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Polyphenols, as widely existing natural bioactive products, provide a vast array of advanced biomedical applications attributing to their potential health benefits that linked to antioxidant, anti-inflammatory, immunoregulatory, neuroprotective, cardioprotective function, etc. The polyphenol compounds could dynamically interact and bind with diverse species (such as polymers, metal ions, biomacromolecules, etc.) via multiple interactions, including hydrogen bond, hydrophobic, π—π, and cation—π interactions due to their unique chemical polyphenolic structures, providing far-ranging strategies for designing of polyphenol-based vehicles. Natural polyphenols emerged as multifaceted players, acting either as inherent therapeutics delivered to combat diverse diseases or as pivotal assemblies of drug delivery vehicles. In this review, we focused on the rational design and application of metal-phenolic network (MPN) based delivery systems, polyphenol-based coating films, polyphenol hollow capsules, polyphenol-incorporated hydrogels, and polymer-polyphenol-based nanoparticles (NPs) in various diseases therapeutic, including cancer, infection, cardiovascular disease, neurodegenerative disease, etc. Additionally. the versatility and mechanisms of polyphenols in the field of biomacromolecules (e.g., protein, peptide, nucleic acid, etc.) delivery and cell therapy have been comprehensively summarized. Going through the literature review, the remaining challenges of polyphenol-containing nanosystems need to be addressed are involved, including long-term stability, biosafety in vivo , feasibility of scale-up, etc., which may enlighten the further developments of this field. This review provides perspectives in utilizing natural polyphenol-based biomaterials to rationally design next generation versatile drug delivery system in the field of biomedicine, which eventually benefits public health.

The aim of this study was to isolate, identify and quantify soluble free phenolics, conjugated acid-hydrolysable phenolics (AHP) and alkaline-hydrolysable phenolics, and bound phenolics (BP) fractions from two tomato varieties (saladette and grape) and an industrial tomato by-product, as well as, to determine their antioxidant capacity. Phenolic composition was determined using Folin–Ciocalteu’s method and HPLC–DAD. AHP were predominant in grape and saladette tomato extracts (91.47 ± 17.28 mg gallic acid equivalents (GAE) per g dry extract (DE) and 57.41 ± 8.80 mg GAE per g DE, respectively), while BP form was predominant in tomato by-product (51.30 ± 10.91 GAE per g DE). AHP extract of grape tomato presented the highest antioxidant capacity by DPPH assay (252.35 ± 42.55 μmol trolox equiv (TE) per g DE). In the case of ORAC assay, AHP fractions from both grape (1005.19 ± 138.52 μmol TE per g DE) and saladette tomatoes (804.16 ± 131.45 μmol TE per g DE), and BP fraction from by-product (852.40 ± 71.46 μmol TE per g DE) showed the highest ORAC values. Caffeic acid was the most abundant phenolic acid and it was found mainly in its conjugated forms. Naringenin was the most abundant flavonoid and it was mainly detected in bound form. Our analysis allowed a better characterization of phenolic compounds in whole tomato and by-product, remarking the importance of the fractionation. The valorization of the industrial tomato by-product, through the use of its different fractions of phenolic antioxidant compounds, could generate additional income to the tomato industry and reduce the waste disposal problem.

Polyphenolics in plants exist in free, soluble-bound, and insoluble-bound structural forms. The concentration of these structural forms depends on the plant’s developmental stage, tissue type, soil water availability, and food preparation methods. In this study, for the first time, the effects of growth temperature (RT—room temperature—23 °C day/18 °C night, HT—high temperature—38 °C day/33 °C night, LT—low temperature—12 °C day/7 °C night) on variations of polyphenolic structural forms—free, soluble-bound (esterified and glycosylated), and insoluble-bound—in broccoli (Brassica oleracea L. convar. botrytis (L.) Alef. var. cymosa Duch.) microgreens were investigated. Using spectrophotometric, RP-HPLC, and statistical analyses, it was found that the highest amount of total phenolics (TP) in broccoli microgreens was present in the esterified form, regardless of the temperature at which they were grown (63.21 ± 3.49 mg GAE/g dw in RT, 65.55 ± 8.33 mg GAE/g dw in HT, 77.44 ± 7.82 mg GAE/g dw in LT). LT significantly increased the amount of free (from 13.30 ± 2.22 mg GAE/g dw in RT to 18.33 ± 3.85 mg GAE/g dw) and esterified soluble TP (from 63.21 ± 3.49 mg GAE/g dw in RT to 77.44 ± 7.82 mg GAE/g dw), while HT significantly increased the amount of TP glycosylated forms (from 14.85 ± 1.45 mg GAE/g dw in RT to 17.84 ± 1.20 mg GAE/g dw). LT also enhanced free and esterified forms of total flavonoids, tannins, hydroxycinnamic acids, and flavonols. HT, on the other hand, increased glycosylated forms of TP, flavonoids, tannins, hydroxycinnamic acids, flavonols, and phenolic acids, and decreased insoluble-bound tannins. According to the ABTS method, HT induced antioxidant potential of free and glycosylated forms, while LT increased antioxidant capacity of free forms only. According to the FRAP method, LT increased antioxidant potential of free and esterified polyphenolic forms. Also, based on ABTS and FRAP assays, esterified polyphenolics showed significantly higher antioxidant capacity than any other form. Principal component analysis showed that structural form had a greater impact than temperature. Hierarchical clustering showed that RT-, HT- and LT-broccoli microgreens were most similar in their glycosylated polyphenolics, but differed the most in esterified forms, which were also the most distinct overall. In conclusion, HT and LT induced specific shifts in the structural forms of broccoli polyphenolics and their antioxidant capacity. Based on the results, we recommend applying LT to increase the amount of free and esterified polyphenolics in broccoli microgreens, while HT may be used to enhance glycosylated forms.

