The reduction of ingoing amounts of nitrate and nitrite in dry fermented sausages was studied together with the impact of Debaryomyces hansenii inoculation on aroma generation. Three different formulations of sausages were manufactured: control (C), reduced in nitrate and nitrite ingoing amounts (R) and reduced R inoculated with D. hansenii (RY). Changes in physicochemical and microbiological parameters, volatile compounds and aroma were investigated at different drying times. Nitrite/nitrate reduction did not seem to affect microbial growth but affected their metabolic activity. Moreover, nitrite/nitrate reduction decreased lipid oxidation and generation of derived volatile compounds. Yeast inoculation limited lipid oxidation and prevented nitrite oxidation. Sausage aroma profile was positively affected by D. hansenii inoculation which contributed to the generation of potent aroma compounds like ethyl ester compounds and 3-methylbutanal. Long drying time impacted sausage aroma profile as well as yeast metabolism. Yeast inoculation counteracted the negative influence of nitrite/nitrate reduction due to its antioxidant capacity, aroma generation and hindered nitrite oxidation.

Slow fermented sausages with reduced ingoing amounts of sodium nitrate were manufactured: control (250 ppm), 15% (212.5 ppm) and 25% (187.5 ppm) reduction. The effect of nitrate reduction on microbiology and chemical parameters, volatile compounds and aroma production was studied. Parameters like, pH, a and colour decreased during ripening, without being affected by nitrate reduction. Lipid oxidation increased during ripening and it was higher in control sausages due to fat content. Residual nitrite was below the detection limit during the whole process and residual nitrate decreased during ripening, with higher reduction in RN25 sausages. Lactic acid bacteria, total mesophilic bacteria and yeasts and moulds increased during ripening but Gram positive cocci decreased. Microbial counts from nitrate reduced sausages at the end of the manufacturing process were not statistically different from the control sausages with nitrate. Regarding volatile compounds formation, compounds derived from amino acid degradation were increased by nitrate reduction. Aroma compounds derived from amino acid degradation and responsible for strong odours, dimethyl disulphide (toasted, garlic) and methional (cooked potato) and, to a lesser extent, compounds derived from esterase activity producing fruity odours (ethyl acetate, ethyl butanoate, ethyl‑2‑hydroxypropanoate, ethyl‑2‑methylbutanoate and ethyl‑3‑methylbutanoate) and several compounds from carbohydrate fermentation acetic acid (vinegar odour) and 2-butanone (fruity) were related to the high nitrate reduction (25%). Despite nitrate reduction up to 25% produced minor effect on microbial growth, their metabolism is regulated by nitrate content and therefore by nitrite generation affecting the production of key aroma compounds that alter the sausage aroma profile.

The ability of Debaryomyces (D.) hansenii to produce volatile sulfur compounds from sulfur amino acids and the metabolic pathway involved has been studied in seven strains from different food origins. Our results proved that L-methionine is the main precursor for sulfur compounds generation. Crucial differences in the sulfur compound profile and amino acid consumption among D. hansenii strains isolated from different food sources were observed. Strains isolated from dry pork sausages displayed the most complex sulfur compound profiles. Sulfur compounds production, such as methional, could result from chemical reactions or yeast metabolism, while, according to this study, thioester methyl thioacetate appeared to be generated by yeast metabolism. No relationship between sulfur compounds production by D. hansenii strains and the expression of genes involved in sulfur amino acids metabolism was found, except for the ATF2 gene in L1 strain for production of methyl thioacetate. Our results suggest a complex scenario during sulfur compounds production by D. hansenii.

Slow fermented sausages with reduced ingoing amounts of sodium nitrate (control, 15% and 25% reduction) were stored under vacuum up to three months. Changes in microbiology, chemical parameters and volatile compounds were studied. Residual nitrate was not affected by vacuum storage and its reduction resulted in a reduction of sausage redness. General microbial counts decreased during vacuum storage, though nitrate reduction increased the growth of total mesophilic bacteria and Gram positive cocci. Long storage time and 25% nitrate reduction affected microbial activity and sausage aroma profile. Short vacuum storage times and moderate nitrate reduction (15%) were related to compounds producing pleasant odours (3-hydroxy-2-butanone, ethyl octanoate, ethyl-3-methylbutanoate and 2,3-pentanedione) and cheesy/buttery odour (2,3-butanedione and ethyl-2-hydroxypropanoate). In contrast, 25% nitrate reduction increased compounds like heptanal (green, unpleasant odour) and those related to unpleasant odours, methanethiol (rotten odour) and methional (cooked potato).

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