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.     

Combined Microwave-Vacuum and Freeze Drying of Carrot and Apple Chips

A combination of microwave-vacuum (MWV) drying and freeze drying was investigated as potential means for drying carrot and apple chips. The sample was first dried by microwave-vacuum to dehydrate some amount of internal free water and then by freeze drying to a final moisture content of less than 7% (wet basis). Chemical properties (carotene and vitamin C retention) and physical properties (shrinkage, color, texture, and rehydration ratio) of carrot and apple slices dried by this method were evaluated and compared with those dried by freeze drying alone, MWV drying alone, and conventional hot air drying, respectively. The comparison showed that the carotene retention of carrot slices and the vitamin C retention of apple slices dried by the current method were close to those of freeze-dried carrot and apple slices and much better than those of conventional hot air–dried ones. The samples prepared by the current method exhibited very close rehydration capacity, color retention, and texture with those of the freeze-dried ones but with a little higher shrinkage. However, the samples still showed the attractive external appearance without marked warp.     

Study on quality attributes and drying kinetics of instant parboiled rice fortified with turmeric using hot air and microwave-assisted hot air drying

Abstract

This study investigated the quality and drying kinetics of instant parboiled rice fortified with turmeric (IPRFT) by using hot air (HA) and microwave-assisted hot air (MWHA) drying. The cooked long grain parboiled rice (LGPR) fortified with turmeric was dried with HA at temperatures of 65, 80, 95, and 110?°C. The microwave power density of 0.588 Wg^?1 was incorporated for drying with MWHA. Drying was performed until the dried IPRFT reached 16% (d.b.) of moisture content. The quality of the dried IPRFT was evaluated in terms of color, total phenolics content (TPC), total antioxidant capacity (TAC), rehydration ratio, volume expansion ratio, texture and microstructure. The results showed that the incorporation of microwave power with HA drying helped to reduce the drying time by 50% compared to conventional HA drying. A prediction of the moisture ratio by using the Page model provided the best R² and RMSE in drying kinetics. The drying conditions had small effects on the color, TPC, TAC, and microstructure of the dried IPFRT. The rehydration ratio, volume expansion ratio and texture of the rehydrated IPFRT showed minimal variations from changes in the drying conditions. The TPC and TAC of the dried IPRFT clearly increased compared to the TPC and TAC of the initial LGPR.     

Effects of Different Drying Methods on the Quality Changes of Granular Edamame

In this article, the quality changes of the granular fruits and vegetables dried by vacuum microwave drying, freeze drying, hot air drying, and combined hot air–vacuum microwave drying are investigated, and the quality parameters compared on the basis of vitamin C and chlorophyll contents, shrinkage and rehydration capacity, color, texture, and microstructure changes. The quality parameters of products dried by vacuum microwave drying are slightly lower than those obtained by freeze drying, but much better than those obtained using conventional hot air drying. The quality characteristics of product dried by combined hot air–vacuum microwave are significantly improved compared to those simply hot air–dried.     

Effects of Different Drying Methods on the Quality Changes of Granular Edamame

In this article, the quality changes of the granular fruits and vegetables dried by vacuum microwave drying, freeze drying, hot air drying, and combined hot air-vacuum microwave drying are investigated, and the quality parameters compared on the basis of vitamin C and chlorophyll contents, shrinkage and rehydration capacity, color, texture, and microstructure changes. The quality parameters of products dried by vacuum microwave drying are slightly lower than those obtained by freeze drying, but much better than those obtained using conventional hot air drying. The quality characteristics of product dried by combined hot air-vacuum microwave are significantly improved compared to those simply hot air-dried.     

Study and comparison of different drying processes for dehydration of raspberries

The aim of the present study was to evaluate and compare different drying methods (microwave, hot air?+?microwave, and osmotic dehydration?+?microwave) in raspberries (cv. Heritage). A portion of raspberries was pretreated with osmotic dehydration (60°Brix sucrose solution at 20°C for 360?min) and another with hot air drying (HAD) (1.5?m/s air speed at 60°C for 300?min). Pretreated raspberries were then dried by microwave and at three different intensities (3.5, 7.5, and 11?W/g). Physicochemical properties (moisture content, water activity, and drying rate) and quality parameters (optical properties, mechanical properties, antioxidant capacity, and rehydration capacity) of dried raspberries were evaluated. Results showed that the microwave drying (MWD) at 7.5?W/g (50?min and final temperature of 79?±?5.1°C) allowed a high yield of dried raspberries. The combined processes were not efficient to accelerate the decrease of moisture content, due to the low drying rate of the pretreatments. In terms of quality, none of the drying processes allowed a high retention of the antioxidant capacity. However, they allowed an appropriate rehydration performance. The combination of HAD with MWD allowed obtaining a good appearance and desirable texture on the dried product. Thus, this last option seems to be the best among the drying methods tested, but additional studies are required to improve the efficiency of the process and the effect on the antioxidant capacity during drying.     

