Characterization of Ice Crystals in Pork Muscle Formed by Pressure-shift Freezing as Compared with Classical Freezing Methods

Effects of oxidative stability variation on lamb meat quality and flavor during postmortem aging

This study evaluated the effects of oxidative stability variation on meat quality and flavor in biceps femoris (BF) and longissimus dorsi (LD) muscles of lambs during postmortem aging. The samples were stored at 4±1℃; the meat quality, flavor and muscle oxidative stability were measured on day 0, 1, 2, 3, and 4 of postmortem aging. The results showed that malondialdehyde (MDA) content increased in both muscle types; superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) activities decreased, as did total antioxidative capacity (T-AOC). LD muscle showed lower MDA content and antioxidative activity than BF muscle. Meat quality analyses indicated that aging increased the lightness (L*), redness (a*), and yellowness (b*) values of meat while improving its tenderness. Gas chromatography-mass spectrometry results showed that volatile flavor compounds were more abundant in LD muscle than in BF muscle. As the aging time extended, relative contents of aldehyde and alcohol increased in both muscles. The key flavor compounds during postmortem aging including heptanal, octanal, nonanal, and decanal were screened by relative odor activity value (ROAV), and the content of key flavor compounds showed the trend of increasing, which were usually associated with fresh green grass, nutty, and fat descriptors. In conclusion, the oxidative muscles displayed better antioxidative capacity, and postmortem aging altered the oxidative stability of lamb muscle, which affected the meat quality and flavor. PRACTICAL APPLICATION: Meat aging is an important strategy to improve the quality of various meat traits (including flavor). The results of this work could be of interest to meat professionals who will be able to apply in actual production by choosing the best aging time based on flavor and meat quality for different muscle parts.

Comparison of the immersion chilling and freezing and traditional air freezing on the quality of beef during storage

Compared to traditional air freezing, immersion chilling and freezing shows an improvement in the freezing effect on meat quality, but it is not known whether this advantage persists over longer storage periods. Therefore, the objective of the current study was to compare the effects of immersion chilling and freezing (ICF) and traditional air freezing (TAF) on the physical and chemical indexes in beef longissimus muscle during a storage period of 150 days. In the current study, the longissimus muscle from Luxi cattle (aged 20-24 months) was analyzed, with samples independently frozen by ICF and TAF. After the core temperature was frozen to below -18 degrees by the two chilling methods, samples were transferred to a -18 degrees cold room for further storage. During the storage period, physical and chemical indexes, mainly including color and texture qualities, total volatile base nitrogen (TVB-N) and peroxide value (POV) were measured and comparatively analyzed at several fixed time points. A higher freezing rate was observed in ICF (5.124 cm/h) than in TAF (0.194 cm/h), and better microstructure was observed in ICF treatment. Besides, peak force values and total energy values were significantly lower in the TAF group than in the ICF group during the first 45 days of freezing storage time (p < .05). ICF also showed better color quality due to higher L* values than TAF samples during the first 75 days of frozen storage (p < .05). In addition, the thawing loss (after 75 days of storage), total volatile base nitrogen, and peroxide value (in the 30 to 75 days of storage period) were lower in the ICF than in the TAF group. In conclusion, the immersion chilling and freezing is more conducive to the quality of beef during storage at -18 degrees compared to traditional air freezing.

Frozen/thawed meat quality associated with muscle fiber characteristics of porcine longissimus thoracis et lumborum, psoas major, semimembranosus, and semitendinosus muscles

To evaluate the relationship between muscle fiber characteristics and the quality of frozen/thawed pork meat, four different muscles, M. longissimus thoracis et lumborum (LTL), M. psoas major (PM), M. semimembranosus (SM), and M. semitendinosus (ST), were analyzed from twenty carcasses. Meat color values (lightness, redness, yellowness, chroma, and hue) changed due to freezing/thawing in LTL, which showed larger IIAX, IIX, and IIXB fibers than found in SM (P < 0.05). SM and ST showed a significant decrease in purge loss and an increase in shear force caused by freezing/thawing (P < 0.05). Compared with LTL, SM contains more type IIXB muscle fibers and ST had larger muscle fibers I and IIA (P < 0.05). PM was the most stable of all muscles, since only its yellowness and chroma were affected by freezing/thawing (P < 0.05). These results suggest that pork muscle fiber characteristics of individual cuts must be considered to avoid quality deterioration during frozen storage.

Do animal slaughter age and pre-cure freezing have a significant impact on the quality of Iberian dry-cured pork loin?

