Drying Of Fruits Research Articles

Foam-mat Drying of Carrot Juice and Thin Layer Modeling of Drying

Drying of fruit and vegetables are critical step of processing which can be very destructive for nutrients and especially for bioactive compounds. However, novel drying methods like foam-mat drying helps to decrease the drying period and exposure to drying air therefore protect the bioactives against thermal degradation as well as improving final powder quality. The foam-mat drying of carrot juice foams and modelling of experimental drying data with theoretical models has not yet been studied in the literature. In this study, the effects of foam-mat drying at 50, 60 and 70°C on the drying behavior of carrot juice with the addition of 15% egg albumen (EA) and 15% egg albumen+ 10% whey protein isolate (WPI) as foaming agents and thin-layer modeling of the foams at different thicknesses was evaluated. Compared to control sample (only carrot juice), the drying time of the foamed carrot juice was reduced by 25% to 60% depending on the foam thickness and drying temperature. This result was consistent with the effective diffusion coefficients, since the control sample had comparably low values than the 15% EA and 15% EA+10% WPI foams. Among the fitted mathematical models, Midilli et al. had better prediction capacity with the highest adjusted correlation coefficients, the lowest sum of squared error and root mean square error values for every formulation, foam thickness and drying temperatures compared to other theoretical models.

Effect of Spray Dryer Scale Size on the Properties of Dried Beetroot Juice.

Experiments detailing the spray drying of fruit and vegetable juices are necessary at the experimental scale in order to determine the optimum drying conditions and to select the most appropriate carriers and solution formulations for drying on the industrial scale. In this study, the spray-drying process of beetroot juice concentrate on a maltodextrin carrier was analyzed at different dryer scales: mini-laboratory (ML), semi-technical (ST), small industrial (SI), and large industrial (LI). Selected physicochemical properties of the beetroot powders that were obtained (size and microstructure of the powder particles, loose and tapped bulk density, powder flowability, moisture, water activity, violet betalain, and polyphenol content) and their drying efficiencies were determined. Spray drying with the same process parameters but at a larger scale makes it possible to obtain beetroot powders with a larger particle size, better flowability, a color that is more shifted towards red and blue, and a higher retention of violet betalain pigments and polyphenols. As the size of the spray dryer increases, the efficiency of the process expressed in powder yield also increases. To obtain a drying efficiency >90% on an industrial scale, process conditions should be selected to obtain an efficiency of a min. of 50% at the laboratory scale or 80% at the semi-technical scale. Designing the industrial process for spray dryers with a centrifugal atomization system is definitely more effective at the semi-technical scale with the same atomization system than it is at laboratory scale with a two-fluid nozzle.

Solar conduction dryer for drying of fruit and vegetables in Bangladesh

Solar drying is a cost-effective method for preserving fruits and vegetables and most suitable for rural farmers in developing countries. The spatial and temporal distribution of temperature in a solar conduction dryer (SCD) and its drying performance were investigated. The quality of the dried product was also evaluated by nine-point hedonic scale test. Eight products were selected and dried in SCD and open sun drying (OSD) with three trials. Experimental data were fitted to three thin layer drying models. Results revealed that the drying air temperature was 1–14°C higher than the ambient air temperature depending on the solar radiation and drying position. The dryer saved 16%–35% drying time compared with OSD with an overall efficiency of 6.04%–19.8%. The overall acceptability of SCD-dried products was higher than that of OSD-dried products. Kinetic modeling showed Page model to be the best model in describing the drying characteristics of fruits and vegetables. Novelty impact statement The drying of fruits and vegetables in a solar conduction dryer (SCD) showed significantly higher drying rate and less drying time than traditional open sun drying (OSD). The overall acceptability of SCD-dried products was found higher than OSD-dried products. The dryer could be an effective means of preserving excess amount of seasonal fruits and vegetables for improving the dietary intake of farm households throughout the year.

