3.4.1. O2 and CO2

Table 3 summarizes the monitoring of the O2 contents and production of CO2 in the lettuce bags over the 10 days of cold storage. While oxygen was practically kept constant around 19% for the reference samples treated with water, for shredded lettuce sanitized with fermented whey, a reduction from 19 to 18% on the first day was observed, and then it remained practically constant. With chlorine, the reduction continued until the third day to values around 16%.

**Table 3.** Oxygen and carbon dioxide measurements for packed sanitized shredded lettuce with different sanitizer treatments, over 10 days in cold storage.


For the CO2 production, more pronounced differences are shown, becoming apparent that the bags treated with chlorine showed a higher reduction in O2 levels and a larger production of CO2 compared to the reference and whey treated bags. Consumption of O2 and production of CO2 could come from the respiration of the lettuce leaves and AM, as well as further production of CO2 from anaerobic fermenting microorganisms. Although results suggest that water- and whey-treated samples have lower biological activity, the higher changes detected in the samples treated with chlorine could be due to the response of the lettuce cell leaves to the chemical stress of the chlorinated compounds.
