Influence of osmotic dehydration and freezing on the volatile profile of kiwi fruit

The effect of osmotic dehydration on the volatile fraction of kiwi fruit was studied, as well as the effect of freezing and frozen storage. Osmotic treatments were carried out in sucrose solutions until the kiwi fruit reached 30°Brix, at atmospheric pressure (OD) and by applying a vacuum pulse (PVOD), by using 45 and 65°Brix sucrose. Volatile compounds of fresh, dehydrated and frozen-stored (at −18 °C for 1 month) samples were obtained by simultaneous distillation-extraction, and analyzed by GC-MS. Osmotic dehydration provoked formation of esters and a decrease in aldehydes and alcohols, depending on the dehydration treatment applied, which is similar to what occurs during kiwi ripening. A severe reduction of all volatile compounds occurred after one month in frozen storage, which smoothes the changes induced by osmotic treatments. Only small differences between dehydrated and non-pretreated frozen/thawed samples could be recognized.     

Development of volatile fraction of fresh cut osmotically treated mango during cold storage

The influence of minimal processing by osmotic treatment and cold storage on the volatile profile of mango was studied by comparison with the volatile profile of fresh samples. Osmotic treatments, at atmospheric pressure and by applying a vacuum pulse, were carried out using a 45 Brix sucrose solution with (2%) and without calcium lactate, at 30 °C. Samples were treated until they reached 20 Brix in all cases. The volatile profile of the samples was characterised at 0, 1, 4 and 8 days of cold storage at 10 °C, using purge and trap thermal desorption and GC–MS. Osmotic treatment provokes a decrease in the terpene concentration (the most abundant compounds in the volatile fraction mango) and an increase in ethyl acetate and 1-butanol. This fact was especially observed in treatment applying vacuum impregnation with calcium. Treatment at atmospheric pressure, with calcium in the osmotic solution, was the best way to prevent aroma alterations during processing and to ensure its stability throughout cold storage.     

Osmotic dehydrofreezing of strawberries: Polyphenolic content, volatile profile and consumer acceptance

We evaluated dehydrofreezing in strawberries in terms of retention of healthy compounds (i.e. polyphenolics) and sensory qualities for direct consumption in substitution of fresh fruit. Different osmodehydration (OD at 30 °C and 5 °C), vacuum osmodehydration (VOD at 30 °C) and immersion chilling freezing (ICF) processes were applied in sucrose syrup. Samples were analyzed for dry matter, soluble solids, pH, titratable acidity, mass transfers, polyphenolic content by HPLC-DAD/MSD, volatile profile by SPME-GC/MSD and consumer acceptance. The results of sensory evaluation, in particular, confirmed the cryoprotective effects of osmotic processes of fruits with respect to untreated frozen control samples. The OD samples at 5 °C presented a water loss to solid gain ratio comparable to OD at 30 °C and VOD samples. Moreover, while osmo-dehydrofreezing at relatively high temperatures caused a slight depletion of phenolic compounds, the samples osmodehydrated at 5 °C showed higher polyphenolic retention. Data on aromatic compounds showed that some compounds increased (e.g. ethanol and acetaldehyde), while others did not appear to be affected by the pre-treatments.     

Volatile profile of dehydrated cherry tomato: Influences of osmotic pre-treatment and microwave power

Vegetable flavour is a quality characteristic for consumer acceptability. Sun and air are traditionally used for drying tomatoes; however, the optimal combination of techniques such as osmotic dehydration or microwave-assisted air-drying could lead to high quality self-stable products. The aim of this paper was to study the influence of different process variables on the volatile profile of dehydrated cherry tomato halves. The analysed variables were: air-drying temperature (40 and 55 °C), microwave power (0 and 1 W/g) and previous osmotic dehydration with a 55 Brix binary sucrose solution at 30 °C for 120 min (OD1) or ternary solution of 27.5% sucrose + 10% NaCl (w/w) at 40 °C for 60 min (OD2). Twenty major volatile compounds were identified in fresh tomatoes. Among them, 2-isobutylthiazole and 6-methyl-5-hepten-2-one stand out as impact volatile compounds. Dehydration modified the volatile profile, mainly due to the changes induced in some typical fresh-like tomato compounds, but also due to the generation of five new compounds: 1-butanol, 2-methyl-2-butenal, 3-hydroxy-2-butanone, furfural, acetonitrile, related to Maillard reactions, and the catabolism of carotenoids and polyunsaturated fatty acids. Principal component analysis showed the possibility of obtaining dried cherry tomatoes with different volatile profiles, depending on drying conditions.     

