title: Inactivation of Enterobacter aerogenes in reconstituted skim milk by high- and low-frequency ultrasound.
abstract: The inactivation of Enterobacter aerogenes in skim milk using low-frequency (20kHz) and high-frequency (850kHz) ultrasonication was investigated. It was found that low-frequency acoustic cavitation resulted in lethal damage to E. aerogenes. The bacteria were more sensitive to ultrasound in water than in reconstituted skim milk having different protein concentrations. However, high-frequency ultrasound was not able to inactivate E. aerogenes in milk even when powers as high as 50W for 60min were used. This study also showed that high-frequency ultrasonication had no influence on the viscosity and particle size of skim milk, whereas low-frequency ultrasonication resulted in the decrease in viscosity and particle size of milk. The decrease in particle size is believed to be due to the breakup of the fat globules, and possibly to the cleavage of the κ-casein present at the surface of the casein micelles. Whey proteins were also found to be slightly affected by low-frequency ultrasound, with the amounts of α-lactalbumin and β-lactoglobulin slightly decreasing.
authors.affiliation: School of Chemical Sciences, The University of Auckland, Private Bag 92019, Auckland, New Zealand; School of Biological Sciences, The University of Auckland, Private Bag 92019, Auckland, New Zealand; Institute of Food and Agricultural Standardization, China National Institute of Standardization, Beijing 10088, China.
authors.forename: Shengpu
authors.initials: S
authors.lastname: Gao
authors.affiliation: School of Chemical Sciences, The University of Auckland, Private Bag 92019, Auckland, New Zealand. Electronic address: y.hemar@auckland.ac.nz.
authors.forename: Yacine
authors.initials: Y
authors.lastname: Hemar
authors.affiliation: School of Biological Sciences, The University of Auckland, Private Bag 92019, Auckland, New Zealand.
authors.forename: Gillian D
authors.initials: GD
authors.lastname: Lewis
authors.affiliation: School of Chemistry, University of Melbourne, VIC 3010, Australia; Chemistry Department, King Abdulaziz University, Jeddah, Saudi Arabia.
authors.forename: Muthupandian
authors.initials: M
authors.lastname: Ashokkumar
mesh_terms: D000818:Animals; D021902:Enterobacter aerogenes / Q000502:physiology*; D050296:Microbial Viability; D008892:Milk / Q000737:chemistry / Q000382:microbiology*; D008894:Milk Proteins / Q000032:analysis; D010316:Particle Size; D013010:Sonication; D014783:Viscosity; D014871:Water Microbiology
chemical_list: D008894:Milk Proteins
keywords: Bacteria inactivation; Enterobacter aerogenes; High-frequency; Low-frequency ultrasound; Skim milk