Microbial and biochemical analysis of dried fish and comparative study using different drying methods

In the present study, certain quality parameters of raw and traditionally sun-dried (TSD) Bombay duck samples are compared with dried fish samples obtained from hot air dryer (HAD), freeze dryer, and a newly developed and patented solar conduction dryer (SCD). The parameters analyzed are total viable count, total fungal count, total volatile nitrogen, and trimethylamine (TMA) content and color. It is found that the experimentally dried fish have better microbial and biochemical quality as compared to TSD fish. This study addresses the issue of unhygienic open sun drying and handling of dried products and the need to adopt use of dryers based on the recently developed appropriate drying technology such as SCD which is expected to be transformed into sustainable technology.     

Influence of Drying Temperature on the Physical and Microbiological Parameters and the Quality of Dried Green Onion

The aim of this research was to determine the influence of drying temperature on the physical and microbiological parameters of the green onion and to evaluate the quality and shelf stability of the dried product. To evaluate the stability during storage, measurements of water activity, color parameters, and microbial survival were taken. Drying temperature had little influence on the adsorption isotherms and rehydration rates but had a strong influence on the color parameters and microbial survival. All stability parameters were improved at drying temperature of 70°C. Changes in color limit the shelf life of this product to about 30 days.     

A Novel Atmospheric Freeze-Drying System Using a Vibro-Fluidized Bed with Adsorbent

Atmospheric freeze drying (AFD) in a vibro-fluidized bed dryer coupled with an adsorbent and multimode heat input is proposed for dehydration of food products at lower cost than the traditional freeze-drying process under vacuum. The aim of this project is to study the proposed AFD system using a vortex tube to produce low-temperature dry air, an alternative for producing dried food products of high quality. An experimental setup was designed and built to permit simultaneous application of convection, conduction, and radiation heat input to the drying material above its freezing point to ensure sublimation. A parametric evaluation over a broad range of possible parameter values was carried out using cubic-shaped potato and carrot as model heat-sensitive products. The influence of various system parameters on drying kinetics, quality, and functional properties of the dried products (color, rehydration properties, and morphology) were investigated. Comparison between physical quality and drying characteristics of the AFD system with AFD using fixed bed, fluidized bed dryer, and also with traditional vacuum freeze drying were carried out to investigate the viability of this new system. Results indicate that proposed system is an alternative to reduce the process time as well as to maintain the product quality at lower cost.     

A Novel Atmospheric Freeze-Drying System Using a Vibro-Fluidized Bed with Adsorbent

Atmospheric freeze drying (AFD) in a vibro-fluidized bed dryer coupled with an adsorbent and multimode heat input is proposed for dehydration of food products at lower cost than the traditional freeze-drying process under vacuum. The aim of this project is to study the proposed AFD system using a vortex tube to produce low-temperature dry air, an alternative for producing dried food products of high quality. An experimental setup was designed and built to permit simultaneous application of convection, conduction, and radiation heat input to the drying material above its freezing point to ensure sublimation. A parametric evaluation over a broad range of possible parameter values was carried out using cubic-shaped potato and carrot as model heat-sensitive products. The influence of various system parameters on drying kinetics, quality, and functional properties of the dried products (color, rehydration properties, and morphology) were investigated. Comparison between physical quality and drying characteristics of the AFD system with AFD using fixed bed, fluidized bed dryer, and also with traditional vacuum freeze drying were carried out to investigate the viability of this new system. Results indicate that proposed system is an alternative to reduce the process time as well as to maintain the product quality at lower cost.     

Novel Aspects of Formation of Food Structure during Drying

The acceptance of processed or minimally processed food products by consumers is highly dependent on several quality and nutritional attributes as well as their organoleptic characteristics. Shelf-life is an additional factor that influences consumer behavior. Moreover, consumers now demand high-value food products that are healthier and have high nutritional value. The quality, nutrition level, and perception of processed foods is governed, among other attributes, by the structure of the dried product. Hence, examination of the structure of dried foods is of significant importance. Dehydration methods have a great impact on the structural properties of most food products. The effect of various dehydration methods on shrinkage and porosity of dried foods is discussed in this article following a comprehensive review of the available literature. Novel drying processes and combination of various conventional drying methods are discussed with regard to their expected impact on food structure. Finally, aspects of food formulation during diverse drying processes and recommendations for future research are presented.     

Freeze Drying of Saffron (Crocus sativus L.)

