The influence of the storage conditions heat and humidity on conformation,state transitions and degradation behaviour of dried pectins

For testing the influence of long-term storage on pectins, differently prepared samples were incubated under defined temperature and relative humidity in a climate chamber. This caused pectin demethoxylation, depolymerisation and non-enzymatic browning and influenced the dissolution behaviour and pH. The extent of chemical changes and the reaction mechanisms depended on incubation conditions, type and “history” of the pectins and on their conformation (⁴C₁ or ¹C₄ chair). Higher temperature and higher humidity increased demethoxylation and browning. Depolymerisation was high even at low degree of methoxylation. Therefore, an additional mechanism besides β-elimination and glycosidic linkage cleavage was suggested.     

Effect of drying method on the sorption characteristics of model fruit powders

Pectin-sugar gels were dehydrated with four different drying methods: freeze, microwave, vacuum and conventional drying to a moisture content of about 5%. The effect of the drying method on the water sorption properties of dehydrated products was evaluated at 25 °C. Freeze-dried gel adsorbed more water vapour than microwave-dried gel, which had a higher sorption capacity than vacuum- and conventional-dried product. The sorption isotherms were in agreement with the reported shape for high sugar foodstuffs. Three different equations proposed in the literature (GAB, Oswin, Hasley) were used to fit the sorption data. The GAB equation gave the best fit to the experimental data. The porosity of the dehydrated products depended on the drying method, ranging between 0.2 and 0.5. Freeze- and vacuum-dried pectin developed the highest porosity, whereas the lowest porosity was obtained using conventional and microwave drying. Hunter colour parameters (L, a, b) also depended on the drying method. The colour of freeze- and vacuum-dried pectin was close to that of commercial pectin, while the colour of the conventional- and microwave-dried product changed significantly.     

Influence of pectin properties and processing conditions on thermal pectin degradation

Texture degradation of fruits and vegetables during thermal processing is partly due to pectin depolymerization. In this contribution we investigate the influence of pectin properties (degree and pattern of methoxylation) and processing conditions (pH 2.0, 3.0, 5.0 and 7.0; temperatures of 80 up to 110 °C) on pectin degradation rate constants. Pectins with different degrees and patterns of methoxylation were prepared and heated, the extent of acid hydrolysis, β-elimination and demethoxylation was assayed as a function of treatment time. As the degree of methoxylation and pH decreased, β-elimination rate constants decreased while acid hydrolysis rate constants increased. Demethoxylation rate constants were minimal at pH 3.0 and increased both at lower and higher pH. Reaction rate constants were not considerably influenced by the pattern of methoxylation. All reaction rate constants increased with increasing temperature. As β-elimination rates are reduced by competing demethoxylation, both rate constants were compared. The ratio of these reaction rate constants showed no trend with pH. However, an increase in degree of methoxylation or temperature resulted in a more pronounced increase in β-elimination rate constants than in demethoxylation rate constants.     

Effect of high-pressure/high-temperature processing on chemical pectin conversions in relation to fruit and vegetable texture

Heat sterilization of plant derived food products entails considerable organoleptic and nutritional quality losses. For instance, texture loss of fruits and vegetables occurs, next to turgor pressure losses, mainly due to chemical changes in the cell-wall pectic polysaccharides. High-pressure sterilization, i.e. the combination of high temperature (?90 °C) with high pressure (?500 MPa), could present a positive alternative assuring safety while minimizing quality losses. In this study, the potential of high-pressure sterilization in preserving fruit and vegetable texture was evaluated by investigating the effect of combined high-pressure/high-temperature (HP/HT) treatments on two texture related chemical pectin conversions in model sytems. First, a protocol was developed to perform reproducible kinetic studies at HP/HT under constant processing conditions. Subsequently, apple pectin solutions at pH 6.5 were subjected to different HP/HT combinations (500, 600 and 700 MPa/90, 110 and 115 °C) and the extent of chemical demethoxylation and β-eliminative depolymerization was determined. At atmospheric pressure, both zero-order reaction rate constants increased with increasing temperature. At all temperatures, demethoxylation showed a higher rate constant than β-elimination. However, a temperature rise resulted in a stronger acceleration of β-elimination than of demethoxylation. When combining high temperature with high pressure, β-elimination was retarded or even stopped, whereas demethoxylation was stimulated. These results are very promising in the context of the texture preservation of high-pressure sterilized fruits and vegetables, as β-elimination is accepted to be one of the main causes of thermal softening and low methoxylated pectin can enhance tissue strength by forming cross-links with calcium ions present.     

