Effect of pulsed-vacuum and ohmic heating on the osmodehydration kinetics, physical properties and microstructure of apples (cv. Granny Smith)

The influence of pulsed vacuum (PVOD) and ohmic heating (OH) on the osmotic dehydration (OD) kinetics and structure of apples was evaluated. Apple cubes (1 cm³) were immersed in a 65 ºBrix sucrose solution at 30, 40 and 50 °C for 300 min. The PVOD treatment was conducted at 5 kPa for 5 min, and the OH treatment was conducted at 100 V (electric field of 13 V/cm). The water loss, solid gain, a_w, color and firmness were measured, and the microstructure was analyzed using electronic microscopy. The largest water loss was observed with the OD/OH treatment at 50 °C. The greatest amount of solute uptake and smallest firmness loss were obtained with the PVOD/OH treatment at 50 °C. Color differences were associated with the loss of clarity and corresponded to the transparency gain. OH treatments led to changes in the microstructure, cell walls and tissues of the apples due to the electroporation effect, which explained the increase of mass transference.

Industrial relevance

The aim of this research was to determine the response of apple samples to osmotic dehydration using combined treatments of pulsed vacuum and ohmic heating. Two different technologies, vacuum and ohmic heating at mild temperatures, were used to determine and observe the mass transfer kinetics and microstructure of osmodehydrated apples. In several ohmic heating treatments, the time reduction reached 50% as compared to conventional heating. The increases of temperature, vacuum application and electroporation effect promoted the gain of osmotic solution into the tissue pores, thus reaching equilibrium in the sample with less water loss. Among the investigated conditions, the PVOD/OH treatment at mild temperatures was the best minimal processing method to preserve the fresh-like properties of the apples.     

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     

Cold storage of apples (cv. Granny Smith) and changes in phenolic compounds

 The Granny Smith variety of apple behaves differently to other apple cultivars, in that it needs an abnormally long time to ripen at room temperature. Its maturation has been accelerated by low-temperature stress. Fruit collected at commercial maturity were chosen and submitted to storage at 4 °C for 10 days and rewarming at 22 °C, to assay the influence of cold storage on their content of phenolic compounds. The behaviour of phenolic compounds was different in peel and in pulp. In the pulp, apple phenolic compounds decreased during the development period and during the cold treatment. In the peel, the quantity of phenolic compounds increased with time after the cold treatment, reversing their normal behaviour during the development period. Received: 11 March 1996     

Influence of ohmic heating and vacuum impregnation on the osmotic dehydration kinetics and microstructure of pears (cv. Packham’s Triumph)

The effect of ohmic heating (OH) and vacuum impregnation (VI) on the osmotic dehydration kinetics and microstructure of pears was studied. Three different dehydration levels (30, 40 and 50 °C) were used, by applying VI or not (OD) and OH (100 V). Dehydrated samples showed that the application of OH during the osmotic treatments had significant effects on the kinetics of water loss and sugar gain as well as on the microstructure of samples. The greatest water loss was observed with the OD-OH. The largest amount of solute gain and the smallest firmness loss were obtained in the VI-OH. In some treatments, the process time was reduced by as much as 40%. The SEM observations showed that cell deformation and cell rupture were significant in the OD-OH than on the VI-OH samples. The increases in the permeability of cell by OH explain the acceleration of mass transference and process time reduction.     

Relationships between rheological properties, texture and structure of apple (Granny Smith var.) affected by blanching and/or osmotic dehydration

The objective of this work was to evaluate and correlate rheological properties (small-scale dynamic oscillatory and creep/recovery measurements and large-scale compression force-deformation testing), texture (sensory evaluation by trained panel) and structure (optical and transmission electronic microscopy observations) of apples osmotically dehydrated to water activity (a _w) 0.97 with glucose, with or without previous blanching. All apple samples showed a solid behavior (G′?>?G″) dominating the viscoelastic response, but both dynamic moduli were reduced due to processing. The instantaneous elastic compliance (J ₀) and the retarded compliances (J ₁ and J ₂) increased for treated tissues and the steady-state viscosity (η _N) was approximately 15% to 29% of the value of fresh apple. In general, compression parameters decreased for all treated tissues. Changes in structural features were mainly evidenced in heated samples. Partial least squares regression analysis regression models revealed that texture could be well predicted by rheological properties (compression and creep parameters). Juiciness, crispness and sensory hardness were negatively correlated to J ₀, J ₁ and J ₂, and η _N was negatively correlated to sensory fracturability. Some mechanical parameters (fracturability, hardness 2, area 2, modulus of deformability and cohesiveness) were positively related to sensory fracturability, crispness and sensory hardness; and juiciness was negatively correlated to hardness. Compression and creep parameters showed ability to evidence structure differences (rupture of membranes, swelling of cells and degradation of cell walls) and to explain texture of treated apples.     

