Onion Slices Research Articles

Modeling of Osmotic Dehydration Kinetics of Banana Slices using Artificial Neural Network

Osmotic dehydration of fruits is one of the oldest forms of food preservation techniques known to man. Osmotic dehydration is affected by several factors such as osmotic agent, solute concentration, temperature, time, size, and shape and tissue compactness of the material, agitation and solution/sample ratio. The application of osmotic dehydration includes musk melon, banana, papaya, mango, onion slices cucumber and carrot. Artificial Neural Network is a black box tool for the modeling of processes involving multivariable non linear relationships. The present work is aimed at the study of effect of time, temperature and concentration of osmotic solution on the weight reduction for the process of osmotic dehydration of banana slices. The experimental data of osmotic dehydration kinetics generated have been used to develop a mathematical model using regression analysis. Artificial neural network models having different topologies are developed. The comparison between ANN models is carried out based on the relative error values of all the output data points. ANN model 1 is observed to be superior than model 2. The comparison is also carried out between the output values obtained by ANN model 1 and the mathematical model using regression analysis.

Kinetics Modeling and Moisture Diffusivity of Onion Slices in Fluidized Bed Drying

Drying characteristics of onion (Allium cepa L.) was studied with different combinations of air temperature (50, 60, 70 and 80C), air velocity (1, 2.5 and 4 m/s) and slice thickness (2, 4 and 6 mm) in a fluidized bed dryer. The drying behavior of onion such as drying rate and moisture diffusivities and their variation with change in drying air parameters were analyzed. Drying took place mainly under falling rate period and drying rate decreased with the moisture content of the samples. It was observed that the drying behavior of onion was better represented by the Page's model as compared with the exponential model. Moisture diffusivity values of onion ranged between 2.148 × 10−9 and 1.474 × 10−7 m2/s for the drying conditions under study. PRACTICAL APPLICATIONS The research results of the article will be useful for the industries involved in onion drying. Further, this article will help the researchers and academicians working in drying of agricultural commodities in general and onion in particular.

DEHYDRATION OF ONION SLICES USING IR-REFRACTANCE WINDOW DRYING SYSTEM

The aim of this research work was to study the drying behavior of onion slices using infrared radiation refractance window drying system, which the infrared radiation passed throw plastic membrane surface , where the water in the moist product creates a window, that allows for the passage of infrared energy and heat behaves as it and directly transferred to water present in the product, the water in the product on the plastic membrane surface evaporates, and the window of infrared energy closes and refracts back into the heated source, no longer exposing the product to heat and good quality product. The experiments of this work carried out at food engineering and packaging research dept. , Food Techn. Res. Institute, Agric. Research center. The drying behavior of onion slices using suggested dryer was examined and simulated for three different thin layer drying models ( Page , modified Page and Hendreson and Padis ) . Four levels of radiation intensity ( 1100 , 1750 , 2400 , 3050 W / m2) and for levels of drying air velocity ( 0.1 , 0.5 , 1 and 1.5 m / s ) were studied at 45 oC temperature and 20 % relative humidity . The results showed that : The recorded drying time for drying whole onion slices from an initial moisture content of about 612 - 614.28 % d.b. to a final moisture content of about 13.75 – 15 % d.b. were 50 – 140 minutes under different drying parameters . - The following equation can described the relation ship between drying time ( T ) , radiation intensity ( I ) and air velocity ( V ) with the best fit : T = 80 + 100V - 1600 I, (R² = 0.9911) - The thermal efficiency of the IR-refractance window drying system was varied between 54.47% to 46.43% , specific energy consumption varied between 4.39 KJkgˉ¹to5.15 KJkgˉ¹under different drying parameters. - The total capacity of the dryer is a bout 0.326 Kg/h the calculated operation cost of the dryer approaches about 8.89 LE/kg of dried whole onion slices .

Onion slice shaped assembled ZnS quantum wires

Ultra-narrow wurtzite ZnS quantum wires assembled towards an onion slice shape are synthesized in water using a simple hydrothermal procedure. Wires are formed through an oriented attachment mechanism from wurtzite ZnS spherical particles. Strong confinement effect originated from the narrow width was observed and holds promise for use in broad optoelectronic device application.

