Antioxidant activity and biochemical composition of Morus alba and Morus nigra species

Mulberry ( Morus L.), a woody plant popular in Russia is of great economic benefits. On the territory of the Dagestan Republic, there are two Morus species, the Morus alba L. and Morus nigra L. The mulberry fruits, from leaf, bark and root extracts have powerful antioxidant, anti-inflammatory, antimicrobial properties and analgesic effects. In this paper, we revealed for the first time a high antioxidant status for two species, M. alba and M. nigra (cv. Hartut) growing in the Republic of Dagestan. Biochemical analysis revealed variability of the antioxidant level in the mulberry fruit pomace, leaves, bark, and roots. It was revealed that fruit pomace contains the required amount of mono-, disaccharides and bioactive compounds (e.g., water-soluble vitamins, organic acids) and has a rich mineral composition. The aim of the research was to assess the biological activity and biochemical composition of the fruit pomace, leaves, bark, and roots of mulberry plants grown in Dagestan. Plant material was sampled in the second decade of June 2020 (OOO Nizam, the suburbs of the city of Makhachkala, settlement Leninkent, Republic of Dagestan). The total content of antioxidants was measured amperometrically (a Tsvet Yauza 01-AA device, OAO NPO Khimavtomatika, Russia). The concentrations of water-soluble vitamins, organic acids and sugars were measured by capillary electrophoresis (a Kapel-105M system, OOO Lumex-marketing, Russia). Micro- and macro elements were quantified by atomic absorption spectrometry using ordinary acetylene-air flame atomization (a SavantAAΣ atomic absorption spectrometer, GBC Scientific Equipment Pty Ltd., Australia). The research results showed a high antioxidant status of fruit pomace, especially for white-fruited M. alba (400.73 mg/g) and M. nigra cv. Hartu (363.77 mg/g). A high level of antioxidants also occurred in leaves, bark, and roots. The antioxidant concentration in the leaves and roots of black-fruited form of M. alba was the highest, 44.56 mg/g and 71.79 mg/g, respectively. M. nigra plants have the highest amount of antioxidants in the bark, 36.33 mg/g. The quantitative determination revealed a higher content of vitamins C (ascorbic acid) and B9 (folic acid) in mulberry fruit pomace, and the white-fruited form of M . alba (31.4 and 5.2 mg%) and M. nigra cv. Hartut (29.0 and 6.0 mg%) were most prominent. Qualitative and quantitative analysis revealed 10 chemical elements in plants, of which five (Na, K, Ca, Mg, Fe) were of leading importance. Potassium in a larger amount (342.6 mg%) occurred in M. alba (black-fruited form), a high concentration of Ca (50.6 mg%) was characteristic of M. alba (pink-fruited form). M. nigra stood out by the accumulation of Mg (54.6 mg%). M. alba (black-fruited) contained the largest amount of Na (16.5 mg%). M. alba (pink-fruited) was distinguished by the content of Fe (3.1 mg%). As to organic asides of M. alba and M. nigra , in the samples, we revealed only malic and citric acids. In all samples, the content of citric acid was 1.5-2 times higher than that of malic acid, except for the pink-fruited M. alba . Of mono- and disaccharides (fructose, glucose, sucrose), glucose dominated quantitatively in all samples, especially in black-fruited M. alba (10.40 %). Our findings indicate the high biological value of the M. alba and M. nigra species and their high potential for the development of therapeutic and prophylactic food products, bioactive additives, etc. Therefore, more phytochemical studies are necessary to search and reproduce the most valuable forms for practical use and improvement.