Because of the warm, humid conditions normally utilized for fermentation of semidry sausages, meat ingredients must be of very high quality. Fermentation encourages microbial growth and accelerates chemical reactions, both of which have potential to affect final product quality and may even result in spoilage. Fresh meat with no microbiological or chemical age is essential for manufacturing fermented sausage. If initial microbiological counts on meat are high, undesirable growth may occur during fermentation even if a starter culture is added. If chemical changes have begun to occur, most notably lipid oxidation, they may then accelerate under the conditions used for fermentation and result in significant off-flavors.
Problems in fermented sausage that may result from low-quality meat ingredients can also include ''greening,'' a color change from peroxides produced by undesirable bacteria. The peroxides typically are produced during fermentation and may cause greenish colors from the meat pigment when the pigment is exposed to air. Other problems that can develop from undesirable bacterial growth during fermentation include a mushy texture, resulting from proteolysis by some organisms. Production of carbon dioxide gas during fermentation is highly undesirable and may occur if high numbers of heterofermentative microorganisms are present. The result of gas production is gas bubbles in the product or even breakage of casings if gas production is extreme. Product pH may be altered if micrococci are present in the early stages of fermentation. Some conversion of carbohydrates may occur without formation of lactic acid and this could result in a higher final pH in the product than expected. Fresh meats should also be well trimmed of glands, blood clots, and other nonmuscle materials. Glandular materials, in particular, can be a source of spoilage microorganisms, proteolytic enzymes, and pathogens such as Staphylococcus aureus.
Meat trimming also becomes important for the removal of connective tissue originating from sinews, tendons, and similar structures in skeletal muscle. Most semidry sausages are not heated to the extent that hydrolysis and tenderization of the collagen in connective tissue occurs. Further, the semidry sausage products are typically ground or chopped to a relatively coarse texture. This means that any connective tissue in the product will remain tough and will be present in large enough particles to be detected during consumption. Excessive collagen may also appear as unattractive ''fish eyes'' when a product is sliced. Removal of connective tissue is an important quality control point for semidry sausages, and many processors employ desinewing machines for the meat ingredients that are designated for semidry sausage formulations.
The color of both lean and fat of the meat materials will affect semidry sausage quality. Yellow fat, for example, is not acceptable for the appearance of semidry sausage. Generally speaking, more intensely pigmented (redder) lean is preferable to provide a greater color contrast (red lean/white fat) in the finished product. This is one reason why pork shoulder meat is preferable to the paler ham and loin trimmings as a meat ingredient for semidry sausage (12).
Chemical quality, particularly of the fat, is also a concern for meat ingredients. Fat begins to oxidize almost immediately after slaughter, but the oxidative reactions occur very slowly at first. As time goes on, the oxidation reactions that produce rancid flavors accelerate and continue to do so in a logarithmic fashion. Because of this, it is extremely important that meat ingredients have minimal oxidation history prior to use for semidry sausage. This is one area where frozen meat, if used, should be carefully chosen for these products. Frozen meat is often held for variable periods of time in frozen storage and slow oxidation occurs even though microbial growth may not. An ''old'' frozen meat ingredient may trigger rapid rancidity development if the chemical quality is poor coming out of the freezer.
The initial pH of the raw meat ingredients may also be an important consideration for fermented sausage. Generally, a lower initial pH will facilitate the pH change desired during fermentation and will permit shorter fermentation time. For this reason, dark, firm, and dry (DFD) pork and dark-cutting beef are not ideal meat ingredients because these meat sources will have a high initial pH. In the case of pork, it is not uncommon to encounter pale, soft, and exudative (PSE) pork with a lower-than-usual initial pH. This meat ingredient will ferment more quickly and releases moisture readily but will also result in a crumbly, mushy texture in fermented sausage because meat proteins have been damaged. The pale color inherent to PSE pork can also result in uneven color in the finished product, depending on the proportions used. Therefore, PSE pork, even though it sometimes has a low initial pH, is very undesirable as a meat ingredient for semidry sausage.
Meat ingredients may also affect fermentation and fermentation rates in other ways. For example, a lean product formulation will contain higher moisture content than a high-fat formulation and with more moisture, the fermentation may develop more quickly. There has also been a suggestion that glycogen (carbohydrate in muscle) content of lean meat may contribute to total acidity. However, residual glycogen in lean muscle is typically quite low and generally would not be expected to contribute significantly to fermentation.
Meat sources derived from different muscles and from different animal species may demonstrate significantly different buffering capacity. Meat with a greater buffering capacity will absorb more acid with less pH change during fermentation and would require more acid production to reach a target pH. In general, beef is viewed as having a greater buffering capacity than pork and, in addition, is often at a somewhat higher initial pH. Consequently, it typically takes longer to ferment an all-beef product than a pork-beef mixture. An additional hypothesis suggested for the different fermentation rates between beef and pork is that pork contains a much greater concentration of thiamine, which could serve as a microbial growth stimulant and facilitate faster growth rates by the culture (1).
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