Optimization of ultrasound- and enzymatic-assisted extractions of polyphenols from dried red onion peels and evaluation of their antioxidant activities

There is a recognized need for exploring new natural antioxidants that have high antioxidant potential. Thus, the aim of this study was to optimize the extraction process of onion peels using ultrasound- and enzymatic-assisted extractions (UAE and EAE) methods to utilize the optimal extracts as natural antioxidants. Box-Behnken Design (BBD) was implemented to reach the optimal extracts with the highest simultaneous content of total phenolic content (TPC) and total flavonoid content (TFC). The optimal UAE and EAE extracts were subjected to High Performance Liquid Chromatography (HPLC) analysis to identify their chemical profile. The antioxidant activities of optimal extracts obtained by UAE and EAE were evaluated in vitro using DPPH and FRAP assays and their abilities to increase the oxidative stability of sunflower oil were studied using Rancimat test. The optimal conditions for UAE were 34.02 W, 26.87 mL/g solid, and 45.43 min, meanwhile they were 30.00 mL/g solid, 45.43 min at enzyme concentration of 0.52% for EAE method. DPPH and FRAP assays results revealed that EAE optimal extract show superior antioxidant activity over UAE optimal extract. The protection factor of optimal EAE extract against sunflower oil oxidation was close to that of butylated hydroxytoluene (BHT).

Extraction and Identification of Anthocyanins in Corn Cob and Corn Husk from Cacahuacintle Maize

Pigmented maize has been extensively studied due to its high anthocyanin content. This study has been focused mainly on kernel, although the whole plant of purple corn is a potential source of anthocyanins. First, general parameters of extraction (solvent system, solvent-to-solid ratio, number of extractions, and acid type) were established depending on the total anthocyanins content. Then, three extraction methods to access anthocyanins were compared: maceration extraction (ME), ultrasound-assisted extraction (UAE), and microwave-assisted extraction (MAE). Since the residual material still possessed an intense color, a further treatment was performed by application of enzymatic-assisted extraction (EAE). Three enzymatic cocktails (Xylanases, Celluclast, and Depol), pH, and temperature were evaluated to establish optimal reaction conditions. Subsequent analysis and identification of the anthocyanins obtained by four different extraction techniques were performed using HPLC and HPLC-mass spectrometry, respectively. The most efficient method was UAE using 20 min of ultrasound (100 W) preceded by sample treatment in the following conditions: ethanol/water/lactic acid mixture (80:19:1), two extractions, 1:10 solvent-to-solid ratio. As a result, anthocyanins from corn cob and corn husk were extracted at concentrations of 24.32 and 25.80 mg/gDW, respectively. No difference in the anthocyanins profile for samples extracted by three different methods was observed. However, an enhanced presence of cyanidin-3-(6''malonyl)glucoside was detected in the sample corresponding to the EAE method. Therefore, the Cahuacintle corn husk can be considered as a competitive source of anthocyanins with the available commercial sources. PRACTICAL APPLICATION: The by-products obtained from Cacahuacintle purple corn can be potentially used as natural colorants thanks to their anthocyanins content. In this work, we established the most efficient extraction method of anthocyanins from corn husk and corn cob, and demonstrated that their anthocyanins profile is comparable to other Peruvian purple corns, which are currently used as natural colorants. Therefore, the extraction procedure described in this study might be scaled-up in an industrial process to get access to anthocyanins from undervalued wastes.