ANN modeling for optimum storage condition based on viscoelastic characteristics and sensory evaluation of frozen cooked rice

The optimum frozen condition of cooked rice has been predicted by artificial neural network (ANN) based on the data obtained from sensory evaluations as well as viscoelastic measurements. Cooked rice was frozen and stored at −5, −15, and −45 °C for 0, 10, 30, 60 and 90 days. Then, after the samples were thawed by natural convection air at room temperature or microwave heating, the viscoelastic parameters were measured with the Tensipresser and sensory scores were evaluated by a 7-point scale. The sensory scores were predicted with high accuracy from the viscoelastic parameters by ANN models. In addition, the ANN model analysis using the dataset of storage conditions and palatability scores showed that to achieve palatability score greater than the central value of 4.0 after 40 days, storage temperature must be below −25 °C if air thawing by natural convection is used and below −15 °C if microwave thawing and heating are used.     

Direct contact ultrasound assisted freezing of mushroom (Agaricus bisporus): Growth and size distribution of ice crystals

To reduce the size of ice crystals in mushroom (Agaricus bisporus) contact ultrasound (300 W, 20 kHz) was applied during freezing and frozen storage. Stereomicroscopy was used to observe the ice crystal morphology, and DSC and NMR spectroscopy were performed to evaluate the water states in the samples. Results indicated that ultrasound irradiation initiated the nucleation of ice and reduced the mean size of ice crystals during freezing and frozen storage, and therefore improved the frozen product quality compared to the control samples. Most of the ice crystals in the ultrasound assisted frozen (UAF) samples were in the size range of 0–80 microns while that for the control samples were in the size range of 50–180 microns. SEM photos also proved that due to the application of ultrasound, the sizes of the ice crystals was reduced. This micro-scale information on the documentation of ice crystals will assist in understanding the ice crystal growth phenomena in an ultrasound assisted freezing process.     

Reversed Brayton cycle for food freezing at very low temperatures: Energy performance and optimisation

Freezing is a valuable method to increase food shelf life and to ensure high quality standards during long-term storage. Additional benefits to frozen food quality can be achieved by freezing at very low temperatures (< −50 °C): small ice crystal formation during fast freezing reduces food cell wall rupture, preventing water and texture loss during thawing. This paper presents the design of an innovative food freezing system operating at very low temperatures, based on a modified reversed Brayton cycle (rB cycle). The plant is composed of two interconnected sub-systems: a primary thermodynamic closed loop, operated by an rB cycle, and a secondary airflow loop which is devoted to food freezing by batch process. Relevant features of the designed rB cycle rely on the adopted environmentally safe working fluid, the optimised thermodynamics working conditions and the innovative cycle layout. A modelling framework for the system was developed to identify and design efficient operative settings for the plant components (turbo-machineries, heat exchangers, etc.) and to assess, via sensitivity analysis, the influence of the main design parameters on the global energy performance. The proposed system configuration, designed to maximise the coefficient of performance (CoP) value of the plant, was determined by means of nonlinear multivariable optimisation. In addition, the energy performance of the system can be increased by recovering waste heat available from the rB cycle.     

The freezing and supercooling of garlic (Allium sativum L.)

This work shows that peeled garlic cloves demonstrate significant supercooling during freezing under standard conditions and can be stored at temperatures well below their freezing point (?2.7 °C) without freezing. The nucleation point or ‘metastable limit temperature’ (the point at which ice crystal nucleation is initiated) of peeled garlic cloves was found to be between ?7.7 and ?14.6 °C. Peeled garlic cloves were stored under static air conditions at temperatures between ?6 and ?9 °C for up to 69 h without freezing, and unpeeled whole garlic bulbs and cloves were stored for 1 week at ?6 °C without freezing.     

Emerging pulsed electric field (PEF) and static magnetic field (SMF) combination technology for food freezing

The potential of an innovative freezing technique by applying combined pulsed electric field (PEF) and static magnetic field (SMF) was successfully tested and validated. 0.9% sodium chloride (NaCl) solution was frozen under the PEF (1.78 V cm⁻¹, duty ratio: 0.5) at the frequencies of 0–20 kHz and different SMF conditions (attractive and repulsive). At −20 °C, an increase in the working frequencies reduced the phase transition time and the shortest phase transition time (1443 ± 2 s) was obtained at 20 kHz. The patterns of ice crystals became uniformly round (roundness: 0.88–0.90) under the PEF. The effects of attractive and repulsive SMFs showed different patterns in ice crystal formation with the shortest phase transition time under the repulsive SMF. The combined PEF (1.78 V cm⁻¹ at 20 kHz) and repulsive SMF resulted in an effective and synergistic freezing process, forming uniformly round and the smallest mean size of ice crystals in the shortest phase transition (1004 ± 3 s).     

