Food Phenolics, Pros and Cons: A Review

Phenolic compounds like simple phenols, flavonoids, and phenolic acids are commonly in foods of plant origin. Several studies, including animal and epidemiological investigations, have demonstrated that phenolic compounds in foods possess positive attributes such as anticarcinogenesis, antioxidant potential, antiviral activity, antimicrobial activity, and antimutagenic activity. However, other studies have shown that the same phenolics have negative attributes such as carcinogenic activity and antinutritional activity, as well as imparting negative attributes to foods. This review summarizes the information about food phenolics and presents the most current knowledge with respect to its role in human health, food attributes, and toxicity among others.     

Antioxidant activity and antimicrobial effect of berry phenolics--a Finnish perspective

In Finland, berries are part of the traditional diet significantly contributing to the intake of flavonoids and other phenolic compounds. Compositional data on phenolic compounds in berries has been rapidly accumulating and included in the national food composition database. Among the different bioactive substances in berries, phenolic compounds including flavonoids, tannins, and phenolic acids have received considerable interest due to their effects in food and health. A great amount of in vitro evidence exists showing that berry phenolics are powerful antioxidants. However, the antioxidant effect of berry phenolics is strongly dependent on the choice of berry raw material, as the antioxidant activity differs between the different phenolic constituents, including anthocyanins, ellagitannins, and proanthocyanidins. In foods, the antioxidant effect is also influenced by the structure of food. Tannin-containing berries exhibit antimicrobial properties against pathogenic bacteria, thus offering many new applications for food industry. Much of the interest in berry phenolics has focused on cranberries and both cultivated and wild blueberries, although also other berries including black currants, cloudberries, lingonberries, and red raspberries possess promising bioactivities that may have relevance to human health. Antioxidant activity of berry phenolics, in addition to other mechanisms, may contribute to human health, but the possible relationship remains yet to be scientifically substantiated.     

Interactions between proteins and phenolics: effects of food processing on the content and digestibility of phenolic compounds

Phenolic compounds have recently become one of the most interesting topics in different research areas, especially in food science and nutrition due to their health-promoting effects. Phenolic compounds are found together with macronutrients and micronutrients in foods and within several food systems. The coexistence of phenolics and other food components can lead to their interaction resulting in complex formation. This review article aims to cover the effects of thermal and non-thermal processing techniques on the protein–phenolic interaction especially focusing on the content and digestibility of phenolics by discussing recently published research articles. It is clear that the processing conditions and individual properties of phenolics and proteins are the most effective factors in the final content and intestinal fates of phenolic compounds. Besides, thermal and non-thermal treatments, such as high-pressure processing, pulsed electric field, cold plasma, ultrasonication, and fermentation may induce alterations  in those interactions. Still, new investigations are required for different food processing treatments by using a wide range of food products to enlighten new functional and healthier food product design, to provide the optimized processing conditions of foods for obtaining better quality, higher nutritional properties, and health benefits. © 2024 Society of Chemical Industry.     

Occurrence,types, properties and interactions of phenolic compounds with other food constituents in oil-bearing plants

ABSTRACT

Phenolic phytochemicals have become of interest due to their therapeutic potential, particularly with regards to their anti-cancer, anti-inflammatory, hypolipidemic, and hypoglycemic properties. An evolving area of research involving phenolics in foods and their products pertains to the functional, biological, and nutritional consequences resulting from the binding between certain phenolic compounds and the macronutrient and micronutrient constituents of foods. The goal of this review is to provide a summary of studies investigating endogenous phenolic interactions with major components in food systems, including carbohydrates, proteins, lipids, minerals and vitamins, with a focus on the phenolic compounds and nutrients in oil-bearing plants. Another major objective is to provide a comprehensive overview of the chemical nature of phenolic interactions with food constituents that could affect the quality, nutritional and functional properties of foods. Such information can assist in the discovery and optimization of specific phenolic complexes in plant-based foods that could be utilized towards various applications in the food, nutraceutical and pharmaceutical industries.     

The Importance and Potential Uses of Olive Leaves

Since phenolic compounds have been known as strong antioxidants, studies on olive leaves have attracted the investigators due to the richness of phenolic compounds in olive leaves. Recently, olive leaves are used in medicine, cosmetics, and in pharmaceutical products. It has a high potential for industrial exploitation in the food industry. In this study, the importance of olive leaves is briefly given, the composition of olive leaves, main phenolics in olive leaves and their health effects are described. Studies conducted on technological usage of olive leaves are reviewed. The future of olive leaves for the food industry is discussed. It is expected that this study will be beneficial to academic and industrial researchers interested in antioxidants, food additives, functional foods, and olive leaves.     