A comprehensive review on polarity,partitioning, and interactions of phenolic antioxidants at oil–water interface of food emulsions

There has been a growing interest in developing effective strategies to inhibit lipid oxidation in emulsified food products by utilization of natural phenolic antioxidants owing to their growing popularity over the past decades. However, due to the complexity of emulsified systems, the inhibition mechanism of phenolic antioxidants against lipid oxidation is rather complicated and not yet fully understood. In order to highlight the importance of polarity of phenolic antioxidants in emulsified systems according to the polar paradox, this review covers the recent progress on chemical, enzymatic, and chemoenzymatic lipophilization techniques used to modify the polarity of antioxidants. The partitioning behavior of phenolic antioxidants at the oil–water interface, which can be influenced by the presence of synthetic surfactants and/or antioxidant emulsifiers (e.g., polysaccharides, proteins, and phospholipids), is discussed. In addition, the emerging phenolic antioxidants among phenolic acids, flavonoids, tocopherols, and stilbenes applied in food emulsions are elaborated. As well, the interactions of polar–nonpolar antioxidants are stressed as a promising strategy to induce synergistic interactions at oil–water interface for improved oxidative stability of emulsions.     

Effect of Novel Processing Techniques on Texture Softening and β-Carotene Content of Thermally Processed Carrots

Effect of novel processing methods was evaluated on product texture and β-carotene content of carrots following acidification to reduce pH from 6.0 to 4.4. Thermal treatments under Conventional (CH-T) and Ohmic heating (OH-T) conditions at 87, 92, and 97 °C, individually and/or in combination with high-pressure processing (HP-T; 400–600 MPa/40–60 °C), were given up to 90 min. A fractional conversion model was used to compute texture softening rate constant, k, and activation energy, E _a. Acid-infused carrot samples had lower k values than the control, implying a better texture retention in acidified products. In order to explore this further, acid-infused and control samples were subjected to selected processing methods for 0, 7, and 25 min representing minimal, optimum, and over-processing conditions, respectively. Texture value, pectin depolymerization by β-elimination, demethoxylation, cell microstructure modification, and β-carotene content were evaluated. Results showed that acid-infused samples retained significantly (p?≤?0.05) better texture than the untreated ones. Pectin depolymerization by β-elimination was greater (p?≤?0.05) in control samples than acid-infused samples. In contrast, pectin depolymerization by demethoxylation showed no such differences (p?>?0.05) with acid-infused samples. This indicates that pectin degradation was more dominated by β-elimination than demethoxylation, and these results concurred with the cell microstructure observations of processed carrots. Thermal and HP-T processing after acid infusion reduced the β-carotene content of carrots more than in control. However, mild heat treatment of carrots at 97 °C under CH-T and OH-T enhanced the β-carotene levels to higher than in raw control carrot samples.     

Influence of Edible Coating on the Drying and Quality of Papaya (Carica papaya)

The edible coating applied to food pieces prior to hot air drying is a technology that can improve the nutritional and sensory qualities of dehydrated products. The effects of the pectin coating technique on the drying efficiency and quality of papaya slices of the Formosa cultivar were investigated, determining the cell structure, color, and vitamin C contents of the fresh and dried fruits, with and without a pectin coating. The drying kinetics was evaluated based on Fick’s Law. The analytical solution for a plane sheet was used to estimate the water effective diffusion coefficients, and, in order to take into account shrinkage during drying, the average and variable thicknesses were considered in an approximate manner. Diffusion modeling presented a better fit when considering the thickness of the slices as variable. Regarding fruit quality, the coating applied to papaya slices before drying enhances vitamin C retention in comparison to papaya dried without coating, showing that pectin coating efficiently prevented oxidation of this bioactive compound. In addition, the moisture diffusivity of the coated samples was higher than that of the non-coated slices, due to the hydrophilic nature of the pectin. Light and transmission electron microscopy images revealed intense rupturing of the cell membranes in the dried tissues. The cell tissue arrangement in the coated papaya slices was similar to that found in the fresh papaya slices, before and after drying.     