Effect of ohmic heating and vacuum impregnation on the quality and microbial stability of osmotically dehydrated strawberries (cv. Camarosa)

The combined effect of osmotic dehydration/ohmic heating (OD–OH) and vacuum impregnation/ohmic heating (VI–OH) on physicochemical and quality parameters of strawberry (a_w, color, firmness and microstructure), as well as on microbial stability of storage samples at 5 and 10 °C, was analyzed. Treatments were carried out with a 65% (w/w) sucrose solution at 30 °C, and ohmic heating at 9.2, 13, and 17 V/cm electric field strengths, corresponding to applied voltages of 70, 100, and 130 V. Dehydrated samples showed that water loss was greater in OD–OH treatments at 17 V/cm. The greatest solute gain, least firmness loss and least color loss were obtained in the VI–OH treatment at 13 V/cm. The shelf-life of strawberries treated with VI–OH at 13 V/cm and stored at 5 °C was extended from 12 d (control samples) to 25 d. Furthermore, the VI–OH treatment at 13 V/cm was the best processing condition for dehydrating strawberries.     

Osmodehydration assisted by ohmic heating/pulse vacuum in apples (cv. Fuji): retention of polyphenols during refrigerated storage

Apples are a widely consumed fruit and have a high polyphenol content. The aim of this study was to analyse the combined effects of osmotic dehydration (OD) and ohmic heating (OH) with a pulsed vacuum (PV) on polyphenol retention during the stored refrigeration of apple cubes. Treatments were performed using a 65°Brix sucrose solution at 30, 40 or 50 °C for 120 min, and then, samples were stored for 28 days at 5 °C. OH provides an electric field of 13 V cm^?1, and a pulsed vacuum was applied for 5 min at the beginning of the process. The results indicated that a lower temperature process (30–40 °C) resulted in the retention of more polyphenol compounds after treatment than a higher temperature process (50 °C). Nevertheless, during refrigerated storage, we observed that 50 °C preserved these compounds better due to polyphenol oxidase inactivation. PVOD/OH treatment at 50 °C was determined to be the best retention of polyphenols from the fresh apple for dehydrating apples.     

Headspace volatile compounds during osmotic dehydration of strawberries (cv Camarosa): Influence of osmotic solution composition and processing time

The influence of the type of sugar in the osmotic solution and of the time of processing on the volatile compounds of strawberries was studied, in order to optimize the technique as a pre-treatment to further processing. Strawberries of cultivar ‘Camarosa’, cut into 1 cm thick slices, were subjected to osmotic dehydration at 30 °C for 1, 2, 4 and 6 h using either 60% (w/w) sucrose or 60% (w/w) sorbitol solutions. Volatile compounds of fresh and processed strawberry slices were analyzed by static headspace—gas chromatography. Osmotic treatments provoked a loss in volatile compounds due to the migration, mainly of esters, into the osmotic media. The variations in the volatile pattern depended on both time of treatment and type of osmotic solution. The greater changes occurred after 2 h in sucrose; with a promotion of fermentative volatiles (acetaldehyde, ethyl acetate), and a decrease in the other volatiles. Using sorbitol as osmotic agent, the major variations in the volatile pattern occurred after 4 h of osmosis, and the fermentative process was less important than in sucrose, as sorbitol could be less effective in forming a peripheral layer at the fruit surface and/in reducing tissue porosity.     

