Physicochemical and Thermal Evaluation of a Mixed-Mode Greenhouse Solar Dryer for Guava (Psidium guajava L.).

The present study aimed to evaluate the quality and nutritional properties of guava slices dried in a greenhouse solar dryer (operated under mixed and direct modes) and an electric stove at 50°C. The results showed that mixed-mode solar drying resulted in greater retention of vitamin C (112.60 mg/100 g), carotenoids (0.37 mg/g), and antioxidant activity (95.77%). The proximate analysis showed that mixed-mode drying yielded better nutrient results, such as protein (3.29%), fat (3.33%), and ash (3.50%). The colorimetric analysis revealed that guava samples dried in mixed-mode solar drying exhibited a lower total color difference (ΔE = 8.92) compared to those dried in direct solar mode (ΔE = 14.62) and electric stove (ΔE = 14.95). Dryer efficiency varied between experiments. The mixed-mode configuration achieved a solar collector efficiency of 34.89% and a drying efficiency of 13.16%. In contrast, the direct-mode dryer achieved higher efficiency on the first day (18.43%), but its performance declined significantly on the second day of drying. These findings underscore the potential of mixed-mode greenhouse solar drying as a promising technique for preserving guava quality while reducing overall drying time. Moreover, the system benefits from utilizing solar energy as its primary source, offering a sustainable and cost-effective alternative to conventional drying methods. PRACTICAL APPLICATIONS: The results of this research are of great importance for fruit drying using a greenhouse solar dryer, since the introduction of solar drying technologies will help the agricultural sector better conserve its crops, reduce losses, and increase the commercial value of its products. Furthermore, it presents an opportunity to introduce a new product-dehydrated guava-which, due to its concentrated active compounds, can be incorporated into dietary supplements, nutrition bars, fortified flours, and functional extracts used as additives in beverages, liquid supplement formulations, or capsules.