The influence of various animal slaughter age and of pre-cure freezing times on the quality traits of dry-cured loins from Iberian × Duroc (IBxD) crossbreed animals was assessed. Three animal batches (n = 15) were selected (IBxD8, IBxD10 and IBxD12) to be slaughtered at the age of 8, 10 and 12 months, respectively. Following slaughter, longissimus thoracis et lumborum muscles were extracted and submitted to curing (T0) or freezing storage during three (T3) or six (T6) months prior to curing. The dry-cured loins from IBxD12 yielded lower intramuscular fat and lightness, a less saturated fatty acid profile and the highest hardness and shear force (P ≤ 0.05). The pre-cure freezing process increased weight loss, saturated fatty acids, lipid oxidation, and most of the textural parameters (P ≤ 0.05). So, both slaughter age and pre-cure freezing should be taken into account in order to obtain quality and productive performance.

Polarimetric comparison of fresh and frozen skeletal muscle tissues of goat

Optical properties can provide rich information about morphology and structure of tissues. Fresh and frozen muscle tissue samples of goat are investigated using imaging polarimetry to understand its structural nature. The outcomes demonstrate that the muscle tissues lose, to some extent, their integrity and organization on freezing. The fresh tissues offer very small circular retardance as compared to frozen samples. However, linear retardance is the main contributor in fresh muscle samples. Ultimately, linear and circular retardance can be used to differentiate fresh and frozen tissues. These investigations illustrate the capabilities of optical polarimetry for the characterization of muscle tissue structures. Specifically, the structure of biological tissue samples can be differentiated using real-time, cost effective and non-invasive optical polarimetry in the field of meat industry and biomedical diagnosis.

Changes in antioxidant enzymes in postmortem muscle and effects on meat quality from three duck breeds during cold storage

This study was conducted to evaluate changes to antioxidant systems in the postmortem muscle of three duck breeds and to analyze their relationship with meat quality. Pekin ducks, Muscovy ducks, and Mulard ducks were euthanized at the age of 70 d. The antioxidant enzyme activities and related gene expressions as well as meat quality in muscle tissues were examined. The breed of the duck had a significant effect on the antioxidant capacity of muscle tissues (P < 0.05), with the exceptions of superoxide dismutase (SOD) activity at 96 h as well as total antioxidant capacity (T-AOC) at 120 h. The SOD, glutathione peroxidase (GPx/GSH-Px), and T-AOC activities from highest to lowest were Muscovy duck > Mulard duck > Pekin duck, whereas the malondialdehyde (MDA) concentration followed the opposite pattern. During cold storage (0–120 h), a decrease in the GPx, SOD, and T-AOC activities was noted, although MDA concentration increased gradually. The GPx1 and Cu/Zn-SOD gene expression levels in Muscovy duck muscle tissues were significantly higher than those in other breeds at both 0 and 24 h. Correlation analysis showed that higher antioxidant enzyme activity in duck muscle tissues was associated with higher water-holding capacity (WHC) and more stable meat color. Higher antioxidant enzyme activity in duck meat similarly resulted in higher pH values, higher WHC, and more stable meat color. These data indicate that antioxidant enzymes may inhibit lipid oxidation and participate in the regulation of meat quality.

Qualitative and quantitative assessment of DNA quality of frozen beef based on DNA yield, gel electrophoresis and PCR amplification and their correlations to beef quality

Freezing is a practical method for meat preservation but the quality of frozen meat can deteriorate with storage time. This research investigated the effect of frozen storage time (up to 66 months) on changes in DNA yield, purity and integrity in beef, and further analyzed the correlation between beef quality (moisture content, protein content, TVB-N value and pH value) and DNA quality in an attempt to establish a reliable, high-throughput method for meat quality control. Results showed that frozen storage time influenced the yield and integrity of DNA significantly (p < 0.05). The DNA yield decreased as frozen storage time increased due to DNA degradation. The half-life (t_1/2 = ln2/0.015) was calculated as 46 months. The DNA quality degraded dramatically with the increased storage time based on gel electrophoresis results. Polymerase chain reaction (PCR) products from both mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) were observed in all frozen beef samples. Using real-time PCR for quantitative assessment of DNA and meat quality revealed that correlations could be established successfully with mathematical models to evaluate frozen beef quality.

Fundamental interfacial mechanisms underlying electrofreezing

This article reviews the fundamental interfacial mechanisms underlying electrofreezing (promotion of ice nucleation via the application of an electric field). Electrofreezing has been an active research topic for many decades, with applications in food preservation, cryopreservation, cryogenics and ice formation. There is substantial literature detailing experimental and simulations-based studies, which aim to understand the complex mechanisms underlying accelerated ice nucleation in the presence of electric fields and electrical charge. This work provides a critical review of all such studies. It is noted that application-focused studies of electrofreezing are excluded from this review; such studies have been previously reviewed in literature. This review focuses only on fundamental studies, which analyze the physical mechanisms underlying electrofreezing. Topics reviewed include experimental studies on electrofreezing (DC and AC electric fields), pyroelectricity-based control of freezing, molecular dynamics simulations of electrofreezing, and thermodynamics-based explanations of electrofreezing. Overall, it is seen that electrofreezing can enable disruptive advancements in the control of liquid-to-solid phase change, and that our current understanding of the underlying mechanisms can be significantly improved through further studies of various interfacial effects coming into play.