Structure,physicochemical properties and in vitro fermentation of enzymatically degraded cell wall materials from apples

Cell wall materials (CWM) prepared from apple parenchyma tissue by treatment with commercial enzymes for maceration, mash fermentation and liquefaction were characterised with regard to their composition and structure as well as their physicochemical and physiological properties. Increasing enzymatic degradation of the CWM resulted in growing loss of the pectin matrix, decreasing porosity as well as increasing particle aggregation. Due to these structural alterations the water binding, the viscoelastic properties of the CWM-water-suspensions and the in vitro fermentation, forming short chain fatty acids, were reduced. The investigations showed that interrelations exist between enzymatic treatment and changes of (i) structure and state of matrices (evaluated by means of thermal analysis), (ii) physicochemical properties and (iii) physiological properties. So the application of liquefying enzymes can lead to a complete removal of the pectin matrix, causing an essentially improved thermal stability of the CWM preparation, but strongly reduced water binding and reduced structure-forming properties into the CWM-water-suspensions. The formation of short-chain fatty acids during in vitro fermentation of the CWM preparations by fresh human faeces flora depended on the portion and the state of the pectin matrix and the cellulose network, respectively.     

Freeze-dried snacks obtained from frozen vegetable by-products and apple pomace – Selected properties,energy consumption and carbon footprint

Valorisation of food waste is one of the goals that food industry needs to achieve in terms of sustainable development. The aim of the research has been to analyse selected properties of freeze-dried vegetable snacks obtained from wholesome waste derived from the fruit and vegetable industry, such as frozen vegetable by-products and apple pomace as well as to estimate carbon footprint as the technological process output on the basis of the energy used for the purpose of producing snacks. Properties of snacks, such as water content and activity, shrinkage, density, porosity and hardness, were determined using common methodology. The water content of the finished products was very low (<1.5%) and determined the water activity below 0.02. Technological operations, such as grinding, caused destruction of the cell structure of the ingredients, which subsequently made the product structure inhomogeneous and more dense than most of the freeze-dried plant tissues. The snacks were porous and featured by hardness of 79.43–113.26 N. The colour depended on their composition, and freeze-drying caused the products to brighten significantly. The estimated carbon footprint (CF) depended on the technological process. Freeze-drying had the most significant impact upon the CF, accounting for 86–87%. The use of apple pomace powder as a structure- and texture-forming additive constitutes the subject matter representing great prospects for further research.     

Thermodynamic compatibility of sodium caseinate with different pectins. Influence of the milieu conditions and pectin modifications

Combinations of pectins and caseins are ingredients of many food products. Therefore the thermodynamic compatibility of both components was examined to investigate the influences of environmental factors as well as of the structure of the pectin. High‐methoxyl pectin was demethoxylated and amidated, respectively, and tested for the compatibility with sodium caseinate under varying conditions of pH and ionic strength. The compatibility increased with increasing pH and decreasing ionic strength. Demethoxylated pectins were more and amidated pectins less compatible with the caseinate. Changes in the pectin hydrophilicity, solubility and molecular weight and possibly local interactions such as electrostatic attraction, hydrogen bonding and calcium bridges are involved in the compatibility of the components. The type and degree of the pectin modifications as well as the type, composition and properties of the protein were found to be of great importance for the thermodynamic compatibility.     

Thermodynamic compatibility of sodium caseinate with different pectins. Influence of the milieu conditions and pectin modifications.

Combinations of pectins and caseins are ingredients of many food products. Therefore the thermodynamic compatibility of both components was examined to investigate the influences of environmental factors as well as of the structure of the pectin. High-methoxyl pectin was demethoxylated and amidated, respectively, and tested for the compatibility with sodium caseinate under varying conditions of pH and ionic strength. The compatibility increased with increasing pH and decreasing ionic strength. Demethoxylated pectins were more and amidated pectins less compatible with the caseinate. Changes in the pectin hydrophilicity, solubility and molecular weight and possibly local interactions such as electrostatic attraction, hydrogen bonding and calcium bridges are involved in the compatibility of the components. The type and degree of the pectin modifications as well as the type, composition and properties of the protein were found to be of great importance for the thermodynamic compatibility.     

