Water Loss Kinetics Research Articles

Temperature affects organic acid, terpene and stilbene metabolisms in wine grapes during postharvest dehydration.

The partial dehydration of grapes after harvest is a traditional practice in several winegrowing regions that leads to the production of high quality wines. Postharvest dehydration (also known as withering) has a significant impact on the overall metabolism and physiology of the berry, yielding a final product that is richer in sugars, solutes, and aroma compounds. These changes are, at least in part, the result of a stress response, which is controlled at transcriptional level, and are highly dependent on the grape water loss kinetics and the environmental parameters of the facility where grapes are stored to wither. However, it is difficult to separate the effects driven by each single environmental factor from those of the dehydration rate, especially discerning the effect of temperature that greatly affects the water loss kinetics. To define the temperature influence on grape physiology and composition during postharvest dehydration, the withering of the red-skin grape cultivar Corvina (Vitis vinifera) was studied in two conditioned rooms set at distinct temperatures and at varying relative humidity to maintain an equal grape water loss rate. The effect of temperature was also studied by withering the grapes in two unconditioned facilities located in geographic areas with divergent climates. Technological, LC-MS and GC-MS analyses revealed higher levels of organic acids, flavonols, terpenes and cis- and trans-resveratrol in the grapes withered at lower temperature conditions, whereas higher concentrations of oligomeric stilbenes were found in the grapes stored at higher temperatures. Lower expression of the malate dehydrogenase and laccase, while higher expression of the phenylalanine ammonia-lyase, stilbene synthase and terpene synthase genes were detected in the grapes withered at lower temperatures. Our findings provide insights into the importance of the temperature in postharvest withering and its effect on the metabolism of the grapes and on the quality of the derived wines.

Manufacture of β-chitin nano- and microparticles from jumbo squid pen (Dosidicus gigas) and evaluation of their effect on mechanical properties and water vapour permeability of polyvinyl alcohol/chitosan films

Polyvinyl alcohol/chitosan (PVA/CS) films, which may be a good alternative for food packaging, have a limited vapour water barrier. This study investigated, the effect of β-chitin micro- and nanoparticles (MPs and NPs, respectively) obtained from jumbo squid (Dosidicus gigas) pens on the water vapour permeability (WVP) of PVA/CS films. By milling β-chitin, squid MPs (sizes of 128 μm; MpQ128) were obtained, and an aqueous acid dispersion of MpQ128 was ultrasonicated to obtain NPs. Besides, PVA/CS films with three different proportions were prepared. The addition of MpQ128 did not increase the thickness or tensile strength (TS) of these films. The percentage elongation (%E) of the film increased only in one of the PVA/CS film proportions. The addition of NPs in this PVA/CS film did not increase the film thickness; however, the TS and %E increased significantly compared to those of the control sample, and the increase in %E was significantly higher with NPs than with MPs.Moreover, the PVA film exhibited biphasic water loss kinetics, and the film showed three-phase behaviour for various CS amounts. The WVP values did not significantly change for different PVA/CS proportions during each experimental period. However, in the second period, the WVP was significantly lower than in the first and third periods. The addition of MPs or NPs did not significantly decrease the WVP compared to that of the control sample. Nevertheless, it decreased slightly for some NP additions in the films. The effectiveness of β-chitin NPs in reducing the WVP can be improved by avoiding the aggregation of NPs in hydrophilic PVA/CS films.

Approximate Mathematical Modeling of Osmotic Dehydration of Cone-Shaped Fruits and Vegetables in Hypertonic Solutions

Water loss kinetics in osmotic dehydration of cone-shaped fruits and vegetables was modeled on the basis of diffusion mechanism, using the Fick‘s second law. The model was developed by taking into account the influences of the fruit geometrical characteristics, initial water content of fruit, water diffusion coefficient in fruit, and the water concentration in hypertonic solution. Based on the obtained model, it was shown that the water diffusion coefficient and the initial water concentration of fruit have direct effects on the dehydration rate and also inverse influence on the dehydration duration. The geometrical parameters of fruit and water concentration in hypertonic solution showed direct effect on the dehydration duration as well as inverse effect on the dehydration rate. The presented model seems to be useful tool to predict the dehydration kinetics of cone-shaped fruit during osmotic dehydration process and to optimize the process prior to perform the experiments.

Correlation between volatile profiles of Italian fermented sausages and their size and starter culture

The aroma profiles of 10 traditional Italian fermented sausages were evaluated. The volatile organic compounds (VOCs) obtained by solid-phase microextraction and gas chromatograph–mass spectrometry were analysed using principal component analysis (PCA) and linear discriminant analysis (LDA). PCA allowed an acceptable separation but some sausage typologies were not well separated. On the other hand, the supervised approach of LDA allowed a clear grouping of the samples in relation to sausage size and starter culture. In spite of the extreme variability of the volatile profiles of the sausage typologies, this work showed the influence of diameter on VOC profile. The differences observed can be related to the effects that some fundamental physicochemical characteristics (such as water loss kinetics and oxygen availability) have on the results of ripening processes. Differences in VOC profiles were also observed due to the lactic acid bacteria used as starter cultures, with differences mainly attributable to compounds deriving from pyruvate metabolism.