Effect of ohmic heating and vacuum impregnation on the osmodehydration kinetics and microstructure of strawberries (cv. Camarosa)

The influence of ohmic heating (OH) and vacuum impregnation (VI) on the osmotic dehydration (OD) kinetics and microstructure of strawberries were studied. Samples were immersed in a 65 °Brix sucrose solution and treated with OH (100 V) and VI (5 kPa). Osmotic treatments were carried out at 30, 40 and 50 °C for 300 min. Water loss, solid gain, color and firmness of the strawberries were measured. In addition, the microstructure was analyzed using electron microscopy (SEM) and (TEM). The results showed that applying OH during osmotic dehydration had significant effects on the mass transference kinetics and the microstructure of the treated samples. The greatest water loss was observed for the OD–OH treatment. The largest amount of solute gain was obtained for the VI–OH treatment. A loss in firmness was observed in the OD–OH samples at 50 °C. Color differences were related to an increase in clarity and a decrease in color chrome, and the least significant differences were observed for the samples treated at 30 °C. SEM observations showed that cell rupturing were more significant in the OD–OH than in the VI–OH samples. The application of OH and VI had beneficial effects on the acceleration of mass transference.     

不同渗透条件对琯溪蜜柚品质的影响

以琯溪蜜柚为原料,采用正交实验设计,研究不同渗透液含糖量(55%、60%、65%),不同渗透温度(50、55、60℃),不同料液比(1∶6、1∶8、1∶10)对蜜柚品质的影响。测定的指标包括失水率、抗坏血酸保存率、还原糖保存率、蔗糖增加率和总酸保存率。由多指标综合评分法得出的结果表明:渗透液含糖量65%,渗透温度60℃,料液比1∶10为最佳渗透脱水条件。不同渗透条件对蜜柚各营养指标均有影响,且呈现不同的影响效果。      

Novel inactivation methods of Doenjang (fermented soybean paste) by high pressure and ohmic heating

The changes of the total cell number in doenjang (Korean traditional fermented soybean paste) by conventional conduction heating, high pressure non-thermal treatment, and ohmic heating were compared. A total of (10¹–10²) CFU/g cells were decreased by heating at (100–105) °C for 10 min. The inactivation rate was improved when heated to a temperature higher than 110 °C, but the taste, color of doenjang were severely changed. Inactivation by high pressure at (200–800) MPa was not achieved, because the total cell did not reach a reduction of 10¹ CFU/g. The total bacterial counts of 10³ CFU/g were decreased during ohmic heating at 15 V and 60 Hz for 10 min, and showed the most effective inactivation. Therefore, application of the ohmic heating in doenjang with high viscosity can kill target microorganisms related to quality deterioration, and rapid and uniform ohmic heating leads to reduction in sensory quality damage.     

Application of microwaves dielectric spectroscopy for controlling osmotic dehydration of kiwifruit (Actinidia deliciosa cv Hayward)

Dielectric spectroscopy studies have been performed on fresh and osmotically dehydrated kiwifruits (Actinidia deliciosa cv Hayward). The osmotic treatment consisted on the immersion the samples into 65% (w/w) sucrose aqueous solution at 30 °C during different treatment times from 5 to 1440 min. Some physical–chemical parameters were measured in fresh, treated and reposed (24 h at 30 °C) samples. Dielectric spectra were measured in the frequency range from 500 MHz to 20 GHz by an Agilent 85070E Open-ended Coaxial Probe connected to an Agilent E8362B Vector Network Analyzer in the fresh, treated and reposed samples. It has been demonstrated that the dielectric technique is a good method to control the osmotic treatment in kiwifruit.Industrial relevance: The results of this research article are demonstrated to be useful for controlling candying of kiwifruits in bakery industries. Thus, the industrial relevance is clear in order to optimize the osmotic dehydration times and the final quantity of sugars added by using a non destructive technique that can be implemented in process line. Dielectric spectroscopy, which can be considered an emerging technology, has the advantage of being an objective and a rapid technique. For all these reasons we are sending to this journal “Innovative Food Science and Emerging Technologies” our results.     

Analysis of chemical and structural changes in kiwifruit (Actinidia deliciosa cv Hayward) through the osmotic dehydration

Osmotic dehydration experiments of kiwifruit (Actinidia deliciosa cv Hayward) were carried out in order to apply a nonlinear irreversible thermodynamic model. Samples were immersed into 65% (w/w) sucrose aqueous solution at 30 °C during 5, 10, 15, 20, 30, 45, 60, 90, 120, 180, 250, 320, 400, 720, 1440 min. Some physical-chemical parameters were measured in fresh, treated and reposed (24 h at 30 °C) samples. It was possible to apply the enthalpy-entropy compensation coupled to a nonlinear thermodynamic model, obtaining the apparent bulk modulus and explaining the elastic answer of the tissue throughout the osmotic process. The osmotic dehydration also produces losses in the native compounds of kiwifruit such as citric acid and Calcium and Potassium.     

