干制状态气体对胡萝卜干燥过程特性及制品品质的影响

分别以空气及氮气、二氧化碳气体置换部分空气等3种状态的气体作为干燥介质，采用QTM干制实验设备对胡萝卜粒进行对比干燥试验，探讨干制状态气体对胡萝卜粒的干燥过程特性及制品品质的影响。结果表明，干制状态气体与胡萝卜粒的干燥过程特性及制品的品质关系密切。降低干燥室内气氛了体的氧气含量，可维持较佳的糖酸比及显著提高Vc保存率，制品的质量较好；在气体的氧气含量相同状态下，充人氮气置换部分空气的制品质量最好，且具有较高的干燥速度和复水比。     

Far-infrared and microwave drying of peach

Little detailed information is available for the far-infrared and microwave drying characteristics on peach and far-infrared combined with microwave drying on other food products. Experiments were conducted to study microwave and far-infrared dehydration characteristics and two-stage drying process involving far-infrared following microwave drying on peach. As microwave drying power and infrared drying power increased, dehydration rate of peach increased and whole drying energy consumption decreased. Peach experienced two falling rate periods when dried with microwave drying or far-infrared drying, and the first falling rate period under moisture content of peach more than 1.7 (dry basic, d. b.), the second falling rate period under less than moisture content 1.7 (d. b.). The same water loss will consume more energy and the steeper curve of energy versus moisture content were obtained when the moisture content is less than 1.7 (d. b.). However, differed from microwave drying, an accelerating dehydration rate period existed in the initial period of far-infrared drying. The effects of infrared drying power, microwave drying power and exchanging moisture content at former far-infrared drying converting into latter microwave drying (three factors) on energy consumption rate and sensory quality (two indices) are significant. The interaction effect of infrared drying power and exchanging moisture content on two indices is significant. The effects of second-order of microwave drying power and of interaction between infrared drying power and microwave drying power on energy consumption rate were not significant. The effects of second-order of exchanging moisture content and of interaction between exchanging moisture content and microwave drying power on sensory quality were not significant.     

Studies on the effects of microwave drying and cabinet tray drying on the chemical composition of volatile oils of garlic powders

Garlic cloves in the form of bits were dried in a cabinet tray dryer and a microwave dryer, and pulverized to obtain free flowing powder. The volatile oil was obtained by hydro-steam distillation method. Fresh cloves and the powders resulting from the two drying methods were used for obtaining the volatile oil, which was analyzed by GC-MS. The studies were mainly restricted to comparing the effect of drying methods on the volatile oil composition of the powders. Although the drying time was reduced considerably from 8 h in a cabinet dryer to 0.25 h in a microwave dryer, essential oil yield and color values were lower, and flavor quality varied considerably. The relative concentrations of major peaks such as diallyl disulfide, diallyl tetrasulfide increased in both the drying methods, and it was more so in microwave-dried samples. However, the concentrations of the other two major peaks, diallyl trisulfide and allyl methyl trisulfide, decreased in both drying methods, and they were lower in microwave-dried samples. Hunter values of L and b were lower for samples obtained by microwave drying as compared to those of cabinet-dried samples.     

Carrot volatiles monitoring and control in microwave drying

Volatiles emanating from carrot [Daucus carota L. cv. ‘Enterprise’] samples dried in a microwave oven were monitored throughout the drying process with a zNose™. Drying temperatures were first set to 50 °C, 60 °C, 70 °C, and 80 °C. Six typical volatile peaks were recorded every 4 min for each of the three replicate runs. Color and sensory evaluation were performed after drying. Samples could be dried in a short time at high temperatures but the interior of some samples was charred. Longer time and more energy were required at low temperature drying. A fuzzy logic control system was then designed and employed to control the drying temperature throughout the whole drying process, using detected volatile peaks as variables. Based on the fuzzy logic controlled temperature curve, a simple linear control method was developed. It was shown that carrot quality was intact and time and energy were saved with these new control strategies.     

