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FIG.1. The change in water activity associated with an unexpected change in moisture content
ATER ACTIVITY
Dr Brady Carter explains why water activity, not moisture content is the key for safer food production
water activity-based release specification would have prevented any problems and saved millions in lost revenue.
to water activities higher than 0.70 aw THE SOLUTION M
oisture content is commonly measured on food products for the purpose of making sure it will have the desired safety
and quality. However, water activity, not moisture content, determines the safety of food products. Recently, a major food manufacturer became painfully aware of the importance of releasing product based on water activity and not moisture content. Te company has been producing high quality product for over 20 years with little to no complaints. Ten, out of nowhere, it started receiving multiple complaints about mouldy product. How could this happen? It had released product based on a set moisture content for 20 years with no problems. Without making any changes to its moisture content specification, it suddenly had mould. Te cost of the subsequent recalls, public relations efforts, and causal discovery activities were in the millions of dollars.
WHAT WAS THE CAUSE? Te first mistake made by this company was using a moisture content specification to control mould growth instead of water activity. Water activity is the energy status of water in the food and microorganisms don’t care how much water is present, only if the water activity (energy) is high enough for them to access it. Mould growth will be prevented if the water activity is less than 0.70 and any problems with mould growth
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would have been avoided if the company was using 0.65 aw
as their release specification instead of moisture content.
Te other contributing factor that led to the sudden appearance of mould was a change in the instrument being used to measure moisture content. Tis new method was unknowingly giving lower moisture content readings than the actual moisture content (Fig. 1). Tis means that although the company thought it was making product to the same moisture content specification; the actual moisture content was 3-4% higher. Tis higher moisture level now corresponded with a water activity higher than the growth limit for mould. If the company had been tracking water activity, it would have known immediately that something had changed, and that the product was now being made
FIG.2. The change in moisture content possible at a safe water activity from formulation adjustment
reject any product that does not meet this specification, regardless of its moisture content. Tis immediately stopped all complaints about mould. Te second change was to correct the moisture content measurement to make sure it was giving results consistent with historical values. In so doing, the company realised that current formulations limit the amount of moisture that can be in its products and still maintain a safe water activity level. Consequently, the next step was to adjust the formulations to maximise the achievable moisture level while still meeting the newly implemented water activity release specification (Fig. 2). Tis will allow the food manufacturer to maximise profitability while having the security of knowing that the painful days of mouldy product are behind it.
Te first change to be implemented was to immediately implement a water activity release specification below 0.70 aw
and
Dr Brady Carter is application scientist with Neutec Group.
www.neutecgroup.com
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