Microbial stability, phytochemical retention, and organoleptic attributes of dense phase CO2 processed muscadine grape juice

Dense phase CO2 processing (DP-CO2) is a promising alternative to thermal pasteurization potentially inactivating microorganisms without affecting food phytochemicals or organoleptic characteristics. To demonstrate these effects, studies were conducted by changing processing pressure and CO2 concentration in relation to microbial destruction. Subsequent storage stability (10 weeks at 4 degrees C) of muscadine grape juice processed by DP-CO2 (34.5 MPa at 8% or 16% CO2) was evaluated and compared to a heat-pasteurized juice (75 degrees C, 15 s). Thermal pasteurization decreased anthocyanins (16%), soluble phenolics (26%), and antioxidant capacity (10%) whereas no changes were observed for both DP-CO2 juices. DP-CO2 juices also retained higher anthocyanins (335 mg/L), polyphenolics (473 mg/L), and antioxidant capacity (10.9 micromol of Trolox equivalents/mL) than thermally pasteurized juices at the end of storage. Insignificant differences in sensory attributes (color, flavor, aroma, and overall likeability) were observed between unprocessed and DP-CO2 juices, while significant differences were observed between unprocessed and heat-pasteurized juices. Panelists preferred DP-CO2 over heat-pasteurized juices throughout the first 6 weeks of storage, whereby the growth of yeast and mold adversely affected the juice aroma. Comparable microbial counts were observed between DP-CO2 and thermally pasteurized juices during the first 5 weeks of storage. DP-CO2 protected phytochemicals in muscadine juice during processing and storage without compromising microbial stability or sensory attributes over 5 weeks of storage.     

Phytochemical composition and antioxidant stability of fortified yellow passion fruit (Passiflora edulis)

Yellow passion fruit juice (PFJ, Passiflora edulis f. flavicarpa) is an important component of many tropical fruit beverages, but limited data exist on its antioxidant chemical composition and stability during processing and storage. PFJ fortified with ascorbic acid (450 mg/L) and sucrose (10%) was compared to a nonfortified control, and each was evaluated with and without vacuum deaeration to remove dissolved oxygen. Following pasteurization, juices were stored for 28 days at 37 degrees C to accentuate physicochemical changes. Pasteurization (85 degrees C for 30 min) resulted in minor changes to physicochemical attributes, but appreciable changes occurred during storage that resulted in termination of the study after 28 days. Oxygen control strategies proved to be ineffective for quality retention and indicated oxygen-independent reactions affecting juice color, phytochemical content, and antioxidant activity. Ascorbic acid and sucrose fortification had an overall preservation effect on total carotenoids, the former resulting in hyperchromic shifts in absorbance, indicating their chemoprotection. Pasteurization resulted in a 25% loss in l-ascorbic acid, which was completely destroyed after 14 days of storage; losses coincided with increased juice browning and formation of 5-hydroxymethylfurfural. Numerous polyphenolics were present in PFJ, and 16 of them were tentatively characterized on the basis of spectral similarities to known standards. Individually, polyphenolics increased during pasteurization, only to decline during storage at elevated temperatures. Antioxidant activity was measured in PFJ and in two subfractions (hydrophilic and lipophilic) after processing and storage, but antioxidant values were nonadditive. A significant chemical interaction affecting antioxidant capacity was found for hydrophilic juice components, but none was observed in the presence of lipophilic phytochemicals. Physicochemical attributes and overall quality of PFJ were retained following pasteurization but were significantly impacted by degradative reactions during accelerated storage.     