胡萝卜片的微波干燥工艺条件优化

对胡萝卜片的微波干燥工艺条件进行了初步研究，通过单因素及正交试验探讨了不同微波处理对胡萝卜片的失水率、感官品质、复水性等的影响，得到了微波干燥胡萝卜片的最佳工艺条件。     

Effect of simultaneous infrared dry-blanching and dehydration on quality characteristics of carrot slices

This study investigated the effects of various processing parameters on carrot slices exposed to infrared (IR) radiation heating for achieving simultaneous infrared dry-blanching and dehydration (SIRDBD). The investigated parameters were product surface temperature, slice thickness and processing time. A three-factor factorial design was conducted to determine the influence of processing parameters on moisture reduction, drying rate, residual peroxidase (POD) activities, surface color change and vitamin C retention. High surface temperature and/or thin slices had faster inactivation of enzymes and quicker moisture removal compared to the low surface temperature and/or thick slices. A Middili model performed well for describing drying behavior during the treatment, while a biphasic model and a quantic model fit well for describing the POD inactivation and the surface color change during the process, respectively. The process which produced 1 log reduction in POD activity has resulted in moisture reduction from 40.2 to 88.8 g/100 g, overall color change (ΔE) from 3.17 to 5.13 and retention of vitamin C from 56.92 to 77.34 g/100 g compared to control. It was concluded that SIRDBD could be used as an alternative to produce high quality blanched and partially dehydrated fruits and vegetables.     

胡萝卜片的微波干燥工艺条件优化

对胡萝卜片的微波干燥工艺条件进行了初步研究,通过单因素及正交试验探讨了不同微波处理对胡萝卜片的失水率、感官品质、复水性等的影响,得到了微波干燥胡萝卜片的最佳工艺条件。     

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.     

Production of bread crumbs by infrared-assisted microwave drying

This study is aimed to investigate the possibility of using infrared-assisted microwave drying for production of bread crumbs and to determine drying conditions in halogen lamp-microwave combination oven to produce bread crumbs with the highest quality. Bread crumb dough were dried from about 40.9 to 8% moisture content by conventional, microwave, infrared and infrared-assisted microwave drying separately and in combinations. Halogen lamp and microwave power levels of 30, 50 and 70% were used. Percent reduction in the drying time were 80.2–94.0 for infrared, 96.5–98.6 for microwave and 96.8–98.6 for infrared-assisted microwave drying. ΔE values were lower in microwave drying and higher in infrared drying. Infrared-assisted microwave dried crumbs generally had similar color values with the conventionally dried ones. Effect of power on color change was not observed. All drying methods were found to be effective in increasing water binding capacity, which increased with microwave power in microwave drying but the influence of halogen lamp power was not seen in infrared drying. At fixed microwave (halogen lamp) powers increase of halogen lamp (microwave) power did not affect the water binding capacity in infrared-assisted microwave drying.     

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 rate control in the middle stage of microwave drying

Microwave drying of apples at constant temperatures follows typical drying curves. The middle stage of the drying process shows a faster drying rate and accelerated moisture evaporation. Meanwhile, more flavors are lost, surface color is degraded, and charring often occurs in this stage. To improve the drying effects, drying curves were controlled and changed in this study. The drying curve was linearized by automatically varying drying temperatures in the middle stages. The controlled drying process therefore led to an optimized temperature profile. To simplify the drying methods, apples were further dried with the obtained temperature profile, while drying curves were online monitored but not controlled. It was proved that slowing down the drying rate in the middle stage could improve the product quality in terms of color, flavor, and overall appearance, while the drying time and energy consumption were still acceptable (within 200 min and 22 kJ/g, respectively).     

