Search

In citrus juices pectin is one of the major components of the suspended cloud material that imparts desirable appearance, texture and flavor. Citrus pectin is a structurally diverse polysaccharide with a backbone of α-(1,4)-galacturonic acid (GalA) residues, a variable proportion of which may be methylesterified, and interspersed with regions containing repeating rhamnogalacturonan dimers. We have acid extracted pectin from commercial Frozen Concentrated Orange Juice (FCOJ) and assessed its macromolecular properties, including soluble sugar composition and molecular weight as well as its degree (DM) and pattern (DB, DBabs) of methyl-esterification. The extracted material was composed mainly of polysaccharides (82%) dominated by galacturonic acid (39.2%), arabinose (13.2%) and galactose (25.6%). Protein accounted for approximately 4% of the extracted material and included arabinogalactan protein (AGP). The Number Average Molecular Weight (M n ) of the extracted material as determined by MALLS-SEC was estimated at 1.462 × 106 Da indicating the presence of aggregates. The pectin DM was relatively high at 74.7% with very few contiguous demethylesterified GalA residues (DB = 15.92, DBabs = 4.03). Treatment with various pectinolytic, hemicellulytic, or proteolytic enzymes allowed us to evaluate the contribution of various structural domains to the macrostructural architecture of the extracted material. Various enzyme treatments of the extract produced of a second, lower M n peak and a loss of material in the larger M n peak. The M n varied according to the enzymatic digestion method employed, from 1.5 × 106 Da for the parent material, to 1.4 × 103 Da when treated with Rapidase Adex-P. [ABSTRACT FROM AUTHOR]

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. Published 2013. This article is a U.S. Government work and is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

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 āere (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 āere 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 āere 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 āere 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. [ABSTRACT FROM AUTHOR]

Abstract: Non-calcium sensitive pectin (NCSP), with a 94% degree of methylation (DM) was demethylated at pH 4.5 and 7.5 using monocomponent citrus salt-independent pectin methylesterase (PME). In a companion publication [Cameron, R. G., Luzio, G. A., Goodner, K., & Williams, M. A. K. (2008). Demethylation of a model homogalacturonan with the salt-independent pectin methylesterase from citrus: I. Effect of pH on demethylated block size and distribution. Carbohydrate Polymers], average demethylated blocks size (), average number of demethylated blocks per molecule () and enzyme mode of action were characterized for a series of pectins using a limited digest with endo-polygalacturonase (EPG) to release demethylated blocks (DMBs) from each demethylated pectin. Rheology and calcium sensitivity measurements, on the same series of pectins, are presented herein to relate and values to functional properties. For the pH 4.5 – 50% DM sample with an excised and , greater than 95% of the molecules appeared to be crosslinked with calcium ion and a storage modulus (G′) value of 7.31Pa was observed. For the pH 4.5 – 70% DM. The data indicated that for the pH 7.5 series, block number could be a limiting factor. The excised block size for the pH 7.5–60% DM sample was comparatively large at 12.2 compared to the pH 4.5 series. In contrast, block number of at least 2.0 appeared to be required before a significant level of calcium sensitivity was observed in the pH 7.5 series. Mixing the pH 4.5 – 70% DM sample with narrow-range size-classes of oligogalacturonic acids (OGalA) showed that small galacturonic acid oligomers with a degree of polymerization (DP) less than 13 could lower yield point (YP) and affect gelation, suggesting that even small excised DMBs need to be considered when relating pectin block size to functional properties. [Copyright &y& Elsevier]

Abstract: A model homogalacturonan (HG) was used to produce a demethylated series by reacting it with a citrus salt-independent pectin methylesterase (PME) at pH 4.5 and 7.5. HGs with a predicted degree of methylesterification (DM) of 90%, 80%, 70%, 60% and 50% were produced. HG structural properties and PME mode of action were probed by performing a limited digest with an endo-polygalacturonase. Liberated demethylated blocks (DMB) were separated and quantified by HPAEC coupled to an evaporative light scattering detector. A significant increase in maximum and average size of released DMBs was observed between 80% and 70% DM at pH 7.5 and between 70% and 60% at pH 4.5. The observed distribution of fragment lengths was compared to theoretical modeled distributions. A multiple-attack mechanism with a degree of processivity (p) of p =1 at pH 4.5 and p =10 at pH 7.5 modeled the observed shorter fragments well, while in all cases the amount of larger fragments detected was more successfully described by a single-chain mechanism. [Copyright &y& Elsevier]

