Relationship between heat transfer parameters and the characteristic damage variables for the freezing of beef

One of the most suitable parameters for relating the freezing rate to the volume of drip produced during the thawing of meat is the characteristic time, defined as the time necessary to reduce the temperature of the sample from −1·1°C (initial freezing point in beef) to −7°C (80% of the water frozen).

However, as the freezing of beef in factories takes place with important temperature gradients, distributions of these characteristic times must be expected along the pieces of frozen meat.

In order to relate these characteristic time distributions to heat transfer parameters under industrial freezing conditions, a mathematical model which simulates the freezing of beef is developed in this paper.

The model establishes the heat transfer equations with simultaneous change of phase, taking into account the dependence of the thermal properties with the ice content and considering the anisotropy of the thermal conductivity according to the direction of the fibres.

Boundary conditions include the possibility of thermal resistances in the refrigerated interphase.

The model developed was compared with laboratory experiments performed under factory freezing conditions and showed a satisfactory agreement between theory and experiment.     

A model for the thermal conductivity of frozen meat

Even though extensive work on the experimental determination of the thermal conductivities of foodstuffs at different temperatures has been published, only a few predictive models for this important property have been developed.

Calculation of freezing times in foods, such as meat, over the range from −1°C to −30°C, requires the use of mathematical models in which information on the thermal conductivity of partially frozen meat as a function of ice content in the tissue is provided.

In the present paper a model for the thermal conductivity of meat as a function of temperature, which also accounts for its anisotropic properties, is proposed. Both directions, parallel and perpendicular to meat fibres, are considered and the model applies to unfrozen as well as to partially frozen meat.

Results show good agreement with published experimental data obtained by a steady state method for different temperatures.     

Effects of freezing, thawing and storage on some quality factors for portion-size beef cuts

Portion-size beef cuts packaged in oxygen impermeable plastic bags were used to study the effects of rates of freezing and thawing, and storage time and temperature on drip and cooking losses, shear force, destruction of glutathione and accumulation of protein-breakdown products in meat. Portions weighing 150 g or over and frozen in an air-blast at −30°C gave lower losses of drip and lower amounts of nitrogenous constituents in drip than samples weighing less than 150 g or samples frozen in cardboard boxes in still air at −18°C. Freezing and thawing or frozen storage had no significant effect on shear force of meat frozen after ageing. During frozen storage, the destruction of glutathione and accumulation of protein-breakdown products increased, depending directly on storage temperature and time. The results show that a test based on these two biochemical changes would be suitable for assessing the quality of frozen beef.     

Calpains from thaw rigor muscle

Pre-rigor beef M. Longissimus lumborum and diaphragma were frozen at −70 °C and thawed at different temperatures and the activities of extracted calpains and the toughness of heated meat compared with those in chilled muscle.

Fresh muscle contained about 14 μg of μ-calpain/g and was unaffected by freezing, but was reduced after thawing. Rapid thawing at 30 °C for 20 min reduced the μ-calpain to 14%. When cooked from the frozen state, extensive shortening occurred and tender meat was obtained.

By storing at −3 °C for 1 day, thaw-shortening was prevented, but tougher meat obtained. The μ-calpain decreased to 70% whilst the m-calpain was unaffected. Toughness decreased after further storage at −3 °C, as did the μ-calpain. The latter changes were similar to those during development of rigor mortis and ageing of non-shortened meat stored at 4 °C. Variation in calpain activity, rather than in sarcomere length, are likely to be the cause of toughness variation in thaw rigor muscle.     

Effect of freezing, thawing and frozen storage on physico-chemical and sensory characteristics of buffalo meat

A study was conducted on some physico-chemical and sensory characteristics of buffalo meat frozen by plate and blast freezing and stored at −15 ± 3°C for a period of 3 months. A marginal increase in pH values and drip losses were observed during the storage period. Drip losses were less in blast frozen samples. WHC, cooking losses thermal shrinkage and WB Shear values indicated inconsistent results, during storage. Similar observations were recorded with regard to tyrosine and TBA values. No significant differences in the physico-chemical characteristics were observed between meat cuts and minced meat. Plate frozen meat samples scored higher for texture, juiciness and aroma. Both the plate and blast frozen meat samples, however, were similar in overall quality according to taste panel results.     

