Polyphenoloxidase (PPO) activity and osmotic dehydration in Granny Smith apple

Osmotic dehydration (OD) permits the preservation of foods via a decrease in water content and an increase in solute concentration. Osmotically dehydrated fruits such as apple are suitable for the manufacture of desserts, cakes, salads, yoghurts, etc. Different microstructural and engineering aspects of OD are already known, but its effects on enzymatic activity are still unknown. This study analyses the activity of polyphenoloxidase (PPO) in fresh Granny Smith apples and the effect that OD by immersion in sucrose‐saturated syrup has on this activity. The low PPO activity found in the edible parenchyma of osmotically dehydrated apples is attributed to penetration by the osmotic agent and flooding of the intercellular spaces, which produces a low moisture content and a limited O₂ concentration in the immediate environment of the enzyme. These results show that OD prevents enzyme–substrate interaction. Thus the low PPO activity would reduce browning of this type of product. Copyright © 2005 Society of Chemical Industry     

Impact of mass transport on microstructure of Granny Smith apple parenchyma during osmotic dehydration

The chemical components of foods are organized in microscopic structures that can modify mass transfer. The study of material penetration in foods can be made using X‐ray microanalysis. In order to study the microstructural behaviour when fruit was osmotically dehydrated, a glucose molecule modified with chloral (1,2‐O‐2′,2′,2′‐trichloroethylidene‐α‐D ‐glucofuranose) was used as an osmotic standard with chlorine detectable by energy‐dispersive X‐ray analysis. Parenchyma of Granny Smith apple is a simple tissue, so it was chosen as reference. The results show that both the apoplastic and symplastic routes played an active role in mass transfer. The osmotic agent penetrated both the symplast and apoplast well into the depths of the fruit, although greater deterioration of cells was observed near the surface. Copyright © 2003 Society of Chemical Industry     

Influence of ohmic heating/osmotic dehydration treatments on polyphenoloxidase inactivation,physical properties and microbial stability of apples (cv. Granny Smith)

The combined effect of ohmic heating (OH) and osmotic dehydration (OD) with vacuum impregnation (VI), on the polyphenoloxidase (PPO) inactivation, physical properties and microbial stability of apples stored at 5 °C or 10 °C was analyzed. The treatments were performed using a 65% (w/w) sucrose solution and with ohmic heating at 13 V/cm at 30 °C, 40 °C or 50 °C for 90 min. Examination of the dehydrated samples showed that the water loss and the solid gain were greater with the OD/OH and VI/OH treatments at 50 °C. PPO was completely inactivated by the OD/OH and VI/OH treatments at 50 °C. There was a correlation between the PPO activity, the color change and the browning index of the treated and stored samples; the values for these parameters were stable when PPO was inactivated. The lowest loss of firmness and color was obtained with the VI/OH treatment at 50 °C. The shelf-life of the apples treated with VI/OH at 50 °C and stored at 5 °C was extended to more than 4 weeks. Therefore, the VI/OH treatment at 50 °C was determined to be the best process for dehydrating apples.Industrial relevanceThe aim of this research was 1 to study the combined effect of ohmic heating (OH) and osmotic dehydration (OD) with vacuum impregnation (VI) on the polyphenoloxidase inactivation and microbial stability of osmotically dehydrated apples stored at either 5 °C or 10 °C. Two technologies, OH and OD were performed at 30, 40 or 50 °C with an electric field intensity of 13 V/cm and conventional heating for 90 min. The results showed a correlation between the PPO activity, the color change and the browning index of the treated and stored samples; the values were stable when PPO was inactivated. PPO was completely inactivated by the OD/OH and VI/OH treatments at 50 °C. The shelf-life of the apples treated was extended to more than 4 weeks. Under the investigated conditions, VI/OH treatment at 50 °C and stored at 5 °C may be considered the better minimal processing that preserves the fresh-like properties.     

Relationships between texture,mechanical properties and structure of cornflakes

Hominies and flours derived from four corn varieties were prepared according to industrial recipes and processed as petals by extrusion cooking (SME = 150 J g⁻¹, T_die = 130 °C) and a batch thermal process (100 °C, 50 min). Flake texture was evaluated by crushing bulk petals in a Kramer cell and comparing measurements to those obtained for commercial cornflakes, previously graded by a trained sensory analysis panel. Depending on the corn variety, various results were found in regard to crispness. Bending moduli of dense extruded materials (E_s from 0.5 to 2.1 GPa) were found to be correlated to the texture of petals derived from the same blends. Results obtained at different scales showed that the expanded microstructure of flakes, determined by X-ray tomography, and the morphology of their constitutive materials, deduced from confocal scanning light microscopy and RVA, primarily depended on the process used rather than on the corn variety. Adhesion between protein aggregates and amorphous starch matrix was inferred from the mechanical properties involved in texture.     

