Activity and concentration of polyphenolic antioxidants in apple juice. 3. Stability during storage

Kinetic data are reported describing the stability of various classes of polyphenolic antioxidants in an apple juice enriched in these compounds as a function of storage temperature and oxygen concentration. The most thermally sensitive compounds were the various quercetin glycosides and epicatechin, whereas phloridzin and chlorogenic acid were more stable. The quercetin glycosides showed differences in their stability: quercetin galactoside approximately quercetin rhamnoside > quercetin glucoside/rutinoside > quercetin arabinoside. The effect of the presence of oxygen on the degradation rates was clear for only quercetin and to a lesser extent for epicatechin. Accelerated shelf-life testing of enriched apple juice during 4 days at 80 degrees C showed decreases in the antioxidant activity of 20-40%. The parameters obtained were used to predict the stability at different storage conditions. Calculations showed that polyphenolic antioxidants and antioxidant activity of enriched apple juice will be quite stable at ambient or refrigerated storage conditions up to half a year.     

Inhibition of apple polyphenol oxidase activity by procyanidins and polyphenol oxidation products

The rate of consumption of dissolved oxygen by apple polyphenol oxidase in cider apple juices did not correlate with polyphenol oxidase activity in the fruits and decreased faster than could be explained by the decrease of its polyphenolic substrates. The kinetics parameters of a crude polyphenol oxidase extract, prepared from apple (Braeburn cultivar), were determined using caffeoylquinic acid as a substrate. Three apple procyanidin fractions of n 80, 10.5, and 4 were purified from the parenchyma of cider apples of various cultivars. Procyanidins, caffeoylquinic acid, (-)-epicatechin, and a mixture of caffeoylquinic acid and (-)-epicatechin were oxidized by reaction with caffeoylquinic acid o-quinone in order to form oxidation products. All the fractions were evaluated for their inhibitory effect on PPO activity. Native procyanidins inhibited polyphenol oxidase activity, the inhibition intensity increasing with n. The polyphenol oxidase activity decreased by 50% for 0.026 g/L of the fraction of n 80, 0.17 g/L of the fraction of n 10.5, and 1 g/L of the fraction of n 4. The inhibitory effect of oxidized procyanidins was twice that of native procyanidins. Oxidation products of caffeoylquinic acid and (-)-epicatechin also inhibited polyphenol oxidase.     

Improved HPLC determination of phenolic compounds in cv. golden delicious apples using a monolithic column

A rapid HPLC-DAD determination of phenols in apple using an RP monolithic column is reported. Because of the hydrodynamic advantages offered by this kind of column and the use of acidified acetonitrile as eluent, assays of apple extracts can be performed in <21 min. Assays of pulp and peel extracts were carried out without the need for time-consuming sample pretreatment except filtration. Several flavanols, hydroxycinnamic acids, dihydrochalcones, and six quercetin glycosides were identified and quantified. A seventh quercetin derivative, two chalcone-related compounds, and three hydroxycinnamic derivatives were also found. Peels proved to be richer in phenols than pulps, the former being composed mainly of (-)-epicatechin, procyanidin B2, chlorogenic acid, phloridzin, hyperin, and avicularin. In pulps, where the chlorogenic acid was the principal phenolic compound, quercetin glycosides were found in very low amounts.     

Major phenolics in apple and their contribution to the total antioxidant capacity

The contribution of each phytochemical to the total antioxidant capacity of apples was determined. Major phenolic phytochemicals of six apple cultivars were identified and quantified, and their contributions to total antioxidant activity of apples were determined using a 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging assay and expressed as vitamin C equivalent antioxidant capacity (VCEAC). Average concentrations of major phenolics and vitamin C in six apple cultivars were as follows (mg/100 g of fresh weight of apples): quercetin glycosides, 13.20; procyanidin B(2), 9.35; chlorogenic acid, 9.02; epicatechin, 8.65; phloretin glycosides, 5.59; vitamin C, 12.80. A highly linear relationship (r (2) > 0.97) was attained between concentrations and total antioxidant capacity of phenolics and vitamin C. Relative VCEAC values of these compounds were in the order quercetin (3.06) > epicatechin (2.67) > procyanidin B(2) (2.36) > phloretin (1.63) > vitamin C (1.00) > chlorogenic acid (0.97). Therefore, the estimated contribution of major phenolics and vitamin C to the total antioxidant capacity of 100 g of fresh apples is as follows: quercetin (40.39 VCEAC) > epicatechin (23.10) > procyanidin B(2) (22.07) > vitamin C (12.80) > phloretin (9.11) > chlorogenic acid (8.75). These results indicate that flavonoids such as quercetin, epicatechin, and procyanidin B(2) rather than vitamin C contribute significantly to the total antioxidant activity of apples.     

