19 November 2024

No chlorine, No problem

The implementation of minimum chlorate technologies across the dairy chain has facilitated the production of milk and dairy products with levels of chlorate residue superior to European Union and customer demands, whilst maintaining microbiological quality. 

Photo credit: nevodka/istockphoto.com

Chlorate is a degradation byproduct of chlorine that can disrupt proper functioning of the thyroid. In response to concerns about chlorate, dairy processors in the Republic of Ireland decided to prohibit the use of chlorine-based chemicals for cleaning on farms and in milk processing plants, effective as of January 1, 2021.

This decision stemmed from the need to ensure that milk complied with the legislative limits being placed on chlorate at European Union level, as a maximum residue limit (MRL) of 0.10 mg/kg for chlorate in milk came into effect in 2020.

However, little was known about the extent to which chlorine-free cleaning would reduce the risk of chlorate contamination, explains Lorna Twomey, a Walsh scholar at Teagasc Moorepark.

“Furthermore, there was a scarcity of information regarding chlorate levels in farm bulk milk and dairy products produced in Ireland. There was also a lack of understanding about the contribution of chlorinated water to chlorate in bulk milk. Of most concern was the fact that little was known about the microbiological impact of switching to chlorine-free cleaning.”

Removing chlorine as a cleaning and disinfection agent meant removing a versatile and highly effective means of maintaining the cleanliness and hygiene of milk handling and processing equipment, potentially compromising the microbiological quality and safety of milk and dairy products.

To address these knowledge gaps, Teagasc, in conjunction with industry stakeholders, led a research project into chlorate residue in milk and dairy products and its relationship with cleaning protocols and milk quality, Lorna explains.

“This project aimed to develop a cross-dairy chain understanding of chlorate, as well as evaluate the efficacy of minimum chlorate technologies – chlorine-free cleaning and chlorine gas water treatment – from a microbiological perspective.”

Setting the baseline

Research was conducted to determine the baseline levels of chlorate in farm bulk milk and dairy products. A total of 3,625 bulk milk samples sourced from six milk processors were analysed for chlorate residue. Of these, 1,741 were sourced in 2020 when chlorine-based cleaning was still employed on some farms, while 1,884 were taken in 2021, once chlorine-free cleaning had become mandatory.

In 2020, chlorate was present at detectable levels (≥0.0020 mg/kg) in 266 bulk milk samples (15% detection rate). With the imposition of chlorine-free cleaning this reduced to 149 samples (8%) in 2021. Moreover, the majority of samples (≥95%) analysed in both 2020 and 2021 were in compliance with the EU’s MRL for chlorate in milk (<0.10 mg/kg).

To ascertain the typical levels of chlorate present in dairy products produced and consumed in Ireland, a total of 1,238 product samples were procured in supermarkets across 2021 and subsequently analysed for chlorate; product types sampled were whole milk, cream, cheddar cheese, butter and yoghurt. Although chlorate levels were detected in approximately half of all whole milk, cream and yoghurt samples analysed, these were significantly less than the EU MRL for the most part, and were virtually absent from butter and cheddar. 

Minimising contamination

Aside from its use in cleaning and disinfecting milking and milk processing equipment, chlorine is also used for water disinfection, Lorna explains.

“Therefore, risk of chlorate contamination is not limited to chlorine-based cleaning. Field trials conducted as part of this project confirmed, for the first time, that chlorinated water is a source of chlorate residue. The mixing of water and milk is the prerequisite for contamination; if this contamination is to be minimised, thorough drainage of milking equipment is essential.”

At manufacturing level, many milk processors – especially those producing specialist products such as infant milk formula – have invested in chlorine gas water treatment as a means of eliminating the water supply as a source of chlorate. Chlorine gas technology is not prone to chlorate formation, in contrast to other types of chlorine, i.e. sodium hypochlorite and chlorine dioxide, Lorna continues.

Chlorine-free cleaning measured total bacteria counts of 3,168 cfu/mL vs 12,454 cfu/mL in chlorine-based cleaning

“Chlorate levels detected in skim milk powder were at 0.0183mg/kg when chlorine gas was used in production. By contrast, in previous research when chlorine was still commonly used, detected levels were at 0.057mg/kg – more than three times higher. Furthermore, we found that it is possible to produce high quality milk using chlorine-free cleaning. The total bacteria counts (TBC) and thermoduric counts (heat-resistant bacteria) of milk from farms using chlorine-free cleaning were lower than those achieved on farms using chlorine-based cleaning.”

Chlorine-free cleaning measured 3,168 cfu/mL and thermoduric count 43 cfu/mL vs. chlorine-based TBC 12,454 cfu/mL; thermoduric count 92 cfu/mL.

Meeting the standard

Chlorine-free cleaning’s ability to deliver milk with lower bacterial counts was attributed to the fact that on the study farms, chlorine-free cleaning was employed in accordance with a recommended protocol, i.e. having a hot water temperature of 75- 80^oC; employing the required number of acid washes each week; and using double the amount of liquid caustic detergent when washing with cold water (0.5% solution required when using hot water and a 1% solution being required when using cold water).

A subsequent research study focusing on the employment of chlorine-free cleaning protocols found that the majority of dairy farms in the Republic of Ireland were not fully adhering to recommended chlorine-free cleaning protocols, with 70% failing to use hot water of sufficient temperature (75-80^oC at the start of the hot wash cycle), 50% failing to conduct the required number of acid washes, and 60% of farms failing to use extra caustic detergent when using cold water.

At milk processor level, the use of chlorine-free cleaning was found to deliver dairy products with ‘in-spec’ levels of bacteria, including mesophilic and thermophilic thermoduric bacteria. Moreover, the use of chlorine-free cleaning in conjunction with chlorine-gas water treatment does not compromise milk product microbiological quality. 

“The aforementioned research demonstrates that eliminating chlorine as a cleaning and disinfection agent leads to a reduction in the incidence of chlorate in bulk tank milk and finished dairy products, all whilst preserving microbiological quality – provided chlorine-free cleaning is employed correctly,” concludes Lorna.

“Moreover, when chlorine-free cleaning is combined with cognisant management of the water supply – thorough drainage of chlorinated water from milking equipment and the use of chlorine gas treatment at milk processing sites – effective minimisation of chlorate residue can be achieved.” 

Funding

This project was funded by the Department of Agriculture, Food and the Marine’s Food Institutional Research Measure (FIRM) and Dairy Research Ireland. Lorna Twomey was in receipt of a Teagasc Walsh Scholarship funded by FIRM.

Contributors

• Lorna Twomey, Walsh Scholar (PhD Student), AGRIP, Teagasc Moorepark.
• David Gleeson, Research Officer, AGRIP, Teagasc Moorepark. david.gleeson@teagasc.ie 
• Bernadette O’Brien, Principal Research Officer, AGRIP, Teagasc Moorepark.
• Tom Beresford, Senior Principal Research Officer, Food Research Centre, Teagasc Moorepark.