Rots and browning reduce the visual quality of the produce especially in fresh cut products.
Minor discolouration leads to loss of consumer appeal whilst majorr problems lead to rejection of the product
An investigation into the role of bacteria on rots and browning of cut lettuce is reported here.
Lettuce (Lactuca sativa L.) is an econorrically important food crop grown worldwide.
Demand far quality lettuce in the Australian domestic and export markets is high.
Visual quality of lettuce can be threatened by rots and browning, often leading to reduced shelf life and product quality issues with consumers.
We believe that the presence of plaM pathogenic bacteria may play a role in the elicitanon of the plant’s defence mechanisms and be a major cause of browning at the cut surface.
This project has shown that fluorescent pseudomonads are capable of either causing a rapid browning reaction on the cut surface of lettuce or exacerbating the problem over a 48-hour period on bought lettuce or lettuce grown under sterile conditions.
The natural levels of fluorescent pseudomonads in soils of lettuce growing regions have been shown to vary over the seasons and also vary between crop types.
The finding that the after-harvest lettuce waste contained high populations of fluorescent pseudomonads resulted in a recommendation for a time lapse between harvest and replanting of seedlings.
Experiments conducted at Knoxfield have shown that different Pseudomonas species can induce browning of cut lettuce within 48 hours.
Browning is quite severe and rapid compared with other bacteria such as Erwima and Xanthomonas species.
The project has also shown that fluorescent pseudomonad levels on cut lettuce can be reduced, whilst maintaining good quality produce.
Also bacterial levels in the field were found to increase with the use of mulches, but the overall yield and quality of the lettuce heads were increased.
The results indicate that bacteria have an important role in not only rotting the cut surface of lettuce leaves but also in eliciting a browning response.
The cut surface of all leaves inoculated with bacteria turned brown whereas the cut surface of leaves that were not inoculated remained free of browning.
The completion of this project would have not have been possible without the assistance of a large number of people :
This project was commissioned by Horticulture Australia Limited�with funds frrom the Vegetable R&D levy and the Victorian State Government..
The Australian Government provides matched funding for all HAL’s R&D activities.