U.S. Food & Drug Administration Center for Food Safety & Applied Nutrition APPLE CIDER FOOD SAFETY CONTROL WORKSHOP July 15-16, 1999

Background

Within the past 10 years, fresh, unpasteurized apple cider has been responsible for foodborne illness outbreaks across the United States and Canada. The microorganism responsible for these outbreaks is Escherichia coli O157:H7. In an attempt to curtail the incidence of foodborne illness associated with the consumption of fresh apple cider, recommendations for processing apple cider prior to consumption were made. Unfortunately, the sole processing technique available prior to one year ago was thermal pasteurization. This single processing alternative restricted a large proportion of apple cider producers by the cost, space restrictions, taste defects or complexity of operation. In response to the processing limitations, alternative processes such as ultraviolet (UV) light were investigated.

Extensive research on the application of ultraviolet light yielded a production model based on ultraviolet light for the treatment of apple cider. The production model is essentially ultraviolet lamps exposing a thin film of apple cider. The flow rate is controlled by a computer interface that reads the ultraviolet penetration every 20 milliseconds using ultraviolet sensors. Depending on the UV intensity at that point in time, the computer controls the pump automatically to increase or decrease the flow rate to achieve a 5-log reduction for the cider passing through the unit at that point in time.

Apple cider composed of different varietals, solids content and darkness were used to test the CiderSure unit. Changes in all these variables are compensated for by the unit and ensures a 5-log or greater reduction in the pertinent pathogen, E. coli O157:H7. A production unit of the CiderSure was used to test the efficacy against three different strains of E. coli O157:H7 which included ATCC 43889, 933 and 43895. All three pathogenic strains were inoculated into various blends and variations of apple cider and passed through the CiderSure unit with numerous repetitions. All three strains of E. coli O157:H7 showed the same UV sensitivity/resistance with no statistical difference between repetitions or strains.

A nonpathogenic surrogate microorganism, E. coli ATCC 25922, was selected with the same UV sensitivity/resistance as the three pathogenic strains of E. coli O157:H7. Numerous strains of microorganisms were tested and it was observed that there are differences in the response to ultraviolet light. Since ATCC 25922 showed almost identical UV sensitivity, it was used as the surrogate microorganism to test additional productions units and for the validation of each unit to ensure its compliance with the required 5-log reduction.

All of the testing up until this point was carried out in a microbiology laboratory at Cornell University to prevent the potential environmental contamination. The FDA/USDA test cider mill in the Apple Hill region allowed for the examination of the efficacy of the CiderSure unit in a typical cider mill production setting. With the cooperation of various federal and state government agencies, Cornell University and FPE Inc., the CiderSure model was tested for its effectiveness in an apple cider production setting.

The following are the results obtained from the testing carried out at Cornell University and in the FDA/USDA test cider mill in Placerville, California.

Methodology

Apple cider was prepared from a variety of blends of different apple varietals, as well as different degrees of filtration.

The various samples of apple cider was inoculated with an overnight culture of E. coli ATCC 25922 grown in Tryptic Soy Broth (TSB). The inoculated apple cider was then passed through the CiderSure unit. Samples for microbiological analysis was taken before and after processing.

For all the microbiological analysis, the samples were serially diluted in 0.1% peptone and plated onto appropriate media. E. coli ATCC 25922 was enumerated on tryptic soy agar and incubated at 35°C overnight. The plates were counted the following day. Total plate count was performed using plate count agar and incubating at 22° C for 2 days. Yeast and mold were enumerated using acidified Potatoe Dextrose Agar (pH 3.5) or YM petri-film and incubated for 4 days before enumerating.

TABLE 1

Ultraviolet light eradication of E. coli O157:H7 strains in apple cider.

Target Microorganism	Single pass log number reduction
Escherichia coli 0157:H7 ATCC 43889	6.12± 0.36
Escherichia coli 0157:H7 ATCC 43895	5.83± 0.11
Escherichia coli 0157:H7 ATCC 933	5.87± 0.11

The results from the test cider mill confirmed the existing data that has been obtained from extensive laboratory research at Cornell University. The large volume inoculated apple cider runs reconfirmed the ability to achieve a 5-log reduction of E. coli ATCC 25922 with the CiderSure 3500. The surrogate microorganism E. coli ATCC 25922 showed a greater than 5-log reduction consistently throughout the processing run.

The CiderSure UV unit is programmed to automatically compensate for differences that may exist in apple ciders such as total solids and color. Increased solid content and darker color due to extended storage of apples decreases the UV penetration through the apple cider but the calibration curve programmed into the computer interface of the unit ensures that all the apple cider achieves the appropriate UV exposure to achieve a 5-log reduction.

The original work was performed in a contained biosafety microbiology laboratory at Cornell University using E. coli O157:H7 strains. The identification of a surrogate organism allows for each of the CiderSure units to be validated for its ability to achieve a 5-log reduction in the surrogate organism prior to being placed in an actual apple cider mill. The experiments conducted in the FDA/USDA test cider mill allowed for the confirmation that the CiderSure UV units were capable of achieving a 5-log reduction in the surrogate microorganism in a typical apple cider mill and production setting. Since the FDA/USDA apple cider mill will eventually be returned to a commercial production cider mill, it was not possible to use pathogenic strains of E. coli O157:H7.