Changes in Volatile and Non-Volatile Flavor Chemicals of "Valencia" Orange Juice over the Harvest Seasons.

Florida "Valencia" oranges have a wide harvest window, covering four months after first reaching the commercial maturity. However, the influence of harvest time on juice flavor chemicals is not well documented, with the exception of sugars and acids. Therefore, we investigated the major flavor chemicals, volatile (aroma), non-volatile (taste) and mouth feel attributes, in the two harvest seasons (March to June in 2007 and February to May in 2012). Bitter limonoid compounds, limonin and nomilin, decreased gradually. Out of a total of 94 volatiles, 32 increased, 47 peaked mid to late season, and 15 decreased. Juice insoluble solids and pectin content increased over the season; however, pectin methylesterase activity remained unchanged. Fruit harvested in the earlier months had lower flavor quality. Juice from later harvests had a higher sugar/acid ratio with less bitterness, while, many important aroma compounds occurred at the highest concentrations in the middle to late season, but occurred at lower concentrations at the end of the season. The results provide information to the orange juice processing industry for selection of optimal harvest time and for setting of precise blending strategy.

Formation of Stylet Sheaths in aere (in air) from eight species of phytophagous hemipterans from six families (Suborders: Auchenorrhyncha and Sternorrhyncha).

Stylet sheath formation is a common feature among phytophagous hemipterans. These sheaths are considered essential to promote a successful feeding event. Stylet sheath compositions are largely unknown and their mode of solidification remains to be elucidated. This report demonstrates the formation and solidification of in aere (in air) produced stylet sheaths by six hemipteran families: Diaphorina citri (Psyllidae, Asian citrus psyllid), Aphis nerii (Aphididae, oleander/milkweed aphid), Toxoptera citricida (Aphididae, brown citrus aphid), Aphis gossypii (Aphididae, cotton melon aphid), Bemisia tabaci biotype B (Aleyrodidae, whitefly), Homalodisca vitripennis (Cicadellidae, glassy-winged sharpshooter), Ferrisia virgata (Pseudococcidae, striped mealybug), and Protopulvinaria pyriformis (Coccidae, pyriform scale). Examination of in aere produced stylet sheaths by confocal and scanning electron microscopy shows a common morphology of an initial flange laid down on the surface of the membrane followed by continuous hollow core structures with sequentially stacked hardened bulbous droplets. Single and multi-branched sheaths were common, whereas mealybug and scale insects typically produced multi-branched sheaths. Micrographs of the in aere formed flanges indicate flange sealing upon stylet bundle extraction in D. citri and the aphids, while the B. tabaci whitefly and H. vitripennis glassy-winged sharpshooter flanges remain unsealed. Structural similarity of in aere sheaths are apparent in stylet sheaths formed in planta, in artificial diets, or in water. The use of 'Solvy', a dissolvable membrane, for intact stylet sheath isolation is reported. These observations illustrate for the first time this mode of stylet sheath synthesis adding to the understanding of stylet sheath formation in phytophagous hemipterans and providing tools for future use in structural and compositional analysis.

Determination of degree of methylation of food pectins by chromatography.

BACKGROUND: In Florida, 90% of citrus is processed into juice, leaving large amounts of peel waste that could be processed into food ingredients such as pectins for other applications. Pectins of low degree of methylation (DM < 50) have important functional properties for use in foods and pharmaceuticals. Thus determination of DM is important, but DM analyses are difficult to perform and assays can have interference due to the presence of salts or neutral sugars. RESULTS: A chromatography method has been developed for determination of DM of food pectin using alkaline hydrolysis followed by pectin digestion with a commercial pectinase. Analysis was performed by ion exclusion chromatography (IEC) to obtain methanol (MeOH) concentrations and by anion exchange chromatography (AEC) to obtain galacturonic acid (GalA) concentrations. Data were compared with values obtained using other DM analysis procedures. For example, a 55-75 DM pectin assayed as 55.5, 59.6, 60.1 and 57.0 DM by IEC, AEC, colorimetric and conductivity detection methods respectively. CONCLUSION: The chromatography procedure described in this paper provides an alternative method for determination of DM of food pectins for accurate and efficient analysis when confronted with limited quantities or large numbers of samples.

Effect of extraction, pasteurization and cold storage on flavonoids and other secondary metabolites in fresh orange juice.