Conventional freezing plus high pressure-low temperature treatment: Physical properties, microbial quality and storage stability of beef meat

Meat high-hydrostatic pressure treatment causes severe decolouration, preventing its commercialisation due to consumer rejection. Novel procedures involving product freezing plus low-temperature pressure processing are here investigated. Room temperature (20 °C) pressurisation (650 MPa/10 min) and air blast freezing (−30 °C) are compared to air blast freezing plus high pressure at subzero temperature (−35 °C) in terms of drip loss, expressible moisture, shear force, colour, microbial quality and storage stability of fresh and salt-added beef samples (Longissimus dorsi muscle). The latter treatment induced solid water transitions among ice phases. Fresh beef high pressure treatment (650 MPa/20 °C/10 min) increased significantly expressible moisture while it decreased in pressurised (650 MPa/−35 °C/10 min) frozen beef. Salt addition reduced high pressure-induced water loss. Treatments studied did not change fresh or salt-added samples shear force. Frozen beef pressurised at low temperature showed L, a and b values after thawing close to fresh samples. However, these samples in frozen state, presented chromatic parameters similar to unfrozen beef pressurised at room temperature. Apparently, freezing protects meat against pressure colour deterioration, fresh colour being recovered after thawing. High pressure processing (20 °C or −35 °C) was very effective reducing aerobic total (2-log₁₀ cycles) and lactic acid bacteria counts (2.4-log₁₀ cycles), in fresh and salt-added samples. Frozen + pressurised beef stored at −18 °C during 45 days recovered its original colour after thawing, similarly to just-treated samples while their counts remain below detection limits during storage.     

Definition of the optimum freezing rate-1. Investigation of structure and ultrastructure of beef M. longissimus dorsi frozen at different freezing rates

The influence of freezing rate on location, shape and size of ice crystals formed during freezing of beef M. longissimus dorsi, as well as its influence on ultrastructure, were investigated. Muscle samples were frozen at different rates: 0·22 cm/h and 0·39 cm/h (cooling agent was chilled air), and 3·33 cm/h, 3.95 cm/h, 4·92 cm/h and 5·66 cm/h (cooling agent was liquid carbon dioxide which expanded in the sucking-pipe of the tunnel freezer).

It was found that by slow freezing (freezing rates 0·22 cm/h and 0·39 cm/h) 30·00 μm). An increase in the freezing rate was followed by a change in ice crystal location. In this case they had also been formed intracellularly. The number of crystals increased while their size decreased.

The most intensive fibre damage was found in samples frozen at a rate of 0·22 cm/h, and the least in samples frozen at a rate of 3·95 cm/h with a freezing temperature of −50°C.     

The effects of antifreeze proteins on chilled and frozen meat

The effects of cryoprotectant proteins, trivially termed ‘antifreeze proteins’, from the Antarctic Cod and the Winter Flounder were assessed in meat during chilling and freezing. In light-microscopy studies, bovine muscle (Sternomandibularis) samples were soaked in phosphate buffered saline with and without 0·1 mg/ml antifreeze protein. Samples were then held frozen (−20°C) or chilled (2°C) for 3 days. Samples were freeze-substituted, embedded in resin and sectioned. With antifreeze protein present, transverse sections of frozen samples had many small intracellular spaces, probably representing ice crystals. Frozen controls had much larger intracellular single spaces. Antifreeze protein had no effect on chilled samples.

