Controlling temperature and drying rate plays a decisive role in food safety by inhibiting growth of undesired microbes but this control is needed also for a consistent sensory quality. As a result of drying (i.e., aw-reduction), less resistant microorganisms gradually disappear (members of Enterobacteriaceae, pseudomonads, bacilli, etc.); less sensitive ones (micrococci, staphylococci, enterococci, listeriae, EHEC, etc.) may survive for a longer period of time. In the final product of long-ripened dried sausages, spoilage microflora has practically no chance to grow and cause deterioration. The situation is somewhat similar with pathogenic microorganisms, yet their very presence is not accepted by food authorities requiring sometimes zero tolerance—a standard that is hard to support scientifically.
In order to meet safety requirements, a complex strategy has to be followed by adding and/or supporting growth of useful microorganisms in the hygienically produced sausage and by controlling ripening-drying parameters, thus favoring growth of useful microorganisms and inhibiting growth of undesired ones, as discussed above. While doing so, not only are safety requirements met but also aroma formation is contributed to.
Starter cultures and bacteriocin-producing microorganisms can help in inhibiting pathogenic microbes (8-12) where inhibition of staphylococci and listeriae is desired mostly because these bacteria are difficult to combat, a result of their resistance to low aw, the main controlling factor in long dried sausages.
It should be kept in mind that bacteriocin producers are in general more effective under laboratory conditions on media than in a food matrix (12).
Unlike in dried ham, tissue endoenzymes in long-dried sausages play a less important role in aroma formation, and they are active mainly in the first part of ripening (13). In long-dried sausages, the metabolic activity of microorganisms contributes more to aroma but other factors— such as spices, lipolysis, etc.—may be involved in this complex process, too.
As mentioned already, smoking and pH changes (low- and high-acid sausages) do influence aroma characteristics, but the types and concentrations of spices used determine aroma even more (14). In this respect, spices that can be evenly distributed in sausage batter and react immediately with meat and fat matrix have a much more pronounced impact on aroma characteristics than occurs in long-ripened hams, where spices are generally not applied or they are rubbed on the muscle surface only. Natural spices in sausages influence aroma as well as safety indirectly, too, by enhancing metabolic activity of starter cultures (11,15).
As for taste and aroma formation by microbial metabolism, the breakdown of proteins, peptides, lipids, and carbohydrates will be discussed next.
Depending on application of lactic starters and addition of carbohydrate, lactic acid is produced through homofermentation, reducing the pH level (9,16). Concentration of D-lactate may be 5 times higher in high-acid sausages than in low-acid products (17). At a later stage, pH also increases in sausages with lactic starters; this is related to the formation of ammonia and some amino acids (9). Nevertheless, this occurs mainly in products in which apathogenic staphylococci are used without lactobacilli (18). In traditionally manufactured molded dry sausage (e.g., genuine Hungarian salami), no starter culture and very small amounts of carbohydrate are added; as a result, pH in the final product is around 6.0 (7).
As for breakdown of muscle proteins, endoenzymes (cathepsin D) are active at the beginning of ripening (13) and are enhanced by lower pH (17). Lower pH, on the other hand, does not favor endogenic aminopeptidases. Microbial aminopeptidases that break down peptides into amino acids also contribute to aroma development (19). Their activity is influenced by aw, pH, and temperature, too. Bacterial enzymes play a role in proteolysis at a later period of ripening (20).
Of microorganisms, the proteolytic activity of lactobacilli, micrococci, and molds has been more thoroughly investigated, and it has been found that some lactobacilli (L. casei and L. plantarum) can break down sarcoplasmic and myofibrillar protein (21). Intensity of protein metabolism is higher by micrococci (staphylococci) that are also responsible for formation of volatile and nonvolatile aroma compounds (22,23).
Nielsen and Coban (24) found that Penicillium nalgiovense has proteolytic activity, breaking down peptides in addition to muscle protein stimulated by salt. Ordonez et al. (25) found strong proteolytic (and lipolytic) activity with P. aurantiogriseum.
In lipolysis, endo- and exoenzymes participate, yet microbial enzymes also play a more intensive role here (26). Typical flavors and aromas are related to the hydrolitic and oxidative changes occurring in the lipid fraction during ripening. Lipid oxidation may cause off-flavor but may contribute to the development of desirable flavor, too (27). Lipid oxidation is mostly associated with unsaturated fatty acids and is often autocatalytic. For this reason, risk is higher if the raw material contains a higher ratio of unsaturated fatty acid (8,28) either by partially replacing fat with vegetable oil or by using the fat of animals that consumed elevated levels of unsaturated fatty acid. Risk of oxidation, on the other hand, can be reduced by smoking and by mold ripening because of the light protection and direct oxygen consumption provided by mold, as pointed out by Ordonez et al. (25).
It is interesting to note that as a result of microbial lipolysis in mold-ripened Hungarian salami, a significant increase in the acid number of the fat fraction takes place, reaching a value of 15 without any sign of rancidity as judged by peroxide or TBA number or organoleptically (29). Such a high acid number can be detected only in strongly rancid lard with high peroxide number, where because of high temperature rendering no microbial activity takes place and moisture is also very low.
Because physical, chemical, biochemical, and microbiological changes in mold-fermented sausages are rather similar to that of dry sausages without mold, the reader is referred to publications on these topics (2,14,17,19,22,23,27,30-32); mainly those features have been discussed that are characteristic to mold-ripened sausages. It has to be mentioned that sensory characteristics may significantly differ depending on the diameter for two reasons: the metabolic pathway is different in the case of anaerobiosis (large-diameter salamis) compared to small-diameter sausages, in which anaerobiosis occurs to a lesser extent; a thinner sausage has much less time for aroma formation because of the significantly faster drying.
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