In vitro availability of flavonoids and other phenolics in orange juice

Hand-squeezed navel orange juice contains 839 mg/L phenolics, including flavanones, flavones, and hydroxycinnamic acid derivatives. The flavanones are the main phenolics in the soluble fraction (648.6 mg/L) and are also present in the cloud fraction (104.8 mg/L). During refrigerated storage of fresh juice (4 degrees C), 50% of the soluble flavanones precipitate and integrate into the cloud fraction. Commercial orange juices contain only 81-200 mg/L soluble flavanones (15-33%) and the content in the cloud is higher (206-644 mg/L) (62-85%), showing that during industrial processing and storage the soluble flavanones precipitate and are included in the cloud. An in vitro simulation of orange juice digestion shows that a serving of fresh orange juice (240 mL) provides 9.7 mg of soluble hesperidin (4'-methoxy-3',5,7-trihydroxyflavanone-7-rutinoside) and 4.7 mg of the C-glycosylflavone vicenin 2 (apigenin, 6,8-di-C-glucoside) for freshly squeezed orange juice, whereas pasteurized commercial juices provide 3.7 mg of soluble hesperidin and a higher amount of vicenin 2 (6.3 mg). This means that although orange juice is a very rich source of flavanones, only a limited quantity is soluble, and this might affect availability for absorption (11-36% of the soluble flavanones, depending on the juice). The flavanones precipitated in the cloud are not available for absorption and are partly transformed to the corresponding chalcones during the pancreatin-bile digestion.     

Carotenoids, color, and ascorbic acid content of a novel frozen-marketed orange juice

A recently developed food, the so-called ultrafrozen orange juice (UFOJ), has been characterized in terms of carotenoid pigments, ascorbic acid, and color. The juice, obtained from Valencia late oranges, is frozen immediately after the squeezing of the oranges, which makes it a product showing good organoleptic and nutritional quality. In relation to the carotenoid profile, it was observed that the 5,6-epoxy carotenoids violaxanthin and antheraxanthin (specifically (9Z)-violaxanthin and (9Z)- or (9'Z)-antheraxanthin), were by far the major pigments and that dihydroxycarotenoids predominate over monohydroxycarotenoids. As far as color was concerned, it was seen that there were little differences among the juices analyzed. The hue of the samples, ranging from 77.19 degrees to 80.15 degrees and from 79.99 degrees to 83.04 degrees depending on the kind of instrumental measurement, and their chroma (ranging from 63.06 to 72.25 and from 44.40 to 58.38) revealed readily that the juice surveyed exhibited a deep orangeish coloration, the color coordinate best correlated with the total carotenoid content being b*. The levels of ascorbic acid ranged from 332.64 to 441.44 mg/L, with an average content of 391.06 +/- 28.86 mg/L.     

Phytochemical stability and color retention of copigmented and processed muscadine grape juice

Muscadine (Vitis rotundifolia) grape juice was assessed for color and phytochemical stability as influenced by anthocyanin copigmentation with a water-soluble rosemary extract, fortification with ascorbic acid, and processing by heat or high hydrostatic pressure (HHP). The roles of polyphenolic cofactors in the presence and in the absence of ascorbic acid were assessed as a means to improve the overall processing stability of the juice. Addition of rosemary extract from 0 to 0.4% (v/v) readily formed copigment complexes with anthocyanins and resulted in concentration-dependent hyperchromic shifts from 10 to 27% that corresponded to increased antioxidant activity. The presence of ascorbic acid was generally detrimental to juice quality, especially in the presence of rosemary extract, and resulted in overall anthocyanin, ascorbic acid, and antioxidant activity losses. Although thermal and high-pressure processing methods were detrimental to juice quality, HHP resulted in greater losses after processing, likely due to action from residual oxidase enzymes. Although physicochemical attributes were enhanced by copigmentation with rosemary extract, methods to inactivate residual enzymes should be addressed prior to copigmentation to prevent degradation of anthocyanins in the presence of ascorbic acid.     