Mould growth on meat at freezing temperaturesDéveloppement des moisissures sur la viande congelée

Meat is usually spoiled by bacteria, which grow more rapidly than moulds. It is usually suggested that mould spoilage occurs mainly with frozen meat when the temperature permits growth of moulds but not bacteria. Moulds were thought to grow at —10°C or even lower temperatures, while bacteria cannot grow much below —2°C, the freezing point of meat. It has also been suggested that the reduced water activity of frozen media rather than the temperature per se may determine the minimum growth temperatures for moulds. Examination of meat spoilage moulds showed most to be moderately xerotolerant with minimum growth temperatures of —5°C or higher. In only one species was growth limited by reduced water activity rather than temperature. During prolonged storage at —5°C, meat developed a flora dominated by yeasts. Visible mould colonies did not appear until the eighth month of storage. It therefore seems that most cases of mould spoilage arise when the temperature of meat surfaces approaches 0°C with surface drying inhibiting bacterial growth.     

The effect of supercooling on ice structure in tuna meat observed by using X-ray computed tomography

Several studies have reported that freezing a homogeneous food such as soy bean curd with deep supercooling (supercooled freezing) results in the formation of many particle ice and homogenous ice structure. However, ice crystal morphology may be affected by the cellular structure of the food. In this study, the ice crystal structure in tuna meat, a cellular food, frozen by the supercooled freezing method was investigated by X-ray computed tomography and compared with ice structures in tuna meat frozen by conventional freezing methods. The results showed that rod-like ice crystals grew parallel with the myofibers, and inhomogeneous ice structures formed in tuna meat frozen by the supercooled freezing method regardless of the degree of supercooling, in contrast to the ice structure in frozen soy bean curds. These ice crystals linked with each other to form rod-like ice structures due to mobility limitations imposed by the cellular structure.     

Increased strength and related mechanisms for mortars at cryogenic temperatures

Properties of cement-based materials at cryogenic temperatures are quite different from those at room temperatures. The strength of mortars at cryogenic temperatures was experimentally studied and an empirical model was established. The freezing thermodynamic process of pore water and pore size distribution in mortars were characterized by differential scanning calorimeter (DSC) and thermoporometry (TPM), respectively. The relationship between the increased cryogenic strength and pore ice formation was discussed. The results showed that flexural strength of mortars increased at a higher rate than compressive strength. Water content and initial strength at room temperatures were the main factors influencing the cryogenic strength. Higher water content and higher initial strength resulted in higher cryogenic strength. Ice formation in pores is one of the main reasons for the mortar’s cryogenic strength increase. Nearly half of the water remained unfrozen in pores with radius less than 40 nm at −40 °C. Both ice formed in capillary pores and gel pores contributes to the strength increase observed at cryogenic temperatures.     

Conversion of a direct to an indirect commercial (HFC134a/CO2) cascade refrigeration system: Energy impact analysis

Energy impact of conversion of a direct HFC134a/CO₂ cascade refrigeration system to an indirect HFC134a-secondary fluid / CO₂ cascade for commercial applications is experimentally analysed. Refrigeration systems, fully described, have been tested in laboratory conditions, at three condensing temperatures (25, 35 and 45 °C), providing the cooling needs to a cabinet for fresh product (2 °C) and to another for frozen product (−20 °C), both placed inside a climatic chamber simulating the indoor conditions of a supermarket. Energy evaluation considered 24 hour tests of stable operation in each test condition. A decrease from 1.9 to 3.5 K of the evaporation temperature of the high temperature cycle has been measured when using an indirect system. It resulted in a variation of the energy consumption of the whole system between 7.6 to 14.0% when using propylene-glycol/water and between −0.3 to 11.1% when using Temper −20^® as secondary fluid.     

