Nutrition

Imported frozen berries need careful preparation if you want to avoid potential illness.

Imported frozen berries need careful preparation if you want to avoid potential illness.

The ministry recommends boiling frozen imported berries or bringing them up to 85°C for at least a minute.

Question:

I avoid any frozen berries that are not locally grown. My concern is not limited to pesticide residues.

Is my wariness justified?

Answer:

In a word, yes, your wariness is not only justified but also logical, given the health risks associated with eating improperly prepared frozen berries. Frozen fruits, particularly berries, have been a significant vehicle for foodborne illnesses in the past decade, according to a 2019 review published in the journal Epidemiology and Infection.

Frozen berries have been linked to increasing reports of norovirus and hepatitis A virus outbreaks since 2003, said a 2015 report published by the European Centre for Disease Prevention and Control (ECDC). However, it’s important to note there is no link between fresh berries and these problems – we’re talking about imported frozen berries. In 2013, for example, norovirus and hepatitis A outbreaks occurred around the world. Investigations revealed frozen berries were the source of the infections, which put the safety of this product in the spotlight. This perhaps explains why I feel like throwing myself in front of the blender when I see someone about to add frozen berries to their smoothie maker.

Frozen imported berries were also the cause of an outbreak of hepatitis

A in 2015 in New Zealand. Hepatitis A is a highly contagious liver infection caused by the hepatitis A virus that can last a few weeks to several months. People infected by this virus may feel sick, with an upset stomach, vomiting, diarrhoea and other liver-associated symptoms such as yellowed skin or eyes.

In contrast, noroviruses cause inflammation of the stomach or intestines and can lead to feeling extremely ill. Norovirus is the most common cause of vomiting, diarrhoea and foodborne illness. However, most people get better within one to three days.

These viruses are transmitted through the faecal-oral route, with as little as one milligram of infected faeces containing hundreds of copies of the virus. Thus, even microscopic amounts of infected faeces can cause large outbreaks and illnesses.

Berry production is labour intensive and involves hand-picking, so we depend on the growers’ sanitary handling of the produce. The main risk factors for contamination of berries have been identified as cross-contamination via equipment, through contaminated water (used for irrigation or washing) and via human handling. The processing may also lead to larger-scale contamination as the result of berries from different sources being mixed before freezing and packaging, researchers said.

In 2013, norovirus and hepatitis A outbreaks occurred around the world. Frozen berries were the source of the infections.

Manufacturers want to maintain the taste and texture of the packaged berries, so have only limited decontamination methods. UV treatment, high doses of gaseous ozone and various acidic solutions may reduce the volume of contamination, but do not remove the foodborne virus altogether. And, unfortunately, these exceptionally hardy viruses can survive in a frozen state for several months.

The hepatitis A virus is uncommon in this country, but is widespread in developing countries. High-risk areas include Africa, Asia, Central and South America and the Middle East. If frozen berries are imported from these regions, the potential exists for the virus to be present.

The Ministry for Primary Industries recommends boiling frozen or thawed imported berries or bringing them up to 85°C for at least a minute. The 2019 report from the European Centre for Disease Prevention and Control also recommended heat treatment of frozen berries before use, for one to three minutes.

In other words, do not put frozen berries directly into a smoothie or dessert. The frozen berries must be boiled or heated to above 85°C to destroy any virus particles, which can survive temperatures lower than this.

It is also vital to wash your hands thoroughly to prevent crosscontamination of your kitchen after handling frozen berries.