Fate of apple peel phenolics during cool storage

Consumption of certain phenolics in the diet is considered beneficial to human health. In this study, individual phenolics were measured by diode-array HPLC at monthly intervals in the peel of Granny Smith, Lady Williams, and Crofton apple cultivars stored in air at 0 degrees C for 9 months. The concentrations of total phenolics significantly differed among the cultivars examined, with Lady Williams peel having significantly more phenolics (over 4000 microg x g(-1) peel fresh weight) than Crofton (2668 microg x g(-1) peel fresh weight) and Granny Smith, which had the lowest concentration of total phenolics (1275 microg x g(-1) peel fresh weight). There were also significant differences in individual phenolics among cultivars and during storage. Quercetin glycosides were the only flavonols identified, with quercetin rhamnoglucoside being the most abundant phenolic in the peel. Chlorogenic acid was the major cinnamic acid derivative, with high concentrations, up to 412 microg x g(-1)) peel fresh weight, in Crofton peel. A pre-storage diphenylamine (DPA) treatment had few significant effects on peel phenolic metabolism. Where differences did occur, fruit treated with DPA retained higher concentrations of total peel phenolics during storage than fruit not treated with DPA. Storage of all cultivars for up to 9 months in air at 0 degrees C induced few significant changes in the peel phenolic concentrations. This indicates that phenolic metabolism in apple peel is relatively stable, and the health benefits of phenolics in apple peel should be maintained during long-term storage.     

Phenolic profile, antioxidant property, and anti-influenza viral activity of Chinese quince (Pseudocydonia sinensis Schneid.), quince (Cydonia oblonga Mill.), and apple (Malus domestica Mill.) fruits

To evaluate the phenolic extracts of Chinese quince, quince, and apple fruits, their phenolic profiles, antioxidant properties, and anti-influenza viral activities were investigated. Chinese quince had the largest amount of phenolics consisting mainly of high polymeric procyanidins. Quince had considerable amounts of hydroxycinnamic derivatives mainly composed of 3-caffeoylquinic acid and 5-caffeoylquinic acid and polymeric procyanidins. Apple (cv. Fuji) had the lowest amount of phenolics, mainly 5-caffeoylquinic acid and monomeric and oligomeric procyanidins. The antioxidant functions of Chinese quince and quince phenolic extracts were superior to that of chlorogenic acid standard or ascorbic acid evaluated in both the linoleic acid peroxidation system and the DPPH radical scavenging system. However, those extracts were less effective than apple phenolics or (-)-epicatechin in linoleic acid peroxidation system. On the other hand, Chinese quince phenolics showed the strongest anti-influenza viral activity on the hemagglutination inhibition test.     

Activity and concentration of polyphenolic antioxidants in apple juice. 2. Effect of novel production methods

There is a great interest in food components that possess possible health-protecting properties, as is the case with flavonoids. Previous research showed that conventional apple juice processing resulted in juices poor in flavonoids and with a low antioxidant activity. This paper shows that it is possible to improve flavonoid content in juice and its antioxidant activity by applying an alcoholic extraction either on the pulp or on the pomace. The levels of flavonoids and chlorogenic acid in enriched juice were between 1.4 (chlorogenic acid) and 9 (quercetin glycosides) times higher than in conventional apple juice. In enriched juice the antioxidant activity was 5 times higher than in conventional apple juice, with 52% of the antioxidant activity of the originating fruits present. The novel processing method had similar effects for three apple cultivars tested (Elstar, Golden Delicious, and Jonagold). The taste and color of enriched juice were different from those of conventional juice.     

