Air Blast Freezing Research Articles

Effects of Refreezing on Microbiological and Physiochemical Properties of Barramundi (L ates calcarifer , Bloch) Fillets

The aim of this study was to investigate the effects of different numbers of freeze–thaw cycles (0, 1, 2 and 3) on barramundi (Lates calcarifer) fillets. Quality and shelf life of fillets were evaluated using the microbiological and physiochemical analyses. The fillets were individually frozen on a polystyrene dish in an air blast freezer at −80C for 8 h, stored in a freezer at −20C for 20 days and then analysis was carried out on the 21st day from the beginning of frozen storage. The results obtained were compared with those of fresh fillets. This study revealed that the pH, total volatile base nitrogen, total viable counts, and L* and b* values of freeze-thawed fillets increased significantly (P < 0.05) with number of freezing cycles whereas ash, protein content and rheological parameters of fillets decreased significantly (P < 0.05) after three freeze–thaw cycles compared with fresh fillets. Practical Applications The purpose of the study was to assess the effect of repeated freeze thawing on barramundi fillets in order to prevent frozen-thawed related yield losses and deterioration in shelf life. This is essential to improve fillet utilization for better economic returns. The expansion of barramundi markets is presently limited because of quality loss during the freezing process. Surprisingly, little attention has been paid to the freezing techniques of this economically profitable species. However, if the barramundi freezing process could be refined, then quality and shelf life could be significantly extended. The present study demonstrates that it is important to prevent temperature variations or abuse during freezing and transport to avoid the detrimental effect of freezing and thawing so as to extend the quality and shelf life of barramundi fillets.

Heat transfer analyses using computational fluid dynamics in the air blast freezing of guava pulp in large containers

Heat transfer during the freezing of guava pulp conditioned in large containers such as in stacked boxes (34 L) and buckets (20 L) and unstacked drums (200 L) is discussed. The air velocities across the cross-section of the tunnel were measured, and the values in the outlet of the evaporator were used as the initial conditions in computational fluid dynamics (CFD) simulations. The model tested was turbulent standard k-e. The CFD-generated convective heat transfer coefficients were mapped on the surfaces for each configuration and used in procedures for the calculation of freezing-time estimates. These estimates were compared with the experimental results for validation. The results showed that CFD determined representative coefficients and produced good correlations between the predicted and experimental values when applied to the freezing-time estimates for the box and drum configurations. The errors depended on the configuration and the adopted mesh (3-D grid) construction.

Effect of freezing method and frozen storage duration on odor-active compounds and sensory perception of lamb

The effects of different freezing methods (nitrogen freezing tunnel, air blast freezer and home freezer) and frozen storage duration (1month and 10months) have been studied by sensory analyses and chemical analyses of odor-active compounds. The sensory analyses showed that fresh meat was significantly (p<0.05) juicier than frozen meat. Meat frozen in the air blast freezer (ABF) and stored during 10months had the highest lamb flavor intensity, significantly different from meat frozen in a home freezer (stored for 1 and 10months) or in a nitrogen tunnel and stored for 1month. The fresh sample was characterized by lower levels of Strecker aldehydes, 2-phenoxyethanol, cresols and to a lesser extent 2-methylbenzaldehyde, and higher levels of furaneol, which was not even detected in frozen samples. These compounds, together with the relative levels of octanoic acid and ethyl hexanoate, could be used as markers to detect whether lamb meat has been frozen. In chemical terms, the ABF samples were the most similar to fresh meat. Remarkably, in most cases the relative chemical aroma composition had no significant differences as a result of freezing. This helps explain the high sensory similarity observed. Only pyrazine levels changed significantly with frozen storage duration. No oxidation aromas or rancidity have been detected in fresh or frozen lamb.