Design of microwave hot-airflow vibrating drying equipment for initial drying and enzymatic inactivation of fresh fruits and vegetables

We developed and optimized microwave hot-airflow vibrating drying (MHAVD) equipment to improve drying efficiency and control the quality of dried agricultural products such as fruits and vegetables. Through three-dimensional modeling and finite element analysis, we simulated and demonstrated microwave source distribution modes and field intensity uniformity. We proposed two flow diversion modes, parallel deflection mode and V-shaped deflection mode, for the hot air distribution system, and we used finite element modeling to analyze them and determine the most optimal modes for use with the dryer. The microwave field strength that achieved the greatest uniformity on the surface of the material tray was used with feeding ports at X = 60 mm, Y = 80 mm, and H = 70 mm. The V-shaped deflector reduced the difference in the wind speeds on the material from 1.1 m/s to 0.36 m/s, thereby significantly increasing the uniformity, although no significant improvement in the local uniformity was noted when the parallel deflector was used. We used fresh balsam pear slices as a representative raw material to measure temperature distribution variations, moisture states, and distribution variations, and we also measured the polyphenol oxidase (PPO) enzymatic activity of the material during the primary drying with MHAVD. The results showed that balsam pear slices could be uniformly and efficiently dried in an environment below 70 °C, and the dry basis moisture content can be reduced from 15.82 to 12.35 in 12 minutes. The NMR/MRI results indicate that mainly free water in the balsam pear slices was decreased in the MHAVD process, with good moisture reduction uniformity. The PPO enzymatic activity decreased from 15.92 U/g to 0 U/g after drying. MHAVD provides a feasible method of enzyme killing, which also has the function of pre-drying for fruits and vegetables. Highlights A microwave hot-airflow vibrating drying experimental apparatus was designed Hot-air and vibrated can improve the uniformity of microwave drying There is a perfect correlation between moisture content and signal amplitude Free water can transform into immobilized water and combined water Microwave pretreatment can inactivate PPO enzyme

Hot air convective drying of hog plum fruit (Spondias mombin): effects of physical and edible-oil-aided chemical pretreatments on drying and quality characteristics

This aim of this study was to evaluate the effects of pretreatments and temperature on the hot air drying characteristics of hog plum fruits. Hog plum fruits were pretreated with olive oil/K2CO3 or sunflower oil/K2CO3 at 28 °C and olive oil/NaOH cum blanching at 96 °C for 15s, hot water at 96 °C for 15s, and dried in a hot air drier at 50, 60, and 70 °C. Mathematical models were used to fit the data of drying and rehydration kinetics. Results showed that increase in temperature reduced drying time, increased effective diffusivity and shrinkage. Sunflower oil aided chemical pretreated sample had the shortest drying time (780 min) and highest effective diffusivity (6.3 × 10−8 m2/s) at 60 °C, faster rehydration ability at 60 °C, highest retention rate for ascorbic acid (15 %), phenolic content (29 %), and antioxidant activity (12.3 %), while olive oil aided chemical (K2CO3) pretreated sample had the shortest drying time at 50 °C (990 min) and 70 °C (600 min), lowest shrinkage (48.5 %), slower rehydration capacity at 40 °C, and lowest colour change (ΔE = 11.5). Modified Henderson and Pabis and Vega-Gálvez were superior to other fitting models in predicting the drying and rehydration kinetics. Sunflower oil/K2CO3 pretreatment could help improve the drying and quality characteristics of hog plum.

Evaluation of two different diffusive models to describe the drying of passion fruit peels with and without blanching

Evaluation of two different diffusive models to describe the drying of passion fruit peels with and without blanching

Convective drying of cambuci, a native fruit from the Brazilian Atlantic Forest: Effect of pretreatments with ethanol and freezing

