Aggregative sampling performs similar to composite produce samples to recover quality and safety indicators throughout romaine lettuce production.

Abstract

Aggregative sampling using polymer cloth swabs is a non-destructive, potentially more representative food safety sampling alternative for leafy greens. This study compared aggregative and produce tissue grab sampling to recover aerobic bacteria, total coliforms, and generic Escherichia coli, from commercial romaine grown in 120 m fields, with 5-36 samples at various stages. Aggregative swabs and grab samples were collected preharvest. During harvest, aggregative swabs were collected from romaine exiting the harvester chute, transport bin tops, and as gloves worn by harvesters. Romaine grabs were collected from transport bin tops and trim leftover on the ground. During post-harvest, gloves, swabs, and grabs were collected from romaine exteriors, and swabs and grabs from head interiors. In preharvest, swabs had 1.2 log(CFU/g) higher means of aerobic bacteria than romaine tissue grab samples (p<0.001), but 1.7 log(CFU/g) lower coliforms (p<0.001). In-harvest, aerobic bacteria means from gloves worn by harvesters and swabs from harvester chute were 0.5 log(CFU/g) higher than romaine samples from leftover trims (p<0.001) and bin tops (p=0.01), respectively. Coliform recovery means from gloves was not significantly different from romaine leftover trims (p=0.99). Swabs from harvester chute and bin tops recovered 1.6 and 1.4 log(CFU/g) lower coliforms means (p<0.001) than romaine from bin tops, respectively. Generic E. coli was only recovered from one romaine leftover trim grab sample. During post-harvest processing, aerobic bacteria (p=0.25) and total coliforms (p=0.16) recovery from the exterior of heads was not significantly different between gloves and romaine samples, nor was aerobic bacteria (p=0.17) and total coliform (p=0.86) recovery from head interiors. These results suggest that aggregative sampling performs similar to produce grab sampling to recover quality and safety indicators and justifies testing these methods for pathogen sampling in leafy greens.