BACKGROUND: Fresh orange juice is perceived to be more wholesome than processed juice. Fresh juice may have nutrients and phytonutrients that differ from pasteurized or processed juice. RESULTS: 'Hamlin' and 'Valencia' oranges were extracted using a commercial food service juicer, pasteurized or not, resulting in fresh-commercial juice (FCJ) or pasteurized FCJ (FCPJ) for comparison with pasteurized processed juice (PPJ) in 2009, and gently hand-squeezed 'Valencia' juice (HSJ) in 2010 for nutrient and phytonutrient content. Regardless of pasteurization, FCJ/FCPJ contained 25-49% lower insoluble solids than the PPJ, while in HSJ the insoluble solids content was between that of FCJ and PPJ. The major orange juice flavonoid glycosides were twofold higher in PPJ than in FCJ/FCPJ and HSJ, indicating that the extraction and finishing process led to more peel tissue in the juice than fresh juice extraction methods. The total phenolic content (TPC) in the juices followed a similar pattern to the flavonoid glycoside content. The polymethoxylated flavones (PMFs), associated with peel oil, occurred at the highest levels in the FCJ/FCPJ and lowest in HSJ. Limonoids and alkaloids occurred at higher levels in PPJ and HSJ than in FCJ/FCPJ. CONCLUSION: The high peel oil content of FCJ/FCPJ resulted in higher PMF levels compared to PPJ and HSJ, while flavonoid glycosides, limonoids and alkaloids, which occur at high concentrations in the inner peel albedo, occurred at higher concentrations in PPJ.

Effect of extraction method on quality of orange juice: hand-squeezed, commercial-fresh squeezed and processed.

BACKGROUND: Fresh orange juice is perceived to be more wholesome than processed juice. Fresh juice may have flavor and nutrients that differ from pasteurized or processed juice. RESULTS: 'Hamlin' and 'Valencia' oranges were extracted using a commercial food service juicer, pasteurized or not, resulting in fresh-commercial juice (FCJ) or pasteurized juice (FCPJ) for comparison with pasteurized processed juice (PPJ) in 2009, and gently hand-squeezed 'Valencia' juice (HSJ) in 2010 for quality attributes. There was higher peel oil, lower pectin content, and less cloud loss in FCJ/FCPJ compared to PPJ and HSJ regardless of pasteurization. Titratable acidity was generally higher and the ratio of solids to acids lower in FCJ/FCPJ or HSJ compared to PPJ. FCJ/FCPJ had generally higher levels of most aroma volatiles than did PPJ and, overall, the highest esters and terpenes, while methanol and ethanol levels were highest in HSJ. For sensory evaluation, FCJ/FCPJ had more peel oil and PPJ more cooked flavor than other samples, while 'Valencia' HSJ was preferred over the other juices. CONCLUSION: High peel oil content and thermo-pasteurization process decreased cloud loss of orange juice. Extraction and finishing processes rather than pasteurization or oil content were major factors in influencing orange juice flavor quality.

Enzymatic modification of a model homogalacturonan with the thermally tolerant pectin methylesterase from Citrus: 1. Nanostructural characterization, enzyme mode of action, and effect of pH.

Methyl ester distribution in pectin homogalacturonan has a major influence on functionality. Enzymatic engineering of the pectin nanostructure for tailoring functionality can expand the role of pectin as a food-formulating agent and the use of in situ modification in prepared foods. We report on the mode of action of a unique citrus thermally tolerant pectin methylesterase (TT-PME) and the nanostructural modifications that it produces. The enzyme was used to produce a controlled demethylesterification series from a model homogalacturonan. Oligogalacturonides released from the resulting demethylesterified blocks introduced by TT-PME using a limited endopolygalacturonase digestion were separated and quantified by high-pressure anion-exchange chromatography (HPAEC) coupled to an evaporative light-scattering detector (ELSD). The results were consistent with the predictions of a numerical simulation, which assumed a multiple-attack mechanism and a degree of processivity ∼10, at both pH 4.5 and 7.5. The average demethylesterified block size (0.6-2.8 nm) and number of average-sized blocks per molecule (0.8-1.9) differed, depending upon pH of the enzyme treatment. The mode of action of this enzyme and consequent nanostructural modifications of pectin differ from a previously characterized citrus salt-independent pectin methylesterase (SI-PME).

Effect of liberibacter infection (huanglongbing disease) of citrus on orange fruit physiology and fruit/fruit juice quality: chemical and physical analyses.

