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.     

Role of pectic polysaccharides in structural integrity of apple cell wall material

Texture modulating properties of aqueous dispersions of apple cell wall material differed from those of tomato or kiwifruit, particularly under high shear. It was previously hypothesized that this may be due to the fact that the apple cell wall showed less in vivo solubilization of pectic polysaccharides during ripening compared to tomato or kiwifruit. However, in vitro solubilization of the pectic polysaccharide content of apple CWM by endo-polygalacturonase and/or extraction with 0.05 M sodium carbonate, did not affect the loss in wall integrity shown by tomato or kiwifruit CWMs under shear. In addition, the pectin-depleted residue after Na₂CO₃ extraction possessed better water retaining and viscosity generating properties than the original cell wall material. Following treatment of apple CWM with cellulase, the viscosity of suspensions decreased, emphasising the role that the cellulose–hemicellulose network plays in the water-retaining capacity of the cell wall. Residue from CWM after cellulase treatment consisted of ∼85% pectic polysaccharides. Surprisingly, the integrity of these “cellulose-free” walls was maintained after shear. It is concluded that differences in structural properties of the CWMs of apple compared to kiwifruit or tomato are not simply related to pectin solubilization but to a fundamental difference in the architecture of the apple cell wall.     

Effect of air-drying temperature on physico-chemical properties of dietary fibre and antioxidant capacity of orange (Citrus aurantium v. Canoneta) by-products

Dehydration promoted important modifications affecting both the physico-chemical properties of dietary fibre (DF) and the antioxidant capacity of orange by-products (peel and pulp remaining after juice extraction). The significance of such changes was largely dependent on the air-drying temperature used (from 30 °C to 90 °C). The major modifications on the DF components were observed when either extended drying periods, i.e. at lower temperatures, or elevated drying temperatures were applied. Dehydration around 50–60 °C apparently promoted the minor disruption of cell wall polymers, in particular of pectic substances. Pulp samples exhibited higher values of swelling (SW) and fat adsorption capacity (FAC) than those derived from orange peel. Although, significant decreases in water retention capacity (WRC), FAC and solubility values were detected for both by-products as the air-drying temperature increased. The antioxidant capacity associated to dehydrated citrus by-products was significantly higher for orange peel than for pulp samples. In general, the by-products studied proved to be quite resistant to the different heat treatments applied within the range of 40–70 °C. In overall, the study shows that, in order to preserve either the DF quality and/or the antioxidant capacity, air-drying temperature should be controlled since both types of compounds, DF components and antioxidants, might be degraded or modified either when extended drying periods and/or high drying temperatures are applied.     

Ripening-associated changes in the amounts of starch and non-starch polysaccharides and their contributions to fruit softening in three banana cultivars

BACKGROUND: Fruit softening is generally attributed to cell wall degradation in the majority of fruits. However, unripe bananas contain a large amount of starch, and different banana cultivars vary in the amount of starch remaining in ripe fruits. Since studies on changes in pulp firmness carried out with bananas are usually inconclusive, the cell wall carbohydrates and the levels of starch and soluble cell wall monosaccharides from the pulps of three banana cultivars were analysed at different ripening stages. RESULTS: Softening of Nanicão and Mysore bananas seemed to be more closely related to starch levels than to cell wall changes. For the plantain Terra, cell wall polysaccharide solubilisation and starch degradation appeared to be the main contributors. CONCLUSION: Banana softening is a consequence of starch degradation and the accumulation of soluble sugars in a cultivar‐dependent manner. However, contributions from cell wall‐related changes cannot be disregarded. Copyright © 2011 Society of Chemical Industry     

Effect of methyl jasmonate on cell wall modification of loquat fruit in relation to chilling injury after harvest

