Mint is an industrial plant that is a good source of essential oil and many phenolic compounds that have several positive benefits to human health and can be used to prevent the development of many diseases. The aim of this research was to investigate the possibility of increasing essential oil and flavonoid content, changing the chemical composition of these compounds in different mint cultivars under foliar application with precursors (phenylalanine, tryptophan, and tyrosine) at two concentrations, 100 and 200 mg L⁻¹, to enable the possibilities for wider use of these plants when they are grown in field conditions. Spraying with phenylalanine at 100 mg L⁻¹ concentration increased essential oil content in Mentha piperita ‘Granada’ plants by 0.53 percentage units. Foliar application with tyrosine solutions at 100 mg L⁻¹ concentration most effectively influenced the essential oil odor profile Mentha spicata ‘Crispa’. The highest number of total flavonoids was in Mentha piperita ‘Swiss’ sprayed with tyrosine at 100 mg L⁻¹ concentration. The flavonoid content depended on the mint cultivar, amino acids, and their concentration. The results showed that the effect of amino acid solutions on different secondary metabolites’ quantitative and qualitative composition differed depending on the mint cultivar; therefore, amino acids and their concentrations must be selected based on the cultivar they are targeting.

Phenolic compounds have a number of benefits to human health and can be used as preventive compounds for the development of some chronic diseases. Mentha plants are not only a good source of essential oils, but also contain significant levels of wide range of phenolic compounds. The aim of this research was to investigate the possibility to increase phenols content in Mentha plants under the foliar application with L-phenylalanine, L-tryptophan, L-tyrosine at two concentrations (100 mg L⁻¹ and 200 mg L⁻¹) and to create preconditions for using this plant for even more diverse purposes. Quantitative and qualitative analyses of phenols in mints were performed by HPLC method. Foliar application of amino acids increased the total phenol content from 1.22 to 3.51 times depending on the treatment and mint variety. The most pronounced foliar application to total phenols content was tryptophane especially in Mentha piperita “Swiss”. Mentha piperita “Swiss” was affected most by foliar application and the amount of total phenolic acids depending on the treatment ranged from 159.25 to 664.03 mg 100 g⁻¹ (DW), respectively, non-sprayed and sprayed with tryptophane 100 mg L⁻¹. Our results suggest that the biophenol content varies according to such factors as foliar application and variety, and every single mint variety has individual response to different applications of amino acids.

Functional foods and herbs are becoming more and more popular as a way to improve health and at the same time improve diet. One of these plants is fireweed, which is abundant in fibers, proteins, and vitamin C in addition to polyphenols and carotenoids. Limited study is being carried out and there is limited information available about how the solid-phase fermentation and different growth systems change the proximate composition, as well as quantities of vitamin C, and sugars in the fireweeds leaves. The experiment was conducted in 2022 on an organic farm (Jonava district, Lithuania). The objective of this research was to determinate the impact of various growing systems (naturally, organically, and biodynamically) and duration (24, 48, and 72 h) effect of solid-phase aerobic fermentation on the changes of fibers, ash, proteins, vitamin C, and sugars. The fibers were established using the Kjeldahl method. High-performance liquid chromatography was used for sugars and vitamin C identification. The study found significant differences in the effects of various growing systems and solid-phase fermentation on the quantitative composition of substances in the fireweed leaves. Based on the data available, it is recommended to consume fermented fireweed leaves that are organically grown and fermented for a period of 48 h as they are a good source of vitamin C and fibers. Biodynamically grown fireweed leaves are a good source of ash and proteins. Naturally grown fireweed leaves, which are not fermented, are a good source of sugars.