Cryogenic and air blast freezing techniques and their effect on the quality of catfish fillets

The effects of cryogenic and air blast freezing techniques on catfish fillet quality during frozen storage was evaluated. Fresh channel catfish fillets were cryogenically frozen by liquid carbon-dioxide using a pilot plant size cabinet type cryogenic freezer (CF) and by air blast (BF) frozen to −21 °C, separately. Freezing time (FT), freezing rate (FR), and energy removal rate (ERR) for freezing depend on the freezing techniques, which affect energy consumption and frozen seafood quality. The frozen fillets were stored at −20 °C and analyzed for weight loss, relative moisture loss, color, and lipid oxidation (Thiobarbituric acid; TBA) after 1-day, 1-month, 3-months, and 6-months of storage. Triplicate experiments were conducted and data were statistically analyzed at α = 0.05. FT for cryogenic freezing and air blast freezing were 19.3, and 55.1 min, respectively. Cryogenic freezing had higher FR (1.29 °C/min) and ERR (10.62 J/s) than BF (0.46 °C/min and 3.38 J/s, respectively). The cryogenically frozen catfish fillets had a lower freezing loss than fillets frozen by air blast freezing. TBA (mg MDA/kg sample) of the fillets frozen by CF was 0.94 which was lower than BF (1.25). The study demonstrated that catfish fillets cryogenically frozen had better quality characteristics than blast frozen catfish fillets after 6-months of storage.

Virtual Processing of Fish Fillets

This paper presents the application of digital simulation to explore the processing of fish fillets of different geometries in an air blast freezer. The main advantage of this virtual processing approach is that it allows for the comparison of the freezing times, production rates, energy consumptions and the costs of freezing fillets of different shapes and sizes. These parameters could be critical for production planning and are discussed in the paper.

Non-uniform Heat Transfer During Air-Blast Freezing of a Fruit Pulp Model in Multilayer Boxes

Effective heat transfer coefficients were measured using an aluminum test body and compared with the results obtained from a Gnielinski correlation for air-blast freezing of a fruit pulp model in multilayer boxes, with the internal airflow through rectangular ducts and the hydraulic diameter as characteristic dimensions. The quantities of products inside the boxes were varied, and the inlet air velocities and temperature profiles during freezing were measured. The inlet air velocities were applied in dimensionless Gnielinski correlations to estimate the local heat transfer coefficient values. The experimental and predicted heat transfer coefficient values were used to determine an average convective heat transfer coefficient weighted by the heat transfer area. The results from this methodology were used in an analytically derived procedure for freezing-time estimates and then compared with experimental results. The average effective heat transfer coefficient underestimated freezing times and demonstrated a higher level of accuracy than the Gnielinski correlation when applied to boxes containing smaller product amounts. For experiments with greater quantity of products, the use of average heat transfer coefficients from the Gnielinski correlation yielded errors lower than 20%. Based on boundary layer theory, the Gnielinski correlation can be used to explain the isotherm behaviors observed during freezing. Many of the results satisfy the standards of accuracy used in engineering, and the procedure does not require extra computational effort.

The art of air blast freezing: Design and efficiency considerations

Abstract Air blast freezing is a common freezing technique used throughout the world to freeze various food commodities from carcasses to packaged goods. The New Zealand Cold Storage industry identified blast freezing as the most energy intensive operation in the frozen food storage industry, consuming 8.1 GWh of electricity in New Zealand in 2005. This paper presents an overview of various types of blast freezers, their common design flaws, common energy saving measures and a best practice guide. A simulation model has also been presented to predict the performance and to design an optimal system under range of operating conditions.

Effects of freezing treatments on the fermentative activity and gluten network integrity of sweet dough

The effect of freezing treatments on sweet dough was studied. The dough was frozen at −20°C, −30°C and −40°C in air-blast freezer cabinet and by immersion in liquid nitrogen. The yeast viability, gassing power, dough volume and dough network integrity from fresh and thawed sweet doughs were assessed. The results showed that both parameters depend on the freezing rate, which controls ice crystals size and location. Dough volume loss after freezing was attributed to reduced yeast fermentative activity and gluten network alteration in frozen dough. Fermentative activity reduced significantly in frozen dough using liquid nitrogen, causing 70% decrease on yeast population. Gluten integrity seemed to be affected by slow freezing treatment, i.e. −20°C and −30°C. Gas loss was also evaluated as a decrease of 25%±2 in dough volume. A correlation was observed between the freezing rate and osmotic pressure effects which influence strongly the yeast viability.

Effect of freezing method and frozen storage duration on lamb sensory quality

This study assessed the effect of three freezing methods with three frozen storage durations (1, 3, and 6months) on the sensory quality of lamb. Methods were: air blast freezer, freezing tunnel+air blast freezer, and nitrogen chamber+air blast freezer. Meat was frozen after 48h of ageing (0–4°C). Fresh meat (72h ageing at 2–4°C) was used as control. Sensory analyses (trained panel and consumer tests) were performed on loin chops (Longissimus lumborum) after 24h of thawing. Results from the trained panel test showed that freezing (method and/or storage duration) had no significant effect. Consumers found that freezing affected sensory quality. Cluster analysis for overall acceptability divided the population into four classes with different preference patterns, and none of them showed a significant preference for fresh meat. The small differences between fresh and thawed meat shown in this study should not give consumers concerns about buying frozen meat or consuming thawed meat.