This contribution provides a review of the topic of insoluble-bound phenolics, especially their localization, synthesis, transfer and formation in plant cells, as well as their metabolism in the human digestive system and corresponding bioactivities. In addition, their release from the food matrix during food processing and extraction methods are discussed. The synthesis of phenolics takes place mainly at the endoplasmic reticulum and they are then transferred to each organ through transport proteins such as the ATP-binding cassette (ABC) and multidrug and toxic compound extrusion (MATE) transporter at the organ’s compartment membrane or via transport vesicles such as cytoplasmic and Golgi vesicles, leading to the formation of soluble and insoluble-bound phenolics at the vacuole and cell wall matrix, respectively. This part has not been adequately discussed in the food science literature, especially regarding the synthesis site and their transfer at the cellular level, thus this contribution provides valuable information to the involved scientists. The bound phenolics cannot be absorbed at the small intestine as the soluble phenolics do (5%–10%), thus passing into the large intestine and undergoing fermentation by a number of microorganisms, partially released from cell wall matrix of foods. Bound phenolics such as phenolic acids and flavonoids display strong bioactivities such as anticancer, anti-inflammation and cardiovascular disease ameliorating effects. They can be extracted by several methods such as acid, alkali and enzymatic hydrolysis to quantify their contents in foods. In addition, they can also be released from the cell wall matrix during food processing procedures such as fermentation, germination, roasting, extrusion cooking and boiling. This review provides critical information for better understanding the insoluble-bound phenolics in food and fills an existing gap in the literature.

Phenolics, which are secondary metabolites of plants, exhibit remarkable bioactivities. In this contribution, we have focused on their protective effect against chronic diseases rather than their antioxidant activities, which have been widely discussed in the literature. A large body of epidemiological studies has proven the bioactivities of phenolics in both standard compounds and natural extracts: namely, anticancer, anti-inflammatory, and antibacterial activities as well as reducing diabetes, cardiovascular disease, and neurodegenerative disease. Phenolics also display anti-analgesic, anti-allergic, and anti-Alzheimer’s properties. Thus, this review provides crucial information for better understanding the bioactivities of phenolics in foods and fills a gap in the existing collective and overall knowledge in the field.

[This corrects the article DOI: 10.1371/journal.pone.0321255.].

In this study, the polyphenols composition and antioxidant properties of 12 blue highland barley varieties planted on the Qinghai-Tibet Plateau area were measured. The contents of the free, bound and total phenolic acids varied between 166.20–237.60, 170.10–240.75 and 336.29–453.94 mg of gallic acid equivalents per 100 g of dry weight (DW) blue highland barley grains, while the free and bound phenolic acids accounted for 50.09% and 49.91% of the total phenolic acids, respectively. The contents of the free, bound and total flavones varied among 20.61–25.59, 14.91–22.38 and 37.91–47.98 mg of catechin equivalents per 100 g of dry weight (DW) of blue highland barley grains, while the free and bound flavones accounted for 55.90% and 44.10% of the total flavones, respectively. The prominent phenolic compounds in the blue hulless barley grains were gallic acid, benzoic acid, syringic acid, 4-coumaric acid, naringenin, hesperidin, rutin, (+)-catechin and quercetin. Among these, protocatechuic acid, chlorogenic acid and (+)-catechin were the major phenolic compounds in the free phenolics extract. The most abundant bound phenolics were gallic acid, benzoic acid, syringic acid, 4-coumaric acid, benzoic acid, dimethoxybenzoic acid, naringenin, hesperidin, quercetin and rutin. The average contribution of the bound phenolic extract to the DPPH• free radical scavenging capacity was higher than 86%, that of free phenolic extract to the ABTS•+ free radical scavenging capacity was higher than 79%, and that of free phenolic (53%) to the FRAP antioxidant activity was equivalent to that of the bound phenol extract (47%). In addition, the planting environment exerts a very important influence on the polyphenol composition, content and antioxidant activity of blue highland barley. The correlation analysis showed that 2,4-hydroxybenzoic acid and protocatechuic acid were the main contributors to the DPPH• and ABTS•+ free radical scavenging capacity in the free phenolic extract, while chlorogenic acid, vanillic acid, ferulic acid and quercetin were the main contributors to the free radical scavenging capacity in the bound phenol extract. The study results show that the blue highland barley grains have rich phenolic compounds and high antioxidant activity, as well as significant varietal differences. The free and bound phenolic extracts in the blue hulless barley grains have an equivalent proportion in the total phenol, and co-exist in two forms. They can be used as a potential valuable source of natural antioxidants, and can aid in enhancing the development and daily consumption of foods relating to blue highland barley.

