Thawing and freezing of selected meat products in household refrigerators

Recently, several manufacturers of domestic refrigerators have introduced models with “quick thaw” and “quick freeze” capabilities. In this study, the time required for freezing and thawing different meat products was determined for five different models of household refrigerators. Two refrigerators had “quick thaw” compartments and three refrigerators had “quick freeze” capabilities. It was found that some refrigerator models froze and thawed foods significantly faster than others (P<0.05). The refrigerators with the fastest freezing and thawing times were found to be those with “quick thaw” and “quick freeze” capabilities. Heat transfer coefficients ranged from 8 to 15 Wm⁻²K⁻¹ during freezing, and the overall heat transfer coefficients ranged from 5 to 7 Wm⁻² K⁻¹ during thawing. Mathematical predictions for freezing and thawing time in the refrigerators gave results similar to those obtained in experiments. With the results described, manufacturers can improve their design of refrigerators with quick thawing and freezing functions.     

Frozen storage, refrigeration equipment and freezing systems in the seafood industry

The status of frozen storage, refrigeration equipment and freezing systems in the seafood industry is considered in relation to the importance of seafood in the diet and the need to increase supply and provide transport and storage. Preservation methods include chilling, chilling in a controlled atmosphere, and freezing. The best methods of cold storage, followed finally by thawing are discussed.     

Mould growth on meat at freezing temperatures

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.     

Energy efficiency in mechanical refrigeration systems for the meat industry

This paper describes various ways of increasing the efficiency of a mechanical refrigeration system. It compares the cost of operation with capital costs. Relative energy usage of the various cryogenic refrigerants is discussed in comparison to mechanical refrigeration systems. An analysis of the costs to chill beef using the conventional methods, using hot boning methods and using a suggested chill pack (−2°C) method indicate substantial savings in energy.     

Microbiological aspects of the freezing of meat and prepared foods

This paper gives some basic views on microbiological activity during freezing and subsequent storage at low temperature. The problem of microbiological activity in meat cuts and meat products as well as prepared foods is discussed. The problems of freezing carcass meat are, from a microbiological viewpoint, of less significance. However, processing of the meat increases the problem and great attention must be paid to the freezing method as well as the handling prior to freezing. Modern in-line freezing has proved to be of great value in this respect and is discussed in relation to the effect of superfast freezing.     

A survey of commercial meat block freezing in the United Kingdom and Fire

The results of a survey of meat block freezing in the UK and Eire have been compared with experimental and calculated data. This comparison showed that only 58% of the throughput is being frozen within ±20% of the actual time required. There was little standardization of block size, type of wrapping and carton, freezing and storage conditions. The weight of the majority of blocks was between 25 and 30 kg and 80% of the meat was frozen in cartons between 14.6 and 15.9 cm thick. The survey concludes that refrigeration and meat companies must aim for more realistic freezing times and conditions in order to avoid either incomplete freezing or wasting energy by freezing for longer than necessary.     

Behaviour of frozen meat products in fire situations

Over the last decade several large scale fires occured in New Zealand slaughter-houses. Some aspects of these fires are reported in detail, mainly the damage to frozen meat. The real fire situations confirm laboratory tests that frozen meat does not propagate fire spread horizontally, packaging materials permit the spread to a limited degree and frozen meat constitutes a low fire risk storage material.     

Thermodynamic analysis of a novel ejector-cascade refrigeration cycles for freezing process applications and air-conditioning

Waste heat from the gas cooler is a form of free energy, which can be utilized to drive an ejector cooling cycle. This paper presents a new CO₂ ejector-cascade refrigeration cycle. The effects of important parameters on the thermodynamic performance of the new cycle are theoretically investigated based on energetic and exergetic analyses. Furthermore, the performance comparison of the proposed cycle and conventional cycle is carried out. The theoretical study shows that the new cycle exhibits a reasonable value of COP (coefficient of performance) and system second law efficiency. For the same cooling capacity, the improvements of the maximum COP and second law efficiency could reach 37% and 12%, respectively, over those of the conventional cascade cycle under the given operating conditions and at the optimum gas cooler pressure.     

我国制冷空调主要产品能效现状分析

介绍我国能源状况、能源政策,以及制冷空调行业现状、制冷空调产品标准状况。在试验数据的基础上,分析我国制冷空调主要产品能效水平,并从政策、标准、技术等方面对我国制冷空调行业发展情况进行分析。     

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.     

Heat and mass exchange during freezing of meat prepacks in a dynamic disperse medium

This paper presents data on heat and mass exchange processes obtained during the freezing of meat prepacks in a bed of fluidised ice particles, which is referred to as a dynamic disperse medium (DDM), at different temperatures and velocities of air flow.The experimental results confirm the feasibility of using a DDM in the form of ice granules as an excellent coolant capable of shortening the time of technological cycle to between 75 and 50% and reducing the weight losses by a factor of 2.5 to 3.5 times those of conventional air-blast freezing methods.     

Determination of freezing rates of some fruit and vegetable products

Experimentally determined freezing rates of selected fruit and vegetable varieties together with samples of simulated test substances were compared with freezing rates given by Planck's equation using the computer program developed in Marmara Research Institute. The modified Charm's program was applied to the fruit and vegetable samples with predicted thermal properties. The freezing rates determined were 6.8, 6.3, 6.6, 7.5 and 6.3 cm h⁻¹ for carrot, strawberry, sour cherry, plum and leek samples respectively. Good production was achieved based on test substances with similar water content.     

