There is increased interest in following a healthy lifestyle and consuming a substantial portion of secondary plant metabolites, such as polyphenols, due to their benefits for the human body. Food products enriched with various forms of fruits and vegetables are sources of pro-health components. Nevertheless, in many cases, the level of their activities is changed in in vivo conditions. The changes are strictly connected with processes in the digestive system that transfigure the structure of the active compounds and simultaneously keep or modify their biological activities. Much attention has focused on their bioavailability, a prerequisite for further physiological functions. As human studies are time consuming, costly and restricted by ethical concerns, in vitro models for investigating the effects of digestion on these compounds have been developed to predict their release from the food matrix, as well as their bioaccessibility. Most typically, models simulate digestion in the oral cavity, the stomach, the small intestine and, occasionally, the large intestine. The presented review aims to discuss the impact of in vitro digestion on the composition, bioaccessibility and antioxidant activity of food polyphenols. Additionally, we consider the influence of pH on antioxidant changes in the aforementioned substances.

Monoterpenes make up the largest group of plant secondary metabolites. They can be found in numerous plants, among others, the Lamiaceae family. The compounds demonstrate antioxidative, antibacterial, sedative and anti-inflammatory activity, hence, they are often employed in medicine and pharmaceuticals. Additionally, their fragrant character is often made use of, notably in the food and cosmetic industries. Nevertheless, long-lasting studies have revealed their toxic properties. This fact has led to a detailed analysis of the compounds towards their side effects on the human organism. Although most are safe for human food and medical applications, there are monoterpene compounds that, in certain amounts or under particular circumstances (e.g., pregnancy), can cause serious disorders. The presented review characterises in vitro and in vivo, the toxic character of selected monoterpenes (α-terpinene, camphor, citral, limonene, pulegone, thujone), as well as that of their original plant sources and their essential oils. The selected monoterpenes reveal various toxic properties among which are embryotoxic, neurotoxic, allergenic and genotoxic. It is also known that the essential oils of popular plants can also reveal toxic characteristics that many people are unaware of.

Neurodegenerative disorders are among the most studied issues both in medicine and pharmacy. Despite long and extensive research, there is no effective treatment prescribed for such diseases, including Alzheimer's or Parkinson's. Available data exposes their multi-faceted character that requires a complex and multidirectional approach to treatment. In this case, the most important challenge is to understand the neurodegenerative mechanisms, which should permit the development of more elaborate and effective therapies. In the submitted review, iron and zinc are discussed as important and perfectly possible neurodegenerative factors behind Alzheimer's and Parkinson's diseases. It is commonly known that these elements are present in living organisms and are essential for the proper operation of the body. Still, their influence is positive only when their proper balance is maintained. Otherwise, when any imbalance occurs, this can eventuate in numerous disturbances, among them oxidative stress, accumulation of amyloid β and the formation of neurofibrillary tangles, let alone the increase in α-synuclein concentration. At the same time, available research data reveals certain discrepancies in approaching metal ions as either impassive, helpful, or negative factors influencing the development of neurodegenerative changes. This review outlines selected neurodegenerative disorders, highlights the role of iron and zinc in the human body and discusses cases of their imbalance leading to neurodegenerative changes as shown in vitro and in vivo studies as well as through relevant mechanisms.