This research, published in Food Microbiology, investigated the efficacy of gaseous ozone on the inactivation of Escherichia coli ATCC 25922 and NCTC 12900 strains in apple juice of a range of pH levels, using an ozone bubble column.
The pH levels investigated by the researchers based at the Dublin Institute of Technology in Ireland were 3, 3.5, 4, 4.5 and 5.
E. coli and juice
Previous research reported that E. coli O157:H7 may survive well in acidic pineapple juice at 20-25ºC and 4ºC and could also grow rapidly in fruit juices with relatively higher pH (more than 5.7) values when stored at both temperatures.
Apple juice traditionally has a pH of between 3.3 and 4.1 and therefore it has not been considered as a possible vector for foodborne pathogens. However, said the authors, enhanced acid resistance of E. coli O157:H7 has led to foodborne outbreaks in acidic fruit juices, continued the authors.
Apple juice products, report the researchers were implicated in a disease outbreak caused by E. coli 56 O157:H7 in the early 1980s in Canada, while the frequency of outbreaks has increased over the last decade, they add.
From 1995 to 2005, the authors cite 21 juice associated outbreaks being reported to the US Centers for Disease Control and Prevention (CDC), with 10 of these implicating apple juice.
“These outbreaks led the US Food and Drug administration (FDA) to issue hazard analysis and critical control points (HACCP) regulations for safe and sanitary processing of juice (USFDA, 2001). A primary performance standard is a minimum 5-log reduction of the pathogens of concern in the juice being processed (USFDA, 2001),” report the authors.
Traditionally, fruit juices are pasteurized at temperatures below 100ºC for seconds or up to a few minutes. Although this is a short heat treatment, states the article, loss of nutritional and organoleptic properties is normally associated with conventional thermal pasteurization.
The authors said that non-thermal processing technologies such as ozone represent a preferred alternative method for juice processors to produce a minimally processed food with minor quality changes.
The FDA’s approval of ozone as a direct additive to food in 2001 triggered interest in ozone applications development, and industry guidelines for apple juice and cider were published by the FDA in 2004, which the authors said highlighted gaps in the scientific knowledge.
The authors said that their objective was to determine whether direct ozone treatment can be used to inactivate E. coli in apple juice of different pH levels.
They explained that they inoculated preservative free apple juice with E. coli strains (106 CFU/mL) and treated it with ozone gas at a flow rate of 0.12L/min and ozone concentration of 0.048mg/min/mL for up to 18 minutes.
Their results show that inactivation kinetics of E. coli by ozone was affected by pH of the juice.
The ozone treatment duration required for achieving a 5-log reduction was faster (4 minutes) at the lowest pH than at the highest pH (18 minutes) studied, the researchers added.
They added that the relationship between time required to achieve 5 log reduction (t5d) and pH for both strains was described mathematically by two exponential equations.
The authors conclude that ozone treatment appears to be an effective process for reducing bacteria in apple juice and the required applied treatment for producing a safe apple juice is dependant on its acidity level.
However, further studies are warranted to determine the effect of ozone on sensory and nutritional quality retention for apple juice, they stress.
Source: Food Microbiology
Published online ahead of print: doi:10.1016/j.fm.2010.05.002
Title: Inactivation of Escherichia coli by ozone treatment of apple juice at different pH levels
Authors: Patil, S., Valdramidis, V.P., Cullen, P.J., Frias, J., Bourke, P