Masters Theses

Date of Award

5-2002

Degree Type

Thesis

Degree Name

Master of Science

Major

Food Science and Technology

Major Professor

David A. Golden

Committee Members

John R. Mount, P. Michael Davidson

Abstract

Two studies were conducted to determine the survival of E. coli O157:H7 and Salmonella in pasteurized apple cider and orange juice treated with chemical preservatives. In the first study, a nalidixic-acid resistant four- or five-strain mixture of E. coli O157:H7 or Salmonella spp., respectively, was inoculated (7 log cfu/ml) into apple cider and orange juice containing no preservatives (control) and juices containing 75, 150, and 250 ppm dimethyl dicarbonate (250 DMDC); 250 ppm DMDC + 46 ppm sodium bisulfite (250 DMDC/BI); 250 ppm DMDC + 450 ppm sodium benzoate (250 DMDC/BE); 100, 200, and 300 ppm hydrogen peroxide (HP); 150ppm DMDC + 100 ppm HP (stored for 5 days) or 75 ppm DMDC + 200 ppm HP (stored for 24-h). Inoculated juices were stored at 4°C for 24 h or 5 d. Samples were withdrawn at 4-h intervals (24-h storage) or 24-h intervals (5-d storage), neutralized with 1N NaOH, serially diluted in 0.1 M phosphate buffer, and surface plated onto tryptic soy agar containing 50 ppm nalidixic acid. Survival of both pathogens was better in orange juice than apple cider (P<0.05), and E. coli O157:H7 remained viable longer than Salmonella (P<0.05). After 5 d of storage, pathogens in control juices were reduced by < 1 log cfu/ml. E. coli O157:H7 was reduced to undetectable levels (<1 log cfu/ml) after 120, 96, 72, 72, 48, 48, and 12 h, respectively, in apple cider treated with 100 ppm HP, 200 ppm HP, 250ppm DMDC, 150 ppm DMDC, 300 ppm HP, 250 DMDC/BE, and 75 ppm DMDC + 200 ppm HP. After treatment with 75 ppm DMDC and 250 DMDC/BI, E. coli O157.H7 in apple cider was reduced by 4.34 and 3.3 log cfu/ml, respectively, during storage. Salmonella in apple cider was reduced to undetectable levels by 150ppm DMDC + 100 ppm HP, 75 ppm DMDC + 200 ppm HP, 250 DMDC/BE, 250 DMDC/BI, 250 ppm DMDC, 150 ppm DMDC, 75 ppm DMDC, 200 ppm HP, 300 ppm HP, and 100 ppm HP in 0, 0, 24, 48, 48, 48, 72, 72, 96, and 96 h, respectively. In orange juice treated with 75 ppm DMDC and 100 ppm HP, E. coli O157:H7 and Salmonella reductions of 2.16 and 3.86, and 1.41 and 1.99 log cfu/ml, respectively, were achieved during 5-d storage. Addition of 150 ppm DMDC to orange juice resulted in a 3.22 log cfu/ml decrease in E. coli O157;H7during 5-d storage. E. coli O157:H7 in orange juice was reduced to undetectable levels in 24, 48, 48, 48 72, 72, and 72 h by 75 ppm DMDC + 200 ppm HP, 250ppm DMDC, 300 ppm HP, 250 DMDC/BI, 200 ppm HP, 150ppm DMDC + 100 ppm HP, 250 DMDC/BE, respectively. Salmonella was undetectable in orange juice containing 75 ppm DMDC + 200 ppm HP, 250 DMDC/BE, 250 DMDC/BI, 150ppm DMDC + 100 ppm HP, 300 ppm HP, 250 ppm DMDC, 200 ppm HP, and 150 ppm DMDC in 8, 24, 24, 24, 48, 72, 72, and 120 h, respectively. Alternatives to pasteurization may include the addition of chemical preservatives to apple cider and orange juice to provide acceptable (5-log) inactivation of E. coli O157:H7 and Salmonella spp.

In the second study (comprised of two parts), inactivation of E. coli O157:H7 and Salmonella in pasteurized apple cider treated with ozone (O3) in combination with chemical preservatives was evaluated. A nalidixic-acid resistant four- or five-strain mixture of E. coli O157:H7 or Salmonella spp., respectively, was inoculated (7 log cfu/ml) into apple cider. In part 1 of this study, ozone (0.9 g ozone/h) was pumped into refrigerated cider for 30, 45, or 60 min. Following ozonation, juice was treated with no preservatives (control), 250 ppm DMDC (250 DMDC), or 75 ppm DMDC + 200 ppm HP (DMDC/HP) and stored at 4°C for up to 90 (30 min O3 treatment) or 60 min (45 and 60 min O3 treatment). In part 2, inoculated juices were treated with no preservatives (control), 250 ppm DMDC (250 DMDC), or 75 ppm DMDC + 200 ppm HP (DMDC/HP) and stored at 4°C for 0,1, 2, 3, or 4 h followed by a 30-, 45-, or 60-min ozone treatment. Samples were withdrawn immediately after preservative addition and at 15-min intervals during storage, neutralized with 1N NaOH, serially diluted in 0.1 M phosphate buffer, and surface plated onto tryptic soy agar containing 50 ppm nalidixic acid.

Part 1. E. coli O157:H7 remained viable longer than Salmonella (P<0.05), and inactivation of both pathogens increased with O3 treatment time (P<0.05). Reductions of pathogens in control cider was 1.02, 3.09, and 4.51 log cfu/ml E. coli O157:H7 and 1.36, 2.48, and 3.60 log cfu/ml Salmonella for 30, 45, and 60 min O3 treatment, respectively. E. coli O157:H7 was reduced to undetectable levels (<1 log cfu/ml) after 75, 15, and 30 min storage with 250 DMDC and 75, 15, and 15 min storage with DMDC/HP following 30, 45, and 60 min O3 treatment, respectively. Undetectable levels of Salmonella were attained by addition of 250 DMDC in 45, 30 and 30 min following 30, 45, and 60 min ozonation, respectively. After O3 treatment of 30, 45, and 60 min, Salmonella populations were undetectable in 60, 30, and 15 min in cider subsequently treated with DMDC/HP.

Part 2. Inactivation of both pathogens was better with treatment of 75 ppm DMDC + 200 ppm HP than with 250 ppm DMDC (P<0.05), and no difference in survival was observed between E. coli O157:H7 and Salmonella (P>0.05). E. coli O157:H7 and Salmonella treated with 250 ppm DMDC for all storage times were reduced to undetectable levels immediately after ozone treatment, except E. coli O157:H7 stored for 0 h followed by 30 min ozone treatment, which reached undetectable levels within 30 min after ozonation. Treatment of both pathogens with 75ppm DMDC + 200 ppm HP stored up to 4 h reduced populations to undetectable levels immediately after ozonation, except E. coli O157:H7 stored for 0 h followed by 30 min ozone treatment, which reached undetectable levels within 15 min of storage after ozonation. Ozone treatment in combination with chemical preservatives can serve as an alternative to pasteurization of apple cider to provide acceptable (5-log) inactivation of E. coli O157:H7 and Salmonella spp.

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