Direct consumption of pasteurised milk can be harmful to health as these commercially produced products are found contaminated with bacteria at every stages of the dairy value chain, says a new study.

The study published in the International Journal of Food Microbiology, said that the level of contamination is above national and international standards.

Funded by CARE Bangladesh, the study was conducted under its ‘Strengthening the Dairy Value Chain (SDVC)’ project in the northern part of Bangladesh, said a release of International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b) on Wednesday.

The research team collected 438 samples from milk producers, collectors, chilling plants, and local restaurants in 18 upazilas of Bogra, Gaibandadha, Nilphamari, Dinajpur, Joypurhat, Rangpur and Sirajgonj to assess the microbiological quality of milk at different stages of the dairy value chain.

More 95 samples of commercially processed milk were collected from retail stores in Dhaka and Bogra.

Scientists found that at the primary producers lever, 72 percent and 57 percent milk samples collected were contaminated with coliform and faecal coliform bacteria, respectively and 11 percent of samples were contaminated with high number of E. coli.

The faecal coliform bacteria are considered as a hygiene indicator and presence of bacteria in the milk.

Dr Mohammad Aminul Islam, who led study said, “The presence of bacteria in milk at different stages indicates that the core quality of milk - its nutrition is highly compromised.”

“Several factors are involved in the contamination of milk at the primary producers’ level including the breed of the cow, volume of milk produced by the cow, the time of milking, and farmers hand washing practices,” said Islam, who is an Associate Scientist and head of the Food Microbiology Laboratory at icddr,b.

Contaminated samples were found with a high number of coliform bacteria and faecal contamination -- 91 percent while more than 40 percent of samples had a high E. coli count.

Scientists also found that about 77 percent of all pasteurised milk samples have a high level of total bacterial counts (aerobic plate count), which is beyond Bangladesh Standards and Testing Institution standards.

The scientist recommended that dairy companies in Bangladesh should have end-to-end compliance of hygienic milking practices, collection and delivery, preservation and pasteurisation practices to ensure safe and nutritious milk.

The study, however, did not cover the test of milk for chemical contamination or adulteration, according Islam.