Aroma composition changes in early season grapefruit juice produced from thermal concentration

Differences in aroma components and total volatiles between a single unpasteurized Marsh grapefruit juice and its 65 Brix concentrate reconstituted to 10 Brix were examined using GC-olfactometry (GC-O) and GC-FID. Total volatiles (FID) in the reconstituted concentrate were reduced to less than 5% of initial values, but 57% of total aroma (GC-O) remained. Forty-one aroma-active compounds were observed in unpasteurized single strength juice, whereas 27 components were found in the unflavored reconstituted concentrate. Aroma-active compounds were classified into grapefruit/sulfury, sweet/fruity, fresh/citrusy, green/fatty/metallic, and cooked/meaty groups. Five of six components in the sweet/fruity and 14 of 18 green/fatty/metallic components survived thermal concentration. However, only 4-mercapto-4-methyl-2-pentanone in the grapefruit/sulfury group, and linalool and nootkatone from the fresh/citrusy group, were found in the reconstituted concentrate. Methional was the only aroma compound in the cooked/meaty category found in both juice types. beta-Damascenone and 1-p-menthen-8-thiol were found only in the reconstituted concentrate. 4-Mercapto-4-methyl-2-pentanol was found for the first time in grapefruit juice.     

Using an ion-trap MS sensor to differentiate and identify individual components in grapefruit juice headspace volatiles

An ion-trap mass spectrometer chemical sensor has been utilized to differentiate between grapefruit juices that differ only in the concentration of a single component, and the sensor was able to identify that component. Grapefruit juice was fortified with 40 to 2000 ppm vanillin, a low-level naturally occurring compound in citrus juices. Principal components analysis and discriminant analysis of mass spectral data (m/z 50-200) provided clear separation of the grapefruit juice samples. Vanillin was observed in the juice headspace at the 40 ppm level, with identification possible at the 100 ppm level using either MS or MS/MS.     

Objective measurement of red grapefruit juice color

The color properties (CIE Lab, hue, and chroma) of 90 red grapefruit juices were studied by tristimulus reflectance measurement for two growing seasons. Juices were prepared from six red grapefruit cultivars including Ruby Red, Rio Red, Star Ruby, Ray Ruby, Flame, and Marsh Red grown in Florida. Very wide varietal and seasonal variations on juice color were observed, and most notably, CIE a values varied widely from -1.41 to 9.06 (CV = 82.6%). Lycopene is the major colored pigment in red cultivars with lesser amounts of beta-carotene as determined by HPLC on a carotenoid C(30) column with gradient elution using MeOH and MTBE. The highest correlation coefficients (r = 0.963) found between CIE a values and lycopene contents in juices from all cultivars combined suggest the possibility that the CIE a value would be a good indicator for pigmentation in red grapefruit juice.     

Liquid chromatographic determination of naringin and neohesperidin as a detector of grapefruit juice in orange juice

Naringin/neohesperidin ratios can be used to differentiate orange juice which may contain added grapefruit juice from orange juice which may include juices from other naringin-containing cultivars. The naringin/neohesperidin ratios in juice vary from 14 to 83 in grapefruit (C. grandis) and from 1.3 to 2.5 in sour orange (C. aurantium) cultivars; the ratio is always less than 1 for the K-Early tangelo. Concentrations of both naringin and neohesperidin can be determined in orange juice by using a single liquid chromatographic isocratic reverse-phase system with a C-18 column. The detection limit for both compounds is 1 ppm with a linear working range to 500 ppm. Concentration relative standard deviations range from 0.47 to 1.06% for naringin and from 0.4 to 1.27% for neohesperidin. Naringin and neohesperidin recoveries ranged from 93 to 102% at concentrations of 5 and 50 ppm. Naringin values from blind duplicate samples of orange/grapefruit juice blends could be duplicated to +/- 3%.     

Quantitative analysis of limonin in grapefruit juice using an enzyme-linked immunoassay: interlaboratory study

Eleven laboratories participated in an interlaboratory study of an enzyme-linked immunoassay for limonin in grapefruit juice. Participating laboratories received training and practice samples until familiar with the procedure. Laboratories then received 8 sample pairs of grapefruit juice as blind duplicates. Samples were refrigerated and analyzed within 4 days of receipt. Results from 1 laboratory and 6 individual samples were excluded from the statistical analysis. Method performance was measured by the one-way component of variance analysis. Repeatability relative standard deviations (RSDr) ranged from 7.0 to 15.6%. Reproducibility relative standard deviations (RSDR) ranged from 12.9 to 29.4%.     

