Hot Water Treatment Reduces Microbes on Blueberries

MISSISSIPPI STATE, Miss.Hot water treatment on fresh blueberries may be an effective solution to maximize microbial reduction without affecting the quality of the blueberries, according to a new study published in the Journal of Food Science.

Researchers at Mississippi State University designed the study to optimize conditions for hot water treatment (temperature, time, and antimicrobial concentration) to remove biofilm and decrease microbial load on blueberries. Scanning electron microscopy (SEM) image showed a well-developed microbial biofilm on blueberries dipped in room temperature water. The biofilm consisted of yeast and bacterial cells attached to the berry surface in the form of microcolonies, which produced exopolymer substances between or upon the cells. Berry exposure to 75 degrees C and 90 degrees C showed little to no microorganisms on the blueberry surface; however, the sensory quality (bloom/wax) of berries at those temperatures was unacceptable.

They found increasing temperature was a significant factor on reduction of aerobic plate counts (APCs) and yeast/mold counts (YMCs) while adding Boxyl® did not have significant effect on APC. Overlaid contour plots showed that treatments of 65 degrees C to 70 degrees C for 10 to 15 seconds showed maximum reductions of 1.5 and 2.0 log CFU/g on APCs and YMCs, respectively; with acceptable level of bloom/wax score on fresh blueberries.

The study showed SEM, response surface and overlaid contour plots proved successful in arriving at optima to reduce microbial counts while maintaining bloom/wax on the surface of the blueberries.