Ohmic heating and pulsed vacuum effect on dehydration processes and polyphenol component retention of osmodehydrated blueberries (cv. Tifblue)

Blueberries are highly perishable fruits; therefore, emerging technologies focus on improving the bioactive compound retention and extending the shelf life. The aim of this study was to evaluate the effect of ohmic heating and vacuum pulses on the dehydration processes and polyphenol compound retention of osmodehydrated blueberries (cv. Tifblue). The treatments were performed using a 65% (w/w) sucrose solution, an electric field of 13 V/cm (100 V) at 30 °C, 40 °C or 50 °C for 300 min, and air drying at 50, 60 or 70 °C to obtain dried blueberries. The moisture content, soluble solids and phenolic compounds were analyzed. The combination of ohmic heating/pulsed vacuum treatments intensifies mass transfer in osmodehydrated blueberries, especially at higher temperatures. Nevertheless, the polyphenol retention was greater at lower temperatures; hence, the application of an intermediate process temperature (40 °C) was selected as a pre-treatment prior to further drying. The treated samples improve the retention of polyphenols after drying compared with untreated samples. Therefore, the results of this research study suggest that the use of a pulsed vacuum and ohmic heating in the osmotic dehydration (PVOD/OH) treatment at 40 °C for 240 min and subsequent drying at 60°C could be the best process for dehydrating blueberries, considering that it improved mass transfer, achieved lower losses of phenolic components and reduced the drying time.Industrial relevanceBlueberries are an important fruit due their high bioactive compound content, especially polyphenols. Studies that involve emerging technologies application could add value to blueberries. Ohmic heating and pulsed vacuum as pre-treatments improve the efficiency of dehydration processes, focused toward bioactive compounds retention and achieving commercial viability. In this work have been applied PVOD/OH treatments at moderated temperatures and subsequently dried at 60 °C, obtaining promissory results.     

Ohmic heating blanching of Agaricus bisporus mushroom: Effects on polyphenoloxidase inactivation kinetics,color, and texture

The effect of ohmic heating blanching (OHB) on the inactivation kinetics of polyphenol oxidase (PPO), color, and texture from Agaricus bisporus mushroom treated at different temperatures (67–90 °C) for 1 to 5 min was investigated in the present work. OHB and conventional blanching (CB) treatments were able to inactivate mushroom PPO. However, the inactivation kinetics results showed a lower energy activation (E_a) value during OHB (16.03 ± 1.34 KJmol-1) compared to conventional blanching (20.07 ± 1.85 KJmol-1). Significant differences were observed in color (L*, h° and ΔE) and mushroom texture between the blanching treatments. Nevertheless, both treatments caused minimal physicochemical changes. Therefore, OHB is a promising technology for mushroom blanching because it promotes PPO inactivation in less time and reduces the impact on the color and texture of mushrooms compared to CB.     

Effect of ohmic heating on texture,microbial load,and cadmium and lead content of Chilean blue mussel (Mytilus chilensis)

