Free radicals and antioxidants in food and in vivo: What they do and how they work

A wide variety of oxygen free radicals and other reactive oxygen species can be formed in the human body and in food systems. Transition metal ions accelerate free‐radical damage. Antioxidant defenses, both enzymic and nonenzymic, protect the body against oxidative damage, but they are not 100% efficient, and so free‐radical damage must be constantly repaired. Nonenzymatic antioxidants are frequently added to foods to prevent lipid peroxidation. Several lipid antioxidants can exert prooxidant effects toward other molecules under certain circumstances, and so antioxidants for food and therapeutic use must be characterized carefully. Methods of measuring oxidative damage and trapping free radicals in vivo are briefly discussed. Such methods are essential in checking proposals that increased intake of food‐derived antioxidants (such as antioxidant vitamins) would be beneficial to humans.     

Recent Trends in the Use of Natural Antioxidants for Meat and Meat Products

Antioxidants are added to fresh and processed meat and meat products to prevent lipid oxidation, retard development of off‐flavors, and improve color stability. In the food industry, they can be divided into natural and synthetic antioxidants. Synthetic antioxidants have been confirmed for their toxicological and carcinogenic effects. Thus, the food industry now chooses natural products over synthetic ones. This review provides an overview of the current trends in the use of antioxidants from natural sources, for potential applications in meat and meat products. These natural antioxidants contain some active compounds, which exert antioxidative potential in meat and meat products by different mechanisms of action. The efficient extraction of these antioxidants from their natural sources, along with establishing their in vitro and in producto antioxidant activity, has been a great challenge for researchers engaged in this field. Therefore, this review is focused on all these aspects, along with current studies related to this area, to provide in‐depth information to readers.     

Concentration‐dependent antioxidant activities of conjugated linoleic acid and α‐tocopherol in corn oil

BACKGROUND: Antioxidants prevent rancidity (lipid peroxidation) and natural antioxidants, e.g., α‐tocopherol, likely provide additional value to oil‐based food products because of their health benefits. Conjugated linoleic acid (CLA) has potential health benefits and may exhibit antioxidant properties. The main aim of this study was to compare the antioxidant efficacy of α‐tocopherol, trans‐10, cis‐12‐CLA and cis‐9, trans‐11‐CLA (in graded concentrations) added to antioxidant‐stripped corn oil. RESULTS: As compared to α‐tocopherol, both CLA isomers displayed significant inhibition of corn oil lipid peroxidation induced by copper. Inhibition of thiobarbituric acid reactive substances (TBARS) were CLA concentration dependent for both isomers but with significant inhibition occurring at 0.1 and 1 ppm of CLA isomers or α‐tocopherol, respectively (P < 0.05). Graded concentrations of α‐tocopherol, and for both CLA isomers and time, had significant effects on TBARS formation (P < 0.0001). There were significant effects in interactions between graded concentrations and time for both CLA isomers (P < 0.0001) but not for α‐tocopherol (P > 0.05). CONCLUSION: CLA compounds could serve as useful food antioxidants and provide additional value because of their potential bioactivity in disease prevention. Copyright © 2007 Society of Chemical Industry     

Alkylresorcinols as antioxidants: hydrogen donation and peroxyl radical‐scavenging effects

Alkylresorcinols, resorcinol derivatives with a long hydrocarbon chain at position 5 of the phenolic ring, have been reported to act as antioxidants and protect polyunsaturated fatty acids against peroxidation. Their structures with meta‐dihydroxy substitutions do not, however, support active hydrogen donation and scavenging of peroxyl radicals responsible for propagation of lipid oxidation. This study compares the antioxidant properties of 5‐n‐pentadecylresorcinol and α‐tocopherol using two model systems: (i) the DPPH· model to test their ability for hydrogen atom donation; and (ii) a triacylglycerol oxidation model to test their ability for scavenging peroxyl radicals. In agreement with theoretical expectations, results from both models showed 5‐n‐pentadecylresorcinol to have very low hydrogen donation and peroxyl radical‐scavenging potency. © 2000 Society of Chemical Industry     

Effect of malting on antioxidant capacity and vitamin E content in different barley genotypes

