Organic, Non-Thermal Pasteurization Method for Nuts, Seeds, and Grains

Consumer preferences for plant-based foods and the growing popularity of vegan and paleo diets are driving demand for nuts, seeds, and grains. Market research projects the compound annual growth rate (CAGR) for nuts and seeds to be approximately 4.7% between 2018 and 2024.

To keep up with that growth, processors will need to increase output in the coming years. Companies that process nuts, seeds, and grains are also thinking about how to maintain food safety and the healthy characteristics of the food itself as they grow to meet demand. Consumers don’t want to sacrifice the essential nutrition in nuts, seeds, and grains for price or availability. They want it all.

For some time, regulations have been in place that require pasteurization of common and high-risk foods such as dairy products. But, to maintain high food safety standards, pasteurization should be considered for many other types of foods, including nuts, seeds, and grains.

Pasteurization of Nuts, Seeds, and Grains Achieves Food Safety

There’s a common assumption that dry or low-moisture foods don’t have to be pasteurized. Low-moisture foods present fewer risks for foodborne illness, but they’re not immune to the possibility. In fact, in 2016, CDC attributed an outbreak of Salmonella infections in multiple states to raw pistachios.

Indeed, low-moisture foods can become contaminated with pathogens such as Salmonella and E. coli. Although pathogens cannot successfully grow and multiply on low-moisture foods, the environment can be adequate for pathogens to survive. Without pasteurizing low-moisture foods, there is no kill step to eliminate pathogens and ensure food is safe for consumption.

Moreover, some nut varieties, such as almonds and pecans, are harvested in a unique way that can potentially expose them to contamination. Almonds and pecans grow on large trees and pass through many different stages during their maturation.

For example, in the last stage of development, the hull of an almond starts to crack, allowing air to dry it and the almond. To harvest the almonds from the hulls and the trees, farmers use mechanical tree shakers to shake the almonds from the shells. The dried almonds then drop to the ground and dry there for up to 10 days, during which time they can come into contact with debris, insects, and potential pathogens on the ground.

This is one of the reasons the almond industry began to self-regulate more than a decade ago. Now, the Almond Board of California (ABC) requires that all almonds grown in California be pasteurized. Research conducted by the ABC states that “there is a low level presence of Salmonella in the soil across the California almond growing region, regardless of location, soil type, growing practices or age of orchard.” As a result, in 2007, the board began regulating that all California almonds shipped within North America be pasteurized.

Researchers Danyluk and Brar note in Microbiology Spectrum that nuts and grains could be “contaminated with foodborne pathogens at any stage during production, processing, storage, and distribution.” They state that sources of contamination can range from “soil, animal intrusion, contaminated harvesting equipment, harvest and preharvest handling, and storage conditions.”

Enough evidence exists to make a case for nut, seed, and grain pasteurization.

Methods of Pasteurization

Pasteurizing low-moisture foods is challenging because they are not liquid. Processors utilize several technologies to pasteurize nuts, seeds, and grains. These include steam pasteurization, fumigation, irradiation, and emerging methods in non-thermal pasteurization.

The traditional approach has been a heat treatment, such as steam pasteurization, that uses high levels of heat to kill pathogens. However, heat treatment can be perceived as “cooking” the food to some extent, and changes the sensory and nutritional qualities of nuts, depending on the duration of the heat exposure.