Bioactive phytochemicals

Phytochemicals, often referred to as phytonutrients, are natural bioactive components rich in foods like vegetables, fruits, whole grain products, nuts and seeds, legumes, tea and dark chocolate. Although there are tens of thousands of phytochemicals, only a small number have been isolated and identified from plants (Cao et al. 2017; Singh and Chaudhuri 2018). The most common phytochemicals in food include polyphenols, carotenoids, flavonoids, coumarins, indoles, isoflavones, lignans, organosulfures, catechins, phenolic acids, stilbenoids, isothiocyanates, saponins, procyanidins, phenylpropanoids, anthraquinones, ginsenosides, and so on (Xiao 2017; Zhao et al. 2018a). Biodiversity of resources of phytonutrients provided a unique and renewable resource for the discovering of potential new function food and novel biological activities (Bacanlı et al. 2017; Chen et al. 2018; Curti et al. 2017; Vinayagam, Xiao, and Xu 2017; Zhao et al. 2017). This special issue focused on the resources, bioactivities, functions of bioactive phytochemicals, which will provide a comprehensive viewpoint on the relationship between dietary phytochemicals and health.

The traditional Mediterranean diet (MedDiet) is a well-known dietary pattern linked with longevity and improvement of life quality due to it reduces the risk of the most common chronic diseases. Battino et al. (2018) presented the recent evidence on the potential roles exerted by olive oils, berries and honey, the main food in MedDiet, on the prevention and progression of cancer and cardiovascular diseases. It was demonstrated that these foods play key roles in cancer prevention by inactivating carcinogens, decreasing cell proliferation, inducing cell cycle arrest and apoptosis, and inhibiting angiogenesis in many types of tumors. Furthermore, they exert cardio-protective effects by decreasing oxidative stress and inflammation, modulating carbohydrate digestion through the reduction of glucose absorption, improving blood lipid levels, augmenting the resistance of LDL to oxidation, normalizing endothelial function, vascular elastic properties of the arterial tree, blood pressure and platelet functions.

Some Arbutus species revealed promising biological activities including antioxidant, anti-inflammatory, anti-proliferative, anti-diabetic, and antimicrobial activities, and deserve for that reason further consideration for new drug discovery. Tenuta et al. (2018) reviewed the main chemical constituents, biological properties, and potential toxic effects of three Arbutus species common in the Mediterranean area (A. andrachne, A. pavarii, and A. unedo). The fruits and leaves of Arbutus species have been used as traditional medicines for laxative, antiseptic, hypoglycemic, and diuretic effects. In view of the interesting chemical and biological profiles, the use of Mediterranean Arbutus species in some food products may be suggested. Coffee leaves have a long history for use as ethnomedicines and drinking beverages. Significant attentions have been paid to the benefits of coffee leaves due to abundant bioactive components. Chen (2018) highlighted the phytochemicals, bioactivities and applications of coffee leaves. Coffee leaf is a valuable resource to produce value added coffee leaf tea, food, medicine, therapeutic agents, personal hygiene products and other industrial products. The author pointed out that the mechanisms related to the health benefits of coffee leaves and the structure-relationships of their bioactive phytochemicals need further research, as well as how the processing methods influence the bioactivities.

