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A novel drying method for frozen-thawed whole cranberries was developed by combining microwave osmotic dehydration under continuous flow medium spray (MWODS) conditions with microwave vacuum finish-drying. A central composite rotatable design was used to vary temperature (33 to 67 °C), osmotic solution concentration (33 to 67 °B), contact time (5 to 55 min), and flow rate (2.1 to 4.1 L/min) in order to the determine the effects of MWODS input parameters on quality of the dried berry. Quality indices monitored included colorimetric and textural data in addition to anthocyanin retention and cellular structure. Overall it was found that the MWODS-MWV process was able to produce dried cranberries with quality comparable to freeze dried samples in much shorter time. Additionally, cranberries dried via the novel process exhibited much higher quality than those dried via either vacuum or convective air drying in terms of color, anthocyanin content, and cellular structure.

Bovine semitendinosus and longissimus dorsi, both freshly slaughtered and aged, were prepared by various techniques prior to examination by SEM. The important problems of sample preparation were freeze damage, production of surface artifacts, and tissue shrinkage. Ethanol freeze fracture of fixed material followed by critical point drying or air drying from solvent circumvented most of the difficulties and provided the most useful specimens. Cleavage of muscle tissue by freeze fracture exposed muscle cell structures for observation. Useful magnifications up to 20,000 × were obtained and identification was made of A, I and H bands, nuclei, and structures suggestive of mitochondria and muscle cell triads. The structural consequences of cold shortening and rigor were observed.

This study examined the concentration of cetylpyridinium chloride (CPC) required to control Listeria monocytogenes on the surfaces of raw and cooked, peeled and shell-on shrimp. Shrimp (5 g) were inoculated by immersion into a 24 h culture of L. monocytogenes (decimally diluted in PBS) for 1 min, followed by air drying for 1 h, to yield between 6.2 log and 7.0 log CFU/g. The raw and cooked shell-on samples had higher L. monocytogenes counts than the peeled shrimp groups after this inoculation process. The shrimp samples were treated by soaking in different concentrations of CPC (0.05, 0.1, 0.2, 0.4, 0.6, 0.8, or 1.0%) solutions for 1 min, with or without a water rinse for 1 min. The samples were bagged, stored at 4 °C for 24 h, and then plated onto Oxford selective media for determination of log CFU/g. All CPC treatments (0.05% to 1.0%) that were followed by a water rinse reduced L. monocytogenes counts on cooked shrimp by about 2.5 log CFU/g. Conversely, treatments not followed by a water rinse reduced L. monocytogenes counts on cooked shrimp by 3 log CFU/g with 0.1, 0.2, or 0.4% CPC, 5 log CFU/g with 0.6% CPC, 6 log CFU/g with 0.8% CPC, and 7.0 log CFU/g with 1.0% CPC. These results indicate that a soaking treatment of CPC has a strong potential to eliminate or reduce L. monocytogenes on the surfaces of shrimp.

Superheated steam drying, which is an airless drying technology, has recently received much attention as an alternative to conventional hot air drying, which is a relatively oxygen-rich drying process and causes much product quality degradation. However, because most food products are damaged when subjected to superheated steam at atmospheric or higher pressures, lowering the dryer operating pressure is preferred. In this study, the effects of a low-pressure superheated steam drying (LPSSD), vacuum drying, and hot air drying on the drying and degradation kinetics of β-carotene in carrot were investigated experimentally. LPSSD and vacuum drying led to less degradation of β-carotene in carrot than in the case of hot air drying. The empirical models, which can describe the experimental data of β-carotene degradation in carrot undergoing different drying techniques, were also proposed. β-Carotene degradation in carrot depended more on the carrot temperature than its moisture content in all cases.

Mexican oregano ( Lippia berlandieri Schauer) was dried using a freeze drier, conventional hot air drier,and a recently developed vacuum-microwave drier. The effect of the drying method on the relative content of majorflavor volatiles, rehydration rate, color, and structural integrity of the herb was evaluated. Dynamic headspaceanalysis of volatiles present in fresh or dried oregano revealed that b-myrcene, a-terpinene, g-terpinene, p-cymene,and thymol were the major volatile compounds of the plant. The level of thymol in vacuum-microwave-driedoregano was found to be comparable to that of fresh or freeze-dried samples (1.3 times the thymol concentration ofair-dried). Air-dried samples of oregano were darker, were less green, and exhibited lower rehydration rates thanthose prepared by vacuum-microwave or freeze-drying. Structures of vacuum-microwave and freeze-dried oreganoappeared to be quite similar as observed on electron micrographs.Key Words: oregano, volatiles, vacuum-microwave, drying