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.     

The effect of freezing on the hot air and microwave vacuum drying kinetics and texture of whole cranberries

Abstract

The aim of this study was to evaluate the effect of convective and cryogenic freezing, hot air convective drying (HACD) at 60, 70, 80, and 90?°C and microwave vacuum drying (MWVD) at 100, 150, 200, 300, 450, and 500?W on the drying kinetics and texture of whole cranberries. Effective moisture diffusivities and drying rates were higher, whereas drying times were shorter for the samples dried by MWVD compared with the samples processed by HACD. The drying kinetics of cranberries during MWVD was discussed based on the hypothesis postulating that changes in the drying rate of cranberries during MWVD can be explained by and correlated with changes in the pressure gradient on material surface. Cranberries processed by MWVD were characterized by significantly greater hardness, gumminess, and chewiness in comparison with HACD samples. MWVD was found to be an effective method for producing dried snacks characterized by hard and crispy texture and considerable resistance to stress associated with manufacturing, packaging, storage, and delivery. HACD produced brittle fruit that were difficult to store and transport and were not fully suitable for direct consumption. Convective freezing before MWVD improved the overall appearance of cranberries, whereas cryogenic freezing combined with high temperature HACD adversely influenced the drying rate and produced dried cranberries with suboptimal overall appearance.     

Drying Kinetics and Quality of Shrimp Undergoing Different Two-Stage Drying Processes

An innovative two-stage drying concept is presented in this article. The work considered drying of shrimp using a superheated steam dryer followed by a heat pump (SSD/HPD) or a hot air dryer (SSD/AD) both from drying kinetics and dried product quality points of view. The experiments were performed using the first-stage superheated steam drying temperature of 140°C while the second-stage heat pump drying (or hot air drying) was performed at 50°C. The moisture content of shrimp at the end of the superheated steam drying stage was varied between 30 and 40% (w.b.). The effect of tempering between SSD/HPD was also investigated. Shrinkage, color, rehydration behavior, texture (toughness and hardness), and microstructure of dried shrimp were measured. The results showed that SSD/HPD dried shrimp had much lower degree of shrinkage, higher degree of rehydration, better color, less tough and softer, and more porous than single-stage SSD dried shrimp. It was also found that SSD/AD gave redder shrimp compared to shrimp dried in a single-stage superheated steam dryer. No improvement in terms of shrinkage and rehydration behavior was observed, however.     

QUALITY EVALUATION OF OSMO-CONVECTIVE DRIED BLUEBERRIES

Abstract

The color, texture and rehydration ratios of two-stage osmo-convective dried blueberries were evaluated. The parameters analyzed for color were the total color difference (ΔE) and the red-blue (a/b) ratio. The textural parameters of hardness and stickiness of the osmo-convective dried blueberries were evaluated. The results were compared with those of conventionally air-dried blueberries (worst case scenario) and freeze-dried blueberries (best case scenario). The results showed that osmotic dehydration for a short contact time minimized color losses during convective air-drying. The osmo-convective dried blueberries were not significantly harder (p > 0.05) than the conventional air-dried blueberries. The rehydration ratios of the osmo-convective dried blueberries were lower than the rehydration ratios of freeze-dried and air-dried blueberries. The best osmotic dehydration condition under which the osmo-convective dried blueberries had better color and texture and, a shorter drying time than the conventional air-dried blueberries was 50°C – 55°Brix for 4.5 h.     

Drying Kinetics and Quality of Shrimp Undergoing Different Two-Stage Drying Processes

Abstract

An innovative two-stage drying concept is presented in this article. The work considered drying of shrimp using a superheated steam dryer followed by a heat pump (SSD/HPD) or a hot air dryer (SSD/AD) both from drying kinetics and dried product quality points of view. The experiments were performed using the first-stage superheated steam drying temperature of 140°C while the second-stage heat pump drying (or hot air drying) was performed at 50°C. The moisture content of shrimp at the end of the superheated steam drying stage was varied between 30 and 40% (w.b.). The effect of tempering between SSD/HPD was also investigated. Shrinkage, color, rehydration behavior, texture (toughness and hardness), and microstructure of dried shrimp were measured. The results showed that SSD/HPD dried shrimp had much lower degree of shrinkage, higher degree of rehydration, better color, less tough and softer, and more porous than single-stage SSD dried shrimp. It was also found that SSD/AD gave redder shrimp compared to shrimp dried in a single-stage superheated steam dryer. No improvement in terms of shrinkage and rehydration behavior was observed, however.     

