Abstract
High intensity ultrasound (HIU) continues to be researched as a nonthermal inactivation technology of appeal to food manufacturers. The advantages of HIU include maintenance of product quality, freshness, product homogenization, along with simultaneous inactivation of pathogens. Besides, it is simple, relatively inexpensive, and easily adaptable to most processing environments. This study investigated the effect of HIU for Salmonella Enteritidis inactivation in culture and liquid whole eggs (LWEs) to decrease egg-associated outbreaks. Overnight S. Enteritidis cultures and spiked LWE (both at 8 log CFU/mL) were treated with 20-kHz HIU for 0, 1, 5, 10, and 30min (n=6) in a temperature-controlled system, not to exceed 20 °C, and replicated thrice. At each time point, samples were enumerated on XLT4 agar and morphologically analyzed using scanning electron microscopy, with measurements of color and rheological properties. Our results revealed significant reduction of healthy S. Enteritidis cells up to 3.6log CFU/mL and 2.3log CFU/25mL after HIU treatment of merely 10min of overnight culture and 30min in LWE, respectively (P < 0.05). After 5 and 10-min HIU treatment, significant reduction of 1.4-log CFU/25mL healthy S. Enteritidis in LWE was obtained (P<0.05). Even at 1-min exposure time, HIU showed significant 1.9 log CFU/mL reduction of cultures (P<0.05); however, no log-reduction was observed in LWE after 1 min. Scanning electron micrographs showed increased cell structural damage using longer HIU exposure. For product color changes, lower redness and yellowness of LWE were observed visually and instrumentally after 5-min HIU treatment (P<0.05). The rheological properties of LWE measured at 0 to 200s-1 shear rate, showed that shear stress of HIU-treated LWEs decreased after 5-min HIU exposure, but increased after 30-min treatment. This study demonstrated that HIU shows promise for rapid Salmonella control in LWE and other liquid foods, as an alternative inactivation method for use in hurdle approaches.
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