Influence of number of puffing times on physicochemical,color, texture,and microstructure of explosion puffing dried apple chips

The impact of number of puffing times during explosion puffing drying (EPD) on drying characteristics and qualities of apple chips was studied. Physicochemical characteristics, antioxidant capacity, color, texture, expansion ratio, rehydration ratio, hydroscopicity, and microstructure of apple chips dried by EPD with 0 (vacuum drying, VD), 1, 3, 5, 7, and 9 puffing times were analyzed. The apple chips dried by EPD with 3 and 5 puffing times exhibited better color (ΔE 7.27–7.70) and texture (hardness 40.5–40.8 N, crispness 8.8–9.3 N/mm), as well as higher expansion ratio (104.4–109.7%) compared to VD and EPD with fewer or more puffing times. The samples dried with 3 and 5 puffing times also showed relatively higher rehydration ratio and hygroscopicity, and acceptable retention of total phenolic content (0.32–0.37 mg/g) and ascorbic acid content (1.66–1.89 mg/100 g), as well as considerable antioxidant abilities (DPPH 79.45–81.17 AEAC µM/g, FRAP 66.54–68.25 TEAC µM/g, ABTS 73.36–79.21 TEAC µM/g) compared to VD dried samples. In conclusion, experiments with apple chips indicated that EPD drying with 3 to 5 puffing times yielded superior overall quality than that with more or fewer puffing times.     

Effect of sucrose concentration of osmotic dehydration pretreatment on drying characteristics and texture of peach chips dried by infrared drying coupled with explosion puffing drying

Effects of osmotic dehydration (OD) pretreatment on the texture characteristics of peach chips after combination drying were investigated. Peach slices were immersed into 100, 300, and 500?g/L sucrose solution for 4?h, respectively, at room temperature and then predried to a critical moisture content of 0.5?kg water/kg dry matter that was determined by the effective moisture diffusivity (D_eff) curves under infrared drying at 80°C. The peach chips were then dried using explosion puffing drying (EPD). The sucrose solution with lower concentration (100?g/L) would improve the drying rate (DR) of peach slices during infrared drying. However, sucrose solution with higher concentration (500?g/L) might affect water diffusion, resulting in lower drying rate. The changes of texture characteristics of dehydrated peach were ascribed to sucrose uptake during the impregnation step. The content and constitutes of soluble sugars in peach tissue, which was significantly affected by OD treatment, were also detected in the research. The results indicated that the combined infrared and EPD drying, in which OD with appropriate concentration (300?g/L) was applied as pretreatment, could improve the drying characteristics and texture of peach chips.     

Pulsed vacuum drying (PVD) of wolfberry: Drying kinetics and quality attributes

The effects of drying temperature (50, 53, 56, 59, 62, and 65°C) and pulsed vacuum ratio defined as the vacuum pressure duration versus atmosphere pressure duration (3:3, 6:6, 9:2, 12:5, 15:1, 18:4?min/min) on pulsed vacuum drying (PVD) characteristics and quality attributes of wolfberry in terms of polysaccharide content, color parameters (L^*, a^*, b^*, ΔE, and C), rehydration ratio and microstructure were investigated. Results revealed that appropriate PVD can reduce drying time by 73.2% compared to hot air drying at the same drying temperature. The moisture effective diffusivity (D_eff) ranged from 5.23?×?10^?10 to 9.73?×?10^?10?m²/s, calculated using the Weibull distribution model. The polysaccharide content, L^* (lightness), a^* (redness/greenness) of the PVD products were higher than those of the hot air-dried samples at the same drying temperature. The total color difference (ΔE) and color intensity (C) of PVD samples were close to those of the fresh ones. The retention rate of total polysaccharide content of PVD samples was about 49–77%, which was significantly higher than 30% of the hot air-dried samples. The surface of PVD wolfberry was highly porous, which may enhance moisture transfer during drying as well as rehydration processes. The results of current work indicate that PVD is a promising technology for wolfberry process, for the reason that PVD can reduce drying time significantly as well as enhance the quality attributes in terms of the total polysaccharide content, color parameters and rehydration ratio.     

