Processing of leafy vegetables matters: Damage and microbial community structure from field to bag

B.W Alsanius,E Mulaosmanovic,T.U.T Lindblom,M Bengtsson,A.K Rosberg,S.T Windstam,L Mogren

doi:10.1016/j.foodcont.2021.107894

B.W Alsanius, E Mulaosmanovic + Show 5 more

Open Access

https://doi.org/10.1016/j.foodcont.2021.107894

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Abstract

Leafy vegetables undergo abiotic and biotic stresses, and a series of processing steps that cause mechanical injury. Breaching the epidermis alters phyllosphere structural and nutrient conditions, resulting in successional shifts in leaf microbiota and entry of human pathogens. This study examined damage during processing of baby leaves (Swiss chard, spinach) and concomitant microbial successional events. Machine-harvesting, washing, and packaging caused major phyllosphere perturbations, with increasing levels of leaf damage. Older leaves showed most damage, but plant species was influential. Diversity estimates of bacterial and fungal communities revealed shifts in microbiota post-harvest, particularly after the washing step. Relative abundance of Pseudomonadaceae and Enterobacteriaceae increased from field to bag. Bacterial species specific to different harvesting and processing steps replaced core microbiota species. While processing is unavoidable, procedures that mitigate leaf damage can enhance shelf-life and food safety.

Highlights

Baby leaf vegetables are usually eaten raw, with no sanitization step between field and bag
Baseline spinach leaves were larger than chard leaves (Fig. 2), so relative damage provided a better comparison than absolute damage
While the baseline damage was relatively minor compared with that during processing, completely intact leaves were rare, which should be considered in studies on phyllosphere microbiology to avoid confounding

Summary

Introduction

Baby leaf vegetables are usually eaten raw, with no sanitization step between field and bag. In Sweden, leafy greens are mainly field-grown, machine-harvested, and cooled to 4 ◦C directly post-harvest to maintain quality. Each processing step causes pertur bation and possible leaf damage (Kays, 1999; Snowdon, 1990), which can significantly alter the leaf micro-environment and associated mi crobes. Harvesting and post-harvest injuries impair the physical quality and chemical characteristics (nutrient leakage) of packaged leafy vegetables (Ariffin, Gkatzionis, & Bakalis, 2017). Damage to the epidermis alters the 3-D landscape, increases surface area, and disrupts internal leaf structure, causing water loss (Aruscavage, Miller, Lewis Ivey, Lee, & LeJeune, 2008; Tukey & Morgan, 1963), localized cell death (Iakimova & Woltering, 2018), and passive leakage of nutrient-rich cellular fluids (Leveau & Lindow, 2001). Leaf tissue damage reduces sensory and nutritional product attributes

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