Wavelength Modulation Spectroscopy to Measure Fruit Respiration in Real Time from CO2 Concentration

Climacteric fruit respiration generates carbon dioxide (CO2), making its real-time monitoring crucial for optimizing storage and transport conditions, minimizing economic losses and waste. This work demonstrates the application of Wavelength Modulation Spectroscopy (WMS) for the development of a sensor capable of measuring CO2 concentration in real time with high precision and reproducibility. For the technique, a Distributed-Feedback diode laser was used, tuned to the 1572.3 nm CO2 absorption line. The temporal evolution of CO2 concentration released by tomato and banana at different ripening stages was measured. The sensor exhibited a detection limit for CO2 variations ranging from 122 to 488 parts per million (ppm). The results demonstrate the applicability of WMS for monitoring fruit respiration. The normalization technique second harmonic/first harmonic (2f/1f) proved essential for mitigating thermal effects, as the 1f signal corrects for laser power and non-absorption losses, thus enhancing data reliability. Analysis of CO2 evolution curves suggests the potential to study gas diffusion phenomena within fruits, evidenced by the sigmoidal profile. This sensor has potential for future applications in modified atmosphere packaging (MAP) and quality control.