4. Discussion
In our study,microwave heating at high power level for 40 s reduced
the surface Salmonella contamination by more than 1.6 log, and
microwave heating at medium power level for 50 s achieved greater
than 1.7 log reduction of Salmonella enterica, but both of them changed
the texture quality of tomato. Microwave heating at medium power
level for 40 s might be the best treatment, not only because it could
reduce Salmonella by more than 1.45 log, but also did not change the
texture quality of tomato. From our results, the microwave heating
increased surface temperatures on the tomatoes, and average heating
rates were 0.76 °C /s and 0.62 °C /s for high and medium power level,
respectively, which might contribute to damage of texture quality of
tomatoeswhen tomatoeswere heated at high power level for 40 s or at
medium power level for 50 s.
To our best knowledge, there was no report on Salmonella enterica
survival on grape tomatoes during householdmicrowave heating. Based
on our results, it might be helpful for consumers to decrease the risk of
Salmonella contamination on grape tomatoes by using household
microwave heating for short-time (around 40 s) depending on the
power level. The tomatoes should be immersed inside water during the
microwave heating to minimize the negative impacts on their sensory
quality and nutritive values.
The survival of pathogens such as Salmonella spp. in food heated by
microwave ovens,might be attributed to the uneven distribution of heat
on food product surface cooked in microwave oven (Heddleson et al.,
1996; Schnepf and Barbeau, 1989). Temperature uniformity might be
improved by using wave stirrers or turntables. Also, power level is a
source of variability between microwave ovens, because the pulsing
time for a given power level may vary with microwave oven type
(Schiffman, 1990).
In conclusion, microwave heating had some efficacy on reducing
Salmonella enterica depending on heating conditions, such as time and
power level. Bacteria destruction was more evident at high power
level than at medium power level. Among the heating treatments
resulting N1.5 log reduction of Salmonella enterica, heating at medium
power for 40 s was the only treatment that did not change the overall
quality including texture quality of grape tomato. Therefore, it might
be a potentially convenient way for consumers to reduce Salmonella
population on grape tomatoes by heating the water immersed
tomatoes at medium power level for 40 s in a household microwave
oven (700 W).