What Are Beef Crystals? The Full Guide

When you freeze meat to keep it fresh, you use low temperatures to make the food last longer, mostly by slowing down the rate at which microbes break down and spoil the food. Characteristics of meat that are important to be preserve include tenderness, water holding capacity, color, and flavor. In general, freezing improves meat tenderness, but negatively impacts other quality attributes. How much these things change depends on the size and distribution of the ice crystals, which are affected by how fast it freezes and how long it is stored at a certain temperature. New technology has made it possible to lessen the bad effects of freezing, but because muscle tissue is so complex, it’s hard to know for sure what will happen to the quality of meat after freezing. This review gives an outline of what we know about how energy and heat move during freezing and how that affects the quality of meat. Furthermore, the review provides an overview of the current novel technologies utilized to improve the freezing process.

Preserving food to extend its shelf-life has been practiced for several millennia. At its core, food preservation is changing the product’s natural properties, mostly its pH and water activity (Aw), to stop the growth of harmful microorganisms, molds, and spores. Controlling chemical reactions that break down food, like lipolysis, lipid oxidation, and proteolysis [1], is another use of preservation techniques. When semidry and dry fermented meat products are processed, they are often inoculated with a microbial culture to lower the pH and then dried, which lowers the Aw [2]. This is an example of how both intrinsic hurdles (pH and Aw) can be changed. But because the product’s natural qualities have been changed so much, it is no longer seen as “fresh,” which is a word that most people like to use for food [3], especially meat products. On the other hand, food can be kept fresh without having to change much about its natural properties if it is stored at very low temperatures. There are many kinds of foods that can be kept fresh by freezing them, but this review is mostly about refreshing meat.

Because fresh meat has a lot of water, it’s easy for microbes to break down and for chemicals to react in ways that hurt the quality of the meat, affecting things like its color, texture, and flavor [5]. Freezing is extensively utilized by the meat industry as a method of preservation during transport and storage. The quality characteristics that freezing was meant to protect can be damaged, though, leading to products that customers are unhappy with [6]. The result is that a lot of time and research has gone into figuring out what causes the physical and biochemical changes that happen to meat when it is frozen [7]. With the help of freezing, fresh meat products can last longer. This review also looks at how freezing affects meat quality and the technological advances that have been made to make frozen meat products better. But before we talk about these things, we need to have a good understanding of how water freezes and crystallizes to begin with.

Aspects of Meat Quality in Relation to Freezing

The cooling rate during freezing can greatly influence the microstructure and overall quality of meat ( ). A slow rate of cooling helps big ice crystals form, which leads to a more noticeable change in the original cell structure. When it comes to meat, big crystals can also damage the myofibrillar structures and lower the product’s water holding capacity (WHC) [44]. This can make the product look, taste, and be less juicy [45]. Higher cooling rates, on the other hand, cause smaller crystals to form, which means less damage to the structure of the cells. This is the main reason why fast cooling rates are best for freezing food in general and meat in particular. a list of studies that looked at how freezing and thawing rates affected the quality of meat, such as its color, tenderness, and workable heat content (WHC). The effect of freezing/thawing on each of these attributes will be further discussed in the following sections.

Along with the rate of cooling, another important thing to think about when freezing meat is how long it was exposed to freezing temperatures in the first place. Something that is often used to show this is meat that has been through thaw rigor or thaw contracture. Thaw rigor occurs when a muscle is frozen prior to the completion of rigor mortis and then thawed. When something freezes, it breaks up the sarcoplasmic reticulum in muscle cells. This causes calcium to suddenly leak into the cytosol when the thing thaws. When ATP is present, like in pre-rigor muscle, calcium starts a strong muscle contraction that makes the sarcomere shorter and the product tougher [59]. Hence, it is imperative to freeze meat following the completion of rigor mortis (i. e. It takes 2–4 hours for chicken and turkey, 8–12 hours for pork, and about 24 hours for lamb and beef [60].

Under freezing conditions, meat can be stored for an extended period of time before quality defects are noticeable. Several studies [53,61,62] have looked at how long meat is frozen and how that affects its quality. They all found a negative link between the two. Vieira, Diaz, Martínez, and García-Cachán [53] discovered that beef steaks that had been frozen for 90 days lost more water and had lower L* (lightness), a* (redness), and b* (yellowness) values than steaks that had been frozen for 30 days. In a different study, Muela, et al. [63] found that lamb chops that had been frozen for 21 months were less tender and had less a* than chops that had been frozen for only one month. Previous studies have attempted to determine optimal storage duration during freezing [51,55,64]. According to Soyer, Özalp, Dalmış, and Bilgin [64], chicken stored at -18 °C can stay stable for up to 3 months before going bad. For lamb, it can stay stable for 3–21 months [63,65], and for beef, it can stay stable for 42 days to 12 months [53,61]. When you store meat for a long time at a temperature between -18 °C and -20 °C, the unfrozen water can react chemically with other parts of the meat, such as g. , proteins and lipids), which leads to a loss of quality [7]. Estévez, et al. [66] say that meat should be frozen at -40 °C because at that temperature, only a small amount of water is still liquid. Overall, it’s hard to say how long something should be stored to keep its quality as low as possible because species, freezing rate, and storage temperature are all things that affect quality [7]. To correctly understand how freezing affects meat quality, it also includes details about the type of meat, storage temperature, and time used in each study.

