The influence of predrying treatment and of suspension solution conditions on the rehydration of apple cell wall materials

The aim of this work was to investigate the influence of structure variations, predrying treatment and the suspension solution conditions on the hydration properties of cell wall materials from apples. For this purpose, materials with high methoxylated (HM) as well as with low methoxylated (LM) pectin components were treated in the wet state (predrying treatment) and as dried preparations (rehydration) with water (W, reference) or with potassium acetate (K) and malic acid (A) solutions, respectively. It was found that the results were determined by interactions of the examined influencing factors to a great extent. The best hydration properties of all the samples investigated were achieved by a combined demethoxylation and a charging with potassium ions during predrying treatment. In this way, mean values for the maximum W-retention capacities from 73–82 g W/g dried sample were obtained. In contrast, all other LM samples were characterised by reduced hydration properties, independent of the conditions applied (W-retention capacities 30–46 g/g). In the case of HM materials, predrying treatment with K or A decreased the hydration properties compared with the reference material (treatment with W, W-retention capacities 53–57 g/g). In comparison with the rehydration of HM preparations with W, the use of A solution affected the hydration properties negatively, but the application of K solution enhanced the velocity of rehydration. The results of the hydration properties and of the rheological properties of the rehydrated samples were interpreted regarding the preformation of the structure/state during predrying treatment as well as the changes occurring during drying and rehydration.     

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.     

Physicochemical properties of cell wall materials from apple, kiwifruit and tomato

Cell wall materials (CWMs) were isolated from the fruit of ripe apple, kiwifruit and tomato using methods of isolation which maximised the water retaining capacity and viscosity generating properties of the CWMs. Aqueous suspensions of all three CWMs were able to form a gel-like matrix at a concentration of 1%. There was a dramatic enhancement in gel firmness of kiwifruit and tomato following a high shear treatment, but no such effect was apparent with apple CWM. Confocal microscopy showed that the shear-induced increase in viscosity was accompanied by fragmentation of the CWMs of kiwifruit and tomato which increased the available surface area for particle–particle and/or particle–solvent interaction. The viscosity of kiwifruit and tomato CWM dispersions was reduced in the presence of electrolytes indicating an important role for the double electrical layer in the gelling properties of the CWMs. The viscosifying properties of apple CWM were however independent of both shear and added electrolyte. This was attributed to the fact that CWM from apple resisted breakup under high shear. The greater connective integrity of the apple cell walls compared to that of kiwifruit and tomato is discussed in relation to differences in ripening induced changes to the pectic polysaccharides of the cell walls.     

An approach to modeling the rheological properties of food materials

The aim of this study was to develop a mathematical model describing the rheological properties of food materials, including the elastic modulus, consistency index, flow index and flow limit, that are not dependent on the tests (creep and compression stress relaxation) used to establish those values. A rheological model was designed as a parallel combination of spring, viscous and plastic elements. The model was verified logically and empirically based on the results of creep tests and compression stress relaxation tests performed on 10 × 10 × 10 mm cubes cut out from roasted turkey breast muscles. An analysis of the model’s susceptibility to variations in rheological properties indicates that the model is sensitive to changes in the values of the elastic modulus, flow limit and flow index, but it is less susceptible to changes in the consistency index. The model generates similar values of the rheological properties of the studied materials regardless of whether they had been determined based on the results of the creep test or the compression stress relaxation test.     

Calcium effect on mechanical properties of model cell walls and apple tissue

Bacterial cellulose alone, with pectin added and with both pectin and xyloglucan added were produced as models for plant cell walls. The artificial cell wall materials and natural apple tissue were treated with calcium and then subjected to tests of mechanical properties; a tension test for the artificial cell wall materials and a compression test for the apple tissue. It was found that pectin and xyloglucan had a significant effect on the mechanical properties of artificial cell wall materials, making them more extensible. A high concentration of calcium increased the failure strain and decreased the failure stress of these materials. Treatment of apple tissue with calcium had similar effects on the failure stress and the secant modulus, whereas the differences of failure strain and work to failure resulted in behaviour different from that of the artificial material.     

