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INTERVENTIONS TO REDUCE MICROBIAL LOAD OF FOODBORNE PATHOGENS AT THE SURFACE OF FRESH PRODUCE
thesisposted on 2021-10-12, 12:26 authored by Yezhi FuYezhi Fu
Fresh produce has been the leading source of foodborne illness outbreaks in the US, surpassing typical pathogen carriers such as meat, dairy, and seafood. Among the fresh produce popular to the consumers, cantaloupe and sprouts are mostly susceptible to pathogen contaminations and outbreaks. However, it has been a challenge to address the key factor in the contamination - the biofilms formed by pathogens are highly resistant to conventional washing and cleaning procedures. For cantaloupe, the net-like and porous surface forms a barrier for washing. For sprouts, the fragile texture of seedlings prevents aggressive cleaning operation and biofilm removal.
In this study, innovative interventions were developed to improve microbial safety of fresh produce, using cantaloupe and alfalfa sprouts as models. For cantaloupe, abrasive brushing was designed to remove pathogen biofilm from cantaloupe. Our research found pathogens could form biofilm at cantaloupe rind surface as the residence time of pathogens increased. Biofilm formed on cantaloupe rind was imaged by cryo-scanning electron microscopy (cryo-SEM), and its resistance to sodium hypochlorite and lauroyl arginate ethyl (LAE) was confirmed. Furthermore, abrasive brushing with peroxyacetic acid (PAA) could effectively remove biofilm formed at cantaloupe rind. The efficacy of this novel cleaning technique was highly desirable, which could achieve 3 log reduction in pathogen population. Mechanism of abrasive brushing to remove biofilm at cantaloupe rind surface was also proposed. Conceivably, brushing with diatomaceous earth (DE) and PAA could be an innovative and cost-effective method to remove pathogen biofilm from cantaloupe rind.
For alfalfa sprouts, since most of the outbreaks are linked to the sprouting seeds, seed disinfection treatments are considered to be the most effective method to improve microbial safety of sprouts. In this study, a newly developed alginate-based, antimicrobial seed coating treatment was evaluated for its efficacy to reduce foodborne pathogens from alfalfa seeds and sprouts. The calcium alginate coating in the presence of 2.5% lactic acid (CA-LA coating) reduced foodborne pathogens inoculated on alfalfa seeds to an undetectable level on day 1 during 28 day-seed storage, while chlorine (20,000 ppm) or lactic acid (2.5%) treatment took longer time to reach the same level. With sprouts, CA-LA coating resulted in > 2.5 log reduction for pathogen cells. In contrast, log reduction was < 0.6 for either chlorine (20,000 ppm) or lactic acid (2.5%) treatment. In general, this study indicated the effect of calcium alginate coating on reducing bacterial load of alfalfa seeds and sprouts, however, the germination rate of treated seeds was compromised due to the addition of lactic acid in the seed coating. Further study is needed to select antimicrobial compounds with minimum impact on germination rate of seeds.