Antioxidant and antiulcerative properties of phenolics from Chinese quince, quince, and apple fruits

To evaluate the health benefits of Chinese quince and quince phenolics, their antioxidant properties and antiulcerative activity were investigated in comparison with apple phenolics as a reference. The strength of antioxidant activity and DPPH radical scavenging activity of these fruit phenolics varied according to different in vitro evaluation systems, whereas the antioxidative property of rat blood increased in all rats orally administered phenolics. Ferulic acid and isoferulic acid were detected as major metabolites in rats given apple phenolics, quince phenolics, and 5-caffeoylquinic acid standard. (-)-Epicatechin and its 3'-O-methyl ether could be detected in rats administered apple phenolics and (-)-epicatechin standard. In the ethanol-induced gastric ulcer, pre-administration of Chinese quince and quince phenolics suppressed the occurrence of gastric lesions in rats, whereas apple phenolics seemed to promote ulceration. The trend of myeloperoxidase activity was similar to that of the ulcer index. The results showed that Chinese quince and quince phenolics might have health benefits by acting both in blood vessels and on the gastrointestinal tract.     

Comparative effects of food-derived polyphenols on the viability and apoptosis of a human hepatoma cell line (HepG2)

Consumption of fruits and vegetables, which are rich in polyphenols, has been associated with a reduced risk of chronic diseases such as cancer. Dietary polyphenols have antioxidant and antiproliferative properties that might explain their beneficial effect on cancer prevention. The aim of this study was to investigate the effects of different pure polyphenols [quercetin, chlorogenic acid, and (-)-epicatechin] and natural fruit extracts (strawberry and plum) on viability or apoptosis of human hepatoma HepG2 cells. The treatment of cells for 18 h with quercetin and fruit extracts reduced cell viability in a dose-dependent manner; however, chlorogenic acid and (-)-epicatechin had no prominent effects on the cell death rate. Similarly, quercetin and strawberry and plum extracts, rather than chlorogenic acid and (-)-epicatechin, induced apoptosis in HepG2 cells. Moreover, quercetin and fruit extracts arrested the G1 phase in the cell cycle progression prior to apoptosis. Quercetin and strawberry and plum extracts may induce apoptosis and contribute to a reduced cell viability in HepG2 cells.     

Phenolic compounds and chromatographic profiles of pear skins (Pyrus spp.)

A standardized profiling method based on liquid chromatography with diode array and electrospray ionization/mass spectrometric detection (LC-DAD-ESI/MS) was used to analyze the phenolic compounds in the skins of 16 pears (Pyrus spp.). Thirty-four flavonoids and 19 hydroxycinnamates were identified. The main phenolic compounds (based on peak area) in all of the pear skins were arbutin and chlorogenic acid. The remaining phenolics varied widely in area and allowed the pears to be divided into four groups. Group 1, composed of four Asian pears (Asian, Asian brown, Korean, and Korean Shinko), contained only trace quantities of the remaining phenolics. Yali pear (group 2) contained significant amounts of dicaffeoylquinic acids. Fragrant pear (group 3) contained significant quantities of quercetin glycosides and lesser quantities of isorhamnetin glycosides and the glycosides of luteolin, apigenin, and chrysoeriol. The remaining 10 pears (group 4) (Bartlett, Beurre, Bosc, Comice, D'Anjou, Forelle, Peckham, Red, Red D'Anjou, and Seckel) contained significant quantities of isorhamnetin glycosides and their malonates and lesser quantities of quercetin glycosides. Red D'Anjou, D'Anjou, and Seckel pears also contained cyanidin 3-O-glucoside. Thirty-two phenolic compounds are reported in pear skins for the first time.     

