13 research outputs found
Validation and application of a standardized procedure for evaluating freshness of Citrus juices based on pectin methylesterase activity quantitation
A method developed for freshness authentication of freshly squeezed Citrus juices (FSCJ) was evaluated for routine application. It involved titrimetric assessment of pectin methylesterase (PE) activity after enzyme extraction from pulp-standardized juice samples. Standard test conditions enabled reliable discrimination between FSCJ and chilled Citrus juices that had comparative advantages due to extended shelf life. Unlike the latter, FSCJ always displayed PE activities in the linear range between the limit of identification (LOI, 0.42 units g-1 of juice) and the maximum activity found for FSCJ (1.94 units -1), equivalent to 0.0035-0.016 units during titration. However, for model samples having activities < LOI due to production by respective dilution of FSCJ, the responses abruptly fell to unspecific levels below the limit of detection (LOD, 0.21 units g-1). Accuracy was substantiated by 100 -106 % recovery for model juices with PE activities of 0.87 -1.22 units g-1 resulting from FSCJ dilution or PE standard addition, but it was lower (76 - 80 %) near LOI. The average of the mean activities, which were detected by 3 analysts with intraassay precision ≤ 8.4 %, varied with relative standard deviations of 8.2 % for FSCJ and 3.9 % for a sample of the same juice diluted to 60 % (w/w), thus proving reproducibility. FSCJ batches were unambiguously distinguished from four commercial chilled juices, because the activities detected for the latter were by far ≤ LOD and thus confirmed labeled mild preservation
Quantitative Determination of β-Carotene Stereoisomers in Fresh, Dried, and Solar-Dried Mangoes ( Mangifera indica
An Acetate–Hydroxide Gradient for the Quantitation of the Neutral Sugar and Uronic Acid Profile of Pectins by HPAEC-PAD without Postcolumn pH Adjustment
An
HPAEC-PAD method was developed and validated to quantitate seven neutral
sugars and two uronic acids of hydrolyzed pectic polysaccharides without
postcolumn pH adjustment. Due to a short gradient phase minimizing
the ion concentrations after equilibrating the CarboPac PA20 column
with sodium acetate and hydroxide, subsequent isocratic separation
of the neutral sugars was characterized by almost baseline resolution
of rhamnose and arabinose (1.45 ± 0.15) and xylose and mannose
(1.21 ± 0.02) at their maximal concentrations. Linearity was
shown (<i>R</i><sup>2</sup> = 0.9975–0.9998) for
the relevant ranges (0.28–30.3 μmol L<sup>–1</sup>; galacturonic acid, 1.7–128 μmol L<sup>–1</sup>) above the limits of detection (30–81 nmol L<sup>–1</sup>; galacturonic acid, 179 nmol L<sup>–1</sup>) and ∼3.8
times higher limits of quantification. Conformity of the findings
for four pectins after methanolysis plus hydrolysis in trifluoroacetic
acid with those of reference procedures (total uronic acids, 95–102%;
total neutral sugars, 97–105%) proved the accuracy
Effects of Thermal Treatments and Storage on Pectin Methylesterase and Peroxidase Activity in Freshly Squeezed Orange Juice
Occurrence of Alk(en)ylresorcinols in the Fruits of Two Mango (Mangifera indica L.) Cultivars during On-Tree Maturation and Postharvest Storage
Regarding
their relevance for the fungal resistance of mangoes
in long supply chains, the alk(en)ylresorcinols (AR) were quantitated
in peel and mesocarp throughout storage (27 days, 14 °C, ethylene
absorption). The 12 ‘Chok Anan’ and 11 ‘Nam Dokmai
#4’ lots picked between 83 and 115 days after full bloom (DAFB)
had different harvest maturity indices. The development of dry matter
and fruit growth indicated physiological maturity ∼100 DAFB.
During storage, all fruits ripened slowly, mostly until over-ripeness
and visible decay. The total AR contents always ranged at 73 ±
4.5 and 6.4 ± 0.7 mg hg<sup>–1</sup> of ‘Chok Anan’
and ‘Nam Dokmai #4’ peel dry weight, respectively, but
only at 6.7 ± 0.7 and 0.9 ± 0.1 mg hg<sup>–1</sup> for the corresponding mesocarp (<i>P</i> ≤ 0.05).
These narrow concentration ranges were contradictory to the decreasing
fungal resistance. Accordingly, the alk(en)ylresorcinols have not
been a deciding factor for the fungal resistance
In Vitro Bioaccessibility of Carotenoids, Flavonoids, and Vitamin C from Differently Processed Oranges and Orange Juices [<i>Citrus sinensis</i> (L.) Osbeck]
Carotenoid,
flavonoid, and vitamin C concentrations were determined
in fresh orange segments and a puree-like homogenate derived thereof,
as well as freshly squeezed, flash-pasteurized, and pasteurized juices.
Lutein and β-cryptoxanthin were slightly degraded during dejuicing,
whereas β-carotene levels were retained. Vitamin C levels remained
unaffected, whereas flavonoid levels decreased 8-fold upon juice extraction,
most likely due to the removal of flavonoid-rich albedo and juice
vesicles. Likewise, the presence of such fibrous matrix compounds
during in vitro digestion was assumed to significantly lower the total
bioaccessibility (BA) of all carotenoids from fresh fruit segments
(12%) as compared to juices (29–30%). Mechanical disruption
of orange segments prior to digestion did not alter carotenoid BA,
whereas pasteurization of the freshly squeezed juice slightly increased
BA by 9–11%. In addition to carotenoid BA, the stabilities
of hesperidin, narirutin, and vitamin C including dehydroascorbic
acid during in vitro digestion were monitored, and applied analytical
methods were briefly validated
Processes involving selective precipitation for the recovery of purified pectins from mango peel
c-Jun N-terminal kinase-3 (JNK3)/stress-activated protein kinase-beta (SAPKbeta) binds and phosphorylates the neuronal microtubule regulator SCG10.
The neuronal growth-associated protein SCG10 is enriched in the growth cones of neurons where it destabilizes microtubules and thus contributes to the dynamic assembly and disassembly of microtubules. Since its microtubule-destabilizing activity is regulated by phosphorylation, SCG10 may link extracellular signals to rearrangements of the neuronal cytoskeleton. To identify signal transduction pathways that may lead to SCG10 phosphorylation, we tested a series of serine-threonine-directed protein kinases that phosphorylate SCG10 in vitro. We demonstrate that purified SCG10 can be phosphorylated by two subclasses of mitogen-activated protein (MAP) kinases, c-Jun N-terminal/stress-activated protein kinase (JNK/SAPK) and p38 MAP kinase. Moreover, SCG10 was found to bind tightly and specifically to JNK3/SAPKbeta. JNK3/SAPKbeta phosphorylation occurs at Ser-62 and Ser-73, residues that result in reduced microtubule-destabilizing activity for SCG10. Endogenous SCG10 also undergoes increased phosphorylation in sympathetic neurons at times of JNK3/SAPKbeta activation following deprivation from nerve growth factor. Together these observations indicate that activation of JNK/SAPKs provides a pathway for phosphorylation of SCG10 and control of growth cone microtubule formation following neuronal exposure to cellular stresses