Specific energy consumption of vacuum filtration: Experimental evaluation using a pilot-scale horizontal belt filter

Abstract

Horizontal vacuum belt filters are used for continuous solid–liquid separation in a wide variety of industrial processes. Despite the low pressure difference (usually Δp?<?0.8?bar), the high air pumping requirement to maintain the pressure difference results in considerable energy consumption. In this article, the specific energy consumption of vacuum filtration and air flow rates of a pilot-scale horizontal vacuum belt filter unit are investigated. The results show that a claw-type vacuum pump consumes only half the energy compared to a conventional liquid ring vacuum pump at corresponding operating points. A comparison between the specific energy consumption of vacuum filtration and thermal drying of the filter cake to zero moisture revealed that vacuum filtration accounted for less than half of the total energy consumption in the applied experimental conditions at Δp?=?0.2–0.5?bar. The majority of the total pumping requirement of the pilot-scale filter resulted from leaks, and only 2–25% of the air flow found its way through the cake and the filter medium. The results suggest that there is a combination of the pressure difference level and the mass of solids deposited per filtration area that together with thermal drying consumes the least amount of energy per solids mass.     

A Study of Vacuum-Drying Characteristics of Sugi Boxed-Heart Timber

In this study, we evaluated the effects of drying under atmospheric and vacuum pressure on the drying time, checking, and color change of sugi boxed-heart timber dried at the same dry-bulb temperature and the same wet-bulb depression. The results obtained were as follows: Sugi boxed-heart timber specimens dried at any temperature under vacuum pressure had a shorter drying time than the specimens dried under atmospheric pressure. At moisture content above fiber saturation point and at the same dry-bulb temperature, the specimens dried under vacuum pressure had a drying rate that was almost twice as fast as that of the specimens dried under atmospheric pressure. Sugi boxed-heart timber specimens dried under both atmospheric and vacuum pressure at a higher drying temperature had a shorter drying time than the specimens dried at a lower drying temperature. Apart from the sugi boxed-heart timber specimen dried at a temperature of 100°C under atmospheric pressure, no surface checks were observed for the specimens dried under vacuum pressure or at the other temperatures dried under atmospheric pressure. Slight internal checks were observed in sugi boxed-heart timber specimens dried at a temperature of 100°C under both atmospheric and vacuum pressure. After planer shaving, there was no significant difference between kiln drying under atmospheric pressure and that done under vacuum pressure in terms of the color change (ΔE*) for both sapwood and heartwood of sugi boxed-heart timber specimens.     

Pulsed vacuum drying (PVD) technology improves drying efficiency and quality of Poria cubes

The objective of this research was to examine the drying characteristics of pulsed vacuum drying (PVD) system as an alternative drying technology for a functional food—Poria cocos. Poria cubes in thin layer were dried at different temperatures (55, 65, and 75°C), vacuum duration (5, 15, and 25?min), and atmospheric pressure duration (4, 8, and 12?min) to evaluate the operating conditions on the drying kinetics and quality attributes of P. cocos. The quality attributes included volume shrinkage ratio, firmness, water-soluble polysaccharide content. Volume shrinkage ratio was determined by image processing technology and analyzed by Bigot’s curves. The material internal temperature was also recorded during the whole drying process. Considering the drying rate and quality attributes, drying temperature of 65°C, vacuum pressure duration of 15?min, and atmospheric pressure duration of 4?min were proposed as the most favorable drying conditions for drying Poria cubes. The current work indicates PVD is a promising technology for P. cocos drying as it not only enhances the drying process but also improves the quality attributes of it.     