Plant phenolics behave as radical scavengers in the context of insect (Manduca sexta) hemolymph and midgut fluid

To evaluate the prooxidant versus antioxidant properties of plant phenolics toward leaf-feeding caterpillars, quenching of the stable ABTS radical by five phenolics was measured in two physiological contexts: hemolymph and midgut fluid. Addition of tannic acid, chlorogenic acid, quercetin, or catechin to Manduca sexta (L.) gut fluid increased its total antioxidant capacity by 12-45%, with tannic acid and quercetin being the most powerful in this regard. The antioxidant contribution of the phenolics increased with longer (30-60 min) incubation time in gut fluid. Chlorogenic acid and caffeic acid exhibited the weakest antioxidant activity in gut fluid. The total antioxidant capacity of hemolymph is considerably less than that of gut fluid, and in hemolymph chlorogenic and caffeic acids sometimes acted as mild prooxidants, particularly after longer incubation periods (30-60 min), although this trend was not statistically significant. Tannic acid, catechin, and quercetin behaved as antioxidants in hemolymph. These results suggest that many phenolics have radical scavenging activity in the digestive tract, but some may have more detrimental effects after absorption into the hemolymph compartment.     

Chemical Composition and Anti-inflammatory and Antioxidant Activities of Eight Pear Cultivars

The contents of total phenolics, total flavonoids, total anthocyanins, and total triterpenes of eight pear samples were determined, and the monomeric compounds were identified and quantitated using high-performance liquid chromatography. The in vitro antioxidant and in vivo anti-inflammatory activities of the different pear cultivars were compared. Arbutin and catechin were the dominant polyphenol compounds in the eight pear varieties, followed by chlorogenic acid, quercetin, and rutin. In addition, Xuehua pear and Nanguo pear had significantly higher total phenolics and flavonoids contents, while Dangshansu pear had the largest total triterpenes value (209.2 mg/100 g). Xuehua pear and Nanguo pear also were the highest in total anthocyanins. The pears with high total phenolics and total flavonoids contents had significantly higher antioxidant and anti-inflammatory abilities than those of other species. Anthocyanins were correlated to antioxidant capacity in pears, whereas total triterpenoids were strongly correlated to anti-inflammatory activity.     

Contribution of individual polyphenolics to total antioxidant capacity of plums

To study the effect of polyphenolics on antioxidant capacities of plums, the amounts of total phenolics, total flavonoids and individual phenolic compounds, and vitamin C equivalent antioxidant capacity (VCEAC) of eleven plum cultivars was determined. There was a good linear relationship between the amount of total phenolics and total antioxidant capacity (r2 = 0.9887). The amount of total flavonoids and total antioxidant capacity also showed a good correlation (r2 = 0.9653). Although the summation of individual antioxidant capacity was lower than the total antioxidant capacity of plum samples, there was a positive correlation (r2 = 0.9299) of total antioxidant capacity of plum samples with the sum of the VCEACs calculated from individual phenolics. Chlorogenic acids and glycosides of cyanidin, peonidin, and quercetin were major phenolics among eleven plum cultivars. The antioxidant capacity of chlorogenic acids and anthocyanins showed higher correlation (r2) of 0.7751 and 0.6616 to total VCEAC, respectively, than that of quercetin glycosides (r2 = 0.0279). Chlorogenic acids were a major source of antioxidant activity in plums, and the consumption of one serving (100 g) of plums can provide antioxidants equivalent to 144.4-889.6 mg of vitamin C.     

Biochemical study of leaf browning in minimally processed leaves of lettuce (Lactuca sativa L. var. acephala)

A series of biochemical parameters, including the concentration of total ascorbic acid (ASA(tot)) and the activities of phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), and peroxidases (PODs), was investigated during cold storage (72 h at 4 degrees C in the dark) in fresh-cut (minimally processed) leaves of two lettuce (Lactuca sativa L. var. acephala) cultivars differing in the susceptibility to tissue browning: Green Salade Bowl (GSB), susceptible, and Red Salade Bowl (RSB), resistant. The two cultivars showed differences also at the biochemical level. The content in ASA(tot) increased in RSB, as a consequence of increased DHA concentration; conversely, ASA(tot) diminished in GSB, in which ASA was not detectable after 72 h of storage, thus suggesting a disappearance of ascorbate (both ASA and DHA) into nonactive forms. The antioxidant capacity (as determined by using FRAP analysis) decreased significantly during storage in RSB, while a strong increase was observed in GSB. PAL activity increased soon after processing reaching a maximum by 3 h, then it declined to a relatively constant value in RSB, while in GSB it showed a tendency to decrease in the first few hours from harvest and processing. POD activity, at least for chlorogenic acid, increased significantly during storage only in GSB.     

