A survey of the quality of fish sauce on sale across the nation has found just over one-third of the samples were not up to standard, the Department of Medical Sciences announced on Thursday.
The three-year survey, from 2012 to 2015, involved 1,121 samples of fish sauce sold under 422 brands from 245 producers.
Of the total analysed, 410 samples, or 36.5%, did not meet the set standard, said department director-general Pichet Banyat.
The survey covered 576 samples of genuine fish sauce and 545 of mixed fish sauce. The quality analysis showed that 159 samples of genuine sauce and 251 of mixed sauce were not up to standard.
He said major reasons for the substandard fish sauce were nitrogen readings too low and the ratio of glutamic acid to nitrogen too high or lower than the required standards.
Dr Pichet said the glutamic acid ratio was needed to ensure that the producers did not put too much monosodium glutamate in the product, as that could be a health risk for people allergic to the substance.
The low nitrogen problem was caused by improper fermentation or mixing processes.
The survey also found that levels of benzoic acid were too high in 10.9% of samples, but the highest level was still safe for consumption because its salty taste limited the amount consumed each time.
The Public Health Ministry puts fish sauce into three categories – products made from fish; products made from other marine animals, and mixed fish sauce.
All products made from fish and other marine animals must have at least 9 grammes of nitrogen per litre and a ratio of glutamic acid to nitrogen of 0.4-0.6 times. Mixed fish sauce must have at least 4 grammes of nitrogen per litre and the ratio of glutamic acid to nitrogen at 0.4-1.3 times.
All fish sauce must have at least 200 grammes per litre of sodium chloride, while the combined maximum amount of preservative substance (benzoic and sorbic acid) is 1,000 milligrammes per kilogramme.
Dr Pichet said the quality of fish sauce has improved with time. The department found the highest percentage of substandard fish sauce in 2012, and a quality campaign and monitoring system had since been introduced.