AbstractCambuci is a native fruit from the Brazilian Atlantic Forest, with high sensorial and nutritional potential. However, this fruit is very perishable, which impairs its exploration and study. This work reported the convective drying of cambuci for the first time, as an approach to achieve stability. Moreover, it also evaluated for the first time the combination of ethanol and freezing pretreatments to convective drying. Pretreatments were performed by immersion of fresh and previously frozen and thawed cambuci slices in ethanol (5 min at 25°C). Pretreated samples were then convectively dried (50°C, 1 m/s). Drying time was reduced up to ~36% by combining the pretreatments, which was associated with the reduction in the external resistance to mass transfer, once the convective mass transfer coefficient increased up to 94%. In contrast, pretreatments that include freezing had a greater influence on reducing the internal resistance to mass transfer, increasing the effective diffusive coefficient. In addition, the thermal surface profile evidenced the temperature increased faster and reached high levels in pretreatments that include freezing, which could be correlated to their higher drying rates and structure modifications. The obtained results corroborate the modifications produced by freezing and the effects of ethanol on the surface of samples significantly accelerate the convective drying of cambuci.Practical ApplicationsThe present investigation shows that convective drying is a feasible alternative for cambuci processing. Further, being this fruit very perishable, with short harvest and production far from the markets, freezing is a common practice to preserve them in the farms. Consequently, the impact of this unit operation was also evaluated. In addition, the proposed pretreatments (freezing and ethanol) have great application potential to improve the conventional convective drying of fruits. It has been shown that the combination of pretreatments accelerated drying, reducing the processing time by 36%.

Drying of persimmon fruit (Diospyros kaki L.) pretreated by different osmotic processes

AbstractPersimmon is a short shelf life fruit with interesting potential for application in different industrial segments. The immersion of food in a hypertonic (30 and 45 °Brix) or even hypotonic medium can be used as a pretreatment for the drying process. In this study, the convective drying of persimmons was preceded by osmotic dehydration (OD) with fructose in a standard atmosphere, pulsed vacuum osmotic dehydration (PVOD), ultrasound (US)‐assisted OD, and US pretreatment in distilled water. Pretreatment times were 0, 10, and 30 min. The samples were subjected to convective drying at 40 and 60°C, 0.5 m s−1. The effects of the pretreatments on the drying kinetics, volumetric shrinkage, and rehydration capacity were investigated. Fick's model and the Dincer and Dost model were used to fit the drying evolution. In addition to the influence of the osmotic solution concentration, moisture content and solid gain were functions of the treatment type. Convective drying required 260–740 min. The use of PVOD and US pretreatments resulted in the shortest drying times. The dried fruits showed particular characteristics with each different pretreatment. Both tested models presented satisfactory adjustments, but Fick's model was the best approach. In general, the treatments caused structural modifications in the persimmon fruits that modified the drying kinetics and the properties of the dried food.Practical ApplicationsConvective drying is a food processing method used to extend the shelf life of fruits, such as persimmons. The use of pretreatments is an interesting strategy to improve the drying process. However, the combination of these technologies can influence drying kinetics. Therefore, the use of mathematical models is important to represent the behavior of these processes.

Numerical analysis of heat and mass transfers during intermittent microwave drying of Chinese jujube (Zizyphus jujuba Miller)

A 3-D coupled electromagnetics, heat transfer, and mass transfer model for intermittent microwave drying of jujube fruit was developed to understand and optimize the effect of duty cycle (power level) and initial moisture on the temperature and moisture distributions and the rate of drying. The model was validated using measured temperature, pressure, and moisture content histories. A comprehensive understanding of the spatial and time evolutions of temperature, moisture, pressure, microwave power absorption, and evaporation rate were obtained. A uniformity index for temperature and moisture, that more closely relates to quality, was computed as drying progressed, providing unique insight into how the power level can affect quality in such a complex drying process. The effect of duty cycling was clearly seen, showing a sharp increase in temperatures, evaporation rate and pressure during the ON-phase, followed by decrease during the OFF-phase. Moisture profiles tracked the temperature cycling. Low moisture samples heated more spatially uniformly at relatively lower temperatures and with more uniform moisture profiles. Lower duty cycles (effectively lower power) reduced both the rate of temperature rise and the moisture loss, while improving the uniformity of temperature and moisture. The model provided a comprehensive mechanistic insight into the complex microwave drying process that would greatly reduce the time and resources in the design of product, process, and equipment.