Adsorption Isotherms for Red Onion Slices Using Empirical and Neural Network Models

Moisture sorption isotherms of red onion slices were determined at 30, 40, 50, and 60°C using the standard gravimetric static method over a range of relative humidity from 0.11 to 0.83. The experimental sorption curves were fitted by seven empirical equations: modified Henderson, modified Chung–Pfost, modified Halsey, modified Oswin, modified Smith, modified BET, and GAB. Also three types of Artificial neural network models: linear, multilayer perceptron, and radial basis function were tested and developed to predict the equilibrium moisture content of onion slices and the selected models were trained by using related algorithms. The modified Oswin model was found acceptable for predicting adsorption moisture isotherms and fitting to the experimental data, based on the coefficient of determination (R2= 0.991), mean relative percent error (MRE=15.019), and standard error of estimation (SEE=1.371). Besides, multilayer perceptron model with four layers (2: 17: 14: 1) was selected as the best artificial neural network for estimation of onion slices’ equilibrium moisture content by considering R2= 0.993 and good performance. The net isosteric heat of adsorption of moisture was determined by applying the Clausius–Clapeyron equation to the sorption isotherms at different temperatures. The net isosteric heat of adsorption of red onion slices varied between 1.46 and 4.96 kJ/mol at moisture content varying between 2% and 52% (d.b.).

Process optimisation of vacuum drying of onion slices

Dehydration of untreated and pre-treated onion slices under vacuum was optimised using the response surface methodology. The effects of the drying temperature (50–70°C), slice thickness (1–5 mm), and treatment (5% NaCl and 0.2% K<sub>2</sub>S<sub>2</sub>O<sub>5</sub>) were observed on the responses, viz. final moisture content, colour change, flavour content, and rehydration ratio of the dehydrated onion slices. Full factorial design was employed for the analysis. Optimisation of the vacuum drying process was achieved based on the criteria of maximum flavour retention, 3–3.5% db moisture content, acceptable colour, and rehydration ratio using numerical technique. The optimum condition for the treated sample was found at 58.66°C drying temperature and 4.95 mm slice thickness. Optimum values of the response parameters, namely the moisture content, colour, flavour content, and rehydration ratio were obtained as 3.5% d.b., 30.33 OI/g dried sample; 4.35 μmol/g dried sample and 4.82, respectively.

INVESTIGATION OF CHANGES IN PHYSICAL PROPERTIES AND MICROSTRUCTURE AND MATHEMATICAL MODELING OF SHRINKAGE OF ONION DURING HOT AIR DRYING

The effect of air drying temperature on shrinkage, rehydration ratio and microstructure of dried onion slices (3±0.2 mm thickness and 30 mm diameter) was studied. The different drying conditions led to distinctive structural changes in the samples, affecting the shrinkage and rehy dration ratio. Experiments showed that the intensity of structural changes depends on temperature and drying times. A higher temperature and time caused greater damage to the microstructure of onion slices, resulting in the formation of a highly porous str ucture. The results also indicated that increasing time and temperature increased the shrinkage and rehydration ratio of samples. In mathematical modeling of shrinkage, the model proposed in this study, which had R 2 values higher than 0.978 and SSE values pretty low, predicted accurately the experimental data.

Comparison of sanitizing technologies on the quality appearance and antioxidant levels in onion slices

BackgroundA Portuguese landrace onion variety grown in Póvoa do Varzim (Northwest of Portugal) was selected for this study. It is a red onion known as “vermelha da Póvoa”. The effect of different chemically- and irradiation-based disinfectant procedures of fresh-cut onions on their flavonoid content was compared. Amongst the chemical treatments the most used were selected: sodium hypochlorite, amukine, hydrogen peroxide, and sodium dichloroisocyanate. UV-C irradiation was also selected amongst all irradiation treatments. ResultsThe main effect contributing to the loss of flavonols in fresh-cut onion slices is their solubility in immersion water (17–23% both at 4 or 50 °C). The acidification of sodium hypochlorite with sulphuric acid is also rendering losses (6–19%) vs. the use of citric acid. Anyway, in dry decontaminantion treatments, like UV-C irradiation, the natural levels of flavonoids in fresh-cut onion slices significantly increase at 35% for flavonols, and at 29% for anthocyanins. ConclusionsOnion flavonoids decreased by chemically disinfectant procedures of fresh-cut onion by solubility in immersion water. UV-C irradiation does not only maintain the initial levels of flavonoids but increases them; therefore, this is the recommended treatment.