Correlations of Antioxidant Activity against Phenolic Content Revisited: A New Approach in Data Analysis for Food and Medicinal Plants

ABSTRACT:  This study presents a new approach to analyze data correlating total antioxidant activity and total phenolic compounds in foods. The correlation of both variables is a common practice found in the literature. The purpose of these correlations is to determine the contribution of phenolics to the total antioxidant activity of foods. When low  R ² values are obtained, the general conclusion is that other compounds have a higher relevance than phenolics in the total antioxidant activity of the samples. However, these correlations do not consider differences in the phenolic profiles that can be qualitatively (type of phenolics present) and quantitatively (the relative amounts or proportions of phenolics present) among the samples under investigation. The new approach to analyze these simple correlations presented herein takes into consideration the phenolic profiles and provides information on the effectiveness of phenolics present in the samples to neutralize free radicals. Data obtained from carrots stored under conditions of air and hyperoxia (superatmospheric oxygen) are used to exemplify how to apply this new approach.     

Nonthermal Food Processing Alternatives and Their Effects on Taste and Flavor Compounds of Beverages

Food drinks are normally processed to increase their shelf-life and facilitate distribution before consumption. Thermal pasteurization is quite efficient in preventing microbial spoilage of many types of beverages, but the applied heat may also cause undesirable biochemical and nutritious changes that may affect sensory attributes of the final product. Alternative methods of pasteurization that do not include direct heat have been investigated in order to obtain products safe for consumption, but with sensory attributes maintained as unchanged as possible. Food scientists interested in nonthermal food preservation technologies have claimed that such methods of preserving foods are equally efficient in microbial inactivation as compared with conventional thermal means of food processing. Researchers in the nonthermal food preservation area also affirm that alternative preservation technologies will not affect, as much as thermal processes, nutritional and sensory attributes of processed foods. This article reviews research in nonthermal food preservation, focusing on effects of processing of food drinks such as fruit juices and dairy products. Analytical techniques used to identify volatile flavor-aroma compounds will be reviewed and comparative effects for both thermal and nonthermal preservation technologies will be discussed.     

Antioxidant phenolics and their microbial production by submerged and solid state fermentation process: A review

BackgroundBioactive phenolic compounds have recently received great attention in the food and clinical sectors due to their antioxidant potential. Extensive studies have been carried out to explore antioxidant potential of different phenolics from various natural sources in order to replace the use of health hazard synthetic antioxidants in food products.Scope and approachThe present review aims to provide an update of existing state-of-art and future prospect of both submerged fermentation (SmF) and solid-state fermentation (SSF) processes for the production/extraction of bioactive phenolics utilizing various substrates and microorganisms. Studies on enhancement of antioxidant potentials by increasing phenolics content of food materials including cereals and legumes by mainly SSF are reviewed and discussed thoroughly.Key findings and conclusionsMicrobial fermentation processes have been established as a potent tool for the production of antioxidant phenolic compounds due to their cost-effectiveness and environmental advantages. Extraction of phenolics through fermentation process is by far a more efficient process considering that conventional extraction methods using organic solvents do not allow complete release of bound phenolics from plant materials. During fermentation process, antioxidant phenolics are either produced by microorganisms through secondary metabolic pathway or released from the matrix of the substrate by extracellular enzymatic action. Fermentation technology is no doubt proving to be a boon for the food industry; however, extensive in vivo and toxicological researches are essential before the application of antioxidant-rich fermented foods for human health benefits.     

Millet grain phenolics and their role in disease risk reduction and health promotion: A review

Millets rank six in the world cereal grain production. In Africa and Asia, these underutilized grains play a major role in the food security of millions of people. In addition to being a rich source of nutrients, millet grains have an abundance of phytochemicals, particularly phenolic compounds. This review will focus on the bioactivities and health benefits of millet phenolics as revealed by in vitro and in vivo studies. Phenolic compounds in millets are found in the soluble as well as insoluble-bound forms. Both hydroxybenzoic and hydroxycinnamic acids and their derivatives are notably present in different types of millet grains in varying proportion. Meanwhile, flavonoids exist mainly in the free form. A wide variation exists in the phenolic content and antioxidant capacity of millet grains. Further, millet grain phenolics, are bioaccessible, possess bioactivities against several pathophysiological conditions and may serve as potential natural sources of antioxidants in food and biological systems. While this review also shows the existence of a substantial body of evidence for in vitro antioxidant activity of millet grain phenolics, there is a clear gap for in vivo information. However, the use of millets, as nutraceuticals and specialty foods in disease risk reduction and overall health and wellness is warranted.     