Loquat fruit were pretreated with 10 μM methyl jasmonate (MeJA) for 24 h at 20 °C, and then stored at 1 °C for 35 days to investigate the effect of MeJA treatment on cell wall modification in relation to chilling injury. Loquat fruit developed chilling injury, manifested as increased fruit firmness and internal browning, decreased extractable juice during storage. These chilling injury symptoms were significantly reduced by MeJA treatment. MeJA also markedly delayed the increases in lignin, alcohol insoluble residues, hemicellulose and cellulose. Meanwhile, the MeJA-treated fruit exhibited significantly lower activities of phenylalanine ammonia lyase, peroxidase, polyphenol oxidase and higher polygalacturonase activity than the control during storage. The levels of water- and CDTA-soluble pectins in MeJA-treated fruit were also significantly higher than that in the control. These results suggest that the reduction in chilling injury by MeJA may be due to inhibited lignin accumulation and enhanced cell wall polysaccharides solubilisation.     

Dehydrofreezing of pineapple

Dehydrofreezing technique involves one step of partial dehydration before freezing, in order to diminish the tissue damage by removing part of water from vegetable tissue prior to freezing. The objective of the present study was to evaluate the effect of osmotic dehydration and hot air-drying, applied previous to the freezing process, on the end quality of pineapple slices. Quality loss was quantified through drip loss, ascorbic acid content and mechanical properties changes of tissue. Freezing was carried out in a conventional air-blast tunnel at −31.5 ± 2 °C. Mechanical properties of fresh and dehydrated fruit, with and without the later process of freezing, were evaluated through compression tests. Ascorbic acid content was quantified by liquid chromatography. Osmotic dehydration and hot air-drying have the beneficial effect of reducing the time necessary for pineapple samples freezing. The freezing–thawing process affects the values of pineapple samples mechanical properties. Ascorbic acid losses were somewhat greater during the osmotic dehydration than with air dehydration.     

Effect of mash maceration and ripening stage of apples on phenolic compounds and antioxidant power of cloudy juices: A study using chemometrics

The effects of different enzymatic preparations on total phenolic content, phenolic profile (HPLC), and ferric reducing antioxidant power (FRAP) of cloudy juices from Lis Gala and Fuji Suprema apples varieties, at three ripening stages (unripe, ripe and senescent) were investigated using Principal Component Analysis and Hierarchical Cluster Analysis. The commercial preparations enzymatic (Ultrazym^® AFPL; Pectinex^® Ultra Clear; Pectinex^® SMASH XXL; Panzym^® YieldMASH) increased the total phenolic compounds and ferric reducing capacity of the cloudy juice from unripe and ripe Lis Gala (respectively by 67 and 49% for unripe apples, and 28 and 33% for ripe apples) and unripe Fuji Suprema apples (23 and 55%), while for the ripe Fuji Suprema apples only Pectinex^® Ultra Clear and Panzym^® YieldMASH had this effect. No significant (p > 0.05) was observed on senescent stage, whatever the enzymatic preparation. Enzymatic preparations could increase phenolic compounds concentration and antioxidant capacity of cloudy apple juice, but this effect depended on the maturity of the apples.     

Influence of strawberry tree (Arbutus unedo L.) fruit ripening stage on chemical composition and antioxidant activity

Arbutus unedo is a widespread shrub with economic importance, derived from the use of its berries in the production of alcoholic beverages and in folk medicine. This work intends to evaluate for the first time the effect of fruit ripening stage on antioxidant activity, total phenolic content, fatty acid profile and tocopherol composition. Ripe fruits shown higher extraction yield (45.04 ± 2.23%) when compared to other fruit ripening stages. By contrast, total phenol contents were higher in the unripe and intermediate stage of ripeness (108 and 111 mg GAES/g dry fruit, respectively, against 60 mg/g dry fruit when ripe). Ripe and intermediate fruits shown the lower EC₅₀ values on the DPPH radicals (0.25 ± 0.02 mg/mL) and reducing power assay (1.09 ± 0.05 mg/mL), respectively. A significant correlation was established between antioxidant activity and fruits ripening stage. Fatty acid profiles were very similar between the ripening stages, being alfa-linolenic, linoleic and oleic, the three major ones. Polyunsaturated fatty acids (PUFA) represent as much as 60% of the total fatty acids, with a highly favorable omega 3/omega 6 ratio. From the analysis of the vitamin E vitamers, the most important was ??-tocotrienol, with a clear reduction in the total free vitamin E content with ripening.These results highlight that the fruits of intermediate ripeness can be regarded important sources of biologically active compounds with a fatty acid profile rich in omega-3 PUFA, properly supplemented with high vitamin E amounts.     