LOW‐COST GREENHOUSE TECHNOLOGY FOR DRYING ONION (ALLIUM CEPA L.) SLICES

ABSTRACT The performance of the greenhouse solar heat collector was highly dependent on the solar radiation, ambient temperature and relative humidity. Increase in air temperature inside greenhouse varied from 0.7 to 19.0C, and relative humidity inside greenhouse varied from −16 to 25.7% by air exchange at a flow rate of 6.1 m3/s. The average midday thermal efficiency was around 20.82%. The cured red onion (Allium cepa L.) bulbs were cleaned, outer layer was peeled and trimmed manually, and washed in water to remove dirt and infection. Edible bulb of onion was sliced into 3‐mm thick slices by using manual stainless steel slicer. The onion slices were pretreated with sodium chloride, and potassium metabisulphite, for 5 min in three concentration levels (0.25, 0.50 and 0.75%) and drained onion slices were spread in thin layers in trays before keeping them in greenhouse for drying. Onion slices were dried in 19 sunshine hours. Preservatives used as pretreatment in 3‐mm sliced onion were found to be significantly different (probability, P < 0.05) from each other. It was found that 0.50% potassium metabisulphite was best.PRACTICAL APPLICATIONSAvailability of solar energy is abundant in the Indian subcontinent and drying of agricultural produce using low cost greenhouse is one of the latest developments when crop production is not possible in greenhouse duringsummer season. Low cost greenhouse can be utilized to dry the onion slice asalternative to conventional mechanical dryers. Greenhouse drying can be used for the preparation of shelf‐stable dehydrated onion slices for the purpose of use during off‐season. The quality of dehydrated onions is good and it can be stored for months together. Dried onion slices can be used same as fresh onion after rehydration, apart from this, it can be added directly into soups, etc., before cooking.

Effects of Drying, Packaging, and Temperature on the Quality of Fried Onion Slices

Onion is used widely as a condiment for meat and other types of food in Iran. Because of the high sensitivity of this product to storage conditions and having not enough storage under controlled atmosphere (CA), the effects of drying method, packaging, and temperature during storage on thin slices of fried red Azershahr variety onion were investigated. To prepare this processed food with excellent organoleptic properties and useful in the food service industry onions were sliced (2 mm), deep-fried with corn frying oil in a batch fryer at 150 degrees C, and dried to a water content of 3-4% in a hot-air dryer at 70 degrees C for 24 h and a microwave system. Samples were packed in aluminum foil, which was purged by nitrogen gas, and cellophane-sealed with thermal sewing. Then these samples were kept for one year at laboratory temperature and in a freezer at -18 degrees C. During the storage time the moisture content, peroxide value, vitamin C content, total microbial count (TMC), and organoleptic characteristics of the samples were analyzed every 2 mo. The results of microbial analyses indicated that after 6 mo all of the samples had higher TMCs than the permission limits so the expiration date was set before that. The moisture contents and peroxide values showed a noticeable increase, probably due to seal failure, whereas vitamin C decreased up to 66% during storage. The loss of sensory properties was parallel to the microbial and chemical results. The findings revealed that the best sample was oven-dried, packed in aluminum foil under inert gas, and kept in a freezer (OAF) up to 6 mo.

First Report of Leaf Spot of Dracaena reflexa Caused by Burkholderia gladioli Worldwide.