Unprocessed barley is known to contain relatively high levels of antioxidants, which play a critical role in human health and the preservation of food and drink products. However, there are limited data on how the antioxidant levels in barley are affected by malting, and whether the level of antioxidants in the processed malt differs between barley varieties. This study aimed to determine the levels of individual vitamin E isomers, total vitamin E content and total antioxidant capacity before, during and after malting in 12 covered and two hulless barley genotypes. Vitamin E content and antioxidant capacity were determined by high‐performance liquid chromatography (HPLC) and ability to scavenge DPPH radicals, respectively. The vitamin E content of most genotypes was reduced after steeping, germination and kilning compared with the unprocessed samples. However, the antioxidant capacity in the malt was higher than in the unprocessed samples for the majority of the genotypes. While there was variation in the percentage change in antioxidant capacity between varieties, the antioxidant capacity of samples after malting was directly correlated with their antioxidant capacity before processing (r = 0.9, n = 14, p < 0.05). These results indicate that barley varieties that have higher antioxidant capacity at harvest retain their antioxidants after malting. Thus, these varieties are likely to be the most suitable for producing malts with the added health benefits and anti‐spoiling properties associated with greater antioxidant content. Copyright © 2015 The Institute of Brewing & Distilling     

Macromolecular Antioxidants and Dietary Fiber in Edible Seaweeds

Seaweeds are rich in different bioactive compounds with potential uses in drugs, cosmetics and the food industry. The objective of this study was to analyze macromolecular antioxidants or nonextractable polyphenols, in several edible seaweed species collected in Chile (Gracilaria chilensis, Callophyllis concepcionensis, Macrocystis pyrifera, Scytosyphon lomentaria, Ulva sp. and Enteromorpha compressa), including their 1st HPLC characterization. Macromolecular antioxidants are commonly ignored in studies of bioactive compounds. They are associated with insoluble dietary fiber and exhibit significant biological activity, with specific features that are different from those of both dietary fiber and extractable polyphenols. We also evaluated extractable polyphenols and dietary fiber, given their relationship with macromolecular antioxidants. Our results show that macromolecular antioxidants are a major polyphenol fraction (averaging 42% to total polyphenol content), with hydroxycinnamic acids, hydroxybenzoic acids and flavonols being the main constituents. This fraction also showed remarkable antioxidant capacity, as determined by 2 complementary assays. The dietary fiber content was over 50% of dry weight, with some samples exhibiting the target proportionality between soluble and insoluble dietary fiber for adequate nutrition. Overall, our data show that seaweed could be an important source of commonly ignored macromolecular antioxidants.     

Polyphenols: food sources,properties and applications – a review

There is currently much interest in phytochemicals as bioactive compounds of food. The roles of fruit, vegetables and red wine in disease prevention have been attributed, in part, to the antioxidant properties of their constituent polyphenols (vitamins E and C, and the carotenoids). Recent studies have shown that many dietary polyphenolic constituents derived from plants are more effective antioxidants in vitro than vitamins E or C, and thus might contribute significantly to the protective effects in vivo. Polyphenols are abundant micronutrients in our diet, and evidence for their role in the prevention of degenerative diseases is emerging. Dietary polyphenols show a great diversity of structures, ranging from rather simple molecules (monomers and oligomers) to polymers. Higher‐molecular‐weight structures (with molecular weights of ～500) are usually designated as tannins, which refers to their ability to interact with proteins. Among them, condensed tannins (proanthocyanidins) are particularly important because of their wide distribution in plants and their contributions to major food qualities. This paper focuses on polyphenols; we illustrate their sources from food, properties and their beneficial uses.     

