A comparative study of drying methods on physical characteristics,nutritional properties and antioxidant capacity of broccoli

Abstract

Broccoli is considered one of the attractive raw materials for dehydrated vegetables owing to its high nutritional value. However, information about how drying methods affect the physicochemical and nutritional properties of broccoli is limited. In this study, broccoli pieces were subjected to freeze drying (FD), hot air drying (HAD), microwave vacuum drying (MVD), vacuum drying (VD), MVD combined with HAD (MVD?+?HAD), and MVD combined with VD (MVD?+?VD). Quality attributes of dehydrated broccolis were contrasted in terms of color, texture, volume shrinkage, nutritional components, antioxidant activity, and rehydration capacity. Results demonstrated that FD better preserved the nutrients while HAD displayed the worst effect. The combination of MVD?+?HAD and MVD?+?VD resulted in higher retention of nutritional compositions, better antioxidant activity, and lower energy consumption than that of HAD. Furthermore, combined drying processing exhibited similar rehydration capacity but lower hardness compared to that of HAD.     

Microwave-Assisted Pulse-Spouted Vacuum Drying of Apple Cubes

Microwave-assisted pulse-spouted vacuum drying (MPSVD) of apple cubes was examined in a laboratory-scale apparatus. Aside from the drying time, structural and textural properties of the dried cube were measured. Results are compared with alternative drying techniques developed earlier in our laboratory. These include microwave-spouted bed drying (MSBD), microwave vacuum drying (MVD), and conventional vacuum drying (VD). Comparison is made in terms of the key quality parameters, viz. color, texture, apparent density, rehydration property, and sensory evaluation. Over the range of operating conditions tested, MPSVD apple cubes had the best color and significantly highest sensory evaluation score.     

Quality evaluation of Panax notoginseng extract dried by different drying methods

Quality control still remains a big issue, affecting herbs, formulations, and even the practice of Traditional Chinese Medicine. A promising solution to the problem is to take advantage of innovative process techniques including alternative drying methods within the pharmaceutical processing. Nowadays, vacuum belt drying (VBD) has gained more and more importance in food and pharmaceutical processing. In this work, Panax notoginseng extract was made into powder by the gentle VBD as well as by classical spray drying (SD), freeze drying (FD), and vacuum drying (VD). Certain chemical and physical properties of the dried powders such as moisture content, drying time, porosity, density, saponins content, pH value and hydroxyl radicals scavenging activity were evaluated. The results showed the qualities of dried products were influenced to different extent by drying methods certainly. Vacuum belt drying was suggested to dry P. notoginseng extract for its high quality assurance of hygroscopic products and suitable for sticky or high viscous products.     

Drying Characteristics and Quality of Restructured Wild Cabbage Chips Processed Using Different Drying Methods

The drying characteristics of restructured wild cabbage chips dried using microwave vacuum (MVD), hot air (AD), and microwave freeze drying (MFD) were compared. Some of the key quality parameters of restructured wild cabbage chips such as fracturability and color and sensory characteristics were measured. Results showed that the drying time was reduced with the increase of microwave power (MVD/MFD) and in the case of air drying by the temperature (AD). Drying time was the shortest in the MVD process. Optimal quality of dried chips was obtained with the MFD process at a microwave power level 2.0 W/g.     

Quality of restructured cookies made from old stalks of Asparagus officinalis using various drying methods

The restructured crisp cookies were made from the old stalks of Asparagus officinalis. Temperature distribution, expansion ratio, moisture content, and color were measured to evaluate the drying uniformity of the cookies by applying pulse-spouted microwave-assisted vacuum drying (PSMVD) and microwave-assisted vacuum drying (MVD). Besides, bulk density, expansion ratio, microstructure, and textural properties were used to compare the products’ quality obtained by three different drying methods including vacuum drying, MVD, and PSMVD. Results showed that the products dried by PSMVD were more uniform compared to those samples dried by MVD. The pulse-spouted mode in drying chamber substantively improved the microwave-vacuum-dried products’ quality, drying uniformity, and drying characteristics.     

Effect of three drying methods on the drying characteristics and quality of okra

The objective of this study was to compare the drying characteristics and quality of dried okra obtained by vacuum freeze drying (VFD), microwave vacuum drying (MVD), and pulse-spouted microwave vacuum drying (PSMVD). The quality parameters include color (L*, a*, and b*), texture (hardness and fracturability), shrinkage ratio (SR), nutrient retention (chlorophyll, flavonoids, and vitamin C), and sensory score was investigated. Vacuum freeze drying maximally preserved the original properties of samples. And the samples dried by PSMVD showed higher quality and more uniformity compared to MVD. Considering of all aspects comprehensively, such as cost-effectiveness, practicability, and scale-up, PSMVD was a promising technique which would match results obtained by vacuum freeze drying.     