Impact of combined ascorbic acid/CaCl2, hydrogen peroxide and ultraviolet light treatments on structure,rheological properties and texture of fresh-cut pear (William var.)

This work aimed to evaluate and correlate rheological properties (dynamic oscillatory, creep/recovery and double compression tests), texture (sensory evaluation) and structure (optical and transmission electron microscopy observations) of fresh-cut pear as affected by ascorbic acid/CaCl₂ dipping, hydrogen peroxide and short-wave ultraviolet light radiation (UV-C). All pear samples showed a solid behavior (G′ > G’’), but both dynamic moduli decreased in response to the treatments. For treated tissues, the instantaneous elastic (J₀) and the retarded (J₁, J₂) compliances increased, while the steady-state viscosity (η_N) and all mechanical parameters decreased. PLS regression models revealed that texture could be well explained by rheological properties. Deformability modulus (E_d) was positively correlated to sensory fracturability and hardness and negatively correlated to juiciness. J₀, J₁ and J₂ were negatively related to sensory hardness. Compression and creep parameters evidenced changes in structure (mainly rupture of membranes, degradation of middle lamella and cell walls) of surface tissues.     

Osmotic dehydration of apple: Influence of sugar and water activity on tissue structure,rheological properties and water mobility

Osmotic dehydration of apple tissue (Malus pumila, Granny Smith cultivar) to water activity (a_w) 0.97 or 0.94 with maltose or maltose syrup solutions was studied and compared with previous results using glucose or trehalose as humectants. Structure (optical and transmission electronic microscopy observations), rheological properties (small scale dynamic oscillatory and creep/recovery measurements and large scale compression force-deformation testing), and water mobility (¹H NMR spectra) of parenchymatous apple tissue were significantly affected by osmotic treatments. Osmotically dehydrated apples became soft and extensible and lost crispness and hardness, while the behavior of the moduli G′ and G″ indicated weaker gels after osmosis. Compression properties of the tissues abruptly changed after osmotic dehydration to a_w 0.97, while reduction to a_w 0.94 led to a compression response more similar to that of untreated apples. Compression behavior and state and distribution of water in apple tissues were influenced by the osmotic agent employed and the a_w level, while in general mechanical spectra and creep analysis were not able for distinguishing physical differences between osmotic treatments assayed.     

Volatile profile of mango (Mangifera indica L.), as affected by osmotic dehydration

The effect of osmotic dehydration on the volatile fraction of mango fruit was studied. Osmotic treatments were carried out at atmospheric pressure (OD) and by applying a vacuum pulse (PVOD). Sucrose at 35, 45, 55 and 65 °Brix was used as osmotic solution until reaching 20 or 30 °Brix in the liquid phase of dehydrated mango. Volatile compounds of fresh and dehydrated samples were obtained by simultaneous distillation–extraction, and analyzed by GC–MS. In general, osmotic dehydration provoked changes in the concentration of analyzed compounds to different extents, depending on process conditions. The use of highly concentrated osmotic solutions, and the high level of sample osmodehydration, induced losses of volatiles with respect to the fresh samples. On the other hand, more heavily diluted solutions and shorter treatment times (lower osmodehydration level) could give rise to the enhancement of volatile production. In these cases, sample mass loss was reduced during treatment since sugar gain was promoted against water loss.     

Composition,structure, rheological properties,and sensory texture of processed cheese analogues

Processed cheese analogues were made with different fat and moisture in nonfat solids (MNFS) contents and used to study relationships between composition, microscopic structure, rheological properties and sensory texture. Fat contents ranged from 58 to 230 g kg^?1 and MNFS from 487.6 to 603.3 g kg^?1. Regressions showed that those rheological parameters measured by uniaxial compression at large deformations and moderately high rates were best explained by linear combinations of MNFS, protein and fat. The moisture in the protein network acted as a plasticiser lowering the rheological parameters. Fat alone had little direct effect on the rheological characteristics under these conditions but at small deformations and low deformation rates it formed elastic inclusions that contributed to the properties. Examination of fracture surfaces in the SEM suggested that, during fracture, fat was squeezed out and acted as a lubricant. Maximum stress and work to maximum stress measured at moderately high deformation rates related best to the sensory results and described fracture of the cheeses. From the regressions, for 95% confidence limits, sensory analysis could theoretically measure changes within the range of composition tested of <0.1% in MNFS or fat. Of the rheological parameters only work to maximum stress was as sensitive. However, interaction between these compositional factors reduced the sensitivity in practice.     