Ellagic acid and flavonoid antioxidant content of muscadine wine and juice

Antioxidant properties of flavonoids and ellagic acid were characterized in eight wines and juices produced by various processing methodologies from red and white muscadine grape cultivars (Vitis rotundifolia). Juices and wines were produced by hot- and cold-pressed techniques, and additional wine was produced following on-hull fermentation for 3, 5, and 7 days. Chromatographic conditions were developed to simultaneously separate anthocyanins, ellagic acid, and flavonols and correlated to a measurement of overall antioxidant capacity (AOX), and their changes were monitored after storage for 60 days at 20 and 37 degrees C. Regression coefficients between concentrations of individual polyphenolics and AOX ranged from 0.55 for ellagic acid to 0.90 for kaempferol. Both red and white wines had higher AOX values after storage than juices made from an identical grape press, despite lower concentrations of individual polyphenolic compounds. Red wines fermented on-hull had higher initial concentrations of antioxidant polyphenolics as compared to a corresponding hot-pressed juice, but changes in AOX during storage were more affected by time than by storage temperature despite lower concentrations of flavonoids and ellagic acid present at 37 degrees C as compared to 20 degrees C. Oxidative or polymerization reactions significantly decreased levels of monomeric anthocyanins during storage with the greatest losses observed for delphinidin and petunidin 3,5-diglucosides. Processing methods for muscadine wine and juice production were important factors influencing concentrations of antioxidant flavonoids and ellagic acid, while the role of fermentation and time had the greatest influence on retention of AOX properties during storage.     

Processing strawberries to different products alters contents of vitamin C, total phenolics, total anthocyanins, and antioxidant capacity

Strawberries were processed to juice, nectar, wine, and puree. For investigation of the antioxidant capacity as well as the contents of ascorbic acid, total phenolics and total anthocyanins, samples were taken after different stages of production to determine the effects of processing. The content of vitamin C was measured spectrophotometrically. The total phenolic content was analyzed by using the Folin-Ciocalteu method, and the amount of total anthocyanins was determined by using the pH-differential method. Two different methods-the trolox equivalent antioxidant capacity assay and the ferric reducing antioxidant power test-were used to determine the hydrophilic antioxidant capacity. This study showed the decrease of all investigated parameters within processing strawberries to different products. The content of ascorbic acid decreased with production time and processing steps, especially during heat treatment. The investigations on total phenolics in strawberry products proved fining to be a mild method to clarify berry juices and wines without removing high amounts of total phenolics. Fermentation did not lead to heavy losses of total phenolics, probably due to polymerization and condensation of monomer phenolics such as anthocyanins. Total anthocyanins and the hydrophilic antioxidant capacity decreased while using high temperatures. Anthocyanins also decreased considerably during the processing of wines, mainly caused by fermentation and pasteurization.     

Ellagic acid and ellagitannins affect on sedimentation in muscadine juice and wine

A mechanism for the formation of water-insoluble sediments in wines and juices made from red and white muscadine grapes (Vitis rotundifolia) was investigated as a function of processing methodology and storage. Sediments are considered quality defects in muscadine grape products, and their presence may influence consumer acceptability and expansion of retail markets. Processing regimes included both hot (70 degrees C) and cold (25 degrees C) press techniques for wine or juice production, and fermentations in contact with grape skins for 3, 5, and 7 days. Relationships between free ellagic acid (FE), total ellagitannins (ET), and total ellagic acid (TE) concentrations were evaluated initially in each product and in sediments that formed during storage for 50 and 120 days at 20 degrees C. Processing techniques influenced initial concentrations of these compounds and the extent of sediment formation. Following storage, juices generally had higher concentrations of FE in sediments compared to wines, but sedimentation was independent of initial FE or TE concentrations. Decreases in ET were observed for hot-pressed juice and skin-fermented wines after storage indicating their hydrolysis during storage and possible contribution to FE in sediments. However, quantitative analysis of the collected sediments revealed that no more than 12% FE by weight was actually present in the sediments, with the remainder consisting of either unidentified compounds or conjugated forms of ellagic acid. This work elucidated a potential mechanism for the presence of FE in muscadine wine and juice sediments through ellagitannin hydrolysis and suggests that sedimentation from mechanisms other than ellagic acid precipitation may also contribute to wine and juice quality.     

