猪肉新鲜度指示标签的制备及应用

基于猪肉在腐败过程中产生的挥发性含氮化合物会使包装中气体酸碱性发生变化的原理，以甲基纤维素和聚乙二醇-6000为基材，添加溴甲酚紫、溴百里酚蓝等酸碱指示剂，最终制得6 种方便、无损的新鲜度指示标签。将标签置于不同质量浓度的NH3环境中，6 种标签的颜色均发生显著变化，且随NH3质量浓度的增加而差异变化明显；将标签应用于生鲜猪肉贮存中，通过测定4 ℃条件下不同贮存时间猪肉各项腐败指标以及指示标签的颜色变化，探究其用于监测生鲜猪肉新鲜度的可行性。结果表明：初始pH值为4.24的溴甲酚紫指示标签可较好地区分出猪肉的3 个新鲜度等级；利用此标签的颜色测定数据建立偏最小二乘模型，对挥发性盐基氮含量和菌落总数进行预测的回归系数（R2）均大于0.92，通过标签颜色变化可以判断猪肉新鲜度。

Preparation and Application of Indicator Labels for Identification of Pork Freshness

Methylcellulose and polyethylene glycol-6000 were used as film-forming substrates, and synthetic dyes were added to prepare six easy-to-use indicator labels (FIL) for pork freshness assessment based on the fact that the color of indicator labels will change when absorbing the volatile ammonia released from pork during spoilage. When used for the detection of NH3, all color labels exhibited significant color changes showing obvious differences with the increase of gas concentration. To explore their feasibility for evaluating the freshness of pork stored at 4 ℃, the color changes of these labels were recorded and various spoilage indicators were measured at different storage times. The results also showed that the FIL made with bromocresol purple (at an initial pH of 4.24) was able to discriminate freshness, medium freshness, and spoilage. The statistical models obtained by partial least squares based on the color changes of labels 3 and 4 successfully predicted total volatile basic nitrogen (TVB-N) contents and aerobic plate counts (APC) of pork with regression coefficients (R2) greater than 0.92. Accordingly, pork freshness could be judged by the color changes of the labels.