Soluble phenols and antioxidant activity in mamey sapote (Pouteria sapota) fruits in postharvest

Mamey sapote (Pouteria sapota (Jacq.) H. E. Moore & Stearn) is a tropical species from the Sapotaceae family native to Mexico and Central America. Its tree produces an edible climacteric fruit, whose weight can range from 250 to 900 g. The flesh is soft, comprises about 78% of the fruit, and has high sugars to acidity ratio, which gives it a sweet taste when ripe. Because of current public interest to consume products that promote health, the aim of the work was to characterize soluble phenolic content and antioxidant activity in mamey sapote fruits from Chiapas, Mexico, at different maturity stages. Storage at 12 (± 1) °C was conducted for 18 d. When fruits ripened firmness flesh varied, in average, from 41.8 to 3.0 N, soluble solids content from 17.7 to 28.1 ºBrix, hue angle from 56.4 to 46.3º, and lightness from 67.3 to 42.0. Phenolic content was affected by ripening since average values of 2563 and 234 ??g/g were found in unripe and consumption maturities, respectively. In a soluble phenolics extract from flesh, gallic acid (GA), gallocatechin-3-gallate (G3G), epicatechin (ECT), and catechin (C) were found, being the latter the most abundant compound, which increased with ripening from 9.9 to 113.1 ??g/g, while GA, G3G, and ECT had average values of 4.7, 11.9, and 5.8 ??g/g, respectively, without significant variation. Antioxidant activity, expressed through the IC₅₀ parameter, remained practically unchanged and showed an average value of 12.9 ??g/mL. Based on phenolic composition the mamey sapote fruit may constitute a good source of antioxidant compounds.     

The influence of the pre-treatment of apple cell wall samples on their functional properties

Apple cell wall materials (CWMs) exhibiting different degrees of cell wall degradation were prepared by the application of maceration and liquefaction enzymes (control sample without treatment), and their physico-chemical properties were investigated. Different methods were used for the determination of the water binding behaviour and the rheological properties. It was found that the standardized analysis methods gave results of limited correctness depending on the sample type and on the sample pre-treatment. Aggregates, formed during the drying of apple CWM that was treated with liquefaction enzyme, could be re-dissolved by mechanical stress (stirring) during rehydration. The stirring improved the detected functional properties (water binding and rheology) of the material to a great extent. It has to be realized that the analysis methods including the sample pre-treatment have to be adapted to the type of sample material. Furthermore the investigations showed that the water binding properties of CWMs do not simply correlate with separate parameters such as porosity, pectin content or the remaining natural grown cell structure. Probably, the functional properties are influenced mutually and multivariately by many material attributes.     

Non-starch polysaccharide compositions of rice grains with respect to rice variety and degree of milling

The chemical compositions of cell wall materials (CWM) in brown and milled rice were investigated using four rice varieties, Taichung Sen 10 (TCS10, indica), Tainung 67 (TNu67, japonica), Taichung Sen Waxy 1 (TCSW1, indica waxy), and Taichung Waxy 70 (TCW70, japonica waxy). The yield of CWM preparation, equivalent to total dietary fiber content, followed the order of TNu67 > TCS10 > the waxy cultivars. This order also held for the water solubility and pectic substance content of the CWM preparations and the compositional ratio of arabinose to xylose of all CWM samples. Comparatively, the nonwaxy CWM were rich in pectic substances and glucans; whereas the waxy CWM counterparts were dominant with hemicellulose plus cellulose and arabinoxylan-related polysaccharides. These results were more significant for the hot-water-soluble than insoluble parts and mainly dependent of rice variety rather than the degree of milling.     