Heat transfer and energy consumption in the freezing of guava pulp in large containers

Abstract The heat transfer process, including the convective transfer coefficients (h), freezing times and power consumption, was evaluated during the air blast freezing of 600 kg of guava pulp. Three packaging configurations were tested: plastic boxes (34 L), buckets (20 L) and metal drums (200 L). The air velocity inside the freezer tunnel was measured at several points, and sensors were installed to monitor the temperature. The heat infiltration from external ambient air was also verified. Correlations of the Nusselt number versus the Reynolds and Prandtl numbers were used to estimate the convective heat transfer coefficients according to the configuration of the systems. The coefficients were applied to freezing-time prediction models. The h values and consequent freezing time prediction were found to be more precise for the packaging in the bucket configuration. For the drum configuration, the correlation that considered the turbulence factor effects was found to be satisfactory. In the box configuration, the correlation produced good results only for the boxes located in the central area of the stack. The results indicate that the correlations may be applicable to the analysis and the differences explained by airflow and the difficulty of maintaining constant heat flow on the surfaces.

Qualidade do pequi submetido ao cozimento após congelamento por diferentes métodos e tempos de armazenamento

O pequi um fruto do Cerrado, de alto valor nutricional e potencial econômico. O objetivo deste trabalho foi avaliar a qualidade do pequi cozido após ter sido submetido a diferentes métodos de congelamento e tempos de armazenamento. Os frutos, oriundos de Bocaiúva, Norte de Minas Gerais, foram selecionados, lavados, sanificados, descascados, branqueados, resfriados, embalados em sacos de polietileno, selados a vácuo, em parcelas de 300g, submetidos ao congelamento por ar estático e por ar forado e armazenados em congelador (-18ºC ±2ºC) por seis meses. A cada dois meses (0, 2, 4 e 6 meses), os frutos foram analisados após cozimento, em água, por 20 minutos (300g . L-1), em panelas de aço inox. As seguintes análises foram realizadas: microscopia eletrônica de varredura, firmeza, umidade, cor (L*, h* e C*), carotenoides totais, β-caroteno e vitamina C. Houve diferença significativa entre os dois métodos de congelamento apenas para as variáveis vitamina C e β-caroteno. As demais variáveis sofreram influência apenas do fator tempo de armazenamento. Conclui-se que o pequi cozido após congelamento é influenciado mais pelo tempo de armazenamento do que pelo método de congelamento, sendo o congelamento eficiente para preservação da qualidade desse fruto.

Effect of a Pulsed Electric Field and Osmotic Treatment on Freezing of Potato Tissue

This work discusses the effects of pulsed electric field (PEF) and osmotic pre-treatments on potato tissue structure and on the freezing and freeze-drying behaviour of this tissue. Potato samples (26-mm diameter, 10-mm height) were treated by PEF (400 V/cm) to high level of disintegration (conductivity disintegration index Z was ≈0.95) and were subjected to osmotic treatment in an aqueous solution of NaCl. The samples were either frozen in an air-blast freezer at air temperature of −80 °C and velocity of 2 m/s or freeze-dried at 0 °C and 0.04-mbar pressure. The scanning electron microscope (SEM) images evidenced similarity in structure of the cell walls and area and morphology of starch granules for untreated and PEF-treated potato tissues. However, sequential (PEF + osmotic) pre-treatment of potato tissue resulted in starch granules with rougher surface. The profiles of freezing curves were strongly dependent on pre-treatment. The longest effective freezing time t f was observed for untreated tissue, and the values of t f were decreasing in the following sequence: untreated > PEF pre-treated > PEF + osmotically pre-treated. The faster freezing and freeze drying and visually better quality of the dried samples were observed for PEF or sequential PEF + osmotic pre-treatments. The SEM analysis revealed also a noticeable disorder of starch granule surface morphology inside the cells of the freeze-dried potatoes after sequential PEF + osmotic pre-treatment.

