Non-contact interactance NIR spectroscopy for estimating TSS and sensory sweetness in conveyor-belt transported cherry tomatoes (Lycopersicon esculentum ’Piccolo’)

Sweetness in tomatoes is a crucial quality feature, especially for high-cost varieties. Without efficient measurements, producers cannot guarantee sweetness, which may lead to low repurchase rates and increased food waste. In this article we report how total soluble solids (TSS), a measure for total sugar content, can be measured in cherry tomatoes using non-contact near-infrared (NIR) interactance spectroscopy. A prototype system working in the wavelength range 760-1080 nm was tested and compared with a commercial handheld NIR reflection instrument operating in the range of 909-1676 nm. The instruments were calibrated using data collected from 200 tomatoes and tested on 5 independent sets harvested over the next 14 months, a total of 611 single tomatoes and 22 tomato trusses. TSS for single tomatoes was in the range 5.3-14 %. NIR interaction obtained typical standard errors of prediction in the range 0.38-0.52 %, significantly lower (p < 0.05) compared to NIR reflection (0.70-0.98 %). Approximately the same accuracy was obtained by interaction measurements on tomatoes moving on a conveyor belt, both in lab (0.47-0.53 %) and in industry (0.39 %). Whole tomato trusses were measured in movement, and TSS could successfully be measured in each tomato on the truss. Three of the test sets were subjected to sensory analysis performed by a trained panel of 10 assessors, revealing high correlations (0.88-0.99) between sensory sweetness and NIR estimated TSS. The results demonstrate that a carefully designed NIR interaction instrument can be used for rapid and non-contact monitoring and sorting of cherry tomatoes according to sweetness.