Determination of oil palm fruit phenolic compounds and their antioxidant activities using spectrophotometric methods

There is scarce information on the phenolics of oil palm fruits (Elaeis guineensis). In this study, phenolics were extracted from oil palm fruits and analysed using spectrophotometry for information on the different types of palm phenolics and their antioxidative activities. Analyses of the total phenolic content (TPC), total flavonoid content (TFC), o‐diphenols index, hydroxycinnamic acid index, flavonols index and phenol index showed ranges between 5.64 and 83.97 g L^?1 gallic acid equivalent (GAE), 0.31–7.53 g L^?1 catechin equivalent, 4.90–93.20 g L^?1 GAE, 23.74–77.46 g L^?1 ferulic acid equivalent, 3.62–95.33 g L^?1 rutin equivalent and 15.90–247.22 g L^?1 GAE, respectively. The antioxidant assay, 2,2‐diphenyl‐2‐picrylhydrazyl radical scavenging assay, showed antioxidative activities in all the extracts with results ranging from 4.41 to 61.98 g L^?1 trolox equivalent. The high antioxidant activities of the oil palm fruit phenolics were also found to increase with increasing TPC and TFC.     

Juice components and antioxidant capacity of four Tunisian Citrus varieties

BACKGROUND: Juices from four Citrus species of Tunisia were investigated mainly for quality parameters and antioxidant capacity. RESULTS: Citrus reticulata (mandarin) juice had the highest content of total flavonoids (85.33 mg CE L^?1). The latter also occurred in high quantity (82.01 mg CE L^?1) in Citrus lemon (lemon) juice which was also marked by its richness in total aroma (70.16 µg mL^?1) and in total fatty acids (48.10 µg mL^?1). Mandarin and lemon juices had the highest antioxidant activity, as determined b the β‐carotene bleaching assay (26.67% and 22.67%, respectively). Citrus aurantium (bitter orange) juice was characterised by the highest content of total polyphenols (784.67 mg GAE L^?1) and by the greatest inhibition of DPPH (96.10%). Citrus sinensis (blood orange) juice was only marked by the high quantity of ascorbic acid (36.90 mg mL^?1). GC/MS analysis of juice aroma showed the predominance of limonene (48.85–69.59%) in mandarin and in bitter and blood oranges, but of camphene (89.05%) in lemon. GC analysis of juice fatty acids revealed their richness in oleic acid (23.13–39.52%). HPLC analysis of juice phenolics indicated the predominance of phenolic acids (73.13–86.40%). CONCLUSION: The Citrus species used in this study were considered valuable varieties from the point of view of antioxidant capacity and nutrition. Copyright © 2010 Society of Chemical Industry     

Effect of High Pressure Homogenization and Dimethyl Dicarbonate (DMDC) on Microbial and Physicochemical Qualities of Mulberry Juice

In this study, the effect of high pressure homogenization (HPH) and dimethyl dicarbonate (DMDC) on microbial and nutrient qualities of mulberry juice was evaluated. Results showed that repeated HPH passes at 200 MPa or adding DMDC at 250 mg/L significantly inactivated the indigenous microorganisms in mulberry juice (P < 0.05), whereas some surviving microorganisms recovered to grow during storage of 4 °C. The combined treatment with 3 passes of HPH and 250 mg/L of DMDC (HPH‐DMDC) decreased the population of surviving indigenous microorganisms to the level attained by heat treatment at 95 °C for 1 min (HT) with no significant increase (P > 0.05) in the population of microorganisms during subsequent storage at 4 °C. Moreover, no significant changes (P > 0.05) in the physical attributes, including pH, TSS (^oBrix), L*, a*, and b* values were observed in the samples treated by the HPH‐DMDC or by HT. Compared with HT, HPH‐DMDC treatment resulted in a higher degree of retention in total phenolics, and α‐glucosidase inhibitory activity, although the treatment led to higher losses in cyanidin 3‐glucoside, cyanidin 3‐rutinoside, and antioxidant capacity. Overall, HPH‐DMDC treatment can be a useful alternative to conventional thermal pasteurization of mulberry juice, considering its ability to inactive, and inhibit indigenous microorganisms.     