Effect of freezing method and frozen storage duration on instrumental quality of lamb throughout display

This study evaluated the effect of freezing method (FM) (air blast freezer, freezing tunnel, or nitrogen chamber) and frozen storage duration (FSD) (1, 3, or 6 months) on the instrumental measurements of quality of thawed lamb, aged for a total of 72 h, throughout a 10-d display period, compared to the quality of fresh meat. pH, colour, lipid oxidation, thawing, and cooking losses in Longissimus thoracis and lumborum muscle, were determined following standard methods. FM affected yellowness, FSD redness and thawing losses, and both affected oxidation (increased as freezing rate decreased and/or as storage duration increased). When compared with fresh meat, the main differences appeared on oxidation (where a significant interaction between treatment (3FM x 3FSD + fresh meat) with display duration was detected), and on total losses (thaw + cook losses). Oxidation was lower in fresh meat, but values were not significantly different from those stored frozen for 1 month. Fresh meat had smaller total losses than did thawed meat, but losses were not significantly different from meat frozen in the freezing tunnel and stored frozen for 1 month. Display duration had a greater effect on instrumental quality parameters than did FM or FSD. pH, b*, and oxidation increased, and L* and a* decreased with an increase in the number of days on display. In conclusion, neither freezing method nor frozen storage up to 6 months influenced extensively the properties of lamb when instrumental measurements of quality were measured in meat that had been displayed for 1d after thawing. The small deterioration shown in this study should not give consumers concerns about frozen meat.

Freezing of tilapia fillets in an air blast freezer

SummaryThis paper explores the numerical simulation of freezing tilapia fillets of five different geometries, which are the slab, elliptical, disc, spherical and cylindrical shapes, in an air blast freezer. The air velocities and temperatures inside the freezer are varied in the simulation to determine the freezing times and energy consumptions for freezing the tilapia fillets of different shapes. The results show that the cylindrical‐shaped fillet has the longest freezing time and also required the most energy for freezing. The slab‐shaped fillet has the shortest freezing time, but the spherical‐shaped fillet requires the least energy to freeze. The simulation is also applied to a case study to compare the processing rate, energy consumption and the cost of freezing the fillets of different shapes. The freezing cost for a tray of spherical‐shaped fillet is the lowest among all.

The Influence of Geometrical and Operational Factors on Supercooling Capacity in Strawberries: A Simulation Study

Supercooling is still today one of the most challenging physical phenomena to be modelled in food bioprocess engineering. In this study, we evaluate the capacity of a finite-element-cellular automata (FEM-CA) approach to model the propagation of nucleation inside supercooled strawberries with five different morphologies (higher and lower volumes of vascular tissue, pulp, and central air void) frozen inside an air blast freezer under different operational conditions: initial temperature (0 to +20 °C), air temperature (−45 to −20 °C), and velocity (1 to 10 m s − 1). Results show that nucleation is highly affected by the initial temperature and heat transfer rate during phase change. The stochastic nature of nucleation only allowed us to consider it a random variable inside the model temperature restriction interval, it not yet being possible to know what triggers nucleation. However, this study allowed us to conclude that: (1) the structure of liquid water in the supercooled region plays a very significant role during the supercooling effect, (2) nucleation temperatures increase in the supercooled region due to the release of latent heat, and (3) strawberry morphology and operational variables have a profound effect on the supercooling capacity. In our opinion, supercooling is still an open subject, and only a deeper understanding of the structuring of water and dynamics of nucleation at the molecular level may lead to significant advances in the quality of frozen foods and cryopreservation.

Effects of sodium bicarbonate containing traces of citric acid in combination with sodium chloride on yield and some properties of white shrimp (Penaeus vannamei) frozen by shelf freezing, air-blast and cryogenic freezing

Effects of sodium bicarbonate with traces of citric acid in combination with sodium chloride on yield, freezing time, freezing rate, freezing loss and cutting force of white shrimp frozen by shelf, air-blast and cryogenic freezing with/without precooking were investigated. Shelf freezing was done at −40 °C ± 2 °C while air-blast freezing was carried out at −35 °C ± 2 °C, and cryogenic freezing was done at −35 °C, −40 °C and −60 °C. The freezing loss in the non-treated samples was 8.25, 4.6–5.84 and 1.92–3.48 g/100 g fresh shrimp for peeled samples frozen without precooking and increased to 21.85, 17.54–26.97, 17.92–20.31 g/100 g fresh shrimp in the precooked samples frozen by shelf, air-blast and cryogenic freezing, respectively. The treatment of sodium bicarbonate containing traces of citric acid at 4 g/100 ml with sodium chloride at 3 g/100 ml lead to the increase of yield thus reduced the freezing loss by about 6.83–10.28 and 6.41–12.4 g/100 g fresh shrimp for the frozen–thawed samples frozen as uncooked and cooked products, respectively. The toughening of shrimp was observed while sodium bicarbonate containing traces of citric acid treatment with sodium chloride could reduce the texture change occurred during the freezing.