Characterization of color fade during frozen storage of red grapefruit juice concentrates

Color changes in red grapefruit juice concentrates during storage at -23 degrees C for 12 months were studied. Concentrate (38 degrees Brix) was packed in both plastic (16 oz) and metal (6 oz) cans. Decrease in red intensity (CIE a) in juice color and slight increases in CIE L*, b*, and hue values from analysis of reconstituted juices were the characteristic color changes in concentrate during frozen storage. With respect to fresh concentrate, juice color in stored concentrate shifted toward the direction between negative DeltaC* and positive DeltaL*, indicating the color became slightly paler. A color difference seems to exist between the two containers, especially for the magnitude of DeltaE*; color changes were more pronounced in concentrates packed in plastic. There are significant changes (P < 0.05) in major carotenoid pigments (beta-carotene and lycopene) in the concentrates. More than 20% loss of lycopene and about 7% loss of beta-carotene occurred with plastic containers after a 12-month period. Regression analysis showed that the rate of decline was about 0.291 ppm per month (r = 0.990) for lycopene compared to 0.045 ppm (r = 0.817) for beta-carotene in concentrate stored in plastic. In the metal can, the same trends were observed but pigment losses were slightly smaller than those with plastic. An estimated shelf life for lycopene was 26.1 months in the metal can compared to 18 months in plastic. Shelf life for beta-carotene was more than 39 months, more than twice that of lycopene in plastic container.     

Determination of vanillin in orange, grapefruit, tangerine, lemon, and lime juices using GC-olfactometry and GC-MS/MS

The presence of vanillin in orange, tangerine, lemon, lime, and grapefruit juices has been identified and confirmed using high-resolution GC retention index values, mass spectra, and aroma quality. The impact of vanillin on the flavor score for grapefruit juice is discussed and reported to be minimal. Vanillin concentrations are determined to be in the low parts-per-million range for the various citrus juices. The calculated concentrations in the orange, tangerine, lemon, lime, and grapefruit juices are 0.20, 0.35, 0.41, 0.35, and 0.60 ppm, respectively. Pasteurization produced an average 15% increase in the concentration of vanillin in grapefruit juices. Vanillin did not correlate well with the overall flavor score despite a rather intense signal using OSME gas chromatography-olfactometry software.     

Orange, mandarin, and hybrid classification using multivariate statistics based on carotenoid profiles

A study was undertaken to differentiate citrus on the basis of a carotenoid profile obtained from the HPLC determination of 12 carotenoids found in saponified fresh juice. Mandarin, orange, and various hybrid varieties were analyzed to determine their carotenoid profiles. The resulting peak areas were analyzed using principal component analysis (PCA), canonical discriminate analysis (CDA), and Mahalanobis distances. These were used to develop models for classifying the juices into appropriate groups. Thirty-two samples were analyzed to determine classification techniques. Mandarin and orange juices were quite distinct, with the hybrids scattered throughout the mandarin and orange clusters using PCA. CDA resulted in three distinct groups with only a few of the hybrids in the orange grouping.     

Distribution of various peptides in citrus fruits (grapefruit, lemon, and orange)

Tissue- and species-specific peptides of the grapefruit have been investigated by SDS-PAGE and Western blot. Five peptides from the juice and one peptide from the peel were isolated by preparative gel electrophoresis. Polyclonal antibodies were developed against them in mice. It can be established that 82, 63, and 46 kDa peptides occurred exclusively in the samples prepared from the grapefruit and the lemon juice, whereas in the orange juice, only the 82 kDa peptide could be detected. The 31 kDa peptide is characteristic for the peel samples of grapefruit and lemon. The 210 kDa peptide did not show any specificity. A 117 kDa peptide appeared in the juice and peel of grapefruit and in the peel of lemon but not in the orange. From the data of this study, it is supposed that some of the polyclonal antibodies developed against characteristic juice and peel peptides can be used to test commercial grapefruit juice products for adulteration.     