Fruit maturity and juice extraction influences ellagic acid derivatives and other antioxidant polyphenolics in muscadine grapes

Polyphenolic compounds including ellagic acid, ellagic acid derivatives, and anthocyanins were characterized and quantified by novel chromatographic conditions in eight muscadine grape (Vitis rotundifolia) cultivars and evaluated for antioxidant capacity as influenced by two ripening stages and their location within the fruit (skin, pulp, and juice). All polyphenolics generally increased as fruit ripened and the highest concentrations were located in the skins. Free ellagic acid, ellagic acid glycosides, and total ellagic acid ranged from 8 to 162, 7 to 115, and 587 to 1900 mg/kg, respectively, in the skin of ripe grapes. Hot-pressed juices contained considerably lower polyphenolic concentrations than were present in whole grapes. Five anthocyanidins were present in each cultivar in variable concentrations (delphinidin > petunidin > malvidin + peonidin > cyanidin). Antioxidant capacity was appreciably influenced by cultivar, maturity, and location in the fruit with good correlations to soluble phenolics found in both methanolic and ethyl acetate extracts (r = 0.83 and 0.92, respectively).     

Protease-assisted clarification of black currant juice: synergy with other clarifying agents and effects on the phenol content

Conventional clarification with gelatin and silica sol removes a considerable amount of antioxidant phenolics from berry juices. This study examined the clarification and haze-diminishing effects of alternative clarification strategies on black currant juice including centrifugation and addition of acidic protease and pectinolytic enzyme preparations and gallic acid. Centrifugation of freshly pressed juice (10,000 g for 15 min) resulted in a approximately 95% reduction of immediate turbidity and had a decreasing effect on haze development in the juice during cold storage without significantly compromising the total phenols levels. The extent of clarification and haze diminishment varied after individual treatments with five different acidic proteases, but one of the protease preparations, Enzeco, derived from Aspergillus niger, consistently tended to perform best. The individual and interactive effects on juice turbidity, total phenols, and total anthocyanin contents of clarification treatments involving the use of two selected acid proteases (Enzeco and Novozyme 89L), a pectinase (Pectinex BE 3-L), and gallic acid were evaluated in a full factorial 2(4) experimental design. Haze development during cold storage decreased when gallic acid or any of the enzyme preparations were employed individually, but negative interaction effects resulted when the pectinase was employed in combination with any of the proteases. After 28 storage days at 2 degrees C, the lowest levels of haze formation were achieved when the Enzeco protease preparation, added at 0.025 g/L, was added with 0.050 g/L of gallic acid and allowed to react in the juice for 90 min at 50 degrees C. The corresponding anthocyanin reduction was approximately 12% (compared to approximately 30% with gelatin silica sol treatment). The data support the hypothesis that phenol-protein interactions are involved in juice turbidity development during cold storage of berry juices and demonstrate that precentrifugation and protease-assisted clarification show promise as an alternative, phenolics-retaining clarification strategy in black currant juice processing.     

Using LC-MSMS to assess glutathione levels in South African white grape juices and wines made with different levels of oxygen

The effect of oxygen on the levels of glutathione, an important antioxidant, in must and wine was studied using a novel LC-MSMS method for the analysis of reduced and oxidized glutathione. This study found that the storage of grape juice at high SO2 and ascorbic acid levels at -20 degrees C did not lead to a decrease in reduced glutathione levels. The effect of varying the oxygen levels in South African white grape juices, which included a reductive treatment (less than 0.3 mg/L dissolved O2 added), a control treatment (between 1.0 and 1.5 mg/L dissolved O2 added), and an oxidative treatment (3.5-4 mg/ L dissolved O2 added, without SO2) on reduced glutathione levels in the juice and resulting wine was also investigated. A custom build press was used to press whole bunches of two different Sauvignon Blanc and Colombard grapes. Alcoholic fermentation and oxygen additions to the must led to lower reduced glutathione levels in the wine. Reduced glutathione levels were only significantly higher in the wine made from reductive juice that had the highest initial reduced glutathione levels in the grapes.     