Microwave vacuum drying of lotus seeds: Effect of a single-stage tempering treatment on drying characteristics,moisture distribution,and product quality

This study evaluated the effects of a single-stage tempering treatment during microwave vacuum drying (MVD) on drying characteristics and quality of lotus (Nelumbo nucifera Gaertn.) seeds using two parameters: intermediate moisture content (IMC) and tempering temperature (4 and 25°C). Magnetic resonance imaging (MRI) was used to examine moisture migration and distribution in individual lotus seed during tempering. Results from MRI showed tempering could reduce the moisture gradient in lotus seeds during MVD. The tempering treatments led to increased moisture diffusivity (3.96–43.56%) and a shortened drying time (6.25–31.25%) when compared with continuous MVD. Furthermore, tempered samples exhibited a greater rehydration capacity, a limited overall color change, and increased amounts of taste-active amino acids when compared with nontempered lotus seeds. High IMC improved rehydration ratios of dried samples. Low tempering temperature provided favorable free amino acid content and desirable product color.     

Effects of Spray-Drying Conditions on the Physicochemical Properties of Blackberry Powder

The purpose of this work was to study the effects of spray-drying conditions on the physicochemical characteristics of blackberry powder using a central composite rotatable design. Inlet air temperature (140–180°C) and maltodextrin concentration (5–25%) were employed as independent variables. Moisture content, hygroscopicity, anthocyanin retention, color, powder morphology, and particle size were analyzed. A higher inlet air temperature significantly increased the hygroscopicity of the powder, decreased its moisture content, and led to the formation of larger particles with smooth surfaces. Powders produced with higher maltodextrin concentrations were less hygroscopic, slightly lighter and less red, and had a lower moisture content. Anthocyanin retention was mainly affected by drying temperature due to the heat sensitivity of the pigment. The optimal processing conditions were an inlet air temperature of 140–150°C and maltodextrin concentration of 5–7%. Overall, these results indicate that good quality powders can be obtained by spray drying, with potential applications for the food industry.     

COMBINED CONVECTIVE AND INFRARED DRYING OF A CAPILLARP POROUS BODY

Abstract

This work investigates the effect of spray drying conditions on some properties of tomato powder prepared by spray drying of tomato pulp. A pilot scale spray dryer (Buchi, B-191) with cocurrent regime and a two-fluid nozzle atomizer was employed. Sixty-four different experiments were conducted keeping constant the feed rate, the feed temperature, and the atomizer pressure, and varying the compressed air flow rate, the flow rate of drying air, and the air inlet temperature. Tomato powders were analyzed for moisture, solubility, density (bulk and packed), and hygroscopicity. Analysis of experimental data yielded correlations between powder properties and the above-mentioned variable operating conditions. Regression analysis was used to fit a full second order polynomial, reduced second order polynomials and linear models to the data of each of the properties evaluated. F values for all reduced and linear models with an R ² ≥ 0.70 were calculated to determine if the models could be used in place of full second order polynomials.     

Development of cantaloupe (Cucumis melo) pulp powder using foam-mat drying method: Effects of drying conditions on microstructural of mat and physicochemical properties of powder

In this study, the effects of drying conditions on moisture content, water activity (a_w), dissolution time, solubility, hygroscopicity, β-carotene, color, glass transition temperature (T_g), and sticky point temperature (T_s) of foam-mat-dried cantaloupe pulp powders and microstructure of dried cantaloupe pulp foams were investigated. Drying was performed in three temperatures (40, 55, and 70°C) on 3- and 5-mm thicknesses. The analysis of scanning electron microscopy micrographs with grey-level co-occurrence matrix showed that there is wide porous structure of dried foams at higher speeds drying. The temperature increase reduced moisture content and a_w, and increased hygroscopicity, and thickness rise increased moisture content and a_w and consequently decreased powders’ hygroscopicity under the same thickness and drying temperature, respectively. Increase in drying temperature would increase the reconstitution speed of powders into water and therefore the dissolution time decreased. In addition, results showed that the powder produced at 40°C have higher β-carotene content than those of produced at 55 and 70°C. With increasing drying temperature from 40 to 70°C, Lightness parameter (L) was increased while redness parameter (a) was decreased. The T_g and T_s were compared by plotting them in a graph against moisture content. For all drying processes the T_s was higher than the T_g. The drying conditions at 70°C (higher drying temperature) and 3?mm (lower thickness) led to a shorter drying time and consequent lower energy demand to produce a powdered cantaloupe pulp with high stability (low moisture content, a_w, and high T_g and T_s) and reconstitution speed of powder into water.     

