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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. [ABSTRACT FROM AUTHOR]

Reliable plant analysis is a challenging task due to the physical character and chemical complexity of plant matrices. First of all, it requires the application of a proper sample preparation procedure to fully isolate the analyzed substances from the plant matrix. The high-temperature liquid-solid extraction is commonly applied for this purpose. In the light of recently published results, however, the application of high-temperature extraction for polyphenolics analysis in plants is disputable as it causes their transformation leading to erroneous quantitative estimations of these compounds. Experiments performed on different plants show that the transformation/degradation of quercetin and its glycosides is not induced by sea sand disruption method (SSDM) and prove the method to be most appropriate for the estimation of quercetin and its derivatives in plants. What is more, the application of SSDM in plant analysis allows the researcher, to determine which quercetin derivatives are native plant components and what is their true concentration. In other word, the application of SSDM in plant analysis eliminates errors in the study of plant metabolism involving quercetin and its derivatives. [ABSTRACT FROM AUTHOR]

Hydroxyanthraquinones represent a group of pharmacologically active compounds characteristic for plants of the Rumex and Rheum genera. These compounds in the human intestine act as laxative compounds. As they cause the greatest side effects and are often abused by the public, their accurate analysis in plants and plant-derived laxatives is much needed. To isolate compounds from plants, pressurized liquid extraction (PLE) is frequently applied. The technique has been regarded, so far, as very effective, even in isolation of sensitive compounds for which exposure time in high temperature has a negative impact. This work demonstrates some interesting and surprising results accompanying PLE of hydroxyanthraquinones from the Rumex crispus L. root using methanol/water mixtures as extractant. The presented results demonstrate that glycoside forms of hydroxyanthraquinones (emodin -8 -O-β-D-glucopyranoside, chrysophanol -8 -O-β-D-glucopyranoside, and physcion -8 -O-β-D-glucopyranoside) are hydrolytically unstable even in the short-lasting PLE. The increase of water concentration in the extractant leads to the increase of the transformation degree of the glycoside forms to the corresponding aglycones (emodin, chrysophanol, and physcion), increasing the concentration of the latter. The rise in the PLE temperature accelerates the hydrolytical degradation of the glycoside forms. The extension of the extraction time also intensifies this process. The presented results show that extraction of glycosides using extractants containing water can lead to false conclusions about the chemical composition of plants. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]