Temperature and Quality Characteristics of Infrared Radiation–Dried Kelp at Different Peak Wavelengths

Drying experiments on kelp (seaweed species) were conducted using air drying (AD) and infrared radiation drying (IRD) at different emission peak wavelengths of 2.4, 3.0, 5.0, and 6.0 µm. Temperature characteristics of the dried kelp were determined in terms of temperature distribution and surface–interior temperature variation. Rehydrated ratio, color, and texture before and after rehydration were measured to evaluate the quality of dried kelp products. Dielectric properties were also studied to observe the characteristics of rehydrated dried products. The results indicated that the total drying time required for IRD products was approximately 120 min, reduced by 56% compared to AD (275 min). Infrared-dried products at 2.4 μm wavelength and AD products were found to be more uniform from the thermal images and had higher rehydration ratios compared to others. IR-2.4 rehydrated products were the closest to blanched samples in hardness, springiness, cohesiveness, and chewiness. This research work concluded that infrared radiation drying has potential to be used for drying of kelp.     

A Comparative Study of Four Drying Methods on Drying Time and Quality Characteristics of Stem Lettuce Slices (Lactuca sativa L.)

This article presents experimental results and analysis of four drying methods, viz. hot air drying (AD), hot air-assisted radio frequency drying (ARFD), infrared drying (IRD), and microwave-assisted hot air drying (MAD), on color, microstructure, density, rehydration capacity, and texture after rehydration of stem lettuce slices (Lactuca sativa L.). The drying time required for these drying protocols was also compared. These four drying tests were conducted at fixed air temperature (60°C) and velocity (1 m/s), as well as identical sample load (300 g), bed depth (20 mm), and the power level for ARFD, IRD, and MAD, which was fixed at 4 W/g. The results showed that the drying time required for stem lettuce slices using ARFD was the shortest (120 min), followed by MAD (140 min) and IRD (180 min); AD required the longest time (360 min). Notably, ARFD yielded uniform drying and the quality of the dried samples using ARFD was also the best among these four drying methods.     

Comparison of Drying Characteristics and Quality of Shiitake Mushrooms (Lentinus edodes) Using Different Drying Methods

The objective of this study was to compare the drying characteristics and the quality of dried Shiitake mushroom (Lentinus edodes) cubes obtained by hot-air drying (HAD), intermediate-infrared drying (IIRD), and vacuum microwave spouted-bed drying (VMSD). Several quality parameters of products, including color, texture, and rehydration capacity, were investigated. Compared to IIRD and VMSD, HAD turn out to be the most undesirable method due to its longer drying time and poor product quality. With similar rehydration capacity, the color of the VMSD product was closest to the original material. In terms of texture, total sugar content, and sensory evaluation, the VMSD product has the best quality.     

Rehydration and Sensory Properties of Dehydrated Russet Potatoes (Solanum tuberosum) Using Microwave Vacuum,Heated Air,or Freeze Dehydration

Russet potatoes (Solanum tuberosum) dehydrated by microwave-vacuum (MVD), heated air (HAD), and freeze drying (FD) were compared by measuring color, texture, rehydration properties, and sensory properties. Scanning Electron Microscope (SEM) images were taken to observe cell damage in the dried potatoes. The MVD potatoes remained intact following rehydration and retained suitable textural and color properties based upon sensory evaluation. The FD potatoes became friable and lost color. Sensory panelists preferred MVD, FD, and HAD in that order. MVD can provide consumers with a dehydrated product that has characteristics similar to or better than those dried by HAD or FD.     

Microwave-Convective and Microwave-Vacuum Drying of Cranberries: A Comparative Study

Abstract

Two drying methods of cranberries (microwave-vacuum and microwave-convective) are reviewed, and their advantages and disadvantages regarding the quality of dried product and the process performance are presented. Mechanically and osmotically pretreated berries were subjected to drying and quality evaluation. Quality parameters are color (in Hunter L*a*b* coordinates), textural characteristics (toughness and Young's modulus), and organoleptic properties (color, texture, taste, and overall appearance). Special emphasis was given to the energy performance of the process, monitoring of the real-time temperature profile, and the total microwave power-on time. Two microwave power densities are assessed, as well as different microwave power-on/power-off cycling periods. In almost all observed parameters, microwave-vacuum drying exhibited enhanced characteristics when compared to microwave-convective drying. Drying performance results (defined as mass of evaporated water per unit of supplied energy) showed that microwave-vacuum drying is more energy-efficient than microwave-convective. Tasting panel results exhibited slight preference in all parameters for microwave-convective dried samples.     