Polyphenolic profiles in eight apple cultivars using high-performance liquid chromatography (HPLC)

Polyphenolic compounds of apple may play an important role in physiologic functions related to human health. Different polyphenolics may have varied biological activities including antioxidant activity. The objective of this study was to investigate the profiles of polyphenolic compounds in different apple varieties and different parts of an apple. The total and individual polyphenolics differed significantly among the eight apple cultivars grown in Ontario, and the peels had higher concentrations than the flesh. Among the tested cultivars, Red Delicious and Northern Spy had the highest concentrations and Empire the lowest. Five major polyphenolic groups with a total of 16 identified individual compounds were found, among which the dihydroxycinnamic acid esters, phloretin glycosides, and flavan-3-ols were found in both flesh and peel, whereas quercetin glycosides were almost exclusively found in the peel. Cyanidin 3-galactoside was unique to and found only in red apple peels. In both apple peel and flesh, the predominant group of polyphenolics was the procyanidins, followed by quercetin glycosides in the peel and hydroxycinnamic acid esters in the flesh. 3-Hydroxyphloretin 2'-xyloglucoside was newly identified in apple. The results obtained in this study will further the understanding of the polyphenolic composition of apples and their roles in health-promoting physiological functions.     

Effect of drying conditions and storage period on polyphenolic content, antioxidant capacity, and ascorbic acid of prunes

In this study the main chemical parameters, ascorbic acid and polyphenol content, and antioxidant activity of two varieties of prunes, dried by high-temperature (85 + 70 degrees C) and low-temperature (60 degrees C) procedures, were monitored during storage. Ascorbic acid content was higher in the prunes dried at 60 degrees C but significantly decreased in both varieties during storage. The different classes of polyphenols analyzed (cinnamates, anthocyanins, flavonols) showed different stabilities during storage. Neochlorogenic acid decreased only in the President variety, whereas chlorogenic acid increased in both varieties; anthocyanins, present only in the President prunes, disappeared in the first months of storage, and the flavonol content fell significantly in both cultivars during the year of the study. Drying temperature significantly affected the polyphenol content, with different effects according to the class of polyphenols. Antioxidant activity showed a significant increase at the end of the storage period and in the President variety was higher in the sample dried at the higher temperature.     

Solid-state bioconversion of phenolics from cranberry pomace and role of Lentinus edodes beta-glucosidase

Cranberry pomace contains large amounts of phenolic glycosides, which are important sources of free phenolics that have many food uses such as antioxidants, flavorings, and nutraceuticals. Our hypothesis was that these glycosides in cranberry pomace could be hydrolyzed by beta-glucosidase produced by Lentinus edodes during solid-state fermentation. On the basis of this hypothesis, our objective was to investigate the potential of using cranberry pomace as a substrate for the production of free phenolics and beta-glucosidase through solid-state fermentation by a food-grade fungus L. edodes. Our results suggested that L. edodes beta-glucosidase played a major role in release of phenolic aglycons from cranberry pomace during solid-state fermentation. After 50 days of cultivation, the yield of total free phenolics reached the maximum of 0.5 mg per g of pomace, while the beta-glucosidase activity was about 9 units per g of pomace. The enzyme exhibited optimal activity at 60 degrees C and at pH 3.5 and was stable at temperatures up to 50 degrees C and between pH 3 and 6.5. The major free phenolics produced from cranberry pomace were identified by HPLC as gallic acid, chlorogenic acid, p-hydroxybenzoic acid, and p-coumaric acid. These results suggest that cranberry pomace is a potential substrate for producing food-grade phenolics and fungal beta-glucosidase. The L. edodes beta-glucosidase showed good stability and tolerance to low pH and, therefore has potential applications in wine and juice processing for aroma and flavor enrichment through enzymatic hydrolysis of glucoside precursors.     