One of the four pectin methylesterase types isolated from Citrus sinensis var. Valencia fruit was used to demethylesterify a model homogalacturonan (HG) to 30%, 50% and 70% degree of methylesterification (DM) at pH 4.5 and 7.0, respectively. Introduced demethylesterified blocks (DMBs) were released by a limited endo-polygalacturonase (EPG) digestion, separated and quantified by HPAEC. Average DMB size ( B S ¯ ) and number of such blocks per molecule ( B N ¯ ) differed depending on final DM and reaction pH ( P < 0.05). B S ¯ and B N ¯ were significantly higher in 30% DM HG than 50 and 70 DMs. pH 4.5 series showed significantly larger B S ¯ compared to pH 7.5 series ( P < 0.01). Distribution of DMBs released by limited EPG digest was predicted by mathematical modeling and in silico modeled processive (degree of processivity = 10), multiple attack mode of action best explains the experimental block distributions. Absolute degree of blockiness (DB abs ) obtained from exhaustive EPG digestions, displayed a linear relationship with DM regardless of reaction pH (P < 0.001). Significant correlation coefficients between B S ¯ , B N ¯ , DB abs , and DM manifested the effectiveness of the block information gained from both EPG digestion to estimate DMB distribution pattern (P < 0.05). However, comparison of block distribution information of three isozymes revealed that difference in block pattern could be manifested by parameters from limited EPG digest ( B S ¯ , B N ¯ ) but not by those from exhaustive digest (DB/DB abs ). The results suggested the possibility to control B S ¯ and to customize specific population of demethylesterified pectin molecules using PME isozymes from Valencia orange. [ABSTRACT FROM AUTHOR]

Abstract: Pectin comprises one of the major components of cloud material in citrus juices. Juice cloud is a complex mixture of polysaccharides, proteins and lower molecular weight compounds that are responsible for the turbid appearance of citrus juices. The stability of juice cloud depends on a number of factors, including pectin degree of methylation (DM) and the availability of sufficiently-sized, charged demethylated blocks, but detailed information on the precise relationship between cloud state and pectin architecture is limited. To address this gap, we have systematically treated commercial frozen concentrated orange juice (FCOJ) with pectin methylesterases extracted from orange pulp cells to mimic the aggregation of pectin that naturally occurs in the presence of calcium in unpasteurized or under pasteurized juice. We then assessed the pectin structural and functional properties, including juice optical density (OD) and soluble sugar composition, DM, degree of blockiness (DB), degree of absolute blockiness (DBabs) and rheological capacity from juice in various states of cloud loss. A strong positive correlation ([r] = 0.916) was observed between juice OD and DM, while a strong negative correlation ([r] = −0.914) was observed between OD and DBabs. Most critically, a reduction of average DM from 74.7% to 68.3% in the course of cloud loss resulted in the formation of rheologically active pectin. [Copyright &y& Elsevier]

