A Central Composite Design in increasing the quercetin content in the aqueous onion waste isolates with antifungal and antioxidant properties

Abstract

In this study, to increase the content of quercetin in the isolates obtained from the white and red onion scales, in accordance with the zero waste philosophy, using water as an environmentally and healthy friendly extractant, a mathematical model was constructed, based on the Central Composite Design. The suitability of the model for the accurate and quick study of complex relationships was demonstrated by obtaining a statistically insignificant difference in the yield predicted by the model and that determined experimentally under optimal extraction conditions, i.e., 44.14 mg/g (33.57 mg/g) and 45.54 mg/g (33.31 mg/g) for white (red) onion scales, respectively. To present the obtained isolates applicability, their biological activity was assessed in terms of antioxidant activity and antifungal activity against various fungi, showing properties that are sufficient to encourage the use of this material, previously treated as worthless waste, for the production of various functional ingredients, including functional food additives. Moreover, they can be also used to produce safe and effective protectants meeting the GRAS criteria.

Correlation Study of Biological Activity with Quercetin and Phenolics Content in Onion Extracts

“…Among all the tested methods, the highest activity (the highest values of the percent of inhibition, the highest bars) is shown by the beta(β)-carotene bleaching method, and the lowest by the DPPH method. This result is consistent with the previously published research results [ 10 ]. Regardless of the method of testing the antioxidant activity, the highest antioxidant properties are shown by the methanol extracts, and the weakest by the chloroform extracts.…”

“…The greatest amount of quercetin is found in the EtOAC and MeOH extracts obtained during maceration. The use of extraction in the Soxhlet apparatus reduces the quercetin yield, which confirms the instability of the compound to long-term exposure to high temperature, as known from the literature [ 5 , 6 , 7 , 8 , 9 , 10 ]. The smallest amounts of quercetin are present in the chloroform extracts.…”

“…The PHWE system is described in detail in [ 10 ]. Extractions were performed in a dynamic mode on the weighed portions of edible and inedible parts of onion (0.5 g) which were mixed with sand and placed into the extraction vessels (22 mL).…”

“…The literature reports also the papers combining the use of pro-ecological techniques of quercetin isolation with superheated water with the possibility of a mathematical design of extraction conditions for the optimal yield of this compound, showing a wide range of possible biological activities, including antioxidant and antifungal ones of quercetin-rich isolates obtained from the onion waste materials [ 10 ]. This research trend is in line with the “zero-waste” philosophy, the results of which can be useful in many different industries.…”

Differences in Antioxidant Potential of Allium cepa Husk of Red, Yellow, and White Varieties

“…Concerning onion varieties, quercetin and its derivatives, along with glucosides, are the predominant flavonols in all types of onions, regardless of the white, yellow, or red color, while anthocyanins are mainly present in red onions, wherein they make up approximately 10% of the total flavonoid content in fresh weight [ 7 , 9 ]. Contents of prominent flavonoids such as quercetin and its glucosides are the highest in pearls, followed by red, yellow, and white onion husks [ 11 , 14 ], and strongly depend on extraction conditions [ 15 ].…”