Researcher
研究者名
Tomoko T. Asai
研究者名
Kenji Sato
Overview
Kyoto, Japan -- The development of cooking was a major milestone in the evolution of human civilization, as it made our food easier to digest and thus more energy efficient. Heating our food can also kill harmful pathogens, and simply makes certain foods taste better. Overcooking, on the other hand, can have adverse effects, particularly on proteins.
Severe heating can modify proteins in a way that reduces their nutritional value. For this reason we do not tend to overcook our food, but some of the processed food we now consume may be subject to severe heating during production.
Scientists have suspected that a diet including high-temperature-treated proteins may have nutritional deficiencies, yet how exactly long-term intake of these treated proteins affects physiological and behavioral responses has not been well understood. This motivated a team of researchers at Kyoto University to investigate how such a diet would affect mice.
"What happens to food-derived molecules after we eat them?" says first author Tomoko T Asai. "I wanted to know whether food processing changes these proteins' absorption as well as their biological effects."
The team prepared soy protein isolate as a ten percent aqueous solution and heated it at 121 degrees Celsius for 20 minutes. They then conducted in vitro digestion to examine the soy protein isolate's amino acid composition and digestibility. After examining the effects of heating on the soy protein, the team fed it to mice for six weeks. Following this feeding period, the researchers observed the physiological and behavioral outcomes of this diet.
The results revealed that the 20-minute heat treatment decreased amino acid levels and increased the amount of insoluble protein and larger soluble peptides in the soy protein isolate. This in turn led to lowered blood amino acid levels in the mice, which reduced bioavailability, or the amount that can be absorbed by an organism. The heated soy protein diet also lowered peripheral serotonin levels and altered social novelty behavior, which refers to responses to unknown individuals.
These findings suggest that the effects of severe heating in food processing could not only decrease amino acid availability and protein digestibility, but may also extend to broader physiological and behavioral responses. While other behaviors such as anxiety and sociability remained unaffected, the researchers were particularly surprised to observe this diet's effect on social novelty behavior.
"Clearly, the same amount of protein does not always mean the same nutritional availability," says Asai.
In the future, the team intends to identify the precise changes taking place in proteins under severe heating, and investigate processing conditions that may be able to reduce these adverse effects while still maintaining food safety.
