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.

The structure of a metabolite, C10H10O5 (I), obtained as a weakly toxic substance from the culture filtrate of Alternaria kikuchiana, was determined as 3,6,8-trihydroxy-3-methyl-3,4- dihydroisocoumarin (Ia). Though three tautomeric forms—lactol form (Ia), keto form (Ib) and enol form (Ic) were possible for (I), it was found that the compound (I) existed as the lactol form (Ia) both in a crystalline state and in acetone, chloroform and methanol solutions. This metabolite gave weak necrotic symptom to pear leaves, but stimulated the root elongation of rice and radish seedlings (ca. 20~30%) at 5 ppm and also showed synergistic activity with gibberellin A3 on the stem elongation of rice seedlings (ca. 30%).

Studies on Metabolites of Alternaria kikuchiana Tanaka, a Phytopathogenic Fungus of Japanese Pear

Formation of free-radical products by the reaction of dehydroascorbic acid with amino acids

Effect of oxidative damage induced by γ irradiation on germination potentials of rice seeds

Ausgehend von α-Furyllithium werden Derivate des Furan-thiols-(2) (8) und -selenols-(2) (9) dargestellt. Freies 8 und 9 sind nur in alkalisch-wasrigem Medium stabil.

Furan-thiol-(2) und Furan-selenol-(2)

The desmutagenic activity of various food components on C-nitro mutagens formed by the nitrite/sorbic acid reaction was assayed and several vegetable juices were found to be effective for eliminating the mutagenicity of the nitrite/sorbic acid system. Especially, the desmutagenic activity of pumpkin juice was investigated, and ascorbic acid, cysteine and other reducing compounds were found to be responsible for desmutagenic actions on 1,4-dinitro-2-methyl pyrrole, the main mutagen formed by the reaction of sorbic acid with sodium nitrite, by reduction of the conjugated C-nitro group to a C-amino group.

Mitsuo Namiki

Papers

Studies on Metabolites of Alternaria kikuchiana Tanaka, a Phytopathogenic Fungus of Japanese Pear

Formation of free-radical products by the reaction of dehydroascorbic acid with amino acids

Effect of oxidative damage induced by γ irradiation on germination potentials of rice seeds

Furan-thiol-(2) und Furan-selenol-(2)

Desmutagenic Action of Food Components on Mutagens Formed by the Sorbic Acid/Nitrite Reaction