Three-dimensional measurement of ice crystals in frozen beef with a micro-slicer image processing system

A novel technique has been developed for measuring the three-dimensional (3-D) structure and distribution of ice crystals formed in frozen beef by using a micro-slicer image processing system (MSIPS). The system has functions to reconstruct the 3-D image based on the image data of exposed cross-sections obtained by multi-slicing of a frozen sample with the minimum thickness of 1 μm and to display the internal structure as well as an arbitrary cross-section of the sample choosing observation angles. The size and distribution of ice crystals can be determined from the 2-D quantitative information, such as the periphery and area of the crystals. The effects of freezing conditions on the morphology and distribution of the ice crystals were demonstrated quantitatively from the observations of raw beef stained by fluorescent indicator. For the samples frozen at −15 °C, the network structure of ice crystals were observed mainly at intercellular space, having approximately 100 μm in cross-sectional size, while that prepared at −120 °C showed the spherical crystals of 10–20 μm in diameter within the cells. The 3-D image of the sample demonstrated that the growth of ice columns was restricted by the intrinsic structure of muscle fibers. The proposed method provided a new tool to investigate the effects of freezing conditions on the size, morphology and distribution of ice crystals.     

Cooking at low temperatures: energy and time requirements

A flat plate solar collector can easily supply hot water at temperatures upto 90–95°C. At these temperatures, rice, potatoes and vegetables can be cooked without much difficulty. However, to design an efficient solar system for cooking, one must know the exact energy and time required for cooking at these temperatures. Our experiments show that the actual energy consumed in cooking rice, potatoes or green vegetables is only 0.06 to 0.10 kWh/kg at cooking temperatures of 82–88°C and the cooking time at these temperatures is 30–45 min.     

Reactions in frozen foods; the reactions of myosin and single amino acids with some aldehydesRéactions dans les aliments congelés; les réactions de la myosine et des acides aminés simples avec des aldéhydes

Malonaldehyde and related substances occur in foods as secondary decomposition products of oxidized polyunsaturated fatty acids. The reaction of malonaldehyde (and glycoaldehyde) with rabbit myosin or single amino acids (glycine, lysine methionine or asparagine) was studied in vitro for its potential to cause protein denaturation in muscle. The reactions were followed at nine temperatures between 45°C and ?40°C. At each temperature the influence of pH (5.2, 7.0, 9.2) and ionic strength (0.3, 0.6) was examined, and the influence of the freezing rate on the reaction rates was also investigated. The decrease of malonaldehyde concentration in the reaction mixture was followed by the TBA-test.The temperature-dependence of reaction rates was very similar for all the reactions. As expected, the rate of reaction decreases when the temperature is reduced from 45°C to freezing point. However, when the mixture is frozen the reaction rate increases with decreasing temperature down to ?24°C. Further lowering of the temperature to ?40°C showed a reduction again in the reaction rate. There was no difference in the reaction rate for different ionic strengths. Lowering of pH gave an increase in reaction rate. A low freezing rate gave a higher reaction rate than was obtained with a fast freezing rate.The observed increase in the rate of reaction between malonaldehyde and protein components when lowering the temperature from the freezing point to the eutectic point is explained on the basis of the so-called ‘freeze concentration effect’ and a consequent pH-shift to values more favourable to the reactions.     

Optimization of the lyophilization process for long-term stability of solid–lipid nanoparticles

Objectives: To optimize a lyophilization protocol for solid–lipid nanoparticles (SLNs) loaded with dexamethasone palmitate (Dex-P) and to compare the long-term stability of lyophilized SLNs and aqueous SLN suspensions at two storage conditions.

Materials and Methods: The effect of various parameters of the lyophilization process on SLN redispersibility was evaluated. A three month stability study was conducted to compare changes in the particle size and drug loading of lyophilized SLNs with SLNs stored as aqueous suspensions at either 4°C or 25°C/60% relative humidity (RH).

Results and Discussion: Of nine possible lyoprotectants tested, sucrose was shown to be the most efficient at achieving SLN redispersibility. Higher freezing temperatures, slower freezing rates, and longer secondary drying times were also shown to be beneficial. Loading of the SLNs with Dex-P led to slightly larger particle size and polydispersity index increases, but both parameters remained within an acceptable range. Drug loading and particle shape were maintained following lyophilization, and no large aggregates were detected. During the stability study, significant growth and drug loss were observed for aqueous SLN suspensions stored at 25°C/60% RH. In comparison, lyophilized SLNs stored at 4°C exhibited a consistent particle size and showed <20% drug loss. Other storage conditions led to intermediate results.

