Phenolic compounds in plants and agri-industrial by-products: Antioxidant activity, occurrence, and potential uses

The antioxidant activity of pomegranate juices was evaluated by four different methods (ABTS, DPPH, DMPD, and FRAP) and compared to those of red wine and a green tea infusion. Commercial pomegranate juices showed an antioxidant activity (18-20 TEAC) three times higher than those of red wine and green tea (6-8 TEAC). The activity was higher in commercial juices extracted from whole pomegranates than in experimental juices obtained from the arils only (12-14 TEAC). HPLC-DAD and HPLC-MS analyses of the juices revealed that commercial juices contained the pomegranate tannin punicalagin (1500-1900 mg/L) while only traces of this compound were detected in the experimental juice obtained from arils in the laboratory. This shows that pomegranate industrial processing extracts some of the hydrolyzable tannins present in the fruit rind. This could account for the higher antioxidant activity of commercial juices compared to the experimental ones. In addition, anthocyanins, ellagic acid derivatives, and hydrolyzable tannins were detected and quantified in the pomegranate juices.

http://ucce.ucdavis.edu/files/datastore/234-60.pdf

Antioxidant activity of pomegranate juice and its relationship with phenolic composition and processing

Phenolics and polyphenolics in foods, beverages and spices: Antioxidant activity and health effects – A review

Tannins (commonly referred to as tannic acid) are water-soluble polyphenols that are present in many plant foods. They have been reported to be responsible for decreases in feed intake, growth rate, feed efficiency, net metabolizable energy, and protein digestibility in experimental animals. Therefore, foods rich in tannins are considered to be of low nutritional value. However, recent findings indicate that the major effect of tannins was not due to their inhibition on food consumption or digestion but rather the decreased efficiency in converting the absorbed nutrients to new body substances. Incidences of certain cancers, such as esophageal cancer, have been reported to be related to consumption of tannins-rich foods such as betel nuts and herbal teas, suggesting that tannins might be carcinogenic. However, other reports indicated that the carcinogenic activity of tannins might be related to components associated with tannins rather than tannins themselves. Interestingly, many reports indicated negative association between tea consumption and incidences of cancers. Tea polyphenols and many tannin components were suggested to be anticarcinogenic. Many tannin molecules have also been shown to reduce the mutagenic activity of a number of mutagens. Many carcinogens and/or mutagens produce oxygen-free radicals for interaction with cellular macromolecules. The anticarcinogenic and antimutagenic potentials of tannins may be related to their antioxidative property, which is important in protecting cellular oxidative damage, including lipid peroxidation. The generation of superoxide radicals was reported to be inhibited by tannins and related compounds. The antimicrobial activities of tannins are well documented. The growth of many fungi, yeasts, bacteria, and viruses was inhibited by tannins. We have also found that tannic acid and propyl gallate, but not gallic acid, were inhibitory to foodborne bacteria, aquatic bacteria, and off-flavor-producing microorganisms. Their antimicrobial properties seemed to be associated with the hydrolysis of ester linkage between gallic acid and polyols hydrolyzed after ripening of many edible fruits. Tannins in these fruits thus serve as a natural defense mechanism against microbial infections. The antimicrobial property of tannic acid can also be used in food processing to increase the shelf-life of certain foods, such as catfish fillets. Tannins have also been reported to exert other physiological effects, such as to accelerate blood clotting, reduce blood pressure, decrease the serum lipid level, produce liver necrosis, and modulate immunoresponses. The dosage and kind of tannins are critical to these effects. The aim of this review is to summarize and analyze the vast and sometimes conflicting literature on tannins and to provide as accurately as possible the needed information for assessment of the overall effects of tannins on human health.