Preparation of Cold Brew Tea by Explosion Puffing Drying at Variable Temperature and Pressure

Cold brew tea was prepared using explosion puffing drying at variable temperature and pressure. The influences of moisture content of predried tea leaves, freezing pretreatment times at ?18°C, and puffing temperature on water extracts content of cold brew tea were studied according to the orthogonal experiments of processing of cold brew tea based on single factors. The biochemistry ingredients of cold brew tea and hot air–dried green tea were determined and compared. The optimum processing conditions of cold brew tea were obtained as follows: predried tea leaf moisture content 50%, freezing pretreatment three times, puffing temperature 105°C. Under these optimized processing conditions, cold brew tea was obtained. When cold brew tea was soaked in cold water for 30 min at 20°C, the water extracts content, caffeine, tea polyphenols, and free amino acids of cold brew tea reached 18.21, 0.88, 11.86, and 1.02%, respectively. High-performance liquid chromatography (HPLC) analysis showed that the amount of tea catechins in cold brew tea and hot air–dried green tea were 11.74 and 11.47%, respectively. The caffeine in cold brew tea was 3.06%, equal to that in hot air–dried green tea. Experimental results showed that biochemistry ingredients of cold brew tea prepared by explosion puffing drying at variable temperature and pressure difference were easy to extract by low-temperature water. This research provides theory and technical support for industrialized production of cold brew tea.     

Effect of microwave pretreatment on the color degradation kinetics in mustard greens (Brassica juncea)

In the present work, the impact of microwave pretreatment on the thermal degradation of color (chlorophylls) in mustard greens was studied. The drying experiments were conducted in the range of temperatures from 50 to 80°C. The degradation in the levels of chlorophylls has been quantified using Hunter color values (L*, a*, and b*) and calculating total color difference (ΔE). From the color results, the changes in color values (L*, a*, and b*) were observed as inappreciable, and changes in ΔE were found to be increased during drying. Analysis of kinetic data displayed a first-order reaction kinetics for chlorophyll degradation. Arrhenius equation was used to calculate the activation energies for rate constants, and it has been varied from 13.3 to 27.4?kJ/mol. Thermodynamic parameters, enthalpy of activation (ΔH^#), and entropy activation (ΔS^#) were found to be in the range of 1.40–2.63?J/mol and ?293 to ?305?J/mol?·?K, respectively. The data from the present work revealed that the microwave pretreatment of mustard greens remarkably influenced the retention of chlorophylls in the final dehydrated powder.     

Application of the reaction engineering approach (REA) for modeling intermittent drying under time-varying humidity and temperature

A ‘good’ drying model is important for the design of dryer, evaluation of dryer performance and prediction of product quality. Among the available models, the reaction engineering approach (REA) is a lumped model, proven to be simple, robust and accurate to model drying of several materials. In this paper, the REA is implemented to model intermittent drying, which is usually practiced for saving energy consumption and maintaining product quality during drying, under time-varying drying air temperature and humidity, which is a challenging drying case to model. For this purpose, the equilibrium activation energy (ΔE_v,b) is defined according to the drying settings in each time period and combined with the relative activation energy (ΔE_v/ΔE_v,b) generated from the convective drying experimental data obtained under constant drying conditions. The mass and heat balances also implement the corresponding drying settings in each time period during the intermittent drying. The results indicate that the REA can describe both the moisture content and temperature profiles of the intermittent drying under time-varying drying air temperature and humidity well. The accuracy, simplicity and robustness of the REA for the intermittent drying under time-varying drying air temperature and humidity are proven here. This has provided a major and significant extension of the REA on modeling challenging drying cases.     

Design and performance evaluation of a pilot-scale pulsed vacuum infrared drying (PVID) system for drying of berries