Fresh Israeli Jaffa blond (Shamouti) orange and Israeli Jaffa red Star Ruby (Sunrise) grapefruit juices affect plasma lipid metabolism and antioxidant capacity in rats fed added cholesterol

The bioactivity of Israeli Jaffa blond (Shamouti) fresh orange and Israeli Jaffa red Star Ruby (Sunrise) grapefruit juices was investigated in vitro and in vivo. The contents of bioactive compounds of these juices were determined. The influence of bioactive compounds on plasma lipids and plasma antioxidant activity in rats fed cholesterol-containing and cholesterol-free diets was assessed. Significant differences in the contents of dietary fibers were not found. The contents of total polyphenols, flavonoids, and anthocyanins in fresh orange and grapefruit juices were 962.1 +/- 27.2 and 906.9 +/- 27.1; 50.1 +/- 3.3 and 44.8 +/- 3.2; and 69.9 +/- 5.6 and 68.7 +/- 5.5 microg/mL, respectively. The antioxidant potential measured by the scavenging activity against nitric oxide, the beta-carotene-linoleate model system (beta-carotene), and the 1,1-diphenyl-2-picrylhydrazyl and 2,2'-azino-bis(3-ethyl-benzothiazoline-6-sulfonic acid) diamonium salt assays was higher in orange juice but not significantly. A high level of correlation between contents of total polyphenols and flavonoids and antioxidant potential values of both juices was found. Diets supplemented with orange and to a lesser degree with grapefruit juices improved plasma lipid metabolism only in rats fed added cholesterol. However, an increase in the plasma antioxidant activity was observed in both groups. In conclusion, fresh orange and grapefruit juices contain high quantities of bioactive compounds, which guarantee their high antioxidant potential, and the positive influence on plasma lipid metabolism and plasma antioxidant activity could make fresh orange and grapefruit juices a valuable supplement for disease-preventing diets.     

Variation of flavonoids and furanocoumarins in grapefruit juices: a potential source of variability in grapefruit juice-drug interaction studies

Grapefruit juice (GFJ) has been found to interact with several medications, increasing their oral bioavailability and the risk of toxicity. Inhibition of CYP3A4 in the small intestine by flavonoids (such as naringin and naringenin) and furanocoumarins (including bergamottin and 6',7'-dihydroxybergamottin) present in GFJ seems to be the predominant mechanism, although P-glycoprotein and influx transporters in the small intestine are also involved. The quantity of interactive compounds ingested may affect the magnitude and mechanism of the food-drug interaction. Therefore, these four compounds were quantified by HPLC analysis in commercially available and fresh-squeezed GFJ and in grapefruit tissues. Considerable variability in naringin (174-1492 micromol/L), bergamottin (1.0-36.6 micromol/L), and 6',7'-dihydroxybergamottin (0.22-52.5 micromol/L) was observed, whereas naringenin could not be detected. White grapefruit showed higher concentrations of naringin and furanocoumarins located in the albedo and flavedo compared with red varieties. Findings from this study suggest considering concentrations of components with a potential for drug interactions in GFJ-drug interaction studies. The concentration of potentially contributing compounds may crucially influence the magnitude of observed interaction and impair direct comparison of studies in which different juices have been used.     

Betaines in fruits of Citrus genus plants

Numerous compounds, many of them osmolytes, were quantified in natural juices and in frozen concentrate juices from fruits of plants of the Citrus genus. L-proline, N-methyl-L-proline (hygric acid), N,N-dimethyl-L-proline (stachydrine), 4-hydroxy-L-prolinebetaine (betonicine), 4-hydroxy-L-proline, γ-aminobutyric acid (Gaba), 3-carboxypropyltrimethylammonium (GabaBet), N-methylnicotinic acid (trigonelline), and choline in the fruit juices of yellow orange, blood orange, lemon, mandarin, bitter orange (Citrus aurantium), chinotto (Citrus myrtifolia), and grapefruit were analyzed by sensitive HPLC-ESI-tandem mass spectrometry procedure. It was found that the most represented osmolytes in the juices, that is, L-proline, stachydrine, and betonicine, can be quantified with minimal sample preparation and short analysis time (about 1 min) also by flow injection analysis (FIA) ESI-MS/MS with the same results as obtained by HPLC ESI-MS/MS. In all of the juices, discrete amounts of choline and trigonelline were present. Conversely, GabaBet was always below detection limits. Notably, N-methyl-L-proline and 4-hydroxy-L-prolinebetaine, which were discovered for the first time in the juice of bergamot (Citrus bergamia Risso et Poit), are also present in all of the citrus juices examined.     

