Optimization of supercritical CO2 extraction process for oleoresin from rotten onion waste

•The aim of the research is converting the agricultural waste/by-products to value-added products.•The maximum oleoresin yield of 1.012% can be achieved at 80°C temperature, 400bar pressure, 0.53mm particle size and 60min dynamic time.•At the above processing conditions, Sulphur and pyruvate content were 31gkg and 10.41μmole per g fresh weight of onion.•SFE with optimized condition can be useful for revenue generation and get value from the waste of onion. Supercritical fluid extraction technique (SFE) was utilized to obtain the superior quality of onion oleoresin from the dried rotten onion. The effects of temperature (50, 60, 70, 80 and 90°C), pressure (150, 225, 300, 375 and 450bar), dynamic time (30, 60, 90, 120 and 150min) and particle size (0.4, 0.6, 0.8, 1.0 and 1.2mm) were evaluated with respect to oleoresin yield, sulphur content and pyruvate content in oleoresin. The optimization of supercritical fluid extraction was carried out by using a central composite rotatable design (CCRD). From the responses, optimized condition for SFE of onion oleoresin was found as 80°C temperature, 400bar pressure, 0.53mm particle size and 60min dynamic time. Oleoresin extracted at optimized SFE condition had a yield of 1.012% oleoresin, 31g sulphur content per kg of oleoresin and 10.41 μmole pyruvate per g fresh weight of onion. It was observed that SFE provided shorter extraction time, comparatively similar oleoresin yield and a higher percentage of sulphur content which represents the useful sulphur containing compounds in onion.