Innovative Formulation and Quality Optimization of Herbal Pain Relief Oil Using Solar Thermal Technology

This study focused on preparing and optimizing herbal pain relief oil using solar thermal technology, specifically a solar box cooker, during winter and summer seasons. The performance of solar device was assessed through stagnation temperature and full-load tests using water and herbal pain relief oil, separately, measuring temperatures inside the cooker and pot, as well as ambient temperature, relative humidity, and solar radiation. Figures of merit (F<sub>1</sub> and F<sub>2</sub>) were calculated to evaluate device efficiency. The herbal pain relief oil was formulated with mustard oil and varying proportions of nirgundi leaves (5%, 10%, 15%) and 5% of other raw herbs like ajwain, garlic, fenugreek and turmeric, processed for one or two days. The resulting oil was filtered, stored in sealed glass or plastic bottles, and subjected to laboratory analysis to determine pH, specific gravity, viscosity, acid value, saponification value, and refractive index. Sensory and organoleptic evaluations, including colour, odour, sensitivity, irritation, and overall acceptance, were conducted by 18 panellists, comparing the formulated oil to a commercial product. The optimal formulation, using 15% nirgundi leaves and 5% other herbs heated for two days in the box type cooker, yielded high quality yellowish green oil with a pH of 7.8, specific gravity of 0.92, viscosity of 29.09, acid value of 0.70, saponification value of 29.45, and refractive index of 1.38. This formulation, processed using the box type solar cooker, also demonstrated a profit margin of 50–60 ₹/L, highlighting the economic and environmental benefits of solar thermal technology for herbal oil production.