Polyphenolic compounds, plant secondary metabolites essential for plant survival, are known for their high antioxidant and anti-inflammatory activity. In addition, several polyphenols, such as phloretin, also have potential antiviral effects, making these compounds potential ingredients of biofunctional foods. A promising source for the extraction of phloretin is a by-product of apple production—apple tree leaves. Focusing on green technologies, the first aim of the present study was to optimize the direct ultrasound-assisted extraction conditions to gain the maximum yield of phloretin from air-dried apple leaves. For the optimization of process parameters, we applied the response surface method with Box–Behnken design. The optimal extraction conditions were extraction time 14.4 min, sonication amplitude 10% and 10 g of sample per 100 mL solvent (70% ethanol, w/w). Using these conditions, we assessed the content of individual and total polyphenolic compounds along with antioxidant activity in the leaves of different autumn and winter apple cultivars grown in Estonia. The analyses were carried out with chromatographic (HPLC-DAD-MS/MS) and spectrophotometric methods. The phloretin concentration ranged from 292 to 726 µg/g and antioxidant activity from 6.06 to 11.42 mg GA eq./g, these being the highest in the local winter cultivars ‘Paide taliõun’ and ‘Tellissaare’, respectively.

This study aimed to identify promising candidates of rowanberry cultivars for a wider cultivation and utilization. Antioxidant properties and phenolic content were evaluated for fruit, juice, and pomace samples of 16 different sweet rowanberry cultivars (cvs) and wild rowanberry (S. aucuparia L.), while the antioxidant potential was assessed using three different methods, based on the capacity to scavenge ABTS^●+ and DPPH^● and measure the oxygen radical absorbance capacity (ORAC). In general, the radical scavenging capacity was higher for hybrid cultivars, e.g., for cvs Likernaja, Burka, Granatnaja, and Rubinovaja in all assays. The highest value in the ABTS^●+ assay was determined for the fruit sample Likernaja, and in DPPH^● assay in the pomace sample of cv. Likernaja, at 527.55 and 1068.28 µM TE/g dw, respectively. The highest ORAC value was found in the fruit sample of Burka (456.53 µM TE/g dw). Among the Nevezhino rowans, the highest radical scavenging values of all fractions were determined in cv. Solnechnaja. Regarding the total phenolic content (TPC), higher values were obtained in the whole fruits than in separated fractions, juice, and pomace. The tested hybrids had higher TPC values, either in fruit and pomace or in juice extracts, than those in the other analyzed S. aucuparia L. cultivars. While the fruit and juice samples showed higher anthocyanin (ACY) values, the pomace samples had higher hydroxycinnamic acid (HCA) contents on average. The results revealed that the different fractions of selected rowanberry cultivars can be a promising source of antioxidants and polyphenols for further potential applications. It is envisaged that the results of this study will serve in valorizing sweet rowanberry cultivars as value-added functional ingredients for food and non-food applications.

Grapevine shoots and canes represent a significant amount of biomass, considered as a waste in viticulture. In cooler climates, grapevines are pruned in the autumn (October) and spring (March) due to harsh winter conditions (e.g., snow, low temperatures), and large amounts of biomass are produced at these different pruning times. This work was undertaken in order to investigate the potential of vineyard pruning waste for recovery of polyphenolic compounds for biomass valorization. Qualitative and quantitative analyses of grapevine shoot and cane polyphenols, including flavonoids and stilbenoids were performed using UHPLC MS/MS method. The results revealed the flavonols (quercetin) to be the most abundant compounds in shoots among all the three cultivars screened (Zilga, Hasansky Sladky, Rondo). Stilbenoids (ε-viniferin) dominated in the canes, while increased level of flavonols with lower contents of stilbenoids was detected in the endo-dormant canes, and higher amounts of flavanols and stilbenoids were recorded in eco-dormant canes. In conclusion, the content of polyphenols in grapevine shoots and canes differed among the cultivars and dormancy phases. The results generated from the present study contribute to the sustainable and environmentally friendly viticulture practice via valorization of vineyard pruning wastes.

Vine growing and wine production is gaining in popularity around the Baltic Sea Region. The first aim of the experiment was to determine the variability of the total phenolic and anthocyanin content (from 2010 to 2018) and of individual anthocyanin content (from 2016 to 2018) in the hybrid grape cultivars ‘Hasansky Sladky’, ‘Zilga’, and ‘Rondo’. In field conditions ‘Rondo’ had winter cold damage to canes in two years. Therefore, the second aim was to determine the effect of high polyethylene tunnel and field conditions on fruit total and individual anthocyanin content of ‘Rondo’ from 2016 to 2018. Over nine years, the total phenolic content ranged from 192 to 671 mg 100 g⁻¹ and anthocyanins from 30 to 405 mg 100 g⁻¹ spectrophotometrically. The anthocyanin (delphinidin-3-O-glucoside, cyanidin-3-O-glucoside, petunidin-3-O-glucoside, peonidin-3-O-glucoside, malvidin-3-O-glucoside) content depended on cultivar properties and climatic parameters. Antioxidant activity was cultivar dependent and ranged from 40 to 88%. Polytunnel cultivation increased the content of total anthocyanins in ‘Rondo’ from 447 to 1472 mg 100 g⁻¹ (by chromatographically) in cooler year, but in warmer years it decreased from 3645 to 1618 mg 100 g⁻¹. Individual anthocyanins showed the same tendency. Grapevine cultivar ‘Rondo’ is recommended for tunnel growing in very cool climate conditions.