In December 2008 (austral summer), a new disease of Dracaena reflexa Lam. cv. Anita was observed in a postentry quarantine greenhouse near Auckland, New Zealand on plants imported from Costa Rica. Symptoms included rust-colored, water-soaked lesions with chlorotic margins approximately 5 by 10 mm. When the disease was first noticed, incidence approached 80%, but subsequent reduction in greenhouse temperature dramatically reduced symptom expression and lesions were only visible on some leaf tips. Bacteria consistently isolated from the lesions on King's medium B (KB) were cream-colored, shiny, and produced a yellow, diffusible, nonfluorescent pigment. All isolates were able to rot onion slices. On the basis of BIOLOG (Hayward, CA) carbon utilization profiles, isolates were initially identified as Burkholderia gladioli (Severini 1913) Yabuuchi et al. 1993 with a probability index of 100% and a similarity index of 0.85. For molecular identification, a near full-length sequence of the 16S rDNA gene was amplified from all isolates using primers fD2 and rP1 (1), obtaining a PCR product of approximately 1,500 bp. The nucleotide sequences were 100% identical to a number of B. gladioli GenBank entries, including Accession Nos. EF193645 and EF088209. To confirm pathogenicity, three isolates (two isolated prior to greenhouse temperature reduction and one after) were used. Three D. reflexa plants were inoculated per bacterial isolate by wounding three young fully expanded leaves on each plant (four wounds per leaf) and spraying the leaves with a bacterial suspension in sterile distilled water at 108 CFU/ml. At the same time, Gladiolus nanus plants were inoculated in a similar manner. Control plants (D. reflexa and G. nanus) were wounded and sprayed with sterile distilled water. All inoculated plants were covered with plastic bags to maintain humidity and placed in a growth chamber at 25°C. At 3 days, all inoculated plants began to show water soaking and reddish coloration around the inoculation sites, and by 7 days, the lesions had expanded to resemble natural infection. Bacteria isolated on KB from the leading edge of each lesion were morphologically identical to the initial isolates. No bacteria were recovered from the wound sites on the control plants. The 16S rDNA sequences of selected isolates from inoculated plants showed 100% identity to the sequences of the initial isolates, thereby fulfilling Koch's postulates. To our knowledge, this is the first report of B. gladioli causing leaf spot of D. reflexa in the world. Reference: (1) W. G. Weisburg et al. J. Bacteriol. 173:697, 1991.

Vacuum dehydration kinetics of onion slices

Onion slices were dried in a single layer of thickness varying from 1 to 5 mm in the temperature range of 50–70 °C in a laboratory scale vacuum dryer. The effect of pretreatment, drying temperature and slice thickness on the drying kinetics of onion slices was studied. Four thin layer drying models namely Lewis model, logarithmic model, Page model and Fick's law model were applied on the experimental moisture loss data with respect to time to predict the drying pattern properly on the basis of coefficient of determination and standard error. The Page model showed better fit to the experimental data compared to other models. Effective moisture diffusivity of the slice was measured using Fick's second law of unsteady state diffusion. The diffusivity values were found ranging from 1.32E−10 to 1.09E−09 m 2/s for untreated and 1.32E−10 to 1.09E−01 m 2/s for treated onion slices. Effective moisture diffusivity showed increasing trend with increase in temperature and thickness.

Study the effect of sun, oven and microwave drying on quality of onion slices

Sun, oven (50 and 70 °C) and microwave oven (210 and 700 W) drying of onion slices were carried out to monitor the drying kinetics and quality degradation of the product. Page, “Modified Page” and “Midilli and Küçük” models exhibited high coefficient of determination ( R 2) values, ranging between 0.994 and 0.999. The calculated effective diffusivity ( D eff) values (m 2/s) of onion slices for the sun, oven 50 °C and oven 70 °C, microwave 210 W and microwave 700 W drying process were 8.339 × 10 −10, 7.468 × 10 −10, 1.554 × 10 −9, 4.009 × 10 −8 and 4.869 × 10 −8, respectively. Fresh and dried onion slices had high amounts of K (696.82–16357.55 mg/kg), Ca (69.64–340.03 mg/kg), Na (37.72–1895.43 mg/kg), Mg (3.31–964.77 mg/kg) and P (46.47–3384.07 mg/kg) minerals. The highest mineral values were determined in oven dried samples. Sun ( L ∗ 58.00 ± 4.83, a ∗ 0.27 ± 0.10, b ∗ 14.36 ± 2.40) and microwave oven drying (210 W) ( L ∗ 54.78 ± 7.54, a ∗ −0.71 ± 0.09, b ∗ 13.17 ± 1.05) revealed better colour values in the dried products. The phenolic contents of microwave oven dried samples (1664.39 ± 134.12 and 1623.59 ± 140.02 for 210 W and 700 W, respectively) were higher than those of the other dried onion slices.

