Aggregative Sampling Performs Similar to Composite Produce Samples to Recover Quality and Safety Indicators Throughout Romaine Lettuce Production

Overall experimental sampling design during preharvest, in-harvest and postharvest stages of commercial romaine lettuce. This sampling process was performed in two replicates. For each replicate, commercial romaine grown on eight beds was sampled preharvest, during harvest and postharvest. For preharvest sampling (1 d before harvest), aggregative, composite produce (60 grabs, 150 g/sample) and high-resolution produce samples were collected (60 grabs, 25 g/sample). During harvest, romaine was sampled by collecting aggregative gloves worn by the harvesting crew, composite produce samples from leftover romaine leaf trims on the ground (60 grabs, 150 g/sample), aggregative swabs of harvested romaine heads as they exited the harvester chute, and aggregative swabs and composite produce samples (60 grabs, 150 g/sample) of romaine heads from the top of transportation bins. For postharvest sampling (∼6 hrs after harvest), ∼800 lb of romaine was sampled by using aggregative gloves to manipulate and place individual heads on a moving conveyor belt; as the heads exited the conveyor belt, they were sampled by an aggregative swab placed at the exit chute, before they fell onto smaller bins. Once there, composite romaine samples (60 grabs, 150 g/sample) were collected from the exterior of the heads. All sampled heads were then chopped in half lengthwise and were sampled by rubbing their interior against an aggregative swab placed on a cartridge and collecting composite romaine samples (60 grabs, 150 g/sample) from the interior of the heads.

Highlights

Aggregative and tissue sampling were compared pre-, during-, and postharvest.
Aggregative glove and swab sampling recovered similar aerobic bacteria to tissue grabs.
Aggregative gloves recovered similar coliforms to tissue grabs.
Aggregative swab recovery could be improved for coliforms and generic E. coli.

Abstract

Aggregative sampling using polymer cloth swabs is a nondestructive, 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 postharvest, 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 postharvest 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.

DOI

https://doi.org/10.1016/j.jfp.2025.100481