The Minnesota Dept. of Health data showed that levels of con- tamination of retail poultry remain high despite interventions made at the processing plant (Smith and others 1999). Stern and Line (1992) detected Campylobacter spp. in 98% of retail-pack- aged broilers sampled from grocery stores. Another study by Will- is and Murray (1997) found 69% (229/330) of raw commercial broilers were positive for C. jejuni. A study from New Zealand showed that Campylobacter could be isolated from 63% of chick- en carcasses at retail outlets (Bongkot 1997).
Kinde and others (1983) indicated that the presence of Campy- lobacter in market broilers diminishes over time during refrigerat- ed storage. Blankenship and Craven (1982) detected viable strains of C. jejuni stored in sterile ground chicken meat. The growth and extended survival observed at 37 °C with ambient atmosphere in- cubation suggest that the test strains were readily able to locate fa- vorable microaerophilic conditions for growth within the ground meat after surface inoculation.
A study in the United Kingdom estimated a population range of Campylobacter organisms on the surface of fresh chicken car- casses from 3 to 6 log10 CFU per chicken (Friedman and others 2000). Kanenaka (2000) conducted a survey from 2 large retail markets in Hawaii to characterize strains of C. jejuni isolated from clinical and poultry samples. She found that samples collected at Oahu were 83.3% positive for C. jejuni on whole chicken sam- ples and 91.7% positive on chicken parts, whereas mainland samples were 93.8% positive for whole chickens, 35.7% for chicken parts, and 56.8% for the total number of C. jejuni posi-
Chlorine. Chlorine has been used in poultry processing for more than 40 y to reduce spoilage bacteria, control the spread of pathogens, and prevent build-up of microorganisms on working surfaces and equipment such as chill tanks (Bailey and others 1986). When sodium hypochlorite is injected into water, it forms hypochlorous acid, the form of chlorine responsible for its antimi- crobial properties (Gavin and Weddig 1995). The addition of chlorine gas to processing water is easily controlled. However, most waters contain organic impurities that will react with the ini- tial amount of added chlorine reducing the amount of available chlorine to form hypochlorous acid. Chlorine added to water will continue to react and be reduced by these impurities until the im- purities have been completely oxidized. The amount of chlorine required for this purpose is known as the chlorine demand of the water.
Any chlorine present over the chlorine demand of the water ex- ists as combined residual chlorine or free residual chlorine. The concentration of chlorine where free residual chlorine exists is called the break point. Chlorine combines loosely with nitroge- nous (organic) matter to form chloramines and other chloronitro- gen compounds. These are forms of combined residual chlorine and exhibit relatively weak germicidal properties (Gavin and Weddig 1995).
The rate at which bacteria are killed is proportional to the con- centration of free residual chlorine. The pH of the water after the addition of chlorine determines how fast the microorganisms will be killed. The lower the pH (below 7.5), the faster the microorgan- isms are killed, and as the pH increases, the effectiveness of the chlorine decreases (Gavin and Weddig 1995). Many present-day chill tank water treatment programs operate with the cooling water pH in the range of 8.0 to 8.5 or higher. As a result, oxidizing mi- crobiocides such as chlorine are less effective. At a pH of 6.0, chlorine hydrolyzes almost completely to hypochlorous acid (HOCl), which is the most effective form of chlorine for microbio- logical control; however, at a pH of 8.5, only 8% goes to HOCl, thus requiring a much higher dosage of chlorine to control bacte- ria. Contamination of processing equipment is progressively re- duced by increasing the chlorine concentration to 70 mg/L at pH 6.5 (Bailey and others 1986). Chlorine is active against a wide range of microorganisms, with various degrees of susceptibility. At a pH of 6.0, 0.1 mg/L of free available chlorine killed 99% of C. jejuni (Blaser and others 1986). The necessary contact time varied between 5 min and 15 min at 25 °C.
Under conditions of commercial processing, not all studies in- volving chlorine have shown a reduction in carcass contamina- tion. Mead and others (1975) showed that neither the levels of contamination of bacteria nor the occurrence of cross-contamina- tion were reduced by spray-washing in chlorinated water after evisceration. Sanders and Blackshear (1971) showed little effect of chlorine in the final carcass wash unless at least 40 mg/L were used. Washing carcasses post-chilled with water containing 50 mg/L of chlorine did not reduce the proportion of Salmonella- positive samples (Kotula and others 1967). These studies empha- sized the importance of adequate contact time, which is not usu- ally achieved in a washing operation.
A study by Waldroup and others (1993) examined the modifi- cation of broiler processing procedures to include 20 ppm of chlorine through the processing line and include 1 to 5 ppm of free chlorine in the chill tank overflow. These concentrations re- sulted in a 0.2 log10 to 0.6 log10 reduction in aerobes, 0.0 log10 to 0.3 log10 reduction in coliforms, and 0.0 log10 to 0.4 log10 reduc- tion in E. coli.
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