Classification of juices and fermented beverages made from unripe,ripe and senescent apples based on the aromatic profile using chemometrics

The aim of this study was to assess differences between apple juices and fermented apple beverages elaborated with fruits from different varieties and at different ripening stages in the aroma profile by using chemometrics. Ripening influenced the aroma composition of the apple juice and fermented apple. For all varieties, senescent fruits provided more aromatic fermented apple beverages. However, no significant difference was noticed in samples made of senescent or ripe fruits of the Lisgala variety. Regarding the juices, ripe Gala apple had the highest total aroma concentration. Ethanal was the major compound identified in all the samples, with values between 11.83 mg/L (unripe Lisgala juice) and 81.05 mg/L (ripe Gala juice). 3-Methyl-1-butanol was the major compound identified in the fermented juices. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were applied and classified the juices and fermented juices based on physicochemical and aroma profile, demonstrating their applicability as tools to monitor the quality of apple-based products.     

Effect of temperature on the cell wall composition of raisins during storage under a modified atmosphere

 Raisins obtained from seedless grapes ("Flame" variety) were kept under a modified atmosphere (MA) composed of CO₂ (60%) and N₂ (40%), and stored at 10  °C (10MA), 20  °C (20MA), 30  °C (30MA) and 40  °C (40MA). An additional sample was stored under air at 20  °C (20A). Colour, and changes in cell wall components were monitored during storage. At the end of the storage period, the 40MA and 20A samples showed a significant decrease (∼18–19%) in the yield of cell wall material (CWM), whereas less than 6% of CWM had been degraded in the 10MA sample. The decrease in CWM was mainly due to pectic polysaccharide degradation, although for 20A and 40MA samples, hemicelluloses were also affected. Throughout storage, 10MA, 20MA and 30MA samples exhibited similar CWM solubility; however, that of the 40MA sample underwent a significant decrease, from 10% to 4.5%, probably due to the formation of new pectic chains of higher molecular weight. In contrast, the CWM solubility of sample 20A increased from 10% to 15%, suggesting that MA may have promoted the inhibition of pectic-polysaccharide-degrading enzymes. In general, the combined use of relatively low temperatures and a MA helped to preserve both the colour of raisins and maintain the levels of their CWMs at values similar to initial concentrations. Received: 5 October 1998     

Functional properties of square banana (Musa balbisiana) starch

Starch was isolated from unripe square banana (Musa balbisiana) fruit and its functional properties were determined. Square banana starch peak gelatinisation temperature was 79.8 °C and the transition enthalpy was 17.3 J/g. At 90 °C, the solubility was 16.8%, the swelling power was 17.1 g water/g starch and the water absorption capacity was 14.3 g water/g starch. The paste properties were: temperature, 81 °C; maximum viscosity, 326 BU; breakdown, 22 BU; setback, 40 BU and consistency, 18 BU. The clarity, expressed as transmittance, was 17.5%, and gel deformation was 32.4% with a 0.03 kgf maximum load. This starch had high syneresis and low stability in refrigeration and freezing cycles. Given its properties, square banana starch has potential applications in food systems requiring high temperature processing, such as jellies, sausages, bakery and canned products. It is inappropriate, however, for use in refrigerated or frozen foods.     

