A bulletin for the Australian Food Industry November 1999
Contents: Genetically modified foods | International Food Safety Conference | Foodborne outbreaks in Australia | Salmonella in unpasteurised orange juice - US | Preliminary treatment of fruit for fresh juice | High pressure processing of foods | Listeriosis from fruit salad | Cold Chain Guidelines
Preliminary treatment of fruit for fresh juice
The growth of the fresh juice market in Australia has been dramatic, with the result that a major share of the market for orange juice is now occupied by juices stored under refrigeration. These juices have received little or no heat treatment (Food Safety & Hygiene March 1997).
It is standard practice to subject the whole fruit to washing and sanitizing procedures prior to juice extraction. However, the efficacy of chemical sanitizers, including the common chlorine based ones, on the surface microflora of fruits and vegetables is limited or unpredictable. (Critical Reviews in Food Science and Nutrition 1994. 34. 371).
A recent report (Journal of Food Protection, 1999. 62. 756) compares the effectiveness of hot water treatments and chemical sanitizers in reducing the microbial load on fresh citrus fruit prior to extraction. Trials were conducted on oranges contaminated by the natural microflora and fruit inoculated on the surface with Escherichia coli. Chemical sanitizers tested included 200 mg/L chlorine, 100 mg/L chlorine dioxide, 80 mg/L peroxy acetic acid and 2 percent trisodium phosphate.
Sanitizing capacity of the chemical solutions proved limited in all cases. At the stem-scar area, reduction of E. coli after eight minutes in any solution was less than 10-fold. On the remainder of the skin surface, the reduction in E. coli after the same time was usually 100 to 1000-fold.
The same organism was effectively reduced by hot water immersion treatments. As with the chemical treatments, hot water was less effective in the stem-scar area. An approximate 100,000-fold reduction in E. coli was attained by immersing inoculated fruit in water at 80°C for one minute or 70°C for two minutes. Longer heating times increased the kill but compromised the flavour of the juice subsequently extracted.
The authors conclude that a rapid hot water immersion technique may be used on fresh citrus fruit to reduce fruit surface and initial juice microbial loads without altering sensory quality.
In a related study on sanitizing of apple surfaces prior to juicing, (Journal of Food Protection, 1997.62. 778), researchers in the United States found that a hot water dip of 82.2°C for 13 seconds or a chlorine spray wash (initial concentration 160 mg/L, pH 6.5) each resulted in 100 to 1000-fold reduction in coliforms from surface inoculated fruit. None of a number of individual treatments studied achieved a 1000-fold reduction. The authors suggest that a combination of treatments may be more effective in reducing bacterial levels in apples.
They also recommend strict adherence to good manufacturing practice and sanitation practice to support a HACCP program.
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