Drying Kinetics and Modelling of Convective Drying of Kedondong Fruit

Kedondong is an underutilized fruit cultivated in a small scale in Malaysia and it contains nutrients that can be preserved through drying. The dried product can be sold as a premium fruit snack that could generate revenue for the producer. We studied the drying of peeled and unpeeled kedondong fruits using hot air (60-80°C). This study aims to investigate the drying kinetics (drying rates and effective diffusivities) of kedondong fruits and model the drying curves using thin layer models. Ten thin layer models were employed and solved using non-linear regression. Drying kinetics showed that only falling rate periods were observed, which implied that internal diffusion was the dominant mechanism for moisture release. Mathematical models showed that Modified Hii et al. (I) and (II) models were able to predict the drying curve well with the highest R2 (0.9992-0.9999), the lowest RMSE (8.0 x 10-4 - 2.5 x 10-3) and the lowest χ2 (4.0 ×10-5 - 2.0 x 10-4). Peeled samples showed higher effective diffusivities (average 3.2 x 10-11 m2/s) than unpeeled samples (average 2.7 x 10-11 m2/s). The activation energy was lower in peeled samples (25.8 kJ/mol) as moisture diffusion could occur more easily than unpeeled samples (32.1 kJ/mol). Results from this study provide kinetic information that can be used in scaling up of dryer and optimizing dryer performances.

Heat transfer analysis of convective and microwave drying of dragon fruit

AbstractThe purpose of this study was to develop a predictive three‐dimensional analytical model for predicting the temperature profile during microwave and convective drying of dragon fruit. A combined electromagnetic (Maxwell's equation) and heat transfer model was used for modeling of microwave drying. This heat transfer modeling is applicable to describe the thermal dissipation during the microwave and convective drying of agricultural produces. In this process, the dragon fruit cube of 15 mm was dried at a microwave power of 200, 400, and 600 W during the microwave drying process and hot air temperature of 60°C during the convective drying process. During microwave drying, the core or center temperature was maximum compared with the temperature at the surface of the dragon fruit cube. The predicted temperature at the center of the dragon fruit cube exposed to the microwave power of 200, 400, and 600 W for 60 s of drying time was 34.67, 44.34, and 54.02°C, respectively. In convective drying, the temperature at the edges was higher than the temperature at the center point of the dragon fruit cube. During convective drying, the fruit sample attained the maximum temperature of 60°C after being exposed to hot air for 8 min. The RMSE and values between experimental and model projected values were less than 0.988 and 0.029 in microwave drying and less than 0.891 and 0.018 in convective drying, indicating that the model projected values were in good agreement with the experimental values.Practical ApplicationsThe importance of thermal processes in deciding the safety and quality of food products is emergent. This model can predict food product temperature distribution during the hot air drying and microwave drying of Dragon fruit cubes. The economy of the drying process is often influenced by the nature and operation of these processes and hence modeling of the drying process is a crucial factor for the industry. These results can be used to quantify heat and moisture distribution, as well as to monitor the drying process of fruits and vegetables, saving energy and time.

Performance evaluation and economic analysis of modified solar dryer with thermal energy storage for drying of blood fruit ( Haematocarpus validus )

In the present work, a modified solar dryer (MSD) assembled with a solar collector consisting of phase change material (PCM)—thermal storage unit has been designed and the dryer performance investigated while drying blood fruit. The proposed design of MSD with double-glazed glass on a solar collector increased the drying air temperature by 15%–18%. The mean temperature in the drying chamber of MSD was 60°C with 10–12 hr of the continuous drying period. The Midilli model was well suitable to explain the drying kinetics of the blood fruit in MSD. The quality parameters like color, TPC, TFC, and antioxidant activity of dried slices were compared with fresh samples. Simulated model behaviors were similar to experimental values with an RMSE and RMSE% remaining below 1.2°C and 0.86%, respectively. Environmental impact analysis of MSD showed that the energy payback and cost payback periods were estimated as 1.23 and 2.16 years, respectively. Practical application A proposed modified solar dryer with thermal energy storage was designed and investigated for drying of blood fruit. The energy storage unit in the MSD increases the drying time by 19%, effective at off-sunshine hour and retains the quality of dried products as well as improves the drying rate compared to tray dryer. The exergy analysis, energy payback period, CO2 emission, and cost payback period are performed for MSD and found to be better than tray dryer (TD). The MSD's energy payback time is 1.23 years, and the calculated CO2 reduction is 4.14 tons in 5 years, 9.64 tons in 10 years, and 20.65 tons in 20 years, respectively. The solar dryer that has been built will be ideal for marginal farmers and small scale entrepreneurs and can be extended to any capacity.

