The content of nitrates, nitrites and important groups of microorganisms in Edam-type cheeses.
The objective of the research work was to determine the content of nitrates, nitrites and important groups of microorganisms in Eesti and Pühajärve cheeses, and to study their changes and interaction during the process of ripening.
The content of nitrates and nitrites of cheeses was determined according to the Nordic Standard NMKL No. 165, 2000 by using liquid chromatograph. For microbiological analyses the respective IDF and EV standard methods were applied. After pressing, the fresh Eesti cheese contained 55 mg NaNO3 /kg on the average. During ripening for 3–4 weeks, the content of nitrates decreased by 10 mg/kg, maintaining the average level of 45 mg NaNO3 /kg in fully ripened cheeses.
After pressing, the average nitrate content of fresh Pühajärve cheeses was 69.8 mg NaNO3/kg. During the average ripening period of 14 days, similarly to that of Eesti cheese the content of nitrates decreased by 10 mg/kg. Thus, the average level of nitrates 59.8 mg NaNO3 /kg (range 37–88 mg/kg) in ripe Pühajärve cheeses exceeded the EU limits (50mg/kg) by 9.8 mg/kg.
The content of nitrites in all the studied cheese batches of both Eesti and Pühajärve cheeses was <5 mg NaNO2 / kg, i.e. in compliance with the norms set by the EU.
The average total bacterial count of Eesti cheese after pressing was 480 million cfu/g, count of lactococci, lactobacilli and that of spores of anaerobic bacteria 360 million cfu/g, 3800 cfu/g and 31.4 cfu/g, respectively. In the course of ripening, both the total bacterial count and content of lactococci dropped, retaining the level of 7.8 million cfu/g and 3.1 million cfu/g, respectively. The count of lactobacilli and spores of anaerobic bacteria increased, reaching in ripened cheeses the average of 4.7 million cfu/g and 229 cfu/g, respectively.
The average total bacterial count of Pühajärve cheese after pressing was 98 million cfu/g, the count of lactococci, lactobacilli, and spores of anaerobic bacteria was 75 million cfu/, 14 thousand cfu/g and 170 cfu/g, respectively. During ripening the total bacterial count and count of lactococci decreased, ranging between 9.9 million cfu and 8.2 million cfu per gram, on the average, whereas the count of lactobacilli and spores of anaerobic bacteria increased up to 12 million and 201 cfu per gram, respectively.
Statistical analysis of the obtained data (Spearman correlation) revealed that higher activity and content of starter lactococci inhibited the development of anaerobic bacteria at the ripening stage (P<0.01). The nitrate content of cheeses also suppressed the development of anaerobic bacteria and lactobacilli, whereas it did not affect the reproduction of lactococci of starter cultures (P<0.05).
Keywords: nitrates, nitrites, total count of bacteria, lactococci, lactobacilli, spores of anaerobic bacteria, Edamtype cheese.