The influence of genotype and drying methods on the characteristics of organically grown mint (Mentha)

Abstract

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.