More than 90% of oranges in Florida are processed, and since Huanglongbing (HLB) disease has been rumored to affect fruit flavor, chemical and physical analyses were conducted on fruit and juice from healthy (Las -) and diseased (Las +) trees on three juice processing varieties over two seasons, and in some cases several harvests. Fruit, both asymptomatic and symptomatic for the disease, were used, and fresh squeezed and processed/pasteurized juices were evaluated. Fruit and juice characteristics measured included color, size, solids, acids, sugars, aroma volatiles, ascorbic acid, secondary metabolites, pectin, pectin-demethylating enzymes, and juice cloud. Results showed that asymptomatic fruit from symptomatic trees were similar to healthy fruit for many of the quality factors measured, but that juice from asymptomatic and especially symptomatic fruits were often higher in the bitter compounds limonin and nomilin. However, values were generally below reported taste threshold levels, and only symptomatic fruit seemed likely to cause flavor problems. There was variation due to harvest date, which was often greater than that due to disease. It is likely that the detrimental flavor attributes of symptomatic fruit (which often drop off the tree) will be largely diluted in commercial juice blends that include juice from fruit of several varieties, locations, and seasons.

Total antioxidant activity and fiber content of select Florida-grown tropical fruits.

Fourteen tropical fruits from south Florida (red guava, white guava, carambola, red pitaya (red dragon), white pitaya (white dragon), mamey sapote, sapodilla, lychee, longan, green mango, ripe mango, green papaya, and ripe papaya) were evaluated for antioxidant activity, total soluble phenolics (TSP), total ascorbic acid (TAA), total dietary fiber (TDF), and pectin. ORAC (oxygen radical absorbance capacity) and DPPH (1,1-diphenyl-2-picrylhydrazyl, radical scavenging activity) assays were used to determine antioxidant activity. The TSP, ORAC, and DPPH ranged from 205.4 to 2316.7 g gallic acid equiv/g puree, <0.1 to 16.7 micromol Trolox equiv/g puree, and 2.1 to 620.2 microg gallic acid equiv/g puree, respectively. The TAA, TDF, and pectin ranged from 7.5 to 188.8 mg/100 g, 0.9 to 7.2 g/100 g, and 0.20 to 1.04 g/100 g, respectively. The antioxidant activities, TSP, TAA, TDF, and pectin were influenced by cultivar (papaya, guava, and dragon fruit) and ripening stage (papaya and/or mango). Antioxidant activity showed high correlations with levels of TSP compounds (r = 0.96) but low correlations with levels of ascorbic acid (r = 0.35 and 0.23 for ORAC and DPPH data, respectively). The antioxidant activities evaluated by both ORAC and DPPH showed similar trends where red guava and carambola exhibited the highest and sapodilla and green papaya exhibited the lowest levels. Guava and mamey sapote exhibited the highest TDF and pectin levels. Many of the tropical fruits were shown to contain an abundance of hydrolyzable tannins, ellagic acid conjugates, and flavone glycosides. Preliminary descriptions are given of the phenols in red/white pitaya (dragonfruit), lychee, and mamey sapote, these fruit being thus far uncharacterized in the literature.

Enzymatic modification of pectin to increase its calcium sensitivity while preserving its molecular weight.

A commercial high-methoxy citrus pectin was treated with a purified salt-independent pectin methylesterase (PME) isozyme isolated from Valencia orange peel to prepare a series of deesterified pectins. A series of alkali-deesterified pectins was also prepared at pH 10 under conditions permitting beta-elimination. Analysis of these pectins using high-performance size exclusion chromatography (HPSEC) with on-line multiangle laser light-scattering, differential viscometer, and refractive index (RI) detectors revealed no reduction in weight-average molecular weight (M(w); 150000) in the PME-treated pectin series, whereas a 16% reduction in intrinsic viscosity (IV) occurred below a degree of esterification (DE) of 47%. In contrast, alkali deesterification rapidly reduced both M(w) and IV to less than half of that observed for untreated pectin. PME treatment of a non-calcium-sensitive citrus pectin introduced calcium sensitivity with only a 6% reduction in the DE. Triad blocks of unesterified galacturonic acid were observed in (1)H nuclear magnetic resonance spectra of this calcium-sensitive pectin (CSP). These results demonstrate that the orange salt-independent PME isozyme utilizes a blockwise mode of action. This is the first report of the preparation of a CSP by PME treatment without significant loss of the pectin's M(w) due to depolymerization.