Tenderness is an important quality attribute that determines the overall acceptance of meat products by consumers [67,68]. Some studies [52,56] found that freezing had no effect on the tenderness of meat, while others [54,55] found that it did. However, most of the studies [50,51,53,69,70] show that freezing does make meat more tender. Lagerstedt, et al. [50] saw a 10 Newton drop in the Warner–Bratzler Shear Force (WBSF) of beef steaks that had been frozen before being aged compared to aged steaks that had never been frozen. Likewise, sensory panelists perceived frozen/thawed beef steaks to be more tender than their fresh counterparts [53]. It has also been seen that freezing pork [71], chicken [72], and lamb [54] makes them more tender. Part of the reason for this increase in tenderness is that the ice crystals damage the myofibrillar structure of the meat [7]. Using transmission electron microscopy, Qi, et al. [73] observed weakened sarcomere M- and Z-lines after 5 freeze-thaw cycles. It’s more important that they linked these changes in ultrastructure to a lower level of hardness, chewiness, and cohesiveness, all of which are signs of a more tender product. The same effect has been seen in cooked meat as well. For example, when lamb was cooked and then frozen, the myofibrillar structure was broken down more and the meat became more tender [74]. It is possible to make meat more tender by physically breaking it down and breaking down myofibrillar proteins by endogenous proteases (proteolysis). Postmortem proteolysis has been widely considered as one of the most significant events that dictates end-product tenderness [75]. Indeed, Aroeira, et al. [76] and Grayson, et al. [77] showed that enhanced tenderness of frozen/thawed beef steaks was associated with greater postmortem proteolysis.

Several groups of proteolytic enzymes are involved in breaking down proteins after death. These include cathepsins, caspases, and calcium-dependent proteinases (calpains). Among these systems, calpains, more specifically, calpain-1, have been recognized for their role in postmortem tenderization [78]. Calpain-1 is the main protease that breaks down myofibrillar proteins like titin, nebulin, troponin-T, and desmin as meat ages, which makes it more tender [79,80]. So, it has been suggested that the higher proteolysis in frozen and thawed meat is because calpain-1 activity is higher. This is likely because ice crystals disrupt the sarcoplasmic reticulum, which raises the concentration of calcium in the cytosol. As it turns out, Zhang and Ertbjerg [81] found calcium levels 400–900 µM in a pork longissimus muscle that had been frozen and then thawed. This is a level that is much higher than the 3–50 µM calcium level needed to activate calpain-1 [82]. To back up this idea, Koohmaraie [83] showed that calpastatin (the body’s own calpain-1) activity dropped quickly when it was separated from frozen beef longissimus muscle. This effect was also seen in frozen lamb chops [84,85]. The decrease in calpastatin activity following freezing/thawing is likely a function of increased cytosolic calcium concentration. When calcium levels are low, calpastatin binds to calpain-1 and stops it from working. But when calcium levels rise, calpain-1 and other endogenous proteases break down calpastatin, which makes it less effective at stopping calpain-1 [86]. As far as we know, though, no previous research has shown that calpain-1 activity goes up after freezing and thawing. This means that more research needs to be done in this area.

It is thought that calpain-1 is the main factor that makes meat tender as it ages, but new research suggests that cathepsins and caspases may also play a role in making meat tender after death [87]. Scientists have found that ice crystals can damage the lysosome, which is where cathepsins are stored. This lets the cathepsins escape into the sarcoplasm and start breaking down proteins [88]. In support of this, Lee et al. [89] found that cathepsin B activity was higher in beef semitendinosus muscle that had been frozen at -20 °C for 24 hours before it was aged compared to samples that had not been frozen. To our knowledge, no previous research has investigated the participation of caspases in proteolysis of frozen/thawed meat. However, it has been shown that freezing skeletal muscle tissue damages the mitochondria [90], which lets the cell death protein cytochrome c enter the cytosol. Many things happen in the cytosol because of cytochrome c. These things eventually turn on the intrinsic apoptotic pathway, which is needed for the caspase system to work [91,92]. Studies have shown that when the mitochondria in meat were damaged early on, caspase-3 activity went up. Caspase-3 is the main effector caspase that is involved in apoptosis [93,94]. However, the area of research regarding meat freezing and activation of the caspase system requires additional investigation. Taken together, freezing can induce macro- and micro-level changes in meat, which, in most cases, improves meat tenderness. But the ice crystals in the meat can damage it mechanically, making it less able to hold water [7]. Because of this, freezing has been shown to lower the quality of other parts of meat, like its WHC [95].

Freezing as a Form of Meat Preservation

Yeast, molds, and pathogenic bacteria love to grow in meat [37], which means that meat products go bad very quickly. Acinetobacter, Aeromonas, Alternaria, Enterococcus, Micrococcus, Manoscus, Pseudomonas, and Penicillium are some genera of microorganisms that are often found on meat products [5]. Because pathogenic microorganisms like Salmonella and Escherichia coli are so dangerous to human health, the meat industry has to follow strict food safety rules [38]. It’s important to note, though, that meat products aren’t really contaminated until the animal has been killed and the carcass has been dressed. In fact, the tissue under the animal’s hide is clean until it is cut during the harvest [39]. Further contamination may also take place during carcass fabrication, processing, and handling. In general, microbial contamination happens on the surface of whole meat cuts. On the other hand, because ground meat is mixed so much during production, microbial contamination is spread out throughout the product.

Meat products can be kept in the fridge for a short time before going bad at the retail and consumer level. On the other hand, frozen meat has an extended shelf-life. Even though freezing doesn’t kill microbes, it stops them from multiplying, which slows down the rate at which food goes bad. Being careful is important when thawing meat, though, because it can allow microbes to grow [7]. During thawing, meat exudes internal moisture to the surface, carrying along with it nutrients for microbial growth [7,40]. It may be because of this that bacteria on frozen or thawed meat have a shorter lag phase than bacteria on fresh meat [41,42]. This means that meat products may not last as long after they’ve been thawed. The USDA says that frozen meat should be thawed in the fridge to keep it from going bad and to keep the quality better [43]. Even though freezing is mostly used to keep meat from going bad, it can change other things about the meat as well.

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