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Związki powstające w czasie fermentacji winiarskiej
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IntroductionComputational Design of the Power Ultrasonic System: Numerical Study by FEM of the Constituent ElementsDevelopment of the Power Ultrasonic Transducer PrototypeUltrasonically Assisted Convective DrierComputational Analysis of Ultrasonically Assisted Convective DryingFuture TrendsAcknowledgmentsNotationReferences
A contact ultrasound system for the integration into freeze-drying processes for vegetables was developed and process parameters were estimated. Red bell pepper cubes were freeze-dried on a stainless steel screen used as the sound transmitting surface. Ultrasound induced heating effects due to attenuation and absorption in the product and relevant process parameters were investigated. Continuous ultrasound application at an excitation amplitude of 6.7 μm resulted in immediate sample heating at reduced ambient pressure and a loss of freeze-drying conditions. A reduction of the excitation amplitude to 4.9 μm and of the net sonication time to 10% by applying an intermittent treatment with an interval of 10 s ultrasound and 90 s recovery phase allowed freeze-drying at increased sublimation rates without causing sample heating for 7 h of freeze-drying. As drying proceeds less sublimation energy is required in the process and sound energy was partially transformed into heat, which could be used for accelerated moisture removal during secondary drying in combination with further ultrasound effects improving heat and mass transfer (moisture migration, effect on boundary layers, improved evaporation at low pressure cycles). The ultrasound treatment reduced the drying time required to reach a final moisture content of 10% d.b. by 11.5%. The ultrasound treatment did not affect product quality in terms of bulk density, color, ascorbic acid content, and rehydration characteristics.
The effects of ultrasound assistance during a pre-drying treatment (soaking) on water mobility, polyphenoloxidase activity, microstructure and the drying kinetics of apple (var. Granny Smith) have been studied. Pre-drying treatments were carried out using three different soaking media: distilled water, apple juice, and citric acid; at 25 °C during 5 min; without the assistance of ultrasound (S) and then with two acoustic densities: 2.1 W/cm2 (U1), and 12.9 W/cm2 (U2). Transverse relaxation times (T2) of vacuole and cytoplasm water of treated samples were longer than those in untreated samples (fresh apples) especially when the soaking assisted by ultrasound was used, resulting in greater mobility of internal water, and easier water removal during convective drying. SEM observation showed that the ultrasound assistance promoted changes in the apple microstructure of treated samples regardless of the soaking medium. The polyphenoloxidase activity was affected by the soaking medium and the use of ultrasound during treatment, being higher reduction in samples treated with apple juice and citric acid, when the highest acoustic density was used (40% and 58%, respectively). The effective water diffusion during hot air drying (50 °C, 1 m/s) was higher in apples treated with and without power ultrasound, than in the fresh ones, causing a significant decrease in the drying time. This figure was higher when the soaking was carried out using citric acid and at an acoustic density of 12.9 W/cm2.
In this study, the effect of osmotic pretreatments (with or without ultrasound) in combination with hot‐air or microwave‐assisted hot‐air drying methods on the texture, microstructure, color and water activity of dried cranberries were investigated. Osmotic pretreatments were done in a ternary solution (sucrose–NaCl–water) under three different temperatures: 30, 40 and 50C. The concentrations of osmotic solutions were 40, 50 and 60% of sucrose and 0, 4 and 8% of NaCl. Also, the influence of the two levels of frequency of ultrasound (35 and 130 kHz) on the quality properties was investigated. Our results showed lower hardness and water activity (a w) when higher temperature, sucrose and salt were used. Applying ultrasound reduced the hardness and a w of samples. With increasing the frequency of ultrasound, hardness (N) and a w were decreased. Microwave energy reduced drying time and can modify the structure, texture strength and color of the final product. PRACTICAL APPLICATIONSCranberry contains high levels of phytochemicals, which have health‐promoting properties. Some of these phytochemicals, such as anthocyanins, act as an antioxidant, reducing the oxidative damage to cells, which can lead to cancer, heart disease and other degenerative diseases. Recently, cranberry products have been used with the hope of preventing or treating urinary tract infections or Helicobacter pylori infections, which can lead to stomach ulcers, or to prevent dental plaque. Osmotic dehydration is a suitable way to produce shelf‐stable products or partially dehydrated foods without enduring heat damage. The osmotically dehydrated cranberries can be consumed as healthy snacks or can be suited to a wide range of food formulations, including jams or sweets.
