A Validated Ultrasound-Assisted Extraction Coupled with SPE-HPLC-DAD for the Determination of Flavonoids in By-Products of Plant Origin: An Application Study for the Valorization of the Walnut Septum Membrane

Abstract

Walnut byproducts have been shown to exert functional properties, but the literature on their bioactive content is still scarce. Among walnut byproducts, walnut septum is a dry ligneous diaphragm tissue that divides the two halves of the kernel, exhibiting nutritional and medicinal properties. These functional properties are owing to its flavonoid content, and in order to explore the flavonoid fraction, an ultrasound-assisted (UAE) protocol was combined with solid phase extraction (SPE) and coupled to high-performance liquid chromatography with diode array detection (HPLC-DAD) for the determination of flavonoids in Greek walnut septa membranes belonging to Chandler, Vina, and Franquette varieties. The proposed UAE-SPE-HPLC-DAD method was validated and the relative standard deviations (RSD%) of the within-day and between-day assays were lower than 6.2 and 8.5, respectively, showing good precision, and high accuracy ranging from 90.8 (apigenin) to 97.5% (catechin) for within-day assay, and from 88.5 (myricetin) to 96.2% (catechin) for between-day assay. Overall, seven flavonoids were determined (catechin, rutin, myricetin, luteolin, quercetin, apigenin, and kaempferol) suggesting that the walnut septum is a rich source of bioactive constituents. The quantification results were further processed using ANOVA analysis to examine if there are statistically significant differences between the concentration of each flavonoid and the variety of the walnut septum.

Assembly-Induced Emission Enhancement in Glutathione-Capped Bimetallic Gold and Copper Nanoclusters by Al3+ Ions and Further Application in Myricetin Determination

“…A comparison of the present method with previous approaches for myricetin determination is listed in Table S1 . Both the LOD and linear range of the proposed method are better than or at least comparable to those of previous approaches [ 25 , 26 , 27 , 28 , 29 , 30 , 31 ]. Particularly, most previous methods require expensive instruments, professional techniques, or complicated sample preparing; in contrast, our fluorescent method needs only a low-cost spectrometer with a very simple preparation, making it more suitable for routine analysis of myricetin in real samples.…”

“…Myricetin was also used in cosmetics to regulate the ultraviolet-B-induced H 2 O 2 generation or to inhibit the production of photoaging free radicals in skin [ 21 ]. Considering the wide distribution and benefits to human health, several traditional determination methods, such as capillary electrophoresis [ 22 ], chemiluminescence [ 23 , 24 , 25 ], high-performance liquid chromatography [ 26 , 27 ], spectrophotometry, and voltammetry [ 28 , 29 , 30 ], have been established for myricetin determinations. These methods have enough sensitivity and accuracy, but the complicated operations and cost instruments limit their applications.…”

Phytochemicals and Biological Activities of Walnut Septum: A Systematic Review

“…The phytochemical composition of walnut septum was examined in 13 out of the 28 studies selected for this review. Five of these provided quantitative determination results that could be analyzed and compared in our study [ 24 , 27 , 32 , 37 , 40 ] ( Table 2 ).…”

“…The extractions were conducted in ethanol [ 20 , 22 , 38 , 40 ] or methanol [ 26 , 27 , 32 ] at various concentrations, as well as in solvent mixes such as acetone:water [ 24 ], acetone:acetonitrile [ 25 ], and acetone:cyclohexane [ 27 ]. The extraction methods were generally based on ultra-turrax homogenization and stirring [ 24 ], vibrating [ 25 ], ultrasonic extraction [ 26 , 27 , 37 ], condensation and reflux, or enzyme-assisted extraction [ 32 ], then centrifugation, solvent evaporation, and lyophilization. A number of studies described preserving the lyophilized material at −20 °C [ 25 , 26 , 32 ], while others stored it at room temperature [ 24 ] ( Table 2 ).…”

“…The reviewed studies used various chromatographic techniques for identifying phenolic compounds: liquid chromatography-mass spectrometry (LC-MS) [ 24 ], liquid chromatography with tandem mass spectrometry (LC-MS/MS) [ 32 ], high-performance liquid chromatography (HPLC) [ 20 , 22 , 26 , 37 , 38 ], or ultra-performance liquid chromatography (UPLC) differently equipped: UPLC-MS (17), UHPLC-Q-Orbitrap coupled with high-resolution mass spectrometry HRMS [ 27 ], or UPLC-Q-Exactive Orbitrap MS [ 40 ].…”