Fluidised and Convective Drying Kinetics of Onion Slices

Onion (Alium cepa L.) is an important tuber crop widely used for culinary purposes and pharmaceutical industries. Dried onion powder has gained commercial importance in food industry. The fluidized and convective drying techniques were used for dehydration of onion and the effect of temperature and drying mode on the drying of onion slices were investigated. Increase in drying temperature from 50 to 70°C decreased the drying time from 480 to 360 min under fluidised drying and from 1200 to 900 min under convection drying. Four thin-layer drying equations were investigated for their suitability to describe the drying behaviour of onion slices. The Page model showed the best fit with high values for the coefficient of determination for fluidised and convective drying low values ofχ 2 , EMB and ERMS. Activation energy for fluidised and convective air drying was 44.13 and 11.20 kJ.mol-1, respectively. Quality parameters, like colour, water activity and flavour strength were found to be better for fluidised drying compared to convective type. However, the quality of dried onions was superior at 60oC in both drying modes.

Influence of pre‐treatments on microbial load of stored dehydrated onion slices

SummaryOnions slices were pre‐treated in potassium meta‐bisulphite (KMS) and sodium chloride with different concentration levels to study the microbial load of tray and greenhouse‐dried onion slices up to 6 months of storage. Data were analysed as per procedure of one‐way classified anova using DMRT of AgRes statistical package for bacteria, yeast, fungi and Lactobacilli. Results revealed that in almost all samples, permissible levels of bacteria [18.33 × 101 colony‐forming units (CFU) per gram], yeast (ND), fungi (0.5 × 101 CFU g−1) and Lactobacilli (0.25 × 101 CFU g−1) were observed after 5 months of storage. All the samples were also found to be free from Escherichia coli and no Mac Conkey growth was noticed. Onion slices pre‐treated in 0.25% and 0.50% KMS and dried in tray and greenhouse, respectively, were found best after 6 months of storage period.

First Report of Pectobacterium carotovorum subsp. carotovorum on Spathiphyllum wallisii in Argentina.

Peace lily (Spathiphyllum wallisii Regel) is a popular ornamental potted plant in Argentina. During May of 2008 (austral autumn), necrotic lesions of unknown etiology were observed on S. wallisii in a nursery in Pontevedra (34°45'6″S, 58°42'42″W). Plants first showed water-soaked areas starting from the leaf tips. Infected tissue became irregular, brown, dark-to-black lesions on leaves ~12 to 14 mm in diameter surrounded by yellowish haloes. Disease incidence approached 30%. Abundant bacterial streaming was observed from lesions when examined at ×100. Bacteria isolated from lesions formed white-to-cream, glistening, convex colonies on yeast dextrose calcium carbonate agar. Three bacterial strains isolated from different symptomatic plants were selected for comparative analysis with Pectobacterium carotovorum subsp. carotovorum type strain ATCC 15713. All were facultatively, anaerobic, gram-negative rods, pectolytic on crystal violet pectate agar, nonfluorescent on King's medium B, and elicited a hypersensitive response in tobacco plants. All strains were oxidase and arginine dihydrolase negative, fermented glucose, did not hydrolyze starch, did not produce lecithinase, indole or the blue pigment indigoidine, reduced nitrates, hydrolyzed gelatin and esculin, able to rot onion slices, caused soft rot of potato tubers, resistant to erythromycin, and grew at 37°C. Acid was produced from cellobiose, d-glucose, d-melibiose, d-mannitol, d-mannose, l-rhamnose, d-sucrose, and l-arabinose but not from inositol and d-sorbitol. Bacteria utilized N-acetyl-glucosamine and citrate but not tartrate, benzoate, or propionate. Their identity was confirmed by 16S rRNA gene sequencing of strain F402Pcc (GenBank Accession No. FJ717337) showing a 99% homology with that of strain ATCC 3326 (FJ 5958691). Pathogenicity was verified on S. wallisii, Dieffenbachia picta, Aglaonema commutatum, and Anthurium andraeanum within the Araceae family by spraying two plants per strain tested with bacterial suspensions (108 CFU/ml) in sterile distilled water with and without wounding the leaves with sterile needles. Controls were sprayed with sterile distilled water. After 48 h in a humidity chamber, inoculated plants and controls were maintained at 25 ± 3°C in a greenhouse. Water-soaked areas developed from 24 to 48 h after inoculation and became necrotic within 4 to 5 days. Lesions expanded to resemble natural infection in S. wallisii within 20 days, while in the rest of the hosts tested, lesions were smaller and remained brown surrounded by yellowish haloes. All strains were reisolated from each host tested. The original and all reisolated strains were compared by enterobacterial repetitive intergeneric consensus-PCR (4) confirming that DNA fingerprints of the reisolated strains were identical to those of the original strains. No lesions were observed on controls. The pathogen was identified as P. carotovorum subsp. carotovorum based on biochemical, physiological, pathogenicity tests, and 16S rRNA sequencing (1-3).To our knowledge, this is the first report of this pathogen on S. wallisii in Argentina although it has been reported as causing tomato pith necrosis (1) and soft rot of vegetables after harvest (3).