Structure,physicochemical properties and in vitro fermentation of enzymatically degraded cell wall materials from apples

Cell wall materials (CWM) prepared from apple parenchyma tissue by treatment with commercial enzymes for maceration, mash fermentation and liquefaction were characterised with regard to their composition and structure as well as their physicochemical and physiological properties. Increasing enzymatic degradation of the CWM resulted in growing loss of the pectin matrix, decreasing porosity as well as increasing particle aggregation. Due to these structural alterations the water binding, the viscoelastic properties of the CWM‐water‐suspensions and the in vitro fermentation, forming short chain fatty acids, were reduced. The investigations showed that interrelations exist between enzymatic treatment and changes of (i) structure and state of matrices (evaluated by means of thermal analysis( (ii) physicochemical properties and (iii) physiological properties. So the application of liquefying enzymes can lead to a complete removal of the pectin matrix, causing an essentially improved thermal stability of the CWM preparation, but strongly reduced water binding and reduced structure‐forming properties into the CWM‐water‐suspensions. The formation of short‐chain fatty acids during in vitro fermentation of the CWM preparations by fresh human faeces flora depended on the portion and the state of the pectin matrix and the cellulose network, respectively.     

Corn Syrup Solids and Their Saccharide Fractions Affect Crystallization of Amorphous Sucrose

The effects of corn syrup saccharides on the glass transition (Tg) and crystallization of freeze-dried sucrose were studied using differential scanning calorimetry. Corn syrup (CS) solids were fractionated into samples with differing ranges and types of glucose polymers. Tg of the sucrose/CS additive mixtures depended on number-average molecular weight, rather than weight-average molecular weight, of CS material. Additive levels of 10% and 20% (w/w) of CS solids and their fractions interfered with crystallization of amorphous sucrose, whereas levels 50% prevented crystallization. The mechanism by which CS saccharides interfered with crystallization of amorphous sucrose depended not only on Tg but was also influenced by specific interactions between molecules.     

Emulsion gels: The structuring of soft solids with protein-stabilized oil droplets

Many food products can be categorized as emulsion gels. This is especially the case for protein-based oil-in-water emulsions which can be converted into soft-solid-like materials by common food processing operations such as heating, acidification, and enzyme action. This review article outlines how the rheological and structural properties of protein-stabilized emulsion gels are influenced by the dispersed oil volume fraction, the oil–water interfacial composition, and the colloidal interactions of the constituent emulsion droplets. For model systems of variable oil content and containing different food proteins, some general trends of rheological behaviour at small and large deformations are identified. Experimental rigidity data are considered in relation to: (i) material science theories of the reinforcement of solid materials by active and inactive filler particles, and (ii) Brownian dynamics simulations of aggregated particle networks containing bonded and non-bonded particles. Influences of interfacial composition and particle–matrix interactions on microstructure and rheology are explained with particular reference to the role of small-molecule surfactants. Compositional and structural factors affecting the large-deformation rheology and fracture properties are described. Finally, the practical relevance of the model system studies to the behaviour of real food products is critically assessed.     

The Emulsifying and Emulsion‐Stabilizing Properties of Pectin: A Review

Pectin, a plant cell wall polysaccharide, is a natural multifunctional ingredientwhich imparts textural and rheological properties to a wide range of food systems. Up to the last decade, most pectin blank applications stemmed from its gel‐forming ability. Nowadays, pectin is gradually gaining acceptance as an effective emulsifier in numerous food applications. Accordingly, the emulsifying and emulsion‐stabilizing properties of this hydrocolloid are increasingly being assessed. These pectin functionalities are controlled by both the properties of the carbohydrate moieties and of the often attached protein groups. Generally, the protein moiety, feruloyl, and acetyl groups, play a major role in pectin emulsifying activities, while the emulsion‐stabilizing properties of the polymer are controlled by the homogalacturonan (HG) domain and the neutral sugar side chains of the rhamnogalacturonan‐I (RGI) structural element. However, the neutral sugar side chains might obstruct the accessibility of pectin hydrophobic species to the oil/water interface, thereby hampering emulsification. In addition, the contribution of HG to emulsion stabilization might be dependent on the polymer HG:RGI ratio. Hence, the influence of pectin structural features on the polymer emulsifying potentials is yet to be fully unraveled, as identified in this review. Furthermore, the emulsifying and emulsion‐stabilizing properties of pectin are influenced by the composition of emulsions.     