Bioavailability of phenolic compounds

Phenolic compounds in foods originate from one of the main classes of secondary metabolites in plants. They are essential for the growth and reproduction of plants, and are produced as a response for defending injured plants against pathogens. In recent years, there is a growing interest in phenolic compounds and their presumed role in the prevention of various degenerative diseases, such as cancer and cardiovascular diseases. The importance of antioxidant activities of phenolic compounds and their possible usage in processed foods as a natural antioxidant have reached a new high in recent years. The absorption and bioavailability of phenolics in humans are also controversial. Data on these aspects of phenolics are scarce and merely highlight the need for extensive investigations of the handling of phenolics by the gastrointestinal tract and their subsequent absorption and metabolism. In this article, absorption, metabolism, and the bioavailability of pheniolic compounds are reviewed.     

A Polyvinylpolypyrrolidone (PVPP)-Assisted Folin–Ciocalteu Assay to Assess Total Phenol Content of Commercial Beverages

The use of a Folin–Ciocalteu (FC) assay to assess total phenolics in certain foods may be limited by the inability of this assay to discriminate between phenolics and non-phenolic reducing compounds. In the present study, we have mentioned the usefulness of an insoluble water-synthetic polymer, polyvinylpolypyrrolidone (PVPP), to separate phenolics and non-phenolic reducing compounds (i.e., sugars, ascorbic acid, and sulfite) from their original food matrix. After employing three consecutive cycles adding PVPP, all polyphenols tested (including phenolic and cinnamic acids) showed an adsorption percentage (AP) to PVPP higher than 90 %. When tested in various beverages, the PVPP-based pretreatment affected in different ways the FC index, depending on the food matrix. A low AP was evidenced in the case of orange juice, most probably related to the high content of ascorbic acid in such samples. In contrast, a high adsorption to PVPP was observed in red wine and in powdered fruit samples, showing a higher fraction of polyphenols than non-polyphenolic reducing compounds. We consider that our results strongly support that this PVPP-based procedure allows the evaluation of total phenolic content, by the FC methodology of beverages without the contribution of non-phenolic FC-reducing compounds.     

Infusion of grape phenolics into fruits and vegetables by osmotic treatment: Phenolic stability during air drying

Osmotic treatment (OT) was applied to infuse grape phenolic compounds into plant tissue. The stability of the grape phenolics after a post-treatment, such as convective air drying, was evaluated. A model food made of agar gel and three plant commodities (two fruits, apple and banana, and one vegetable, potato) were osmo-treated and subsequently air-dried (55 °C). In the osmotic solution, sodium chloride (10%, w/w) and sucrose (50%, w/w) were used when treating vegetables and fruits, respectively, while a commercial grape seed extract was the source of phenolics (0.63%, w/w). During OT, total phenolic content and antiradical scavenging capacity of plant foods were significantly increased. The extent of grape phenolic impregnation was controlled by food structure and the kind of osmo-active solute: plant tissue showed a lower grape phenolic infusion than that of the model food. OT, as a pre-treatment, protected against grape phenolic degradation during further convective air drying, even though the mechanisms controlling the phenolic degradation process require further research.     

Practical interventions that influence the sensory attributes of red wines related to the phenolic composition of grapes: a review

The phenolic composition of red wines is complex and intimately involved in colour, taste, mouth‐feel and aroma. There have been significant advances in knowledge of compounds with relatively simple structures, but understanding of those with more complex and probably diverse structures is challenging. A number of phenolic compounds may form temporary complexes with anthocyanins and/or be involved in reactions that lead to relatively stable coloured compounds. A wide range of phenolic compounds is implicated in the oral sensory attributes of red wines. Of particular importance are flavan‐3‐ols, including proanthocyanidins (PAs). The generally observed decline in the extractability of PAs during berry ripening is due to binding with cell wall material, which may occur within the developing berry and also from tissues brought into contact during processing. Studies have shown that exposure/reduced vigour results in an increasing proportion of skin PAs being extractable during wine making. Temperature and light influence anthocyanin with temperature probably being more important and the most sensitive stage being 1–3 weeks after véraison. Skin PAs are extracted earlier than those from seeds during wine‐making. Recent results suggest some rearrangement of skin and/or seed PAs occurs during vinification which involves the cleavage of large polymers or the aggregation of small ones. The polymeric material is particularly influential in wine astringency and is transformed by incorporation of anthocyanins into tannin‐like compounds during wine‐making and storage. Although some grape‐derived phenolic compounds contribute to the aroma of red wines, likely of greater importance are the effects of nonvolatile phenolics on the volatility of a diverse range of aroma compounds. Advances in analytical techniques are likely to provide greater insights into the structures and conformations of phenolic polymers and the role of cell wall material in relation to phenolic extraction and reaction during vinification. In relation to aroma, much more research is required to reveal the details of the interactions involving phenolics with volatile compounds. It seems likely that the ability to influence the relative extraction and subsequent reaction of skin and seed phenolics is important in the production of full colour, aromatic and long‐lived wines.     

