白胡椒粉末与面粉颜色非常接近, 因此在白胡椒粉末中掺入少量的面粉很难通过人的视觉或嗅觉判别。 高光谱成像不仅可以获得物质的光谱信息, 还可以获得物质的空间位置信息, 因此利用高光谱成像识别白胡椒粉末中掺入面粉的含量及其掺入位置成为可能。 按照1%~60%的配比和1%的梯度将纯面粉掺入到纯白胡椒粉末中, 再加上纯胡椒粉末和纯面粉共制备62份样品; 每份样品单独进行高光谱扫描, 共获得62份光谱数据; 随机选择其中42份样品用于偏最小二乘法建模, 余下20份用于测试。 将每份样品的平均光谱经一阶微分预处理后, 利用偏最小二乘法建立预测白胡椒粉末中面粉含量定量分析建模, 其校正集的均方根误差为0.83%, 预测集的均方根误差为2.73%, 校正集与预测集的相关系数分别为RC=0.99和RP=0.98。 为了在掺杂的白胡椒粉末中定位面粉的具体掺入位置, 提出了相关系数法和最大最小判别准则。 计算掺杂样品与纯白胡椒粉末和面粉的相关系数分别记为R1和R2, 若某位置点为纯面粉则R1达到最大R2达到最小。 将R1与R2的差值R按由小到大的次序排列, 以PLSR回归模型的预测结果为门限将R中小于等于门限值的位置点判别为面粉, 然后在掺假样品中标记出掺入面粉的位置, 以便直观显示。 本研究为实现快速、 无损和可视化鉴别白胡椒粉末真假提供一种参考方法。

White pepper powder is very similar to flour, so it is difficult to distinguish a small amount of flour from white pepper powder by human vision or smell. Hyperspectral imaging technology can not only obtain spectral information but also obtain spatial position information. Therefore, it is possible to predict the content of flour adulteration in white pepper powder and locate the mixing position in white pepper powder by hyperspectral imaging technology. Sixty-two samples are prepared, including 60 samples of pure flour mixed with pure white pepper powder at a ratio of 1% to 60% by weight and a gradient of 1%, in addition, two samples of the pure pepper powder and the pure flour. Each sample was scanned by the hyperspectral image, and a total of 62 hyperspectral data were obtained. Forty-two samples were selected randomly as correction set for partial least squares regression (PLSR) modeling, and the remaining 20 samples were used for prediction set. The pretreatment method of first derivatives was applied to the average spectrum of each sample, and then the PLSR was used to establish a quantitative analysis model for predicting the flour content in white pepper powder. The experimental results show that the root means square error of the correction set is 0.83%, and the root mean square error of the prediction set is 2.73%. The correlation coefficients between the correction set and the prediction set are 0.99 and 0.98 respectively. In order to locate the specific mixing position of flour in the white pepper powder, the Correlation Coefficient Method and the Maximum and Minimum Criterion were proposed. R1 are used to indicate the correlation coefficient between the sample and the pure flour, and R2 indicates the correlation coefficient between the sample and the pure white pepper powder. If the location is pure flour, R1 reaches the maximum and R2 reaches the minimum. The difference between R1 and R2 is calculated to get R, and R is arranged in order from small to large. Using the prediction result of the PLSR regression model as a threshold, the location of R in less than or equal to the threshold value is identified as flour. Then the position of the flour was marked in the adulterated sample so that it could be visually displayed. This research provides a reference for fast, nondestructive and visual identification of white pepper powder adulteration.