Optimization of Fluidized Bed Drying Process of Green Peas Using Response Surface Methodology

The fluidized bed drying process of green peas was optimized using the response surface methodology for the process variables: drying air temperature (60–100°C), tempering time (0–60 min), pretreatment, and mass per unit area (6.3–9.5 g/cm²). The green peas were pretreated by pricking, hot water blanching, or chemical blanching. Product quality parameters such as rehydration ratio, color, texture, and appearance were determined and analyzed. Second-order polynomial equations, containing all the process variables, were used to model the measured process and product qualities. Rehydration ratio was influenced mostly by pretreatment followed by tempering time, temperature, and mass per unit area. Pretreatment and mass per unit area significantly affected color and texture. Higher levels of temperature and lower levels of tempering time and mass per unit area increased the rehydration ratio. The optimum process conditions were derived by using the contour plots on the rehydration ratio and sensory scores generated by the second-order polynomials. Optimum conditions of 79.4°C drying air temperature, 35.8-min tempering time, pretreatment of the once pricked peas with chemical blanching in a solution of 2.5% NaCl and 0.1% NaHCO₃, and mass per unit area of 6.8 g/cm² were recommended for the fluidized bed drying of green peas. At these conditions the rehydration ratio was 3.49.     

Dehydration of Garlic Slices by Combined Microwave-Vacuum and Air Drying

Combination of microwave-vacuum drying and air drying was investigated as a potential mean for drying garlic slices. The sample was dried by microwave-vacuum until the moisture content reached 10% (wet basis), and then by conventional hot-air drying at the temperature of 45°C to final moisture content less than 5% (wet basis). Pungency, color, texture, and rehydration ratio of garlic slices dried by this method were evaluated and compared with those dried by freeze drying and conventional hot-air drying. The comparison showed that the quality of garlic slices dried by the current method was close to that of freeze dried garlic slices and much better than that of conventional hot-air dried ones. The lab microwave-vacuum dryer which the materials to be dried could be rotated in the cavity was developed by the authors.     

Dehydration of Garlic Slices by Combined Microwave-Vacuum and Air Drying

Abstract

Combination of microwave-vacuum drying and air drying was investigated as a potential mean for drying garlic slices. The sample was dried by microwave-vacuum until the moisture content reached 10% (wet basis), and then by conventional hot-air drying at the temperature of 45°C to final moisture content less than 5% (wet basis). Pungency, color, texture, and rehydration ratio of garlic slices dried by this method were evaluated and compared with those dried by freeze drying and conventional hot-air drying. The comparison showed that the quality of garlic slices dried by the current method was close to that of freeze dried garlic slices and much better than that of conventional hot-air dried ones. The lab microwave-vacuum dryer which the materials to be dried could be rotated in the cavity was developed by the authors.     

Red pepper (Capsicum annuum L.) drying: Effects of different drying methods on drying kinetics,physicochemical properties,antioxidant capacity,and microstructure

Results of an experimental study are presented and discussed for pulsed vacuum drying (PVD), infrared-assisted hot air-drying (IR-HAD), and hot air-drying (HAD) on drying kinetics, physicochemical properties (surface color, nonenzyme browning index, red pigments, rehydration ratio, water holding capacity, and ascorbic acid), antioxidant capacity (ferric reducing antioxidant power and 2,2-diphenyl-1-picrylhydrazyl radical scavenging capacity), and microstructure of red pepper. As expected, the drying time decreased with an increase in drying air temperature, IR-HAD needed the shortest drying time, followed by HAD and PVD. The effective moisture diffusivity (D_eff) of red pepper under PVD, HAD, and IR-HAD was computed to be in the range 1.33–5.83?×?10^?10, 1.38–6.87?×?10^?10, and 1.75–8.97?×?10^?10 m²/s, respectively. PVD provided superior physicochemical properties of dried red pepper compared to samples dried by HAD and IR-HAD. In detail, PVD yielded higher rehydration ratio, water holding capacity, red pigment and ascorbic acid content, brighter color, lower nonenzyme browning index, and comparable antioxidant capacity compared to samples dried by HAD and IR-HAD at the same drying temperature. Furthermore, PVD promoted the formation of a more porous structure, while HAD and IR-HAD yielded less porous structure. The current findings indicate that PVD drying has the potential to produce high-quality dried red pepper on commercial scale.