Improving the bioavailability of phenolic compounds by loading them within lipid-based nanocarriers

BackgroundPhenolic compounds¹ are one of the main interested nutraceuticals in the food and pharmaceutical industries. The application of phenolics is limited due to their low bioavailability, low solubility, low stability, and un-targeted release. These limitations could be overcome by novel ‘‘lipid-based nano-encapsulation technologies’’ capable of appropriated and targeted delivery functions into foods.Scope and approachIn this review, preparation, application, and characterization of lipid-based nanocarriers for phenolics have been considered and discussed including nano-emulsions, nano-scale phospholipids, and nanostructured lipid carriers. The bioavailability of nano-encapsulated phenolic products and capability of them to produce functional foods have been considered as well.Key findings and conclusionsIn the food and nutraceutical industries, the main aims of loading phenolics into nanocarriers are masking their undesirable flavor for oral administration, providing high stability and high absorption, and better release in gastrointestinal (GIT) conditions. Compared with micro-sized carriers, nanocapsules based on lipid formulations provide more surface area and have the potential to enhance solubility, improve bioavailability, and ameliorate controlled release of the nano-encapsulated phenolic compounds.     

Nutritional composition and antioxidant activity in hazelnut shells from US‐grown cultivars

The hard shell of a hazelnut is a major waste of the hazelnut industry. The chemical composition, phenolic compounds (total phenolics, tannins and condensed tannins), antioxidant activity (DPPH and ABTS free‐radical scavenging assays), and the relationships between phenolic compounds and antioxidant activities of the hazelnut shells from twelve US grown cultivars were investigated to for potential commercial development. Crude fibre accounted for over 85% of total carbohydrate. The shells contained high concentrations of phenolic compounds. Concentrations of phenolic constituents and ABTS^?+ ‐scavenging capacities were significantly higher (P > 0.05) in the Oregon cultivars than their Nebraska counterparts. There were significant positive correlations between ABTS^?+ scavenging capacities and the phenolic compounds, whereas DPPH^? ‐scavenging capacity demonstrated a weak negative correlation with ABTS^?+ scavenging capacity and the phenolics. The results suggest that hazelnut hard shell may serve as a potential source of natural antioxidants for food applications.     

Use of phenolic compounds from olive mill wastewater as valuable ingredients for functional foods

ABSTRACT

Olive mill wastewater (OMW) is a pollutant by-product from the virgin olive oil production. Its high content in phenolic compounds makes them play an important role for their use in foods, for their high antioxidant significance. The present paper gives an overview on the techniques for OMW valuable ingredient separation, focusing on the most effective ones for their use in food products as functional ingredients. We report on effective methods to recover OMW phenolics, and give several examples on the use these extracts in foods. When added into vegetable oils, their effect on retarding lipid oxidation improves the oxidative status of the product, whilst several challenges need to be faced. OMW phenolic extracts were also used in food emulsions, milk products or other model systems, showing promising results and little or no negative impact on the sensory characteristics or other properties. Their possible use as antimicrobial agents is also another promising approach, as positive results were obtained when applied in meat products. Other examples of using natural phenolic extracts from other sources are suggested also for OMW extracts, to expand their use and thus to improve the nutritional and technological quality of foods.     

Functional implications of bound phenolic compounds and phenolics–food interaction: A review

Sizeable scientific evidence indicates the health benefits related to phenolic compounds and dietary fiber. Various phenolic compounds-rich foods or ingredients are also rich in dietary fiber, and these two health components may interrelate via noncovalent (reversible) and covalent (mostly irreversible) interactions. Notwithstanding, these interactions are responsible for the carrier effect ascribed to fiber toward the digestive system and can modulate the bioaccessibility of phenolics, thus shaping health-promoting effects in vivo. On this basis, the present review focuses on the nature, occurrence, and implications of the interactions between phenolics and food components. Covalent and noncovalent interactions are presented, their occurrence discussed, and the effect of food processing introduced. Once reaching the large intestine, fiber-bound phenolics undergo an intense transformation by the microbial community therein, encompassing reactions such as deglycosylation, dehydroxylation, α- and β-oxidation, dehydrogenation, demethylation, decarboxylation, C-ring fission, and cleavage to lower molecular weight phenolics. Comparatively less information is still available on the consequences on gut microbiota. So far, the very most of the information on the ability of bound phenolics to modulate gut microbiota relates to in vitro models and single strains in culture medium. Despite offering promising information, such models provide limited information about the effect on gut microbes, and future research is deemed in this field.     

