Low-cost and handheld detector on soluble solids content and firmness of kiwifruit

Abstract

Soluble solids content (SSC) and firmness are two important internal quality indices of kiwifruit. The traditional methods used to measure these properties are destructive, thus result in fruit wasting. To make the measurement nondestructive and simultaneous, a handheld detector on SSC and firmness of kiwifruit was developed based on multi-spectral technology. An STM32F429IGT6 was used as the microprocessor of the detector. Twelve light-emitting diodes (LEDs) at selected wavelengths (705, 735, 740, 780, 810, 835, 840, 860, 880, 890, 935, and 970nm) based on our previous works were used as light sources. A TSL2561 was used as optical sensor. The 12 LEDs surrounded the optical sensor with an illumination angle of 45°. A plane-convex lens was used to focus light emitted by LEDs. The LEDs, optical sensor, and plane-convex lens were fixed on a support. The diffuse reflectance multi-spectral were collected on 1532 kiwifruit samples, of which, 1149 samples were used to develop the partial least-squares regression models to predict SSC and firmness, and 383 samples were used to test the performance of the developed detector. The test experiment showed that the root-mean-square errors of the developed detector were 0.42 % and 1.11 N cm−2 for SSC and firmness, respectively. The cost of the detector’s hardware was no more than 100 USD, and its weight was 380 g. The measurement time on SSC and firmness of one sample was less than 2 s. The developed low-cost, precise, and handheld detector could be potentially used to improve kiwifruit production and management.