Hydrogen Peroxide Effects on the Quality of Chilled Carrot

Abstract

To determine the bacteriolytic effect of H2O2, three microorganisms, isolated from carrots (MC) as well as Escherichia coli, Erwinia carotovora, Salmonella CECT 443 and S. typhimurium, were prepared in 0.1% peptone water (PW) containing 0, 0.5, 1, 2 and 5% H2O2 to obtain suspensions of about 108 and 1010 cfu mL-1. After 4 h of chilled exposure at 0.5% H2O2, the number of viable cells in bacterial suspensions was reduced by 1 logarithmic unit, which represents a 90% reduction. Since viable cells were not detected in the decimal dilutions analyzed (3rd-5th) when 2 and 5% H2O2 were used, the chemical at these concentrations seems to kill >99% of the bacterial population after the first 4h of exposure.

To check if cell lyses is involved in the inhibitory effect of H2O2, cells of MC and Salmonella were incubated for 24 h at 4ºC, 30ºC and 37ºC in PW containing 2% of the chemical. Significant changes in optical density (O.D.) were not observed in these conditions, which suggests that the bactericidal action of the H2O2 does not involve cell lyses.

The effect of treatment with 1% and 2% H2O2 , on the quality of carrots stored at +0.5ºC, were observed with respect to color ( external, internal and puree) , soluble solids , total solids , pH, titratable acidity , total phenolics and carotenoid total ( µg β-carotene g-1 ).

Polymeric films used in the packaging were of two different types: oriented 35µm polypropylene (OPP), of high permeability (ca. 240,000 ml O2 m2 day-1 atm-1 at 25ºC) and polyethylene (PE) of 30µm thickness. H2O2 (>0.5 % for 4 hours) is capable of achieving >90% reduction of viable cells in suspension of microorganisms isolated from carrot, and consequently it seems to be bactericidal, while cell lyses does not appear to be involved in the inhibitory effect. Highest quality corresponds to the sliced carrot treated with 2%H2O2 , and those packed in OPP film gave the best natural color .