The Effect of Brine Ingredients on Carrot Texture during Thermal Processing in Relation to Pectin Depolymerization due to the β-Elimination Reaction

ABSTRACT:  Thermal texture degradation of carrots was studied at a temperature of 100 °C in aqueous solutions containing sodium chloride, citric acid, ascorbic acid, and ethylenediaminetetraacetic acid (EDTA) at different concentrations. To enhance the texture of the final product, the carrot samples were pretreated at 65 °C for 30 min in an aqueous calcium chloride solution (5 g/L). For all case studies considered, the pH of the solutions was adjusted to pH = 6.0. In parallel, both the changes in degree of esterification (DE) and the progress of the β-elimination reaction of carrot pectin under the same conditions were investigated. The kinetic parameters for texture degradation (rate constant k_t and final texture value [TP_∞/TP₀]) were estimated using a fractional conversion model. The results indicate that both the rate constant for texture degradation ( k_t ) and the rate constant for the β-elimination reaction ( k_b ) increased with increasing additive concentration, while the final texture values (TP_∞/TP₀) and DE decreased with increasing additive concentration in all systems studied. A high correlation was observed between the relative rate constant for texture degradation and the relative rate constant for the β-elimination reaction on the one hand, and the relative final texture value and the relative rate constant for the β-elimination reaction on the other hand, suggesting that the influence of the solutes on texture degradation can be explained by their influence on the β-elimination reaction.     

Influence of Pretreatment Conditions on the Texture and Cell Wall Components of Carrots During Thermal Processing

ABSTRACT: Diced carrots ( Daucus carota var. Nerac) were subjected to different pretreatment conditions. The pretreated carrots were subsequently thermally processed in an oil bath (100°C) and in a static retort (equivalent processes [F_oΔ 6 min] at 115°C, 120°C, and 125°C). Changes in texture were analyzed as well as changes in the degree of methylation (DM) of pectin. From all the pretreatment conditions tested, high-pressure pretreated carrots (400 MPa, 60°C for 15 min) exhibited the highest resistance to texture loss. The textural properties were significantly improved when calcium infusion was combined with low-temperature blanching condition (60°C for 40 min). A significant reduction in the DM of carrot pectin was observed for all pretreatment conditions that resulted in a reduced texture loss after thermal processing. A strong negative correlation (r ≥−0.90) exists between the changes in the degree of methylation of carrot pectin and the observed changes in texture.     

Low‐Temperature Blanching as a Tool to Modulate the Structure of Pectin in Blueberry Purees

Blueberry composition was characterized for 6 cultivars. It contains a good amount of dietary fiber (10% to 20%) and pectin (4% to 7%) whose degree of methylation (DM) is sensitive to food processing. A low temperature blanching (LTB: 60 °C/1 h) was applied on blueberry purees to decrease pectin DM, in order to modulate puree properties and functionalities (that is, viscosity and stability), and to enhance pectin affinity toward other components within food matrices. Fiber content, viscosity, pectin solubility, DM, and monosaccharide composition were determined for both pasteurized, and LTB+pasteurized blueberry purees. The results showed that neither the amount of fiber, nor the viscosity were affected by LTB, indicating that this treatment did not result in any significant pectin depolymerization and degradation. LTB caused a decrease both in pectin DM from 58–67% to 45–47% and in the amount of water‐soluble pectin fraction, the latter remaining the major fraction of total pectin at 52% to 57%. A LTB is a simple and mild process to produce blueberry purees with mostly soluble and low‐methylated pectin in order to extend functionality and opportunities for interactions with other food ingredients.     

Effects of High-Pressure Pretreatment and Calcium Soaking on the Texture Degradation Kinetics of Carrots during Thermal Processing

ABSTRACT: Carrots ( Daucus carota ) pretreated under different high-pressure conditions were thermally processed at temperatures in the range of 90°C to 110°C. Texture degradation (hardness) was monitored objectively using a texture analyzer. For a given thermal treatment, the rate constant (k-value) decreased with increasing pretreatment pressure. A high-pressure pretreatment (200 to 500 MPa) at 60°C for 15 min resulted in a more pronounced texture improvement compared with the same pretreatment at 20°C and 40°C, respectively. Calcium impregnation conferred more beneficial effects when applied immediately after the high-pressure pretreat-ment. The observed changes in texture characteristics were associated with the degree of methylation of carrot pectins, which is dependent on pectinmethylesterase (PME) activity.     

Enzyme infusion and thermal processing of strawberries: Pectin conversions related to firmness evolution

Strawberries were infused with fungal pectinmethylesterase (PME) and/or calcium chloride with the aim of minimising tissue damage during subsequent thermal processing (95 °C). Firmness measurements and micrographs provided information on the extent of tissue damage. These observations were linked to the chemical structure of pectin. When PME was infused in absence of Ca²⁺, the degree of methoxylation of pectin was lowered, but chains remained water soluble, indicating that they were not crosslinked. Thermal processing of PME-infused strawberries resulted in pectin solubilisation and depolymerisation which was reflected in pronounced firmness decrease and tissue damage, comparable to non-infused processed strawberries. On the other hand, when a combination of both PME and Ca²⁺ was infused, an important decrease in processing-related tissue damage was perceived. This can be explained by increased crosslinking of pectin chains with low degree of methoxylation, rendering them insoluble and less susceptible to thermal depolymerisation.     

