Storage lives of chilled and frozen fish and fish products

This Paper describes a meeting that was timely and clearly of wide international interest. It brought together people of diverse backgrounds — academics, Government research workers, inspectors, industrialists and others and, although no clear conclusions emerged, there was general agreement that the participants gained considerably from the information presented and discussed. It focussed attention on the areas where information is still lacking and hopefully it will have stimulated endeavours in one way or another to further our understanding of fish as food and thereby improve the quality available to the consumer.     

Literature reporting of shelf life data. What does it all mean?

This paper presents an analysis of reported shelf life data in the scientific literature, and a critique of the methods used to determine shelf life and the manner in which the data are reported.     

Chilling and freezing fishery products: changes in views and usages

Some of the main criteria used in the assessment of quality of fish and fish products are discussed. Objective and subjective tests are contrasted. Various methods of shipboard preservation are reviewed, including chilling and deep chilling and freezing. The significance of TTT and PPP studies are stressed.     

Controlled atmosphere storage of celery with the silicone membrane system

Laboratory experiments were performed to assess the potential of the silicone membrane system for long term storage of celery under controlled atmosphere (CA) conditions. Designed CO₂ levels of 1.5, 3.5 and 5.5% were selected to calculate the silicone membrane areas to be installed on the chambers. Visual observations, mass losses and physiological analyses were the means selected to assess the quality of the product. Pascal celery, imported from California (USA), was stored at 1.5°C for 29 days under regular atmosphere (RA) with 80% relative humidity (RH), and 128 days under averaged carbon dioxide (CO₂)+oxygen(O₂) concentrations of 0.8+17.7, 2.0+12.6 and 4.0%+9.2% with RH close to saturation. The results showed that the first two CO₂+O₂ combinations were the most suitable CA compositions, among those tested, for long term storage of that cultivar, with total mass losses of less than 30 and 23% respectively. Clean cut celery, grown locally in Québec on organic soil, was stored at 1.5°C under RA with 80% RH and under three CA compositions (1.1+ 14.8, 2.3+7.9 and 3.2% CO₂+5.5% O₂) with RH close to saturation for 62 and 71 days, respectively. The total mass loss averaged 25% and no significant difference was observed between the RA and CA stored celery. In the experiment with Clean cut celery, the losses were mainly attributed to bacterial infections. Both celery cultivars stored under CA with high RH showed better texture and crispness than those stored under RA. It was also noted that the total sugar content significantly increased with storage.     

Influence of cryogenic temperatures on food products and packaging during rail transport

Six commercially packaged frozen food products were subjected to simulated railway shock and vibration conditions and manual handling abuse at both cryogenic (−70°C) and non-cryogenic (−18°C) temperatures. The amount of package and food product damage under different temperatures and levels of abuse were determined. The effects of cryogenic temperatures upon sensory and various analytical quality attributes of the food products were examined. The test results indicated that frozen food can be shipped at cryogenic temperatures in railcars equipped with cushioned draft gears with minimal product or packaging damage, provided there is not excessive manhandling abuse.     

Modelling of temperature fluctuations within frozen foods stored in cylindrical containers

A mathematical model is presented for the prediction of temperature response in cylindrically shaped frozen foods when exposed to a periodically varying environmental storage temperature. The one-dimensional conduction equation in cylindrical co-ordinates was solved including the effect of surface resistances. The prediction model was verified against experimental temperatures obtained from frozen ice-cream samples exposed to two different storage regimes. The experiments were conducted with and without commercial packaging cardboard. Experimental and predicted temperatures presented excellent agreement in both cases. Packaging materials and plastic overwraps of small cylindrical containers can provide an effective resistance against ambient temperature variations.     

Problems in cold storage of citrus fruit

The three main problems (moisture loss, fungal rotting and chilling injury) limiting cold storage of citrus fruit are reviewed. The factors influencing the nature and importance of breakdown are considered and the procedures to overcome these problems are outlined.     