Changes in plasma lipid and antioxidant activity in rats as a result of naringin and red grapefruit supplementation

The aim of this investigation was to compare the influence of naringin versus red grapefruit juice on plasma lipid levels and plasma antioxidant activity in rats fed cholesterol-containing and cholesterol-free diets. The antioxidant activity of a correlated quantity of red grapefruit juice was higher than that of naringin. Forty-two male Wistar rats were randomly divided into six groups of 7 named control, naringin, grapefruit, Chol, Chol/naringin, and Chol/grapefruit. The rats of the control group were fed basal diet (BD) and 1-2 mL of distilled water. To the BD of the other five groups were added 0.46-0.92 mg of naringin dissolved in 1-2 mL of distilled water (naringin), 1-2 mL of red grapefruit juice (grapefruit), 1% of nonoxidized cholesterol (NOC) and 1-2 mL of distilled water (Chol), 1% of NOC and 0.46-0.92 mg of naringin in 1-2 mL of water (Chol/naringin), and 1% of NOC and 1-2 mL of red grapefruit juice (Chol/grapefruit). After 30 days of different feeding, it was found that diets supplemented with red grapefruit juice and to a lesser degree with naringin improved the plasma lipid levels mainly in rats fed cholesterol and increased the plasma antioxidant activity. In conclusion, naringin is a powerful plasma lipid lowering and plasma antioxidant activity increasing flavonone. However, fresh red grapefruit is preferable than naringin: it more effectively influences plasma lipid levels and plasma antioxidant activity and, therefore, could be used as a valuable supplement for disease-preventing diets.     

Total oxidant scavenging capacities of common European fruit and vegetable juices

The total oxidant scavenging capacity (TOSC) assay in a modified and automated version was applied for a comparative and detailed survey of the antioxidant capacities of 14 common European fruit and vegetable juices (ACE, apple, beetroot, blueberry, carrot, elderberry, lemon, lingonberry, multivitamin, orange, pink grapefruit, sauerkraut, and tomato juices as well as sour cherry nectar). The juices were ranked according to their scavenging capacity against the three reactive oxygen species (ROS) peroxyl and hydroxyl radicals and peroxynitrite. These ROS are of physiological and technological relevance and cover a broad range of reactivity. Nonlinear correlations between concentrations of all studied samples and antioxidant capacity were taken into account for the assessment of the results. Due to the more complex assay design, results are only partially in accordance with those of the literature. Because of its outstanding TOSC values against two of the three ROS, lingonberry juice deserves special attention.     

Chemometric characterization of fruit juices from Spanish cultivars according to their phenolic compound contents: I. Citrus fruits

The data set composed by phenolic compound profiles of 83 Citrus juices (determined by HPLC-DAD-MS/MS) was evaluated by chemometrics to differentiate them according to Citrus species (sweet orange, tangerine, lemon, and grapefruit). Cluster analysis (CA) and principal component analysis (PCA) showed natural sample grouping among Citrus species and even the Citrus subclass. Most of the information contained in the full data set can be captured if only 15 phenolic compounds (concentration ≥10 mg/L), which can be quantified with fast and accurate methods in real samples, are introduced in the models; a good classification which allows the confirmation of the authenticity of juices is achieved by linear discriminant analysis. Using this reduced data set, fast and routine methods have been developed for predicting the percentage of grapefruit in adulterated sweet orange juices using principal component regression (PCR) and partial least-squares regression (PLS). The PLS model has provided suitable estimation errors.     

