Recirculating carbon dioxide refrigeration unit for freezing food

The article describes the development process of a refrigeration unit using carbon dioxide as a refrigerant. A feature of the plant is the possibility of recirculating carbon dioxide. The authors substantiate the use of the natural substance CO2 as a refrigerant and consider the prospects for using the refrigerant R744. The efficiency of the cycle of a one-stage subcritical refrigeration unit is analyzed. The authors have designed a recirculating carbon dioxide refrigeration unit based on the traditional subcritical cycle. The essential and auxiliary components of the refrigeration machine were presented and described. The developed scheme allows freezing food products by direct contact of the product with snow-like carbon dioxide. After that, the sublimation process takes place in the freezing chamber and the gas-liquid mixture is sent through the liquid separator for recirculation. The article describes the operation of the system diagram, the principle of operation, and the purpose of the elements of automation and regulation.

Evaluation of Finnish apple cultivars (Malus domestica Borkh.)

The purpose of this research was to study apple cultivars obtained from Luke (previously MTT Piikkiö, Finland) in order to have good candidates for breeding within the central zone of Russia. The studies were carried out in accordance with the methods of cultivar study and artificial freezing by modeling damaging factors using a freezing chamber. The assessment of the cultivars by yield, commodity and consumer qualities of fruit, resistance to adverse abiotic factors of the winter period is given. The ‘Vuokko’ cultivar was identified with a yield significantly higher than Antonovka. By modeling winter damage factors, ‘Sandra’, ‘Samo’ and ‘Make’ cultivars were identified with the resistance of the cambium and wood at the level of ‘Antonovka’, when the temperature in the of mid-winter dropped to –40 °C after hardening off, with the ability to keep the frost resistance at –25 °C after thaw and ability to restore the hardy state by lowering the temperature to –30 °C after thaw and re-hardening off. Cultivars ‘Sandra’, ‘Samo’ and ‘Make’ are recommended for creating new hardy cultivars with high-quality fruits for the temperate continental climate of Europe.

Determination Of T-2 And HT-2 Toxin In Wheat Grain By HPLC With Fluorescence Detection

The procedure of the T-2 and HT-2 toxins determination in wheat grain was developed by high performance liquid chromatography according to the following criteria: specificity, linearity, limits of detection (LOD), limits of quantification (LOQ), trueness (recovery), precision, stability. It was found that the correlation coefficient (R2) for T-2 and HT-2 toxin was 0.9999. Mean recoveries from (R, %) for T-2 and HT-2 toxin at the level of 50–150 μg·Kg-1 from wheat (sample blank) were 91 and 87 %, respectively. The relative standard deviation (RSD, %) of the measurement results under conditions of repeatability and intra-laboratory precision ranged from 0.23 to 3.93 %. The limits of quantification of the method for T-2 and HT-2 toxin was 2.2 and 1.2 μg·Kg-1, respectively. These data are within the range of acceptable minimum levels in accordance with Commission Regulation (EC) No 401/2006. It is confirmed that the standards of T-2, HT2 toxins in solutions can be stored up to 7 days in a freezing chamber, a refrigerator and at room temperature in a tightly closed container without actual loss of concentration. It was found that T-2 and HT-2 in a solution cannot be stored in a lit place, because according to the data obtained, sunlight leads to the destruction of these mycotoxins by 52 % and 59 %, respectively.

Effects of air supply operation on the distribution and spatial differences of airflow field in conditioned room: A CFD Study

In air-blast freezer, there are differences in food freezing process at different locations due to the non-uniform airflow distribution in freezing chamber. In this paper, a decoupling method was used to simulate freezing process of food products at different locations. Firstly, the internal airflow distribution model of the freezing chamber was established to simulate the airflow field in freezing chamber under different velocities of air supply. The mainstream air flow rate around each food product was then calculated as the ambient air velocity at which the food freezes. Then, a validated lumped parameter model was used to simulate the freezing process of individual food product, and the effects of freezing conditions on freezing process at different locations were studied. The results showed that there were large differences in the freezing conditions of foods at different locations in freezing chamber, which were mainly reflected by the difference in ambient air velocity. Compared to air velocity, air temperature was distributed rather uniformly in freezing chamber. With the increase of supply air velocity of air coolers, the ambient air velocity around food products in freezing chamber increased almost linearly.

Improvement of Freezing Quality of Food by Pre-Dehydration With Microwave-Vacuum Drying

Partial dehydration through microwave vacuum drying has been applied to tuna, oyster and mackerel before freezing in order to reduce quality damages upon freezing and thawing. Samples were subjected to microwave vacuum drying at pressure of 4 kPa and temperature less than 25°C in order to remove some water from the samples. Two freezing conditions, freezing chamber temperature at −20°C and −80°C, were used in this experiment. The experimental results showed that decreasing the water content in tuna could lower the freezing point temperature and made the freezing time become shorter. It was also found that removing some water in oyster and mackerel was effective to minimize the drip loss. After thawing, the pre-dehydrated mackerel showed better microstructure than mackerel that frozen without pre-treatment. Furthermore, good scores were given by a group of panelist in the evaluation on aroma, flavor, and general acceptability of mackerel that subjected to the pre-treatment.

An investigation of laboratory-grown ice spikes

We have investigated the formation of 10-50 mm long ice spikes that sometimes appear on the free surface of water when it solidifies. By freezing water under different conditions, we measured the probability of ice-spike formation as a function of: (1) the air temperature in the freezing chamber, (2) air motion in the freezing chamber (which promotes evaporative cooling), (3) the quantity of dissolved salts in the water, and (4) the size, shape and composing material of the freezing vessel. We found that the probability of ice-spike formation is greatest when the air temperature is near -7°C, the water is pure and the air in the freezing chamber is moving. Even small quantities of dissolved solids greatly reduce the probability of ice-spike formation. Under optimal conditions, approximately half the ice cubes in an ordinary ice-cube tray will form ice spikes. Guided by these observations, we have examined the Bally-Dorsey model for the formation of ice spikes. In this model, the density change during solidification forces super cooled water up through a hollow ice tube, where it freezes around the rim to lengthen the tube. We propose that any dissolved solids in the water will tend to concentrate at the tip of a growing ice spike and inhibit its growth. This can qualitatively explain the observation that ice spikes do not readily form using water containing even small quantities of dissolved solids.