Water loss from litchi (Litchi chinensis) and longan (Dimocarpus longan) fruits is biphasic and controlled by a complex pericarpal transpiration barrier.

In litchi and longan fruits, a specialised pericarp controls water loss by a protective system consisting of two resistances in series and two water reservoirs separated by a barrier. In the fruits of litchi (Litchi chinensis) and longan (Dimocarpus longan), the pericarp is solely a protective structure lacking functional stomata and completely enclosing the aril that is the edible part. Maintaining a high water content of the fruits is crucial for ensuring the economic value of these important fruit crops. The water loss rates from mature fruits were determined and analysed in terms of the properties of the pericarps. Water loss kinetics and sorption isotherms were measured gravimetrically. The pericarps were studied with microscopy, and cuticular waxes and cutin were analysed with gas chromatography and mass spectrometry. The kinetics of fruit water loss are biphasic with a high initial rate and a lower equilibrium rate lasting for many hours. The outer and inner surfaces of the pericarps are covered with cuticles. Litchi and longan fruits have a unique type of transpiration barrier consisting of two resistances in series (endo- and exocarp cuticles) and two reservoirs of water (aril and mesocarp). The exocarp permeability controls the water loss from fresh fruits while in fruits kept for an extended time at low relative humidity it is determined by the endo- and exocarp permeabilities. Permeances measured are within the range for typical fruit cuticles. The findings may be used to design optimal postharvest storage strategies for litchi and longan fruits.

Effect of temperature on nitrite and water diffusion in pork meat

Nitrites are important food additives. The nitrite movement in meat is assumed to occur by means of a diffusion process. The objective of this study was to investigate the effect of temperature on nitrite and water diffusion mechanisms in meat samples during the curing of pork meat. For this purpose, cylinders of Semimembranosus muscle were salted with sodium nitrite (NaNO2) at 2°C, 7°C and 12°C. Experimental curing and water loss kinetics were modelled by means of a diffusion model. As the curing time lengthened, the water content fell and the nitrite content increased. The values for the nitrite and water diffusion were estimated to be in the range of 4.58·10−12–1.02·10−12m2/s and 5.96·10−9–9.82·10−9m2/s respectively, and they increased as the temperature went up. The activation energy was 32.24kJ/mol for water diffusion and 60.32kJ/mol for nitrite diffusion.

Experimental study of heat and mass transfer phenomena during the contact heating of solid food models

Experimental measurements of temperature rises and water loss kinetics within two types of solid food models during contact heating are discussed. A contact heating device was specially designed to reproduce the operating conditions encountered during domestic pan frying. Two different solid food models were used for the experiments: (i) a non porous solid gel containing an oil-in-water emulsion without crust formation at its lower surface during heating, and (ii) a cereal batter (water with flour) which exhibited crust formation and the development of an internal porous structure during heating. Under similar heating conditions, these products displayed very different drying and thermal behaviours. The temperature of the gel emulsion never exceeded 100°C and was independent of the heating surface temperature in the experimental range from 160°C to 260°C. This limitation in product temperature rise was explained by the evaporation of liquid water exuding from the product in the interstitial space between the heating surface and the product’s lower surface. By contrast, a crust was formed at the lower surface of the cereal batter, reducing the drying rate of the product at this location and allowing the product to reach temperatures higher than 100°C.

Quantification of the types of water in Eudragit RLPO polymer and the kinetics of water loss using FTIR

Coalescence of polymer particles in polymer matrix tablets influences drug release. The literature has emphasized that coalescence occurs above the glass transition temperature (Tg) of the polymer and that water may plasticize (lower Tg) the polymer. However, we have shown previously that nonplasticizing water also influences coalescence of Eudragit RLPO; so there is a need to quantify the different types of water in Eudragit RLPO. The purpose of this study was to distinguish the types of water present in Eudragit RLPO polymer and to investigate the water loss kinetics for these different types of water. Eudragit RLPO was stored in tightly closed chambers at various relative humidities (0, 33, 56, 75, and 94%) until equilibrium was reached. Fourier transform infrared spectroscopy (FTIR)-DRIFTS was used to investigate molecular interactions between water and polymer, and water loss over time. Using a curve fitting procedure, the water region (3100-3,700 cm(-1)) of the spectra was analyzed, and used to identify water present in differing environments in the polymer and to determine the water loss kinetics upon purging the sample with dry compressed air. It was found that four environments can be differentiated (dipole interaction of water with quaternary ammonium groups, water cluster, and water indirectly and directly binding to the carbonyl groups of the polymer) but it was not possible to distinguish whether the different types of water were lost at different rates. It is suggested that water is trapped in the polymer in different forms and this should be considered when investigating coalescence of polymer matrices.

