Drying of chitosan in a spouted bed: The influences of temperature and equipment geometry in powder quality

The influence of temperature and spouted bed geometry in drying chitosan with relation to powder quality (molecular weight, deacetylation degree, particle size, color) and operation characteristics (product recovery and mass accumulated) were investigated. Chitosan paste was obtained from shrimp wastes and dried in a spouted bed (slot-rectangular and conical-cylindrical geometries) with different inlet air temperatures (90, 100 and 110 °C). Thermogravimetric curves, infra-red analysis and scanning electron microscopy were carried out in order to verify powder quality. Chitosan paste used in drying experiments showed solid content 4%, molecular weight 140 kDa and deacetylation degree 85%. In all drying experiments deacetylation degree was not modified and final moisture content was in the commercial range (10%). Temperature increase caused an increase in molecular weight, powder darkening and increased particle size. The best powder quality was obtained in slot-rectangular spouted bed at 90 °C. In this condition product recovery was 65%, accumulated mass was 20% and the powder presented faint yellow coloration, high thermal stability and porous heterogeneous surface.     

MICROWAVE and SPOUTED BED DRYING of FROZEN BLUEBERRIES: the EFFECT of DRYINGAND PRETREATMENT METHODS ON PHYSICAL PROPERTIES and RETENTION of FLAVOR VOLATILES

Frozen blueberries (Vaccinium corymbosum L cv. 'Elliott') were dried in a microwave and spouted bed combined dryer (MWSB) at 70C air temperature and 3.7 W/g microwave power (wet material). the effect of pretreatment using a 2.5% Ethyl Oleate & 0.2 NaOH dipping solution followed by sucrose osmotic treatment was investigated. the drying kinetics of MWSB drying was compared with spouted bed (SB) drying with dipping treatment, and with tray drying. the rehydration ratio, the color, and the bulk density of MWSB dried blueberries were compared with those of freeze, tray, and SB drying. the drying time needed to reduce blueberry moisture content from 82.5% to 15% (wet basis) using MWSB drying was 1/19 and 1/24 (with and without pretreatment) of the time for tray drying. the MWSB drying resulted in a low bulk density and more reddish and less blue color compared with other methods. MWSB dried frozen blueberries exhibited a higher rehydration ratio in short soaking times. Analysis of flavor volatiles by GC/MS identified ten heat-generated compounds. Microwave heating generated three unique flavor compounds (2-Butanone, 2-methyl butanal, and 3-methyl butanal). Freeze-dried frozen blueberries lost several flavor compounds including the typical blueberry aroma, the 1, 8-Cineole.     

Conical spouted bed drying of Baker's yeast: Experimentation and multi-modeling

Baker's yeast drying experiments in a conical spouted bed are used to characterize the effects of operating conditions on drying behavior. A novel multiscale model, describing Baker's yeast drying in a conical spouted bed, is presented; it is based on an intrinsic drying model developed for a single pellet, combined with a gas–solid flow model developed for a conical spouted bed. The resulting phenomenological model, which has only one adjustable parameter, is in good agreement with the experimental results. The model is capable of adequately predicting the drying rate of Baker's yeast pellets during the entire drying period in a conical spouted bed: from the beginning, where the water removal rate is limited by the air saturation with vapor during its residence time in the bed; to the end, where the water removal rate is dictated by internal resistance within the yeast pellets.The quality of dried Baker's yeast was characterized by measuring the gassing power in bread dough. This parameter was monitored during the conical spouted bed drying experiments. It was found that yeast degradation is linked to intracellular water removal (type D, end of the drying below a moisture content of around 0.5 (d.b.)) and it is mostly the rate of this water removal that controls the final quality of the product. Intercellular water removal (type E, beginning of the drying) was found to have no significant influence on yeast degradation. In all the cases, degradation is amplified when solid temperature is higher than 40 °C.     

Microwave Finish Drying of Diced Apples in a Spouted Bed

The combination of a spouted bed with microwave heating to improve heating uniformity was evaluated. Experiments were performed on a laboratory system in which evaporated diced apples of about 24% moisture were dried to about 5% at 70°C air temperature using four levels of microwave power density (0 to 6.1 W/g). With the combination method, temperature uniformity in diced apples was greatly improved as compared to that with a stationary bed during microwave drying. Products had less discoloration and higher rehydration rates as compared to conventional hot air drying or spouted bed (SB) drying. Drying time could be reduced by >80% compared with SB drying without microwave heating.     

