Sybille Neidhart

The role of process technology in carrot juice cloud stability

The effect of various processing measures on carrot juice cloud stability was studied on pilot-plant scale using decanter technology. Production steps investigated were mode of acidification, different enzymatic mash treatments and blanching conditions. Acidification showed the strongest effect on cloud stability. Whereas acidifying the coarse mash resulted in cloud stability, acidification following juice extraction even enhanced cloud sedimentation. The production of stable nonacidified juices was also possible. However, sediment formation was less after coarse mash acidification. Further improvement of cloud stability by enzymatic mash maceration or intensified blanching was negligible. Both measures, however, slightly improved the extraction of cloud particles from the mash, thus resulting in higher turbidity. The limited effect of macerating enzymes and pH-dependent sedimentation suggest that proteins rather than pectic substances influence cloud stability of carrot juices.

In Vitro Bioaccessibility of Carotenoids, Flavonoids, and Vitamin C from Differently Processed Oranges and Orange Juices [Citrus sinensis (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.

Yield and quality of pectins extractable from the peels of Thai mango cultivars depending on fruit ripeness

Pectins, recovered from the peels of four mango ( Mangifera indica L.) cultivars by mimicking industrial techniques, were evaluated in terms of yield, composition, macromolecular properties, and technofunctional quality. Freeze-dried peels of mature-green fruits, after major mesocarp softening, and at full ripeness were extracted using hot acid. The pectins were precipitated in propan-2-ol and their crude yields quantified as alcohol-insoluble substance. Like apple pomace, the dried peels provided hardly acetylated (DAc < 6.3%) rapid-set to ultrarapid-set high-methoxyl pectins at starch-adjusted yields of 11-21 g/100 g. However, despite similar high molecular weight fractions and galacturonic acid/rhamnose ratios, their average molecular weight was markedly reduced by a characteristic, almost monodisperse fraction of 16000-19000. Expanded galactans, indicated by galactose/rhamnose ratios of 15-24 mol/mol, probably represented arabinogalactan side-chain fragments withstanding hot-acid extraction at pH 1.5 and 2.0, as implied by arabinose/galactose ratios of 8-15 and 33-56 mol/100 mol, respectively. Limited galacturonic acid contents made the mango peel pectins less valuable than commercial apple pectins with regard to gelling capacity and thickening properties. Whereas starch and matrix glycan fragments almost completely degraded during ripening, depolymerization of pectins and galactans was insignificant. Technofunctional properties, modulated by extraction at different pH values, were ascribed to structural differences influencing macromolecular entanglements.

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 (R² = 0.9975-0.9998) for the relevant ranges (0.28-30.3 μmol L⁻¹); galacturonic acid, 1.7-128 μmol L⁻¹) above the limits of detection (30-81 nmol L⁻¹; galacturonic acid, 179 nmol L⁻¹) 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.

Sol-Gel Transitions of High-Esterified Pectins and Their Molecular Structure

Molecular structure, molecular heterogeneity and gelling properties of eleven high-esterified pectins with average degrees of esterification (DE) between 50% and 80% were investigated. For rheological studies in the small-strain-oscillation mode, gelation of sugar-acid-model systems was induced by cooling at constant rates from 93 °C to usually 20°C. Junction zones of such physical gel networks are known to be mainly stabilized by hydrogen bonds besides hydrophobic interactions. However, in systems with high gelation temperatures far from 30°C, adverse thermal conditions for junction zone formation must be overcompensated by other effects reducing the mobility of pectin molecules, such as macromolecular entanglements intensified by long side-chains of the rhamnogalacturonan-backbone.

Innovative Strategies for Sustainable Lychee Processing

Litchi chinensis Sonn. is a non-climacteric fruit cultivated in many subtropical areas around the world (Kadam and Deshpande, 1995). In accordance with its main usage as fresh or canned fruit, most studies on the utilisation of lychees describe aspects of cultivars such as their nutritional parameters (Menzel and Simpson, 1991; Kadam and Deshpande, 1995), the discolouration of the pericarp during marketing of fresh fruits (Underhill and Critchley, 1995; Holcroft and Mitcham, 1996; Ray, 1998; Sarni-Manchado et al., 2000) or the risk of pink discolouration of the fruit flesh during canning (Wu and Fang, 1993; Wu and Sheu, 1996). In view of increasing export markets, recent research has focused primarily on the postharvest biology and technology of lychee fruits, with the aim of producing light-coloured, chemical-free fruits without disease or insect infestation (Jiang et al., 2003). The fruits are appreciated for their fine flavour. The nutritional value of lychees is based on vitamin C which is found in its edible aril generally at levels of 40–90 mg/100 g (Kadam and Deshpande, 1995). However, this value is subject to great variation, depending on the cultivar, cultivation area, storage and processing conditions, and can be significantly lower in some cases (Ramma et al., 2003).