Current development trends in drying and available technical solutions indicate that there is a possibility to apply ultrasounds as an efficient intensifying and accelerating factor in the drying process. Such solutions have shown the ability to inhibit the loss of vital bioactive components that occur naturally in fruits and vegetables. Literature sources suggest that ultrasounds can enhance the dehydration process of vegetable tissue, both when applied during conventional drying process, and in preparation and/or enrichment prior to the drying. Applying the acoustic wave energy permits mass transfer intensification, especially in the surface layer of the product being dried without significant increase in the product temperature. This paper summarizes the available literature data on the power and frequencies of ultrasounds applied to various fruits and vegetables submitted for dehydration and drying, as well as the impact on quality and progress of horticultural crops drying.
http://www.tandfonline.com/eprint/IGeureqxyzbnvWWj4dJe/full
A study on the quality parameters of strawberries dehydrated by convection assisted by power ultrasound (US) at 40-70°C and 30 and 60W has been carried out for the first time. In general, the quality of US-treated samples was higher than that of commercial samples. Even under the most severe conditions used (US at 70°C and 60W), high values of vitamin C retention (>65%) and scarce advance of Maillard reaction (2-furoylmethyl derivatives of Lys and Arg<90mg 100g(-1) protein) were observed. Rehydration ratio was not affected by the power applied and the obtained values were similar to those of convectively-treated samples. According to the results here presented, US is a suitable example of an emerging and environmentally friendly technology that accelerates convective drying, allowing the obtainment of dried strawberries with premium quality.
Application of ultrasound to osmotic dehydration of guava slices via indirect sonication using an ultrasonic bath system and direct sonication using an ultrasonic probe system was studied. Pre-treatments were designed in three osmotic solution concentrations of 0, 35, and 70 °Brix at indirect ultrasonic bath power from 0 to 2.5 kW for immersion times ranging for 20–60 min and direct ultrasonic probe amplitudes from 0 to 35% for immersion times of 6–20 min. The calculated ultrasound intensities from calorimetric ultrasound power dissipated indicated that direct sonication was more intensive than indirect sonication. The general linear model (GLM) showed that ultrasound input (power and amplitude), osmotic solution concentrations, and immersion time increased the water loss, solid gain, and total colour change of guava slices significantly with P < 0.0005. Indirect sonication in osmotic solutions contributed to high water loss and solid gain with acceptable total colour change than direct sonication. Applying ultrasound pre-osmotic treatment in 70 °Brix prior to hot-air drying reduced the drying time by 33%, increased the effective diffusivity by 35%, and decreased the total colour change by 38%. A remarkable decrease of hardness to 4.2 N obtained was also comparable to the fresh guava at 4.8 N.
The present work investigates how ultrasound pretreatment modulates the effects of osmotic dehydration (OD) on the water state and microstructure of kiwifruit. Kiwifruit slices (10mm thick) were subjected to ultrasonic waves in a water bath at a frequency of 35kHz for 10, 20 and 30min. OD process was then carried out by immersing the samples in 61.5% sucrose solution equilibrated at 25°C for a contact period of 0, 10, 20, 30, 60 and 120min. The partition of water into the cellular tissue structures (vacuole, cytoplasm, extracellular spaces and cell wall) was investigated by Time Domain Nuclear Magnetic Resonance (TD-NMR). In parallel, the microstructure of kiwifruits slices was examined using a Scanning Electron Microscope. The results showed that US pretreatment performed for more than 10min had a positive effect on the mass exchange caused by osmotic dehydration. A creation of microchannels and an increase of the average cross-section area of cells were observed when the samples were pretreated with US before OD. TD-NMR showed a slight redistribution of water through the substructures of the cells, as a function of the length of the US pretreatment applied.
The application of contact ultrasound in food drying processes can increase drying rates of fruit and vegetable products. In order to get a deeper understanding of the mechanisms involved this study dealt with the analysis of changes in tissue structure and mass transfer in potato (cultivar Belana) during a contact ultrasound treatment. Individual potato cylinders were sonicated on a stainless steel screen that served as sample supporting and sound transmitting surface. Cell injury and water content were analyzed in different tissue layers in dependence of sonication time and intensity. Although ultrasound related cell disruption was limited to a thin tissue layer in direct vicinity to the sonicated surface, mass transfer was influenced throughout the complete sample cylinder with a height of 1 cm. The improved water removal from the product could thus be attributed to ultrasound effects affecting mass transfer at tissue level, e.g. microstirring, reduction of boundary layers, sponge effect, absorption heating and structural changes. Ultrasound effects observed at ambient conditions could be transferred to convective drying of potato cylinders at 70 °C.