Bacterial population dynamics and decay on leaves of different ages of ready‐to‐use broad‐leaved endive

Abstract

Mesophilic, fluorescent, and pectolytic bacteria were quantified on leaves of five different age groups (AG) of broad-leaved endive (Cichorium endivia var. latifolia) before and after readyto-use (RTU) processing and daily over their 7-day French 'sell by' period. At harvest. significant differences in bacterial population sizes expressed as log,, colony-forming units (cfu) cm-' were observed among leaves of the different AG resulting in decreasing contamination from outer (-older) to inner (-younger) leaves of the head. This persisted throughout storage at 6°C for RTU-processed leaves separated by age implicating leaf physiology as one of its causes. Leaf age also affected types and frequencies of decay occurring during storage. Although the population sizes of mesophilic, fluorescent and pectolytic bacteria were always positively correlated, the sizes of fluorescent and pectolytic populations could not consistently be predicted from mesophilic ones. Thus fluorescent and pectolytic populations should be quantified independently due to their potential role in decay. Atmospheric changes in the packs resulting from vegetable respiration and microbial activity confirmed the limiting effect of high CO, and low 0, on the development of spoilage without an effect on bacterial populations sizes. The importance of the effect of leaf AG for plant cultivation and industrial production of RTU salads is discussed.

Interactions Affecting the Proliferation and Control of Human Pathogens on Edible Plants

“…Thompson and others (1993) showed microbial communities on sugar beets were greater on old and senescent leaves than on young leaves. Jacques and Morris (1995) observed more microbial contamination on older leaves of endive than on the younger inner leaves. Plant pathogens caused more decay on these older leaves than on the young leaves, further contributing to leaching and other microenvironmental changes on the plant surface that would favor the survival and proliferation of human pathogens (Jacques and Morris 1995).…”

Influence of Temperature on Shelf Life of Butterhead Lettuce Leaves Under Passive Modified Atmosphere Packaging

“…6. Storage temperature was the most important factor affecting the growth of microorganisms in modified atmosphere packages, despite the fact that packages stored at 15C showed higher CO 2 concentration but it was not enough to slow down or stop microbial activity (Church and Parsons 1995; Jacques and Morris 1995).…”

The Effect of Leaf Age and Position on the Dynamics of Microbial Populations on Aerial Plant Surfaces

“…Individual leaves are often used as the sampling unit for various biological reasons. Incidence, severity and progress of foliar diseases of plants in the field or processed vegetable products in storage are often assessed on individual leaves (Rouse et al, 1985) or leaf pieces (Jacques and Morris, 1995a). This is the case, because inoculum thresholds for symptom expression are more meaningful for single plant organs than for a whole plant or several plants.…”

“…foliosum), broad-leaved endive (Cichorium endivia L. var. latifolia) and sugar beet (Beta vulgaris L.) have been reported to carry smaller bacterial population densities than outer/older leaves at a given sampling time during field cultivation (Ercolani, 1976;Geeson, 1979;van Outryve et al, 1989;Morris and Lucotte, 1993;Thompson et al, 1993;Jacques et al, 1995) and during storage of processed vegetables (Jacques and Morris, 1995a). Differences in population densities of total mesophilic bacteria between the youngest and the oldest leaves of broad-leaved endive could exceed 2 log~0 units at harvest and these discrepancies persisted during storage after minimal processing for leaves separated by age group and stored in polypropylene packs (Jacques and Morris, 1995a;Jacques et al, 1995).…”

“…This will be followed by a discussion of the hypothetical mechanisms by which leafage has its effect and the implications for the experimental approach taken in studies of epiphytic microbial population structure. Specific examples will be provided from studies of the influence of leaf age and position on population dynamics of total mesophilic, fluorescent and pectolytic epiphytic bacteria for broad-leaved endive (Jacques and Morris, 1995a;Jacques et al, 1995). This work allows us to show how leaf age and position may interact with bacterial immigration and growth influencing the quality of leaves within the canopy as a habitat for bacteria.…”