Superchilling of muscle foods: Potential alternative for chilling and freezing

Superchilling is an attractive technique for preservation of muscle foods which freezes part of the water and insulate the food products from temperature fluctuations thereby enhancing the shelf-life during storage, transportation and retailing. Superchilling process synergistically improves the product shelf-life when used in combination with vacuum or modified atmospheric packaging. The shelf-life of muscle foods was reported to be increased by 1.5 to 4.0 times relative to traditional chilling technique. Advantages of superchilling and its ability to maintain the freshness of muscle foods over freezing has been discussed and its potential for Industrial application is highlighted. Present review also unravel the mechanistic bases for ice-crystal formation during superchilling and measures to ameliorate the drip loss. The future challenges especially automation in superchilling process for large scale Industrial application is presented.

Calorimetry and Pressure-shift Freezing of Different Food Products

Rapid depressurisation can create uniform, small and abundant ice nucleation during pressure-shift freezing (PSF) which can then protect the frozen food structure from cell damage. The amount of depressurisation-formed ice was evaluated using a high-pressure calorimeter for different food products (tylose, potato, salmon, pork and water). Experiments were conducted at an initial pressure of 62, 82, 112, 156, 180 and 196MPa, at temperatures set at −5, −7, −10, −15, −18 and −20°C, respectively (slightly above the phase diagram of water-ice I). Calorimetric thermograms recorded during PSF tests were used for computing the quantity of ice formed based on heat balance. A polynomial relationship was established for each product to compute the depressurisation-formed ice ratio as a function of the initial pressure applied. This model accurately predicted the maximum ice ratio for PSF at a given pressure (0.1 to 210MPa) or the minimum ice ratio for PSF at a given temperature (−22 to 0°C). Moisture content was the major factor affecting the sample-mass based (SMB) ice ratio with higher moisture yielding a higher SMB ice ratio. A general relationship between water-mass based (WMB) ice ratio ( R'ice-water) and initial pressure was found from the pooled data from all tested products: R'ice-water 0.114 P+0.00022 P2 (R2 0.94, n 47) which agreed well with relevant literature values for pure water.

The effect of high pressure at subzero temperature on proteins solubility, drip loss and texture of fish (cod and salmon) and mammal's (pork and beef) meat

One of the possibilities of using high-pressure technique in inactivation of microorganism is conducting this process at subzero temperature. However, for its practical application in meat preservation the appropriate properties of meat should be maintained. Therefore, the aim of this work was to examine the effect of pressure at subzero temperature (without freezing of water) on proteins and texture of mammal's and cold-adapted fish meat. The data showed that cod and salmon meat proteins were more susceptible to pressure-induced denaturation/aggregation than beef and pork proteins. Glucose and saccharose exerted protective effect on fish meat proteins treated with pressure of 111 MPa(tc) and -10 degrees C but not at 193 MPa(tc) and -20 degrees C. The pressure treatment under the latter conditions increased cook loss of fish meat but not of mammal's meat. However, after cooking the hardness of all kinds of pressurized meat was at the same level as that for unpressurized cooked samples.

Opportunities and Challenges in High Pressure Processing of Foods

Consumers increasingly demand convenience foods of the highest quality in terms of natural flavor and taste, and which are free from additives and preservatives. This demand has triggered the need for the development of a number of nonthermal approaches to food processing, of which high-pressure technology has proven to be very valuable. A number of recent publications have demonstrated novel and diverse uses of this technology. Its novel features, which include destruction of microorganisms at room temperature or lower, have made the technology commercially attractive. Enzymes and even spore forming bacteria can be inactivated by the application of pressure-thermal combinations, This review aims to identify the opportunities and challenges associated with this technology. In addition to discussing the effects of high pressure on food components, this review covers the combined effects of high pressure processing with: gamma irradiation, alternating current, ultrasound, and carbon dioxide or anti-microbial treatment. Further, the applications of this technology in various sectors - fruits and vegetables, dairy, and meat processing - have been dealt with extensively. The integration of high-pressure with other matured processing operations such as blanching, dehydration, osmotic dehydration, rehydration, frying, freezing / thawing and solid-liquid extraction has been shown to open up new processing options. The key challenges identified include: heat transfer problems and resulting non-uniformity in processing, obtaining reliable and reproducible data for process validation, lack of detailed knowledge about the interaction between high pressure, and a number of food constituents, packaging and statutory issues.