Microwave assisted air drying of osmotically treated pineapple with variable power programmes

Variable power programmes for microwave assisted air drying of pineapple were studied. The pineapple pieces were pre-treated by osmotic dehydration in a 55° Brix sucrose solution at 40 °C for 90 min. Variable power output programmes were designed and ran with different inlet air temperatures between 30 and 70 °C. Results indicated that the use of variable microwave power combined with low air temperatures can result in a fast drying process without significant charring of pineapple pieces. High microwave powers need to be reduced quickly, faster than the decrease in water content would suggest, to minimize charring. In this study an inlet air temperatures of 70 °C was found to be excessive when combined with microwave energy (5 W/g - after compensating for the moisture loss), resulting in fast temperature increase. Microwave power was found to be most effective in the first hour to 1.5 h of processing. It should then be reduced to 0.1 W/g (initial product weight) in the final stages of drying to avoid charring of the fruit pieces. The best microwave programme tested lead to 20% water content with just 1% losses due to charring, but the results allow to conclude that charring could be completely reduced by switching off microwave energy altogether after 1.5 h and then finish off drying with higher air temperatures. The use of low air temperatures (30-50 °C) is advantageous with microwave energy in the first stages of drying as it limits the peaks of specific energy absorption, but it slows down drying towards the end probably because of a too low point of equilibrium (saturation humidity of air). Microwave energy did not significantly influence the drying process towards the end, although drying rates showed a “memory effect”, that is, drying rates in processes with the same conditions after a given time depended on the conditions up to that point.     

Image analysis and quality attributes of malting barley grain dried with infrared radiation and in a spouted bed

The impact of drying two spring barley cultivars (Mauritia and Prestige) in a spouted‐bed and in infrared radiation (IR) dryers on grain dimensions, colour, pigment content, vitality and malt quality was investigated. The results indicate that the investigated drying methods led to kernel dimension changes. Kernel shrinkage was typical of spouted bed drying, while kernel expansion was observed after IR drying at the intensity of 900 W m^?2. An increase in the intensity of yellowness (b*) on the surface of dried grain and a decrease in the yellowness intensity of kernel cross‐section were also observed. The aforementioned changes were associated with the decomposition of carotenoids (endosperm colour) and reduction of soluble proanthocyanidin and total phenolic compounds (surface colour). The drying processes also lowered germination energy and capacity, in addition to susceptibility to moisture diffusion into the endosperm. These adverse results were cultivar dependent and affected the quality of malt and wort only to a limited extent. The main changes were an increase in the Kolbach index in malt from Mauritia cv., and a fluctuation of the diastatic power of malt that did not exceed ±3%. Generally, drying of barley grain in spouted bed should be conducted at an inlet air temperature of 40 °C and using an IR drier at a radiation intensity of 600 W m^?2.     

Microwave, air and combined microwave-air-drying parameters of pumpkin slices

Pumpkin slices (Cucurbita maxima) which weighs 50 g with moisture of 9.31 g water/g dry solids, were dried using three drying methods, microwave, air and combined microwave-air. Drying continued until slice moisture reduced to 0.1 g water/g dry solids. Two different microwave output powers 160 and 350 W were used in the microwave drying. Drying treatments in air-drying were 50 and 75 °C and 1 m/s fan speed. The combination drying in which microwave and air-drying were applied together was four different combination levels. Drying periods lasted 125-195, 45-90 and 31-51 min for microwave, air and combined microwave-air-drying, respectively, depending on the drying level. Energy consumption was 0.23-0.34, 0.61-0.78 and 0.29-0.42 kW h, respectively. In this study, measured values were compared with predicted values obtained from Page's semi-empirical equation. Optimum drying period, colour and energy consumption was obtained when microwave and air-drying was applied simultaneously and the optimum combination level was 350 W microwave applications at 50 °C.     

