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).