Optimal power control strategies in microwave drying

A microwave drying system, which can automatically and continuously adjust microwave power, control sample temperature and measure sample mass, was developed and used in apple drying. At three drying temperatures, i.e., 75, 65, 55 °C, applied microwave power was recorded and analyzed, and a relationship of the power with respect to drying rates was built. With this relationship, apples were further dried at the same three temperatures but using variable power during drying process based on the online obtained drying rates. A better temperature control was achieved and less energy was consumed with this method. Depending on the resulted power profiles, a linear and a three-step power control methods were further developed to simplify the control system. With the developed methods, mass measurements were no longer required and power control could be easily implemented, while temperature control and energy consumption were still acceptable.     

Microwave drying characteristics of potato and the effect of different microwave powers on the dried quality of potato

Little detailed information is available on the microwave drying characteristics of potato and the use of different microwave powers to dry food products. Experiments were conducted to study the microwave drying characteristics and the dried quality of potato. The study focuses on describing the microwave drying characteristics of potato and discussing the effect of sample thickness, drying power and mass. The results show that if the power level increases, the mass load decreases and the thickness of the sample decreases, the dehydration rate increases and the drying energy consumption decreases. There are two falling rate periods during microwave drying of potato: the first falling rate period is for a moisture content of more then 1.1 (dry basis, DB); the second falling rate period is for a moisture content of less than 1.1 (DB). The same water loss will consume more energy when the moisture content is less than 1.1 (DB). A two-stage drying process was employed during microwave drying of potato. The microwave power of the first drying stage differed form that of the second drying stage. The moisture content of the breakpoint for the conversion of the first drying stage into the second drying stage is a moisture content of 1.1 (DB). A quadratic orthogonal regression experiment was conducted, and the effects of slice thickness, the first drying load power and the second drying load power on sensory quality, the rehydration ratio and the energy consumption rate were established. The slice thickness, the first drying load power and the second drying load power linearly affected the three indices. The effect of the product of the second drying load power and the potato slice thickness on the rehydration ratio and the energy consumption rate is significant. The optimum drying parameter combination for the three indices was obtained. The rehydration ratio of the dried products decreased with an increase of the second drying load power and the slice thickness. The concave curves of the sensory quality versus the three factors were shown.     

Study of cooking quality of spaghetti dried through microwaves and comparison with hot air dried pasta

The aim of this work is to evaluate and compare the effects of microwave and conventional drying (hot air) on the quality characteristics of cooked pasta. Experiments were carried out on pasta type spaghetti.A huge difference was noticed between times necessary to dry samples by hot air and by microwaves, in fact in the first case, the drying time was on the average 204.5 min vs. 61.7 s of microwave treatment (average). The gelatinization degree of samples dried by hot air was faster than that of those dried by microwaves: the medium values of kinetic constant of gelatinization of samples dried by hot air and microwaves were 7.5 and 5.2, respectively. Similar total organic matter values suggest that the cooking quality of samples differently dried was comparable. Moreover, samples dried by microwaves were thicker than pasta dried by hot air (37.8 vs. 27.4).     

Stability of quercetin derivatives in vacuum impregnated apple slices after drying (microwave vacuum drying,air drying,freeze drying) and storage

Microwave vacuum drying (MVD) was investigated for apple slices enriched with quercetin derivatives by vacuum impregnation (VI). Additional freeze drying (FD) and air drying (AD) were conducted. Compared to native apples, the impregnated tissue resulted in higher moisture content, elevation of weight and significant browning, due to the incorporated VI solution. The total quercetin content and quercetin glycoside composition were not affected by MVD and FD. The vacuum conditions protect the polyphenols from oxygen dependent degradation and browning reactions. AD resulted in an average quercetin glycoside loss of 44% and undesirable changes, particularly discoloration. The degradation is caused by both non-enzymatic and enzymatic reactions. The pulsed microwave energy intake improved the drying result in structure and led to a faster drying process of 130 min. The bulk density of MVD apple chips (0.69 g/ml) ranged between 0.33 g/ml for FD and 0.75 g/ml for AD. The final moisture content was the lowest after FD (6.8 g/100 g), followed by 9.0 g/100 g after MVD and 12.7 g/100 g after AD. The shelf life was significantly influenced by storage temperature and time. After 12 month at 20 °C, the total quercetin content decreased by 21%.     