UNLABELLED Drying is known to affect various quality attributes of a food product, especially its physical properties. However, changes of physical properties or characteristics are generally due to changes of the product microstructure. Nevertheless, not much quantitative information, as opposed to abundant qualitative information, is available to describe in detail relationships between microstructural and physical changes of food undergoing drying. The present study, thus, aimed at studying quantitative relationships between microstructural and selected physical changes of a test material, that is, carrot, undergoing hot air drying at 60 and 80 °C. The microstructural changes were represented quantitatively in terms of the normalized changes of the fractal dimension (ΔFD/FD(0)) of microstructural images of the samples as well as the normalized changes of the sample average cell diameter (ΔD/D(0)), while the physical changes of interest were shrinkage and hardness. The results showed that during an earlier period of drying ΔFD/FD(0) as well as ΔD/D(0) tended to increase with decreasing moisture content; deformation of the microstructures (represented either in terms of ΔFD/FD(0) or ΔD/D(0)) led to increased shrinkage and hardness. On the other hand, deformation of the microstructures existed, while the moisture content did not change much during the final stage of drying. The relationships between ΔFD/FD(0) and both physical changes were quite well established; ΔD/D(0)were also found to correlate well with the physical changes. Either ΔFD/FD(0) or ΔD/D(0)could thus be used as a tool to monitor the apparent physical changes (shrinkage and hardness) of a sample during drying. PRACTICAL APPLICATION Either the normalized changes of the fractal dimension of microstructural images of a sample or the normalized changes of the sample average cell diameter can be a useful tool in monitoring the drying process by 1st assessing the product volumetric shrinkage, which can be assessed easily on-line and on a real-time basis by such techniques as image analysis, and then relating the obtained results through microstructural changes to other apparent physical changes, including the product texture.

To prevent the shrinkage of aloe vera slices during air drying, a method utilizing a shrink-proof layer was developed. The sample was configured of whole leaf aloe slices, where 1 side or both sides were covered with filter papers as shrink-proof layers. After air drying by varying the air temperature and the slice thickness, the drying characteristics, as well as several quality factors of the dried aloe vera leaf slices, were analyzed. In the simulation of the drying curves, the modified Page model showed the best fitness, representing a diffusion-controlled drying mechanism. Nonetheless, there was a trace of a constant-rate drying period in the samples dried by the method. Shrinkage was greatly reduced, and the rehydration ratios increased by approximately 50%. Scanning electron microscopic analysis revealed that the surface structure of original fibrous form was well sustained. FT-IR characteristics showed that the dried samples could sustain aloe polysaccharide acetylation. Furthermore, the functional properties of the dried slices including water holding capacity, swelling, and fat absorption capability were improved, and polysaccharide retention levels increased by 20% to 30%. Therefore, we concluded that application of shrink-proof layers on aloe slices provides a novel way to overcome the shrinkage problems commonly found in air drying, thereby improving their functional properties with less cost. Practical Application: This research article demonstrates a novel air drying method using shrink-proof layers to prevent the shrinkage of aloe slices. We analyzed extensively the characteristics of shrinkage mechanism and physical properties of aloe flesh gels in this drying system. We concluded that this method can be a beneficial means to retain the functional properties of dried aloe, and a potential alternative to freeze drying, which is still costly.

Effects of factors such as tomato cultivars, drying temperatures (40, 80, and 120 degrees C), and drying time (0 to 240 min) on tomato lycopene and the major antioxidant contents (MACs, herein as the sum of total phenolics and total flavonoids) during an air-drying process were investigated. The results showed that lycopene contents increased under all the drying temperatures during the first 60 min. However, the red tomato cultivars, that is, HR, SN, and TTL, exhibited a significant decrease in lycopene contents under 120 degrees C after drying for 75 min. According to the experimental data, an MAC threshold value of 500 mg/100 g dry matter of tomato is proposed. When the MAC is lower than this value during air-drying, lycopene contents in all tomato cultivars would drop rapidly. In addition, the tomatoes in yellow color group, containing more MACs initially and retaining more MACs under air-drying at 40 to 80 degrees C, are proposed to be the proper tomato cultivars for thermal processing.