Osmotic Dehydration and Vacuum Impregnation on Physicochemical Properties of Chilean Papaya (Carica candamarcensis)

ABSTRACT: The effect of osmotic dehydration (OD) at atmospheric pressure and vacuum impregnation (VI) treatments on some physiochemical parameters of papaya (aw, pH, color, firmness, and microstructure) was analyzed. Osmotic treatments were carried out on papaya with 55°Brix and 65°Brix sucrose solutions at 30 °C. VI with 65°Brix osmotic solution was the most effective in reducing aw due to the highest sucrose gain during osmotic treatment. Color differences were associated to loss of clarity in line with transparency gain. Scanning electron microscopy observations show that osmotic dehydration caused shape changes and size reduction of papaya cells; also differences in microstructural features were observed between OD-treated and VI-treated samples. Moreover, the largest firmness observed in VI samples compared with OD treatments was associated with the thickness of the middle lamella between cells, which was greater in VI than OD treatments. Improvement in texture and palatability of papaya was obtained with VI rather than OD treatment compared with fresh papaya.     

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 postharvest dehydration on the composition of pinot noir grapes (Vitis vinifera L.) and wine

This study was conducted in order to improve our understanding of how phenolics and aroma compounds change in wine grapes during postharvest dehydration. Pinot noir grapes grown in the Willamette Valley of Oregon were harvested at 22.0 and 24.0 °Brix. Grapes harvested at 22.0 °Brix were divided into three equal lots with one lot immediately used for wine production, and the remaining two lots placed inside an air tunnel with an air speed of 1.0–1.8 m s⁻¹, 38% relative humidity and a temperature of 22 °C. The soluble solids content and weight loss were measured daily and wines were made from grapes when they reached 24.8 and 26.7 °Brix. The soluble solids of grapes increased about 1 °Brix per day; therefore, on the third and fourth day the berries reached the desired concentration; weight loss was 14 and 16%, respectively. Results from berry phenolic analysis indicated that per berry anthocyanin amount remained unchanged during dehydration. The composition of proanthocyanidins isolated from berries changed during dehydration. Volatile compounds in wines made from dehydrated grapes contained more terpenes and norisoprenoids (β-ionone, β-damascenone) when compared to wine made from the original fruit. Wines made from increasingly dehydrated grapes tended to resemble the composition and flavour profile of wines made from grapes left on the vine (i.e. with extended ripening). The results of this study suggest that postharvest flavour changes consistent with changes during fruit ripening can occur in grapes when harvested early and allowed to dehydrate under controlled conditions prior to fermentation.     

Effect of the re-use of the osmotic solution on the stability of osmodehydro-refrigerated grapefruit

Osmotic dehydration (OD) of grapefruit (55°Brix sucrose solution, 30 °C) was carried out to obtain ˜75 g water/100 g sample in the final product. Although the grapefruit was replaced each time, the osmotic solution (OS) was reused for five OD cycles, with or without pasteurization. The samples obtained in cycles 1, 3 and 5, were stored at 10 °C. Changes in °Brix, water content, water activity, pH, total acidity, ascorbic acid content, cation concentration, respiration rate and total microbial counts at different storage times were analyzed and compared to fresh-cut grapefruit stored under the same conditions. During OD, a partial loss of the natural soluble substances present in the fruit was observed. In terms of the dehydration level reached by the fruit, it is possible to reuse the OS in up to 5 OD, without any reconcentration treatment. Nevertheless, it is advisable to pasteurize the OS before each cycle in order to obtain a product with a shelf-life of between 7 and 12 days in refrigeration, depending on the number of cycles.     

Optimisation of osmotic dehydration process of carrot cubes in mixtures of sucrose and sodium chloride solutions

In the optimisation of the osmotic dehydration process of the carrot cubes in mixtures of sucrose and sodium chloride by response surface methodology, using face-centred central composite design (CCF), it was shown that the independent process variables for osmotic dehydration process were osmotic solution concentrations (5–15% w/v sodium chloride in 50 °Brix sucrose syrup), temperature (35–55 °C) and process duration (120–240 min). Statistical analysis of results showed that the linear terms of all the process variables have a significant effect on all the responses. The optimum osmotic dehydration process conditions for maximum water loss, minimum solute gain, maximum retention of colour, and sensory score were: 50 °Brix + 15% w/v sodium chloride solution, 54.8 °C solution temperature and 120 min process duration.     