Freezing of potato tissue pre-treated by pulsed electric fields

The effects of pulsed electric fields (PEF) pre-treatment on the freezing, freeze-drying and rehydration behavior of potato were studied. Potato samples (26 mm diameter, 10 mm high) were treated by PEF (400 V/cm) for various durations between 10−4 and 0.3 s. The degree of tissue damage was quantified by the change in electrical conductivity. PEF treated and untreated samples were either frozen in an air-blast freezer with air at −35 °C and 2 m/s velocity or freeze-dried at 0 °C and 0.04 mbar pressure and then rehydrated in water at 25 °C. The freezing times for PEF pre-treated samples reduced as the PEF-induced tissue damage increased. Scanning electron microscope images of the air-blast frozen and then freeze-dried samples showed increased deformation of cells and larger intercellular spaces (frozen samples only) for the PEF pre-treated samples. However, PEF pre-treatment improved the rate of freeze-drying and improved the quality and rehydration of the samples.

Effect of Freezing Time on the Quality of Indian Mackerel (Rastrelliger kanagurta) during Frozen Storage

The present study aims to find the effect of freezing methods on the quality of mackerel (Rastrelliger kanagurta) in commercial plate and air blast freezers during freezing and subsequent frozen storage (-18 degrees C). Total time for freezing was significantly different (P < 0.05) between the plate and air blast freezers (90 and 220 min, respectively). This difference in the freezing time could be attributed to the varied quality of the 2 samples. Upon freezing, the moisture content decreased in air blast frozen samples compared to plate freezer where protein content decreased in both the samples. Upon freezing and during frozen storage, lipid oxidation products (peroxide value, thiobarbutiric acid value, and free fatty acid value) and volatile bases (total volatile base nitrogen and trimethyl amine nitrogen) showed an increasing trend in both the samples with values slightly higher in air blast frozen samples compared to plate frozen samples. The total plate counts showed a significantly (P < 0.05) decreasing trend in both the samples. K value did not show any significant (P < 0.05) difference between the samples where as the histamine formation was significantly (P < 0.05) increased in air blast frozen samples compared to plate frozen samples. The taste and overall acceptability was significantly different (P < 0.05) in plate frozen samples compared to air blast frozen samples on 3rd month. Both samples were in acceptable condition up to 3 mo but the plate frozen samples quality was slightly better than the air blast frozen samples.

Continuous Production of Lime Juice by Vacuum Freeze Drying

An experimental dryer was developed to determine the characteristics of lime juice powder that produced from freeze-drying processes on continuous production. The experimental process consists of two processes, freezing process (the air blast freezer type) and freeze-drying process (tray method with heating plate type). NaHCO3 (2% by weight of lime juice) was dissolved in lime juice as solid aid. The result was found that this experimental dryer can produce lime juice powder which has the similar properties to lime juice. Combining two processes, freezing process and freeze-drying process, the experimental dryer on continuous production can efficiently achieve the sensible result.

The effect of glaze uptake on storage quality of frozen shrimp

Ice-glazing is applied to protect the frozen shrimp from undesirable quality changes during frozen storage. Effects of initial frozen shrimp temperature on glaze uptake; glazing time on glaze uptake; and different glaze percentage on physical and chemical changes of frozen shrimp during storage were investigated. Shrimps were frozen in a spiral freezing machine (−35 °C/15 min); transferred to the air blast freezer until the core temperature reached −18 °C, −25 °C and −30 °C; submitted to glazing process; and stored at −18 °C for 180 days. The glazing percentage, pH and N-TVB levels were monitored every 45 days. This study has demonstrated the effectiveness of the glazing process as a protecting agent for frozen shrimp. A reasonable range of water uptake could be between 15% and 20% to guarantee the final quality. Therefore, it is important to prevent temperature fluctuations during transportation and storage to maintain the quality of the frozen shrimps.