This study reports the feasibility of using Raman spectroscopy for quantification of soluble solids and individual sugars in apples. Six different commercial apple varieties were measured by Raman spectroscopy at three different steps: 1) Intact apples with skin, 2) apples without skin and 3) juices obtained from apples. Results indicated that it is possible to measure Raman signals to a depth of 8 mm into the apple with a wide area Raman probe. Multivariate calibration models were established to evaluate how well Raman spectra can be used to estimate the quality parameters SSC (%), total sugars, glucose, fructose and sucrose. Estimation accuracy for SSC was comparable with what is achievable with near-infrared spectroscopy: Root mean square error of cross-validation (RMSECV) = 0.66, 0.46 and 0.72 % and coefficients of determination (R²) = 0.70, 0.85 and 0.63 for intact apples, apples without skin and juices, respectively. Sucrose and glucose were well estimated with RMSECV of 2.8, 1.9, 2.1 mg/mL for glucose and 5.8, 3.9 and 3.7 mg/mL for sucrose, for the three sample cases, respectively. Coefficient of determination was higher than 0.82 for all models. Regression coefficients for all calibration models highlighted identifiable Raman bands that could be related to the target sugars.

本研究报告了使用拉曼光谱对苹果中的可溶性固体和单个糖进行定量的可行性。通过拉曼光谱法在三个不同的步骤测量了六种不同的商业苹果品种：1) 带皮的完整苹果，2) 不带皮的苹果和 3) 从苹果中提取的汁液。结果表明，可以使用广域拉曼探头测量苹果内部 8 毫米深度的拉曼信号。建立了多变量校准模型来评估拉曼光谱可用于估计质量参数 SSC (%)、总糖、葡萄糖、果糖和蔗糖的程度。SSC 的估计精度与近红外光谱可达到的精度相当：交叉验证的均方根误差 (RMSECV) = 0.66、0.46 和 0.72 % 以及确定系数 (R² ) = 0.70、0.85 和 0.63 分别用于完整苹果、去皮苹果和果汁。对于三个样品情况，蔗糖和葡萄糖得到了很好的估计，葡萄糖的 RMSECV 分别为 2.8、1.9、2.1 毫克/毫升，蔗糖的 RMSECV 分别为 5.8、3.9 和 3.7 毫克/毫升。所有模型的决定系数均高于 0.82。所有校准模型的回归系数突出显示了可能与目标糖相关的可识别拉曼谱带。