Variations in antioxidant properties of strawberries grown in Brazilian savannah and harvested in different seasons

BACKGROUND: Strawberries are nutritive fruits and a source of antioxidants. We evaluated antioxidant properties of ‘Camino Real’ strawberries grown in the Brazilian savannah, harvested in different seasons. Analytical and meteorological data were analyzed by partial least squares regression. RESULTS: Fruits from May showed the lowest contents of total phenolics (1789.78 mg kg^?1 fresh weight (FW)), catechin (21.37 mg kg^?1 FW), quercetins (4.89 mg kg^?1 FW) and total ellagic acid (208.68 mg kg^?1 FW) and the lowest antioxidant activity by 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) (11.39 mg Butylated hydroxytoluene (BHT) eq. g^?1 FW) and ferric reducing antioxidant power (FRAP) (22.01 mg ferrous sulfate eq. g^?1 FW) assays. Strawberries harvested in July presented the lowest concentrations of total (190.61 mg kg^?1 FW) and individual anthocyanins (73.88 mg kg^?1 FW and 5.96 mg kg^?1 FW for pelargonidin‐3‐glucoside and cyanidin‐3‐glucoside, respectively), but the highest contents of vitamin C (685.47 mg kg^?1 FW), DPPH (18.87 mg BHT eq. g^?1 FW) and FRAP (39.30 mg ferrous sulfate eq. g^?1 FW). The highest contents of free ellagic acid (26.11 mg kg^?1 FW), pelargonidin‐3‐glucoside (291.82 mg kg^?1 FW) and cyanidin‐3‐glucoside (11.84 mg kg^?1 FW) were found in strawberries from September. Rain in the previous 30 days to harvest influenced negatively many phenolics and antioxidant activity of strawberries harvested in May. In July, longer photoperiod and lower temperature at 30 days previous to harvest probably led to higher antioxidant activity and vitamin C. Increased photoperiod and temperature at the final stage of maturation seem to raise pigments and free ellagic acid in strawberries. CONCLUSION: It was possible to observe significant relationships among meteorological and antioxidant variables for strawberries grown in the Brazilian savannah. Copyright © 2011 Society of Chemical Industry     

Potential nutritive value and tannin bioassay of selected Acacia species from Kenya

Six Acacia forage species–A. brevispica, A. elatior, A. mellifera, A. nilotica, A. senegal and A. seyal—were analysed for their chemical composition, including phenolics and rumen fermentation characteristics. In vitro gas production technique was used to study the rumen fermentation characteristics and the effect of tannins present in the browse forages on in vitro fermentation by including polyethylene glycol (PEG‐6000) in the incubation. The forages had high crude protein content (145.7–270.1 g kg^?1 DM) and low to moderate content of neutral detergent fibre (220.2–442.8 g kg^?1 DM). The forages had variable content of total extractable phenolics ranging from 18.4 to 384.2 g kg^?1 DM and total extractable tannins ranging from 7.1 to 364.8 g kg^?1 DM (tannic acid equivalent). Fractionation of the condensed tannin flavonoids showed that the delphinidin/cyanidin ratio ranged from not detected:100 to 71:29. The gas production potential ranged from 28.4 to 40.8 mL gas 0.2 g^?1 DM. The rate of gas production was highest in A. elatior and lowest in A. nilotica. Addition of PEG‐6000 increased gas production significantly (P < 0.05) in all species except A. mellifera. PEG‐6000 addition did not have any significant effect on in vitro true dry matter and organic matter degradability but decreased the partitioning factor in all the species. Gas production and degradability parameters correlated positively with the CP content and negatively with the fibre and phenolics contents. Based on chemical composition, gas production and degradability, the forages have high potential nutritive value, especially as supplements to low‐quality feeds in the tropics and particularly during the dry season. However, the presence of tannins in terms of high levels and biological antinutritive activity may limit the nutritive potential of some of the forages, such as A. seyal and A. nilotica. Copyright © 2007 Society of Chemical Industry     

