Abstract
Post-harvest tuna quality degrades rapidly due to autolysis and microbial decomposition, producing toxins such as histamine and harmful volatile compounds. Conventional organoleptic testing methods are subjective, whereas laboratory analyses are time-consuming and costly. This study aimed to develop a portable, non-invasive, rapid, and affordable analytical device by integrating an optical color sensor (TCS3200) and an electronic nose gas sensor array (MQ-136, MQ-137, and TGS 3200) to classify tuna freshness levels (fresh, semi-fresh, and spoiled) at room temperature. The color sensor was mounted at a fixed distance of 2.5 cm inside a dark chamber to measure RGB surface color degradation, while the gas sensor array was positioned at the top of the enclosed chamber to detect decomposition gases such as ammonia (NH3) and hydrogen sulfide (H2S). Gas release kinetics were analyzed using a zero-order reaction model, yielding rate constants (k) of 0.86 for NH3 and 0.81 for H2S. Pearson correlation analysis revealed a strong negative correlation between volatile gas concentrations and RGB color intensities (specifically H2S against the Blue channel, r = -0.82, and the Green channel, r = -0.80), whereas pH parameters showed only a weak correlation (r = 0.16–0.26). RGB frequency thresholds proved effective for precisely categorizing freshness phases, supported by real-time audio feedback from a buzzer. These results demonstrate that integrating optical and volatile gas sensors offers significantly higher accuracy and sensitivity compared to pH-only testing, presenting great potential for implementation as a portable quality testing tool for veterinary authorities and the fishery industry.