Sorghum Grain: From Genotype,Nutrition, and Phenolic Profile to Its Health Benefits and Food Applications

Globally, sorghum is one of the most important but least utilized staple crops. Sorghum grain is a rich source of nutrients and health‐beneficial phenolic compounds. The phenolic profile of sorghum is exceptionally unique and more abundant and diverse than other common cereal grains. The phenolic compounds in sorghum are mainly composed of phenolic acids, 3‐deoxyanthocyanidins, and condensed tannins. Studies have shown that sorghum phenolic compounds have potent antioxidant activity in vitro, and consumption of sorghum whole grain may improve gut health and reduce the risks of chronic diseases. Recently, sorghum grain has been used to develop functional foods and beverages, and as an ingredient incorporated into other foods. Moreover, the phenolic compounds, 3‐deoxyanthocyanidins, and condensed tannins can be isolated and used as promising natural multifunctional additives in broad food applications. The objective of this review is to provide a comprehensive understanding of nutrition and phenolic compounds derived from sorghum and their related health effects, and demonstrate the potential for incorporation of sorghum in food systems as a functional component and food additive to improve food quality, safety, and health functions.     

THE ANTIMICROBIAL ACTIVITY OF PHENOLIC ANTIOXIDANTS IN FOODS: A REVIEW1

Phenolic antioxidants such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and monotertiary butylhydroquinone (TBHQ) are hindered phenols with antimicrobial activity. The antimicrobial activity of phenolic antioxidants appears to depend on the presence of a hydroxyl group on the molecule, the lipid solubility of the compound and the degree of steric hindrance. The use of phenolic antioxidants in food products is regulated by federal agencies. In general, these compounds are permitted in concentrations up to 200 ppm, based on the fat or oil content of the food product. Certain food products have special regulations. The antimicrobial activity of phenolic antioxidants has been studied in meat and its products, poultry and its products, milk and its products, seafood, rice, applesauce and food ingredients. The antimicrobial activity of phenolic antioxidants is modified by at least 10 factors such as microbial species/strain, stressed microorganisms, type and concentration of phenolic antioxidants, concentration of microbial challenge, combination of phenolic antioxidants, combination of phenolic antioxidants with other antimicrobials, combination of phenolic antioxidants with temperature and food additives, food components, carriers of phenolic antioxidants and the mode of addition of phenolic antioxidants. The antimicrobial activity of phenolic antioxidants in foods has been examined against growth and by-products of bacteria (gram positive and negative, spore and nonspore formers, spoilage and pathogenic), molds and yeasts. The concentration of phenolic antioxidants that had antimicrobial activity in food products was in the range of 30–10,000 ppm. The mechanism of inhibition by phenolic antioxidants has been found to affect the function and composition of the cellular membrane, the synthesis of DNA, RNA, protein and lipid, and the function of the mitochondrion.     

Effect of cold plasma on different polyphenol compounds: A review

Thermal processing has been predominantly used in the food industry to improve food safety and shelf life. However, heat treatment induces detrimental effects like cooked flavor, texture change, and alteration in sensory attributes. These disadvantages encouraged the food industry to adopt non-thermal food processing technologies. Cold plasma is a promising non-thermal food processing method that uses charged, highly reactive gaseous molecules and species to inactivate contaminating microorganisms present in foods. Thus, it has attracted the attention of scientists globally. This review gives the reader an overview of cold plasma technology fundamentals and the detailed mechanism of interaction of reactive plasma species with the polyphenol compounds (simple phenolic acid, individual phenolic compounds, flavonoids, and anthocyanin) present in food. The impact of cold plasma on polyphenol compounds mainly depends on the food matrix and plasma process parameters, viz. voltage, feed gas, and treatment time. Among various polyphenols, flavonoids are degraded faster because of their high ability to scavenge plasma-generated free radicals. The reactive species cause oxidative degradation, double bond cleavage of polyphenol compounds, and aid in the extraction of phenolic compounds. The cold plasma technology has both positive and negative impacts on polyphenol concentration.