The influence mechanism and control strategy of relative humidity on hot air drying of fruits and vegetables: a review

Drying temperature, air velocity, material thickness during hot air drying usually have a significant influence on drying kinetics and quality attributes of fruits and vegetables. However, under constant drying temperature, the influence of relative humidity (RH) of hot air on heat and mass transfer is often ignored in drying practice. On the other hand, the current literature about the influence of relative humidity of drying medium on drying kinetics and quality of fruits and vegetables are inconsistent or even contradictory. Usually, the relative humidity is roughly controlled based on experience. Therefore, it is necessary to summarize and reveal the influence mechanism of relative humidity of drying medium on drying kinetics and quality of fruits and vegetables. The RH effect mechanism on drying kinetics is analyzed in two aspects including heat transfer and mass transfer. Increasing RH intensifies heat transfer process while decreasing RH intensifies mass transfer process. Applied high RH in the initial drying stage and then decreasing RH can improve drying efficiency compared to the continuous dehumidification RH drying method. Additionally, step-down RH drying strategy method helps to mitigate the formation of casehardening on product surface and promote pore network, which is benefit for moisture transfer and diffusion. High RH during hot air has the potential to improve the pore network of materials, which is helpful for rehydration ratio. Additionally, low RH increases drying rate so that material surface generates a rigid crust or shell that fixes the volume. Low temperature but high RH drying medium can preheat the sample as soon as possible so as the energy which was used to heat the drying air can be saved. The applicable of step-down RH drying strategy is suitable for those food materials drying, whose β value is more than 1 in Weibull distribution model and Bi value in Bi-Di model is more than 0.1. In other circumstances, continuous dehumidification drying is suitable for food material drying. The auto RH control adjustment drying strategy has been investigated based on material temperature. Such RH control drying strategy provides theoretical foundation for enhancing drying efficiency and quality of fruits and vegetable materials.

Comparative and variability analysis of different drying methods on phytochemical, antioxidant and phenolic contents of Ficus auriculata Lour. Fruit

IntroductionRoxburgh Fig is a deciduous evergreen tree grown in a tropical region with wild edible fleshy fruits. They can be eaten raw or cooked, used in jams, juice and curries. The drying of fleshy fruits using thermal processing is an important method to preserve nutraceuticals. This study describes the effects of sun, hot air oven and microwave drying method on Ficus auriculata fruit polyphenol contents. MethodsThe fleshy fruits were dried and the extraction was made out using 80% methanol with a sonicator. The HPLC-DAD analysis was performed using an analytical instrument equipped with LC 20 AP binary solvent pump, SPD N 20A diode array detector with C18 column with 5 µm size and 4.6 × 250 mm dimension. Principle component analysis (PCA) was performed to analyze the contribution of independent variables. The microstructure of dried fruit samples was observed at 200X magnification at an acceleration voltage of 20kV in SEM. ResultsThe results revealed that the carbohydrates (275.34 ± 5.57mg GE/ g sample), proteins (243.07 ± 4.17mg BSAE/ g sample) and amino acids (21.25 ± 0.82mg LE/ g sample) were higher in hot-air oven dried fruit. The antioxidant activity was reported higher in microwave dried and hot-air oven dried samples due to the moderate distribution of secondary metabolites. The HPLC-DAD polyphenol quantification revealed a higher amount of gallic acid (7.73 mg/ g sample) in HD dried fruit and caffeic acid (6.73 mg/ g sample) and rutin (8.33 mg/ g sample) contents in the MD dried extracts. The SD and HD contributed 94.31% and 5.01% of the variance in the phytochemical components, respectively. The microstructures of the dried samples resulted that the microwave drying showed a loser porous structure gives more shrinkage for preservation. ConclusionThus, microwave drying should be an optimal method for obtaining dried roxburgh fig with high nutritional value.

