Ivana Tomaz

Drought negatively affects plants by altering morphological, physiological and metabolic processes and ultimately reducing yields. Garlic (Allium sativum L.), an important member of the Alliaceae family, is also sensitive to drought and maximizing the yield of garlic bulbs is largely dependent on water availability. The objective of this study was to determine the effects of drought stress on morphological and physiological characteristics, as well as on phenolic, sugar, inulin and free amino acid content and antioxidant activity in two Croatian garlic ecotypes, ‘Istarski crveni’ (IC) and Istarski bijeli (IB). Drought was induced by using polyethylene glycol 8000 (PEG) solution (−0.6 MPa) starting 21 days after clove planting and lasted for 20 days. Drought reduced plant height, number of leaves and plant weight, but increased root length in both ecotypes compared to the control treatment. Among the physiological parameters, significant differences were observed between the two ecotypes studied in the spectral characteristics of the leaves, namely reflection in red, green and blue, VAL, values of the vegetation indices related to the chlorophyll content (CHI, GI), and the anthocyanin content (ARI). Ecotype IC showed higher antioxidant activity in the control treatment due to higher total phenolic content (TPC), but under drought conditions higher DPPH radical scavenging activity was determined in ecotype IB and higher values of FRAP in IC. Sucrose and glucose generally decreased under drought, while inulin increased in IB but decreased in IC. Total free amino acid content increased under drought in both ecotypes. In conclusion, drought tolerance of IB might be associated with increased accumulation of inulin and higher levels of amino acids, especially those shown to contribute to drought resistance. In IC, drought tolerance is associated with an increase in some amino acid compounds and better root growth in depth, probably due to a more efficient translocation of sucrose to the underground part of the plant.

Polyphenols are organic compounds that can be found in food, especially in fruits, vegetables, and their products. It was shown that their presence significantly affects the properties of food products and that the consumption of food rich in phenolic compounds has a beneficial effect on human health. The subjects of this research were polyphenols: anthocyanins, flavonols, and flavan-3-ols in the skin of grapevine variety Regent. Polyphenols from grape skins were extracted via microwave-assisted extraction (MAE) and matrix solid-phase dispersion (MSPD) as unconventional and green techniques. Therefore, the main aim of this work was to optimize the conditions for the extraction of polyphenolic compounds from grape skin using MAE and MSPD. The extracts were analyzed using high-performance liquid chromatography with a diode array detector and fluorescence detector. Analyses showed that MAE was a very effective method for extracting polyphenolic compounds from grape skin with 10 mL of 60% ethanol for 5 min at 40 °C. The best results for the MSPD extraction of polyphenolic compounds from grape skin were obtained with phenyl as an MSPD sorbent with 10 mL of acetonitrile:water 50:50 v/v as an elution solvent. This scientific research can be used for the better use of grapes as a basis for obtaining flavonoids for commercial purposes.