Cauliflower florets were blanched at 55, 60, 65, and 70 o C, held without cooling for 15, 30, 45, 60, and 90 min, blanched again at 100 o C and then dried in a hot air dehydrater. The coefficient for the rate of rehydration (ξ) was calculated using a diffusion model. Rehydrated samples were divided into two equal parts, one part was boiled in water and the other was uncooked. Firmness of rehydrated samples was measured by back extrusion. Blanching cauliflower between 55 o C and 70 o C before dehydration caused a substantial increase in extrusion forces after rehydration. Cooking the rehydrated cauliflower decreased firmness of all samples. However, the degree of softening caused by cooking was proportionally less for the low temperature blanch treatments than for the controls

Mature breadfruit, sliced to 1.25 mm, fried in soy oil at 165°C and salted to 1.5% produced a stable, crisp chip with lipid stability comparable to potato chips. Partial air drying prior to frying reduced oil absorption from 42% to 26%. Sensory evaluations showed the product to be as acceptable as commercial plantain or potato chips. In view of the extreme perishability and high postharvest losses of breadfruit, chip production represents a useful value-adding preservation method meriting consideration in breadfruit producing regions.

An accelerated method for determining the kinetic model which describes the loss of ascorbic acid during air drying was developed. The method is based on tests conducted under dynamic conditions, i.e. ascorbic acid loss is studied in the course of the dehydration process during which temperature and moisture content are changing continuously. The results are used to determine the form of the kinetic model and the kinetic parameters relating rate of loss to moisture content, temperature, and reactant concentration. The method successfully predicted the kinetic model describing the loss of ascorbic acid in a simulated air drying process. This approach may eliminate the necessity for time-consuming experiments conducted at each of several combinations of temperature and moisture content and may be applicable to other deteriorative reactions.

The quality of compressed carrot bars produced by combining freeze drying with air drying was investigated. Quality parameters measured were color, texture, rehydration ratio, carotene, ascorbic acid, alphatocopherol, and sensory acceptance. It was found that a high quality compressed carrot bar could be obtained by freeze drying to 20–40% moisture, equilibrating with microwave energy, compressing, then air drying at 60°C. The scanning electron microscope proved useful in delineating reasons for differences in texture and rehydration.

A simple procedure has been implemented to measure porosity of apples as a function of moisture contents. The method has been applied to apples with change in moisture contents by conventional air drying. It is shown that the pores, which for biological reasons are open, i.e. connected to the outside, at the onset of dehydration, remain so until X = 1.5 g/g. As dehydration proceeds the pores are split into two families of pores: externally connected pores and locked-in bores. Both total and open pore porosity can be predicted from experimental correlations. Alternatively, the total porosity can be estimated from data on bulk volume shrinkage and the average composition of the tissue by means of equations presented. The interpretation of experimental data using this approach confirms that there is a significant change in the three-dimensional arrangement of the cellular tissue below X = 1.5 g/g. The two approaches lead to the conclusion that, probably due to cellular collapse, the open structure that characterizes the fresh foodstuff changes into a structure with locked-in pores. This fact may help to explain the slow and difficult re-hydration which characterizes air-dried foodstuffs. This hypothesis will be followed up in future work. The information developed should be of help in qualitative and quantitative modeling of processes involving moisture changes.

This work proposes a simple method to characterize which of the elemental geometries (slab, cylinder or sphere) would be a better approximation for the diffusion analysis of air drying of grains having “nonconventional shapes.” The method is tested with experimental drying data obtained for soybeans, rough rice, wheat and peanuts.

Individual frozen carrot cubes were suspended on wires and dried in a stream of low temperature dry air. One of the cubes was suspended on a thermocouple. During drying the weight and temperature of the product and the specific humidity, velocity and temperature of the air were recorded. An analytical model, utilizing the concept of external and internal resistances to the transfer of heat and mass, was developed for the prediction of the drying rate. The experimental data were used to determine a functional relationship between the internal resistances and the fraction of the original moisture remaining in the product. The drying rates predicted were in good agreement with experimental results.

Low temperature air drying studies were conducted on bacon slices to determine the practicality and effectiveness of this method for reducing water activity (aw) as an anti-clostridial alternative to sodium nitrite. Isotherms were developed to determine the extent of moisture removal required to achieve aw = 0.92 or lower; these levels have been found to inhibit C. botulinum. Drying to these levels have been found to inhibit C. botulinum. Drying to these levels of inhibition can be accomplished in approximately 1.75 hr. Drying rates are significantly affected by air temperature, air flow rate, and slice overlap. Experimental data indicate drying can be accomplished with no substantial change in product quality.