Studies on preparation,popping and functional properties of bulgur wheat

Wheat was steeped to 36% moisture and agitated for 2 min in sand heated to 170 °C. This dry heat bulgur was comparable to bulgur prepared by steam treatment. The dry heat bulgur of 14% moisture content was popped in hot (230 °C) sand medium. The expansion ratio of popped bulgur was 2.1. Some of the functional properties of popped bulgur flour were compared with native, 48 h malted and roller dried wheat flours. Water absorption index was highest for roller dried followed by popped and malted wheat, whereas water solubility index was highest for malted followed by roller dried and popped wheat. Roller dried wheat exhibited higher cold paste viscosity (360 BU) than popped (30 BU) wheat. Popped wheat had a peak viscosity of 300 BU. The viscogram of malted wheat was typical of cereal flours when the enzyme activity of malt was inhibited. The gel permeation chromatograms of popped and roller dried wheat indicated thermal degradation of starch during popping and roller drying. The in vitro carbohydrate digestibility of popped wheat was higher than roller dried and malted samples. The scanning electron microscopic examination of native and popped bulgur revealed that the endosperm of bulgur wheat was a homogenous mass containing gelatinized starch whereas that of popped bulgur was made up of thin layers of popped starch with irregular air spaces.     

Study of banana dehydration using sequential infrared radiation heating and freeze-drying

The drying and quality characteristics of banana slices processed with a sequential infrared radiation and freeze-drying (SIRFD) method were investigated. Cavendish bananas slices with 5 mm thickness were predehydrated using IR heating at each one of three radiation intensities, 3000, 4000, and 5000 W/m² or hot air at 62.8 °C. The predehydrated samples with 20% and 40% weight reductions obtained using 4000 W/m² IR intensity were then further dried using freeze-drying for various times to determine the effect of predehydration on the drying rate during freeze-drying. To improve the quality of dried banana chips, the banana slices were also treated with a dipping solution containing 10 g/l ascorbic acid and 10 g/l citric acid before the IR predehydration. Control samples were produced using regular freeze-drying without the predehydration. The quality characteristics of dried banana chips, including color, thickness shrinkage and crispness, were evaluated. The predehydration results showed that the drying rate of IR heating was significantly higher than the hot air drying and increased with the increase of IR intensity. For example, it took 10 and 38 min to achieve 40% weigh reduction by using IR at 4000 W/m² and hot air drying, respectively. However, the banana slices with IR predehydration dried slower during freeze-drying compared to the samples without predehydration, which was due to texture changes that occurred during the predehydration. Acid dipping improved product color and also reduced freeze-drying time compared to non-dipped samples. It has been concluded that SIRFD can be used for producing high crispy banana chips and additional acid dipping improved product color and reduced required freeze-drying time.     

Drying kinetics and quality of okara dried in a jet spouted bed of sorbent particles

Okara or soy residue is a byproduct of soymilk and tofu production process. Okara has high protein content and can be used as an ingredient in many food products or can be used as animal feed. However, okara deteriorates rapidly; hence raw okara must be dried as early as possible under appropriate conditions. Drying could also help eliminating undesirable antinutritional factors in okara. The present study investigated the feasibility of drying okara using a combined convection-sorption drying, i.e., the use of a jet spouted bed of sorbent particles. The effects of various parameters such as drying air temperature and velocity, mass ratio of sorbent particles to okara, and initial bed height of okara on the drying kinetics were investigated. Also, various quality attributes of okara viz. color, oxidation level, rehydration ability, urease activity and protein solubility as well as the specific energy consumption during drying were investigated in both low- and high-temperature ranges.     

Experimental and parametric study on drying of green peas in spouted bed

Drying of Green Peas (Pisum sativum) was studied experimentally in a lab‐scale spouted bed. Experiments were carried out at different operating conditions, and the effect of inlet air temperature and its flow rate, bed height (initial mass of wet particles) and average diameter of particles were examined on performance of dryer and rate of drying. The obtained experimental results were fitted by an exponential form equation to model the drying kinetic behaviour of green peas in a spouted bed. The fitting parameters are presented in the form of mathematical correlations as a function of operating parameters. As expected, it was found that by increasing inlet air temperature and air‐flow rate, the rate of drying increases, but by increasing the bed height and diameter of particles, the rate of drying decreases. The results can help the design engineers to choose the optimum drying conditions for industrial applications.     

