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Controlling pathogens in low-moisture foods

June 27, 2017

Colorful spices and seasoningsLow-moisture foods, such as flour and peanut butter, have made national headlines in the past few years due to foodborne illness outbreaks associated with pathogens in these products. At a session on Monday morning on “Recent Developments in Pasteurization of Low-Moisture Foods,” several presenters discussed emerging technologies for controlling pathogens in spices, seasonings, almonds, and food ingredient powders, and new research on the thermal resistance of bacteria in relation to changes in water activity.


Stephen Lombardo with McCormick & Co. discussed various technologies that can be used to treat spices and seasonings. An effective fumigant, ethylene oxide has been used since the 1930s. However, it is banned in Australia and Europe and is classified by the World Health Organization (WHO) as a Class 1 carcinogen. It is not permitted for use in organic products.


Irradiation has been around since the 1960s, according to Lombardo. It is a nonthermal treatment with minimal chemical changes. Irradiated products must be labeled. Steam is permitted for organic products but may present product quality issues such a loss of volatile oils and color.


Some emerging technologies for pasteurization of low-moisture foods include radio frequency (RF), microwave, ozone, high-pressure processing, supercritical fluid extraction, and pulsed UV light, noted Lombardo. RF provides uniform heating and has been traditionally used for drying applications. Microwaves deliver greater energy penetration than RF and faster product heating. Ozone has been used in the beverage industry for water purification and can replace chlorine in equipment sanitation applications.


When it comes to pasteurization, there is no silver bullet, declared Lombardo. A single treatment method is desirable but a combination of technologies is likely the best approach. Product attributes, consumers demands, and labeling requirements will dictate your treatment options, concluded Lombardo.


Juming Tang with Washington State Univ. explored the effects of water activity on the thermal resistance of pathogens in low-moisture foods. Research suggests that water activities of food matrices at elevated treatment temperatures (as opposed to ambient temperature) are an important parameter in determining thermal resistance of bacterial pathogens, and should be incorporated for calculations of thermal pasteurization process parameters for low-moisture foods. For example, studies have shown that elevated treatment temperatures for protein and starch-rich foods increased the thermal resistance of pathogens while elevated treatment temperatures of oil-rich foods decreased the thermal resistance of pathogens.


Tim Birmingham with the Almond Board of California presented a historical perspective on the pasteurization of almonds. Following Salmonella outbreaks in almonds 2001 and 2004, the Almond Board instituted a pasteurization program to treat almonds. Over the years, testing has shown, on average, that about 1% of almonds are contaminated with Salmonella. While good agricultural practices are a mitigation strategy, they alone are not enough. In 2007, the Almond Board chose to apply a kill step to definitively control the Salmonella pathogen.


Almond handlers must provide a minimum 4-log treatment, which requires validation by an Almond Board-approved process authority. The Almond Board has established standard protocols and guidelines for various processes and equipment, such as blanching, oil roasting, dry roasting, and steam and moist heat processes.


Fanbin Kong with the Univ. of Georgia examined the use of radio frequency in pasteurizing dried vegetables, food powders, and spices without impacting the nutritional profile of the final products. RF may be more beneficial than conventional heat treatments.