Date of Award


Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)


Food Science and Human Nutrition


Alfred A. Bushway

Second Committee Member

Rodney J. Bushway

Third Committee Member

Mahmoud El-Begearmi


Lowbush blueberries of the species Vaccinium angustifohm are native to the Northeast United States. In the state of Maine, lowbush blueberries are commercially managed and harvested each year to be marketed as either IQF (individually quick fiozen) or fiesh pack. Since IQF berries are processed at the field level, post-harvest treatments must be effective in ensuring crop quality and safety. Furthermore, with the increase in concern for microbiological and chemical food safety, post-harvest treatment of lowbush blueberries must be effective in reducing microbial populations and pesticide residues. Currently, the Maine Wild Blueberry Industry incorporates a 50-100ppm chlorinated water spray into the processing of lowbush blueberries. However, the possibility of fbture regulatory constraints on the use of chlorine as a sanitizer calls for investigation of alternative treatments that would be equally effective in improving microbial quality and safety. This thesis examined the influence of post-harvest treatments namely chlorine, hydrogen peroxide, citric acid, and distilled water on the microbiological quality and residual phosmet levels of lowbush blueberries. This research also assessed the degradation of phosmet on commercial blueberries in Maine. Field samples were collected fiom one of Maine's commercial blueberry fields immediately after treatment with aerial sprays of Imidan 70-W (phosmet). Sampling continued for a total of five weeks during the summer of 2001. Berries were subjected to 500mL sprays of lOOppm chlorine, 0.5% hydrogen peroxide, 0.5% citric acid, or distilled water. Microbiological analysis of total aerobes, yeast, and mold were conducted using FDA Standard Methods. Residual phosrnet was measured by GCIMSD. Microbial reductions of up to 1.5 log were observed on individual washed samples. Significant differences (pc0.05) in antimicrobial effectiveness existed among treatments allowed the same contact time. Overall, samples treated with lOOppm chlorine had the lowest mean counts of total aerobes, yeast, and mold. No significant differences (px0.05) were observed in treatment effectiveness after holding for 30 seconds versus 300 seconds. During the five weeks pre-harvest, results showed that as the microbial load increased, residual phosmet levels decreased. Residual phosmet levels of treated samples were significantly lower (p<0.05) than residues on unwashed berries. The extent to which treatments removed residual phosmet was influenced by the week of sampling. The greatest reductions in residual levels were observed on blueberries treated during the first three weeks when residual levels on unwashed controls were highest. Although treatments were less effective during the final weeks of the study, the residual phosmet levels on the control samples fell below the EPA tolerance level of 10,000ppb. Furthermore, 100% of all blueberries sampled during the final three weeks of the study contained residual phosmet at levels below the EPA tolerance. Results of this study demonstrate the efficacy of treating lowbush blueberries with 100ppm chlorine sprays to improve the microbiological quality and safety of the crop; however, additional research on alternative sanitizers and their effective concentrations should be conducted to aid the industry should the use of chlorine be restricted.