Saffron obtained from the dried stigmas of a flower scientifically known as Crocus sativus L. is considered to be the most precious and expensive agricultural product due to its labor-intensive harvest and post-harvest processing. The post-harvest processing such as dehydration and storage conditions determine stability, quality, and economical value of the final product. The contents of crocin (degraded carotenoids) and safranal (carotenoid oxidation products) are the key components that characterize color, taste, and aroma characteristics of saffron. In this work, the quality parameters such as crocin and safranal contents of commercial saffron that were obtained by using the freeze-drying method and natural sun drying were studied. The sarfanal contents of the samples dried in a freeze dryer were found to be five times higher than the safranal contents of the samples dried naturally under the sun, while crocin contents of the samples dried in a freeze dryer were about 40% higher than the crocin contents of the samples dried naturally under the sun. These encouraging results indicate that the freeze-drying process can be used effectively for dehydration of saffron by minimal loss of safranal and crocin contents.     

Energy and Quality Aspects of Food Drying

High energy consumption and increasing consumers interest in new products are two problems worthy of note in the drying of food. Difficulties in producing high-quality food and degrading transformations of the material during drying are mentioned. The kinetics of quality degradation due to drying is described. The role of water activity in maintaining product quality is emphasized. Examples of drying methods and tendencies toward a reduction in quality degradation of dried food products are shown.     

Effect of air temperature and velocity on moisture diffusivity in relation to physical and sensory quality of dried pumpkin seeds

Understanding the effect of drying process parameters on food quality is helpful in process optimization and control. The objective of this work is to understand the effect of mild and harsh effective moisture diffusivity (D_eff), varied by air temperature and velocity, of drying processes on the physical and sensory quality of flat food products. Pumpkin seeds were selected as a food representative. It was found that increments of air temperature and velocity resulted in increased D_eff and brown color on seed hull surfaces and embryos, but decreased hardness of seed embryos. Changes in taste and aroma of seed embryos were able to be sensed. Indicating that D_eff is related to seed physical quality. Similar phenomena occurred with both tray and fluidized bed drying. Air temperature, velocity, and D_eff should be controlled to ensure the best dried flat food products. Mild drying conditions are potentially preferred for good physical and sensory quality.     

Lipids as Release Agent Components in the Food Industry

Technical oils and emulsions are of outstanding importance in many different ways in the processing of food: as pan release agents, lubricants for bread cutting machines or separating oils for dried fruit and candy. Since these oils are not intended to become integrated part of the food recipes, even mineral and silicon oils have been used. Nowadays, however, it is becoming increasingly understood that technical oils should have an edible quality, too. Fat and fatty acid chemistry has various products to meet this demand as well as the necessary technical requirements: good releasing properties, high oxidation and polymerization stability, low evaporation losses and viscosity values which can be adopted, however, to any possible need.     

HIGHLIGHTS OF IDS'92

ABSTRACT

High energy consumption and increasing consumers interest in new products are two problems worthy of note in the drying of food. Difficulties in producing high-quality food and degrading transformations of the material during drying are mentioned. The kinetics of quality degradation due to drying is described. The role of water activity in maintaining product quality is emphasized. Examples of drying methods and tendencies toward a reduction in quality degradation of dried food products are shown.     

Response surface methodology (RSM) as relevant way to study and optimize texturing by instant controlled pressure drop DIC in innovative manufacturing of egg white and yolk powders

This study aimed to use the Instant Controlled Pressure Drop as a texturing pretreatment prior to air flow drying as a new way for the manufacturing of egg white and yolk powders evaluating the impact of DIC operating parameters; the saturated steam pressure and processing time, on the physical and functional properties of the end products. The obtained results showed that the DIC-textured egg white and yolk powders had high quality attributes compared to those obtained from classical air flow drying. Moreover, it was better than freeze dried powders in terms of water absorption capacity, emulsifying capacity, and foaming capacity and stability.     