Plant hormone-loaded nanoparticles (NPs) represent a novel class of materials with significant potential in plant cell culture, owing to their unique physico-chemical properties. The utilization of these hormone-loaded NPs as elicitors could enhance the production of bioactive compounds and boost antioxidant enzymatic activity in plant cell suspension cultures. Therefore, this study aimed to synthesize jasmonic acid (JA) loaded Fe3O4 NPs and evaluate their effects on the cell suspension culture of Carthamus tinctorius (safflower). The synthesized material was applied at various concentrations (10, 20, 40 and 80 mg L-1) to assess its impact on cell growth, physio-biochemical, antioxidative activities and specialized metabolites (SMs) of C. tinctorius. The results demonstrated that the addition of JA-loaded NPs significantly enhanced the total chlorophyll (70.37%), soluble protein (154.45%) and total phenolic contents (110.64%) of safflower compared to the control. A linear decrease in all reactive oxygen species (ROS) attributes, such as H2O2 (4.65%) and O2- (22.81%), was observed as the NPs concentration in the culture media was increased to the T2 group (20 mg L-1). Maximum chlorogenic acid (CGAs) accumulation (43.76 mg g-1) was noted on 72 hours after elicitation, representing a 2.26-fold increase over the control group. Furthermore, amino acid profiling revealed substantial variations in the composition of all detected amino acids following treatment with JA-loaded Fe3O4 NPs. In summary, this strategy demonstrates potential for optimizing the production of antioxidant and bioactive metabolites, thereby offering a viable solution for the industrial scale production of high-quality safflower extracts.

Sea cucumbers are considered a luxury food item and used locally in traditional medication due to their impressive nutritional profile and curative effects. Sea cucumbers contain a wide range of bioactive compounds, namely phenolics, polysaccharides, proteins (collagen and peptides), carotenoids, and saponins, demonstrating strong antioxidant and other activities. In particular, phenolic compounds, mainly phenolic acids and flavonoids, are abundant in this marine invertebrate and exhibit antioxidant activity. Protein hydrolysates and peptides obtained from sea cucumbers exhibit antioxidant potential, mainly dependent on the amino acid compositions and sequences as well as molecular weight, displayed for those of ≤20 kDa. Moreover, the antioxidant activity of sea cucumber polysaccharides, including fucosylated chondroitin sulfate and fucan, is a combination of numerous factors and is mostly associated with molecular weight, degree of sulfation, and type of major sugars. However, the activity of these bioactive compounds typically depends on the sea cucumber species, harvesting location, food habit, body part, and processing methods employed. This review summarizes the antioxidant activity of bioactive compounds obtained from sea cucumbers and their by-products for the first time. The mechanism of actions, chemical structures, and factors affecting the antioxidant activity are also discussed, along with the associated health benefits.

Plant foods, their products and processing by-products are well recognized as important sources of phenolic compounds. Recent studies in this field have demonstrated that food processing by-products are often richer sources of bioactive compounds as compared with their original feedstock. However, their final application as a source of nutraceuticals and bioactives requires addressing certain hurdles and challenges. This review discusses recent knowledge advances in the use of plant food processing by-products as sources of phenolic compounds with special attention to the role of genetics on the distribution and biosynthesis of plant phenolics, as well as their profiling and screening, potential health benefits, and safety issues. The potentialities in health improvement from food phenolics in animal models and in humans is well substantiated, however, considering the emerging market of plant food by-products as potential sources of phenolic bioactives, more research in humans is deemed necessary.