The influence of mechanical and enzymatic disintegration of carrots on the structure and properties of cell wall materials

The aim of this study was to investigate the influence of different disintegration procedures on the structure and properties of cell wall materials from carrots. While the cold-water-extracted reference material consisted mainly of tissue particles, wet homogenisation resulted in cell fragments with nearly unchanged composition and a tendency to aggregate during drying. In contrast, enzymatic treatments changed both the particle size and the chemical composition of the prepared materials. Increasing enzymatic degradation (macerated and liquefied materials) led via single cells to cell fragments and to increasing galacturonan loss as well as to a high aggregation tendency. The particle size and the chemical composition of the materials strongly influenced their properties. Thus, different hydration behaviour, rheological properties and physiological effects were found for the homogenised and for the enzyme-treated materials. Additionally, the properties depend essentially on the mechanical stress applied during rehydration. Such mechanical stress can cause the disaggregation of particles, so it can improve markedly the functional properties. In this way, good hydration properties could be achieved for all the materials prepared. The highest binding capacity of bile acids was determined for macerated material. The concentration of short-chain fatty acids, formed during fermentation with human faeces flora, decreased with increasing degradation of the materials. The complex connections between the structure/composition of the materials and their properties are important for food science and nutrition.     

Aspects of material science in food processing: changes in plant cell walls of fruits and vegetables

 Foods can be regarded as complex, dispersed systems which are normally metastable. Food processing causes state transitions (second-order transitions) when raw materials, food components or food systems are subjected to external stresses. The state transitions occurring during processing are detectable as changes in structure and properties of the investigated systems. The processing of fruits and vegetables is often connected with changes in cell walls. Cell wall materials in dispersed fruit and vegetable systems can be regarded as a model substrate of the dispersed phase. During processing, cell walls undergo modifications in terms of their physical state, macrostructure, microstructure, and composition, as well as structure-dependent changes in their functional and material properties. The interactions and connections (dependencies) between state transitions, and various changes in structure and properties, are very complex and multivariate and are not well understood as yet. For the evaluation of changing material properties during processing, examination of hydration, rheological (external mechanical stress) and thermal (external thermal stress) characteristics is important. The changes occurring during the processing of fruits and vegetables are determined by external factors (especially various mechanical and thermal stresses) and by internal factors. External stress in many cases causes solubilisation of the cell wall, loss of firmness and favours cell separation. Thermal processing increases pectin degradation by β-elimination. Internal factors such as pH and modified ionic strength, e.g. by applying soak solutions, can have an important influence on the changes in the cell wall during processing. So, calcium ions on the one hand can favour cell wall degradation by β-elimination and, on the other hand, after low temperature blanching and de-esterification of the pectin by activated pectin methyl esterase, can contribute to stabilisation of the texture by formation of a calcium-pectin complex. Knowledge about cell wall degradation mechanisms can be markedly improved by studies using model substrates such as pectin, or cell wall materials like the alcohol-insoluble residue and materials with cellular structure. This knowledge has been used to improve the technology used to process fruits and vegetables and to produce products with better properties. Moreover, testing and applying cell wall materials as ingredients for the production of textured foods and potential health-related foods is suggested. Received: 21 July 1998     

The effects of transglutaminase on the functional properties of the myofibrillar protein concentrate obtained from beef heart

The aim of the present study was to evaluate the effect of bacterial transglutaminase on the functional properties of the myofibrillar protein concentrate from beef heart. The degrees of hydration and aggregation and emulsifying properties were studied. The degree of polymerization of the myofibrillar proteins depended on the enzyme concentration and setting time; the best results in terms of functional properties were obtained with 0.3 g transglutaminase/100 g protein with 60 min setting at 35 °C. This investigation confirms that transglutaminase may be used for the production of myofibrillar protein aggregates with enhanced functional properties.     

Traditional and industrial oven-dry processing of olive fruits: influence on textural properties,cell wall polysaccharide composition,and enzymatic activity

The preparation of table olives according to the Italian traditional “Ferrandina” method (Fer) includes an initial blanching step of black Cassanese olives, followed by salting and oven-drying. Its industrial implementation, also called the “Sybaris” method (Syb), replaces the blanching procedure by cutting the olives followed by immersion in water. The measurement of tensile properties showed that the Fer processing increased the weakness, softness, and deformability of the skin and the flesh of olive fruits, while the flesh of the Syb fruits became stronger and stiffer. These differences are probably correlated to the degradation and/or reorganisation of cell wall polysaccharides in the fruits. The degradation of pectic and hemicellulosic polysaccharides in the Fer olives was inferred by their increased solubility in aqueous solutions. Contrarily, retention of pectic polysaccharides was observed in Syb olives. As no correlation was found between cell wall degrading enzymatic activities and cell wall polysaccharides extractability, it is probable that these modifications were driven by heat.     

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.     

