Heat treatment can affect the bioactive compounds in sweet potato (SP). In this work, we monitored the influence of heat treatment (boiling, steaming, microwaving, and baking) on the total polyphenols content (TPC), total antioxidant capacity (TAC), total anthocyanins content (TANTC), and phenolics acids (chlorogenic (CGA), neochlorogenic (neo-CGA), and trans-ferulic (tFA)) in two SP varieties grown in Slovakia and Croatia. TPC, TAC, and TANT were determined spectrophotometrically and phenolic acids by HPLC. TPC ranged from 576 (Beauregard, Croatia; Be/HR) to 3828 (414-purple, Slovakia; Pu/SK) mg/kg DW in the raw SP tubers. After heat treatment, TPC increased, most in steamed SP (8438 mg GAE/kg DW; Pu/SK), while only in boiled SP (Be/HR), TPC decreased (353 mg GAE/kg DW). TAC varied from 0.848 (Be/HR) to 8.67 (Pu/HR) (μmol TE/g DW) in raw SP. The TAC increased by heat treatment (max. 14.2 μmol TE/g DW; cooking Be/SK), except for Pu/HR. The TANT ranged from 151 (raw Pu/SK) to 1276 (microwaved Pu/SK) mg CyE/kg FW. Heat treatment had a negative effect on phenolic acid content; the largest reduction was after boiling: CGA by 29% (Pu/SK), neo-CGA by 69% (Pu/HR), and tFA by 29% (Be/HR). The influence of heat treatment on the monitored quantities is not definite.

Processing is one of the most crucial factors affecting polyphenol content in foods. Therefore, the study is aimed at the evaluation of heat treatment effects (microwaving, steaming, baking, and boiling) on the content of chlorogenic acids, total polyphenols, and antioxidant activity of three varieties of sweet potato with different flesh colors (Beauregard—orange-fleshed, O’Henry—white-fleshed, 414-purple—purple-fleshed). According to high performance liquid chromatography analysis, chlorogenic acid was the predominant chlorogenic acid in sweet potatoes. Obtained results also suggested the purple-fleshed variety (414-purple) had significantly (p < 0.05) higher total polyphenol content and thus the highest antioxidant activity. Heat treatment positively influenced the chlorogenic acid content, total polyphenols, and antioxidant activity of sweet potatoes. Among the used methods, steaming had the greatest effect on the chlorogenic acids and total polyphenols, while microwaved samples showed the highest antioxidant activity (DPPH). The content of chlorogenic acids and total polyphenols decreased in the order of steaming > baking > microwaving > boiling > raw. However, the individual varieties differed not only in the flesh color but also in the reaction to the used heat treatment methods. Spearman’s correlation coefficient showed a strong correlation between chlorogenic acid and antioxidant activity.

Potatoes (Solanum tuberosum L.) are an essential food for the human diet and thus represent an important source of biologically active substances. This study aimed at investigating the content of bioactive substances (total anthocyanin and polyphenol contents and chlorogenic acid) in seven potato varieties (Belana, Cecile, Magenta Love, Mozart, Talentine, Toscana, and Violet Queen) with various flesh and skin colors. To evaluate the impact of potato maturity on the analyzed parameters, potato samples were harvested in two different periods (1st harvest—July and 2nd harvest—September). Total anthocyanin and polyphenol contents were determined spectrophotometrically, and chlorogenic acid by the HPLC-DAD method. Varieties with a colored flesh (Magenta Love and Violet Queen) showed the highest content of bioactive substances. The maturity level significantly (p < 0.05) affected the total content of anthocyanins and polyphenols in potatoes. Early to medium early varieties (Belana and Magenta Love) showed an increase in chlorogenic acid content during maturation, while in other varieties, chlorogenic acid decreased due to higher maturity. In terms of the content of bioactive substances with a possible positive effect on human health, the consumption of potatoes with colored flesh could be recommended.

The European blueberry (Vaccinium myrtillus L.) is a low-growing shrub native to northern and central Europe, widespread in the Italian Alps and the Apennines. It also occurs in parts of North America and Asia. The European blueberry belongs to the large genus Vaccinium L., and species from the Ericaceae Juss. family. The fruits have a dark purple to bluish-black color due to the high content of anthocyanins

Grapes and wine are important sources of antioxidants in human diet. Phenolic substances contained in grapevine berries belong to an important group of natural substances that get into wine in the process of wine making. Polyphenols and flavonoids are primarily accountable for the colour and taste of the wine, they affect the perception of bitterness and acerbity. They also have antioxidant properties, thus have a positive effect on human health. Health benefits of polyphenolic substances from wine may be associated with a wide range of biological processes. Thanks to the development of modern analytical methods, wine is constantly being researched in terms of the content of antioxidants, and its importance to human health. Sixteen Slovak white wines of Muscat type produced in different geographical regions were analysed in this study. The object of this work was to determine total polyphenol content and total flavonoid content, and to evaluate antioxidant effects of quality wines of Muscat varieties produced in Slovakia. Antioxidant activity, total polyphenol content, and total flavonoid content of particular wines is described in the study. Studied characteristics were analysed by UV-VIS spectrometry method. Muscat wines showed weak to high antioxidant activity, ranging from 25.2% inhibition of DPPH to 67.7% inhibition of DPPH. Average antioxidant activity was 38.7% inhibition of DPPH. Total polyphenol content in the Muscat type varietal wines varied from 262.1 GAE.L-1 to 568.3 GAE.L-1. Average total polyphenol content was 382.13 GAE.L-1. The content of total flavonoids in Muscat type varietal wines ranged from 24.8 mg CE.L-1 to 169.1 mg CE.L-1. Average total flavonoid content was 100.5 mg CE.L-1.