An overview of smart packaging technologies for monitoring safety and quality of meat and meat products

The food packaging sector has experienced much development since its inception. In the past few decades, innovations in packaging sector have led to the development of smart packaging (SP) systems that carve a niche in a highly competitive food industry. SP systems have great potential for improving the shelf‐life, and safety of food products apart from their basic roles of protecting the products against unwanted biological, chemical, and physical damage and keeping them clean. Indicators and sensors, SP components, are used for real‐time monitoring of meat quality and subsequently inform the retailers and consumers about the freshness, microbiological, temperature, and shelf life status of the products. Barcodes and radio‐frequency identification tags are employed in meat packaging for real‐time information about the authenticity, and traceability of the products in the supply chain. Recently, innovations in SP technologies resulted in fast, sensitive, and effective detection, sensing, and record keeping of freshness, microbiological, and shelf life status of meat and meat products. The SP system shows promise for extensive utilization in the meat industry in response to the consumer appreciation for safe, and quality meat products, as well as their waste reduction notions. This paper gives an updated overview of ongoing scientific research, and recent technological advances that offer the perspectives of developing smart meat packaging systems that are capable of monitoring the physical, microbial, and chemical changes of the package contents from producer to the point of sale and even beyond, and remediating potential adverse reactions.     

Improved dynamic simulation of multi-temperature industrial refrigeration systems for food chilling, freezing and cold storage

Three refrigeration system simulation environments were used to simulate the performance of two large industrial refrigeration systems used for meat processing. A recently published model for predicting heat release during cooling and freezing enabled the performance of freezers to be predicted more accurately than by earlier models. Weaknesses in room air models and a need for models of room walls to consider their thermal capacity, as well as their thermal resistance, were identified. Significant advantages compared to previous simulation environments are demonstrated for an object-oriented environment for refrigeration system simulation. It enables new models for components of a refrigeration system to be quickly incorporated as they become available.     

我国制冷空调产品能效标识制度实施概况

能效标识制度作为能效标准的实施和延伸,以其投入少、见效快、对消费者影响大、节能与环保效果显著的优点,成为世界各国普遍采取的一项节能管理措施。制冷空调产品属于典型的使用量大、应用面广、节能潜力和技术提升空间大的用能产品,对其实行能效标识管理意义重大,效果显著。本文重点介绍我国5类制冷空调产品能效标识制度实施情况,并简要介绍国外部分国家能效标识实施情况,旨在借鉴成功经验,推动我国能效标识制度取得更大进展。     

Advances and future aspects of heat transfer relating to refrigeration and heat pumps

The 16th International Congress of Refrigeration and the 7th International Heat Transfer Conference demonstrated that the exponential growth of the study of heat transfer will continue for at least a few more years. The papers to be quoted are mainly from these conferences. Even restricting the field to only refrigeration and heat pumps will still make it necessary to concentrate on a few special topics.     

The effect of salt concentration on the freezing point of meat simulants

Accurate data on the initial freezing point of cured meat is required to predict freezing rates or identify optimal slicing temperatures. However, little data was found in the literature. Experiments were therefore carried out using the ‘Karlsruhe test substance’ (‘Tylose’) with varying salt concentrations as a cured meat substitute. Initial freezing points were −1.4, −3.1, −4.1, −5.2 and −6.3 °C at salt contents of 0.5, 2, 3, 4 and 5 kg salt/100 kg sample, respectively. These values were within ±0.5 °C of published values for cured pork and within ±0.9 °C of theoretical predictions. Modifying the salt content of Tylose is therefore a simple way of determining the initial freezing point of cured lean meats, and Tylose modified in this way can be used to simulate the freezing of cured meat.     

Development of absorption refrigeration units for cold storage of agricultural products

To meet the requirements of continuous refrigeration installations, powered by low-grade heat sources, e.g. waste heat, flat-plate solar collectors or solar ponds, and providing cooling or refrigeration at subzero (°C) temperatures, rational selection of suitable refrigerant-absorbent pairs is necessary. It is demonstrated that the use of R22 and suitable organic solvent systems is desirable in absorption refrigeration installations. Since no data were available on the vapour-liquid equilibria of these combinations, they were measured over a broad range of pressures, temperatures and concentrations. A rational selection of the optimal combinations was made using results obtained from a computerized simulation model giving the performance characteristics of a specific refrigeration system operating with selected refrigerant-absorbent combinations. An efficient thermodynamic cycle has been constructed for the chosen refrigerant-absorbent pairs. Within the region of feasible operation of the cycle, optimal operating conditions are determined. In selecting these conditions it is also necessary to take into account the heat transferred in the heat exchangers of the unit and the operating stability. On the basis of the research performed a 15 ton refrigeration prototype unit for the storage of agricultural products has been constructed and is in the final stages of being run in. It operates at a coil temperature of −3°C and maintains the storage chamber at 5°C. Hot water is supplied at 95–98°C, and cooling water is provided at 26°C.     

离子色谱法测定肉制品中亚硝酸盐含量

建立了离子色谱法快速定量肉制品中亚硝酸盐含量的分析方法。以1.2mmol/L Na2CO3-1.8mmol/L NaHCO3为淋洗液,分析柱为Dionex AS14,检测器为化学抑制型电导检测器。检出限为0.04mg.L-1,加标回收率为96.8%～99.4%,与GB/T5009.33比色法比较相对偏差小于1%。方法简便,快速,用于肉制品中亚硝酸盐含量的测定结果满意。