Influence of the isolation procedure on the characteristics of fiber-rich products obtained from quince wastes

The upgrading potential of quince (Cydonia oblonga Miller) wastes was evaluated for production of fiber-rich powders with useful functional and physiological properties. As a first approach, three products were obtained by applying different drying conditions without or with a previous extraction either with water or ethanol. Chemical compositions as well as physical and functional properties of the isolated fractions were evaluated in relation to water or oil absorption for characterization. The products obtained presented interesting hydration properties comparable to those reported for citrus and apple pulps. At the same time, all dried fractions showed high spontaneous water absorption rate in the kinetics assay. Oil absorption seemed to essentially depend on the microstructural characteristics of the fiber powders, whereas parameters involving water absorption were really determined by the material’s hydrophilicity. Specific volume, which was also in part a direct function of structural differences, was associated to the ability for oil uptake.     

Material properties of processed fruit and vegetables. II. Water hydration properties of cell wall materials from apples

Apple cell wall material was exposed to different processing steps, commonly used in the fruit and vegetable industry, such as heat and enzymatic treatment (maceration, liquefaction) as well as extraction with diluted acid. The influence of these procedures was investigated with respect to chemical composition and structural features and their effect on the material and functional properties. Besides water binding determinations commonly used, kinetic methods were introduced. In this way it was shown that the treatments influence not only the water retention capacity but also the velocities of swelling and water release under pressure, respectively. Heat treated materials with softened cell walls released water slower than cold water extracted materials. Furthermore, it was found that a high pectin content or a remaining natural grown cell structure are no prerequisites for a good water binding ability. The relationships are rather very complex and multivariate and all factors influence mutually.     

Dietary fiber from coconut residue: effects of different treatments and particle size on the hydration properties

The present work is aimed at the production of dietary fiber from underutilized coconut residue left after the extraction of milk, by subjecting it to physical treatments such as water washing, hot water washing, boiling water washing and pressure cooking, as well as solvent extraction. The fat content was reduced from 62% to 45% and 41% by treatment with boiling water and pressure-cooking, respectively. Water-holding, water retention and swelling capacities increased with decreasing fat content. A marked increase was observed in hydration properties when the fat content decreased from 10 to 2%. The hydration properties were maximum for 550 m particle size coconut fiber. For the higher particle size (1,127 m), the oil was trapped inside the fiber matrix, resulting in decreased hydration properties, whereas for the lower particle size (390 m) the rupture of the fiber matrix was responsible for low hydration properties. An attempt was made to compare the hydration properties of coconut dietary fiber with other commercially available dietary fibers.     

Production of microbial exopolysaccharides in the sourdough and its effects on the rheological properties of dough

Exopolysaccharides (EPS) are exogenous microbial metabolites which are secreted mainly by bacteria and microalgae during growth. In addition to natural polysaccharides present in cereal grains flour and dough, microbial flora is usually involved in production of polysaccharide on sourdough fermentation. Total polysaccharides (microbial and flour) were extracted from sourdough and dough samples dehydrated and were added at the rate of 0%, 0.25%, 0.5%, 1%, 1.5%, 2% and 2.5% (w/w flour based) on the dough to investigate its effects on the rheological properties of the dough. Addition of polysaccharides to the dough increased the water absorption and decreased the dough softening after 20 min. Resistance to extension after 45, 90 and 135 min resting time was decreased by increasing the percentage of the added polysaccharides. Longer fermentation time for each level of polysaccharides led to greater stability. No significant differences were observed in the extensibility of dough. The overall effects of different levels of added polysaccharides resulted in a decrease in resistance to extension ratio of the samples. Energy input decreased in all cases. It seems therefore that addition of polysaccharides may be useful when bread is to be made with stronger flour and longer fermentation time is needed.     

Effect of some hydrocolloids on the rheological properties of different formulated ketchups

Five different hydrocolloids (tragacanth gum, guar gum, carboxy methyl cellulose, xanthan gum and locust bean gum) were added, at levels of 0, 0.5, and 1 g/100 g (w/w), respectively, to three different formulated ketchups which were processed from cold-break tomato paste dilutions, having total soluble solid (TSS) contents of 7.5, 10, and 12.5 g/100 g (w/w), in sequence, and the effect of these hydrocolloids on the rheological properties of tomato ketchups was investigated using a viscometer with smooth surface wide-gap coaxial cylinders. All hydrocolloids increased the consistency of the tested samples; however, guar gum and locust bean gum caused the maximum increase, followed by xanthan gum, tragacanth gum and carboxy methyl cellulose (CMC). Both the ketchup formulation and the hydrocolloid concentration were found to affect the consistency of ketchups. The highest consistency index was obtained by processing dilutions with a TSS content of 12.5%, and the addition of hydrocolloids at the level of 1%. The fluidity of the ketchups decreased with both the addition of all hydrocolloids and the increase in hydrocolloids concentration. Furthermore, the fluidity of the ketchups was also affected by ketchup formulation, and it was found to be the lowest for the samples prepared from the tomato paste dilutions having a TSS content of 12.5%.     