Fruit antioxidant activity, ascorbic acid, total phenol, quercetin, and carotene of Irwin mango fruits stored at low temperature after high electric field pretreatment

Greenhouse-grown tree ripe (TR) and mature green (MG) mangoes (cv. Irwin) were exposed to high electric field treatment before 20 and 30 days of storage at 5 degrees C. MG fruits were allowed to ripen at room temperature after low-temperature storage. Fruit physical quality attributes, ascorbic acid, carotene, quercetin, total phenols, and antioxidant capacity were estimated before and after the storage period. Antioxidant capacity of fruit juice was estimated using the ferric reducing antioxidant power (FRAP) assay. Fruit firmness decreased significantly during storage. Titratable acidity decreased 20 days after storage. Total soluble solids did not change during storage. Antioxidant capacity of fruits remained unchanged up to 20 days of storage period and decreased thereafter. Total phenol and carotenes increased during storage. Antioxidant capacity of fruits was significantly correlated only to ascorbic acids. Peel color and carotenes were higher in TR fruits, whereas titratable acidity and firmness were higher in MG fruits. There was no significant difference in other parameters between the stages of picking. Electric field pretreatment affected the respiration and antioxidant capacity of TR fruits and did not have any significant affect on other parameters. TR mangoes of cv. Irwin are more suitable for low-temperature storage and can be successfully stored for up to 20 days at 5 degrees C without any significant losses in functional properties and quality attributes.     

Effect of clarification techniques and rat intestinal extract incubation on phenolic composition and antioxidant activity of black currant juice

This study examined the phenolic composition and the antioxidant potencies of black currant juices that had been experimentally clarified with acidic proteases and pectinases to retain the phenolics and which had been subjected to rat intestinal mucosa extract incubation to mimic gut cell mediated biotransformation of phenolics. When compared at equimolar levels of 2.5 microM gallic acid equivalents, the black currant juice samples prolonged the induction time of human low-density lipoprotein oxidation in vitro by 2.6-3.6 times, and the order of antioxidant potency of differently clarified black currant juices was centrifuged juice > gelatin silica sol clarified juice > enzymatically clarified juice approximately raw juice. No immediate relationship between the, almost similar, phenolic profiles of the juice samples and their relative antioxidant activities could be established. Incubation of juices with a rat small intestine cell extract for 19 h promoted significant decreases in the contents of the anthocyanin 3-O-beta-glucosides (cyanidin 3-O-beta-glucoside and delphinidin 3-O-beta-glucoside), but did not affect the anthocyanin 3-O-beta-rutinosides (cyanidin 3-O-beta-rutinoside and delphinidin 3-O-beta-rutinoside) of the black currant juice. Black currant juice samples subjected to such intestinal cell extract incubation had approximately 30% decreased antioxidant capacity. Incubation of juices with the rat small intestine cell extracts at neutral pH appeared to decrease the levels of delphinidin glucosides more than the levels of cyanidin glucosides. The results provide an explanation for the predominant detection of anthocyanin rutinosides, and not anthocyanin glucosides, in plasma and urine in in vivo studies and provide important clues to better understand the complex mechanisms affecting dietary phenols in the gut.     

Alterations of vitamin C, total phenolics, and antioxidant capacity as affected by processing tomatoes to different products

This study was conducted to investigate the antioxidant vitamin C, the polyphenol content, and the hydrophilic antioxidant capacity of tomato juice, baked tomatoes, tomato sauce, and tomato soup. During the production of tomato juice and during the preparation of the other tomato products, samples were taken after different times, respectively, after each particular production step. High-performance liquid chromatography was used to determine the content of vitamin C. The total phenolics content was analyzed spectrophotometrically by using the Folin-Ciocalteu method. The hydrophilic antioxidant capacity was measured by using three different methods: the Trolox equivalent antioxidant capacity assay, the ferric reducing antioxidant power test, and the photochemiluminescence assay. The vitamin C contents of the tomato products decreased during the thermal processing of tomatoes. In contrast, the total phenolics concentration and the water soluble antioxidant capacity increased.     

Effect of processing techniques at industrial scale on orange juice antioxidant and beneficial health compounds