Metabolic syndrome can develop to several related chronic diseases, such as obesity, cardiovascular disease, hypertension, diabetes, and fatty liver disease. Dietary and lifestyle modifications are suggested to be effective approaches to manage metabolic syndrome. Significant evidence have confirmed that dietary phytonutrients are beneficial for preventing and managing type 2 diabetes mellitus (T2DM). Zhao et al. (2018b) highlighted the advances on regulation of glucose metabolism by bioactive phytochemicals. Moreover, the authors explored the relationship among metabolic pathways, gut microbiota, obesity, and inflammation. The authors also discussed how microbial metabolites of dietary phytochemicals modulate host glucose metabolism. Alongside the recommended prevention involving diet modifications, optimal treatment with the good combination of drugs and natural phytochemicals remains to be established. Nie et al. (2018) summarized the relationship between T2DM and gut microbiota, as well as the effects of dietary components on gut microflora. Dietary fiber and phytochemicals first change the composition of gut microbiota by inhibiting pathogens and promoting the beneficial bacteria growth and then influence the production of their metabolites, which would further modify the intestinal environment. The microbial metabolites of dietary components can target multiple pathways in intestine, liver, pancreas, etc., which could improve gut health, glycemic control, lipids profile, insulin resistance and inflammation. Understanding the interaction between dietary components and gut microbiota, as well as underlying mechanisms would help design diet formula to manage T2DM. Jiang et al. (2018) the development of studies on anthocyanins with its target cells in metabolic syndrome. Anthocyanins are efficient on adipocytes, endothelial cells, inflammatory cells, hepatocytes, intestinal cells and gut microbiota, but lack of evidence on platelets, skeletal muscle cells, hepatic stellate cells and pancreatic beta cells. Anthocyanins have been proved with direct effects that ameliorate the damage or activation of these cells in various pathways. Additionally, the structure-function relationship of anthocyanins and the metabolites were discussed. Tian et al. (2018) reported the recent data on the absorption of anthocyanins in the upper gastrointestine and the metabolism of anthocyanins by gut microbiota. How to find approaches to improve the bioavailability of anthocyanins in upper gastrointestinal transit is a new researching field. It is difficult to distinguish whether metabolites present in the blood and organs are from endogenous enzymes-degradation of anthocyanins or from metabolism by gut microbiota. Moreover, how to deliver anthocyanins to colon safely and how to balance the absorption sites for certain purpose are still to be investigated.

A circadian rhythm is any physiological activity rhythm driven by internal circadian clocks and entrained by external signals. The disruption of circadian rhythm will lead to develop many diseases, including obesity, metabolic syndrome, and cancer. However, not many medical treatments for circadian rhythm disorder has been applied. Several phytochemicals demonstrate the ability to prevent or even treat circadian-related diseases and function as circadian modulators. Xu and Lu (2018) summarized the effects of phytochemicals on circadian rhythm and related diseases. Phytochemicals affect the circadian rhythm in terms of amplitude, phase, period, and mesor. Most phytochemicals enhance the amplitude or cut no ice, except for myricetin. As for circadian phase, phase delay is more popular than phase advance. Several studies on vanillic acid used the expression “reverse phase delay”. Only theophylline can advance the circadian phase when administrated at a certain time. Only a few phytochemicals can shorten the circadian period. Notably, all alkaloid lengthens the circadian period, which might be due to their structural similarity.

Multiple micronutrient supplementation has been suggested to have a role on health outcomes in patients with heart failure, but the evidence is inconclusive. Dragan et al. (2018) summarized the present evidence about the impact of micronutrients on severity and evolution of heart failure based on randomized controlled trials and meta-analysis. Micronutrients have been found to improve the health outcomes of patients with heart failure by improving symptoms, work capacity and left ventricular ejection fraction, thus increasing the quality of life in these patients. The interaction between the tumor microenvironment and the immune system is a complex topic. Pan et al. (2018) reviewed the immunomodulatory potential of natural compounds on human clinical trials and animal studies and highlighted specific immune cells and their cytokines that have been modulated by carotenoids, curcumin, resveratrol, EGCG, and β-glucans. These phytochemicals exhibited promising immune-modulating effects, such as inhibiting myeloid-derived suppressor cells and enhancing natural killer and cytolytic T cells, in tumor-bearing animal models, but their efficacy in cancer patients remains to be determined.

In our diets, many of the consumed foods are subjected to various forms of thermal processing. Wong et al. (2018) reviewed the effects of thermal processing on the dietary phytochemicals in plant-derived foods (garlic, coffee, cocoa and barley). In some cases, the amazing formation of new compounds were formed. Maillard reaction could be concluded as the predominant pathway leading to the formation of new conjugates, along with other possible reactions including degradation, transglycosylation, deglycosylation and dehydration. Salvia miltiorrhiza (Danshen in Chinese), is a well-known traditional Chinese medicinal and edible plant. Danshen has been extensively used for the treatment of various cardiovascular and cerebrovascular diseases. Phenolic acids such as salvianolic acid B is a major group of bioactive constituents from S. miltiorrhiza. Shi et al. (2018) reported the recent advances in bioactivities, biosynthetic pathway and biotechnological production of phenolic acids in S. miltiorrhiza.

Jianbo Xiao and Weibin BaiDepartment of Food Science and Engineering, Institute of Food Safety and Nutrition, Guangdong Engineering Technology Center of Food Safety Molecular Rapid Detection, Jinan University, Guangzhou, China [email protected]