Oxidative stability of palm‐ and soybean‐based medium‐ and long‐chain triacylglycerol (MLCT) oil blends

BACKGROUND: Medium‐ and long‐chain triacylglyerols (MLCT) enzymatically esterified using Lipozyme RM IM lipase has very low oxidative stability as it does not contain any antioxidants. The aim of this work was to study the ability of various antioxidants to increase the oxidative stability of palm‐ and soybean‐based MLCT blends which assist to bring up the oxidative stability of both MLCT blends. In this study, the effectiveness of rosemary extracts, sage extracts, tert‐butylhydroquinone (TBHQ) and mixtures of tert‐butyl‐4‐hydroxyanisole (BHA) and tert‐butyl‐p‐hydroxytoluene (BHT) in protecting against oxidation of various MLCT blends was investigated. RESULTS: Blending of MLCT oil with either palm olein or soybean oil improved its smoke point values and oxidative stability. TBHQ addition to both palm‐ and soybean‐based MLCT blends increased oxidative stability. Combination of BHA and BHT showed no significant improvement (P > 0.05) in ability to protect blends from oxidation compared to natural antioxidants such as sage or rosemary extracts. CONCLUSION: Blended oils with 500 g kg^?1 MLCT and 500 g kg^?1 palm olein (MP5) were the most suitable for use at high temperature based on the fatty acid composition of the MLCT blends, which subsequently had an effect on thermal oxidative stability. In general, addition of either natural or synthetic antioxidant assisted in improving the antioxidative strength of both MLCT blends. MLCT blends with added TBHQ showed the highest thermal oxidative stability among the antioxidants used. Copyright © 2008 Society of Chemical Industry     

Extraction Efficiency of Hydrophilic and Lipophilic Antioxidants from Lyophilized Foods Using Pressurized Liquid Extraction and Manual Extraction

The efficient extraction of antioxidants from food samples is necessary in order to accurately measure their antioxidant capacities. α‐Tocopherol and gallic acid were spiked into samples of 5 lyophilized and pulverized vegetables and fruits (onion, cabbage, Satsuma mandarin orange, pumpkin, and spinach). The lipophilic and hydrophilic antioxidants in the samples were sequentially extracted with a mixed solvent of n‐hexane and dichloromethane, and then with acetic acid–acidified aqueous methanol. Duplicate samples were extracted: one set was extracted using an automated pressurized liquid extraction apparatus, and the other set was extracted manually. Spiked α‐tocopherol and gallic acid were recovered almost quantitatively in the extracted lipophilic and hydrophilic fractions, respectively, especially when pressurized liquid extraction was used. The expected increase in lipophilic oxygen radical absorbance capacity (L‐ORAC) due to spiking with α‐tocopherol, and the expected increase in 2,2‐diphenyl‐1‐picrylhydrazyl radical scavenging activities and total polyphenol content due to spiking with gallic acid, were all recovered in high yield. Relatively low recoveries, as reflected in the hydrophilic ORAC (H‐ORAC) value, were obtained following spiking with gallic acid, suggesting an interaction between gallic acid and endogenous antioxidants. The H‐ORAC values of gallic acid–spiked samples were almost the same as those of postadded (spiked) samples. These results clearly indicate that lipophilic and hydrophilic antioxidants are effectively extracted from lyophilized food, especially when pressurized liquid extraction is used.     

In vitro procedure to predict apparent antioxidant release from wholegrain foods measured using three different analytical methods

Several methods have been applied to the measurement of antioxidants in biological samples. Extraction methods have previously relied on chemical methods which are non‐physiological. This paper reports the use of an in vitro method with enzymatic and fermentation steps, designed to mimic digestion through the gastrointestinal tract, on release of antioxidants from a range of wholegrain foods. A total of 41 samples, (31 raw foods, 10 of which were also analysed after cooking) were analysed using the ferric reducing antioxidant capacity and Trolox equivalent antioxidant capacity methods. Six samples were also measured using the oxygen radical absorption capacity method. The three antioxidant assay methods gave different apparent antioxidant activity trends, and the range of values was dependent on the type of food. The effects of cooking were mainly observed in the early stages of the incubation procedure, suggesting that cooking may destroy soluble antioxidants but not those bound within the food matrix. For all samples, apparent antioxidant release increased during the incubation period, suggesting that antioxidants bound within the food matrix may be released and exert their effects in different regions of the gastrointestinal tract. Copyright © 2005 Society of Chemical Industry     