Use of low‐voltage direct current electricity treatment to increase phenolics content of postharvest okra: effects of some treatment parameters

Low‐voltage direct current electricity was applied to increase phenolics content of postharvest okra (Abelmoschus esculentus L.) at different values of current (0.10–0.50 A) and application time (900–3600 s). Use of different electrolytes, namely tap water as well as 0.10‐ and 0.15‐mol L^?1 brine, was also investigated. Calcium‐dependent protein kinase was quantified to indicate responses of okra to the treatment. Free and bound phenolics contents were measured and the results used to confirm whether the increased phenolics was due to the applied electricity; initial contents of total, bound and free phenolics were noted to be 6.19, 1.73 and 4.46 g kg^?1, respectively. Total phenolics content (8.12–8.38 g kg^?1) significantly increased when using a current of 0.30 A, application time of 900–3600 s, with brine as the electrolytes. Use of current of 0.30 A and 0.10‐mol L^?1 brine for 900 s is suggested as the appropriate treatment condition.     

Antioxidant capacity and secondary metabolites in four species of Andean tuber crops: native potato (Solanum sp.), mashua (Tropaeolum tuberosum Ruiz & Pavón), Oca (Oxalis tuberosa Molina) and ulluco (Ullucus tuberosus Caldas)

Four species of edible tubers endemic to and domesticated in the Andes, native potato (Solanum sp.), mashua (Tropaeolum tuberosum Ruiz & Pavón), oca (Oxalis tuberosa Molina) and ulluco (Ullucus tuberosus Caldas), were studied for their antioxidant capacity and associated secondary metabolites. The antioxidant capacity was measured using ABTS^? radicals and total phenolics, carotenoids, anthocyanin, betaxanthin and betacyanin content were also characterized. The antioxidant capacity found in the crops studied ranged from 483 to 9800 µg trolox equiv. g^?1, phenolics ranged from 0.41 to 3.37 mg chlorogenic acid equiv. g^?1, anthocyanins ranged from 0.08 to 2.05 mg cyanidin 3‐glucoside g^?1 and carotenoids ranged from 1 to 25 µg β‐carotene g^?1. The content of bioactive compounds was high and variable between crops and within the genotypes studied. In general, mashua tubers showed the highest antioxidant capacity and phenolic, anthocyanin and carotenoid content compared with other crops. Ulluco was the only crop that contained betalains in the acid form of betaxanthins (22–96 µg g^?1) and betacyanins (64 µg g^?1) with no presence of carotenoids or anthocyanins. This is the first publication regarding the antioxidant capacity of and associated secondary metabolites in Andean tubers. This information can be useful in the identification of Andean tubers species and genotypes with potential value as a novel dietary source of antioxidants for food, and also for medicinal use. Copyright © 2006 Society of Chemical Industry     

Red clover (Trifolium pratense L.) isoflavones: root phenolic compounds affected by biotic and abiotic stress factors

