Peanut growers now have clear advice on how to prevent costly contamination of their crops, following research supported by the Grains Research and Development Corporation (GRDC).
In 2008, earthy, musty off-flavours were detected in peanuts in North Queensland, which led to over $1 million of product downgrades.
GRDC-funded research has discovered the major cause of this off flavour contamination, and guidelines for pre-harvest and post-harvest practices to minimise the risk are now available to growers in a GRDC Fact Sheet.
The research led by Dr Graeme Wright, of the Peanut Company of Australia, revealed that microorganisms called actinomycetes, which can grow on freshly harvested and stored peanuts, produce volatile compounds that cause the off-flavours.
“While actinomycetes are present everywhere in the environment, they only produce off-flavour compounds under certain conditions such as high temperature and/or high relative humidity,” Dr Wright said.
“Actinomycetes can grow over a wide temperature range of 10 to 60°C, and stored nuts can develop the problem when kernel and nut-in-shell moisture content is more than about 12 per cent.
“Growth of these microorganisms after digging of the crop can be reduced by making sure peanuts are rapidly dried to safe pod-moisture content after harvest.”
The fact sheet outlines several pre- and post-harvest preventative measures, including:
- Ideally blocks should have had good crop rotation to avoid back-to-back peanut crops, as actinomycete levels in the soil can increase dramatically. There is also some evidence that peanuts following potatoes may have a higher risk of being contaminated.
- A long interval from digging to threshing (more than five days) in combination with poorly aerated windrows (which prevent the plant and pods from drying rapidly down to safe moisture within two to four days) can lead to conditions ideal for microbial growth.
- Post-harvest peanuts should be stored in clean and secure on-farm storage bins to prevent growth of microorganisms, and delivered to the buying point as quickly as possible.
Rapid and low-cost analytical techniques to detect off-flavour compounds are now being developed.
The GRDC Peanut Off-Flavour Fact Sheet is available to growers at www.grdc.com.au/GRDC-FS-PeanutOffFlavour.
Dr Graeme Wright, Peanut Company of Australia
0419 735 036
GRDC Project Code