In vitro β‐Carotene Bioaccessibility and Lipid Digestion in Emulsions: Influence of Pectin Type and Degree of Methyl‐Esterification

Citrus pectin (CP) and sugar beet pectin (SBP) were demethoxylated and fully characterized in terms of pectin properties in order to investigate the influence of the pectin degree of methyl‐esterification (DM) and the pectin type on the in vitro β‐carotene bioaccessibility and lipid digestion in emulsions. For the CP based emulsions containing β‐carotene enriched oil, water and pectin, the β‐carotene bioaccessibility, and lipid digestion were higher in the emulsions with pectin with a higher DM (57%; “CP57 emulsion”) compared to the emulsions with pectin with a lower DM (30%; “CP30 emulsion”) showing that the DM plays an important role. In contrast, in SBP‐based emulsions, nor β‐carotene bioaccessibility nor lipid digestion were dependent on pectin DM. Probably here, other pectin properties are more important factors. It was observed that β‐carotene bioaccessibility and lipid digestion were lower in the CP30 emulsion in comparison with the CP57, SBP32, and SBP58 emulsions. However, the β‐carotene bioaccessibility of CP57 emulsion was similar to that of the SBP emulsions, whereas the lipid digestion was not. It seems that pectin type and pectin DM (in case of CP) are determining which components can be incorporated into micelles. Because carotenoids and lipids have different structures and polarities, their incorporation may be different. This knowledge can be used to engineer targeted (digestive) functionalities in food products. If both high β‐carotene bioaccessibility and high lipid digestion are targeted, SBP emulsions are the best options. The CP57 emulsion can be chosen if high β‐carotene bioaccessibility but lower lipid digestion is desired.     

Towards a better understanding of the pectin structure-function relationship in broccoli during processing: Part I—macroscopic and molecular analyses

To investigate the structure-function relationship of pectin during (pre)processing, broccoli samples (Brassica oleracea L. cultivar italica) were subjected to one of the following pretreatments: (i) low-temperature blanching (LTB), (ii) LTB in combination with Ca²⁺ infusion, (iii) high-pressure pretreatment (HP), (iv) HP in combination with Ca²⁺ infusion, or (v) no pretreatment (control sample), whether or not in combination with a thermal treatment of 15 min at 90 °C. The macroscopic attributes of broccoli were linked to the chemical structure of broccoli pectin. By enhancing the cross-linking of pectic polymers, both LTB and HP reduced the texture loss that occurred during thermal processing of broccoli. During these pretreatments, homogalacturonan was de-esterified by pectin methylesterase, which led to changes in pectin solubility. When LTB or HP was combined with Ca²⁺ infusion, changes in the structure of pectin occurred, however not always reflected at the macroscopic level. The degree of esterification of pectin in Ca²⁺-soaked broccoli samples was lower compared to non-Ca²⁺-soaked samples and, in addition, a higher amount of ionically cross-linked pectin was retrieved.     

Towards a better understanding of the pectin structure–function relationship in broccoli during processing: Part II — Analyses with anti-pectin antibodies

To investigate the structure–function relationship of pectin during (pre)processing, broccoli samples (Brassica oleracea L. cultivar italica) were subjected to one of the following pretreatments: (i) low-temperature blanching (LTB), (ii) LTB in combination with Ca²⁺ infusion, (iii) high-pressure pretreatment (HP), (iv) HP in combination with Ca²⁺ infusion, or (v) no pretreatment (control sample), whether or not in combination with a thermal treatment of 15 min at 90 °C. Anti-homogalacturonan antibodies were used to perform in situ (microscopy) and ex situ (immuno-dot assays) analyses on broccoli pectin which resulted in information concerning the localisation of defined pectic domains in broccoli cell walls and pectin's structure. Water-soluble pectin appears to contain unbranched, high-esterified pectin and some pectic polymers with abundant side chains that are less esterified. Ionically cross-linked pectin, on the other hand, contains low-esterified pectin with either highly branched or unbranched domains. The in situ visualisation of pectin in broccoli suggested that de-esterification of pectin by PME during LTB as well as during HP mainly takes place in the tricellular junctions of adjacent cells in broccoli tissue. Ca²⁺-cross-linked pectin could be found in cell walls lining intercellular spaces and was particularly abundant at the corners of intercellular spaces, indicating its important role in cell–cell adhesion. Both LTB and HP created pectin–Ca²⁺-cross-links in parts of the cell wall where these cross-links were originally absent. The influence of thermal processing and the effect of pressurisation on the pectic components in the cell wall could also be visualised using the antibodies.