Biocides for dairy bacteriophage inactivation

Abstract

One of the main problems encountered in dairy fermentations is phage infection, which can alter the quality of fermented products or delay manufacturing processes. Several control strategies, such as sanitizers, thermal and chemical treatments, strain rotation, spontaneous mutant phage resistant strains and phage inhibitory media are used in dairy industries to minimize this problem. Disinfectants are used in food manufacture to eliminate microbial populations on surfaces and equipments, preventing the spread of contaminations. Besides to have a broad spectrum of activity and a rapid efficiency, a biocide for industrial hygiene must to have a low toxicological risk, to be easy to manipulate and rinse off, biodegradable, not corrosive and economical.Biocides used in dairy industry and tested against dairy bacteriophages could be classified into those used in laboratory and those used in plant. Alcohols (isopropanol and ethanol), oxidant compounds (sodium hypochlorite and potassium monopersulfate) and quaternary ammonium compounds are extensively used in laboratory, while peracids (peracetic acid, mix of peracetic / peroctanoic acids), chloride-based compounds (alkaline chloride foam and p-toluensulfonchloroamide sodium salt) and acid products (ethoxylated nonylphenol / phosphoric acid) are those preferred in dairy plants. In general, alcohols are not very effective against bacteriophages. Low concentrations of sodium hypochlorite (100 ppm ? 400 ppm) have usually a good inactivation effect on LAB phages, but for some phages higher concentration are needed (800 ? 1,200 ppm) in order to completely inactive them. Biocides with potassium monopersufate (1%), as main active agent, have excellent destruction capacity of phages and viruses in general, even though they have not been tested on LAB phages. The information about the antiseptic action of quaternary ammonium compounds against dairy bacteriophages is very limited. One report revealed that a quaternary ammonium chloride-based compound was very efficient against Lactobacillus delbrueckii phages. Peracetic acid is widely used in food industry including dairy plants because degradation products are innocuous and biodegradable. It was assayed (0.15% v/v, 40ºC) against several phages of LAB used in dairy industry and it was able to completely inactivate them in a short time. Chlorine-based compounds revealed different effectiveness against Lb. delbrueckii phages. Alkaline chloride foam produced a rapid inactivation of Lb. delbrueckii phages possibly due to its high pH value, while a p-toluensulfonchloroamide solution showed a low efficiency to destroy phage particles. A biocide composed by ethoxylated nonylphenol and phosphoric acid showed great inactivation activity against the same phages, probably due to its very low pH.