Similarly treated samples were examined by scanning electron microscopy using a cryostage attachment. Chilled ovine muscle samples (Peroneus longus) were soaked for various periods (0–7 days) in 0·9% saline containing various concentrations of antifreeze proteins (0–1 mg/ml). Samples were then held frozen (−20°C) or chilled (2°C) for 5 or 7 days. With frozen samples, antifreeze proteins reduced the size of ice crystals, compared to the control. This effect depended upon the concentration used and the period of soaking before the samples were frozen, but was independent of source. Antifreeze proteins had no effect on chilled samples.     

Effect of freezing and storage on quality factors in Hamburg and leafy parsley

Two types of parsley — the Hamburg cv Berli ska and leafy type cv Paramount — were frozen and stored at temperatures of −20 and −30 °C for 9 months. One half of the material was blanched before freezing and the other half was non-blanched. In 100 g fresh leaves of Hamburg parsley there were 20.0 g of dry matter, 310mg of vitamin C, 7.5mg of β-carotene, 203mg of chlorophyll, 30.8 mg N---NO₃ and 0.078 mg N---NO₂. For the leafy type the corresponding values were 17.3 g, 257 mg, 9.4mg, 68.5mg, and 0.077mg. The material blanched before freezing showed significant losses in the contents of vitamin C (47–51%), nitrates (22–33%), and nitrites (43–55%) and distinctly smaller ones but also significant in the case of dry matter. During freezing and storage of frozen products there were losses in vitamin C, β-carotene, and chlorophyll while the levels of nitrates and nitrites were variable. Particularly great losses of vitamin C and β-carotene were observed in the non-blanched frozen leaves stored at −20 °C. After 9 months' storage, frozen products preserved 10–44% of vitamin C, 37–91% of β-carotene, 78–95% of chlorophyll, and 78–153% of nitrates. Of the types of parsley analyzed the Hamburg type was a better raw material for freezing because of a significantly higher content of vitamin C and chlorophyll and significantly less nitrates in frozen products. When the storage temperature was −30 °C, the blanching of leaves was not necessary, although it helped their pressing into cubes.     

Design, fabrication, and testing of a returnable, insulated, nitrogen-refrigerated shipping container for distribution of fresh red meat under controlled CO2 atmosphere

In today's market, fresh red meat is cut and packaged at both the wholesale and retail level. Greater economies could result if the wholesaler prepared all consumer cuts centrally, but the short storage life of meat limits distribution. Use of CO₂-controlled atmosphere, master packaging, and strict temperature control (−1.5±0.5°C) can enhance storage life and, therefore, distribution ease. An insulated shipping and storage container was designed and tested for its suitability to distribute master-packaged meat. Shelves in the container supported 36 master trays (508 × 381 × 60 mm), with the source of refrigeration being injected liquid nitrogen (N₂). Electric fans dispersed the N₂ gas throughout the container. To reduce costs, 36 saline water bags (10% w/v NaCl) were used to thermally simulate the meat. Temperatures of 20 bags were recorded during storage experiments. The container was tested at outside temperatures of 15, 0 and −15°C with 4 internal fans and at 30°C with 2, 4 and 6 fans. In all instances, bags cooled from 10°C to an equilibrium temperature of −1.5°C within 5.5 h. Minimum equilibrium temperatures during any 8 h trial were −2.6, −2.0 and −2.0°C for 2, 4 and 6 fans, respectively. Correspondingly, maximum temperatures were −0.2, −0.7 and −0.3°C. Initial chilling of the product required, on average, 19 kg of N₂, while equilibrium was maintained at a N₂ consumption rate of 5.5, 4.0, 2.6 and 0.93 kg/h at outside temperatures of 30, 15 0 and −15°C, respectively, with 4 fans. The N₂ use for 2 and 6 fans was 5 and 6.3 kg/h, respectively, at an outside temperature of 30°C. During simulated power failure or when the N₂-tank ‘ran dry', temperatures in the container rose 0.9 and 2.0°C/h, respectively. When the door to the container was opened long enough to remove three trays, temperature was restored within 5 min. Convective heat transfer coefficients between saline water bags and circulating N₂ were in the range of 80–100, 115–135, and 140–155 W/(m²·K) for 2, 4 and 6 fans, respectively. Heat transfer to meat will be limited by conduction in master packaged meat if similar convection coefficients prevail.     