Phenolic compounds, vitamin C (L-ascorbic acid and L-dehydroascorbic acid), and antioxidant capacity were evaluated in orange juices manufactured by different techniques. Five processes at industrial scale (squeezing, mild pasteurization, standard pasteurization, concentration, and freezing) used in commercial orange juice manufacturing were studied. In addition, domestic squeezing (a hand processing technique) was compared with commercial squeezing (an industrial FMC single-strength extraction) to evaluate their influences on health components of orange juice. Whole orange juice was divided into soluble and cloud fractions after centrifugation. Total and individual phenolics were analyzed in both fractions by HPLC. Commercial squeezing extracted 22% more phenolics than hand squeezing. The freezing process caused a dramatic decrease in phenolics, whereas the concentration process caused a mild precipitation of these compounds to the juice cloud. In pulp, pasteurization led to degradation of several phenolic compounds, that is, caffeic acid derivatives, vicenin 2 (apigenin 6,8-di-C-glucoside), and narirutin (5,7,4'-trihydroxyflavanone-7-rutinoside) with losses of 34.5, 30.7, and 28%, respectively. Regarding vitamin C, orange juice produced by commercial squeezing contained 25% more of this compound than domestic squeezing. Mild and standard pasteurization slightly increased the total vitamin C content as the contribution from the orange solids parts, whereas concentration and freezing did not show significant changes. The content of L-ascorbic acid provided 77-96% of the total antioxidant capacity of orange juice. Mild pasteurization, standard pasteurization, concentration, and freezing did not affect the total antioxidant capacity of juice, but they did, however, in pulp, where it was reduced by 47%.     

Commercial scale pulsed electric field processing of tomato juice

Effects of commercial scale pulsed electric field (PEF) processing on the quality of tomato juice were studied and compared with those of thermal processing. Tomato juice was prepared by hot break at 88 degrees C for 2 min or by cold break at 68 degrees C for 2 min and then thermally processed at 92 degrees C for 90 s or PEF processed at 40 kV/cm for 57 micros. Thermally processed, PEF processed, and unprocessed control juices were packed into 50 mL sterilized polypropylene tubes in a sanitary glovebox and stored at 4 degrees C for 112 days. Both thermally and PEF processed juices showed microbial shelf life at 4 degrees C for 112 days. The lipoxygenase activities of thermally and PEF processed juices were 0 and 47%, respectively. PEF processed juice retained more ascorbic acid than thermally processed juice at 4 degrees C for 42 days (p < 0.05). No significant differences were observed in the concentration of lycopene, degrees Brix, pH, or viscosity between thermally and PEF processed juices during the storage (p > 0.05). Sensory evaluations indicated that flavor and overall acceptability of PEF processed juice were preferred to those of thermally processed juice (p < 0.05).     

Antioxidant and antiproliferative activities of raspberries

Raspberries are rich in phenolic phytochemicals. To study the health benefits of raspberries, four fresh raspberry varieties (Heritage, Kiwigold, Goldie, and Anne) were evaluated for total antioxidant and antiproliferative activities. The total amount of phenolics and flavonoids for each of the four raspberry varieties was determined. The Heritage raspberry variety had the highest total phenolic content (512.7 +/- 4.7 mg/100 g of raspberry) of the varieties measured followed by Kiwigold (451.1 +/- 4.5 mg/100 g of raspberry), Goldie (427.5 +/- 7.5 mg/100 g of raspberry), and Anne (359.2 +/- 3.4 mg/100 g of raspberry). Similarly, the Heritage raspberry variety contained the highest total flavonoids (103.4 +/- 2.0 mg/100 g of raspberry) of the varieties tested, followed by Kiwigold (87.3 +/- 1.8 mg/100 g of raspberry), Goldie (84.2 +/- 1.8 mg/100 g of raspberry), and Anne (63.5 +/- 0.7 mg/100 g of raspberry). The color of the raspberry juice correlated well to the total phenolic, flavonoid, and anthocyanin contents of the raspberry. Heritage had the highest a/b ratio and the darkest colored juice, and the Anne variety showed the lowest phytochemical content and the palest color. Heritage raspberry variety had the highest total antioxidant activity, followed by Kiwigold and Goldie, and the Anne raspberry variety had the lowest antioxidant activity of the varieties tested. The proliferation of HepG(2) human liver cancer cells was significantly inhibited in a dose-dependent manner after exposure to the raspberry extracts. The extract equivalent to 50 mg of Goldie, Heritage, and Kiwigold fruit inhibited the proliferation of those cells by 89.4 +/- 0.1, 88 +/- 0.2, and 87.6 +/- 1.0%, respectively. Anne had the lowest antiproliferative activity of the varieties measured but still exhibited a significant inhibition of 70.3+/- 1.2% with an extract equivalent to 50 mg of fruit. The antioxidant activity of the raspberry was directly related to the total amount of phenolics and flavonoids found in the raspberry (p < 0.01). No relationship was found between antiproliferative activity and the total amount of phenolics/flavonoids found in the same raspberry (p > 0.05).     