Relation between mechanical properties and structural changes during osmotic dehydration of pumpkin

This work presents the changes in the mechanical properties of pumpkin (Cucurbita pepo L.) fruits when submitted to osmotic dehydration processes. Cylinders of the parenchymatic tissue were dehydrated with sucrose solutions, varying the concentration (30–60% w/w) and temperature (12–38 °C) of the osmotic solution and process time (0–9 h). As an opposite process to dehydration, water soaking of some cylinders was also performed. Samples were submitted to uniaxial compression until rupture, and four parameters were analyzed: apparent modulus of elasticity, true stress at failure, Hencky strain at failure and failure work (toughness). Values of these mechanical properties for fresh material ranged from 0.96 to 2.53 MPa for apparent modulus of elasticity, 250–630 kPa for failure stress, 0.42–0.71 for failure strain and 85–285 kJ/m³ for toughness. Mechanical properties of osmodehydrated samples showed no dependence on concentration of the osmotic solution and process temperature, whereas they were found to be dependent on moisture content: apparent elastic modulus decreased and failure strain increased during dehydration; toughness and failure stress initially decreased with moisture content, and increased at advanced stages of the process. Water soaked samples showed a decrease in failure strain, failure stress and toughness, but the apparent elastic modulus increased. Simultaneous structural observation during compression showed that the material fails in the contact zones of its fibres. This fact and the observed structural profiles during dehydration could explain the changes in the failure properties (strain, stress, toughness) along the studied processes. Changes in the apparent modulus of elasticity were likely related with the changes in the turgor pressure of cells.     

Mass transfer kinetics during osmotic dehydration of bananas (Musa sapientum,shum.)

Osmotic dehydration is used widely to partially remove water from plant tissues by immersion in a hypertonic solution. In this work, the influence of temperature (25–55 °C), sugar concentration (30–60%) and salt concentration (0–10%) of the osmotic solution was investigated during osmotic dehydration of banana (Musa sapientum, shum.). Mass transfer kinetics were modelled according to Peleg’s equation. Kinetic parameters were evaluated using response surface methodology. Peleg’s equation showed to be suitable for modelling the water removal and solute uptake. Initial rate of water loss and water concentration at equilibrium were influenced by linear factors of the three independent variables. Initial rate of sucrose uptake and sucrose uptake at equilibrium were affected by all factors and interactions. Initial rate of salt uptake and salt concentration at equilibrium showed a positive correlation with temperature and NaCl concentration and a negative correlation with sucrose concentration.     

Monitoring post-harvest quality of Granny Smith apple under simulated shelf-life conditions: destructive, non-destructive and analytical measurements

The purpose of this research was to use destructive and non-destructive measurement methods to evaluate Granny Smith apple quality changes under room storage conditions (20°C, 65% relative humidity) and to relate it to internal structure changes as observed using light microscopy. The Granny Smith apple Firmness was non-destructively measured with forced vibration and acoustic impulse techniques. At the determined time intervals, compression and tensile tests were carried out to determine apple Flesh mechanical properties. The cell-wall rupture was examined with light microscopy. The pH value, internal air space (IAS), soluble solids concentration (SSC), colour changes and weight losses of the apples were also monitored during storage. Apple Firmness measured with forced vibration correlated well with the impulse test. The acoustic impulse measurement had less deviation compared with the vibration test. The pH value and IAS increased during storage at room temperature. The Granny Smith apple has a long storage life and the criteria for the mealiness are suggested from compression and tensile tests.     