Conclusions: A lyophilization protocol was developed that allowed SLNs to be reconstituted with minimal changes in their physicochemical properties. During a three month period, lyophilized SLNs stored at 4°C exhibited the greatest stability, showing no change in the particle size and a minimal reduction in drug retention.     

Optimization and performance experiments of a MnCl2/CaCl2–NH3 two-stage solid sorption freezing system for a refrigerated truck

Based on the earlier-established MnCl₂/CaCl₂–NH₃ two-stage solid sorption freezing system for a refrigerated truck, a series of optimization designs are conducted in this prototype system. For sorption beds consisting of many unit tubes, the arrangement mode is changed to the staggered arrangement. Off-the-shelf heat exchangers from refrigeration industries are chosen as the evaporator and the condenser, and an expansion valve is also used. The total mass of the optimized system is reduced to approximately 150 kg. Firstly, different refrigerating temperatures ranging from −25 °C to 0 °C are investigated, and experimental results show the optimized system can easily satisfy requirement even for transporting frozen goods. The earlier-established system can only satisfy requirement for transporting fresh goods. Simultaneously, the cycle time can be reduced to 45 min. Through the optimization, both the refrigerating capacity and the total mass of the system can satisfy requirement of this refrigerated truck.     

Oxygen transmission rates of packages at ambient,chill and freezing temperatures measured by the AOIR method

The ambient oxygen ingress rate (AOIR) method is an alternative or supplementary method to Ox‐Tran for measuring the oxygen transmission rate (OTR) of packages. The method has high capacity, requires relatively inexpensive equipment and measures OTR at different temperatures and humidity conditions. The aim of this study was, on the one hand, to study the effect of temperature on the OTR for packages produced from different polymer materials and laminates, and on the other hand to evaluate the suitability of the AOIR method at freezing temperature conditions. The OTR for 10 packages with different polymer compositions was measured at 23°C, 6°C and ?25°C. The AOIR method was shown to be a reliable test method for measuring OTR of packages at all the applied test conditions, also at frozen storage temperature. The OTR for the packages decreased with lower temperatures, especially for the packages with the highest OTR values at 23°C. In order to avoid higher packaging expenses than necessary to obtain the required shelf‐life for different food products, the OTR for alternative packages should be measured at the temperature and humidity conditions of intended use. Copyright © 2004 John Wiley & Sons, Ltd.     

The influence of cryostructure on the creep behavior of ice-rich permafrost

Unconfined constant stress creep (CSC) tests were performed in order to look at the influence of cryostructure on the creep behavior of ice-rich undisturbed permafrost soils and remolded frozen soils within the temperature range from − 1 °C to − 2 °C. Undisturbed ice-rich permafrost soils were sampled from a Pleistocene age yedoma or “ice-complex” permafrost deposit in Interior Alaska. Cryostructure or the pattern of ice inclusions within a frozen soil is a direct indicator of the geologic and cryogenic genesis of permafrost soils. The data indicate that cryostructure influences the creep behavior of permafrost soils. Undisturbed soils with massive cryostructure showed higher induced creep strains and minimum strain rates than the more ice-rich undisturbed soils. Remolded soils with massive cryostructure experienced significantly lower creep strains and lower strain rates than the undisturbed soils. Deformation rates increase rapidly above a threshold stress value for remolded soils. From an engineering viewpoint, use of creep rates from remolded soils is non conservative and under predicts the creep rates of undisturbed soils. The orientation of ice lenses can facilitate motion along the ice lens–soil contact. Similarly, folding of ice lenses may occur, thus inducing anisotropic lateral strains. The ice facies tested indicate that for the temperature and stress range tested, ice creeps at a slower rate than frozen soils.     

Freezing-Induced Strains and Pressures in Wet Porous Materials and Especially in Concrete Mortars

A theory based on thermodynamics will be presented by which the pressure in the pore structure of wet porous materials can be deduced during freezing. The pore structure is partly filled with liquid and inert gases such as air. The theory is based solely on thermodynamic relationships; no knowledge of the real geometry of the pore system or the degree of liquid filling in the void space is needed. The only inputs needed in the theory are relative humidity and temperature measured in the sample chamber during the freezing. The validity of the theory will be compared with the test results of mortar samples frozen and thawed in a low temperature calorimeter. During the cooling from 20 to −70°C and subsequent heating of the sample, the strains, heat capacity, and ice evolution of the samples were measured simultaneously in the calorimeter. Two of the three mortar samples were produced using an air-entraining admixture.     