We explored the possibility of controlling charge distribution in the homogalacturonan regions of pectin to produce a population of demethylesterified molecules with desirable functional properties by utilizing consecutive treatments with pectin methylesterases (PME) having different modes of action. A fungal PME from Aspergillus aculeatus ( Aa -PME), with a pseudo-random mode of action, was used to demethylesterify a extremely high methylesterified HG (DM 94%, average degree of polymerization 246) by reducing the degree of methylesterification (DM) from 94% to either 70% or 80%. A second demethylesterification step, to 50% DM, was performed using a processive PME from Carica papaya ( CpL -PME). Introduced demethylesterified blocks were released either by exhaustive or limited endo polygalacturonase (EPG) digestion. Degree of blockiness (DB), absolute degree of blockiness (DB abs ), average demethylesterified block size ( B S ¯ ) and number of average sized demethylesterified blocks per molecule ( B N ¯ ) were estimated. B S ¯ and B N ¯ as well as DB/DB abs differed depending on the initial DM reduction by Aa PME, the number of activity units of CpL PME used and the reaction pH ( P < 0.05). Consecutive demethylesterification of HG by AaPME to 80% DM and then by CpL PME to 50% DM at pH 4.5 produced significantly longer oligomer blocks compared to Aa-PME demethylesterification to 70% DM followed by CpL -PME to 50% DM at pH 7.0. Limited EPG digestion released nearly intact demethylesterified blocks and the released oligomers were coupled with in silico modeling. Resulting oligomer distribution corresponded to the in silico mode of action representing contiguous demethylesterification of 10 GalA residues rather than that of random or complete block-wise demethylesterification. Calcium-mediated gels of the modified HGs displayed G′ higher than G″ values and both moduli differed significantly according to the amount of CpL PME applied even though their final DMs were identical. These results suggest the possibility of controlling B S ¯ and engineering a population of demethylesterified pectin molecules with specified demethylesterified B S ¯ and functional properties. [ABSTRACT FROM AUTHOR]

Abstract: An acidic plant pectin methylesterase from Ficus awkeotsang achenes (FaPME) was used to demethylesterify a model homogalacturonan (HG) at pH 4.5 and 7.5. Introduced demethylesterified blocks (DMBs) were released by a limited endo-polygalacturonase (EPG) digestion, separated and quantified by HPAEC. The average DMB size and number of such blocks per molecule differed depending on the degree of methylesterification (DM) and reaction pH (P < 0.05). Significant increases in and were observed in HGs of 30% DM compared to higher DMs. HGs demethylesterified to 30% and 50% DM at pH 4.5 showed significantly larger compared to pH 7.5. Absolute degree of blockiness (DBabs), obtained using exhaustive EPG digestions, displayed a linear relationship with the DM regardless of reaction pH (P < 0.001). The distribution of DMBs released by the limited EPG digest was predicted by mathematical modeling and compared with the experimental results. The in silico modeled enzyme mode of action suggested that a random, multiple chain, non-processive mode of action best explains the distributions of small blocks and a processive multiple attack mechanism best explains the distributions of longer blocks. Decreasing the DM of the HGs by the FaPME increased the G′ and G″ of calcium-mediated gels. Pearson's correlation displayed significant correlation coefficients between , , DBabs, DM, and G′. The results suggest the possibility to control and to produce a uniform population of demethylesterified pectin molecules, particularly in acidic environments where most basic plant PMEs are less active. [Copyright &y& Elsevier]

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. Published 2013. This article is a U.S. Government work and is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

Abstract: A Carica papaya pectin methylesterase (CpL-PME) present in a commercial papain preparation was used to modify the amount and distribution of anionic charge in a population of a model pectic homogalacturonan (HG) at pH 4.5 and pH 7.5. Introduced negatively charged demethylesterified blocks (DMB) were excised as oligomers with limited endo-polygalacturonase (EPG) digestion, and then separated and quantified by high performance anion exchange chromatography. Exhaustive EPG digestion was also performed and the concentrations of mono-, di- and tri-galacturonic acid (GalA) produced were estimated. The CpL-PME mode of action was modeled while the HG population's nanostructure and the resulting functionality of the modified pectin were characterized. The results indicated that average DMB size and number of these “average” blocks per molecule increased as the overall degree of methylesterification (DM) decreased by CpL-PME treatment (P < 0.05). Average DMB size differed depending on the reaction pH at each DM. Absolute degree of blockiness (DBabs) increased as DM decreased and demonstrated a linear relationship with the DM at both reaction pH values. Significant positive correlations between DBabs and average DMB size were observed for both pH series (P < 0.05). The enzyme mode of action, modeled in silico, demonstrates a processive multiple attack mechanism. Functionally, the storage modulus of ionotropic gels formed from the processed substrates increased as DM decreased, and as DBabs and average DMB size increased with highly significant correlations (P < 0.001). These results indicate it is feasible to engineer pectin nanostructure and functionality with CpL-PME. [Copyright &y& Elsevier]

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. Copyright © 2012 Society of Chemical Industry [ABSTRACT FROM AUTHOR]