Meat Fermentation as a Spontaneous Process As for all raw and salted meat products, the endogenous a
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As for all raw and salted meat products, the endogenous activity of meat enzymes, in particular proteases and lipases, contributes to the aging and ripening of the product being subjected to drying. In contrast to dry-salted hams, the original production of dry-fermented sausages involved a desirable and spontaneous acidification of the meat matrix that serves as an extra preservation hurdle in addition to the primary salting and drying, mostly because a comminuted mixture of meat trimmings and fat particles is less stable than whole muscle. Fermentative acidification to pH values that are usually situated between 4.8 and 5.2 inhibits the growth of undesirable microorganisms that are present on the raw meat and denatures the salt-solubilized protein fractions to a characteristic sliceable and gel-like texture.
Under appropriate temperature conditions (e.g., between 18 and 28 °C), the combination of curing salt and anaerobic conditions that are prevailing in the sausage casings strongly select for specific and desirable microorganisms. As a result, the initial microbial species diversity that is present on the raw materials is narrowed down within a couple of days to a few persistent microbial groups. Largely dominating bacteria are certain mesophilic species of Lactobacillus, in particular Lactobacillus sakei and, albeit to a lesser extent, Lactobacillus curvatus or Lactobacillus plantarum. Other lactic acid bacteria that may occasionally be present but do not or only marginally affect the production process of most traditional, spontaneously fermented sausages include enterococci, lactococci, pediococci, and leuconostocs. In addition to the dominance of meat-associated lactobacilli, a considerable subdominant population consists of catalase-positive cocci, mostly coagulase-negative staphylococci and sometimes kocuriae. Depending on the applied raw materials and processing conditions, different species of catalase-positive cocci may be encountered during spontaneous meat fermentations. In most cases, Staphylococcus equorum, S. saprophyticus, and/or S. xylosus are prevailing. Yet, minor levels of, for instance, S. carnosus, S. sciuri, S. simulans. S. succinus, and S. warneri are not uncommon. Whereas lactic acid bacteria chiefly cause acidification through lactic acid production, catalase-positive cocci prevent oxidative deterioration, generate stable nitrosomyoglobin pigments via nitrate reductase activity, and contribute to an attractive aroma via amino acid and fatty acid conversions. These precursor amino acids and fatty acids are liberated via protease, peptidase, and lipase activities by muscle enzymes, although minor contributions by bacteria have also been described. Flavor maturation of fermented sausages thus correlates with the amounts of branched-chain aldehydes and alcohols from the conversion of branched-chain amino acids and branched-chain and straight-chain methyl ketones derived from microbial β-oxidation of fatty acids.
Besides bacteria, yeasts and molds can be present in some sausage types. Yeasts, such as Debaryomyces hansenii, are probably of a rather minor importance in flavor development but could accentuate certain aromas. In contrast, molds are crucial elements in the elaboration of south European fermented sausages where they develop as a desirable outside layer on the product surface after fermentation, during which they generate additional aroma and contribute to color stabilization through catalase activity, oxygen consumption, and shelter against light. The mycobiota of fermented sausage is diverse, but Penicillium is usually the predominant genus (e.g., Penicillium nalgiovense). In traditional northern European fermented sausages, molds are mostly undesirable. This is due to the rather humid climate conditions in these regions, which are unsuitable for proper, controlled, and safe mold development. As a consequence, such products are frequently smoked after fermentation, as an empirical manner to add additional preservative action and to prevent the unbalanced growth of detrimental molds. Meanwhile, the smoked flavor became a desirable sensory attribute for northern European consumers. In addition, northern European varieties of fermented sausages are generally more acidified to obtain enhanced microbial inhibition, since they are usually more moist and, hence, more vulnerable to hazards than their drier southern counterparts.