Grapefruit juices impair the bioaccessibility of β-carotene from orange-fleshed sweet potato but not its intestinal uptake by Caco-2 cells

Among various factors influencing β-carotene (Bc) bioavailability, information on interactions between carotenoids or other micronutrients such as flavonoids during a meal that contains different plant-derived foods is quite limited. Because orange-fleshed sweet potato (OFSP) is an important Bc-rich staple food, a source of vitamin A in developing countries, this study focused on the effect of citrus fruit juice carotenoids and flavonoids on Bc bioaccessibility from OFSP. In vitro digestion coupled with the Caco-2 cell culture model was used to evaluate the bioaccessibility and cellular uptake of Bc from OFSP in the presence of pink grapefruit (pGF) or white grapefruit (wGF) juices. The addition of grapefruit juices significantly decreased the bioaccessibility, by up to 30%, but not the cellular uptake of Bc from boiled OFSP. Lycopene, but more probably naringin, present in grapefruit juices was suspected to be responsible for the inhibitory effect of the citrus juices on Bc bioaccessibility. This inhibition was apparently due in part to competition for incorporation between Bc and naringin into mixed micelles during in vitro digestion. In contrast, Bc uptake from dietary micelles was not impaired by naringin.     

Organic vs conventionally grown Rio Red whole grapefruit and juice: comparison of production inputs, market quality, consumer acceptance, and human health-bioactive compounds

Most claims that organic produce is better tasting and more nutritious than nonorganic (conventional) produce are largely unsubstantiated. This is due mainly to a lack of rigor in research studies matching common production variables of both production systems, such as microclimate, soil type, fertilizer elemental concentration, previous crop, irrigation source and application, plant age, and cultivar. The aforementioned production variables common to both production systems were matched for comparison of Texas commercially grown conventional and certified organic Rio Red red-fruited grapefruit. Whole grapefruits from each production system were harvested between 800 and 1000 h at commercial early (November), mid- (January), and late season (March) harvest periods for three consecutive years. Within each harvest season, conventional and organic whole fruits were compared for marketable qualities (fruit weight, specific gravity, peel thickness, and peel color), and juices were compared for marketable qualities (specific gravity, % juice, and color), human health-bioactive compounds (minerals, ascorbic acid, lycopene, sugars, pectin, phenols, and nitrates), and consumer taste intensity and overall acceptance. Conventional fruit was better colored and higher in lycopene, and the juice was less tart, lower in the bitter principle naringin, and better accepted by the consumer panel than the organic fruit. Organic fruit had a commercially preferred thinner peel, and the juice was higher in ascorbic acid and sugars and lower in nitrate and the drug interactive furanocoumarins.     

Characterization of the most odor-active volatiles in fresh, hand-squeezed juice of grapefruit (Citrus paradisi Macfayden)

By application of the aroma extract dilution analysis on an extract prepared from fresh grapefruit juice, 37 odor-active compounds were detected in the flavor dilution (FD) factor range of 4-256 and subsequently identified. Among them the highest odor activities (FD factors) were determined for ethyl butanoate, p-1-menthene-8-thiol, (Z)-3-hexenal, 4,5-epoxy-(E)-2-decenal, 4-mercapto-4-methylpentane-2-one, 1-heptene-3-one, and wine lactone. Besides the 5 last mentioned compounds, a total of 13 further odorants were identified for the first time as flavor constituents of grapefruit. The data confirmed results of the literature on the significant contribution of 1-p-menthene-8-thiol in grapefruit aroma but clearly showed that a certain number of further odorants are necessary to elicit the typical grapefruit flavor.     

Multielement analysis of argentinean lemon juices by instrumental neutronic activation analysis and their classification according to geographical origin

Multielement analysis of lemon juices from different Argentinean regions was carried out by instrumental neutronic activation analysis (INAA) with the aim at developing a reliable method in the traceability of the origin of lemon juices. This work presents a characterization of 44 lemon juice samples selected from three different geographical origins in the Northwest region of Argentina. Multivariate chemometric techniques such principal component analysis and lineal discriminant analysis (LDA) were used with the aim of classifying the juices and identifying the most significant parameters. Eleven elements were determined (Br, As, Na, Rb, La, Cr, Sc, Fe, Co, Zn, and Sb). The analytical method was validated by analyzing the standard reference material IAEA V-10 (hay powder); the results are within +/-10% of the reported values for the majority of the elements. Biplots of LDA scores for the INAA data illustrate clear separation between each sample.