The aim of this work was to determine the influence of different drying methods on the content of biochemical compounds and changes in physical properties in leaves and stems of organically grown mint. The research was conducted at Aleksandras Stulginskis University (since 2019 – Vytautas Magnus University Agriculture Academy) in Lithuania, in 2015–2016. Mints were grown in an organic farm in the Panevėžys District of Lithuania. Mints were harvested on the (60 BBCH) stage of mint development in 2015. After the harvest, mint leaves were lyophilized by a SCANVAC Coolsafe 55–9 lyophilizer for 24 h at –60°C temperature and hot air dried by a Termaks TS-8265 dryer at 30°C temperature. In mint leaves and stems, essential oil content, amount of dry matter, amount of photosynthetic pigments and colour parameters (L*, a*, b*) of mint leaves were determined. The biggest amount of essential oil was determined in fresh M. spicata ‘Moroccan’ mint leaves and stems – 3.83% (DW) and 0.59% (DW). Drying showed a negative influence on the amount of essential oil in mint leaves and stems. The amount of essential oil decreased in mint leaves by 0.42–1.59% and in stems by 0.16–0.49% depending on the variety of mint and drying method. In dried and lyophillized mints, the amount of dry matter increased 3.35–3.78-fold in mint leaves and 2.92– 4.30-fold in mint stems depending on the variety and drying method. The variety and drying methods had an influence on the stability of chlorophylls a and b. Dried and lyophillized mints had a higher whiteness index (WI) compared with that of fresh mints. The browning index (BI) showed that dried M. gracilis ‘Ginger’, M. piperita ‘Glacialis’, M. piperita ‘Swiss’, M. spicata ‘Moroccan’ and lyophillized M. suaveolens ‘Apple’, M. piperita ‘Glacialis’, M. piperita ‘Swiss’, M. spicata ‘Moroccan’ mints were browner compared with fresh mints, while lyophillized M. gracilis ‘Ginger’ and dried M. suaveolens ‘Apple’ mints were not so brown as fresh mints. Yellowest (YI) were fresh mints. The smallest total colour difference (ΔE) was in dried M. piperita ‘Glacialis’ 18.74 while the biggest one in lyophillized M. spicata ‘Moroccan’ 111.19 mints. Tyrimo tikslas buvo nustatyti skirtingų džiovinimo būdų įtaką biocheminių junginių kiekiui ir fizikinių savybių pokyčiams ekologiškai augintų mėtų lapuose ir stiebuose. Tirtos sertifikuotame ekologiniame ūkyje augintos mėtos. Tyrimas buvo atliktas 2015–2016 m. Aleksandro Stulginskio universitete (nuo 2019 m. – Vytauto Didžiojo universiteto Žemės ūkio akademija). Derlius nuimtas rugpjūčio mėn. pirmąją dekadą (60 BBCH augalų išsivystymo tarpsnis), lapai atskirti nuo stiebų. Mėtos liofilizuotos 24 val. „SCANVAC Coolsafe 55–9“ liofilizatoriuje ir džiovintos „Termaks TS-8265“ džiovinimo spintoje 30 °C temperatūroje. Mėtų lapuose ir stiebuose nustatyti eterinio aliejaus, sausųjų medžiagų, chlorofilo a ir b, karotenoidų kiekiai. Nustačius spalvos L*, a* ir b* koordinačių vertes apskaičiuoti mėtų lapų spalvos išvestiniai rodikliai: bendrasis spalvos pokytis (ΔE), baltumo indeksas (WI), rudumo indeksas (BI), geltonumo indeksas (YI). Didžiausias eterinio aliejaus kiekis buvo nustatytas M. spicata ‘Moroccan’ veislės šviežiuose mėtų lapuose (3,83 % s. m.) ir stiebuose (0,59 % s. m.). Priklausomai nuo mėtų veislės ir džiovinimo būdo, eterinio aliejaus kiekis lapuose, palyginti su šviežiais, sumažėjo 0,42–1,59 %, o stiebuose – 0,16–0,49 %. Džiovintuose ir liofilizuotuose mėtų lapuose sausųjų medžiagų koncentracija padidėjo 3,35–3,78, o stiebuose – 2,92– 4,30 karto. Mėtų veislė ir džiovinimo būdas turėjo įtakos chlorofilo a ir b stabilumui lapuose ir stiebuose. Vertinant apskaičiuotus spalvos rodiklius džiovintų ir liofilizuotų mėtų baltumo indeksas (WI) buvo didesnis nei šviežių. Apskaičiavus rudumo indeksą (BI) nustatyta, kad, palyginti su šviežiomis, rudesnės buvo džiovintos M. gracilis ‘Ginger’, M. piperita ‘Glacialis’, M. piperita ‘Swiss’, M. spicata ‘Moroccan’ ir liofilizuotos M. suaveolens ‘Apple’, M. piperita ‘Glacialis’, M. piperita ‘Swiss’, M. spicata ‘Moroccan’, o liofilizuotos M. gracilis ‘Ginger’ ir džiovintos M. suaveolens ‘Apple’ mėtos išsiskyrė mažesniu rudos spalvos intensyvumu, palyginti su šviežiomis. Gelsviausios buvo šviežios mėtos. Mažiausias bendrasis spalvų pokytis (ΔE) buvo džiovintų 18,74 M. piperita ‘Glacialis’, o didžiausias – liofilizuotų 111,19 M. spicata ‘Moroccan’ mėtų.