BACKGROUND: Phenolic compounds have recently received considerable attention for their ability to protect plant and human cells from oxidative stress‐induced damage. Red clover (Trifolium pratense L.) is a rich source of isoflavonoids with multiple potential protective functions. The aim of this study was to identify and characterise phenolic compounds in red clover roots by high‐performance liquid chromatography and mass spectrometry and to study the effects of stress factors and growth stage on root phenolics. RESULTS: A total of 28 phenolic compounds were tentatively identified in red clover roots. The most abundant phenolics in pot‐grown roots were formononetin glycoside malonate (G‐M) (1.51–4.26 mg g^?1), formononetin (2.21–3.57 mg g^?1) and biochanin A (1.73–2.17 mg g^?1), whereas field‐grown roots were rich in formononetin‐G‐M (3.90–4.27 mg g^?1), maackiain‐G‐M (2.35–3.02 mg g^?1) and pseudobaptigenin‐G‐M (1.80–2.58 mg g^?1). Concentrations were affected by the growth stage. Ozone exposure slightly affected the total phenolic content in roots and also had minor effects on individual compounds. CONCLUSION: Elevated ozone, cultivation regime and growth stage affected the levels of phenolics in red clover roots, suggesting sensitivity of root phenolics to biotic and abiotic stress conditions. The high levels of phenolics found in roots even in late autumn may be utilised in many applications. Copyright © 2009 Society of Chemical Industry     

Activated Carbon and Ion Exchange Treatments for Removing Phenolics and Phytate from Peanut Protein Products

Commercial defatted peanut flour and laboratory defatted peanut meal contained 1.5 and 1.7% phytate, 1756 and 2033 μg g^?1 total phenolic acids and 50 and 120 μg g^?1 neutral phenolics, respectively. Laboratory peanut protein isolate contained undetectable amounts of neutral phenolics, 810 μg g^?1 total phenolic acids and about 1% phytate. The ion exchange treatment removed ≥85% of the phytate and the ion exchange and activated carbon treatments removed 92 and 82%, respectively, of the total phenolic acids from peanut protein isolate. p-Coumaric acid was the major phenolic acid, accounting for 40–68% of the total phenolic acids in all peanut protein products.     

Preparative separation and purification of phenolic compounds from Canarium album L. by macroporous resins

BACKGROUND: Canarium album L. (also called Chinese olive) is a traditional medicine material in China, and phenolic compounds from C. album possess great pharmacological activities. To obtain high‐purity phenolics from C. album, a crude extract of C. album phenolics was prepared by ethanol extraction. The use of macroporous resins for further separation and purification of phenolics in the extract was studied. RESULTS: Through static adsorption and desorption tests, AB‐8 resin was chosen for the separation of phenolics because of its higher adsorption capacity and desorption ratio than other resins. Then, dynamic adsorption and desorption experiments were carried out on an AB‐8 resin packed column to obtain optimal separation parameters. The highest adsorption capacity of AB‐8 was achieved when variables including initial concentration (C₀), feed flow rate and feed volume were 10 mg mL^?1, 2 mL min^?1 and 9 bed volumes (BV), respectively, and saturated resin was first washed with 5 BV of water to remove impurities, then a purified product containing more than 85% of C. album phenolics was obtained by desorbing the resin with 2.5 BV of 70% (v/v) aqueous ethanol at flow rate of 1 mL min^?1, and the recovery of phenolics was up to 75%. In addition, five phenolic compounds in the product were identified as gallic acid, ellagic acid, corilagin, hyperin and kaempferol‐3‐glucopyranoside by UV and LC–ESI–MS analysis. CONCLUSION: The results in this study could provide scientific references for the large‐scale production of phenolics from C. album. Copyright © 2007 Society of Chemical Industry     

Integrated processing of fresh Indian sea buckthorn (Hippophae rhamnoides) berries and chemical evaluation of products