Physico-chemical and organoleptic properties of patties from hot, chilled and frozen goat meat

The effects of processing hot versus chilled goat meat, as such and after freezing in chunk or mince forms, were studied in relation to physico-chemical and organoleptic properties of patties. The differences in the pH of the meat samples were non-significant (P < 0·05) at 3–4 h post mortem (PM) at room temperature (30°C) and after 24 h at 4°C. The yield of the broiled patties, prepared from hot meat at 3–4 h PM, was significantly lower (P<0·05) as compared to those from chilled meat. However, this trend was reversed, if processing of hot meat into patties was done within 1–2 h PM. Freezing of chilled meat in chunk or mince forms gave significantly higher (P < 0·05) cooking yields than freezing of hot meat in similar forms.

The organoleptic scores of the raw-cooked patties were similar for all treatments. Freezing of precooked patties at −10°C for 10 days, thawing and reheating did not reduce most of the sensory scores significantly (P<0·05). Moisture, protein and fat contents of the broiled patties were not significantly (P<0·05) affected by the treatments. Standard plate count of hot versus chilled meat, for all levels of processing and storage, were within acceptable limits.     

Definition of the optimal freezing rate-2. Investigation of the physico-chemical properties of beef M. longissimus dorsi frozen at different freezing rates

The influence of freezing rate on weight loss during the freezing, thawing and cooking, on water-binding capacity, on sensory and other physico-chemical properties of beef M. longissimus dorsi was investigated. The changes in myofibrillar proteins in muscle samples frozen at different freezing rates were also investigated.

The greatest weight losses during the freezing, thawing and cooking were registered at slow freezing procedures (freezing rate of 0·22 cm/h and 0·29 cm/h), when the meat was tougher and less soft. The solubility of myofibrillar proteins was least from those muscles frozen at such freezing rates.

The freezing of samples at freezing rates of 3·33 cm/h and 3·95 cm/h had less influence on their physico-chemical characteristics. The solubility of the myofibrillar proteins from such samples was greatest, and the cooked samples were the most tender.

From analysis of the results it was concluded that optimal conditions for meat freezing seem to be those when the average freezing rate is 2–5 cm/h.     

Rapid freezing, frozen storage and the tenderness of lamb

Cold-shortening in pre-rigor lamb can be prevented by freezing carcasses very rapidly in less than four hours. Thaw-shortening can also be prevented by storing the carcasses for a period (> 10 days) in the frozen state (− 12°C). By this simple combination of rapid freezing and frozen storage, the hazard of toughness development from cold- and thaw-shortenings is avoided.     

Effect of high-pressure induced ice I/ice III-transition on the texture and microstructure of fresh and pretreated carrots and strawberries

The effect of pressure treatments at −25 °C between 150 and 300 MPa, indicated as high-pressure induced crystallization (HPIC) processes if formation of ice III occurs during pressurization, on the texture and structure of frozen strawberries and carrots were studied. The formation of ice III, which has been proven to inactivate the microbial load of a frozen food, occurred when pressure was increased to 250 MPa or higher. Volume changes related to the formation of ice III affected the cell wall integrity of infused frozen strawberries and caused a 42–46% reduction of the fruit’s hardness. These textural and structural changes were not affected by the pressure holding time (30 s versus 10 min), and thus by partial thawing during the pressure holding time, and were absent in frozen fruits treated at pressures lower than 250 MPa. The structure and texture of frozen carrots were respectively not and only slightly altered during high-pressure–low-temperature (HP–LT) treatments at all pressure levels studied. However, if carrots were blanched (30 min at 60 °C, 2 min at 90 °C and a combination of both) prior to freezing, structural damages during pretreatment and freezing made the tissue, in terms of both structural and textural quality, unsuitable for a post-freezing HP–LT treatment. These observations should be taken in mind when analyzing the possibilities of HPIC processes as a tool for post-freezing microbial reduction when applied to tissue based systems.     

