Potential of nitrogen gas (N2) to control psychrotrophs and mesophiles in raw milk

Abstract

Pure N(2) gas was introduced in the headspace of test bottles containing raw milk that were then stored at either 6.0, 7.0, or 12.0 degrees C. Treatment with N(2) significantly reduced the growth of total bacteria, and the growth of bacterial subgroups such as psychrotrophs, enterobacteria, protease- and lipase-producing bacteria, and Listeria spp, and completely excluded Bacillus cereus growth on MYP plates. The inhibitory effect was maximal at 6.0 degrees C, and bacterial growth could be halted at this temperature for 11 days. At 12.0 degrees C, N(2) was able to inhibit growth during the first 48 h. No alarming or undesirable effects, such as the excessive growth of anaerobes or lactobacilli, were observed during the course of the study. The same treatments also halted the growth of one bacterial isolate in pure culture that expressed multiresistance to antibiotics. The continuous flushing of raw milk with pure N(2) gas in a so-called open system that allows gas exchanges with the environment positively impacted the microbiological quality of the raw milk at a temperature range of 6.0-12.0 degrees C. This procedure should therefore be considered as a possible complementary method to refrigeration in controlling bacterial growth and the spoilage potential of both psychrotrophs and mesophiles in raw milk.

N2 Gas Flushing Limits the Rise of Antibiotic-Resistant Bacteria in Bovine Raw Milk during Cold Storage

“…After the raw milk arrived, 100 ml of each sample were added to 250 ml sterile bottles and placed on a multi-place magnetic stirrer (Variomag, Oberschleißheim, Germany). The bottles were partially immersed in a refrigerated water bath (MGW Lauda MS/2), which allowed, with the help of an immersion thermostat, a constant temperature to be maintained (Munsch-Alatossava et al, 2010a). The raw milk samples were mixed continuously at 220 rpm and kept at 6 ± 0.1°C for 7 days.…”

“…The thiocyanate anion SCN − took the form of NaSCN (Sigma-Aldrich, Steinheim, Germany) and a 1% (w/v) stock solution was sterile-filtered and cold- stored until use. The N 2 gas (AGA Ltd, Riihimäki, Finland) was 99.999% pure and the flow rate for the continuous N 2 gas flushing treatments (N) was adjusted to 120 ml/min (Munsch-Alatossava et al, 2010a). The description of the conditions (which were applied to every sample) is as follows: C, control; HT, H 2 O 2 + SCN − (for the activated lactoperoxidase system); and N, N 2 gas flushing.…”

“…Two studies examined the use of N 2 gas to prevent bacterial growth in raw milk that was kept in a “closed system” (Murray et al, 1983; Dechemi et al, 2005). By considering an “open system,” both culture-dependent investigations and DNA barcoding studies revealed that no pathogen, no spoilage bacteria or any anaerobe was clearly advantaged by the N 2 gas flushing treatment when it was applied to raw milk at the laboratory scale, despite the fact that 10 4 - fold lower bacterial counts differentiated the N 2 -flushed from non-flushed cold-stored raw milk samples (Munsch-Alatossava et al, 2010a,b; Gschwendtner et al, 2016). Recently, the efficiency of N 2 gas flushing and the activated lactoperoxidase system in controlling bacterial growth in raw milk samples stored at 15 and 25°C was compared; overall, the gas treatment showed a time-limited effect that was comparable to the effect of the activated lactoperoxidase system (Munsch-Alatossava et al, 2016).…”

Trends of Antibiotic Resistance (AR) in Mesophilic and Psychrotrophic Bacterial Populations During Cold Storage of Raw Milk, Produced by Organic and Conventional Farming Systems

“…Six bottles were placed on a multi-place magnetic stirrer (Variomag) and partially immersed in a refrigerated water bath (MGW Lauda MS/2) which allowed, with help of an immersion thermostat, a constant temperature to be maintained (modified from Munsch-Alatossava et al, 2010). The raw milk samples were continuously mixed at 220 rpm and kept at 4± 0.1 °C for 4 days.…”

Inhibition of Growth of Pathogenic Bacteria in Raw Milk by Legume Protein Esters

“…These treatments may result in potential hazards and interactions with milk constituents. Nitrogen gas was also proposed to control psychrotrophs and mesophiles in raw milk (27), but this approach requires special equipment and facilities. The efficacy of certain lactic acid bacteria to counteract the proliferation of pathogenic E. coli and Salmonella Enteritidis in raw milk was also investigated (26).…”