Intensification Of The Drying Process With Vibration Method

This article describes the use of intensive technologies in the drying of fruits in the project, including the use of vibration boiling to reduce the duration of the drying process and save raw material consumption for 1 ton of dried products by 0.5-2%. Also shows the organoleptic properties of dried plums in vibrating dryers proved to be superior to products obtained from tape-type dryers.

Physiological Analysis and Contamination of Heavy Metal Contents in Vegetables and Fruits Irrigated with Wastewater

The following research work has been undertaken to examine the presence of heavy metals i.e., lead (Pb), Cadmium (Cd), Copper (Cu), Iron (Fe), Cobalt (Co) in some selected vegetables and fruits supplied in the local market. The process used to determine heavy metals is Atomic Absorption Spectrometer. Iron concentration in spinach, tomato, cauliflower and lady finger showed higher ranges which were exceeding the permissible limits. Cauliflower and spinach were within the limits specified. The pH value, ascorbic concentration and moisture content significantly decreased after oven drying of vegetables and fruits. However, the Total Soluble Solids (TSS) and ash content significantly increased after oven drying as compared with fresh vegetables and fruits. The present research data revealed that the fresh and oven dried vegetables such as Spinach, Cauliflower, Lady finger and Tomato contains 0.13-1.50%, 0.25-2.32%, 0.26-2.52% and 0.19-3.13% Titratable acidity respectively. Similarly, fresh and oven dried Guava Titratable acidity was highest 0.27 and 1.92 as compared with Water melon and Mango. The reduction in acidity may be due to catabolic activities in fruit cells and increased in pH. The pH value of vegetables and fruits dropped after oven drying. Similarly, ascorbic concentration and moisture content significantly decreased after oven drying as compared to fresh vegetables and fruits. However, the Total Soluble solids (TSS) and ash content significantly increased after oven drying as compared with fresh vegetables and fruits. Overall, from the following study we can conclude that vegetables and fruits were found to be contaminated by heavy toxic metals. Regular monitoring is required because these toxic metals will damage human body as well disturb our food chain. The main objective to conduct this study is to monitor the heavy metal toxicity and provide some recommendation, which in future will assure food safety and human health.

Proportion of ripe fruit weight and volume to green coffee: Differences in 43 genotypes of Coffea canephora

AbstractThe processing yield or performance, which includes drying and depulping of coffee fruits, can be calculated as the relationship between the volume of ripe coffee fruits and green coffee weight and is a relevant characteristic for the development of new cultivars. The purpose of this study was to evaluate the processing performance of 42 genotypes and one population of Coffea canephora. The treatments consisted of 42 C. canephora genotypes propagated by cuttings and one seed‐derived population arranged in a randomized block design with three replications. The genotypes were harvested when 80% of the fruits were in the ripe stage (red berries). We evaluated the relationship of the volume to weight of ripe fruit (ripe fruit volume [RFV]/ripe fruit weight [RFW]), the percentage of seed per fruit (% of seeds), the yield (in liters of ripe coffee) required to produce a 60‐kg bag of green coffee, and the relationship between RFW and dry green bean weight (RFW/dry seed weight [DSW]). The results were subjected to ANOVA, and the means were grouped by the Scott–Knott test (p ≤ .05). The mean yield of the evaluated genotypes was 347.57 L bag–1 of green coffee (between 294.01 and 439.72 L bag–1). A lower seed per fruit percentage identifies genotypes with a lower yield and higher RFW/DSW ratio. The genotypes Z21, 700, AD1, LB1, Emcapa 143, and AP required less than 315 L of ripe coffee to produce one 60‐kg bag of green coffee beans.