Measurement and prediction of freezing times of vacuum canned Pacific shrimp

Freshly cooked Pacific shrimp, vacuum packed in cans fitted with monitoring instruments, were frozen under industrial conditions. Surface heat transfer coefficients were determined experimentally using aluminium cyclinders. Freezing times were measured and also calculated using Plank's equation and the formulae of Cleland and Earle. The investigation indicated that the vacuum level had little effect on the freezing time and that freezing time essentially doubled when cans were enclosed in a commercial carton. For the prediction of freezing times, Cleland and Earle's method was found to be more accurate than Plank's for the tests performed, with predicted values within ± 10% of measured values.     

Precooling of cylindrical food products

For homogeneous spherical produce numerically generated time-temperature data are used to develop a relationship between the Fourier number, Biot number, dimensionless radial distance and normalized temperature. This allows determination of thermal diffusivity through time-temperature measurements. The method is used to determine the thermal diffusivity of apples, oranges and portatoes. The results are compared with those from previous studies^1,2, and good agreement is observed.     

Keeping quality and shelf life of frozen stored battered and unbattered portions cut from fillet blocks of Antarctic fish

Standard fish fillet blocks prepared from five Antarctic fish species (Notothenia rossii marmorata, N. kempi, N. gibberifrons, Dissostichus eleginoides, Chaenocephalus aceratus) were tested for their suitability for processing into frozen portions (battered/unbattered) prepared from standard fish fillet blocks. Portions (100 g), coated and uncoated, were sealed separately in plastic pouches and stored at −28°C for up to 3 years. Their frozen storage behaviour was investigated by chemical and sensory methods. The amount of water soluble protein, formaldehyde, dimethylamine and pH value did not change, whereas the total volatile base nitrogen increased slightly. Thiobarbituric acid number was species-specific and changed throughout the study. Isoelectric focusing allowed a differentiation between species independent of frozen storage time. Sensory results obtained for D. eleginoides and Ch. aceratus confirmed the high quality of the raw material and the suitability for long term storage. The judgement for N. kempi indicated that this species was less suitable for the production of portions. Fillet samples were analysed for their proximate chemical composition and mineral content at the beginning of the experiment.     

Modelling temperature fluctuations in stored frozen foods

A finite element computer model was used to predict temperature distribution and time-temperature history for frozen food products when subjected to fluctuating storage conditions. Satisfactory agreement was obtained between computer predicted values and experimental data recorded from commercial ice cream and a model system. A sensitivity analysis was performed to determine the effects of product properties on temperature predictions. The model takes into account thawing, convective and radiative heat gain from the surroundings, and variable thermal properties below the freezing point.     

Will consumers accept food irradiation?

Food irradiation technology has recently been developed and has already gained preliminary regulatory approval. This report discusses the potential of food irradiation and possible consumer reaction to its increased use.     

Changes in sheath properties of rainbow trout eggs during cold and frozen storage

Rainbow trout eggs (V/VI Maier scale maturity stage) stored at 2 and −25°C were studied for hardness, lipid components, peroxides and conjugated diene and triene groups. The egg resistance to crushing after seven days of cold storage decreased from 87.3 to 66.0 g. The concentrates of free fatty acids, peroxides, diene and triene groups showed no tendency to increase. Changes in sheath resistance to crushing during frozen storage were significant, the resistance dropping from 87.3 to 30.0 g after 12 months of storage at −25°C. The temperature of −25°C inhibited lipolytic enzymes. Egg lipids were not oxidized before the third month of storage. After four months of storage at −25°C (hardness 46.5 g), the eggs were salted to determine the extent of hardness changes under the influence of sodium chloride solution and thermal treatment. Egg sheath hardness assays showed salting to result in hardness increasing from 46.5 to 85.0 g. Pasteurization reduced egg hardness, but the extent of reduction was not proportional to the duration of thermal treatment. Hardness reduction (down to 50.0 g) in the rainbow trout eggs during frozen storage has no detrimental effects on the suitability of eggs for delicatessen product manufacture.     

