Abstract
To prevent excessive bacterial growth in raw milk, the FAO recommends two options: either cold storage or activation of the lactoperoxidase system (LPs/HT) in milk with the addition of two chemical preservatives, hydrogen peroxide (H) and thiocyanate (T). N2 gas flushing of raw milk has shown great potential to control bacterial growth in a temperature range of 6–12°C without promoting undesired side effects. Here, the effect of N2 gas (N) was tested as a single treatment and in combination with the lactoperoxidase system (NHT) on seven raw milk samples stored at 15 or 25°C. For the ratio defined as bacterial counts from a certain treatment/counts on the corresponding control, a classical Analyse of Variance (ANOVA) was performed, followed by mean comparison with the Ryan-Einot-Gabriel-Welsch multiple range test (REGWQ). Altogether, the growth inhibition was slightly but significantly higher at 25°C than at 15°C. Except for one sample, all ratios were lower for HT than for N alone; however, these differences were not judged to be significant for five samples by the REGWQ test; in the remaining two samples, N was more effective than HT in one case and less effective in the other case. This study shows that N2 gas flushing, which inhibited bacterial growth in raw milk at 15 and 25°C for 24 and 12 h, respectively, could constitute an alternative to LPs where no cold storage facilities exist, especially as a replacement for adulterating substances.
Highlights
Despite high-tech food production systems, in so-called developed countries, approximately 30–40% of food is lost during retail, in food service or at home; the losses equal those from developing countries, which are mostly attributable to the absence of food chain infrastructure (Gustavsson et al, 2011)
The Ryan-Einot-Gabriel-Welsch (REGWQ) multiple range test, applied to the ratios, led to a significant grouping of the seven raw milk samples (M1–M7) into three categories, depending on the combined inhibitory effects caused by the lactoperoxidase system (LPs)- and N2-based treatments (Table 1)
The efficiency of the treatments to trigger bacterial inhibition appeared to be more dependent on the sample than on the applied temperature as both the highest and lowest inhibitory effects were recorded for two samples (M1 and M2) stored at 15◦C (Table 1)
Summary
Despite high-tech food production systems, in so-called developed countries, approximately 30–40% of food is lost during retail, in food service or at home; the losses equal those from developing countries, which are mostly attributable to the absence of food chain infrastructure (Gustavsson et al, 2011). Hindering Bacterial Growth in Raw Milk handling practices, the types and levels of bacteria vary greatly (Chambers, 2002; Frank and Hassan, 2002). Cooling to about 4◦C is expected to maintain the original quality of raw milk until processing and consumption; within a couple of days, so-called psychrotrophic bacteria take over and promote spoilage of the raw milk due to the production of enzymes (proteases, lipases, phospholipases). Because many of these enzymes withstand the classical heat treatments to which raw milk is subjected, the spoilage action is prolonged until the final products (Chambers, 2002). The list of adulterating substances used to preserve milk from microbial contamination or from excessive microbial growth comprises formaldehyde (formalin), soap, detergents, sodium hydroxide, benzoic acid and antibiotics
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