Development of backfat and individual fat layers in the pig and its relationship with carcass lean

The development of backfat (total and individual layers) was monitored in 140 Yorkshire pigs (71 castrates and 69 gilts) during a growing period extending from 14·5 kg to 137·0 kg live weight using a serial slaughter procedure. The allometric coefficient (b) for fat thickness was calculated at several locations extending from the shoulder to the M. gluteus medius at the mid-line and lateral to the mid-line. The relationships between backfat (total and individual layers) and the yield of trimmed boneless meat were also obtained from 80 carcasses.

Total backfat was the thickest at the shoulder, decreased gradually to the last rib, increased at the maximum loin, decreased to the middle of the M. gluteus medius and then increased posterior to the M. gluteus medius. The development of total backfat relative to weight at slaughter was generally slowest at the shoulder (b = 0·555−0·767), most rapid in the region extending from the 5/6 last rib to the last rib b = 0·729−0·810) and intermediate at the loin and in the region of the M. gluteus medius (b = 0·609−0·834). The development of the middle fat layer (b = 0·609−1·107) was more rapid than that of the outer layer (b = 0·500−0·817), the inner layer being intermediate (b = 0·515−0·966). Consistent with the rate of development observed for the individual fat layers, at light weights, the outer layer was usually more predominant, particularly at positions above the M. longissimus, whereas, at heavier weights, the middle layer became predominant.

It was observed that backfat (total or individual layers) measurements, which were the most precise predictors of yield of trimmed boneless meat, that is, measurements from the 5/6 last rib to the last rib (RSE = 4·6−3·1), also had the most rapid rate of development. Furthermore, the middle layer of backfat which exhibited the fastest rate of development of all three individual layers (b = 0·609−1·107), also contributed the most to the observed precision (RSE = 4·6−3·1).     

Generalization of a method for the characterization of quick frozen beef

The lack of standardized tests for determining if a product can be defined as 'quick frozen' is a source of difficulty in the commercialization of foods. An even greater difficulty is the fact that there is no one definition of a quick frozen food. With the aim of partially filling this gap, a previous paper developed a simple physical method of characterizing quick frozen beef. The study was carried out with meat cuts cooled by means of heat transfer perpendicular, in a sense, to the meat fibres with 'quick frozen' being defined by a minimum average freezing rate. In the present paper the characterization method is generalized for either heat transfer perpendicular with, or parallel to, beef fibres, 'quick frozen' being defined either by a maximum freezing time or a minimum freezing rate.     

Supercooling capacity of Tineola bisselliella (Hummel) (Lepidoptera: Tineidae): Its implication for disinfestation

The variations in weight, water content and supercooling point (SCP) were studied in Tineola bisselliella at different stages in its development.

The egg, with a fresh weight of 0.037 mg and a water content of 314% of the dry weight, is the stage most resistant to freezing with an SCP of −23 °C. The young larva (second instar), with a fresh weight of 2.5 mg and a water content of 145% of the dry weight, is the least resistant stage with an SCP of −13 °C. Despite the large differences in weights and water contents between males and females, they have the same SCP value of −19 °C.

Because of the large individual variations observed in this species, it appears necessary to treat infested materials with a temperature lower than or equal to −29 °C to destroy all stages of development promptly.     