Prediction of freezing and thawing times for foods — a review

This communication presents a review of methods to predict the freezing and thawing times of foods. A bibliography of over 400 references was used.     

Comparison of the contribution of formaldehyde and lipid oxidation products to protein denaturation and texture deterioration during frozen storage of minced ice-fish fillet (Champsocephalus gunnari and Pseudochaenichthys georgianus)

Fillets of the ice-fish Champsocephalus gunnari and Pseudochaenichthys georgianus were minced and mixed with various additives to induce the formation of formaldehyde and oxidation of lipids. The mixtures were frozen and stored for several months and protein denaturation and changes in texture were measured. Samples containing high concentrations of formaldehyde were very tough in texture. However it was found that even severe lipid oxidation (up to 14 mg of malonaldehyde per kg wet mass) had only a slight influence on texture.     

Influence of cryogenic temperatures on food products and packaging during rail transportInfluence des cryotempératures sur les produits alimentaires et leur emballage au cours du transport par chemin de fer

Six commercially packaged frozen food products were subjected to simulated railway shock and vibration conditions and manual handling abuse at both cryogenic (?70°C) and non-cryogenic (?18°C) temperatures. The amount of package and food product damage under different temperatures and levels of abuse were determined. The effects of cryogenic temperatures upon sensory and various analytical quality attributes of the food products were examined. The test results indicated that frozen food can be shipped at cryogenic temperatures in railcars equipped with cushioned draft gears with minimal product or packaging damage, provided there is not excessive manhandling abuse.     

Thawing of frozen strawberries

Frozen strawberries were thawed under different controlled conditions (natural thawing at room temperature, thawing in circulating air, thawing in a refrigerator, thawing in water and thawing in a convection oven). The temperature rise at the geometric centre of the strawberries was monitored until the temperature reached 6°C and thawing diagrams were drawn. The effects of thawing method on the weight loss in strawberries were determined. Strawberries thawed at higher temperatures showed greater weight loss. During thawing in circulating air, thawing time decreased with increasing air velocity.     

Measuring the convective heat transfer coefficient while chilling carcasses

The importance of the heat transfer coefficient when chilling carcasses justifies its re-examination and work to its magnitude and variation. While the air velocity at the surface of carcass (with its rather irregular configuration) is an elusive quantity, the author demonstrates that the measurement of the transfer coefficient and its variation should be based on the rate of air flow over unit mass of carcass and on the rate of weight loss through evaporation.     

Comparative experiments on three-wall and one conventional road vehicle

In 1984 international research took place which compared the transport conditions of quick-frozen foods in thin-wall vehicles and conventional vehicles. This work was done at the request of the group of experts of the UNECE/TRANS/GE.11 in Geneva, Switzerland. In the Netherlands measurements have been carried out on three road vehicles — one conventional and two thin-wall vehicles — in the test station and on the road. The road transport involved taking a commercial cargo of frozen fish from Holland to Italy during the summer (July). Later on an additional test was performed in the test station with a fourth thin-wall vehicle at an ambient temperature of 30°C. The results show, that in the conventional vehicle, equipped with a bulk head and a ceiling air duct, and working on a temperature setting of −25°C, a maximum product temperature of −18°C could be maintained. The maximum temperature difference in the cargo was 6 K. Thin-wall vehicles appeared to have a temperature difference of 12 K between air inlet temperature and warmest product temperature. The maximum product temperature could be held below −12, −15 or −20°C, depending on the air distribution and, in particular, on the cooling power of the thermal appliance.     

Temperature monitor for freezers and cold stores

The production of high quality frozen foods requires careful management of the temperature of freezers and cold stores. This paper describes a monitoring system consisting of a datalogger housed in a temperature-controlled box. The system is a portable, inexpensive device, which allows small processors and laboratories to monitor and analyse performance data during various kinds of freezing and storage.