Evaluation of high pressure pretreatment for enhancing the drying rates of carrot,apple, and green bean

Preservation of fresh produce by drying dates back to ancient times and is still an indispensible technique. Conventional drying of fruits and vegetables is often accompanied by changes in color, texture, and taste. Suitable pretreatments can improve the drying process by reducing the drying time, yielding higher-quality products, and energy savings. In this study, two varieties of apples, Amasya and red delicious, green beans and carrots were pretreated with high hydrostatic pressure (HHP) at different pressure–time–temperature combinations (100–300 MPa for 5–45 min at 20 and 35 °C) prior to drying. The drying experiments were carried out by using a hot-air tunnel dryer at different temperatures (27–85 °C) and air velocities of 0.4 and 0.8 m/s with constant external conditions. Improving the drying conditions by increasing the drying temperature generally masked the effect of HHP pretreatment on drying rate. Generally, pressures of more than 100 MPa caused cell permeabilization resulting in higher drying rates. Among 14 models, the modified Page model was found to best explain the drying behaviors and model constants were evaluated accordingly. The Tukey multiple comparison test was applied on characteristic drying times to evaluate the relative effects of different pretreatments and drying conditions.     

Influences of hot air drying and microwave drying on nutritional and odorous properties of grass carp (Ctenopharyngodon idellus) fillets

Hot air drying and microwave drying were applied to dry fish fillets made of grass carp (Ctenopharyngodon idellus), and the correlative influences on nutritional and odorous properties were evaluated by proximate composition, protein solubility, amino acid composition, fatty acid composition, peroxide value, anisidine value, and odour evaluation. Drying resulted in a significant increase of protein but reduced fat content. There was lack of negative influence of the drying process on the amino acid composition of grass carp fillets. Both saturated and monounsaturated fatty acid contents decreased, while polyunsaturated fatty acids increased by an average of 23.8% after drying. Microwave-dried samples showed lower fat loss, higher protein solubility, and lower anisidine values than hot air-dried samples. There was no significant difference in odour quality between hot air-dried and microwave-dried samples. The present study provides a possible application of microwave drying as an efficient drying process for fish fillets.     

Quick-boiling noodle production by using infrared drying

In this study, infrared treatment at different powers was used at drying stage of noodle production. Drying time was reduced to 3 min 30 s and 50% reduction in cooking time was obtained at the highest power. Lower cooking loss and total organic matter values, higher maximum force values were obtained for noodles dried by using infrared, indicating improved quality. Infrared treatment generally caused an increase in Rapid ViscoAnalyzer viscosity values of the noodles. Starch granules of the noodles dried by using infrared retained their birefringence to a large extent and increase in intensity of some peaks and formation of a new peak at 2θ = 20° (V-type diffraction pattern) were observed in X-ray diffraction patterns. Relative intensities of some protein bands in SDS-PAGE patterns decreased, total dietary fiber and enzyme resistant starch contents increased slightly. Starch digestibility (in vitro) values increased gradually as the infrared power applied increased.     

Temperature and power control in microwave drying

A microwave drying system with the ability of automatic temperature and power control was developed for apple drying. The samples’ mass and the moisture content could be obtained online. Four different drying modes were attempted with different combination of temperature and power controls. Feedback temperature control with predefined variable power profiles resulted in the best temperature control and product quality. All other modes proved their own pros and cons. The study also verified that it was difficult to maintain a constant temperature during microwave drying process when a feedback temperature control was not included. The results can be used to determine microwave power levels in microwave drying practices both with and without temperature control.     

Combined convective and microwave assisted drying: Experiments and modeling

The drying process is largely used in many different industrial applications, such as treatment of foods, production of cosmetics and pharmaceuticals, manufacturing of paper, wood and building materials, polymers and so on.