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Food scientists uncover new way to preserve nutrient and flavour quality

Researchers have developed a method that guarantees food safety for low-moisture products, such as dried milk, while maximising quality by retaining vitamins, minerals, and flavours, they say.

Scientists at the University of Arkansas in the US have experimented with ways to protect food quality while ensuring its safety, which could allow manufacturers to extend products’ shelf life.

In April 2024, the US food researchers published the results of their study, ‘Bootstrapping for Estimating the Conservative Kill Ratio of the Surrogate to the Pathogen for Use in Thermal Process Validation at the Industrial Scale’, in the Journal of Food Production.

They have developed a framework to support food processors in maintaining food safety while preserving its quality by retaining as many vitamins, minerals, and flavour as possible. The results vary depending on the food type.

Discovering a new food safety method

Food safety processes are critical. However, the techniques can sometimes adversely affect food taste and nutritional value. Food scientist Jennifer Acuff, who led the study, has conducted a study on low-moisture food items, such as powdered milk.

“This collaborative approach encompassed microbiology, engineering, and statistics to provide the food industry with what we believe will be a tool to improve safety without compromising the quality of their dried food products,” said Jennifer Acuff.

In the study, the scientists present a novel method to calculate a safe KR (Key Ratio) between a surrogate and a pathogen that minimises excessive processing while guaranteeing food safety with an acceptable level of risk.

“We have proposed a methodology to pick a value between the most liberal and most conservative food processing approaches based on risk tolerances,” Jeyam Subbiah, head of the food science department at the University of Arkansas, said. “The industry can use this methodology to pick a value and petition the [US Food and Drug Administration] FDA for approval,” Subbiah added.

The current government policy does not have a specific FDA rule for the food processing industry. However, it is requested to submit a petition for a case-by-case review by the government. The US Department of Agriculture’s National Institute of Food and Agriculture and Mars Wrigley supported the study.

Achieving safety while maximising quality

Using data from a study on a harmless “surrogate” microorganism and a statistical technique called “bootstrapping”, the researchers developed their framework to determine the most effective method for ensuring food safety without compromising nutritional content and taste. In doing so, they strive to provide food processors with solutions that fall within the FDA guidelines.

Surrogate microorganisms are often employed for food safety challenge studies to ensure the safety of canned foods. “Surrogates are like dummies used in crash testing to validate car safety,” Subbiah said. “They are non-pathogenic microorganisms, which should have similar or higher heat resistance than the actual pathogen. Often, they are a lot more resistant,” Subbaih added.

While low-moisture foods are generally less susceptible to foodborne illnesses than fresh meats and dairy, they are not entirely immune. The researchers said that following several food safety outbreaks, the food industry has become more cautious regarding safety challenge studies. They now require the same level of log reduction of the surrogate as they would for the pathogen. Although this ensures high food safety, it may also lead to nutrient degradation due to severe thermal processing.

To address this issue, the US study’s researchers propose an alternative approach using bootstrap sampling to determine a more practical and conservative KR. The technique generates multiple samples by randomly selecting data points from the original data. By doing so, researchers can better understand how much the results may vary due to chance and consider the experimental and biological variability in different food matrices.

Understanding thermal processing

Researchers collected thermal inactivation kinetics data for Salmonella, acting as the target organism, and Enterococcus faecium, as the test organism, in Non-Fat Dried Milk and Whole Milk Powder at different temperatures of 85, 90, and 95°C.

The data was used to calculate the mean KR, showing that as the temperature increased, KR also increased, with Whole Milk Powder having a higher KR than Non-Fat Dried Milk. The researchers said that food industries can use this framework to validate their processes and reduce the risk of quality degradation by determining the minimum processing temperature and acceptable risk levels.

Milk powder is a frequently used ingredient in various ready-to-eat foods like sweets, infant formula, protein shakes and beverages. It is created by spray-drying pasteurised liquid milk rich in nutrients at a temperature range of 180-220°C. This process results in a fine and powdery substance that can be easily used as an ingredient.

Despite high temperatures, spray drying is not a reliable method of eliminating all bacteria. Some heat-resistant strains like Salmonella enterica and Cronobacter sakazakki can survive through the process, a 2020 study found. Furthermore, even if milk powders are pasteurised, they still have the potential to be contaminated during processing if proper sanitation and quality control measures are not followed, whether intentionally or unintentionally.

Thermal processing is a commonly used method for pathogen inactivation in dairy powders. Milk-related products have been researched to validate thermal processing steps following spray drying. The researchers said these thermal processing findings bring the dairy industry closer to achieving a recognised and validated technique.