The effect of ohmic heating (OH) on the texture, microbial load, and cadmium (Cd) and lead (Pb) content was evaluated in Chilean blue mussel (Mytilus chilensis) at shucking and subsequent canning. Mussel samples were processed by OH and blanching (BLAN) at 50 ± 1 °C, 70 ± 1 °C and 90 ± 1 °C for shucking and then canning at 115 °C for 20 min. The Cd and Pb content in fresh mussels was 2.47 ± 0.18 μg g^− 1 and 5.26 ± 0.55 μg g^− 1 dry weight (dw). The greatest reduction in Cd content was reached at 90 ± 1 °C by OH with 1.67 ± 0.06 μg g^− 1 (dw) and 1.69 ± 0.08 μg g^− 1 (dw) by BLAN. At the same temperature, the Pb content was reduced to 4.18 ± 0.24 μg g^− 1 dw for OH and 4.14 ± 0.30 μg g^− 1 dw for BLAN. The cutting strength of fresh samples (21.35 ± 2.44 N) significantly decreased in samples processed by OH (15.65 ± 1.36 N) at 90 ± 1 °C compared with BLAN samples (20.41 ± 3.16 N) at the same temperature. The initial mean count for mesophilic aerobic microorganisms and Enterobacteriaceae was 3.8 log cfu/g and 2.5 log cfu/g, respectively. The mesophilic aerobic microorganism count was reduced by 1.7 logarithmical units, while Enterobacteriaceae counts were reduced to undetectable levels by OH at 90 ± 1 °C.Industrial relevanceHigh temperature short time (HTST) processes rely on rapid convection heat transfer and are thus well suited to liquid foods. But, they are, however, limited in application to particulates since, for particles more than a couple of millimeters thick, the processing time is insufficient for heat to transfer to the center to give sterility. Ohmic heating is an emerging technology and very promising in food industries. It is a thermal process in which heat is generated internally in food and acts as a resistance to the flow of alternating electric current. This type of treatment prevents overheating by producing less deterioration in food components. It is a rapid procedure that allows food to conserve its natural properties; microorganisms and enzymes are also inactivated. The purpose of the present work was to evaluate the effect of Ohmic heating on mechanical properties, microbial load, Cd and Pb content in the opening and subsequent canning of Chilean blue mussel (Mytilus chilensis). This information could be used for the seafood industries in order to improve thermal heating processes in mussels.     

Purification,properties and heat inactivation of pectin methylesterase from apple (cv Golden Delicious)

Pectin methylesterase from apple (cv Golden Delicious) was extracted and purified by affinity chromatography on a CNBr‐Sepharose®‐PMEI column. A single pectin methylesterase peak was observed. Isoelectric points were higher than 9. Kinetic parameters of the enzyme were determined as K_m = 0.098 mg ml⁻¹ and V_max = 3.86 µmol min⁻¹ ml⁻¹ of enzyme. The optimum pH of the enzyme was above 7.5 and its optimum temperature was 63 °C. The purified PME required the presence of NaCl for optimum activity, and the sodium chloride optimum concentration increased with decreasing pH (from 0.13 M at pH 7 to 0.75 M at pH 4). The heat stability of purified PME was investigated without and with glycerol (50%), and thermal resistance parameters (D and Z values) were calculated showing that glycerol improved the heat resistance of apple PME. © 2000 Society of Chemical Industry     

Effects of high pressure and ohmic heating on shell loosening,thermal and structural properties of shrimp (Pandalus borealis)

This study aimed at understanding the effects of high pressure (HP) and ohmic heating (OH) on the peelability, the underlying mechanisms of HP- and OH-induced shell tightening, the thermal and structural properties of shrimp parts. HP improved the peelability of shrimp at low pressure level (<350 MPa) and short holding time (≤3 min) and the optimum condition for peeling was at 100 MPa for 3 min at 5 °C. However, a higher pressure level (>350 MPa) led to a decrease in the peelability. High pressure at 600 MPa stabilized cuticular and epidermal collagen and formed new collagen-like structures by new linkages, which strengthened the muscle-shell connection and reduced the peelability. Shrimp meat induced from HP at 100 MPa and 600 MPa had minorly denatured myofibrillar proteins. OH as a blanching method did not significantly improve the peelability of shrimp at most of the studied conditions. Some extreme conditions (e.g. at 50 °C) caused a markedly low peelability due to occurrence of collagen gelatinization. The gel formation from collagen-gelatin transformation under heating added strength to adherence of shell to epidermis and muscle, as a consequence, a difficult peeling was experienced. OH also denatured proteins in shrimp meat and caused loss of astaxanthin.Industrial relevance.The industrial processing of ready-to-eat shrimp involves the on-ice or in-brine maturation process which loosens the shrimp's shell from its meat, and therefore enable the mechanical peeling. However, the traditional maturation is time consuming (up to several days), inevitably leads to reduced quality of shrimp meat. This study shows the possibility of the application of HP at mild pressure levels to promote the shell loosening at short HP processing time (≤3 min). However, at more severe HP conditions could lead to the shell tightening which was caused by HP-induced stabilization of collagen in shell and epidermis. The study also shows that ohmic heating (<5 min) might not be a significant blanching method to support the maturation since OH had minor positive effect on shell loosening at some OH conditions (e.g. 2 or 10% NaCl, 92 V, and 30 or 35 °C), but had a counter effect at most OH conditions especially at high temperature.