An efficient pilot‐scale process was developed to produce nutraceutical products from fresh sea buckthorn (Hippophae rhamnoides) berries. Fresh berries were subjected to high‐pressure dewatering using a continuous screw press. The separated liquid phase containing 80–90% of pulp oil was clarified at 80 °C and centrifuged to obtain pulp oil, clear juice and sludge. The pulp oil yield was 2.7–2.8% of fresh berry weight with 66–70% extraction efficiency. The pulp oil was remarkably rich in carotenoids (2450–2810 mg kg^?1), tocopherols (1409–1599 mg kg^?1) and sterols (4096–4403 mg kg^?1), with a characteristic fresh berry flavour and 16:1 as the major fatty acid (45.6–49.1%). The clear juice obtained was free from oil and contained high amounts of vitamin C (1683–1840 mg kg^?1) and phytochemicals such as polyphenols (2392–2821 mg kg^?1) and flavonoids (340–401 mg kg^?1). Isorhamnetin (251–310 mg kg^?1) was the major flavonoid in the juice, along with quercetin (77–81 mg kg^?1) and kaempherol (12–16 mg kg^?1). The juice was very acidic (pH 3), with high concentrations of organic acids (30.8–36.0 g kg^?1). High‐performance liquid chromatography profiling of organic acids revealed quinic acid (18.1–19.9 g kg^?1) as the major acid in the juice. The seeds in the pressed cake were separated and extracted for oil using supercritical CO₂. Copyright © 2006 Society of Chemical Industry     

Quality of minimally processed red chicory (Cichorium intybus L.) evaluated by anthocyanin content,radical scavenging activity,sensory descriptors and microbial indices

Changes in the quality of minimally processed red chicory (Cichorium intybus L.) were studied during storage in a polyvinyl chloride (PVC) film and in a mono‐oriented polypropylene (OPP) film at 4 °C. The maximum limit of 5 × 10⁷ CFU g^?1 for mesophilic aerobic bacterial count was attained after 4 days using the PVC film and after 4.5 days using the OPP film. The loss of fruity aroma occurred after 3 days in the products stored in PVC but not in those stored in OPP. In spite of microbial growth, no off‐odour was perceived by trained panellists. Storage in PVC slightly decreased the contents of cyanidin 3‐O‐malonyl glucoside, total phenolics and antioxidant activity, whereas these parameters increased upon storage in OPP. When red chicory heads subjected to mild stress in the field were minimally processed, OPP packaging decreased the microbial growth with respect to PVC, but antioxidants were degraded in both conditions.     

Biochemical characterisation of the seed oils of four safflower (Carthamus tinctorius) varieties grown in north‐eastern of Morocco

The quality of the oil of four safflower varieties, originating from Spain (Rancho), India (Sharda) and Morocco (Cartamar and Cartafri), which were cultivated at the experimental station in Oujda (a semi‐arid region of eastern Morocco) was evaluated through analysis of their phenolic and carotenoid contents. The composition of the phenolic compounds of safflower oil has not yet been documented. Therefore, in this preliminary study, Thirty different phenolic compounds were identified, and significant differences between the oil varieties were observed (P < 0.05). In the seed oil from the Rancho and Sharda safflower varieties, the main phenolic compound was trans‐chalcone, representing 13.45% and 11.8%, respectively, of the total phenolics, whereas in Cartamar and Cartafri oils, naringin accounted for 26.82% and 16.5%, respectively, of the total phenolics. The total carotenoid contents ranged from 1.13 mg kg^?1 (Rancho) to 1.34 mg kg^?1 (Cartamar and Cartafri). We observed that β‐cryptoxanthin (0.31–0.37 mg kg^?1) and β‐carotene (0.3–0.35 mg kg^?1) were the predominant carotenoids in all of the safflower oils that were studied.     

Slight Fermentation with Lactobacillus fermentium Improves the Taste (Sugar:Acid Ratio) of Citrus (Citrus reticulata cv. chachiensis) Juice

The aim of this study was to evaluate the hypothesis that fermentation with Lactobacillus fermentium, which can metabolize citric acid, could be applied in improving the taste (sugar:acid ratio) of citrus juice. During fermentation, the strain of L. fermentium can preferentially utilize citric acid of citrus (Citrus reticulata cv. Chachiensis) juice to support the growth without the consumption of sugar. After 6 h of fermentation with L. fermentium at 30 °C, the sugar:acid ratio of citrus juice increased to 22:1 from 12:1, which resulted in that the hedonic scores of sweetness, acidity and overall acceptability of fermented‐pasteurized citrus juice were higher than the unfermented‐pasteurized citrus juice. Compared with unfermented‐pasteurized citrus juice, the ORAC value and total amino acid showed a reduction, and no significant change (P > 0.05) in the L*, a*, b*, total soluble phenolics and ascorbic acid (Vc) content in the fermented‐pasteurized citrus juice was observed as compared with unfermented‐pasteurized citrus juice. Hence, slight fermentation with L. fermentium can be used for improving the taste (sugar:acid ratio) of citrus juice with the well retaining of quality.     