Drying of yellow pea starch on inert carriers: Drying kinetics,moisture diffusivity,and product quality

This study aimed at investigating the drying of yellow pea starch dispersions on inert solid carriers and determining the drying kinetics, moisture diffusivity and the product quality, quantified through damage index and final moisture content. Drying kinetics accomplished in a convective drying tunnel show that the overall mass transfer is controlled by internal migration of moisture within the starch particles. For a given inlet air temperature from 100 to 180 °C, the apparent diffusion coefficient derived from the drying curves increases exponentially with the instantaneous moisture content, with values ranging from 4 × 10⁻¹¹ to 3 × 10⁻⁸ m²/s. Due to low diffusivity and the thin coat formed on the surface of solid carriers, the resistance to internal diffusion is negligible as compared to the overall mass transfer resistance when drying of starch dispersions takes place on inert solid carriers. Drying of yellow pea starch dispersion on Teflon particles as inert carriers was studied in laboratory and pilot fast spouted bed dryer for inlet air temperatures from 140 to 240 °C, and initial solid content of 38%, mass (d.b.). The starch damage index for targeted product moisture content was below 2.5% in the inlet air temperature range from 120 to 210 °C, when atomizing from the bottom of dryer.     

Studies on different combined microwave drying of carrot pieces

Three different combined microwave (MW) drying methods were compared, namely microwave‐assisted vacuum drying (MWVD), microwave‐assisted freeze drying (MWFD), microwave‐enhanced spouted bed drying (MWSD), in terms of drying rate, drying uniformity, product colour, rehydration ratio, retention of β‐carotene and vitamin C, and energy consumption. The drying rate of MWVD and MWSD were much faster than that of MWFD. The largest drying rate was obtained in MWSD with 3.5 W g^?1. In general, the colour of MWSD products was very uniform. Rehydration ratio of MWFD carrot pieces was almost the same as the freeze‐dried (FD) products and better than MWVD and MWSD products. In addition, the highest retention of carotene and vitamin C was observed in MWFD carrot pieces. No significant differences were observed in carotene and vitamin C between MWVD and MWSD products. However, the energy consumption in MWFD was the highest.     

Protein quality of dried enzymatic hydrolysate from anchovy produced in a spouted bed of inert particles

The anchovy (Engraulis anchoita) is a pelagic fish and due to its abundance in South America shows a sustainable exploitation. The enzymatic hydrolysis of anchovy protein associated to the drying technique in spouted bed was analysed in order to obtain products with the best characteristics. The drying conditions were inlet air temperature, concentration and flow rate of suspension. The degree of hydrolysis of the anchovy suspension was of 3.8%, and its available lysine and specific antioxidant activity were of 86 g kg^?1_protein and 4.31 mm _DPPH kg^?1 min^?1, respectively. In spouted bed drying, the lowest reduction in available lysine (9%) and loss of specific antioxidant activity (8%) were found at 90 °C, and suspension concentration and flow rate of 65 g L^?1 and 200 mL h^?1, respectively. The dried product was characterised as a protein source of high biological value due to the essential amino acids profile.     

Infrared thermography assisted control for apples microwave drying

A microwave based system was developed for drying of apple slices while on-line controlling their temperatures. An infrared thermography assisted control system allowed to realize temperature control by detecting the instantaneous maximum temperature among the samples under test instead of a chosen slice. The effectiveness of the system at hand in realizing temperature control both in space and in time was proven for three temperatures: 55, 65 and 75 °C. Temperature fluctuations became larger both with time increasing and with rising temperature levels thus causing a negative impact on dried fruit quality. In fact apples slices dried at 75 °C by microwave showed L^∗ (lightness) and white index (WI) values significantly lower (p < 0.05), when compared to the fresh samples and to the apples dried by hot air. To overcome such behaviour a mode stirrer was introduced resulting in halving the temperature spatial oscillations of sample slices.     

Far-infrared radiation assisted drying of longan fruit

Oversupply of fresh longan (Dimocarpus longan Lour.) from seasonal production in Thailand needs to be preserved in the form of dried product (exported value of over US$70 million in 2009) to prevent it from being damaged by microorganism. Due to well known limitations of hot air (HA) drying, a new technique of using far-infrared radiation (FIR) in combination with hot air and heat pump (HP) dryers for longan is proposed in this study. Longan with initial moisture content of approximately 84–86% w.b. was dried to about 18% w.b. at the drying temperature of 55 °C in the case of combined FIR-heat pump drying and 65 °C in the case of combined FIR-hot air drying with 80% recycled air. In both cases, the electric power supplied to FIR rods was set at 250, 350 and 450 W. The experimental results are presented in terms of the drying kinetics, dried product qualities (color, shrinkage, percentage of rehydration, water activity, texture, and microstructure) and sensory characteristics of the dried product. The results show that FIR in combination with hot air and heat pump drying increases the drying rate of longan by reducing the drying time. FIR also helps to create more porous structure in dried longan, with porosity increasing with the power supplied to the FIR heaters. The formation of porous structure results in a product with lower shrinkage, improved rehydration, lower hardness and lower toughness than samples dried in the absence of FIR. In addition, the FIR dried longan had a stronger red color and appeared darker. Dried longans obtained by HP, HA, combined techniques and the product from the local market, were all rated similarly by a sensory panel for color, shape, flavor and taste. It is worth noting that the overall energy used for FIR-assisted drying processes decreased with the increase in the power supplied to the FIR heaters.     