Stability Assessment of Virgin Coconut Oil‐Based Emulsion Products

In recent years, there has been dramatic growth in the market for virgin coconut oil (VCO). VCO, a promising functional food oil, has gained popularity and captured public attention worldwide. Two VCO‐based emulsion products were developed as a new nutritional food supplement with the aim of increasing the consumption of VCO. The stability of VCO‐based emulsion products was assessed during a storage period of 3 months to gauge the quality of the optimized VCO‐based emulsions. The particle‐size distributions of the VCO‐based emulsions remained stable throughout the 3‐month storage period at 25 and at 50°C. However, a slight increase in the particle sizes was observed in the VCO‐based emulsions samples after 2 months of storage at 4 °C. Nevertheless, phase separation did not occur in either of the VCO‐based emulsions products throughout the storage‐stability assessment period. No signs of microbial growth were detected in the emulsion products during the storage period. Furthermore, no significant changes in the free fatty acid contents of the emulsion products were observed during storage at 4 or 25°C throughout the storage period. The VCO‐based emulsion products possessed sufficient emulsion stability to withstand changes at different storage temperatures.     

用升华与蒸发联合法干燥食品的物理性质

Drying is an important unit operation in processing of biological resources. The drying process may influence the product properties and quality, which may shrink, break or undergo rheological, physical and biochemical changes. The important parameters responsible for such changes are drying conditions, type of drying technology and residence drying time. Thermal conductivity, thermal-mass diffusivity, enthalpy, porosity and density are the main material property and heat-mass transfer parameters, which are essential for understanding the changes in product quality and for designing and dimensioning the drying processes. In this paper physical properties of food products undergoing a combined sublimation and evaporation were studied. Pieces of vegetables and potatoes were dried in a heat pump fluidized bed dryer at combined modes with temperatures below the freezing point in the beginning and a final drying step at temperatures above the freezing point. Samples of products were tested at different moisture contents with respect to physical properties. Physical properties of leek and potato samples were measured and mass diffusivities were determined from drying kinetic data. Based on bulk density and rehydration measurements it was clearly observed that drying temperature and modes influenced the final product physical properties. The potato cuberun dried with initial atmospheric freeze-drying step had rehydration ability 430% above a run dried only above the freezing point. The average effective mass diffusivity for 5 mm slabs of leek was 0.5×10^-11m^2·s^-1 for the sublimation stage and 2.2×10^-11m^2·s^-1 for the evaooration stage.     

Effect of microwave freeze-drying on microbial inactivation,antioxidant substance and flavor quality of Ashitaba leaves (Angelica keiskei Koidzumi)

To decrease microbial quantity and conserve antioxidant substances of Ashitaba leaves, microwave freeze-drying was conducted at 1, 1.5, and 2 W/g in pilot scale. After drying, microbial inactivation and quality parameters of color, chlorophylls, flavonoids, moisture content, and flavor of dried Ashitaba leaves were evaluated. After drying, the highest contents of chlorophylls and flavonoids maintained 14.62?g/kg and 15.75?mg/g, respectively; microbial colonies decreased by about 2-log; various tastes of dried sample were improved. It could be a suitable dehydration in processing of Ashitaba leaves.     

Conference Report: Coal Drying and Handling Seminar and Mini-Expo,Organized by Brown Coal Innovation Australia (BCIA), June 2013, Australia

ABSTRACT

Conventional drying of spices, as hot air treatment, often needs an additional downstream inactivation step to decrease the microbial load of the dried product and improve its microbial safety and microbial quality. In this regard, the present work explored the possibility to dry and decontaminate food in a single step using supercritical carbon dioxide (scCO₂) as a drying agent. A case study was focused on the drying of herbs and the antimicrobial effects were evaluated on the naturally present microbiota. For this purpose, experiments were carried out on coriander leaves using a high pressure vessel at 10?MPa, at two different temperatures (40 and 50°C) with drying time of 0 and 150?min to establish the influence of each parameter on the microbial inactivation. Yeasts and molds appeared to be the least resistant to scCO₂ as they could never be detected after the treatment (<2 log CFU/g). Mesophilic bacteria were also significantly reduced, up to 4 log CFU/g, but remained above the limit of quantification. The quality of the dried product was comparable with the quality of air-dried samples in terms of phenolic constituents. Overall, the results indicated that scCO₂ drying was a promising green drying technique combining both drying and microbial inactivation in a single step with a relevant impact on safety and costs.     

Effect of Water on the Quality of Dehydrated Products: A Review of Novel Characterization Methods and Hybrid Drying Technologies

The effect of water on the quality of dried products is reviewed in light of recent applications of novel characterization methods (nuclear magnetic resonance (NMR), X-ray spectroscopy, and Raman spectroscopy) in quantifying the state and mobility of water in dried products. The mechanical configuration and ability of a number of hybrid drying technologies that use novel heating sources (microwave, infrared, radiofrequency) and/or sub-atmospheric pressure in producing better-quality products are reviewed in considerable detail. The drying kinetics models, especially those related to the quality loss, are also reviewed. It appears that more and more drying research is now focused on the development of novel hybrid technologies to produce better-quality products and for energy savings. The novel characterization technologies listed above are capable of quantifying the dynamic mobility and state of water in dried food products; this information can be used to design more efficient drying processes.     