Abstract

The objective of current work was to develop a new pilot-scale pulsed vacuum infrared drying (PVID) system for the drying of berries. The system design and drying performance evaluation for grape and goji berries are reported here. The PVID system consisted of three major sections, including infrared heating section, vacuum section, and a controlling section. Electrical infrared (IR) emitter was made with carbon fiber sheet at the thickness of 2–4?mm, which emitted IR wavelength of 1–30?μm. The control system was used to achieve paused pressure by switching the drying chamber pressure between atmospheric pressure (101?kPa) and vacuum (3–10?kPa) successively and maintaining the pressure for different time periods. Grapes and goji berries were dried in a single layer at three different temperatures (55, 65, and 75?°C) with an atmospheric duration ranging from 1 to 12?min and vacuum duration from 10?min to constant vacuum. The drying characteristic and quality of PVID dried berries were investigated and compared with that of hot air (HA) dried berries. Results showed that the IR heating temperature, atmospheric duration, and vacuum duration had significant effects (p?<?.05) on the drying time. The optimum drying conditions for grapes and goji berries were IR heating at 65?°C, vacuum duration of 15?min, and atmospheric duration of 4 and 2?min, respectively. The corresponding drying time is nearly 720?min for grapes, and 450?min for goji berries. The PVID dried grapes and goji berries had more attractive color than that of HA dried ones. These findings demonstrated that PVID should be a promising method to produce high-quality dried berries. This study laid a good foundation for scaling up the technology in the future.     

OPTIMIZATION OF THE VACUUM DEHYDRATION OF CELERY (APIUM GRAVEOLENS) USING THE RESPONSE SURFACE METHODOLOGY

The response surface methodology (RSM) was used to optimize the vacuum dehydration conditions of celery. The independent variables were drying temperature (65 to 75°C), vacuum pressure (16 to 20 in Hg) and slice thickness (1 to 3 mm). The responses were rehydration ratio, bulk density, final moisture content and over-all acceptability rating. Statistical analysis revealed that temperature, vacuum pressure and slice thickness significantly affected (90% confidence interval) bulk density and final moisture content. Rehydration ratio on the other hand, was affected only by temperature and slice thickness while over-all acceptability rating was not significantly affected by any of the three variables. Contour plots for each of the responses were used to generate an optimum area through superimposition. Model validation was conducted using separate experiments at optimum conditions. Resulting drying curves at optimum conditions showed that vacuum drying of celery occurred in the falling rate period.     

OPTIMIZATION OF THE VACUUM DEHYDRATION OF CELERY (APIUM GRAVEOLENS) USING THE RESPONSE SURFACE METHODOLOGY

The response surface methodology (RSM) was used to optimize the vacuum dehydration conditions of celery. The independent variables were drying temperature (65 to 75°C), vacuum pressure (16 to 20 in Hg) and slice thickness (1 to 3 mm). The responses were rehydration ratio, bulk density, final moisture content and over-all acceptability rating. Statistical analysis revealed that temperature, vacuum pressure and slice thickness significantly affected (90% confidence interval) bulk density and final moisture content. Rehydration ratio on the other hand, was affected only by temperature and slice thickness while over-all acceptability rating was not significantly affected by any of the three variables. Contour plots for each of the responses were used to generate an optimum area through superimposition. Model validation was conducted using separate experiments at optimum conditions. Resulting drying curves at optimum conditions showed that vacuum drying of celery occurred in the falling rate period.     

Effect of processing parameters on the pulsed-spouted microwave vacuum drying of puffed salted duck egg white/starch products

A puffed food using salted duck egg white and starch as ingredients was produced by using a novel pulsed-spouted microwave vacuum drying (PSMVD) technique. In this study, three types of samples (ratios of salted duck egg white to starch 1:10, 3:10, and 5:10) were prepared and the moisture content of these samples was dehydrated to about 12% in a PSMVD dryer, then the samples were under different microwave powers (1.34 kW, 2.01 kW, and 2.68 kW) for puffing. The product volume expansion ratio, textural crispness (breaking forces), color parameters (L*, a* and b*), and sensory scores were determined. It was observed that microwave power and different ratios of salted duck egg white to starch had a significant effect on the expansion effect of the samples. The results indicated that the best product quality was obtained under the ratio of salted duck egg white to starch at 3:10 and microwave power at 2.01 kW.     

