub 2011 Jun 24.
Ethylene vinyl alcohol copolymer (EVOH) films containing green tea extract were successfully produced by extrusion. The films were brown and translucent, and the addition of the extract increased the water and oxygen barrier at low relative humidity but increased the water sensitivity, the glass transition temperature, and the crystallinity of the films and improved their thermal resistance. An analysis by HPLC revealed that the antioxidant components of the extract suffered partial degradation during extrusion, reducing the content of catechin gallates and increasing the concentration of free gallic acid. Exposure of the films to various food simulants showed that the liquid simulants increased their capacity to reduce DPPH(•) and ABTS(•+) radicals. The release of green tea extract components into the simulant monitored by HPLC showed that all compounds present in the green tea extract were partially released, although the extent and kinetics of release were dependent on the type of food. In aqueous food simulants, gallic acid was the main antioxidant component released with partition coefficient values ca. 200. In 95% ethanol (fatty food simulant) the K value for gallic acid decreased to 8 and there was a substantial contribution of catechins (K in the 1000 range) to a greatly increased antioxidant efficiency. Kinetically, gallic acid was released more quickly than catechins, owing to its faster diffusivity in the polymer matrix as a consequence of its smaller molecular size, although the most relevant effect is the plasticization of the matrix by alcohol, increasing the diffusion coefficient >10-fold. Therefore, the materials here developed with the combination of antioxidant substances that constitute the green tea extract could be used in the design of antioxidant active packaging for all type of foods, from aqueous to fatty products, the compounds responsible for the protection being those with the higher compatibility with the packaged product.
采用挤出法成功制备了含有绿茶提取物的乙烯-乙烯醇共聚物（EVOH）薄膜。所制备的薄膜呈棕色半透明状，添加提取物后，薄膜在低相对湿度下的水和氧气阻隔性能提高，但对水的敏感性、玻璃化转变温度、结晶度和热稳定性提高。高效液相色谱分析表明，提取物中的抗氧化成分在挤出过程中发生部分降解，导致没食子酸酯的含量降低，游离没食子酸的浓度增加。将薄膜暴露于不同的食品模拟物中，发现液体模拟物增加了薄膜还原 DPPH(•)和 ABTS(•+)自由基的能力。高效液相色谱监测提取物成分在模拟物中的释放情况表明，绿茶提取物中的所有化合物均有部分释放，尽管释放的程度和动力学取决于食品的类型。在水性食品模拟物中，没食子酸是主要的抗氧化成分，其分配系数值约为 200。在 95%乙醇（脂肪食品模拟物）中，没食子酸的 K 值降低到 8，儿茶素（K 值在 1000 范围内）的贡献显著增加，抗氧化效率大大提高。动力学方面，由于没食子酸的分子尺寸较小，其在聚合物基质中的扩散率较快，因此比儿茶素释放得更快，尽管最相关的影响是酒精对基质的塑化作用，使扩散系数增加了 10 倍以上。因此，采用挤出法制备的含有绿茶提取物中抗氧化物质的材料可以用于设计抗氧化活性包装，适用于从水性到油性产品的各种食品，保护作用主要来自与包装产品相容性更高的化合物。
