What about Fat?
We skipped over fat when we looked at the constituents of muscles and now returns to it. Many people refer to fat as lipids, but fats are only a subgroup of lipids called triglycerides. Lets set some basic concepts up, to begin with. Human body fat, animal, and vegetable fats have triglycerides as its main constituent. Their function in blood is to facilitate bidirectional transference of adipose fat which is the fat layer under our skin, around internal organs), in bone marrow, intermuscular and in the breast tissue.
Let’s look closer at the adipose tissue. It is “composed of a loose collection of specialized cells, called adipocytes, embedded in a mesh of collagen fibers. We looked briefly at collagen when we reviewed the stromal proteins. The main role of adipose tissue in the body is its role as a fuel tank for the storage of lipids and triglycerides.
One gets white and brown adipose tissue with white tissue being the most numerous. “The main role, or function, of white adipose tissue is to collect, store and then release lipids. However, because of the properties of the lipids being stored, the adipose tissue also acts as a protective cushion (resists knocks) and also as a layer of insulation against excessive heat loss.
Lipids conduct heat very poorly (only about a third of the rate of other materials) so even a small layer of adipose cells (about 2 mm) will keep a person warm at 15 degrees centigrade, whereas a person with only a 1 mm layer of protection will be feeling quite uncomfortable.
About 80% of average white adipose tissue is lipid, and of that, about 90% is made up of the six triglycerides: stearic, oleic, linoleic, palmitic, palmitoleic and myristic acid. Also stored are free fatty acids, cholesterol, mono- and di-glycerides.” (brooklyn.cuny.edu)
“Each adipocyte cell has a large, central, uniform, lipid packed central vacuole which, as it enlarges, pushes all the cytoplasm, the nucleus, and all the other organelles to the edge of the cell, making it look a bit like a band or ring under the microscope.
These cells can vary in size from about 30 microns to over 230 microns, and, despite their distorted appearance, contain all the necessary biochemical machinery of other cells.
Every adipose cell must touch at least one capillary or blood vessel (an artery or vein). From this the cells draw all their needed supplies, including lipids.
Fatty foods, with high lipid content, often provide more lipids than can be digested and used right away. The excess is stored in the adipose tissue. Excess carbohydrate and protein taken in with meals can also be converted to fat (usually in the liver) and then moved to the adipose tissue for longer-term storage.
Lipids are the major fuel reserve for humans and most mammals. These molecules are very efficient at storing needed energy. One gram of fat stores about 9 kcal per gram, compared to carbohydrate or protein (4 kcal per gram). For mobile animals, this means that less bulk has to be carried around and a normal sized body that is about 20% fat has enough stored energy to last about 20 – 30 days without eating!” (brooklyn.cuny.edu)
Let’s look more closely at triglyceride. There are many types of triglycerides. We are all familiar with the two main groups of triglycerides, namely saturated and unsaturated types. Saturated fats are “saturated” with hydrogen — all available places where hydrogen atoms could be bonded to carbon atoms are occupied. the importance to us for meat processing is its melting point which is higher and are more likely to be solid at room temperature. It is this saturated fats that, when ingested, raises the level of cholesterol in your blood. (daa.asn.au)
On the other hand are the unsaturated fats which have double bonds between some of the carbon atoms, reducing the number of places where hydrogen atoms can bond to carbon atoms. For our purposes, the net result is that they have a lower melting point and are more likely to be liquid at room temperature. These fats help reduce the risk of high blood cholesterol levels and have other health benefits when they replace saturated fats in the diet. (daa.asn.au)
When one works with pork fat, it is important to keep an eye on the temperature. During processing, highly unsaturated fats will start to melt and form a fat coating on the product which is visually unappealing. (Toldra, 2010) Beef fat is firmer with a more intense flavour in comparison with pork or chicken. Beef fat’s melting point is comparable to pork kidney fat due to the low content of collagen and saturated fats. The reason why pork fat is popular is that it is largely tasteless and flavourless. The rules for making meat emulsions are based on fat choice and temperature. “Pork backfat gives the best suitable product for slicing. Jowl and belly fat can also be used. The endpoint chopping temperature should remain below 18 deg C, 12 deg C, and 8 deg C for beef, pork, and poultry fat respectively to avoid fat melting.” (Toldra, 2010)
