# Selected Antioxidants in Organic vs. Conventionally Grown Apple Fruits
## 1 Introduction  
Apple (_Malus domestica_ Borkh.) is currently the most widely cultivated temperate fruit, with a global production of over 76 million tonnes per year [1]. Besides fresh consumption, apple fruits are also processed into juices, concentrates, purees, ciders, and many other products [2]. They reached such a position due to their high yielding, overall abundance, accessibility on the market, long storage capacity, and their taste and rich phytochemical profile. Due to being widely consumed and available in all seasons, apples became one the most important fruit sources of health-promoting phenolic compounds in the Western diet [3]. This resulted in the growing scientific interest in these fruits' potential to enhance human health. A number of research studies have linked apple consumption to the reduced risk of various non-communicable diseases, including certain cancers, type II diabetes, and cardiovascular disease [3; 4; 5]. Moreover, apple fruit consumption was shown to be associated with positive effects on cognitive functions, weight management, bone density, pulmonary function, and gastrointestinal health [5; 6]. The in vitro experiments reported the antioxidant, cell signaling, and antiproliferative mechanisms of apple extracts action [4]. Many of these effects were associated with phenolics and dietary fibre in apples [7]. The available evidence links consumption of fruit phenolics to the prevention of cancers, neurodegenerative diseases, type 2 diabetes, osteoporosis, cardiovascular diseases, and many other non-communicable diseases through and beyond the oxidative stress modulation [8]. It is, therefore, considered that phenolics significantly contribute to the overall health-promoting effect of vegetable-rich and fruit-rich diets [9]. Increasing public concerns about the negative health impact of synthetic pesticides widely used in conventional agriculture and horticulture became one of significant drivers of the demand for fruit and vegetables coming from alternative systems. One such system gaining popularity in recent decades is organic farming [10; 11; 12; 13]. Organic producers are not allowed to use synthetic pesticides in order to limit both the environmental impacts of production inputs and to decrease the risk of consumers' exposure to pesticide residues in fruit and vegetables [14]. Instead, organic farms rely mainly on natural plant protection and preventive measures (i.e., more resistant or tolerant cultivars, mechanical weed control, and biological pest and disease control measures). Only a limited number of microbial or plant extract-based and mineral (i.e., S-based and Cu-based) plant protection products are available for organic farmers [13]. Moreover, organic and non-organic production differ in respect to fertilisation protocols (organic vs. mineral synthetic fertilizers) as well as crop rotation systems [15; 16]. Such contrasting practices applied in organic and non-organic systems may have an impact on yield, but also on plants' metabolism, which leads to differences in the crops' composition. Recently published research has indicated that replacing synthetic with natural fertilizers in agricultural production affects the profile of secondary metabolites (including phenolics) in plant tissues by changing the protein expression [17; 18]. As reported in the recently published meta-analysis [19], not only the profile, but also the concentrations of plant phenolics may differ significantly between organically and non-organically cultivated fruits and vegetables, with organic ones being, on average, characterized by higher concentrations of these antioxidants. However, it should be pointed out that many of the organic vs. conventional comparison studies carried out, so far, targeted only one cultivar of selected species and/or were undertaken in one vegetation season, and, therefore, did not allow the authors to consider the effects of genetic and season (weather/environment)-related factors on the composition of organic and non-organic fruits and vegetables.