RP-HPLC-DAD Determination of Phenolics in Industrial Apple Pomace

Processing of apple fruits for juice/cider production generates large volume of pomace at industrial scale. This biomass (cell wall material and pulp tissues) is rich in array of nutrients, especially dietary fiber and polyphenols. Apple fruits confront various processing conditions at industrial level, influencing the biochemical composition of generated pomace, including its phenolic profile. In present study, a simple, fast and reproducible reversed-phase high-performance liquid chromatography method using diode array detector was developed and validated for separation of different phenolics present in industrial apple pomace. The present method showed reliable and reproducible intraday (0.2–4.0 % RSD) and interday (3.7–8.1 % RSD) precision with limits of detection and quantification values in range of 0.14–0.58 and 0.48–1.95 μg ml^?1, respectively, for all the phenolics. Different solvent-mediated extraction of dried pomace powder was also performed to evaluate its total antioxidant potential using standard spectrophotometric assays. The major phenolics found in industrial apple pomace extracts were quercetin (1.4–10.3 μg mg^?1), phloretin (1.1–9.3 μg mg^?1) and phloridzin (0.62–2.0 μg mg^?1).     

Unexploited Acacia cyanophylla seeds: potential food sources of ω6 fatty acids and antioxidants?

BACKGROUND: In order to investigate new sources of dietary phytochemicals, recent studies have focused on underexploited seeds. In this study the total lipid contents, fatty acid profiles and levels of soluble proteins, minerals and antioxidants in seeds from 12 Acacia cyanophylla ecotypes commonly grown in Tunisia were determined. RESULTS: Total lipids averaged 101.7 g kg^?1 on a dry weight basis. Linoleic (61.11–65.45% of total fatty acid content), oleic (19.67–22.85%) and palmitic (9.18–9.98%) acids were the principal fatty acids. Smaller proportions of stearic (1.49–1.82%), vaccenic (1.13–2.05%) and palmitoleic (0.34–0.58%) acids were also quantified. Proteins (by Kjeldahl assay) averaged 107.2 g kg^?1 on a dry weight basis. Total phenolics averaged 1.91 g gallic acid equivalent kg^?1 dry weight (DW) and total flavonoids averaged 0.40 g rutin equivalent kg^?1 DW. The free radical‐scavenging activity determined by 2,2‐diphenyl‐1‐picrylhydrazyl assay averaged 0.59 mmol L^?1 Trolox equivalent antioxidant capacity (TEAC), while that determined by 2,2′‐azino‐bis(3‐ethylbenzothiazoline‐6‐sulfonic acid) assay averaged 0.28 mmol L^?1 TEAC. CONCLUSION: The findings of this study confirm the presence of ω6 fatty acids at high levels in A. cyanophylla seeds. These metabolites could be used as such and/or extracted for the formulation of supplements and/or ingredients to provide a ratio close to the ideal for the ω3/ω6 balance. Copyright © 2012 Society of Chemical Industry     

<Emphasis Type="Italic">Aronia melanocarpa</Emphasis> phenolics and their antioxidant activity

