Haematococcus pluvialis, a unicellular green microalga that produces a secondary metabolite under stress conditions, bears one of the most potent antioxidants, namely xanthophyll astaxanthin. The aim of our study was to determine the content of astaxanthin and its esterified forms using three different solvents—methyl tert-butyl ether (MTBE), hexane isopropanol (HEX -IPA) and acetone (ACE)—and to identify them by using high performance liquid chromatography coupled with diode array detection and the quadrupole time-of-flight mass spectrometry (HPLC-DAD and LC-QTOF-MS) technique. We identified eleven astaxanthin monoesters, which accounted for 78.8% of the total astaxanthin pool, six astaxanthin diesters (20.5% of total), while free astaxanthin represented the smallest fraction (0.7%). Astaxanthin monoesters (C16:2, C16:1, C16:0), which were the major bioactive compounds in the H. pluvialis samples studied, ranged from 10.2 to 11.8 mg g⁻¹ DW. Astaxanthin diesters (C18:4/C18:3, C18:1/C18:3) were detected in the range between 2.3 and 2.6 mg g⁻¹ DW. All three solvents were found to be effective for extraction, but MTBE and hexane-isopropanol extracted the greatest amount of free bioactive astaxanthin. Furthermore, MTBE extracted more low-chain astaxanthin monoesters (C16), and hexane-isopropanol extracted more long-chain monoesters (C18 and above) and more diesters. We can conclude that MTBE is the solvent of choice for the extraction of monoesters and hexane-isopropanol for diesters.

Silkworm rearing activities ceased in the 1970′s in several European countries. Attempts on the re-establishment of ecological and sustainable sericulture in Slovenia and Hungary are ongoing. The aim of the study was to assess the usability of locally adapted mulberry genotypes for sericulture and to estimate connections between leaf compound and silkworm performance parameters. A controlled feeding experiment of silkworms was performed to test the influence of leaves from selected trees on the growth of larvae, the health and microbiological status of larvae (e.g., gut bacterial microbiome, Bombyx mori nucleopolyhedrovirus infection), weight of cocoons and raw silk parameters. The Slovenian and Hungarian mulberry genotypes had significantly higher total protein contents, and lower total phenolic contents and differed significantly in some individual phenolics compared to the reference sericultural and fruit varieties. Significant differences were found in the contents of the macro- and microelements, namely S, Mn, Fe, and Sr. Based on correlative statistics and multivariate analysis, a combined positive influence of proteins, specific phenolics, and microelements on larval growth and silk thread parameters was predicted. The results of the study indicate that selected local Slovenian and Hungarian mulberry varieties are suitable for high-quality silk cocoon and raw silk production.

Mulberries are the “essence of the past”, the so-called Proust effect, for the inhabitants of the sericultural regions who enthusiastically remember feeding silkworms with mulberry leaves and picking the different coloured fruits that were their favourite sweets in childhood. To determine the chemistry behind the colour and taste of mulberry soroses, the main metabolites of the local and introduced varieties were studied. The soroses were classified into five different colour types and the size parameters were determined. The main sugars identified were glucose and fructose, while the predominant organic acids were citric and malic acids, which were highest in the darker varieties, and fumaric and tartaric acids, which were highest in the lighter varieties. A total of 42 phenolic compounds were identified. The predominant phenolic acid was chlorogenic acid, followed by other caffeoylquinic acids and coumaroylquinic acids. The predominant anthocyanins were cyanidin-3-glucoside and cyanidin-3-rutinoside. According to PCA analysis, the colour types showed a clear chemotype character. The sweet taste of the yellowish-white soroses was defined by 49% fructose, followed by 45% glucose and 6% organic acids. The sour character of the black genotypes was characterised by a lower sugar and higher (11%) organic acid content. The colour- and species-dependent effect was observed in the proportion of caffeoylquinic acids and quercetin glycosides, which decreased with increasing colour intensity from 60% of the total to 7%, and from 17% to 1%, respectively. An upward trend was observed for flavanols (5% to 29%) and anthocyanins, which accounted for 62% of the total phenolics in black varieties. This article gives an insight into the metabolite composition of mulberry soroses as the sweets of choice between light and sweet and dark and sour.

Phenolic compounds are strong antioxidant and antibacterial agents with great pharmacological, medicinal, nutritional, and industrial value. The potential of Morus nigra in stem node culture was investigated for the production of phenolic compounds and their elicitation with CuSO₄. Individual phenolic compounds in the samples were identified and quantified by using HPLC-PDA and HPLC-MS methods, while the content of total phenolic compounds, the content of total flavonoids, and the antioxidant activity of methanolic extracts were evaluated spectrophotometrically. The highest fresh and dry weights were obtained in plantlets treated with 0.5 mM CuSO₄ for 42 days. The highest total phenolic content, total flavonoid content, and antioxidant activity of the extracts were determined in stem node cultures treated with 3 mM CuSO₄ for 42 days. Under the latter conditions, the predominant representatives of the caffeoylquinic acids, p-coumaric acid derivatives, kaempferol derivatives, and quercetin derivatives also achieved the highest content. The most abundant phenolic compound in all samples was the chlorogenic acid. The nodal culture of M. nigra elicited with CuSO₄ could potentially be used for the industrial production of phenolic compounds, especially caffeoylquinic acids. Moreover, considering the biochemical response to CuSO₄ treatment and the ability to tolerate and accumulate copper, the potential application of M. nigra in phytoremediation is also highlighted.