Changes in skin cell wall composition during the maturation of four premium wine grape varieties

BACKGROUND: Grape skin cell walls form a barrier against the diffusion of colour. The colour of red wines is mainly due to anthocyanins, although their concentration in wine is not always correlated with the anthocyanin content of grape skins. The cell wall composition changes during fruit ripening, so it was thought that a study of the ripening behaviour of four premium varieties might provide information on how the composition changes during ripening and explain the technological differences. RESULTS: The largest quantities of skin cell wall material (CWM) were isolated from Monastrell grapes, probably owing to the greater number of cell layers they contain and the thicker cell walls. During ripening, a loss of skin CWM (e.g. 120–60 and 65–45 mg CWM g^?1 fresh skin for Monastrell J and Cabernet Sauvignon respectively) and galactose (e.g. 36–20 and 55–30 mg g^?1 CWM for Cabernet Sauvignon and Monastrell J respectively) was observed, together with a decrease in the degree of pectin methylation and acetylation, except in Syrah, in which pectin methylation remained unchanged. These changes were accompanied by the accumulation of glucose, while other neutral sugars showed no significant variations. A correlation was found between the degree of ripening and those constituents changing in the grape skin cell wall. CONCLUSION: The cell wall composition differs sufficiently between grape varieties to allow discrimination between them. Ripening was associated with a decrease in the quantity of CWM and galactose in the cell walls. Monastrell showed the largest quantities of both throughout ripening. The differences observed between Monastrell and the other varieties would explain the technological differences between them. Copyright © 2007 Society of Chemical Industry     

Foaming and drying behaviour of ripe bananas

The foaming of ripe bananas and the forced air-drying characteristics of the resulting banana foam mats were studied. Fresh banana puree with a density of 0.93 g/ml was foamed to a density of 0.50 g/ml after 12 min of whipping by the addition of 10 g/100 g soy protein as a foam inducer. Glyceryl monostearate did not induce foaming while commercially available food ingredients, Dream Whip and Gelatine induced foaming but such foams were not suitable for subsequent drying. Banana foam mats were dried at temperatures from 45°C to 90°C in a forced air, cabinet dryer, to a hard, porous and brittle solid which was amenable to grinding so as to produce a dehydrated banana powder. The transient drying behaviour of such mats was described by a capillary model of the form ln(M/M₀)=−Kt and over the bulk of the moisture ratio range, 0.05?M/M₀?1.0. The drying time (t) was directly related to the thickness of the foam mats. K values increased from 0.248 to 0.809 h⁻¹ as the drying air temperature was raised from 45°C to 90°C. Increasing the air velocity from 0.62 to 1.03 m/s did not profoundly influence the drying rate.     

CHARACTERISTICS OF PECTINS ISOLATED FROM SOFT AND FIRM FLESHED PEACH VARIETIES

Pectins obtained from ripe and unripe samples of Elberta (melting fleshed variety) and Babygold 6 (firm fleshed variety) peaches had methoxyl levels ranging from 11.4–12.1% and anhydrogalacturonic acid levels between 84–90%. The apparent molecular weight of the pectin from ripe Elberta peaches was very low compared with that of the other samples, resulting in a low breaking pressure of jelly prepared with this sample. Jelly grades ranged between 102–123 and it is suggested that these low values were a result of the presence of acetyl groups present in peach pectins and their relatively low apparent molecular weights and high methoxyl levels     

Drying kinetics of nopal (Opuntia ficus-indica) using three different methods and their effect on their mechanical properties

Nopal (Opuntia ficus-indica) is an endemic plant of the arid and semiarid lands of America. Preservation problems are associated with nopal utilization and processing, so a practical alternative is dehydration. This work deals with the drying of nopal correlated with the textural properties of the dried product. Convective drying studies were performed and the most representative experimental results at two air flow rates (3 and 5 m/s) and two air temperatures (45 and 65 °C) are displayed here. Experiments of osmotic drying with glucose at 40 and 60 °Brix, and drying temperatures of 25 and 45 °C were tested. A combination of both drying processes was also performed. Results have shown forced convection drying with a mostly decreasing trend at the constant rate period. In the osmotic drying, moisture loss was associated to glucose concentration. Texture profile analysis of dehydrated nopal suggested that samples undergoing convective drying have more cohesiveness than samples treated solely by osmotic drying. On the other hand, samples treated by osmotic drying became more elastic. Between the two drying methods studied, the convective drying has shown the best results at the experimental conditions assayed.