Effects of massaging time on texture, rheological properties, and structure of three pork ham muscles

Changes in texture parameters (hardness, cohesiveness, chewiness), rheological properties (elastic and viscous moduli), and structural elements (fibre cross-sectional area and thickness of peri- and endomysium) of three pork ham muscles: Biceps femoris (BF), Semimembranosus (SM), and Quadriceps femoris (QM), subjected to effective massaging for 2, 4, 6, 8, 10, 12 h were followed. BF, with its higher fibre cross-sectional area thicker peri- and endomysium, compared with QF and SM, was harder, more elastic, and more viscous than the other two muscles. Massaging resulted in an increase in the mean fibre cross-sectional area, changes in thickness of the peri- and endomysium, and a reduction in hardness and chewiness as well as in elastic and viscous moduli of the muscles studied. The lower were the initial values of textural and structural parameters and rheological properties of a muscle, the shorter massage time was necessary. To arrive at comparable values of textural parameters, rheological properties, and a similar sensory acceptance, BF, SM, and QF had to be effectively massaged for 12, 6, and 4 h, respectively.     

Viscoelasticity, texture and ultrastructure of cut apple as affected by sequential anti-browning and ultraviolet-C light treatments

The aim of this work was to analyze the effect of UV-C radiation (fluence: 11.2 kJ/m²), with or without an anti-browning pretreatment containing 1% (w/v) ascorbic acid plus 0.1% (w/v) calcium chloride, on the linear viscoelastic properties (oscillatory shear and creep/recovery), instrumental texture (TPA), sensory texture and ultrastructure (ESEM, TEM) of cut apple. Changes in structural features and viscoelastic parameters were mainly evidenced after refrigerated storage. All samples showed a viscoelastic solid behavior with the storage modulus (G′) dominating the viscoelastic response. Overall, both dynamic moduli decreased, and instantaneous compliance (J₀), decay compliances (J₁ and J₂) and fluidity significantly increased after treatments and storage at 5 °C, while retardation times were in general constant. Fracture properties proved to be the most highly correlated with sensory texture. The test panel only significantly differentiated stored untreated apple from the other samples regarding fracturability and juiciness. Mechanical spectra and creep parameters showed ability to evidence ultrastructural differences (rupture of membranes, swelling of cells, alteration of cell walls) in the surface of cut apples subjected to the different treatments.     

Evaluation of water, sucrose and NaCl effective diffusivities during osmotic dehydration of banana (Musa sapientum, shum.)

Osmotic dehydration of banana (Musa sapientum, shum.) was optimized with respect to temperature (25-55 °C), salt (0-10 g/100 g) and sucrose (30-60 g/100 g) concentrations through response surface methodology. The solution of Fick’s law for unsteady-state mass transfer in a cylindrical configuration was used to calculate the effective diffusivities of water, sucrose and NaCl. Analyses were conducted in triplicate for moisture, sugar and salt contents. Peleg’s model was used to predict the equilibrium condition, which was shown to be appropriate for water loss and solute uptake. For the above conditions of osmotic dehydration, the effective diffusivity of water was found to be in the range of 5.19-6.47 × 10⁻¹⁰ m² s⁻¹, the sucrose effective diffusivity between 4.27-6.01 × 10⁻¹⁰ m² s⁻¹ and that of NaCl between 4.32-5.42 × 10⁻¹⁰ m² s⁻¹. The working conditions that simultaneously optimize these 3 variables were the temperature of 25 °C with a solution composed of 30 g/100 g of sucrose and 10 g/100 g of sodium chloride. This condition provided values of 4.80 × 10⁻¹⁰ m² s⁻¹ for effective diffusivity of water, of 3.21 × 10⁻¹⁰ m² s⁻¹ for effective diffusivity of sucrose and 4.49 × 10⁻¹⁰ m² s⁻¹ for effective diffusivity of sodium chloride.     

Effects of high hydrostatic pressure (HHP) on bioaccessibility,as well as antioxidant activity,mineral and starch contents in Granny Smith apple

The aim of this work was to study the effect of high hydrostatic pressure on the bioaccessibility of specific nutrients (antioxidant, minerals and starch) in apple and to establish processing conditions that maximise the health benefits. The apple was pressurised at 500 MPa during 2, 4, 8 and 10 min. The antioxidant activity, mineral and starch content and bioaccessibility of apple samples were significantly affected by the processing and digestion conditions. Therefore, these results indicated that in vitro digestion has a noticeable effect on the antioxidant concentration, IC₅₀, with much lower values (a smaller IC₅₀ value corresponds to a higher antioxidant activity) of apple samples compared with those untreated and non-digestion. Apple has the highest calcium content (30.33 ± 1.94 mg/100 g), iron (14.46 ± 3.49 mg/100 g) and zinc (6.22 ± 0.91 mg/100 g). High hydrostatic pressure increased the mineral contents availability by 2.11–303.00% for calcium, 4.63–10.93% for iron and 8.68–28.93% for zinc. The dialysability and solubility of calcium, iron and zinc with respect to the values for the untreated sample were reduced by this high pressure technique. Consumption of apple under high hydrostatic pressure may supply substantial antioxidants, mineral and starch, which may provide health promoting and disease preventing effects.     