Online measurement of moisture content,moisture distribution,and state of water in corn kernels during microwave vacuum drying using novel smart NMR/MRI detection system

Moisture content is unevenly distributed and hard to measure when agricultural products are dried using microwave drying. A low-field nuclear magnetic resonance/imaging (NMR/MRI) and microwave vacuum drying (MVD) combination equipment was developed. The residual moisture content, distribution, and state of water (free, immobilized, and bound) in fresh corn kernels during MVD were quickly measured in real time. NMR results indicated that the amplitude of free and immobilized water decreased very rapidly at the early stage of MVD, while the amplitude of bound water experienced a similar rapid decrease at the last stage. MRI results indicated that the moisture content was always distributed unevenly during MVD, especially at the early stage. The moisture distribution tended to become uniform when drying progressed and the bound water became dominant. The residual moisture content of corn kernels and integral (total) amplitude of NMR were found to fit well with a linear model (R²?>?0.991, P?相似文献   

Production of Crispy Granules of Fish: A Comparative Study of Alternate Drying Techniques

Three alternate dying methods—vacuum drying (VD), vacuum microwave drying (VMD), and pulse-spouted vacuum–microwave drying (PSVMD)—were examined experimentally for their potential as an industrial scale technology to produce granules of fish. Drying kinetics as well as key quality parameters such as expansion ratio, texture, color, sensory characteristics, and microstructure of crispy granules produced by these drying techniques were examined. Results showed that the drying time is reduced with an increase in microwave power level and with reduced pressure as expected. The quality of the granules is affected by the drying method and the operating parameters employed. Granules obtained using PSVMD at a microwave power density of 6.0 W/g displayed optimal quality required for the commercial product accepted by consumers.     

A Combination of Freeze Drying and Microwave Vacuum Drying of Duck Egg White Protein Powders

High energy consumption during freeze drying (FD) is a major concern that limits its application on common food product manufacturing. In this research, fresh duck egg white protein (FDEWP) powder and desalted duck egg white protein (DDEWP) powder were obtained by a combined two-stage tandem drying technologies (FD and microwave–vacuum drying [MVD]) in order to reduce energy consumption while maintaining good product quality. The results showed that the drying time for the FDEWP and DDEWP powders was significantly decreased by FD + MVD compared to those obtained by the FD-only process. The FDEWP powders dried by FD + MVD had a better color (higher L* and lower b*), lower apparent density, and lower foaming stability but higher emulsifying index than those dried by FD only. The DDEWP powder dried by FD + MVD had a product quality similar to that of FDEWP powder, suggesting that the DDEWP powder could be widely used as a food ingredient.     

Microwave-Vacuum Drying of Wood: Model Formulation and Verification

Based on the mechanism of moisture and heat transfer in wood during microwave-vacuum drying (MVD), a one-dimensional mathematical model to describe the process of wood MVD was established and verified by experiments in this research. The results showed that the process of MVD of wood experienced three distinct periods: (1) accelerating rate with rapid warming-up drying period, (2) a constant temperature and constant rate drying period, and (3) a heating-up with falling rate drying period. Compared with conventional hot air drying, the total drying process is almost governed by a constant rate period in vacuum-microwave drying of wood. The predicted temperature and moisture content in wood match well with the experimental data, the square of the relevant coefficient of the values of simulation and test is above 0.9, and the simulation precision of the change rule of the moisture is higher than that of the temperature.     

Spray Drying and Process Optimization of Unclarified Pomegranate (Punica granatum) Juice

In this study, production of pomegranate juice powder using a spray dryer was investigated. To prevent stickiness, maltodextrin dextrose equivalent 6 (DE6) was used as a drying agent. While feed flow rate, feed temperature, and air flow rate were kept constant, air inlet temperature (110–140°C), percentage maltodextrin (MD; maltodextrin dry solids/100 g feed mixture dry solids; 39.08–64.12%), and feed mixture concentration (19.61–44.11 °Brix) were chosen as the independent variables. Product properties investigated included moisture content, hygroscopicity, anthocyanin content, color change, solubility, bulk density, total phenolics content, antioxidant capacity, and sensory properties. The products were produced with high yield (86%) and high antioxidant activity (77%). MD and drying temperature were found to be the most important variables in production of pomegranate juice powders. Because total color change (ΔE), bulk density, antioxidant capacity, and powder yield were affected strongly by the independent variables, these parameters were used in optimization of the process. The optimum temperature, feed mixture concentration, and percentage maltodextrin were 100°C, 30.8 °Brix, and 53.5% MD, respectively. This study revealed that by applying these optimal conditions, pomegranate juice powder with a 55% dry solids yield, 9.78 total color change, 0.35 g/mL bulk density, and 57.8% antioxidant capacity were produced.     

