The food company at the centre of a hummus salmonella scare received a substantial fine less than a month ago for food standard offences involving another dip, it has emerged.

Zorba Delicacies, which has been forced to extend a recall of 80 types of hummus products supplied to various supermarkets, was found to have supplied an egg-free branded tzatziki dip which contained egg protein.

The problem emerged when Hayley Lancaster suffered a potentially fatal allergic reaction in February 2018 after eating a dip she had brought from Morrisons in Caerphilly, south Wales.

A subsequent investigation by Caerphilly’s trading standards team found that the company had failed to comply with its own safety standards. Zorba was fined £93,000 after pleading guilty to three food safety charges at Merthyr Tydfil magistrates court on 11 October.

Tim Keohane, a senior trading standards officer at Caerphilly council, told the Guardian that the investigation had revealed “systemic problems” at Zorba.

He said the investigation found it had failed to allow enough time for 20-minute deep cleans to take place between making a mint and beetroot dip, which contained eggs, to processing the supposedly egg-free tzatziki. It also failed to take swabs at the plant or test the final products.

Keohane said he was “surprised” by the current salmonella scare involving the company. “You would have thought that having been fined £93,000 and having to spend an awful lot on enhancements, that things would not go wrong again. But to be fair to them their systems are now better and they may be more likely to pick something like this up.”

He added: “They introduced what they called enhancements to their allergen management system. Our experts said what they introduced was what they were supposed to be doing in the first place.

“The person we employed to do the audit was quite shocked about the way they were operating at the time and they were in breach of their own procedures in relation to allergen management.”

Zorba insisted the egg allergen problem was not linked to the current salmonella scare. A spokesman said the fine “relates to an incident in February 2018 and the two issues are completely unconnected”.

The company has blamed the salmonella contamination on an ingredient supplied by an unnamed third party.

The spokesman added: “Production continues to be suspended and all products have been withdrawn from points of sale. It would be inappropriate to name the likely third party supplier while laboratory testing and our investigations continue.”

Dr Kimon-Andreas Karatzas, a food microbiologist at the University of Reading, said the source of salmonella contamination could be difficult to detect. He said: “Salmonella can cause disease from a very small amount. Even a few cells, like 10 or 100, can make you sick.

“Salmonella can survive in hummus for a very long time, so it makes it harder to speculate on the reason for the contamination.”

Asked about Zorba’s recent fine he said: “Clearly if they put some egg protein where it should not be, this is not a very good sign.”

He said egg protein was unlikely to be the source of the current scare. “Salmonella is not found only in animal products. The biggest ever outbreak was actually on peanut butter in America. Because it comes from animals, salmonella can also be found in the environment.”