The significance of physico chemical properties of plant cell wall materials for the development of innovative food products

Cell wall materials (CWM) are natural constituents of fruits and vegetables. They are added in a growing extent to foods as health ingredients to create innovative products (functional food). CWM or dietary fibres, respectively, have both physiological and technological functional properties, which are considerably modified during the dietary fibre preparation, during the incorporation of the dietary fibre ingredients into foods and generally during processing. Process-dependent external stress and the influence of internal conditions induce changes of the physico-chemical properties of the food constituents (such as particle size and shape, porosity, water binding and structure-forming as well as texturization properties). These changes affect or determine the technological functional, the material and the physiological properties. To evaluate the alterations of structure and properties of plant cell walls during processing without disturbing influences CWM-water-model suspensions and cell wall preparations, carefully dried after a water-ethanol-exchange, can be used. Such model studies and investigations for the improved manufacture of dietary fibre preparations as well as dried fruit and vegetable products show that both the pre-drying treatments (addition of salt, sugar, polysaccharides and surfactants) and the drying step itself considerably influence the extent of shrinkage, cell wall stiffening as well as cell collapse and glass transition. In pre-drying treatments variations of the degree of methoxylation of the pectin component and/or cation charging can be made which cause a pre-formation of structures and/or states of matter that determine essentially the drying process. The ability of rehydration plays an important role for the application and utilization of dried CWM and dietary fibre preparations as well as of dried fruit and vegetable products. The rehydration process is achieved by the plasticizing effect of water, the temperature influence and the external stress, e.g. by stirring, and is supposed to reverse the state transitions, resulting from drying. By application in foods the rehydration of the CWM and dietary fibre preparations can contribute to the formation of texture (texturization). The texturization caused by CWM depends not only on processing and internal conditions but also essentially on the concentration, size, shape, stiffness and deformability of the particles as well as their water binding properties (amount and strength). The investigations show that improved technologies for the production of cell wall and dietary fibre preparations as well as innovative foods with selectively adjusted functional properties require a fundamental understanding of the changes in structure and properties, caused by processing. Furthermore, a well coordinated cooperation of different scientific disciplines using information technology is necessary for a successful development of innovative dietary fibre enriched products.     

Chemistry and uses of pectin — A review

Pectin is an important polysaccharide with applications in foods, Pharmaceuticals, and a number of other industries. Its importance in the food sector lies in its ability to form gel in the presence of Ca²⁺ ions or a solute at low pH. Although the exact mechanism of gel formation is not clear, significant progress has been made in this direction. Depending on the pectin, coordinate bonding with Ca²⁺ ions or hydrogen bonding and hydrophobic interactions are involved in gel formation. In low‐methoxyl pectin, gelation results from ionic linkage via calcium bridges between two carboxyl groups belonging to two different chains in close contact with each other. In high‐methoxyl pectin, the cross‐linking of pectin molecules involves a combination of hydrogen bonds and hydrophobic interactions between the molecules. A number of factors—pH, presence of other solutes, molecular size, degree of methoxylation, number and arrangement of side chains, and charge density on the molecule— influence the gelation of pectin. In the food industry, pectin is used in jams, jellies, frozen foods, and more recently in low‐calorie foods as a fat and/or sugar replacer. In the pharmaceutical industry, it is used to reduce blood cholesterol levels and gastrointestinal disorders. Other applications of pectin include use in edible films, paper substitute, foams and plasticizers, etc. In addition to pectolytic degradation, pectins are susceptible to heat degradation during processing, and the degradation is influenced by the nature of the ions and salts present in the system. Although present in the cell walls of most plants, apple pomace and orange peel are the two major sources of commercial pectin due to the poor gelling behavior of pectin from other sources. This paper briefly describes the structure, chemistry of gelation, interactions, and industrial applications of pectin.     