Modeling Moisture Loss during Vacuum Belt Drying of Low-Fat Tortilla Chips

A continuous vacuum drying method was used to develop low-fat tortilla chips with good sensory properties. To better understand the process, drying models were developed to determine the effects of drying thickness and temperature on drying rate. Drying rates were determined at three conduction plate temperatures (80, 90, and 100°C) and three product thicknesses (0.8, 1.5, and 2.3 mm). An effective diffusion model and semi-empirical models were used to fit the data. In addition, a model was developed from the drying rate curves that incorporated a drying coefficient [k(t)] that varied with time and could be described by a two-term Lorentzian model. All models had good agreement between experimental data and predicted data, with R ² > 0.98. With consideration of other goodness-of-fit indicators (sum of squared errors [SSE] and χ²), the Page and variable coefficient models provided the best fit. The average effective moisture diffusivity was calculated using nonlinear regression and ranged from D _eff = 1.19 to 1.54 × 10^?9 m²/s. D _eff increased with temperature and was described by an Arrhenius equation with E _a  = 14.1 kJ/mol.

Continuous vacuum drying of a presteamed corn dough can be used to produce low-fat tortilla chips with high crispness and acceptable sensory properties. The drying rate models presented in this study will help predict appropriate drying times, optimize process conditions, and better understand the mechanisms of drying.     

Modeling of drying kinetics of green peas by reaction engineering approach

Modeling of particulate or thin-layer drying of materials is necessary to understand the fundamental transport mechanism and a prerequisite to successfully simulate or scale up the whole process for optimization or control of the operating conditions. Simple models with a reasonable physical meaning are effective for engineering purposes. Thin-layer drying of green peas was carried out in a fluidized bed with a newly developed slotted gas distributor. Based on the reaction engineering approach, a drying model of green peas was well established, in which relative activation energy (ΔE_v/ΔE_v,b) was correlated with reduced moisture content (X ? X_b) at a drying air temperature of 80°C. The drying kinetics of green peas was discussed in terms of activation energy. In addition, activation energy based on a simplified material surface temperature profile was recalculated to evaluate the temperature sensitivity to the model establishment.     

Improving head rice yield of glutinous rice by novel parboiling process

Most commercial parboiled rice is produced from high-amylose content rice. Glutinous rice, which is lacking in amylose content, is generally consumed in Southeast Asian countries. Rare study of parboiling glutinous rice has been observed. In this study, glutinous rice was improved in head rice yield by a novel parboiling process. Two rough glutinous rice, rice department 6 (RD6) and black glutinous rice (BGR) cultivars, were soaked in hot water at 70?±?5°C for 3?h. The ricer 3moisture content after soaking was 50–52% (d.b.), it was dried with hot air and superheated steam (SHS) at 110, 130, and 150°C in a fluidized bed dryer. The results show that SHS at all drying temperatures can improve the high head rice yield in both parboiled glutinous rice cultivars better than hot air drying. Higher temperature drying caused L* value to decrease but the b* value increases in RD6, whereas in BGR, all color values decreased and ΔE* was increased when the drying temperature increased. Increasing drying temperature presented a softer texture of both glutinous rice cultivars. Upper 130°C, completed gelatinization of both varieties can be obtained and seen by scanning electron microscope and differential scanning calorimeter (DSC). This technique of using high-temperature fluidized bed drying can produce completely parboiled glutinous rice in a single process instead of two conventional processes, steaming and drying, in series.     

Drying Kinetics and Color Retention of Dehydrated Rosehips

Abstract

Freshly harvested rosehips (Rosa canina L.) were dehydrated in a parallel flow type air dryer at six air temperatures (30, 40, 50, 60, and 70°C) at air velocities of 0.5, 1.0, and 1.5 m/s. Drying air temperature and velocity significantly influenced drying time and energy requirement. Minimum and maximum energy requirement for drying of rosehips were determined as 6.69 kWh/kg for 70°C at 0.5 m/s, and 42.46 kWh/kg for 50°C, 1.5 m/s. In order to reduce drying energy consumption, it is recommended that the drying air velocity must not be more than 0.5 m/s and drying air temperature should be 70°C. In addition, the influence of drying air temperature and air velocity on the color of dried rosehip has been studied. Hunter L, a, b values were used to evaluate changes in the total color difference (ΔE) on dried rosehips. 70°C drying air temperature and 1 m/s air velocity were found to yield better quality product.     