Skin pectin metabolism during the postharvest dehydration of berries from three distinct grapevine cultivars

Background and Aims Postharvest dehydration is used to modify certain grape berry quality traits that affect the characteristics of wine. After harvesting, berries undergo several chemical and physical changes that often reflect ongoing or specifically activated metabolic processes, such as the modification of cell wall polymers in the skin. We compared berry skin pectin metabolism during postharvest dehydration in three Italian wine grape cultivars. Methods and Results Corvina, Oseleta and Sangiovese grapes were postharvest dehydrated under the same environmental conditions and displayed different dehydration rates. The quantitative characterisation of pectins by ion-exchange and size-exclusion chromatography revealed that more demethoxylation and depolymerisation occurred in the Corvina berries, which also showed the strongest induction of pectin methylesterase and polygalacturonase gene expression (by microarray analysis) and enzyme activity (by zymography). Conclusions Postharvest dehydration affected the skin pectin metabolism of grape berries to an extent different in each of the three cultivars, reflecting differences in water loss kinetics and metabolic processes. Significance of the Study This is the first description of dynamic cultivar-specific changes in pectin metabolism during the postharvest dehydration of grape berries.

Effects of Water Content and Chemical Composition on Structural Properties of Alkaline Activated Metakaolin‐Based Geopolymers

In this study, we evaluate the effects of chemistry and curing and aging conditions on water loss kinetics, porosity, and the structure of geopolymers. Geopolymer samples were prepared by mixing metakaolin precursor with K or Na silicate solutions having SiO2/A2O3 molar ratios from 2.5 to 4 and H2O/(SiO2 + Al2O3) molar ratios from 2 to 4. The samples were cured in sealed and unsealed molds at 60°C for 24 h and then aged at room temperature in open containers. The weight changes were monitored during curing and aging until a steady‐state weight was observed. This study shows conclusively that the amount of water [H2O/(SiO2 + Al2O3)] in the initial geopolymer mixture is the most dominant factor affecting density and open porosity of geopolymers after curing and extended aging. The results also indicate that regardless of the amount of water in the initial mixture and curing conditions (i.e., in sealed or unsealed molds), ~6–10 wt% of all K‐activated samples after aging for 21 days is water whereas in the case of all Na‐activated samples that amount ranges between ~15 and 20 wt%. Furthermore, the results demonstrate that SiO2/Al2O3 molar ratio does not have a direct effect on density and open porosity of geopolymers.

Effects of starter cultures and fermentation climate on the properties of two types of typical Italian dry fermented sausages produced under industrial conditions

In this work, two types of traditional Italian dry fermented sausages (Felino-type and Milano-type), were analyzed as a case study. The aim was to evaluate the effect of different environmental conditions in the drying chambers and different starter cultures on the characteristics of the industrially produced sausages. At the end of ripening, the sausages obtained were analyzed to determine microbial counts, biogenic amines (BA) accumulation and volatile aroma profile by using SPME-GC analysis. These profiles were compared with the results of a trained panel group. Felino-type sausages, inoculated only with Staphylococci, were characterized by a slow pH drop and by the presence of higher BA contents. Moreover, specific enzymatic activities of Staphylococci, such as phenylalanine metabolism, were observed and these drastically modified product volatile profiles. Also the different drying conditions applied were able to affect some sensory characteristics of the final products such as hardness and chewiness reflecting different water loss kinetics.

Development of an approximate empirical-CFD model estimating coupled heat and water transfers of stacked food products placed in airflow

This paper reports on the development of an approximate empirical-CFD modelling procedure combining experimental correlations for the heat and mass transfer coefficient determination and specific user-defined functions (UDF) implemented in the commercial CFD code Fluent to simulate the interrelationships at play between airflow and transfers of unwrapped food products bathing in air. Transfer modelling required specific calculation to account for water evaporation from the product surface. Mean transfer coefficients at the air–product interface were determined empirically from validated experimental correlations, where the CFD mean air velocity that is calculated in a small user-defined volume surrounding the product was incorporated. Internal water diffusion was taken into account by considering the product as a motionless fluid composed of dry matter and water. The procedure developed allows, in a single CFD calculation using a single mesh, temperature and water concentration fields to be computed and the water loss kinetics of the products to be determined together with the temperature and relative humidity fields of the air flowing around them. Although the established procedure was set up with the aim of assessing heat and water exchanges occurring in large stacks of unwrapped food products subjected to airflow, this last was validated for modelling, first, one-dimensional drying of a meat cylinder and second, three-dimensional drying of five cylindrical plaster casts placed in a row. Its application to the ripening of a row of six cheeses is also discussed.

Biophysical and Cellular Effects of Microwaves Interacting with Plant Tissues

AbstractMicrowave drying of Spinacia oleracea leaves was experimentally compared to electric heating and room temperature drying. Differences in water loss kinetics have been analyzed and a theoretical model has been proposed. In drastically dried leaves strong alterations of the internal morphological structure are present while surface characteristics appear satisfactorily conserved. Chlorophyll content in acetone extracts of microwave dried leaves does not appear as reduced as in conventional methods.