Drying kinetics and product quality of green soybean under different microwave drying methods

The objective of this study was to investigate the effect of different microwave drying techniques on the drying kinetics and product quality of dried green soybean. Experiments were conducted using microwave vacuum drying (MVD), pulse-spouted vacuum microwave drying (PSMVD), pulse-spouted microwave drying (PSMD), and microwave freeze drying (MFD). Parameters of apparent density, color, processing temperature, expansion ratio, rehydration ratio, texture, and microstructure of the dried products were determined. The results showed that the MFD green soybean had a small change on bright color, compared with the fresh samples, but the drying time was the longest among the four methods. The bright color value of PSMVD/PSMD/MVD, respectively, was 79.77, 71.43, and 55.45, and drying time of them was slightly different. The PSMVD/PSMD showed advantages over MVD by improving the product quality.     

Microwave-Vacuum Drying of Pharmaceutical Powders

Abstract

Due to their temperature sensitive nature, many pharmaceutical products are dried under vacuum to facilitate solvent evaporation at reduced temperatures. However, this necessitates long drying times and represents a processing bottleneck. Microwave heating of such materials at reduced pressures offers a more rapid method of moisture removal, without the risk of product damage. Within this study, the effect of vacuum on the rate of solvent evaporation was investigated, using a range of powders (pharmaceutical actives Paracetamol and Aspirin, and a range of bulk excipients) and solvents including water, ethanol, methanol, and acetone. In general, drying rate increased as system pressure decreased, however, the magnitude and duration was system specific. As expected, the diffusion coefficient decreased from the first to the second falling rate period, with the diffusivity in each drying period increasing with increased vacuum. The findings in this research have significant implications for drying operations in the pharmaceutical industry.     

THE INFLUENCE OF PRESSURE AND TEMPERATURE ON THE KINETICS OF VACUUM DRYING OF KETOPROFEN

ABSTRACT

This paper explores the influence of temperature and pressure on drying kinetics of 2-(3-benzoylphenil propionic acid) ketoprofen, in a vacuum dryer on laboratory scale, Experimentally determined relations between moisture content and drying rate vs time, were approximated with an exponential model. Model parameters were correlated with drying conditions (temperature, pressure) and defined by functions of their potentions.

From an energy balance of the process, a mathematical model for simulating dependence of sample temperature vs drying time, and moisture content of material, has been developed.

Simulation of the drying kinetics and sample temperature, by use of those functional dependencies shows good agreement with experimental results.     

Dielectric properties of thermosonically treated Agaricus bisporus slices during microwave vacuum drying and correlation with the water state

Abstract

The dielectric properties of thermosonically treated Agaricus bisporus slices during microwave vacuum drying were determined, by using a network analyzer and an open-ended coaxial-line probe at microwave frequency (915 and 2450?MHz). The permittivity at 25?°C was also correlated to the water state determined by low field nuclear magnetic resonance (LF-NMR) analysis. Results showed that the dielectric constant ε' and loss factor ε″ of A. bisporus slices were affected significantly by the composition of water state in the sample. Thermosonic pretreatment enhanced the influence of semi-bound water (M₂₂) and bound water (M₂₁) on the permittivities in sample slices during microwave vacuum drying (MVD). The dependency of permittivities on the moisture content and temperature at 915 and 2450?MHz for thermosonically treated A. bisporus samples could be described by third-degree polynomial models, with R² higher than 0.998. Infrared thermal imaging analysis confirmed that thermosonic pretreatment is a potential technology to promote the uniformity of A. bisporus slices during the MVD process.     

Effect of Four Drying Methods on the Quality of Osmotically Dehydrated Cranberries

Abstract

Partially dehydrated cranberries (osmotically dehydrated) were dried to low water contents using one of following four methods: hot air drying; microwave-assisted convective drying; freeze-drying; and vacuum drying. Quality evaluation was performed on all samples, including sensory evaluation (appearance and taste), texture, color, water activity, and rehydration ratio. Hot air drying produced dried cranberries with the best visual appearance while freeze-dried cranberries had the highest rehydration ratio. The other methods presented similar rehydration ratios. There was no significant difference in color measurements and water activity. Few differences in texture were found, except for freeze-dried cranberries, which had a lower toughness compared to the other drying methods including commercially available dried cranberries. Microwave-assisted to hot air drying rate ratios increased as the moisture content decreased.