2 Fruit pigments and their effects on human health
One of the key drivers for research into plant pigments is the association of these compounds with dietary health (Martin & Li 2017). Fruits are particularly rich sources of these phytochemicals and so changes in the composition or concentration are of interest. For carotenoids, one of the most abundant and important of these pigmented phytochemicals is β-carotene, which has provitamin A properties and is converted into retinol (vitamin A) in the body. Other carotenoid sources of provitamin A include α-carotene and β-cryptoxanthin (Rodriguez-Concepcion et al. 2018). Vitamin A is an essential part of our diet and deficiency is still a major problem in developing countries (West & Darnton-Hill 2008), which prompted the development of provitamin A-enriched crops (Giuliano 2017). Carotenoids also provide the macular pigments, xanthophylls including lutein and zeaxanthin, which have antioxidant and short-wavelength light absorption functions in the eye (Bernstein et al. 2016). These are associated with eye health, particularly the prevention of age-related macular degeneration (Carpentier, Knaus & Suh 2009). Consumption of carotenoids has also been associated with disease prevention, including a reduced incidence of cardiovascular disease and some cancers, as well as positive effects on cognitive function (Leermakers et al. 2016; Lindbergh et al. 2018; Mein, Lian & Wang 2008).
An increasing number of clinical trials have shown evidence for the health claims associated with anthocyanins. Many of these studies link anthocyanins to protection against human diseases, including cardiovascular and age-related degenerative diseases, obesity, metabolic syndrome and cancer (reviewed by Gonçalves et al. 2021; Kaltet al. 2020; Pojer et al. 2013). There was earlier speculation about the mechanism of action, as these compounds were not found in human circulatory systems at the site of the action, but it appears now that bioavailability is greater than originally thought (Kayet al. 2017; Lila et al. 2016). If the protection that pigments provide in fruit is due to their antioxidant activities, is this also the mechanism the major human health benefits associated with their dietary consumption? This is less certain, and further research is required to confirm the modes of action. However, it has recently been established that one key mechanism for the health effects is via the extensive impact of an anthocyanin-rich diet on the gut microflora, which further process the final functional compounds (Espley et al. 2014; Groh et al. 2020; Jucá et al. 2020; Lisoet al. 2018; Ntemiri et al. 2020; Ou, Yang & Liu 2020).