Differential microbiota shift on whole romaine lettuce subjected to source or forward processing and on fresh-cut products during cold storage

• Published in: International journal of food microbiology Vol. 416; p. 110665
• Main Authors: Gu, Ganyu, Ding, Qiao, Redding, Marina, Yang, Yishan, O’Brien, Regina, Gu, Tingting, Zhang, Boce, Zhou, Bin, Micallef, Shirley A., Luo, Yaguang, Fonseca, Jorge M., Nou, Xiangwu
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 02-05-2024
• Subjects: 16S rRNA gene amplicon sequencing; Aerobic bacteria; Food safety; Fresh produce; Microbiome; Pre-processing delay; Produce quality; Total coliform; 16S rRNA gene amplicon sequencing; Produce quality; Fresh produce; Aerobic bacteria; Total coliform; Pre-processing delay; Food safety; Microbiome
• ISSN: 0168-1605; 1879-3460
• DOI: 10.1016/j.ijfoodmicro.2024.110665

Romaine lettuce in the U.S. is primarily grown in California or Arizona and either processed near the growing regions (source processing) or transported long distance for processing in facilities serving distant markets (forward processing). Recurring outbreaks of Escherichia coli O157:H7 implicating romaine lettuce in recent years, which sometimes exhibited patterns of case clustering in Northeast and Midwest, have raised industry concerns over the potential impact of forward processing on romaine lettuce food safety and quality. In this study, freshly harvested romaine lettuce from a commercial field destined for both forward and source processing channels was tracked from farm to processing facility in two separate trials. Whole-head romaine lettuce and packaged fresh-cut products were collected from both forward and source facilities for microbiological and product quality analyses. High-throughput amplicon sequencing targeting16S rRNA gene was performed to describe shifts in lettuce microbiota. Total aerobic bacteria and coliform counts on whole-head lettuce and on fresh-cut lettuce at different storage times were significantly (p < 0.05) higher for those from the forward processing facility than those from the source processing facility. Microbiota on whole-head lettuce and on fresh-cut lettuce showed differential shifting after lettuce being subjected to source or forward processing, and after product storage. Consistent with the length of pre-processing delays between harvest and processing, the lettuce quality scores of source-processed romaine lettuce, especially at late stages of 2-week storage, was significantly higher than of forward-processed product (p < 0.05).
•Romaine lettuce from local (source) and remote (forward) processing chains were tracked and tested.•Forward-processed lettuce had higher microbial loads than source-processed product.•Quality score of fresh-cut lettuce in cold storage declined with delayed processing.•A shift in microbiota was detected between source and forward-processed lettuce.