Investigations of the influence of various cations on the rheological properties of high-esterified pectin gels

Abstract The influence of sodium, potassium, calcium and magnesium ions on the gelling behaviour of apple pectins with degrees of methylation between 43% and 73% as well as the effect of these ions on viscoelastic properties and thermal behaviour of the final gels were investigated by means of small amplitude oscillatory shear experiments. The rheological data were obtained for each pectin according to mixture designs for the metal ions with least changes in pH and ionic strength and analyzed by multiple non-linear regression. With each pectin the various rheological properties were shown to be modulated in a complex way. The setting behaviour was always affected in a similar fashion by the ions as the thermal behaviour of the final gel, but not in the same way as the strength or the elasticity of the gels. The rheological results did not reveal any direct dependence on the charge or the size of the cations, suggesting various, more or less specific modes of action to be involved, depending on the nature of the cation and the amount of dissociated carboxylic groups in the sample.

Processes involving selective precipitation for the recovery of purified pectins from mango peel

Three methods for the recovery of purified pectins from directly dried mango peel were developed, using selective precipitation of mango pectin in propan-2-ol (IPA) of adequate volume concentrations for purification. Yields, composition, macromolecular and gelling properties of the resultant pectins were compared. Effluent analyses proved postextractive removal of fruit exudate arabinogalactans. The recovery processes involved (A) washing of raw-pectin powder in IPA of defined volume concentration, (B) fractional alcoholic precipitation of dissolved raw pectin, or (C) selective pectin precipitation from the hot-acid extract of mango peel in adequately diluted IPA. High galacturonic acid contents (≥ 721g/kg) and intrinsic viscosities (≥ 320mL/g) enabled ∼2.2-fold gelling capacities compared to raw mango pectin, which resulted from the standard procedure mimicking industrial pectin recovery from established sources. Removal of the predominant impurities (coextractable exudate arabinogalactans, ash) diminished the yields to ∼49% of the raw-pectin yield. Technical feasibility of the proposed procedures was discussed.

The Control of Postharvest Ripening Processes and its Implications for the Productivity of Mango Processing

The production of high-quality food depends not only on an appropriate processing technology but also on the selection of proper raw materials. This experience, well known among food manufacturers, can be exemplified in the case of mango processing.

Anwendung der analytischen Größenausschluß-Chromatographie zur Untersuchung des Substratahbaus einer kommerziellen Pektatlyase ausErwinia carotovora

Within the scope of the characterization of a commercial pectate lyase (PAL) the pattern of substrate degradation by that enzyme was investigated with oligogalacturonic acids as well as pectins with various degrees of esterification as substrates. For this purpose an analytical size exclusion chromatographie method (HPSEC) was elaborated in order to evaluate the reaction products of the degraded substrates over the whole range of molecular weight with the main interest lying in the emerging oligogalacturonic acids. The degradation of polygalacturonic acid by PAL was additionally investigated by means of thin-layer chromatography (TLC) and viscosimetry. Furthermore spontaneous depolymerization and deesterification of the substrates occurring under the chosen conditions were examined. The PAL showed to be anendo-enzyme both by means of TLC and HPSEC. Polygalacturonic acid was broken down, mainly generating unsaturated tri- and digalacturonic acid; the corresponding monomer was not found. The mode of cleavage is discussed.ZusammenfassungZur Charakterisierung einer kommerziellen Pektatlyase (PAL) wurde das Spaltungsmuster dieses Enzyms an Pektinen mit unterschiedlichen Veresterungsgraden sowie an Oligogalakturonsäuren untersucht. Dazu wurde eine Methode der analytischen Größenausschluß-Chromatographie (HPSEC) ausgearbeitet, um die Spaltprodukte der Substrate über den gesamten Molekulargewichtsbereich hinweg, vor allem aber entstehende Oligogalakturonsäuren, quantitativ zu bestimmen. An Polygalakturonsäure wurde der Abbau durch die PAL zusätzlich mittels Dünnschicht-Chromatographie (TLC) und Viskosimetrie untersucht. Ferner wurde die spontane Depolymerisation und Entesterung der Substrate unter den gewählten Bedingungen über- prüft. Sowohl mittels TLC als auch mittels HPSEC wurde derEndo-Enzym-Charakter der PAL deutlich. Polygalakturonsäure wurde hauptsächlich zu ungesättigter Tri- und Digalakturonsäure abgebaut; das entsprechende Monomer wurde nicht gefunden. Die Spaltungsweise wird diskutiert.