Protein changes in muscle foods due to freezing and frozen storageTransformations des protéines dans les muscles par suite de la congélation et de l'entreposage à l'état congélé

There is a progressive deterioration in the organoleptic and other properties of meat, poultry and fish, frozen and stored at temperatures down to ?25°C, due to undesirable processes taking place in lipids and proteins. Deterioration due to changes in proteins is shown mainly by a loss of extractability of the microfibrillary fraction, changes in enzyme activity and loss of functional properties of the meat such as water-holding capacity, ease of emulsification of the fats, and the ability to form a gel. Long term frozen storage normally results in a marked hardening of the flesh, considered to be due to crossing-over of the fibrillary proteins. However, in species characterised by a low level of protein denaturation, it has not been possible to detect any marked increase in hardness during storage.Since 1951 the author has considered that the properties of proteins in the tissues could be changed or protected by lipids, fatty acids, nucleotide compounds or even by glucides, and that little may be done to avoid deterioration during storage without a better knowledge of the chemistry and physics of muscular proteins. During 25 years many experimental results have been noted on the influence of various factors, depending on the type of frozen muscular tissue as well as the parameters relating to treatment and storage, on the state of proteins in muscles and the quality of the produce. Most of the research dealt with the influence of high concentrations of salts in the meat due to freezing out of water as ice, the break-up of cells of muscle following freezing, mechanical mincing, neutral lipids, fatty acids, oxidation products of lipids, several types of metabloite in tissues compounds, eg formaldehyde from the enzymic breakdown of trimethylamineoxide in fish, and the addition of several antioxidants and hydrophilic cryoprotectors.The type of protein change following freezing and storage in the frozen state is made up from a partial decomposition of molecular and the formation of new primary and secondary linkages. The number and energy of these depend on participation of individual factors of deterioration, the properties of the tissues and also on the parameters of treatment and storage. It is not yet known precisely which microfibrillary proteins take part especially in the reactions which lead to the undesirable changes in the quality of frozen foods, nor how to avoid these interactions. However, to some extent, the knowledge gained during the several past decades help to prolong the shelf life of many products.     

Laboratory investigation on freeze separation of saline mine waste water

The extraction and upgrading process for bitumen from oil sand deposits in Alberta, Canada currently requires large volumes of process water. This water demand is fulfilled by importing water and recycling/reuse of clarified process water. Reuse of the clarified water results in the steady increase of organic and inorganic (salt) contaminant concentrations in the recycle water. Using a specially designed flume housed in a cold room, trickle freeze separation was evaluated for contaminant separation of saline solutions used as a surrogate for mine waste water. Experiments were conducted at various ambient temperatures, salt concentrations and mass flow rates. Melting proved to be more effective at concentrating salts than freezing. The trickle freeze/thaw process developed during the experiment was very effective at separating and concentrating the salts into a smaller volume. For source waters frozen at an ambient temperature of − 15 °C and with 3000 mg/L (NaCl) or less, 80% removal of salts was possible after melting 9% of the produced ice. For source waters with higher concentrations (20,000 mg/L), 80% removal was possible after melting 27% of the produced ice.     

超声辅助冷冻技术在食品浸渍式冷冻中的研究进展

目的 概述超声辅助冷冻技术在食品浸渍式冷冻中的研究进展,为今后新型技术辅助浸渍式冷冻提供研究方向.方法 研究超声辅助冷冻的成核机理和对冰晶生长的影响,以及超声对溶液性质的影响,并对超声辅助冷冻技术在食品浸渍式冷冻中的应用进行综述.结论 超声辅助浸渍式冷冻技术可以广泛应用在各类食品加工中,有很大的研究和发展空间.超声辅助冷冻技术能够进一步加快食品浸渍式冷冻的冻结速率,减小食品内部冰晶尺寸,较好地改善了冷冻食品的品质和风味,在食品加工中具有广阔的应用前景,可以高效应用于食品工业.