Phenolic compounds and related enzymes are not rate-limiting in browning development of fresh-cut potatoes

The effect of minimal processing on polyphenol oxidase (PPO), peroxidase (POD), phenylalanine ammonia-lyase (PAL), and phenolic compounds was studied in five potato cultivars (Agria, Cara, Liseta, Monalisa, and Spunta). Minimal processing caused an overall increase in PPO, POD, and PAL activities. The isoform pattern of PPO was the same for all of the cultivars before and after processing. No latent PPO was detected. The isoperoxidase pattern was approximately the same among cultivars. An increase in POD activity was related to the specific induction of an acidic isoperoxidase. PAL showed an induction pattern characterized by the presence of a maximum peak of activity after 4 days of processing for all of the cultivars. The sequence of browning susceptibility of potato cultivars was as follows: Monalisa > Spunta > Liseta > Cara > Agria. Browning development was only partially correlated to PAL activity (only during the first 4 days after wounding). However, this correlation could not explain the above sequence of browning susceptibility. Minimal processing caused an increase of chlorogenic acid, whereas tyrosine content remained unchanged. In summary, no significant correlation was found between either rate or degree of browning and any other biochemical and physiological attribute investigated (PPO, POD, hydrogen peroxide, ascorbic acid content, and initial phenolics content as well as total and individual phenolics accumulation).     

Effect of wash water temperature and chlorination on phenolic metabolism and browning of stored iceberg lettuce photosynthetic and vascular tissues

Cut tissues from distinct anatomical locations in iceberg lettuce (Lactuca sativa L.) were subjected to washing in cold (4 degrees C) and warm (47 degrees C) water with or without chlorine to assess their propensity to discoloration during storage. Total protein (Bradford method) and phenolic (TPH; Folin-Ciocalteu method) contents and polyphenol oxidase (PPO; spectrophotometric method using catechol as a substrate), peroxidase (POD; guaiacol substrate), and phenylalanine ammonia-lyase (PAL; phenylalanine substrate) activities were determined in photosynthetic and vascular tissue from outer and inner leaves. Unprocessed photosynthetic and inner leaf tissues had significantly higher (P < 0.05) levels of protein and TPH and PPO and POD activities than vascular and outer leaf tissues. PAL activities (on a fresh weight basis) were similar in all tissues. Changes in browning (light reflectance measurement) and phenolic metabolism in all four tissue types were observed during aerobic storage at 5 degrees C over 10 days. PAL activity increased in all tissues after 1-2 days of storage and then gradually decreased. POD activity also increased steadily for the storage duration. Protein content and PPO activity remained constant. Edge browning (measured with a Minolta Chroma Meter) and TPH increased in all tissues, especially in outer vascular tissue. Cut photosynthetic and vascular tissues washed at 4 and 47 degrees C with and without 100 microg mL(-1) chlorine for 3 min were analyzed during 7 days in storage at 5 degrees C. Enzyme activities and accumulation of phenolics in all tissues washed at 47 degrees C were significantly (P < 0.05) lower compared to controls or tissues washed at 4 degrees C. Chlorine had no additional effect at 47 degrees C but significantly (P < 0.05) reduced browning and accumulation of phenolics in lettuce washed at 4 degrees C. These results showed that inherent differences between tissues affect phenolic metabolism and browning in stored, fresh-cut lettuce.     

Antioxidant activity of minimally processed red chicory (Cichorium intybus L.) evaluated in xanthine oxidase-, myeloperoxidase-, and diaphorase-catalyzed reactions

Minimally processed red chicory products (Cichorium intybus L. var. silvestre) were studied for their polyphenol content and antioxidant activity evaluated by using the synthetic 2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl radical and three model reactions catalyzed by relevant enzymatic sources of reactive oxygen species, namely, xanthine oxidase, myeloperoxidase, and diaphorase. Products were analyzed at the time of production and after storage at 4 degrees C within either a gas permeable film or a gas barrier film. The antioxidant activity and contents of hydroxycinnamic acids and flavonoids decreased by less than 20% during storage of the minimally processed red chicory products. Total phenolics were significantly correlated with the antioxidant activity evaluated with both the synthetic radical and the enzyme-catalyzed reactions. On a molar basis, red chicory phenolics were as efficient as the reference compound Trolox in scavenging the synthetic radical. However, red chicory phenolics had a much higher inhibitory activity than Trolox in the model enzymatic systems.