ANTIOXIDANT PROPERTIES OF LENTINUS EDODES AND AGARICUS BLAZEI EXTRACTS

ABSTRACT

This work aimed to evaluate the antioxidant activity of Lentinus edodes and Agaricus blazei mushrooms, as well as to measure the content of total phenolic compounds of mushroom extracts and verify the oxidative stability of soybean oil added with mushroom extracts that showed higher antioxidant activity according to the methods of the 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH^•) free radical scavenging and the β‐carotene/linoleic acid system. According to the DPPH^• method, the maximum antioxidant activity for L. edodes and A. blazei methanol extracts was 92.84 and 95.10%, respectively. For the β‐carotene/linoleic acid system, the highest values of antioxidant activity were 93.06% for L. edodes and 78.96% for A. blazei. The content of total phenolic compounds ranged from 7.21 to 128.44 and 26.67 to 134.67 mg gallic acid equivalent/g for L. edodes and A. blazei, respectively. The oxidative stability values provided by the Rancimat method indicated that the two varieties presented similar induction period of 19.85 h.

PRACTICAL APPLICATIONS

Mushrooms present high content of antioxidant compounds that are capable of reducing the harmful effects of free radicals. Among the antioxidants present in mushrooms, phenolic compounds stand out as phenolic acids, flavonoids and tocopherols. To decrease or prevent lipid oxidation, synthetic antioxidants are used as food additives. Nevertheless, studies have revealed that these compounds are likely to pose risks to human health. The concern regarding the safety of synthetic antioxidants has motivated the search of natural antioxidants that can substitute them totally or partially.

     

Antioxidant activity and free radical-scavenging capacity of a selection of wild-growing Colombian plants

BACKGROUND: The replacement of some synthetic food antioxidants by safe natural antioxidants has fostered research on the screening of raw materials to find new vegetable sources of antioxidants. In this study the antioxidant activity of eight wild‐growing Colombian plants was assessed by four complementary assays. RESULTS: An evaluation of the antioxidant activity of ten ethanolic extracts from Baccharis chilco, Cinnamomum triplinerve, Ilex laurina, Lachemilla orbiculata, Lepechinia conferta, Quercus humboldtii, Rubus urticifolius and Tephrosia cinerea was carried out. Furthermore, the total phenolic content was determined by the Folin–Ciocalteu method, and the relationship between phenolic content and activity was also statistically investigated. Cinnamomum triplinerve, L. conferta and I. laurina were found to have the highest phenolic contents. Baccharis chilco, C. triplinerve, I. laurina, L. conferta, Q. humboldtii and R. urticifolius showed higher radical‐scavenging activity (DPPH and superoxide assays) than commercial rosemary oleoresin (reference). Lachemilla orbiculata and R. urticifolius showed higher antioxidant activity (β‐carotene‐bleaching test) than the reference. The protection factor of all studied plant extracts was below that of the reference according to the Rancimat test. CONCLUSION: On the basis of the results obtained, C. triplinerve, Q. humboldtii and R. urticifolius seem to be the most promising species for further investigation in order to identify the compounds responsible for their activity. Copyright © 2011 Society of Chemical Industry     

Prevention of cataracts by nutritional and metabolic antioxidants

Among aging disabilities, the one associated with the progressive decline of vision is functionally most disadvantageous. Cataracts are one of the more common causes of such visual disability. Several predisposing factors have been identified in the genesis of this disease. While it is perhaps a multifactorial process, significant developments have taken place in recent years suggesting that oxygen radicals are involved in the development of this aging manifestation. Antioxidant enzymes, such as catalase and superoxide dismutase, have been demonstrated to protect the lens cell membrane from oxidative stress as reflected by the prevention of the Na⁺‐K⁺‐ATPase‐dependent pump deterioration due to oxyradical‐dependent oxidation of its proteins and lipids. From the nutritional point of view, antioxidants such as ascorbate and vitamin E also offer significant protection to the lens against damage due to oxidative stress. Evidence regarding the protective effect of these nutrients has been based on lens organ culture studies in the presence of active oxygen, generated photochemically as well as enzymatically. The experiment involving photochemical environs simulate the status of the eye during the photopic vision. In vivo, the effectiveness of ascorbate against cataracts has been tested in rat pups developing cataracts under the oxidative influence of sodium selenite. Certain antioxidants produced metabolically also may be useful in protecting against cataracts. Pyruvate produced in glucose metabolism seems to be an important antioxidant The efficacy of this compound has been tested within in vitro organ culture as well as in vivo, the latter experiments being done with selenite‐treated rats. There is a hope that these and other nutritional and metabolic antioxidants may one day be useful in delaying or even preventing cataract formation in human beings.     