The optimization of the drying of apricots was studied using four treatments: (1) blanching and drying; (2) sulfiting-blanching and drying; (3) blanching-sulfiting and drying; and (4) sulfiting-drying to 50% moisture-blanching and finish drying. Levels of sulfiting were from 0–2000 ppm SO2 and drying was done at 50° to 80°C. The quality of dried apricots was judged by extent of browning development and hardness determination. A surface response statistical design was applied to evaluate the optimum drying conditions. Sulfiting-drying, using 80–1000 ppm SO2 at any temperature in the range 50–80°C, was found to be the best treatment. Thus, sulfite was the major factor in controlling dry apricot quality and would be hard to reduce. Drying time was reduced by 50% when apricots were dried at 80°C compared to 50°C, and blanching reduced the time by 10 to 20%. Loss of SO2 was greater than 50% for all treatments.

The variable grid central finite difference method was used in the solution of simultaneous heat and moisture transfer (SHMT) equations with variable transport parameters, providing predictions of local moisture content, temperature, and dimensional changes in an infinite slab at any time during processing. The model was applied to the air drying of ocean perch (Sebastes marinus). Good agreement between experimental results and model predications indicated that the method could be successfully applied to SHMT operations in foods involving dimensional changes.

A study was made of the effect of protein supplementation on the extrudability of tare flour. The tare flour was prepared from Bun-long taro corms by washing, peeling, slicing, air drying, and grinding prior to extrusion into rice, noodle, and macaroni. To improve the extrudability and nutritional qualities of these tare products, mung bean flour or soy protein were added to the dough before extrusion. Prepared with dough moisture content of 30% and 40% w/w, and dough temperatures of 21° and 82°C, extruded taro products were measured for their organoleptic (color, surface smoothness, and eating qualities) and objective (color, texture, protein level, and energy value) qualities. Results showed that the addition of 15% mung bean flour to taro flour improved the firmness, of the rice and noodle. Soy protein also improved the texture of taro rice with 30% and 40% dough moisture and macaroni with 30% dough moisture. The addition of either mung bean flour or soy protein improved the smoothness of taro rice only very little. Product color intensity (measured with extracts as the absorbance ratio of 520 nm/422 nm) decreased considerably in taro rice after the addition of soy protein or mung bean flour, but only slightly in taro noodle and macaroni. Hunter color measurements indicated we similar color in all the cooked, extruded taro samples. Protein supplement can be incorporated into the extruded taro samples to make them comparable in protein and energy level to conventional wheat products and rice. It was concluded that taro flour can be extruded successfully into rice, noodle or macaroni by proper adjustment of initial dough temperature and moisture content. Protein enrichment improved to a limited extent the overall quality of extruded tare samples.

A mathematical model describing the drying behavior of beet slices was developed based on data from an air-drying experiment which measured average moisture content and temperature. The model was based on application of Fick's law for unidimensional moisture flow in the falling drying rate period. The mathematical model and the data generated from the kinetic studies of temperature- and moisture-sensitive red beet pigments (betanine and vulgaxanthin-I) were combined in a computer program to simulate and predict beet pigment retention, as a function of the process variables. Predicted and actual experimental pigment retention agreed well, which indicates this approach's potential for simulating deterioration of beet pigments during air-drying.

Analysis of literature data on air drying of foods during the first falling rate period, showed that the thickness dependence of drying rate is somewhat lower than is predicted by Fick's law. An explanation based on heat transfer effects is proposed to explain this “anomaly” and a quantitative model was accordingly developed. The model was tested with experimental data on sugar beet root drying and an excellent agreement was now found between theoretical (Fick's law) and experimental thickness dependence of drying rate.

Shrinkage of rectangular slabs of ocean perch (Sebastes marinus) in all three dimensions during air drying at 24.5°C, relative humidity 35% and velocity 35.6 m/min was determined. Percent change in dimensions with volume fraction of water was measured. It was observed that the dimension along the major axis of muscle fibers (length in this case) shrinks far less than the other two dimensions. Maximum shrinkage in length was 20%, while for width it was 50.5% and for thickness, 50.6%. At 95% confidence level, there was no significant difference between thickness and width shrinkage.

Explosion puffing is a processing system which facilitates hot air drying of fruits and vegetables. Explosion puffed foods are easily rehydrated and have excellent sensory properties. The process costs are similar to the cost of conventional hot air drying. Previous publications have reported the results relevant to carrots, potatoes, apples, and blueberries. Sufficient research has been done on other fruits and vegetables to establish that they, too, can be satisfactorily explosion puffed and dried to yield a good product. The processing conditions for explosion puffing of mushrooms, celery, onions, peppers, rutabagas, beets, yams, pears, pineapples, strawberries, and cranberries are presented.