**1. Introduction**

In recent years, common buckwheat is gaining interest in the development of new food products due to health-promoting, biofunctional properties, gluten freeness, and its high nutritional value [1]. The high nutritional value of buckwheat attributed to a balanced amino acid composition and high contents of vitamin B1 and B2, lysine, flavonoids, phytosterols, soluble carbohydrates, D-*chiro*-inositol, fagopyritols, and thiamin-binding proteins has been described [2]. Buckwheat is also rich in antioxidant compounds such as flavonoids, phenolic acids, tocopherols, reduced glutathione, inositol phosphates, and melatonin [3, 4]. Therefore, based on the above evidences, ingredients derived from buckwheat could be attractive for the bakery industry [5].

Wheat flour is usually used in bread making, but more often it is demonstrated that the usage of buckwheat flour as an ingredient in bakery goods can provide

beneficial health effects [6–11]. The buckwheat-enhanced wheat bread is an attractive model of polyphenol-rich bread for an in vitro investigation of the impact of digestion on the bioaccessible reducing/antioxidative capacity as well as on the potential bioaccessibility of wide spectrum of bioactive compounds. The selection on buckwheat flour for formula of model polyphenol-enriched breads was due to the several publications indicating the potential use of buckwheat flour as a functional ingredient in bakery product formulations [12].

Several methods to measure antioxidant properties have been proposed and were recently reviewed [13–17]. Among others, scavenging of stable radicals such as DPPH and ABTS, oxygen radical absorbance capacity (ORAC), total radical-trapping antioxidant parameter (TRAP), ferric-reducing antioxidant power (FRAP), and cupric ion (Cu2+)-reducing power (CUPRAC) were employed in foods [13]. Electrochemical methods, used for the determination of reducing activity, have been still developing. Among different electrochemical techniques, the most widely used for this purpose is cyclic voltammetry (CV). The main advantage of CV is its capability to rapidly observe the total redox behavior over a wide potential range without the necessity of measuring the specific reducing capacity of each component alone. In contrast to the abovementioned methods, electrochemical assays are low-cost and usually do not require time-consuming sample preparation. CV is based on the analysis of the anodic current (AC) waveform, which is a function of the reactive potential of a given compound in the sample or a mixture of compounds. The CV tracing indicates the ability of a compound to donate electrons at the potential of the anodic wave [18]. A CV also provides information describing the integrated reducing capacity without the specific determination of the contribution of each individual component. Therefore, in the past couple of years, CV has been suggested as an instrumental methodology for the evaluation of the reducing capacity of various food products [16, 19–21]. From the current point of view, the electrochemical methods should be used to assess the reducing capacity of food in vitro to cover all aspects of antioxidant efficacy in vivo [22, 23]. Recently it was demonstrated that that in vitro digestion of buckwheat-enhanced wheat breads was the crucial step in the formation of the antioxidant capacity due to the release of the high amount of phenolic compounds [24].

Since the use of electrochemical methods ensures the measurement of the bioaccessible reducing capacity of food as it could occur in vivo, the objective of this work was to show an application of a cyclic voltammetry (CV) technique for determination of the bioaccessible reducing capacity of a soluble fraction from a digestible portion of buckwheat-enhanced wheat breads.