First Report of Leaf Spot of Dieffenbachia picta and Aglaonema commutatum Caused by Burkholderia gladioli in Argentina.

During May of 2008 (austral autumn), an uncharacterized disease was observed on Dieffenbachia picta (Lodd.) Schott and Aglaonema commutatum Schott in commercial greenhouses in Pontevedra (34°45'6″S, 58°42'42″W), Argentina. Affected plants showed irregular, brown lesions on leaves, approximately 15 to 20 mm in diameter, surrounded by water-soaked haloes that progressed inward from the margins. Water-soaked rotting symptoms were also observed in petioles. Disease incidence approached 80%. Abundant bacterial streaming was observed from lesions when examined at ×100. Bacteria consistently isolated from lesions formed cream-colored, glistening, convex colonies on sucrose peptone agar and produced a yellowish green, diffusible, nonfluorescent pigment on King's medium B. Four isolates from different symptomatic plants were selected for further study. All were aerobic, gram-negative rods that accumulated poly-β-hydroxybutyrate inclusions. In LOPAT tests, all induced a hypersensitive response in tobacco plants, caused soft rot of potato tubers, and were positive for levan, negative for arginine dihydrolase, and variable for oxidase. All isolates oxidized glucose, did not hydrolyze starch and were able to rot onion slices. Colonies developed at 41°C but not at 4°C. With the API 20NE test strips and database (bioMerieux, Buenos Aires, Argentina), all isolates matched (99% identity) Burkholderia cepacia, but their inability to metabolize cellobiose and sucrose further identified them as B. gladioli. For molecular identification, 23S rDNA was amplified by PCR using B. gladioli-specific primers LP1 and LP4, which yielded a 700-bp product (3), and PCR-restriction fragment length polymorphism of 16S rDNA using AluI (2). PCR products were identical to those from the type strain for B. gladioli, ICMP 3950, isolated from Gladiolus spp. that had been included in all tests for comparison. Pathogenicity was verified on D. picta and A. commutatum by spraying the plants with bacterial suspensions in sterile distilled water at 108 CFU/ml with and without wounding the leaves with a sterile needle and also by injection-infiltration of bacterial suspensions at 105 CFU/ml. In addition, another host plant, Gladiolus communis L., was inoculated in the same manner. Controls were sprayed or infiltrated with sterile distilled water. After 48 h in a humidity chamber, plants were kept at 25 ± 3°C in a greenhouse. In all hosts, symptoms were first detected 3 days after inoculation and lesions expanded to resemble natural infections within 4 to 7 days. All strains caused necrosis around the inoculation sites and lesions were identical to those induced by the ICMP reference strain. Bacteria were reisolated from each host tested and then the original and reisolated strains were compared by enterobacterial repetitive intergeneric consensus-PCR (1); DNA fingerprints of the reisolated strains were identical to those of the original strains, thereby fulfilling Koch's postulates. No lesions were observed on controls or on plants inoculated by spraying without wounding, suggesting that bacteria gain entry through wounds. On the basis of PCR and physiological tests the pathogen was identified as B. gladioli (2-4). To our knowledge, this is the first report of B. gladioli on Dieffenbachia and Aglaonema spp.