Determining the kinetic and energy parameters for a combined technique of drying apple raw materials using direct electric heating

The development of technology and drying equipment tackles a triune task: to intensify drying processes, to save energy, to ensure that proper product quality is achieved. This issue is resolved by modern advancements by supplying thermal energy throughout the entire sample volume. The simplest option among the known techniques is to heat wet raw materials by passing an electric current directly, with an external blowing by a hot heat carrier.
 This paper reports an experimental study of the combined process of drying apple raw materials using direct electric heating.
 The influence of control factors such as the field intensity and a heat carrier temperature on the kinetic parameters of the process has been determined, namely: the duration of the combined drying of apples, the rate of moisture removal, and a change in the temperature of the sample.
 It was established that the application of additional electric heating with an electric field intensity of 20–40 V/cm during convective drying with a heat carrier temperature of 25–55 °C reduces the duration of apple dehydration by 3‒5 times.
 Permissible limits for changing the combinations of basic technological parameters have been determined, as well as the rational modes for treating raw materials in order to ensure the predefined quality of finished products. Such combinations of technological parameters of heating, in particular the intensity of the electric field and air in the dryer, are 30 V/cm+40 °C, and 25 V/cm+55 °C.
 The energy parameters of the proposed combined technique of drying apple raw materials have been determined. It was established that the specific energy consumption for the removal of 1 kg of moisture at direct electric heating is 2,350–2,400 kJ/kg (0.66 kWh/kg).
 The study performed could provide a prerequisite for devising an energy-efficient technique for the combined drying of fruit and vegetable raw materials using direct electric heating

Assessment of Chokeberry Powders Quality Obtained Using an Innovative Fluidized-Bed Jet Milling and Drying Method with Pre-Drying Compared with Convection Drying

There is a need and great interest among food producers in obtaining powders from fruit and vegetables of both high nutritional value and sensory qualities superior to those hitherto obtained by convection drying (CD) and spray drying methods and cheaper to prepare than the sublimation method. This study is focused on whether powders can be obtained from fruit berries with a sticky structure, using the chokeberry (Aronia melanocarpa) as a test example, by a combined fluidized-bed jet milling and drying (FBJD) of pre-dried fruit by CD to an adequate water activity (aw). The pre-drying step reduced sticking between fruit particles during the simultaneous drying and grinding processes of the FBJD method in order to obtain powders of desired granulation. Three different pre-drying temperatures of 50, 60, and 70 °C were tested for levels of microorganisms in chokeberries at a water activity of 0.4. Vitamin C content and antioxidant properties were also examined along with polyphenol separation. Fruit pre-dried at 60–70 °C had significantly higher vitamin C and polyphenolic content and greater antioxidant properties than those pre-dried at 50 °C. Further studies were thus undertaken on powders pre-dried at 70 °C in which antioxidant properties, vitamin C, and polyphenols content were also compared with CD obtained powders. The FBJD method combined with CD pre-drying proved superior to just using the CD method, where powders had a greater preservation of vitamin C at 84% (CD powders 35%), a 12% higher total polyphenol content, and a 10% higher antioxidant activity. The test method also uses a much shorter drying time than the CD method, because the grinding of the hard-textured material takes only few minutes.

Mathematical Modelling of Single Glazed and Double Glazed Solar Air Heater

This paper focuses on Mathematical Modelling of Single Glazed and Double Glazed Solar air heater (SAH) which is special kind of heat exchanger that transfers thermal energy from the solar radiation to the fluid flowing inside of the collector. The most potential applications of SAH is the supply of hot air for heating of buildings, to maintain a comfortable environment especially in the winter season, air preheating, desiccant refrigeration, and drying of vegetables, fruits, meat, textile and marine products. Solar radiation intensity is less in the morning that increase gradually till noon and again decrease from noon to evening. During simulations it is observed that the heat gain is directly proportional to the mass flow rate. It is maximum for the counter flow SAH and is least for transpired solar air heater. The efficiency of the SAH is directly proportional to mass flow rate. The thermal efficiency is maximum for the counter flow SAH, The useful heat gain increases is highest in the clear days of summer month particularly in the month of April-May and lowest in the cloudy days of winter month particularly in the month of December. The results are in conformation with theoretical aspects.