Impact of Lettuce Washing Methods on the Efficiency of Internal Escherichia coli Removal and Quality Changes during Storage
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Abstract:
Vacuum cooling often results in the penetration of pathogenic bacteria into the stomata of vegetables, hindering their removal using conventional washing methods. A control group (CK) was washed with a cleaning agent alone, whereas experimental groups were subjected to ultrasonic (US) or vacuum-ultrasonic (VC-US) treatment combined with washing with a leaning agent to eliminate Escherichia coli that penetrated the stomata of lettuce after vacuum cooling. The E. coli removal efficiency of these treatments and their impact on lettuce quality during storage were evaluated via measuring bacterial colony counts and key physicochemical indicators before and after treatment. The number of E. coli in the lettuce decreased from 4.33 to 1.97 log CFU/cm² after VC-US treatment, indicating higher removal efficiency than that of the US and CK groups (to 3.03 and 2.85 log CFU/cm², respectively; P<0.05). After two days of storage, the VC-US group had a significantly higher L* value but considerably lower a* and b* values than the CK and US groups (P<0.05). The chlorophyll and vitamin C contents in the VC-US group were slightly, but not significantly, lower than those in the CK and US groups, (P>0.05). Additionally, the weight loss rate in the VC-US group (-18.56%) was significantly lower than those in the CK (0.79%) and US (0.16%) groups (P<0.05). In conclusion, VC-US treatment, as a composite method, effectively removes E. coli from within lettuce and does not significant affect lettuce quality. This study provides a theoretical basis and practical insights for the removal of pathogenic bacteria from within vegetables.