How to deal with visco-elastic properties of cellular tissues during osmotic dehydration

In this work, vacuum impregnated apple discs with different isotonic solutions (sucrose and trehalose) were equilibrated during osmotic dehydration (55°Brix glucose at 40 °C). Changes in sample composition (water and soluble solid contents), weight and volume are analysed. A mathematical model is proposed to describe and quantify the outflow of water from the protoplast as well as the visco-elastic behaviour of the cell. Good correspondence between simulated and measured data of non impregnated samples and samples impregnated with isotonic solutions of sucrose or trehalose during long term osmotic dehydration is obtained. Fitted values of the cell permeability correspond well with tabulated values. Furthermore, also the obtained values of the parameters describing the mechanical properties of the cell wall and Hectian strands seem to reflect the observed structural development of these structures for the different treated samples well.     

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.     

Study of the Influence of Osmotic Dehydration and Freezing on the Volatile Profile of Strawberries

ABSTRACT: The effect of osmotic process conditions on the volatile fraction of strawberries was studied, as well as the effect of freezing and frozen storage. Osmotic treatments were carried out on strawberries in sucrose solutions up to 20 °Brix, at atmospheric pressure (OD), and by applying a vacuum pulse (PVOD). Volatile compounds of fresh, dehydrated, and frozen-stored (at –18 °C for 1 mo) samples were obtained by simultaneous distillation-extraction. Osmotic treatments caused an increase in ester concentration and, in some cases, in furaneol less marked in PVOD. Freezing implied losses in all components, although in pre-dehydrated samples the concentration of some esters (and furaneol) remained greater than in the fresh samples.     

EFFECT OF CaCl2 AND CONVECTIVE-OSMOTIC DRYING ON TEXTURE AND PREFERENCE OF APPLE

Conventional air‐drying combined with osmotic dehydration was researched as a potential method for drying apple cubes of superior quality. Samples were pretreated with CaCl₂ at different temperatures and times. Pretreated apple cubes were dehydrated in a tray dryer. Then, osmotic dehydration with sucrose solutions was carried out. The curves for osmotic dehydration showed that the gain of solids was higher when 40% of water was removed by convective drying while the loss of weight was lower at the same level of dehydration at 65°Brix. Texture measurements indicated that the temperature of pretreatment affected the hardness and cohesiveness. Hardness values were higher at 40C, while cohesiveness values were lower at the same temperature. The CaCl₂ at a given temperature did not have a significant effect on texture. Sensory evaluation showed that samples pretreated at 25C and osmotically dried at 50°Brix had the higher preference by the judges.     

Effect of osmotic pre-treatment and microwave heating on lycopene degradation and isomerization in cherry tomato

Cherry tomato were dehydrated by a combination of different techniques (osmotic dehydration, convective drying, and microwaves assisted air drying) in order to evaluate the effect of the process variables on the degradation and isomerization of lycopene, as well as on the optical properties. Specifically, the effect of prior osmotic treatment, air drying temperature (40, 55, and 80 °C) and level of microwave energy (0, 1, and 3 W/g) were studied. Obtained results showed that the osmotic pre-treatment limited the isomerization during the later stage of drying, whereas both the loss of total lycopene and the trans–cis isomerization, mainly to the 13-cis form, were favored by an increase in temperature and the microwave power. Furthermore, a positive correlation between the degree of isomerization experienced by the samples during drying and the hue (h*) were obtained. This correlation was reflected in the colour of the sample with predominantly more orange tones and less reddish ones.     

Effect of temperature and pretreatment on water diffusion during rehydration of dehydrated mangoes

The kinetics associated with rehydrating dehydrated mangoes was studied at three temperatures: 25, 40, and 60 °C. Besides, we studied how rehydration was affected by pretreating the fruit with osmodehydration in either sucrose or glucose before it was thermally dehydrated. We show that rehydration can be interpreted by Fickian diffusion and that the effective water diffusion coefficient is larger at 40 °C than at either 25 or 60 °C. Consequently, during rehydration of untreated samples at 40 °C, the weight gain, water gain, and loss of solids attain optimal values. We found that the rehydration kinetics of mango was not affected by osmodehydration pretreatments in sucrose. However, pretreatment in glucose significantly improved rehydration; for example, the effective diffusion coefficients of the glucose-treated samples were about twice as large as those of the untreated samples.     

