The Australian New Crops Newsletter, Issue 11, January 1999, 96-97
Maximising freshness but minimising microbial food safety hazards in fresh bamboo shoots
Dr Volker Kleinhenz
Plant Sciences Group
Central Queensland University
Rockhampton Queensland 4702
Cultivation of bamboo for fresh shoots is an emerging industry in Australia. Consumers appreciate “freshness” in horticultural products but are concerned about microbial contamination of vegetables.
In the USA, the reported incidence of foodborne infection from fresh fruits and vegetables increased from two percent in 1973 to eight percent in 1991. However, there are no legal standards for acceptable levels of pathogenic microorganisms in vegetables.
Therefore, it can be recommended that producers optimise their crop-management and postharvest-storage practices to accommodate both, external quality (ie “freshness”) and internal quality (ie minimal microbial infection) of bamboo shoots.
Appropriate cooling and packaging practices can preserve external quality and maintain internal quality of fresh bamboo shoots.
Studies at Central Queensland University (CQU, Plant Sciences Group) in Rockhampton and at the Department of Primary Industry and Fisheries of the Northern Territory (DPIF-NT), Darwin show that storage in closed plastic bags decreased dehydration but increased respiration and microbial infection in bamboo shoots.
Respiration could be minimised and desiccation kept at acceptable levels by storing bamboo shoots in cooled (2° C) and open cardboard boxes for about one week (Fig. 1). This time span should be sufficiently long to transport shoots from producers to the markets within Australia.
Figure 1 Respiration rate and weight loss in fresh bamboo shoots as affected by storage temperature and packing material
Cultivation, harvest and postharvest procedures open pathways for infection of bamboo shoots with microorganisms.
There is well-established agreement that animal manure is a significant source of human pathogens (eg coliform bacteria).
Bamboo shoots are harvested below or shortly above the soil surfaces leaving a severe wound which make them predestinate to microbial infection.
Microbial studies at CQU show that chicken manure increased the total microbial load of the soil and of harvested bamboo shoots.
Although abundance was greater on the surface sheaths which will be removed before consumption, microbes were also present in the edible part (Plate 1).
Plate 1 Growth of microbes from the external surface (a) before and (b) after decontamination with hypochlorite, and (c) from the internal tissue of fresh bamboo shoots
These parts contained members of the coliform bacteria (eg Escherichia coli) which are not heat-tolerant and can easily be destroyed by cooking bamboo shoots.
Other microbes present were species forming heat-resistant endospores and producing toxins potentially harmful to humans (eg Bacillus sp).
These pathogens can survive extended periods of high temperature.
Bamboo growers should recognise that good sanitation practices during harvest can minimise microbial health hazards in fresh bamboo shoots.
Such practices include use of properly treated or composted organic manures at appropriate application dates, clean field and processing equipment, and sanitary processing water.
Postharvest decontamination procedures may have the potential to improve internal quality of fresh bamboo shoots.
Although the optimal procedure (concentration and treatment duration) was not known, sterilisation of bamboo shoots with hypochlorite reduced the microbial load of bamboo shoots (Plate 1).
The procedure is non-time-intensive, financially viable, easy to implement and has been promoted by regulatory bodies for other horticultural products.