The effect of calcium and cellular permeabilization on the structure of the parenchyma of osmotic dehydrated ‘Granny Smith’ apple

Calcium plays a very important role in the maintenance of quality in vegetable foods and it is used as a texturing agent to preserve the structure of minimally processed vegetables. The osmotic dehydration (OD) of ‘Granny Smith’ apple parenchyma by immersion in a sucrose solution allows us to obtain products with sensorial characteristics similar to those of fresh products, but it produces a loss of cellular integrity. Here we study the use of calcium as a possible preservative for the microstructural integrity of the product during OD, as well as to test whether cellular permeabilization improves the impact of calcium on the edible parenchyma of the ‘Granny Smith’ apple. Sodium dodecyl sulfate (SDS) has been used for convenience as a permeating agent although we recognize this may not be used in practice. The microstructure of the OD apple treated with calcium chloride and with SDS has been compared with fresh apple by means of light microscopy, transmission electron microscopy and low temperature scanning electron microscopy. The results show that calcium has a protective effect on the structural integrity during OD: it strengthens the cellular walls cements, avoids cellular collapse and protects protoplasts from plasmolysis. Although SDS favours calcium penetration, its use is not advisable since it encourages the destructuring effect of the OD and counteracts the consolidating effect of calcium. Copyright © 2004 Society of Chemical Industry     

Effect of osmotic dehydration with different osmosis agents on water status,texture properties,sugars, and total carotenoid of dehydrated yellow peach slices

The water status, texture properties, sugars, and total carotenoid of dehydrated yellow peach slices pretreated with or without osmotic dehydration (OD) combined with heat pump drying were studied. In this study, different osmotic agents were used, namely, sucrose and isomaltooligosaccharide (IMO) with 30 °Brix for 1, 3, and 5 h. Results showed that the dehydrated samples pretreated by sucrose-OD with the best shape and cell structure showed lower hardness compared to the dehydrated yellow peach slices with IMO-OD pretreatment and without OD pretreatment. Notably, the highest total carotenoid content was found in dehydrated yellow peach slices pretreated by IMO-OD, followed by samples without OD, and samples with sucrose-OD pretreatment. In addition, the lowest a_W (0.517) was obtained in samples with IMO-OD for 5 h, which was beneficial for storage. The assessment of water status and total carotenoid content of dehydrated yellow peach slices showed that IMO-OD pretreatment could better improve the quality of dehydrated fruits. Moreover, the use of IMO in OD treatment was a good alternative to sucrose.     

Relationships between various physicochemical,thermal and rheological properties of starches separated from different potato cultivars

Various physicochemical, thermal and rheological properties of starches separated from Indian potato cultivars were related to each other using the Pearson correlation. Amylose content, water‐binding capacity (WBC), swelling power, solubility, ash content, transmittance, syneresis and consistency coefficient (K) were determined. Amylose content was significantly correlated with swelling power (r = 0.904), transmittance (r = 0.656) and syneresis (r = 0.777) of the starches. Thermal properties such as transition temperatures (T_o, T_p and T_c), gelatinisation range (R), gelatinisation enthalpy (ΔH_gel) and peak height index (PHI) of the starches were measured using differential scanning calorimetry (DSC). T_o, T_p and T_c were positively correlated with swelling power and negatively correlated with solubility and WBC. PHI was positively correlated with WBC and negatively correlated with ash content and swelling power. R had a negative correlation with WBC (r = ?0.726) and PHI (r = ?0.737). A positive correlation between R and T_c was observed. WBC was negatively correlated with swelling power (r = ?0.749). Syneresis of potato starches was positively correlated with transmittance, ash content, swelling power and amylose content. K was positively correlated with amylose content (r = 0.587). The results showed a significant variation in various functional and thermal properties of starches separated from different potato cultivars. Copyright © 2004 Society of Chemical Industry