Microflora of biofilm on Algerian dairy processing lines: An approach to improve microbial quality of pasteurized milk

Abstract

, 2.5 × 10 5 and 9.7 × 10 7 cfu/cm 2 , respectively, in the different units. Phenotypic identification of isolates revealed predominance of Gram-positive bacilli belonging to Bacillus and notably the Bacillus cereus group, at maximal levels of 72 and 21% respectively. The other Gram-positive microflora included Staphylococcus (30%) and Micrococcus (10%). In contrast, the incidence of the Gram-negative bacteria was relatively low. Two genera, identified as Pseudomonas (9%) and Enterobacter (6%), were found only in two dairies. Three dairies were Gram-negative bacteria-free. That should be the result of common contamination sources or highly environmental selective pressure. Further studies have to address these hypotheses. Treatment of experimental Bacillus cereus sensu lato strains biofilms with a 50, 100 and 150 ppm of quaternary ammonium disinfectant, showed a significant resistance of biofilms to this product even after long exposure time (15 min). This study emphasized the importance of aerobic spore-forming bacteria in dairy-processing equipment as they are able to built recalcitrant biofilms on the inside equipment surfaces with subsequent resistance to conventional CIP system and potential transfer to pasteurized milk. Therefore, in order to reduce the contamination levels of spore-forming bacteria and improve the quality and shelf life of the product, these dairies have, besides improvement in the hygienic status of the plant equipments, also to monitor either the pasteurization process or the contamination from raw material (that is, milk powder).

Formation of biofilms on dairy equipment and the influence of disinfectants on them

“…A presence of microbial biofilms on the surfaces of dairy equipment is regarded as a danger to the health of consumers of products, because the biofilms can contain, in addition to the saprophytic, the pathogenic micro-organisms [1,9,34,35]. It is also obvious that bacteria from the biofilms penetrate dairy products and reduce the time of their shelf life [32,33].…”

“…Studies show that the microbial biofilms formed on the surfaces of dairy equipment negatively impact safety of the finished product and constitute a danger to the health of people since the composition of biofilms, in addition to saprophytic microflora, may contain pathogenic microorganisms [1,9,32]. The biofilms formed by E. coli, Listeria spp., Yersinia enterocolitica, S. aureus, Salmonella spp., Pseudomonas sрp., Bacillus cereus and others were detected on dairy equipment [33][34][35][36].…”

“…Even though there is a significant quantity of commercially available means for sanitary processing of dairy equipment, not all of them are sufficiently effective [1,9]. Recent research [40][41][42] indicate that disinfectants and antibiotics do not always act on bacteria in biofilms.…”

“…The key task of dairy industry is the production of a sufficient amount of quality and safe dairy products. The main factor that reduces the terms of storage and safety of dairy products is the micro-organisms [1][2][3]. Quantitative and qualitative composition of microflora of the products depends on the compliance with hygienic conditions of production and effective sanitation of technological equipment [4][5][6].…”

A Highlight for Non-Escherichia coli and Non-Salmonella sp. Enterobacteriaceae in Dairy Foods Contamination

“…Notably, these bacteria can be resistant to cleaning products, as described by Malek et al (2012), who collected samples from farms producing pasteurized milk and skimmed milk powder in Algeria. The entire production line was constantly subjected to sanitization using ammonia- and peracetic acid-based products.…”