Structure and physical properties of pectins with block-wise distribution of carboxylic acid groups

The physical and the interfacial properties of pectins de-esterified by a specific block-wise enzymatic procedure were investigated. Two major types of block-wise de-esterified pectins with different internal distribution of carboxylic acid on the pectin chains were explored. Type C and type U pectins with the same degree of methylesterification are different and a more block-wise intramolecular distribution in comparison to commercial native apple pectin. The most ordered pectin (U63 pectin, 63% methylesterified pectin) has the highest electrophoretic mobility (ζ-potential). It reveals more pronounced intermolecular interactions since it exhibited, at low pH, the lowest circular dichroism intensity at shorter wavelength. U63 pectin (at acidic pH, without calcium addition) has a higher viscosity and formed a stronger gel compared to the less ordered C63 pectin and/or native apple pectin. X-ray patterns show that powdered U63 pectin is more crystalline than C63 pectin, while apple pectin is mostly amorphous. The modified pectin also, most effectively, reduced the surface tension (55 mN/m) and the interfacial tension (5.6 mN/m), probably due to the preferred surface orientation of the carboxylic groups at the water/air or water/oil interfaces.     

Influence of the overall charge and local charge density of pectin on the complex formation between pectin and β-lactoglobulin

The complex formation between β-lactoglobulin (β-lg) and pectin is studied using pectins with different physicochemical characteristics. Pectin allows for the control of both the overall charge by degree of methyl-esterification as well as local charge density by the degree of blockiness. Varying local charge density, at equal overall charge is a parameter that is not available for synthetic polymers and is of key importance in the complex formation between oppositely charged (bio)polymers. LMP is a pectin with a high overall charge and high local charge density; HMP_B and HMP_R are pectins with a low overall charge, but a high and low local charge density, respectively. Dynamic light scattering (DLS) titrations identified pH_c, the pH where soluble complexes of β-lg and pectin are formed and pH_?, the pH of phase separation, both as a function of ionic strength. pH_c decreased with increasing ionic strength for all pectins and was used in a theoretical model that showed local charge density of the pectin to control the onset of complex formation. pH_? passed through a maximum with increasing ionic strength for LMP because of shielding of repulsive interactions between β-lg molecules bound to LMP, while attractive interactions were repressed at higher ionic strength. Potentiometric titrations of homo-molecular solutions and mixtures of β-lg and pectin showed charge regulation in β-lg–pectin complexes. Around pH 5.5–5.0 the pK_as of β-lg ionic groups are increased to induce positive charge on the β-lg molecule; around pH 4.5–3.5 the pK_a values of the pectin ionic groups are lowered to retain negative charge on the pectin. Since pectins with high local charge density form complexes with β-lg at higher ionic strength than pectins with low local charge density, pectin with a high local charge density is preferred in food systems where complex formation between protein and pectin is desired.     

Analytical Methods for Pectin Methylesterase Activity Determination: a Review

Pectin methylesterase is an enzyme with an important in vivo role in plants as well as in food industry. This enzyme catalyzes the hydrolysis of methyl ester bounds in pectin which is one of the main components of cell wall in plants, producing methanol and free carboxylic groups. The effect of pectin methylesterase in food quality has been extensively studied, producing desirable effects in texture improvement as well as undesirable effects in some beverages. Likewise, the low methoxyl pectin produced by this enzyme has characteristics that contribute to formulate best quality food products. Pectin methylesterase is a ubiquitously enzyme that presents multiple isoforms, but is not only present in plants; it is also found in fungi, bacteria, and yeast, which have specific chemical and physical characteristics. The latter makes the task of analyzing the wide variety of these enzymes with its specific characteristics difficult. Based on this enzyme relevance and the aforementioned, multiple methods have been developed in order to evaluate pectin methylesterase activity with different research objectives. In this paper, the importance of the enzyme as well as advantages and drawbacks of the different methods will be discussed besides applications and evolution of these will be mentioned. Additionally, this paper will improve the understanding of the systems used in pectin methylesterase activity analysis.