Sampling method for studying the activity of lactic acid bacteria during spray drying

In this study, a novel sampling method was established to study changes in the activity of lactic acid bacteria during spray drying. Before spray drying, a sampling device with a refrigerant and a magnet was pre-cooled and positioned in a spray-drying tower. Carbonyl iron powder (CIP) was added to the drying media to increase the sampling mass by the magnetic effect. During drying, a temperature sensor measured the particle contact temperature. After drying, the sample in the sampling device was taken out to analyze the characteristics, including the mass, water content, and bacteria livability in the sample. The sampling device and method were optimized with a sampling cup with a depth of 3.5?cm (for contact temperatures below 79.1°C) or 5?cm (for contact temperatures below 89.1°C). The ratio of CIP to reconstituted skim milk (RSM) was 1:10, and RSM concentration was not lower than 20% (w/w). This method was then applied to spray drying of Lactobacillus bulgaricus sp1.1. Furthermore, it was demonstrated that 2?mL of sterile water placed in the sampling cup prior to drying resulted in a more accurate measurement of cell viability. This sampling method can be used in practical spray drying applications for biological materials without using a special instrument or drying tower.     

Osmotic pretreatment for instant controlled pressure drop dried apple chips: Impact of the type of saccharides and treatment conditions

Instant controlled pressure drop (ICPD) is an emerging drying technique that can produce fruit chips with crispy texture. To improve the qualities of ICPD-dried apple chips, six types of saccharides with different polymerization were used for osmotic pretreatment on apple slices. Firstly, the effects of different saccharides on the osmotic behavior and texture of ICPD-dried apple chips were evaluated. Then, the effects of osmotic conditions of a selected saccharide, i.e. stachyose, on the qualities of ICPD-dried apple chips were studied. The results showed that sucrose, raffinose, and stachyose could significantly enhance the crispness of the ICPD-dried apple chips. In addition, the ICPD-dried apple chips pretreated with stachyose possessed the highest T_g (29.74?°C) and superior porous structure compared with pretreatments using the other saccharides. Moreover, limited color change (ΔE) was found in the samples pretreated with stachyose at 40?°C for 30?min, as well as higher retention of polyphenols. In conclusion, it is confirmed that the types of saccharides significantly influence the qualities of the ICPD-dried apple chips, and osmotic pretreatment at 40?°C for 30?min using stachyose was suggested for improving the overall quality of ICPD-dried apple chips.     

Pulsed vacuum drying of wolfberry: Effects of infrared radiation heating and electronic panel contact heating methods on drying kinetics,color profile,and volatile compounds

ABSTRACT

The drying kinetics and quality attributes of wolfberry were investigated under pulsed vacuum drying based on two different heating ways of far-infrared radiation (PVD-FIR) and electronic panel contact (PVD-EPC) heating. They were operated at different drying values of heating panel temperatures (60, 65, and 70°C) with 15 and 2?min as the constant vacuum pressure and atmospheric pressure duration, respectively. Drying time for wolfberry dried by PVD-FIR was lower by 17–19% compared with that by PVD-EPC at the same drying temperature. The effective moisture diffusivity (D_eff) determined by Weibull distribution model ranged from 3.72?×?10^?10 to 6.59?×?10^?10?m²/s and 3.34?×?10^?10 to 6.88?×?10^?10?m²/s for PVD-FIR and PVD-EPC, respectively. The drying activation energy was 54.30 and 68.59?kJ/mol for the samples dried by PVD-FIR and PVD-EPC, respectively. The color parameters L*, a*, and b* of wolfberry dried by PVD-FIR were higher than those dried by PVD-EPC. The product dried by PVD-FIR contained more vivid luster compared to that dried by PVD-EPC. The contents of aldehydes, esters, phenols, and the heterocyclic compound in PVD-FIR sample were higher than those in PVD-EPC samples. Additionally, the alcohols, ketones, and acid contents in PVD-FIR sample were lower than those in PVD-EPC sample. In summary, PVD-FIR is more suitable for wolfberry drying as it enhances drying rate and product’s quality compared with PVD-EPC.