Neogen develops test protocols to detect yeast and mould in various yogurt types

By Joseph James Whitworth contact

- Last updated on GMT

Neogen said there is no ‘one size fits all’ approach to test different yogurt types for yeast and mould
Neogen said there is no ‘one size fits all’ approach to test different yogurt types for yeast and mould

Related tags: Bacteria

Neogen has developed test protocols to analyse yogurts for any kind or type of yeast and mould.

It allows detection on yogurt products ranging from preservative free to those with a high level of probiotics.

The test uses the Soleris automated rapid microbiology system and the system’s Direct Yeast and Mold test vial.

Automated analysis possible with appropriate testing procedure

The new part is the pre-enrichment bottle and the direct 1g supplement. The bottle allows for high levels of sensitivity and detection in any yogurt type.

DYM-109C Soleris vial
Neogen DYM-109C Soleris vial

The supplement allows for the testing of 1g yogurt directly (no dilution needed) into the Soleris DYM-109C test vial, which is AOAC-RI approved, and it is targeted for preservative-free yogurts.

Protocols can produce results in 48 to 72 hours; conventional methods can take up to five days.

The level of detection is 1 cfu/g yogurt or less. A positive result is known by the vial changing colour in the sensor area.

Oscar Caballero, of Neogen Corporation, told us that the area of yeast and mould testing in yogurts is quite challenging – the proverbial needle in the haystack.

“The lactic acid bacteria must be neutralized/inactivated while at the same time allowing for the growth of any yeast or mould present in the yogurt sample. All yogurts are not created equal. Some yogurts have high levels of probiotics and others may or may not have various preservatives," ​he said. 

“Our solution consists of three methods that together are able to effectively allow for detection of yeast and moulds regardless of yogurt type.”

Testing protocol for different yogurt types

All yogurt types can be tested using Neogen’s YM-EBY pre-enrichment protocol, which favours growth of any yeast and mould in the sample over other bacteria types and provides presence or absence results in 72 hours.

Yogurt types except those with a high probiotic load can be tested using a 1:10 specification monitoring protocol which provides results of less than 10 CFU per gram of sample in 48 to 72 hours.

Another protocol allows direct placement of 1g of yogurt into the Soleris vial, but only yogurts without preservatives or moderate probiotic loads are recommended for this. For most sample types it provides presence or absence results in 72 hours.

Caballero said a great portion of the yogurt industry does “peel and look” so there is no kit or system involved.

“Others will do plating on selective agars for yeast and mould. As far as Soleris goes, time to results is certainly a key feature. However, the level of sensitivity and detection is far greater than any other alternative method. In addition, the new solution provides customers with the ability to test for yeast and mould no matter the yogurt product or type," ​he said.

“The YM-EBY bottle does a great job eliminating any background activity from lactic acid bacteria through selectivity while encouraging proliferation of any yeast or mould that may be found in the yogurt sample of interest.”

For advice on which protocol would be appropriate with the yogurt type of interest, contact the firm.

Neogen’s Ed Bradley, vice president of food safety, said it is notoriously difficult to test for yeast and mould in yogurt.

“They are very slow growing organisms compared to most other bacteria, and the number of live beneficial bacteria in yogurt can confound conventional testing methods for any undesirable microbial contaminant in the product​.

"While there is no ‘one size fits all’ approach for rapidly testing for yeast and mould in the myriad of yogurt types, this is the first time that a set of testing protocols using Soleris provides easy-to-follow guidance to produce rapid, accurate test results regardless of yogurt type.”

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