Effects of Different Drying Methods on the Quality Changes of Granular Edamame

In this article, the quality changes of the granular fruits and vegetables dried by vacuum microwave drying, freeze drying, hot air drying, and combined hot air–vacuum microwave drying are investigated, and the quality parameters compared on the basis of vitamin C and chlorophyll contents, shrinkage and rehydration capacity, color, texture, and microstructure changes. The quality parameters of products dried by vacuum microwave drying are slightly lower than those obtained by freeze drying, but much better than those obtained using conventional hot air drying. The quality characteristics of product dried by combined hot air–vacuum microwave are significantly improved compared to those simply hot air–dried.     

Effects of Different Drying Methods on the Quality Changes of Granular Edamame

In this article, the quality changes of the granular fruits and vegetables dried by vacuum microwave drying, freeze drying, hot air drying, and combined hot air-vacuum microwave drying are investigated, and the quality parameters compared on the basis of vitamin C and chlorophyll contents, shrinkage and rehydration capacity, color, texture, and microstructure changes. The quality parameters of products dried by vacuum microwave drying are slightly lower than those obtained by freeze drying, but much better than those obtained using conventional hot air drying. The quality characteristics of product dried by combined hot air-vacuum microwave are significantly improved compared to those simply hot air-dried.     

Research Needs and Opportunities in the Dry Conservation of Fruits and Vegetables

The consumer demand for healthy convenience meals with 'near fresh' properties challenges researchers and industry to develop new or improved conservation procedures for food products. However, this recent food trend towards fresh image on one ride and convenience on the other side often conflict. In most cases the fresh quality is negatively affected by the processing procedure. Therefore nowadays efforts ars focussed on extending the shelf life of fresh products. However, sophisticated energy demanding facilities are required for storage and transporation, whereas thc use of ecologically unsound cooling agents is a major drawback.

The development of a dehydration process on the basic of electromagnetic energy (EME) may bring about a major breakthrough with respect to the retention of product quality and improved rehydration characteristics. Due to the tenfold weight reduction established in the dehydration process transport and storage costs are minimised thus reducing energy consumption. In comparison with fresh and frozen products minimal storage facilities are required.

The strategy of a consortium of five EC-research centres and two dutch drying companies is to combine and fine tune hot air drying (low processing costs) and EME-drying (quality retention) into a hybrid process, to compare the performance with conventional methods and to include packaging and storage effects.

Optimisation of the rewettability is one of the major concems since food materials with near fresh properties can only be obtained from dry material if rehydration characteristics ars excellent. To establish such dried fruit and vegetables will be considered as blends of polymeric materials. Many quality deterioration mechanisms can be attributed to the mobility of the polymeric matrix and the diffusion of water. Properties thus depend on the composition, the physical properties of the polymers (mobility) and the overall structure of the dried material.     

Oxidative Stability and Sensory Attributes of Fermented Milk Product Fortified with Fish Oil and Marine Phospholipids

Marine phospholipids (PL) are potential ingredients for food fortification due to its numerous advantages. The main objective of this study was to investigate whether a fermented milk product fortified with a mixture of marine PL and fish oil had better oxidative stability than a fermented milk product fortified with fish oil alone. Fortification of a fermented milk product with marine PL was performed by incorporating 1 % w/w lipids, either in the form of neat oil or in the form of a pre-emulsion. Lipid oxidation was investigated in the neat emulsions and fortified products by the measurements of primary, secondary volatile oxidation products and tocopherol content upon 32 days storage at 2 °C and 28 days storage at 5 °C, respectively. Analyses of particle size distribution, viscosity and microbial growth were also performed. In addition, sensory attributes such as sour, fishy and rancid flavor/odor were evaluated in fortified products by a trained panel. The results obtained showed that incorporation of a mixture of marine PL and fish oil into fermented milk products decreased the oxidative stability and sensory quality of fortified products. The pH-dependent behavior of iron seemed to be the main factor that influenced the lipid oxidation in the marine PL emulsion and fermented milk system. In addition, both oxidative stability and sensory acceptability of fortified products varied depending on the quality of the marine PL used for fortification.