Trout‐Skin Gelatin‐Based Edible Films Containing Phenolic Antioxidants: Effect on Physical Properties and Oxidative Stability of Cod‐Liver Oil Model Food

Abstract: Trout‐skin (Oncorhynchus mykiss) gelatin‐based films containing antioxidants (epigallocatechin gallate (EGCG), 50 and 250 ppm w/w) and green tea powder (1% and 20% w/w of gelatin) were tested for tensile strength, elastic modulus, and elongation, and oxygen and water vapor transmission rates, in vitro antioxidant activity using the DPPH (2,2‐diphenyl‐1‐picrylhydrazyl) assay and effect on stabilizing cod‐liver oil held under mild thermal abuse conditions. Cod‐liver oil overlaid with films was stored at 40 °C for 20 d and analyzed for peroxide value (PV) and thiobarbituric acid reactive substances (TBARS). Antioxidant activity was retained in films containing green tea powder, but was reduced (P < 0.05) in EGCG films (20 d, 23 °C). Water vapor transmission rate of the films incorporated with antioxidants did not change significantly (P > 0.05), but the oxygen transmission rate for films with 50 ppm EGCG and 20% green tea powder was significant (P < 0.05). Other physical properties varied with antioxidant incorporation. The TBARS and PV of control oil increased from 0.05 ± 0.01 to 4.71 ± 0.30 g MDA/kg oil and from 3.6 ± 0.2 to 178.3 ± 24.5 millieq peroxides/kg oil, respectively, after 20 d. For cod‐liver oil covered with control or antioxidant‐containing films, TBARS remained below 0.37 g MDA/kg oil and PV below 7 millieq peroxides/kg oil. Incorporation of antioxidants to the films did not reduce oil oxidation (P > 0.05) at the levels tested and this was confirmed by activation energy calculations. The rate of oil oxidation was more dependent upon the inherent oxygen barrier property of the films than the presence of antioxidants. Practical Application: This research has the potential to enhance the utilization of fish skins, a valuable food processing by‐product, as edible films with natural antioxidants to extend the shelf life of foods. The film physical properties and barrier to oxygen and water are investigated.     

Tissue culture‐based Selection of high rosmarinic acid producing clones of Rosemary (Rosmarinus officinalis L.) Using Pseudomonas Strain F.

Natural phenolic antioxidants from genetically heterogeneous plants are becoming important for prevention of lipid oxidation in food. To produce uniform and enhanced levels of antioxidants we have developed elite clonal lines of rosemary using plant tissue culture techniques.

A cytokinin (benzyladenine)‐induced adventitious shoot multiplication was developed for rosemary. Optimum shoot multiplication occurred in Murashige and Skoog medium containing 1 mg/1 benzyladenine and 2 mM proline. About 3–10 adventitious shoots were induced from each expiant originating from a single heterozygous seed in 45–60 days and was designated as a single clonal line. Individual shoots of each clonal line were then transferred to hormone free medium to regenerate whole plants. Using this approach several clonal lines with each originating from a single heterozygous seed were isolated from a heterogeneous seed lot.

It is well established that microbial elicitors can stimulate plant secondary metabolites. Based on this concept, we inoculated several shoots of each clonal line of rosemary with a novel Pseudomonas sp. to stimulate synthesis of total phenolics and rosmarinic acid. Total phenolics and rosmarinic acid content of each clonal line were measured after 25 and 60 days to specifically select fast growing and microbial elicitor‐induced high rosmarinic acid‐containing clonal lines. Using this strategy 5 classes of clonal lines were isolated: (i) low RA containing clonal line—R‐1; (ii) medium RA—R‐7 and R‐12; (iii) high RA—R‐16 and R‐35; (iv) Pseudomonas mediated inhibition of RA—R‐8; (v) high RA with growth inhibition—R‐15. Selection of such genetically uniform phenotypes offer potential for production of phenolic antioxidants from rosemary with consistent quality. Genetically uniform clonal lines can also be used to understand the regulation of biosynthetic pathways associated with phenolic antioxidants in response to microbial elicitors.     

