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The ABTS and DPPH methods are among the most popular assays of antioxidant activity determination. Attempts to adapt them to different analytes and the search for the highest values of antioxidant activity has resulted in a large variety of assay conditions to be presented in the literature, including the way the measurement is made. This makes it difficult to relate the results to real oxidation systems, and often makes it impossible to compare them. Such a comparison is limited in advance by the use of stable radicals that do not exist in nature and that react differently from those generated in food or in vivo. Therefore, it is important to introduce measures aimed at standardizing the conditions of the activity assay, including reaction time and several reaction environments suitable for testing different groups of compounds. In this study, we used natural antioxidants of various structures: phenolic acids, flavonoids, peptides and corresponding amino acids, ascorbic acid and α-tocopherol, and also synthetic analogues of selected compounds. The curves of dependence of the measured absorbance on the concentration of antioxidants were described, the ranges of linearity were determined, and the value of the error made when reading in various ranges of dependencies was estimated. We also determined and compared the activity values using two popular methods (IC50 and TEAC), taking into account different environments and reaction times. Based on the collected data, recommendations were formulated regarding the reaction conditions adapted to the studies of individual groups of antioxidants, and unified reaction times were proposed. Taking into account the state before reaching the equilibrium of antioxidants reacting in a complex manner, this approach may introduce a simplified reference to the competing reaction that occurs in reality.

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The aim of this paper was to study the select physicochemical parameters of 58 honey samples of 4 different botanical origins (buckwheat, linden, rape and acacia) using multivariate methods in order to classify honeys according to the botanical origin. Five standard physicochemical parameters were determined according to the international legislation: water content, electrical conductivity, total ash content, free acidity and pH. The results obtained were mostly in agreement with international regulations. Then, the results obtained were analysed by principal components analysis and cluster analysis. The chemometric analysis of results of determinations of the physicochemical parameters demonstrated such markers as electrical conductivity and ash content (i.e. parameters linked with minerals content) to be the most reliable markers in determining the botanical origin of linden and buckwheat honeys. Unfortunately, they appear insufficient for reliable identification of acacia and rapeseed honeys.

Antioxidant properties and changes in the levels of active compounds in fresh and processed broad beans were determined in the study. Activity of extracted substances was much higher against ABTS (2,2¢-azino-bis [3-ethylbenzothiazoline-6-sulphonic acid]) than towards DPPH (2,2¢-diphenyl-1-picrylhydrazyl) radicals. Phenolics extracted with 70% acetone were also more active comparing to amine compounds obtained with water both in experiments applying radicals and during oxidation of linoleic acid. Steam cooking and freezing had a negative influence on the content of polyphenols and in consequence on their activity. Cooking fresh broad beans decreased the content of those compounds by 16% and freezing -by over 30%, while cooking frozen material resulted in a much lower further decrease (2-8%). Processes applied on fresh material reduced the activity against ABTS •+ to a smaller extent (cooking by 11% and freezing by around 20%), while cooking frozen beans caused a further decrease by 10-17%.

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We found that peptides or amino acids constituted the main fractions of water-soluble nitrogenous compounds in green peas and string beans (44% and 79%, respectively). Their proportion increased after processing, especially in frozen peas and beans (61% and 95%, respectively). The content of phenolic compounds was decreased more after industrial processing (by 40% in peas and 50-70% in beans) than after cooking (by 20% in peas and 0-35% in beans). Antiradical activity against ABTS •+ (2,2¢-azino-bis[3-ethylbenzothiazoline-6-sulphonic acid]) was much higher in aqueous extracts of peas and beans (33 and 45 lmol Trolox g )1 d.m., respectively) than in aqueous acetone extracts (approximately 17 lmol Trolox g )1 d.m. in both). In most cases, the activity decreased after processing. Both aqueous and acetone extracts of peas showed equal activity against DPPH • (2,2¢-diphenyl-1-picrylhydrazyl), whereas in the case of beans this activity was four times lower in aqueous than in acetone extracts. Both reductions and increases of these activities were noted after processing.