Phenolic compounds are secondary plant metabolites with remarkable health-promoting
properties. More than 8000 phenolics have been identified from natural sources [1].
In plants, phenolics play different physiological roles, such as plant growth regulators
and as important chemical precursors for the biosynthesis of other molecules such
as lignin and suberin, which are produced as a defense mechanism against different
biotic and abiotic stresses [2].
Twenty-six contributions (19 research and seven review articles) in this Special Issue
show some of the current advances in bioactive phenolics and polyphenols. Research
articles published were mainly focused on the evaluation of different bioactivities
of phenolics, with an emphasis on the prevention of chronic diseases, whereas another
important number of papers described methods for the production of phenolics by chemoenzymatic
preparations [3], hairy root culture bioreactors [4], and elicitation of the secondary
plant metabolism by preharvest [5] and postharvest [6] abiotic stresses.
Regarding research published on the effect of phenolics to prevent chronic diseases,
it was reported that ellagic acid (a component of ellagitannins, present in crops
such as pecans, walnuts, and berries) and its metabolites urolithins A and B, produced
by the gut microbiota, differentially regulate fat accumulation and inflammation in
3T3-L1 adipocytes, while not affecting adipogenesis and insulin sensitivity [7]. Another
report evaluating the microbial metabolites of chlorogenic acid demonstrated their
anti-proliferative effects, S-phase cell-cycle arrest, and apoptosis in human colon
cancer Caco-2 cell [8]. Furthermore, carnosol was identified as a component of rosemary
extract with potential application as glucose regulating agent by increasing muscle
cell glucose uptake via AMPK-dependent GLUT4 glucose transporter translocation [9].
Likewise, the anti-hypertensive effects of polyphenols from acacia (an evergreen tree
belonging to the genus Acacia in the legume family) was reported, using spontaneously
hypertensive rats as an experimental model [10]. Other published papers in this Special
Issue showed the in vivo attenuation effect of ischemic myocardial damage by phenolic
extracts from Crataegus oxyacanth and Rosmarinus officinalis [11], whereas it was
reported that extracts from Aspidosperma pyrifolium presented in vivo anti-inflammatory
properties in mice with peritonitis [12].
Furthermore, other contributors to this Special Issue reported the potential use of
3,5,6,7,8,3′,4′-heptamethoxyflavone, a Citrus flavonoid, for the preparation of skincare
products due to its capacity to inhibit collagenase activity and to induce type-I
procollagen synthesis in UV-induced human dermal fibroblast neonatal (HDFn) cells
[13]. Other bioactive properties of phenolics reported were the inhibition of Zika
virus infection by isoquercitin [14], the neuroprotective effects of anthocyanin-enriched
extracts from berries [15] and quercetin [16], and the antibacterial effects against
Staphylococcus aureus of flavonoids from the traditional Japanese medicine keigairengyoto
[17]. Isorhamnetin and quercetin derivatives were reported as the anti-acetylcholinesterase
principles of marigold (Calendula officinalis) flowers and preparations [18], whereas
the antinociceptive effect of Arrabidaea brachypoda (DC) bureau phenolic extract was
also demonstrated [19]. The intestinal permeability, cellular antioxidant activity,
and plasma stability of phenolic compounds from mango [20] and isorhamnetin glycoside
from Opuntia ficus-indica (L.) [21] were also reported in the Special Issue.
The Special Issue included seven review papers that describe the current status of
phenolic compounds, covering general aspects of their bioactivity for the suppression
of chronic diseases [1], as well as the bioactivity of specific group of phenolics
such as the stilbenoids [22,23], ellagitannins, and anthocyanins [24]. In addition,
the health-promoting properties of phenolics present in lentils [25] and dry common
beans [26] were also reviewed. Finally, a review article describing nanofiltration
and tight ultrafiltration membrane techniques for the recovery of polyphenols from
agro-food by-products was also presented [27].
The evaluation of phenolics bioactivities from different plant sources is a growing
area of research. Every year, new scientific information supports the increased potential
of phenolics to prevent different chronic and degenerative diseases. Further research
should continue the direction of identifying natural sources rich in phenolics and
evaluating their bioactivities. However, now that the bioactivity of phenolics from
several plant materials has been characterized, further research efforts could be
focused on taking the generated fundamental science into the market through developing
innovative food products and dietary supplement formulations. One interesting emerging
area of research is the design of effective nutraceutical combinations in the form
of foods, beverages, and dietary supplements that could be used not only in the prevention
of chronic disease but also for their treatment [28]. In this context, the synergistic
combination of phenolic compounds with other nutraceuticals should be evaluated for
the prevention and treatment of chronic diseases [29]. Furthermore, the development
of bioprocesses to obtain next-generation functional food and beverages is crucial
to reach the market and provide the desired beneficial effect of phenolic compounds
to the population. In this context, it has been recently proposed that the application
of postharvest abiotic stresses in horticultural crops to increase the content of
phenolic compounds, and their further transformation into processed food products
using nonthermal processing technologies, could be an effective approach to obtain
shelf-stable products with a high content of antioxidant phenolic compounds [30].