猕猴桃糖度是重要的猕猴桃内部品质衡量指标。 传统的糖度检测耗时且有损样品, 有效无损检测猕猴桃糖度含量对于其品质分级、 储藏销售具有重大意义。 基于高光谱成像技术的常见果蔬品质无损检测方法多数是采用竞争性自适应重加权算法(CARS)、 连续投影算法(SPA)、 主成分分析(PCA)、 迭代保留信息变量法(IRIV)等算法中的某个单一算法提取特征光谱变量, 而这些算法单独使用易导致预测结果的稳定性不足。 对此, 开展了基于高光谱成像技术的猕猴桃糖度的无损检测方法研究。 以四川省雅安市“红阳”猕猴桃为研究对象, 依次对猕猴桃样本编号并采集其在400~1 000 nm波长范围内的高光谱图像, 计算感兴趣区域的平均光谱作为样本的有效光谱信息; 分别采用多元散射校正(MSC)、 标准正态变量变换(SNV)、 直接正交信号校正(DOSC)等3种光谱数据预处理方法分析对预测模型精度的影响, 对比结果显示DOSC的预处理效果最好; 对预处理后的光谱分别采用一次降维(CARS, SPA, IRIV)、 一次组合降维(CARS+SPA, CARS+IRIV)算法和二次组合降维算法((CARS+SPA)-SPA, (CARS+IRIV)-SPA))等7种算法提取特征光谱变量, 并分别构建了预测猕猴桃糖度的3种模型, 即支持向量回归机(SVR)、 最小二乘支持向量机(LSSVM)和极限学习机(ELM)模型; 最后对比了基于不同特征提取方法的3种模型的预测精度。 研究结果表明: ELM模型具有最好的预测性能, 而SVR模型的预测性能最差; (CARS+IRIV)-SPA所选特征光谱变量输入LSSVM、 ELM模型, 其获得的预测结果均优于其他算法所选特征光谱变量输入对应模型所得的预测结果, 证明了(CARS+IRIV)-SPA算法在提高猕猴桃糖度含量检测精度方面的有效性。 对比不同方法的预测结果可知, (CARS+IRIV)-SPA-ELM对猕猴桃糖度的预测性能最优, 其相关系数R_c=0.945 1, R_p=0.839 0, 均方根误差RMSEC=0.450 3, RMSEP=0.598 3, 预测相对分析误差RPD=2.535 1, 该方法为猕猴桃糖度的检测无损化、 精准化、 智能化发展提供了可靠的理论依据和技术支撑。

The sugar content of kiwifruit is an important measure of its internal quality. Traditional sugar content detection is time-consuming and destructive sampling, and it is of great significance to non-destructive detect the sugar content of kiwifruit effectively for its quality classification, storage and sales. The common non-destructive detection methods of fruit and vegetable quality based on hyperspectral imaging technology mostly use a single algorithm of competitive adaptive reweighted sampling (CARS), successive projections algorithm (SPA), principal component analysis (PCA) and iteratively retains informative variables (IRIV) to extract features. However, using these algorithms alone will lead to insufficient stability of prediction results. This study designs a non-destructive detection method for kiwifruit sugar content based on hyperspectral imaging technology. The “Red Sun” kiwifruit samples in Ya'an city of Sichuan province were numbered, their hyperspectral images in the wavelength range of 400~1 000 nm were collected, and the average spectrum of the region of interest was calculated as the effective spectral information of the samples. Then, three spectral data preprocessing methods including Multiplicative Scatter Correction (MSC), Standard Normal Variate (SNV), and Direct Orthogonal Signal Correction (DOSC), were used to analyze the influence on the accuracy of the prediction models, respectively. The comparison results showed that DOSC had the best preprocess effect. Further, for the preprocessed spectrum, 7 dimensionality reduction methods including CARS, SPA and IRIV from one-time dimensional-reduction algorithms, CARS+SPA and CARS+IRIV from the first-order combined dimensional reduction algorithms, and (CARS+SPA)-SPA, (CARS+IRIV)-SPA from the second-order combined dimensional-reduction algorithms respectively, were used to extract characteristic spectral variables, and three models for predicting the sugar content of kiwifruit were constructed i. e. Support Vector Regression (SVR), Least Square Support Vector Machine (LSSVM) and Extreme Learning Machine (ELM) models. Finally, the prediction accuracy of the three models based on different feature extraction methods was compared through experiments. This study shows that the ELM model has the best prediction performance, while the SVR model has the worst prediction performance. When the characteristic spectral variables extracted by (CARS+IRIV)-SPA were input into LSSVM and ELM models, respectively, the prediction results are better than those obtained by other methods. Then (CARS+IRIV)-SPA is verified to be effective in improving the prediction accuracy of the models. Comparing the prediction results of these methods, the prediction performance of (CARS+IRIV)-SPA-ELM is better than other methods, with the correlation coefficient R_C=0.945 1, R_P=0.839 0, RMSEC=0.450 3, RMSEP=0.598 3, and RPD=2.535 1, which will provide reliable theoretical basis and technical support for the non-destructive, precise and intelligent development of kiwifruit sugar content detection.