Making sure your nuts are sterile

Nuts, grains, spices and seeds were once considered low risk from a food safety perspective. As they had a low moisture content it was assumed they would not support microbial growth, but Salmonella can survive on nuts and E.coli in non-heat-treated flour. Making matters worse, both Salmonella and E. coli are pathogenic at such low doses that sampling and testing cannot guarantee that products are not contaminated.

In the current massive General Mills flour recall in the US, E. coli O121 and O26 contamination has resulted in 46 people being infected and 13 hospitalisations. Thousands of tonnes of flour have been recalled. The general recommendation now is that food processors should consider the use of pasteurised flour in ready-to-cook or ready-to-bake foods that are likely to be consumed without cooking or baking.

In 2001 and 2004 outbreaks of foodborne disease caused by Salmonella-contaminated almonds in the US resulted in a USDA requirement that all raw, blanched and roasted almonds be treated to achieve a 4-log reduction in Salmonella.

The Almond Board of California’s Technical Expert Review Panel (TERP) has now validated a number of pasteurisation systems, many of which claim to retain the flavour, mouthfeel and nutrition of raw seeds and grains.

Technologies currently in use or in validation process:

• Cosmed H₂0 Express — vacuum steam
• JBT Foodtech JSP-1 — moist steam
• Revetech Steam Pasteurisation — steam/hot air
• Napasol Sterilisation/Pasteurisation — vacuum steam
• Buhler/Barth — moist heat
• RF Biocidics — radiofrequency/heat (In Australia Riverland Almonds has implemented the RF Biocidics APEX 50 System.)
• Ventilex — atmospheric steam
• PPO (propylene oxide)

Dutch firm Log5 has developed a system that mixes humid air with saturated (dry) steam to manipulate water activity and temperature level with moist heat and achieve a 5-log bacterial reduction without adversely impacting product quality. The system can pasteurise up to 9000 kg/h.

Wholegrain, nut and seed consumers want minimally processed products and so some newer technologies are now coming to the fore.

With an even more benign image than steam and vacuum, ultraviolet light-based technologies are emerging. UV technologies in combination with other microbial interventions remain experimental as a pasteurisation solution, but validated lethality exists from radio waves and ionising radiation.

The Almond Board of California (ABC) has approved a non-roasting bulk pasteurisation process for raw almonds at Sran Family Orchards, a producer of organic and conventional almonds.

The ABC’s Technical Expert Review Panel (TERP) has certified RF Biocidics’ APEX 85 chemical-free, pasteurisation system that uses radiofrequency technology to significantly reduce the level of harmful pathogens in raw almonds.

Interestingly, there are three exceptions to the raw almond pasteurisation mandate — exported US almonds do not have to be pasteurised (except if they are going to Canada or Mexico), farmers can sell 45 kg bags of almonds and, most surprising, imports of raw almonds are not required to be treated before sale in the US.

Almonds in Australia

The following has been taken directly from the Almond Board of Australia website:

Food safety is a top priority for the Almond Board of Australia as we want our consumers to have an enjoyable eating experience every time almonds are snacked on or cooked with. However, natural or raw almonds, as with other raw products such as fruit and vegetables, do have a small inherent risk of contamination.

All Australian almond industry processors maintain high standards of Quality Assurance, including HACCP and Safe Quality Foods (SQF2000) accreditation. Facilities are regularly audited to ensure they meet or exceed food safety standards. In addition to extensive internal testing, all almond products are rigorously tested for both quality and food safety by third party laboratories accredited by the National Association of Testing Authorities Australia. Despite this on rare occasions it has been necessary to recall product.

To minimise bacterial risk, almond processors within Australia are progressing with plans to offer customers pasteurised almonds. Foods such as milk, juice, eggs and canned foods are also pasteurised, and pasteurisation has been proven to reduce the presence of harmful bacteria such as Salmonella. US research shows that commercial pasteurisation processes used for raw almonds do not impact on the taste, quality or nutritional value of natural almonds.

Roasting is a recognised way of pasteurising food products, and almonds are no exception.

Image credit: ©FreeImages.com/Jerry Liu