Evaluation of Citrus aurantifolia peel and leaves extracts for their chemical composition,antioxidant and anti‐cholinesterase activities

BACKGROUND: The replacement of synthetic antioxidants by safe natural antioxidants fosters research on the screening of vegetables and food as sources of new antioxidants. Moreover, oxidative degeneration of cells is associated with neurodegenerative diseases such as Alzheimer's disease. On the basis of these considerations this work aimed to investigate the antioxidant properties [by using the diphenyl picryl hydrazyl, 2,2′‐azino‐bis(3‐ethylbenzothiazoline‐6‐sulfonic acid) and ferric reducing ability of plasma assays, and the β‐carotene bleaching test] and the anti‐cholinesterase activity of Citrus aurantifolia peel and leaves from different areas of growth. RESULTS: Methanol extracts of the peel and leaves demonstrated the strongest radical scavenging activity. A similar trend was observed with the reducing ability, with values from 112.1 to 146.0 µmol L^?1 Fe(II) g^?1. The relationship between phenol and flavonoid contents and antioxidant activity was statistically investigated. Based on analysis by high‐performance liquid chromatography, the most abundant flavonoids found in C. aurantifolia extracts were apigenin, rutin, quercetin, kaempferol and nobiletin. n‐Hexane fractions of both peel and leaves showed a good acetylcholinesterase inhibitory activity with IC₅₀ values in the range 91.4‐107.4 µg mL^?1. Gas chromatography‐mass spectrometry analysis revealed the presence of monoterpenes and sesquiterpenes as most common components. CONCLUSION: The findings of this study suggest a potential use of C. aurantifolia peel and leaves for supplements for human health. Copyright © 2012 Society of Chemical Industry     

Citrus Tachibana Leaf Extract Mitigates Symptoms of Food Allergy by Inhibiting Th2‐Associated Responses

Although the incidence of food allergy continues to rise, there have been no effective therapeutic strategies. Citrus fruits contain a number of bioactive flavonoids with immune‐regulatory functions. The objective of this study was to determine whether Citrus tachibana (fruit body with peel, leaves, and branch) can protect against the development of food allergy and the mechanism behind it, and to identify the active compound(s) responsible. We found that C. tachibana leaf extract (CLE) mitigated ovalbumin (OVA)‐induced food allergy symptoms including increased rectal temperature, diarrhea, and anaphylaxis. This mitigation was likely due to CLE‐mediated decreases in cytokine release from T‐helper 2 cells (Th2 cells) in mesenteric lymph nodes. Moreover, higher levels of CLE attenuated systemic Th2 cell–mediated responses in mouse splenocytes sensitized with OVA+Alum. This was evidenced by CLE‐mediated reductions in Th2 cytokine release, including interleukin (IL)‐4, IL‐5, and IL‐13, but not the Th1 cytokines IL‐12 and interferon (IFN)‐γ, which was attributable to decreased gene expression levels. We also identified kaempferol as the most potent compound for reducing Th2‐associated responses in splenocytes. The findings of this study suggest that CLE suppresses Th2‐cell–mediated immune responses, contributing to alleviation of food allergy symptoms, and that kaempferol is a flavonoid with potential antiallergenic activity that targets Th2 cell–induced responses.     

Chemoprevention: Insights into biological mechanisms and promising food factors

Abstract

Chemoprevention with food phytochemical is currently regarded as one of the noticeable scientific fields. A large body of data from epidemio‐logic and rodent studies has demonstrated that ingestion of vegetables and fruits is occasionally beneficial for reduction of cancer risks in humans. Recent clinical trials using ubiquitous antioxidants such as α‐carotene, however, have yet to show their cancer preventive effect despite the fact that they have been reported to be chemopreventive agents in rodent models. One of the goals of this review is to address useful and reliable methodology to detect promising chemopreventive agents from edible plants by highlighting molecular mechanisms of multistage carcinogenesis.