Novel microwave–freeze drying of onion slices

SummaryThe present study aimed to introduce the capability of a novel dehydration technique. To do so, slices with various thicknesses (3.5 and 7 mm) of white onions were dried using commercial freeze drier (abs. pressure 0.005 mbar, temp. 45 °C), our own designed microwave‐vacuum drier (abs. pressure down to 300 mbar) under various microwave powers (120–1200 W) and microwave‐vacuum–freeze drier (onion slices kept at −20 °C for 2 h). Then, their dehydration rates and some quality parameters, such as rehydration ratio, colour (L*, a* and b*) and micro‐structure were investigated. Our findings showed that microwave‐vacuum–freeze drier is practically a rapid, simple, efficient, economic and novel dehydration technique which can be used for dehydration of mainly foodstuffs. The quality properties of slices produced by this novel method were also completely comparable and competitive with commercial freeze drier with over 96% saving on processing time and enormous amount on energy and capital investments.

A SOLAR DRYER PERFORMANCE OF ONION SLICES UNDER FAYOUM CLIMATIC CONDITIONS

A solar drying unit was developed and constructed for drying onion slices under Fayoum conditions. The drying unit consists of a solar collector, which oriented and tilted with an optimum tilt angle and attached with drying chamber. The drying experiments were carried out to examine the effect of onion slice thicknesses (3, 6 and 10 mm) and airflow rate (2.4 and 1.6 m 3 .min -1 ) on the onion slices drying rate. The obtained results indicated that the daily average total solar radiation flux incident on the tilted solar collector surface (7.32kWh.m -2 .day -1 ) was greater than that incident on the horizontal surface (6.13kWh.m -2 .day -1 ) by 19.41%. The higher air temperatures were obtained at the lower airflow rate (1.6 m 3 .min. -1 ) whereas; the amount of heat gained to the air from the solar collector was relatively higher at the higher airflow rate as compared with the lower airflow rate. Consequently the higher efficiency of the solar collector was obtained at the higher airflow rate. The solar collector with the higher airflow rate increased the overall thermal efficiency by 12.56% as compared to the lower airflow rate. The moisture content of dried onion slices was strongly affected by the onion slices thickness and the airflow rate. The final moisture content of dried onion slices ranged from (6.8% to 7.7% dry-basis) depending on the drying temperature cycle. Effect of the individual variables (airflow rate, onion slice thickness, moisture removed, and their interactions) on the drying rate was statistically analyzed. A forward step-wise regression technique was applied to arrive at a reasonable good best set of independent variables. The coefficient of determination (R 2 ) was above 0.97 when

In vivo imaging of dynamic biological specimen by real-time single-shot full-field optical coherence tomography

We demonstrate the feasibility of a compact single-shot full-field time domain optical coherence tomography (OCT) for imaging dynamic biological sample in real-time. The system is based on a Linnik type polarization Michelson interferometer and a four-quadrature phase-stepper optics, which can simultaneously capture four quadraturely phase-stepped interferograms on a single CCD. Using a superluminescent diode as light source with center wavelength of 842nm and spectral width of 16.2nm, the system yields an axial resolution of 19.8μm, and covers a field of view of 280×320μm2 (220×250 pixels) with a transverse resolution of 4.4μm by using a 10× microscope objective (0.3NA). Three-dimensional OCT images of biological samples such as an onion slice and a diaptomus were obtained without any image averaging or pixel binning. In addition, in vivo depth resolved dynamic imaging was demonstrated to show the beating internal structure of a diaptomus with a fame rate of 5fps.