“To make spreadable products fat must be dispersed in the liquid state at “hot” temperatures. The endpoint chopping temperatures should be above the fat melting point (i.e., 35 deg C). To achieve this final temperature, fat is usually pouched in water at temperatures above 80 deg C before being mixed with protein (liver or lean meat). The object is to reach a final internal temperature between 50 and 60 deg C for ham fat and between 70 and 75 deg C for jowl fat. Fat poaching also causes contraction of the connective tissue which will facilitate the grinding; it eliminates low melting fats, which can cause weight losses during cooking and it lowers the microbial content. Thus, for hot emulsions, low melting fat is preferred such as ham and jowl fat remain firm during cooking at high temperatures.” (Toldra, 2010)
Triglycerides are composed of three fatty acids. The fatty acid content in animals depends on age, type of feed and the environment. Diet plays an important role, especially in pork which is one of the reasons why pork, raised in informal settlement environments are very poor substitutes for commercially farmed animals where feed are strictly controlled. The properties of the fat will generally be determined by the composition of the fatty acids. “It will be soft (oily appearance) and prone to oxidation when there is a high percentage of polyunsaturated fatty acid linoleic (typical of feed rich in corn, for instance) and linolenic acids.” (Toldra, 2002)
There are two main groups of lipids in the body. The one is triglycerides which we just had a look at. The other is phospholipids. They are present in very small amounts but have a strong key role in flavour development and the oxidation of postmortem meat. They also have a relatively high proportion of polyunsaturated fatty acids in comparison to neutral lipids. Some of the major constituents are phosphatidylcholine (lecithin) and phosphatidylethanolamine. Phospholipids vary depending on the genetic type of the animal and anatomical location of the muscle. Therefore, the amount of phospholipids tends to be higher in red oxidative muscles than in white glycolytic muscles. (Toldra, 2002)
The interaction of fat and protein is a very important consideration in restructuring meat. “The fat level clearly influenced the structure of the gel/ emulsion network, as reflected by the differences in the type of protein molecular interactions involved in its formation, and this, in turn, affected the fat binding properties and the texture of the end product.” (Sun, 2009)
It is difficult to bind fat effectively to meat. De NG, Toledo, and Lillard (1981) found that water and fat binding by meat batters diminish when temperatures exceed 16°C during comminution. This speaks directly to the preparation of stuffing meat and it requires for the meat temperature to be kept as low as possible, but not so low that it makes it impossible for workers to use it in the restructuring process.
Secondly, when one talks about fat and stuffing meat, one must consider the interaction between a TG blend containing pork gelatin and fat in the meat mix which is less than optimal. TG by itself is not a good binder for fat. The easiest way of handling fat in stuffing meat is to avoid it. I have found pork fillet to be particularly suited due to its lean nature.
Remember that gelatin “works by creating a very fine mesh of proteins, between which the (hydrophilic) liquid gets trapped. A mixture of fat and water isn’t a liquid. It can be either a rough two-phase mixture, with visible fat droplets swimming around in the water, or it can be an emulsion, with invisibly small fat droplets dispersed through the water. Emulsions appear smooth, e.g. milk.” (cooking.stackexchange.com) Fat in the stuffing meat will interfere with the binding.
As far as the whole meat muscles are concerned, it is important to lay the meat pieces fat down in the mold to minimize contact between added meat and fat.
After thermal treatment, the meat must be frozen as soon as possible.
Sun (2009) reports that “although most of the studies using TG for restructuring meat conducted by incubation meat at optimum temperature (37–508C) of MTG or by cooking to obtain sufficient binding strength, some researchers obtained good binding effect by using cold binding (2–58C), with the combination of TG and sodium caseinate, without addition of salt or cooking (Kuraishi et al., 1997; Serrano, Cofrades & Jimenez Colmenero, 2004). Kuraishi et al. (1997) indicated that the TG reaction condition of 58C for 2 h would not enable any bacteria present to increase much and discoloration of the meat was not observed in the raw, refrigerated state. In my experience, IT binds very well at lower temperatures.
The maximum activity observed for TG was at 40 °C for the commercial TG. At temperatures above 45 °C, TG suffered a rapid drop in its activity. Optimal pH for commercial TG was found to be between pH 5.5 and 6.0. (Ceresinoa, 2018)
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