Phenolic content and antioxidant capacity of muscadine grapes

Fruits of 10 cultivars of muscadine grapes (five bronze skin and five purple skin) grown in southern Georgia were separated into skin, seed, and pulp. Each fruit part and the leaves from the corresponding varieties were extracted for HPLC analysis of major phenolics. Total phenolics were determined colorimetrically using Folin-Ciocalteu reagent. Total anthocyanins were determined according to a pH-differential method, using a UV-visible spectrophotometer. Antioxidant capacity was determined by the Trolox equivalent antioxidant capacity (TEAC) assay. Gallic acid, (+)-catechin, and epicatechin were the major phenolics in seeds, with average values of 6.9, 558.4, and 1299.4 mg/100 g of fresh weight (FW), respectively. In the skins, ellagic acid, myricetin, quercetin, kaempferol, and trans-resveratrol were the major phenolics, with respective average values of 16.5, 8.4, 1.8, 0.6, and 0.1 mg/100 g of FW. Contrary to previous results, ellagic acid and not resveratrol was the major phenolic in muscadine grapes. The HPLC solvent system used coupled with fluorescence detection allowed separation of ellagic acid from resveratrol and detection of resveratrol. Reported here for the first time are the phenolic content and antioxidant capacity of muscadine leaves. Major phenolics in muscadine leaves were myricetin, ellagic acid, kaempferol, quercetin, and gallic acid, with average concentrations of 157.6, 66.7, 8.9, 9.8, and 8.6, respectively. Average total phenolics were 2178.8, 374.6, 23.8, and 351.6 mg/g gallic acid equivalent in seed, skin, pulp, and leaves, respectively. Total anthocyanin contents were 2.1 and 132.1 mg/100 g of FW in the skins of bronze and purple grapes, respectively, and 4.3 and 4.6 mg/100 g of FW in seeds and pulps, in that order. Antioxidant capacity values were, on average, 2.4, 12.8, 281.3, and 236.1 microM TEAC/g of FW for pulps, skins, seeds, and leaves, respectively.     

杀菌方式对石榴浊汁微生物和色泽的影响

为探讨不同杀菌方式对石榴浊汁在4℃冷藏期间微生物和色泽品质的影响,本研究采用超高压技术(HPP,450 MPa/1 min、450 MPa/5 min、550 MPa/1 min、550 MPa/5 min)、巴氏杀菌技术(PT,85℃/30 s)和高温短时杀菌技术(HTST,110℃/8.6 s)对石榴浊汁进行杀菌处理,并重点研究了抗坏血酸和色泽参数变化的动力学特征。结果表明,冷藏期间,HPP和HTST处理石榴浊汁微生物在标准范围内。HPP处理能较好地保留石榴浊汁中脱氢抗坏血酸(DHAA)的含量,而PT和HTST处理后DHAA含量较未处理样品(第0天)分别降低了21%和35%;冷藏期间不同杀菌方式处理后DHAA含量均呈下降趋势;经一级动力学模型拟合发现,HPP处理组DHAA的降解速率常数k值高于PT和HTST处理组。与热处理(PT和HTST)相比,冷藏前期,HPP处理能保持石榴浊汁较高的L^*、a^*、b^*值和较低的ΔE值,保持较优的色泽品质;采用一级分数转换动力学模型对L^*、a^*和ΔE值进行拟合,发现HPP处理样品色泽参数在冷藏过程中的k值同样高于热处理样品,即随着冷藏时间的延长,HPP处理组色泽品质逐渐降低。综上所述,HPP处理能在保证石榴浊汁冷藏期间微生物安全的同时,较好地保持其色泽品质。本研究为石榴浊汁工业化生产中杀菌方式的选择提供了理论依据。