Health benefits of apple polyphenols for different chronic diseases are postulated. To exert bioactive properties, absorption into the body is required (bioavailability), which is strongly influenced by matrix release (bioaccessibility). For seven apple varieties, in vitro experiments with simulated saliva fluid (SSF) and ex vivo digestion with centrifuged human saliva were conducted. Polyphenol characterization (high-performance liquid chromatography-tandem mass spectrometry) and quantification (high performance liquid chromatography-diode array detection) was related to an aqueous methanolic extraction. A polyphenol release of 63−82% from flesh and 42−58% from peel was estimated. While hydroxycinnamic acid derivatives were released in total, a significant retention was observed for flavanes and flavones. In particular, procyanidins were retained with increasing molecular weight. The data reveal a considerable polyphenol release during the oral digestion; however, differences among the varieties as well as flesh and peel were obvious. Due to negligible differences between both digestion media, the data supported the use of SSF instead of human saliva in further experiments.
Contamination with Cd, Cu and Pb is a major environmental issue. Cations of those metals may adsorb on negatively charged surfaces of polymeric silicic acid (pSi), altering their environmental fate. Aiming to elucidate the underlying mechanisms and the extent of adsorption, we conducted batch adsorption experiments at pH 4 to 6 and concentrations that excluded precipitation of solid phases. Zeta-potential measurements were conducted to monitor surface charge changes. In addition, isothermal titration calorimetry (ITC) was used to derive thermodynamic parameters of the interaction between the metals and pSi. Surprisingly, neither did batch-adsorption experiments reveal any metal adsorption on pSi after 24 h reaction time, nor did ITC experiments show any evidence for chemical adsorption of the metals, as no heat was released or absorbed during the experiments. However, zeta-potential measurements indicated weak electrostatic interactions between the negatively charged silanol groups and the metals. These electrostatic interactions may be the initial step of metal incorporation into the matrix of polymerizing silicic acid, which were spectroscopically proven in long-term experiments.
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