The two methods differed in washing the whole-head lettuce before or after cutting:
1) Traditional Method (TM): cutting head before washing;
2) New Method (NM): washing head before cutting.
In both cases, the washing was performed with one of the following treatments:
1) Water;
2) Chlorinated water;
3) Peroxyacetic acid in water;
4) Chlorinated water + ultrasound;
5) Peroxyacetic acid in water + ultrasound.
The experiment was conducted in a pilot-plant wash system.
From the experiment, it was found that washing the head before cutting has reduced the E. coli O157: H7 population by 0.8 log10 CFU/g more than the TM with washing after cutting. Furthermore, when washing water with the disinfectant was treated by ultrasounds, the NM has allowed a further reduction in the microbial load from 0.37 to 0.68 log10 CFU/g, reaching a total reduction of 2.43 and 2.24 log10 CFU/g using chlorine and peroxyacetic acid, respectively.
The study has showed that washing the whole head before cutting (NM) has allowed a greater reduction of the microbial load and has improved the efficacy of disinfectants compared to the TM. The researchers conclude that this new method will help the fresh-cut produce industry to increase the sanitization practices efficacy and to reduce the risks related to the microbial contamination.
Source: Palma-Salgado S., Pearlstein A.J., Luo Y., Kyung Park H., Feng H., "Whole-head washing, prior to cutting, provides sanitization advantages for fresh-cut Iceberg lettuce (Lactuca sativa L.)", 2014, International Journal of Food Microbiology, Vol. 179, pagg. 18-23. http://www.sciencedirect.com/science/article/pii/S016816051400141X