Changes in respiration rate and physical properties of strawberries due to osmotic dehydration and storage

The effect of osmotic dehydration on the respiration rate (R) and the mechanical and optical properties of strawberry halves were evaluated throughout six days at 10 °C. Two different dehydration levels (15 and 20 °Brix) were considered, by applying (PVOD) or not (OD) a vacuum pulse and with and without calcium addition. Dehydrated samples showed a faster drop in R than non-treated samples, thus indicating a faster development of senescence. PVOD implied a greater reduction of O₂ consumption. Calcium addition slightly reduced R. Osmotic treatments provoked a decrease in the puncture forces, especially in samples with 20 °Brix, as a consequence of the structural collapse caused by treatments. After storage, calcium addition and PVOD treatments had beneficial effects on the maintenance of the sample texture. Colour of treated strawberries was modified, mainly in the parenchyma zone, when changes in the sample porosity were greater due to the treatment (vacuum impregnation).     

Multi-Objective Optimization of Osmotic–Ultrasonic Pretreatments and Hot-Air Drying of Quince Using Response Surface Methodology

In this study, application of a multi-objective optimization technique based on response surface methodology has been presented. Quince slices were dehydrated using osmotic dehydration with sucrose solutions at different concentration (40 and 60 Brix), processing time (1, 1.5, and 2 h), and ultrasonication time (0, 15, and 30 min) were the factors investigated with respect to water loss, solid gain, and weight reduction. Response surface methodology was used to determine the optimum processing conditions that yield maximum water loss and weight reduction and minimum solid gain during osmotic dehydration of quinces. Dehydrated quince slices at optimized osmo-ultrasound condition were then subjected to air-drying at 60 and 80 °C. Rehydration ratio, shrinkage, and moisture content of dried samples were regarded as responses to the non-thermal and air-drying conditions. Multi-objective optimization led to obtaining the best condition for production of dried quince slices with lowest moisture content, and shrinkage.     

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.     

Changes in optical and mechanical properties during osmodehydrofreezing of kiwi fruit

The influence of osmotic dehydration and freezing–thawing on optical (colour and translucency) and mechanical properties of kiwi slices were analysed. Osmotic treatments were carried out in sucrose solutions up till the soluble solids in kiwi fruit reached 30 °Brix, both at atmospheric pressure (OD) and by applying a vacuum pulse (PVOD). Analyses were carried out on fresh and dehydrated samples before and after frozen storage (at −18 °C for 1 and 30 days). Reflexion spectra (400–700 nm) were measured to obtain the Kubelka–Munk coefficients and CIE-L*a*b* colour co-ordinates. Mechanical properties were analysed through the compression test. A transparency gain was observed in PVOD treated samples and in frozen–thawed samples, which implied a reduction in product clarity and chrome. Colour hue did not change notably, due to either osmotic treatments or freezing. Samples treated with 45 °Brix osmotic solution at atmospheric pressure were the best preserved in mechanical properties after freezing–thawing.     

Electronic Nose to Detect Strawberry Aroma Changes During Osmotic Dehydration

ABSTRACT:  An electronic nose was used to detect the aroma evolution of strawberry fruits, cultivar "Camarosa," during the osmotic dehydration in sorbitol and sucrose solutions. Strawberry slices were subjected to osmotic dehydration at 30 °C for 1, 2, 4, and 6 h using either 60% sucrose or 60% sorbitol solutions. Volatile compounds of fresh and processed strawberry slices were analyzed by electronic nose and gas chromatography. Electronic nose was able to reveal changes in the aroma profile during processing and permitted differentiation between dehydrated strawberry samples obtained by different osmotic treatments. The electronic nose has the advantage of being simple, rapid, and nondestructive. Such characteristics and the promising results of this work suggested that this device could be a useful and innovative tool to monitor strawberry aroma changes during osmotic dehydration, providing real-time information about the effects of processing conditions and allowing the optimization of technological parameters.