Optimizing the Extraction of Effective Compounds from Onion by-products Using Microwave Dry- diffusion and Gravity Method

One of the most advanced extraction techniques of effective components is microwave dry-diffusion and gravity extraction (MDG) which are applicable in both laboratory and industrial scales. The aim of this study was extraction of onion by-products by MDG. In this research, face-center design was used in order to investigate the effect of two independent variations: extraction time (10, 15 and 20 min) and microwave power (300,500 and 700 W) on quality properties consisted of the yield of total phenolic, quercetin, the antioxidant activity and extraction yield. According to the results, the best treatment was in the time of 20 min, extraction power of 500 W. Under these conditions, most antioxidant compounds were extracted consisted polyphenol compounds, 67.47 (mg/kg), quercetin, 30.37 (mg/100g), ferric ion reducing antioxidant power, 542.09 (Mm/g) and DPPH free radical scavenging activity, 37.60%. All concentrations of onion by-product extract had antimicrobial activity, but the effect of the minimum inhibitory concentration of the extract on different microorganisms (Aspergillus niger mites, Staphylococcus aureus and Escherichia coli bacteria) was not the same. So its effect on mold of Aspergillus niger and E. coli bacteria was much higher than that of Staphylococcus aureus. The results showed that, there is a significant difference between the effective compounds of extract with this method and the solvent extraction technique (P<0.05). The process of microwave hydro diffusion and gravity proposed a fast technical and efficient method for extraction of extracts from plants and their by-products in comparison with conventional hydro distillation method.