Tannins and Human Health: A Review

Essential oils are aromatic and volatile liquids extracted from plants. The chemicals in essential oils are secondary metabolites, which play an important role in plant defense as they often possess antimicrobial properties. The interest in essential oils and their application in food preservation has been amplified in recent years by an increasingly negative consumer perception of synthetic preservatives. Furthermore, food-borne diseases are a growing public health problem worldwide, calling for more effective preservation strategies. The antibacterial properties of essential oils and their constituents have been documented extensively. Pioneering work has also elucidated the mode of action of a few essential oil constituents, but detailed knowledge about most of the compounds’ mode of action is still lacking. This knowledge is particularly important to predict their effect on different microorganisms, how they interact with food matrix components, and how they work in combination with other antimicrobial compounds. The main obstacle for using essential oil constituents as food preservatives is that they are most often not potent enough as single components, and they cause negative organoleptic effects when added in sufficient amounts to provide an antimicrobial effect. Exploiting synergies between several compounds has been suggested as a solution to this problem. However, little is known about which interactions lead to synergistic, additive, or antagonistic effects. Such knowledge could contribute to design of new and more potent antimicrobial blends, and to understand the interplay between the constituents of crude essential oils. The purpose of this review is to provide an overview of current knowledge about the antibacterial properties and antibacterial mode of action of essential oils and their constituents, and to identify research avenues that can facilitate implementation of essential oils as natural preservatives in foods.

/pdf/essential-oils-in-food-preservation-mode-of-action-synergies-26gwz54pww.pdf

Essential oils in food preservation: mode of action, synergies, and interactions with food matrix components.

Phenol-type natural antioxidative materials contain analogs of sesamin or sesamolin which are manufactured by processing a processed sesame seed product with an acid catalyst and subsequently condensing and separating the desired materials by a physical means such as extraction, distillation and adsorption.

Method of manufacturing phenol-type natural antioxidants

Onion bulbs of unirradiated and irradiated with 4.2 and 8.1 Krad by 60Co gamma rays were stored at 4° and 10°C for five months, and the relationship between the sprouting and the amounts of di-n-propyl disulfide (DPDS) developed from the sliced onions was investigated. The amount of DPDS increased apparently along with the sprouting. The sprout inhibition with the irradiation was appeared to suppress the development of DPDS.

Effect of storage time and γ-irradiation on the development of di-n-propyl disulfide from onion bulbs

In order to elucidate the radiolysis mechanism of p-bromophenol, quantitative determination of the radiolysis products was carried out by gas chromatography and polarography. G(−p · BP) and G(Br−) were 3.86 and 2.58 at neutral pH, and 1.09 and 0.26 at pH 1.0, respectively, This, together with the radical scavenger effects indicated that hydrated electrons contribute principally to the degradation of p-bromophenol through debromination, followed by the formation of dimer and trimer products by phenylation of the resulting p-hydroxyphenyl radical. This chain-like reaction may cause the difference (G-value = 1.28) between G(−p· BP) and G(Br−). The contribution of OH radicals to G(−p· BP) is known to be small as compared with other aromatic compounds, because of the poor yield of hydroxylated products such as hydroquinone, 4-bromocatechol and 4-bromoresorcinol.

/pdf/decomposition-pathways-of-p-bromophenol-on-g-irradiation-in-2bn53eudsy.pdf

Decomposition Pathways of p-Bromophenol on γ-Irradiation in Aqueous Systems

Redox reaction of tri(2-deoxy-2-L-ascorbyl)amine. Formation of a persisting free radical species in water

The After Effect of Irradiated Halogenophenol Solutions on the Viability of Escherichia coli :Part I. Effect of Irradiation Conditions on the Radiation Induction of Bactericidal Activity

Mitsuo Namiki

Papers

Method of manufacturing phenol-type natural antioxidants

Effect of storage time and γ-irradiation on the development of di-n-propyl disulfide from onion bulbs

Decomposition Pathways of p-Bromophenol on γ-Irradiation in Aqueous Systems

Redox reaction of tri(2-deoxy-2-L-ascorbyl)amine. Formation of a persisting free radical species in water

The After Effect of Irradiated Halogenophenol Solutions on the Viability of Escherichia coli :Part I. Effect of Irradiation Conditions on the Radiation Induction of Bactericidal Activity