The profile of volatile compounds and polyphenols in wines produced from dessert varieties of apples

The aim of this study was to determine the influence of apple variety (Šampion, Idared and Gloster) on the polyphenol profile, volatile composition and sensory characteristics of apple wines. Apples were harvested from the orchard in Garlica Murowana (Poland) and the experiments were conducted on a laboratory scale. Statistically significant differences were detected in the chemical composition of the analyzed wines. The highest antioxidant activity was found in Šampion wines, which was associated with a relatively high concentration of chlorogenic acid and procyanidins. These samples also contained high amounts of acetaldehyde, ethyl acetate and methanol. Idared wines showed a similar polyphenol profile, but they had lower antioxidant capacity and were characterized by a high level of butanol and acetic acid. Gloster wines were distinguished from other samples by a lower concentration of polyphenols and higher concentration of fusel alcohols. During sensory evaluation, wines produced from Idared apples scored the highest value for overall quality.     

Effect of milk source on the rheological properties of yogurt during the gelation process

This paper presents research on the effect of milk source on the rheological properties of curd during the gelation process of yogurt. The highest value for viscosity was exhibited by ovine milk, followed by caprine, bovine and camel milks. For bovine, ovine and caprine milk, three different transient viscosity stages were identified and described by mathematical expressions, whereas camel milk showed no significant variation in viscosity during gelation. The chemical composition of milk, namely total solids and protein content, has a major effect on the rheological properties of curd. A power law model allows the determination of the flow behaviour index and the consistency coefficient of curd made from different milk sources.     

Cell wall proteins of Kluyveromyces fragilis: Surface and emulsifying properties

Yeast cell wall proteins were extracted from homogenized suspensions with 0.75 mol/l NaOH, yielding after precipitation at isoelectric pH a pale-brown sediment. Lyophilized sample was fractionated on Sephadex G-50 to yield three fractions (Fr 1, Fr 2 and Fr 3). Fr 1, which had the highest yields and protein content, showed the highest molecular weight and best surface properties. Fr 2 and Fr 3 were mainly composed by polysaccharide-protein complexes. Fr 1 was further subfractionated on Sephacryl S-300 to produce three fractions (Fr A, Fr B and Fr C). All subfractions, turned out to be highly foamy during evaporation. The highest yields were obtained for Fr A, which also showed the highest molecular weight. Fractions Fr 1 and their subfractions Fr B and Fr C exhibited good surface activity and high emulsifying activity. Emulsions prepared with these fractions were the most stable against creaming and coalescence. Fr 2 cream phase presented a gel-like behavior as a consequence of polysaccharides acting as thickening agents.     

Impact of emulsifiers on the quality and rheological properties of gluten-free breads and batters

The effects of the emulsifiers lecithin (LC), di-acetyl tartaric ester of monoglycerides (DATEM), distilled monoglycerides (DM) or sodium stearoyl lactylate (SSL) were studied in a gluten-free (GF) batter and bread formulation. Three different levels, i.e. low, medium, and high, were evaluated and compared to a control bread with no emulsifier. The rheological properties of the emulsifiers at their optimum level as well as their effect on starch retrogradation were investigated. Standard baking tests were carried out and the breads were tested over 5 days of storage. Rheological tests suggested that LC reduced the elasticity of the batter and increased the batter consistency during gelatinisation (P < 0.05). A significant increase in the specific volume was found with the addition of the various emulsifiers (P < 0.05). Higher volumes were found for breads with DM whereas lower specific volumes were obtained for the breads with DATEM. With regards to cell size and distribution, significant differences were found across the emulsifiers and the levels used (P < 0.05). Crumb staling revealed significant time effects as well as an increase in the shelf-life by the addition of high levels of DM and SSL. The retrogradation of starch over 5-days did not seem to be affected by the addition of emulsifiers. Overall this study demonstrated that the addition of emulsifiers at their respective optimum level enhanced the quality of the GF breads.