20-32°C, 2-5 days
20-24''C, 2-3 days
15 °C, 2-3 weeks
10-15°C, 3-6 weeks
versus 20-21 mmol/100 g DM in northern sausages (6), and 9 mg/g in French sausages versus 15 mg/g in German sausages (4). Acetate contents are also lower in southern sausages (4, 6). The pH values also depend on the ammonia content. High pH in southern products is associated with values between 10 and 14 mg N/g Nitrogen total, and low pH in northern products with smaller values (3-6 mg N/g Nitrogen total) (6).
Acidification and ammonia content largely depend on the microbial flora. Variation in the microflora during sausage manufacturing depends on several factors such as the initial contamination but also on the technology used (7). In salami manufactured according to the southern technology (addition of nitrate, low level of sugar, and fermentation at 18 °C), an increase of Lactobacillus and coccal gram-positive bacteria is noticed during fermentation. During ripening, the Pseudomonas population disappears after 7 days and the level of Enterobacteriaceae decreases. In salami manufactured according to the northern technology (addition of nitrite, high level of sugar, and fermentation at 22-24°C for 5 or 6 days), coccal gram-positive bacteria (Staphylococcus, Kocuria) in the periphery of salami and Lactobacillus in the whole salami grow during fermentation. Enterobacteriaceae and Pseudomonas populations decline very quickly and are totally inhibited within 7 days. Both processes affect the growth of populations of coccal grampositive bacteria, which is higher in less acid products. The level of staphylococci in German salami often remains at the level of inoculation or decline during the process, whereas an increase of 1 to 1.5 log is noticed in French sausages (4). The lack of growth or inhibition of the coccal gram-positive bacteria in the northern technology can be explained by their sensitivity to acidity and anaerobiosis (8). Similarly, the inhibition of undesirable flora (Enterobacteriaceae and psychrotrophs) is noticed from the early stages of processing in nitrite-made sausages compared to nitrate-made sausages (9).
Both northern and southern processes use starter cultures for manufacturing sausages. The bacteria used as starters are inoculated at a rate of 106 viable germs per gram of mixture (10). Bacterial starters are generally made up of a balanced mixture of lactic acid bacteria (Lactobacillus, Pediococcus) and coccal gram-positive bacteria (Staphylococcus, Kocuria) (5). But some differences are noticed between the northern and the southern technology. In southern countries, small traditional producers rely on their own ''house'' flora and thus do not inoculate their sausages. In Italy, some producers use pure cultures of staphylococci to avoid acidification. In Spain, the backslopping technique (i.e., addition of some meat from a previous successful fermentation) is very common in the production of chorizo. In northern countries, rapid acidification is searched for, so starter producers select lactic acid bacteria that acidify very quickly.
In Mediterranean countries, yeasts (Debaryomyces, Candida) and molds (Penicillium) are also inoculated onto the surface in order to make up the covering flora of dry sausages. In northern countries, smoking controls the growth of the external flora.
Southern and northern products are characterized by specific flavors and safety risks; therefore producers at the industrial scale are obviously interested in understanding mechanisms that control safety and flavor development in both types.
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