Abstract
Bacteriophages can cause great economic losses due to fermentation failure in dairy plants. Hence, physical and chemical treatments of raw material and/or equipment are mandatory to maintain phage levels as low as possible. Regarding thermal treatments used to kill pathogenic bacteria or achieve longer shelf-life of dairy products, neither low temperature long time nor high temperature short time pasteurization were able to inactivate most lactic acid bacteria (LAB) phages. Even though most phages did not survive 90°C for 2 min, there were some that resisted 90°C for more than 15 min (conditions suggested by the International Dairy Federation, for complete phage destruction). Among biocides tested, ethanol showed variable effectiveness in phage inactivation, since only phages infecting dairy cocci and Lactobacillus helveticus were reasonably inactivated by this alcohol, whereas isopropanol was in all cases highly ineffective. In turn, peracetic acid has consistently proved to be very fast and efficient to inactivate dairy phages, whereas efficiency of sodium hypochlorite was variable, even among different phages infecting the same LAB species. Both alkaline chloride foam and ethoxylated non-ylphenol with phosphoric acid were remarkably efficient, trait probably related to their highly alkaline or acidic pH values in solution, respectively. Photocatalysis using UV light and TiO2 has been recently reported as a feasible option to industrially inactivate phages infecting diverse LAB species. Processes involving high pressure were barely used for phage inactivation, but until now most studied phages revealed high resistance to these treatments. To conclude, and given the great phage diversity found on dairies, it is always advisable to combine different anti-phage treatments (biocides, heat, high pressure, photocatalysis), rather than using them separately at extreme conditions.
Highlights
Reviewed by: Lorenza Putignani, Children’s Hospital and Research Institute Bambino Gesù Hospital, Italy Anderson De Souza Sant’Ana, University of São Paulo, Brazil Min-Tze Liong, Universiti Sains Malaysia, Malaysia
Ethanol showed variable effectiveness in phage inactivation, since only phages infecting dairy cocci and Lactobacillus helveticus were reasonably inactivated by this alcohol, whereas isopropanol was in all cases highly ineffective
Many works have studied thermal resistance of lactic acid bacteriophages, especially focusing on temperatures traditionally used to sanitize the milk in the dairy industry (63, 72, and 90 ̊C), and on conditions recommended by the International Dairy Federation (IDF; 90 ̊C for 15 min) to guarantee complete phage inactivation (Svensson and Christiansson, 1991)
Summary
Capra et al (2006) Capra et al (2009a) Capra et al (2004) Binetti and Reinheimer (2000). To phage Ib3, destruction of total viral populations for the above mentioned heat-resistant phages was generally not achieved at this temperature, since detectable viable phage particles were found even after 45 min of treatment, which is a much longer period than that normally applied in the dairy industry for milk sanitization (Quiberoni et al, 1999, 2003; Binetti and Reinheimer, 2000; Suárez and Reinheimer, 2002; Briggiler Marcó et al, 2009). The protocol used for microbiological detection of phages in dairy samples includes a heat treatment at 90 ̊C for 15 min of control samples to be tested for non-phage inhibiting agents (Svensson and Christiansson, 1991) This standard protocol might not be appropriate for inactivating high heat-resistant phages (Atamer et al, 2009). 021-4 021-5 0BJ 031-D CYM 001 046 QF12 QP4 BYM YAB Ib3 LL-H Cb1/204 Cb1/342 CNRZ 832-B1 CNRZ 0241 hv ATCC 15807-B1 ATCC 8014-B1 ATCC 8014-B2 FAGK1 FAGK2 PL-1 J-1 MLC-A iLp84 iLp1308
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