Xinfeng Cheng

Effects of Ultrasound and Microwave Pretreatments of Apple Before Spouted Bed Drying on Rate of Dehydration and Physical Properties

Pretreatments of fruits before drying have been proposed as alternative way to improve the quality of dried fruits and reduce drying time. In the present study, the effects of different pretreatments (ultrasound and microwave) on apple cubes prior to spouted bed drying were investigated. Ultrasound pretreatment resulted in a great loss of sugars (25.7% for 15 min) compared to microwave pretreatment, where little rise in sugar content was observed (1.6% at 300 W). Ultrasound pretreatment improved the drying rate more than microwave pretreatment. Nevertheless, microwave-pretreated dried apples were harder and had lower water activity than ultrasound-pretreated ones. Low-frequency nuclear magnetic resonance (LF-NMR) analysis was used to study the water state and revealed that all pretreatments promoted redistribution of water among apple cell compartments and showed that most of the water lost was from the vacuoles. If dried low-calorie fruits are required then ultrasound pretreatment would be preferred.

The principles of ultrasound and its application in freezing related processes of food materials: A review

Ultrasonic processing is a novel and promising technology in food industry. The propagation of ultrasound in a medium generates various physical and chemical effects and these effects have been harnessed to improve the efficiency of various food processing operations. Ultrasound has also been used in food quality control as diagnostic technology. This article provides an overview of recent developments related to the application of ultrasound in low temperature and closely related processes such as freezing, thawing, freeze concentration and freeze drying. The applications of high intensity ultrasound to improve the efficiency of freezing process, to control the size and size distribution of ice crystals and to improve the quality of frozen foods have been discussed in considerable detail. The use of low intensity ultrasound in monitoring the ice content and to monitor the progress of freezing process has also been highlighted.

Effect of ultrasound immersion freezing on the quality attributes and water distributions of wrapped red radish

The microstructures, quality attributes (drip loss, firmness, sensory evaluation, and calcium content), and water distributions of ultrasound immersion frozen red radish (wrapped or unwrapped) were investigated. The results showed that ultrasonic treatment can significantly (p < 0.05) decrease the freezing time and better preserve the quality of frozen radish samples. In addition, ultrasound immersion frozen radish samples had smaller pore size and less destructive effect on microstructures from the scan electron microscopy (SEM) analysis. Wrapped radish had significantly (p < 0.05) lower calcium content, indicating that wrapped treatment was able to effectively prevent the solute uptake from the coolant to the radish samples. The water distributions of unwrapped samples were more uniform from the pseudocolor images of magnetic resonance imaging (MRI). Low-field nuclear magnetic resonance (LF-NMR) relaxation measurements showed that the vacuole water decreased, while the relative cytoplasm and intercellular space water increased under ultrasonic and unwrapped treatment.

Effect of ultrasound-assisted freezing on the physico-chemical properties and volatile compounds of red radish

Power ultrasound, which can enhance nucleation rate and crystal growth rate, can also affect the physico-chemical properties of immersion frozen products. In this study, the influence of slow freezing (SF), immersion freezing (IF) and ultrasound-assisted freezing (UAF) on physico-chemical properties and volatile compounds of red radish was investigated. Results showed that ultrasound application significantly improved the freezing rate; the freezing time of ultrasound application at 0.26 W/cm(2) was shorten by 14% and 90%, compared to IF and SF, respectively. UAF products showed significant (p<0.05) reduction in drip loss and phytonutrients (anthocyanins, vitamin C and phenolics) loss. Compared to SF products, IF and UAF products showed better textural preservation and higher calcium content. The radish tissues exhibited better cellular structures under ultrasonic power intensities of 0.17 and 0.26 W/cm(2) with less cell separation and disruption. Volatile compound data revealed that radish aromatic profile was also affected in the freezing process.

Influence of Ultrasound-Assisted Osmotic Dehydration and Freezing on the Water State, Cell Structure, and Quality of Radish (Raphanus sativus L.) Cylinders

Ultrasound-assisted osmodehydrofreezing technique is a partial dehydration technique prior to freezing to diminish the tissue damage and preserve the quality by quickly removing part of the water from vegetable tissues. In this study, radish cylinders with three different water contents (85%, 80% and 75%, w/w) were dehydrated by osmotic dehydration (OD) and ultrasound-assisted osmotic dehydration (UOD). The effects of OD and UOD pretreatment on the characteristics (e.g., latent heat of fusion of ice, freezable water and microstructure) of dehydrated products and quality attributes (e.g., freezing time, firmness, drip loss and ascorbic acid content) of osmodehydrofrozen products were investigated. Ultrasound application significantly shortened the time of dehydration and subsequent freezing. Compared to OD products with equal water content, UOD products exhibited less freezable water content and better preservation on firmness and microstructure. After freezing/thawing, frozen products of UOD also displayed less drip and ascorbic acid losses and better firmness than that of OD.

Drying of Burdock Root Cubes Using a Microwave-Assisted Pulsed Spouted Bed Dryer and Quality Evaluation of the Dried Cubes

Burdock cube samples were dried using hot air and microwave pulsed spouted bed drying (MPSBD). Hot air drying was carried out at three temperatures (70, 80, and 90°C). MPSBD was carried out at three microwave power levels (1.0, 2.0, and 3.0 W/g). The results showed that MPSBD samples dried at 2.0 W/g for 30 min and at 1.0 W/g for 40 min had desirable color, flavor, and textural attributes. Gas chromatography–mass spectrometry results showed that the samples dried using MPSBD were richer in flavor compounds, especially in esters, compared to the hot air–dried samples.

Effects of ultrasound-assisted thawing on the quality of edamames [Glycine max (L.) Merrill] frozen using different freezing methods

The effects of different freezing and thawing methods on the physicochemical indices and nutritive value of edamame [Glycine max (L.) Merrill] were investigated. Air-blast freezing had less of an impact on the drip loss, color, chlorophyll and ascorbic acid contents, and textural hardness of frozen shelled edamames. Ultrasound-assisted thawing significantly (p<0.05) shortened thawing time, compared to water immersion thawing. Ultrasound-assisted thawing at a 900 W power level showed the best retention of ascorbic acid and chlorophyll, and original hardness, and minimized the drip loss of thawed samples. Ultrasonic assisted thawing at a power level of 1,200 W caused the most pronounced loss of ascorbic acid. A combination of fast air-blast freezing and ultrasound-assisted thawing at a power level of 900 W most effectively retained ascorbic acid and chlorophyll, minimized drip loss, and maintained the textural hardness of shelled edamame samples.

Effect of Ultrasonically Induced Nucleation on the Drying Kinetics and Physical Properties of Freeze-Dried Strawberry

Power ultrasound has proved to be very useful in controlling crystallization processes since sonication can enhance both the nucleation rate and crystal growth rate by producing fresh and/or more nucleation sites. Therefore, in this study, power ultrasound was applied to control the freezing step of freeze-dried strawberry. The results showed that when power ultrasound was applied at different temperatures, it increased the nucleation temperature and shortened the characteristic freezing time. The application of power ultrasound in the freezing step increased the drying time in subsequently freeze-dried strawberry samples. This longer drying time was found to be due to increased resistance to moisture diffusion due to the formation of a network of small pores caused by sublimation of small ice crystals induced by the power ultrasound. Scanning electron microscopic images revealed that the freeze-dried sample frozen by ultrasound-assisted freezing (UAFD) had finer cellular structure compared to those frozen in other freezing conditions. UAFD samples had better textural hardness, while the rehydration capacity was lower compared to those of NRFD and NIFD samples.