Development and testing of a sensor to detect microbiological spoilage in grain

Summary

Sector:
Cereals & Oilseeds
Project code:
PR295
Date:
01 April 1998 - 31 December 2001
Funders:
AHDB Cereals & Oilseeds.
AHDB sector cost:
£299,053 from HGCA (project 2026).
Project leader:
H.M. Brown1 , N. Ratcliffe2 , P.A. Voysey1 , J.S. Williams1 P. Spencer-Phillips2 , B.P.J. de Lacey Costello2 , N. Beales1 , S. Salmon1 , H. Gunson2 , P.S. Sivanand2 and R.J. Ewen2 1 Campden & Chorleywood Food Research Association, Chipping Campden, Gloucestershire, GL55 6LD 2 The University of the West of England Faculty of Applied Sciences, Department of Chemical & Physical Sciences Bristol Frenchay Campus, Coldharbour Lane, Bristol, BS16 1QY

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295_complete_final_report

About this project

Abstract

The handling and storage of wheat can result in the formation of off-odours in grain, in particular musty, sour, 'green' and fishy odours. The sources of these off-odours during storage are due to a combination of fungal or bacterial activity when grain is held at elevated levels of moisture (>14%) and temperature in the grain store. Off-odours can be difficult to detect in both farm and grain processing environments due to the presence of other odours. By the time that spoilage odours can be detected by human senses, spoilage is likely to have spread widely within the store. Grain spoilage when it occurs costs the industry significant amounts of money in lost raw materials, down time and cleaning.

The aim of this project was to develop a sensing device to give an early warning of the onset and presence of microbiological spoilage in grain and to evaluate the sensor device in an industrial environment. The availability of a sensor-based instrument to detect incipient spoilage, and thus potential mycotoxin production, on wheat intake would reduce the need for human odour assessment of grain, which is desirable on safety grounds, and provide an opportunity to standardise an approach to assessing grain spoilage. Laboratory based culturing systems using irradiated grain conditioned to 25% moisture, inoculated with specific spoilage organisms, were developed to generate characteristic grain spoilage odours. These systems provided a means of defining spoilage odours and the time course over which they develop using the human sense of smell. They provided a means for the chemical identification of suitable volatile compounds for use as early warning indicators, to which sensors had to be developed. Novel sensors, constructed from a range of materials, were tested against pure compounds identified as potential early warning indicators of spoilage and spoiled grain. The most promising sensors were incorporated into a prototype device suitable for use in a grain intake laboratory. Sampling conditions (times and temperatures) were optimised and a 'laboratory threshold' defined using samples of spoiled grain submitted from commercial practice, the laboratory-based spoilage systems, and mixtures of spoiled and sound grain.

The prototype sensor system was evaluated in a commercial wheat intake facility where over 100 samples were tested. All samples identified as having an odour related problem were rejected by the prototype system. A number of samples that were passed by the intake laboratory were rejected by the prototype system - this may indicate early detection of spoilage. Of 37 newly harvested wheat samples of different varieties from different geographical locations in the UK, the wheat intake assessors rejected one sample and six were rejected by the prototype sensor system. The 'laboratory defined threshold' may need adjustment to minimise the number of false positives.

The trial highlighted the promise of this prototype for the detection of spoilage in wheat grain. A larger trial is now needed to ascertain the reliability and long-term stability of the device and its usefulness to the industry.

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