Sweet potatoes are reported to be a good source of bioactive compounds. The aim of this study was to evaluate the impact of different heat treatment methods (microwaving, steaming, and baking) and variety on the total polyphenol content and antioxidant activity of three sweet potato varieties – Beauregard (orange-fleshed), O’Henry (white-fleshed), and 414-purple (purple-fleshed). All investigated parameters were determined spectrophotometrically. The total polyphenol content was in the range of 0.53 (O’Henry) – 5.60 mg GAE.g-1 DW (414-purple) for raw flesh and 1.68 (O’Henry) – 7.03 mg GAE.g-1 DW (414-purple) for raw peel of sweet potatoes. Heat treatments caused an increase of total polyphenol content in sweet potatoes (0.98 (steamed O’Henry) – 28.04 mg GAE.g-1 DW (baked 414-purple)). In terms of antioxidant activity, the steamed samples of variety 414-purple showed the highest values of DPPH radical scavenging activity (4.51 µmol TE.g-1 DW) and Ferric reducing antioxidant power assay (19.57 µmol TE.g-1 DW) compared to the other treatment methods. Spearman´s test showed a strong positive relationship between both used methods for evaluation of antioxidant activity. All studied processing methods positively affected the total polyphenol content and antioxidant activity in sweet potatoes.

During evolution in plants, a sophisticated system of receptors and signaling pathways has emerged that allows for appropriate responses and responses to these signals. One of such signals is the plant hormone -phytohormone. Abscisic acid is a sesquiterpene, which has important roles in seed development and maturation, in the synthesis of proteins and compatible osmolytes, which enable plants to tolerate stresses due to environmental or biotic factors, and as a general inhibitor of growth and metabolic activities. Abscisic acid is essential for the initiation and maintenance of tuber dormancy. Its main antagonist is gibberellic acid, which affects carbohydrate metabolism, indicating the budding of tubers. Gibberellic acid is a naturally occurring plant hormone that is used as a plant growth regulator to stimulate both cell division and elongation that affects leaves and stems. Salicylic acid belongs to a group of plant phenols that play an important role in the regulation of plant growth, development, and interaction with other organisms. Salicylic acid (SA), a phytohormone, is a promising compound that can reduce the sensitivity of plants to environmental stresses through regulation of the antioxidant defense system, transpiration rates, stomatal movement, and photosynthetic rate. Phytohormones are essential regulators of plants in two physiological processes that coordinate growth, reproduction, and stress resistance. These molecules also show biological activities on human cells and animal models.

The Horehronie region belongs to the oldest industrial areas in Slovakia. It is contaminated by residual acid tar dumps from times of Petrochema Dubová factory production since 1964. In the presented study, heavy metals (Cu, Cd, Ni, Zn, Pb) were determined in soils and forest fruits (Vaccinium myrtillus L., Vaccinium vitis-idaea L., Fragaria vesca L., Rosa canina L., Rubus idaeus L.) collected over two years from five locations in the Horehronie using Flame AAS method (Zn, Cu, Ni) and Graphite Furnace AAS method (Cd, Pb). The cadmium content, which was higher than its limit value in all analysed soils, poses the biggest threat. We determined more than 20 times the limit value for cadmium in the sample Veľká Smrekovica (9.17 mg/kg).The contamination factor (Cf) values and the geoaccumulation index (Igeo) indicate that this hazardous metal is involved in soil contamination to a large extent. The highest values of the degree of contamination (Cdeg) and the pollution load index (PLI) were determined in samples from the Ždiarska dolina and the Veľká Smrekovica. The contents of nickel and zinc were higher than the limit values only in the 1st sampling year in the Ždiarska dolina sample (46.30 mg/kg; 138.30 mg/kg). The results showed that soil monitoring and remediation of old environmental burdens are important in the territory of the Horehronie region. The highest permissible amounts for cadmium were exceeded in all types of forest fruits (0.03-0.18 mg/kg FW). The contents of nickel and lead were exceeded only in the sample of rosehips (Rosa canina). The contents of zinc and copper were lower than the permissible amounts in all samples. The estimated daily intake (EDI) was lower than the acceptable daily intake of all heavy metals. The bioaccumulation factor (BAF), total hazardous quotient and hazard index of the analysed samples was < 1, which means that the consumption of forest fruits from the Horehronie does not pose a health risk for the consumer.