The purpose of the present study was to evaluate small and high molecular phenolics (tannins) and antioxidant activity of Aronia melanocarpa berries, juice and pomace in order to find new potential sources of natural antioxidants. The fruits of Aronia melanocarpa Elliot were collected in the middle of October at a plantation near Wroclaw, Poland. The pomace has a much higher content of phenolics in comparision to juice and fruits. Results showed that polymeric proanthocyanins, predominantly of (−)epicatechin, are the major class of polyphenolic compounds in chokeberry, represent 66% of fruits polyphenols. The average concentration ranged from 1578.79 mg/100 g of DW for chokeberry juice up to 8191.58 mg/100 g in pomace. The concentration of phenolic acids (chlorogenic and neochlorogenic acids) in juice was higher than in pomace. Anthocyanins in Aronia melanocarpa are second phenolic compound group and represent about 25% of total polyphenols, mixture of four different cyanidin glycosides: 3-galactoside, 3-glucoside, 3-arabinoside and 3-xyloside. The higher antioxidant activity expressed as TEAC was measured in pomace >fruit >juice.     

Extraction,identification and enzymatic synthesis of acylated derivatives of anthocyanins from jaboticaba (Myrciaria cauliflora) fruits

Polyphenols were extracted from the skin of jabuticaba fruits (Myrciaria cauliflora). Their total concentration and in vitro antioxidant activity were analysed by the DPPH and ABTS methods. The corresponding results (dry basis) were 1290 mg gallic acid equivalent (GAE)?(100 g)^?1, 98% of DPPH radical inhibition and 120 μm TEAC?g^?1 (ABTS method). All these values are at least as higher as average values reported in the literature for other fruits. A more specific analysis of the fractions of phenolic compounds was also performed by HPLC‐MS. Ellagic acid, quercetin, rutin, delphinidin‐3‐glucoside and cyanidin‐3‐glucoside were the main compounds detected; the latter two were the most abundant. The crude extract was subjected to enzymatic acylation assays in order to synthesise new esters with new potential techno‐functionalities. Palmitic acid was used as acyl donor and lipase B of Candida antactica (CALB) as biocatalyst. HPLC‐MS evidenced the formation of palmitic monoesters in connection with the delphinidin‐3‐glucoside and cyanidin‐3‐glucoside fractions.     

Studies on retention of antioxidant activity,phenolics and flavonoids in high pressure processed black grape juice and their modelling

The effect of high pressure processing on total antioxidant activity, phenolic and flavonoid content of black grapes juice was studied. Response surface methodology (RSM) was used for designing the experiment keeping high pressure (400–600 MPa), temperature (40–60 °C) and processing time (2–4 min) as independent variables. The data obtained were analysed using multiple regression technique and quadratic models were found to fit well (R², 85.61–96.65%) in describing the effect of high pressure, temperature and time on total antioxidant activity, phenolics and flavonoids. The optimum levels were found to be 550 MPa, 44 °C and 2 min for pressure, temperature and processing time, respectively (desirability, 95.00) for getting the maximum retention of total antioxidant activity, phenolics and flavonoids in the juice. The experimental and predicted valued of responses showed high correlation (R², 99.26–99.90%) at the optimised levels of the variables.     

Influence of different pulsed electric field strengths on the quality of the grapefruit juice

Grapefruit juice was investigated using pulsed electric fields (PEF) with (electric field strengths: 0, 5, 10, 15, 20 and 25 kV cm^?1; flow rate: 80 mL min^?1; pulse frequency: 1 kHz at 40 °C for 600 μs). Total phenolics, DPPH, total antioxidant capacity (TAC), total anthocyanins, total carotenoids, sugars and physicochemical properties of grapefruit juice were studied. In addition, the effect of PEF treatment on micro‐organisms was also observed. Results indicated that no significant change was observed in pH, Brix, titratable acidity, sugars, total anthocyanins and colour attributes with the increase in pulsed electric strength as compared to control treatment. However, significant decrease in nonenzymatic browning (NEB) and viscosity while an increase in cloud value, DPPH, TAC, total phenolics and total carotenoids, while reduction in the activity of micro‐organisms, was also observed with the increase in pulsed electric strength as compared to control treatment. This study suggested that PEF at 25 kV cm^?1 could improve the quality of grapefruit juice.