VIS-NIR portable espectrometer for non-destructive assessment of maturity and quality of ‘Gala’ apples

Abstract Visible and near infrared (VIS-NIR) spectroscopy is a non-destructive, fast, practical and reliable technique to determine maturity and quality attributes in apple fruit. However, the effects of cultivar and growing conditions on the predictive performance of the equipment must be determined before its commercial application in the apple industry. This study was carried out to evaluate the efficiency of a VIS-NIR portable spectrometer for fast and non-destructive determination of quality attributes in apples of the ‘Gala’ group (‘Maxi Gala’, ‘Royal Gala’, ‘Imperial Gala’ and ‘Galaxy’) harvested in three commercial orchards (corresponding to the production sites: Vacaria, Fraiburgo and São Joaquim) in Southern Brazil. At the commercial harvest and after three months of cold storage (1.5 ± 0.3 ºC and relative humidity of 92 ± 2%), fruit were assessed in terms of spectral data in the wavelength range between 310 and 1100 nm with a VIS-NIR portable spectrometer. After collecting the spectral data, fruit were submitted to physicochemical analysis of dry matter (DM), soluble solids content (SSC), flesh firmness and texture. The calibration models were developed using three sets of spectral and physicochemical data: (1) without separating by cultivar and orchard; (2): separating by cultivar, regardless of orchard; (3): separating by cultivar and by orchard. The calibration models were obtained by the partial least squares (PLS) regression technique. The accuracy of the calibration models for each dataset was evaluated in the validation step considering the values of the relative root mean square error of cross-validation (RMSECVr = 10%). Models developed for each cultivar in each orchard (location) were more accurate and efficient to assess DM, SSC and flesh firmness, compared to the models developed for each cultivar, regardless of orchard, or without separating by cultivar and by orchard. Therefore, VIS-NIR spectrometer is a promising tool for the rapid and non-destructive analysis of quality attributes in ‘Gala’ apples. However, the equipment must be calibrated for each cultivar (‘Maxi Gala’, ‘Royal Gala’, ‘Imperial Gala’ and ‘Galaxy’) and growing condition (orchard) in order to obtain more precise analyses of DM, SSC and flesh firmness in the fruit.

摘要 可见近红外（VIS-NIR）光谱技术是一种非破坏性、快速、实用且可靠的手段，可用于测定苹果果实的成熟度与品质属性。然而，在将该技术应用于苹果产业商业化场景前，需明确品种与种植环境对设备预测性能的影响。本研究旨在评估一款可见近红外便携式光谱仪，用于快速无损测定巴西南部三个商业果园（对应产地：瓦卡里亚（Vacaria）、弗赖堡（Fraiburgo）与圣若阿金（São Joaquim））采收的‘嘎啦’（Gala）组苹果（包括‘Maxi Gala’、‘Royal Gala’、‘Imperial Gala’及‘Galaxy’）的品质属性。在商业采收期以及经三个月低温贮藏后（贮藏条件为1.5±0.3℃，相对湿度92±2%），研究人员使用该可见近红外便携式光谱仪，采集了波长范围310~1100nm的光谱数据。完成光谱数据采集后，对果实开展干物质（dry matter, DM）、可溶性固形物含量（soluble solids content, SSC）、果肉硬度与质构的理化分析。本研究采用三类光谱与理化数据集构建校准模型：(1) 不按品种与果园分组；(2) 仅按品种分组，不考虑果园差异；(3) 同时按品种与果园分组。校准模型通过偏最小二乘（partial least squares, PLS）回归技术构建。以10%交叉验证相对均方根误差（RMSECVr=10%）为评估指标，在验证步骤中对各数据集的校准模型精度进行了评价。结果显示，相较于仅按品种分组（不考虑果园）或不按品种与果园分组构建的模型，针对每个果园内各品种构建的模型，在测定干物质、可溶性固形物含量与果肉硬度时，精度与效率均更优异。综上，可见近红外光谱仪是实现‘嘎啦’苹果品质属性快速无损分析的极具潜力的工具。但为实现果实干物质、可溶性固形物含量与果肉硬度的精准分析，需针对各品种（‘Maxi Gala’、‘Royal Gala’、‘Imperial Gala’及‘Galaxy’）与种植环境（果园）分别完成设备校准。