By Dave DeFusco
A Katz School study on the science behind freezing food could lead to more effective food preservation techniques and a profound impact on the economy and food security.
Published in Food Biophysics, , “Inverse Relationship Between Ice Nucleation and Ice Growth Rates in Frozen Foods,” examines the role of ice nucleation and ice growth during freezing. Ice nucleation refers to the initial formation of ice crystals, while ice growth involves the expansion of these crystals as more water freezes. These two processes directly impact the quality of frozen food, affecting both its texture and longevity.
According to the United States Department of Agriculture (USDA), the United States discards more food than any other country in the world—nearly 120 billion pounds, or $218 billion worth of food, every year. “This significant food loss points to the need for improved methods of preserving food and extending its shelf life, particularly during freezing processes,” said Dr. Ran Drori, senior author and associate professor and chair of the Department of Chemistry and Biochemistry in 鶹ýӳ's Stern College for Women.
Researchers utilized a state-of-the-art micro-thermography system to measure ice nucleation and ice growth rates in common food items, such as beef, zucchini, broccoli and potatoes. Surprisingly, the study found that beef and zucchini had significantly higher ice nucleation rates compared to broccoli and potatoes; however, the latter showed faster ice growth once freezing began. For instance, ice grows five times faster in potatoes compared to beef, but ice nucleation rates in potatoes are around 100 times slower compared to beef.
This seemingly paradoxical relationship, where foods with higher ice nucleation rates experience slower ice growth, has important implications. For example, beef and zucchini may begin to freeze quickly but take longer to complete the process, while broccoli and potatoes, once frozen at lower temperatures, experience rapid ice expansion.
“We used computer simulations to understand how heat flows through the food product during cooling and freezing,” said Shriya Jitendra Kalburge, a co-author of the study and student in the Katz School’s M.S. in Biotechnology Management and Entrepreneurship. “These simulations were compared to experimental results and a good agreement was observed.”
The researchers suggest that customized freezing processes based on the specific properties of each food could help preserve its quality. By fine-tuning freezing conditions to match a food’s unique chemical composition and freezing behavior, food manufacturers could reduce spoilage, maintain texture and extend shelf life.
The study, which was supported by the U.S. Department of Agriculture’s National Institute of Food and Agriculture and the Katz School’s Faculty Research Initiative, also linked ice growth rates to the water, sugar and fat content of the foods. Foods with higher water content, such as broccoli and potatoes, showed faster ice growth, while those with higher fat and protein levels, like beef, froze more slowly. This difference in freezing behavior highlights how the nutritional composition of food affects its preservation.
The study's other co-authors were Dr. Martin Zalazar in the Department of Chemistry and Biochemistry and Facultad de Ingenieria at the Universidad Nacional de Entre Rios, and Yining Zhang, a student in the M.S. in Biotech. Zhang measured ice growth rates in aqueous solutions with sucrose. Studying how sucrose influences the rate at which ice forms can provide insights into applications where controlling freezing is important, such as in food preservation, cryopreservation or even in biological and industrial processes where ice formation needs to be managed.
“By applying principles of crystal growth and nucleation, we were able to explain why certain foods freeze faster than others and how these processes can be controlled to improve food preservation,” said Dr. Drori, who is also a professor in the Katz School’s M.S. in Biotechnology Management and Entrepreneurship. “Customized freezing processes could lead to fresher, longer-lasting products on supermarket shelves, reducing the likelihood of spoilage and providing higher quality foods to consumers.”