脉冲喷动床微波冻干方便面品质与能耗研究

以湿面条为实验原料,进行脉冲喷动床微波冻干(PSBMFD)面饼品质与能耗研究,并与传统电加热冻干(CFD)方式进行对比分析。研究表明:PSBMFD面饼的复水时间、复水比及复水前后硬度值分别为150 s、3.07、4 692.36 g、520.45 g,水分、色差及收缩率的均匀度分别为94.51%、94.31%、92.23%,感观评价总分为8.2,干燥时间为3.5 h,干燥产品总耗能为8.05 kWh/kg。PSBMFD技术不仅提高冻干面饼的干燥均匀度,改善冻干面饼的品质,而且与CFD相比,能够明显地缩短冻干时间(58.83%),降低冻干能耗(66.63%)。     

Low-temperature,low-relative humidity drying of rough rice

The use of low air temperatures (26–34 °C) and relative humidities (19–68%) to dry thin-layer samples of rough rice to the desired 12.5% moisture content was investigated. Drying rates and durations and their effects on the quality parameters of head-rice yield, color, and pasting viscosity of long- and medium-grain rice cultivars harvested at 19.6% and 17.5% moisture contents, respectively, were determined. Results showed that dehumidification of the drying air had greater potential for increasing drying rates at 26 °C than at 30 and 34 °C. Low drying air temperatures and relative humidities had no adverse effects on head-rice yield or color compared to controls. Peak and final viscosities of low-temperature and low-relative humidity dried samples were similar to controls.     

Effect of constant and variable temperature drying processes on drying characteristics,quality, and volatile profile of rose petals in infrared-assisted spouted bed drying

The edible rose (Rosa Crimson Glory) petals were dried using infrared-assisted spouted bed drying technology. The effects of different drying temperature conditions (30, 35, 40, 45, and 50°C, as well as stepped heating drying [SHD] and stepped cooling drying) on the drying characteristics, physicochemical properties, antioxidant capacity, and changes in volatile flavor compounds of the rose petals were investigated. The results showed that the drying time was shortened with increasing drying temperature. Both variable temperature drying processes gave the shortest drying times. Optimal color retention of rose petals was achieved at a constant temperature of 40°C and SHD. Increased drying temperature resulted in higher water-soluble polysaccharide content in the dried rose petals, whereas lower temperatures facilitated anthocyanin preservation. The variable temperature drying processes favored the retention of water-soluble polysaccharides in rose petals, but not anthocyanins. Regarding antioxidant capacity, the samples dried at 40°C and those subjected to the two variable temperature drying processes performed better. This study also analyzed the differences in volatile flavor compounds of rose petals dried under different drying conditions. It was found that the majority of volatile flavor compounds in the rose petals dried by SHD exhibited higher content levels than the other drying conditions. Therefore, considering a thorough evaluation of all relevant factors, it was clear that utilizing the SHD process was the most efficient method for obtaining the best quality rose petals overall.     

DRYING METHODS AND QUALITY OF SHRIMP DRIED IN A JET-SPOUTED BED DRYER

The objective of this study was to experimentally investigate the effects of various parameters, i.e., size of shrimp, level and pattern of inlet drying air temperature, on the drying kinetics and various quality attributes of dried shrimp viz. shrinkage, rehydration ability, texture and color during drying in a jet‐spouted bed dryer. It was found that the use of a constant inlet air temperature of 100C yielded dried shrimp of the best quality in terms of low percentage of shrinkage, high percentage of rehydration, low maximum shear force and high value of redness compared to shrimp dried using other conditions. A simple mathematical model that enables prediction of the drying behavior of shrimp in a jet‐spouted bed dryer has also been developed.