Thermophysical properties of processed meat and poultry products

Thermophysical properties of various meat and poultry emulsions were evaluated at four temperatures (20, 40, 60 and 80 °C). Thermal conductivities (0.26–0.48 W m⁻¹ K⁻¹) increased linearly with temperature between 20 and 60 °C. Between 60 and 80 °C, it remained constant for most products except bologna. Curves for thermal conductivity as a function of temperature could be roughly grouped into two different categories: products containing meat particles and those containing meat emulsions. The application of various models was investigated for thermal conductivity prediction. It was found that a three phase structural based Kirscher model had the potential for predicting thermal conductivities with acceptable accuracy. Densities decreased slightly as a function of temperature from 20 to 40 °C. A transition phase was observed from 40 to 60 °C, which was followed by a decrease from 60 to 80 °C. There was a decrease of about 50 kg m⁻³ between the density of a raw product at room temperature (at maximum 1070 kg m⁻³) and the product heated to 80 °C (at minimum 970 kg m⁻³), due to the gelation or setting of the structure. After a transition period from 10 to 30 °C, the heat capacity increased linearly from 30 to 80 °C, and ranged from 2850 to 3380 J kg⁻¹ °C⁻¹, respectively. Densities and heat capacities were strongly influenced by the carbohydrate content (i.e. as the carbohydrate content increased the density decreased). The salt content adversely affected thermal conductivity and thermal diffusivity values. However, these parameters increased with moisture content.     

The effects of spray and blast-chilling on carcass shrinkage and pork muscle quality

Combinations of blast- and spray-chilling of pork carcasses were compared to spray-chilling at conventional chilling temperatures with regard to carcass shrinkage during chilling and pork muscle quality. In experiment 1, pork sides were spray-chilled at 1°C for the first 10 h (40 spray cycles of 60-s duration every 15 min) of cooling or blast-chilled at −20°C for 1, 2 or 3 h followed by spray-chilling for 9, 8 or 7 h duration, respectively. All pork sides were then chilled to 24 h post mortem at 1°C. Experiment 2 followed the same procedures as experiment 1, except that −40°C was used as the blast-chill temperature.

Carcass shrinkage was similar for all treatments in experiment 1 at 24 h ranging from 0·5–0·7 g 100 g⁻¹. Blast/spray-chilling increased the rate of chilling and reduced the rate of post-mortem pH decline in two muscles (longissimus thoracis, LT and semimembranosus, SM) compared to the combined conventional/spray-chill treatment. Carcasses that were blast-chilled for 3 h had LT muscles that were darker with a higher protein solubility, less drip loss, shorter lengths and higher shear values compared to those from carcasses in the conventional/spray-chill treatment. In experiment 2, carcasses blast-chilled for 3 h at −40°C recorded a weight gain at 24 h of 0·4 g 100 g⁻¹, compared to a weight loss in all other treatments (0·2–0·4 g 100 g⁻¹). Muscle colour was darker in both the LT and SM of carcasses blast-chilled for 3 h at −40°C compared to carcasses from the conventional/spray-chill treatment, but most other measurements of muscle quality showed an inconsistent response to chilling treatment.     

Secondary sexual development (Masculinity) of bovine males: 2. Influence on certain meat quality characteristics

Differences in meat quality traits between bulls with secondary sexual development (bulls(+), n = 10), those without this development (bulls(−), n = 10) and steers (n = 10) were investigated. All animals had no permanent incisors (A-age group). Significant differences (P < 0·05) between bulls(+) and bulls(−) were found for the cooking loss percentage of the M. splenius (27·83% versus 31·11%, respectively), iron content of the M. splenius (56·02μg/g versus 49·43μg/g, respectively) and total collagen content of the M. splenius (3·74 versus 4·73 measured as Hyp N/Tot N x 1000, respectively). Drip loss of the wingrib cut (4·01% versus 5·18%, respectively) was also significantly different between bulls(+) and bulls(−). For the M. longissimus thoracis, no significant (P < 0·05) differences in any of the quality-indicating parameters investigated could be found. It is concluded that the M. splenius can be used as an indicator muscle for masculinity, based on meat quality attributes. This is supported by the correlation coefficients obtained between masculinity and the intramuscular collagen content of the M. splenius (r = −0·55) and the iron content of the M. splenius (r = 0·46). For all the other quality attributes investigated, non-significant (P > 0·05) differences between the three sex condition groups were found. It is concluded that the influence of masculinity on meat quality traits of young bulls is of little practical importance in a classification and grading system.