There has been a growing appreciation and understanding of the link between fruit and vegetable consumption and improved health. Research has shown that biologically active components in plant-based foods, particularly phytochemicals, have important potential to modulate many processes in the development of diseases, including cancer, cardiovascular disease, diabetes, pulmonary disorders, Alzheimer’s disease, and other degenerative disease states. Apples and AP3, including juices and extracts, have been included in health-related studies around the world due to their rich content of varied phytochemicals. The potential of AP phytochemicals to reduce disease risk and improve health has caught the attention of scientists, practitioners, and the lay public.
A detailed report of apple phytochemicals and their health benefits was published by Boyer and Liu (1
) in 2004. Their review included an overview of the positive association between AP and health benefits demonstrated in observational studies (1
). In many of these studies, dietary intake was quantified using diet history or FFQ followed by tests for a statistical link between disease risk and defined strata of AP or AP-flavonoid consumption. Early work suggested a potential association between AP intake and reduced risk of coronary artery disease, lung cancer, asthma, and diabetes. AP consumption was also linked to beneficial effects on pulmonary function in healthy participants and those with diagnosed pulmonary disorders (1
). Recent investigations have added to the earlier work as well as identified potential new health benefits of AP consumption.
The nature of the link between diet and disease is complex. Increasingly, research has moved toward studying compounds in individual foods to gain a greater understanding of their specific role(s) and the mechanisms involved in the prevention and reduction of disease in humans. A great deal of work has focused on dietary polyphenols, particularly the most abundant subclasses, including flavonoids (60% of all polyphenols) and phenolic acids (30% of total polyphenols) (2
). More than 4000 flavonoids have been identified and all share a common carbon skeleton structure (C6-C3-C6). Flavonoids are further divided into different classes based on molecular structure, several of which are present in significant quantities in AP, including flavanols, flavonols, and anthocyanidins as well as dihydrochalcones and hydroxycinnamic acids (3
). The chemical structures of several representative polyphenols present in AP are shown in (4
Figure 1 Selected polyphenols in apples and apple products. Adapted with permission from (4).
Polyphenolic compounds account for the color, flavor, taste, and metabolic activity of plant-based foods as well as the putative health benefits to humans. The concentration of polyphenols is influenced by the plant variety as well as environmental factors, including geographic region, growing season, and storage (3
). The wide range of polyphenol content in whole apples and apple juice is depicted in (4
). Typically, the greater values in the ranges shown for juices reflect the higher concentration of polyphenols in fresh juice prepared from cider apples and commercial preparations of “cloudy” juice compared to lower quantities in fresh juice made with dessert apple varieties or commercial juices that are clear.
Polyphenolic concentration of whole apples (freeze dried) and apple juice
The estimated dietary intake of polyphenolic compounds varies widely depending upon methodology, consumption data, the combination of compounds (most commonly flavonoids) included in the analysis, and the food composition database used (6
). In general, AP are among the top 3 or 4 dietary sources of total phenolics consumed in America and worldwide (7
). Furthermore, AP are available on a year-round basis and the per capita utilization of apples and AP in the United States has been on the rise over the past several years (10
). Thus, the study of AP is highly relevant and they have important potential to affect the health of the populations consuming them.
Oxidative stress, known to play a role in the pathogenesis of most diseases, has been the focus of many new studies to determine the effectiveness of AP in an antioxidant capacity. Other disease-related processes that are reportedly influenced by AP include cell proliferation and tumor production, inflammatory responses, apoptosis, cell differentiation (11
), platelet aggregation, lipid metabolism, cell adhesion molecule expression, and endothelial function, among others (12
). The purpose of the present review is to provide an updated summary and analysis of recent findings related to AP and associated compounds with a particular focus on their potential role(s) in disease risk and general human health. Studies are presented below, grouped by disease states and/or disease processes when applicable.