What physical or chemical changes occur when food is cooked by heating?

In fact, there are more than just four such methods—though the four most common ones are heat, mechanical force, light (i.e., electromagnetic radiation), and salt (i.e., ions): namely, heating, mechanical force (typically achieved via ultra-high pressure), electromagnetic wave irradiation, and ionic effects. Generally speaking, protein denaturation does not involve changes to the primary structure—in other words, the polypeptide chain remains intact; only hydrogen bonds are disrupted, causing the original tertiary structure to unravel. In some cases, secondary structures such as α-helices or β-sheets are also damaged. 1. Let’s begin with heating—something we’re all familiar with. But what happens if we go in the opposite direction and freeze food instead? Freezing can also cause denaturation. Don’t assume this has nothing to do with cooking: modern food industries rely almost entirely on freezing technologies. However, this type of denaturation often negatively affects texture and mouthfeel. Thus, minimizing its extent is crucial for culinary excellence—let’s thank those researchers whose work enables us to enjoy more delicious sashimi. (Image sourced from the internet) 2. Mechanical-force-induced protein denaturation does occur during cooking—though not usually via ultra-high pressure, but rather through high shear forces. For instance, using a high-speed blender causes partial protein denaturation. Even without blenders, vigorous stirring with chopsticks while beating eggs achieves the same effect. After denaturation, structural changes in proteins impair many functional properties—for example, their ability to retain lipids weakens, and actin and myosin dissociate, which is precisely why Chaozhou beef balls possess such remarkable elasticity. Shear forces exert another special effect on proteins: molecular orientation—not the kind related to gender! Spider silk and silkworm silk are both composed of proteins, yet their tensile strengths differ dramatically. This largely stems from spiders’ rapid movement: as they spin webs, mechanical forces orient the silk proteins—mainly through breaking and re-forming hydrogen bonds—yielding exceptional toughness. Silkworms, being too plump, lack this capability. Therefore, when mixing minced meat, consistently stirring in one direction (rather than haphazardly back-and-forth) enhances meat elasticity. So I won’t answer the next question here: Why do elders insist on stirring dumpling fillings in a single direction—and is there any scientific basis for this? 3. Electromagnetic waves can also induce protein denaturation—a phenomenon widespread in nature. High-energy electromagnetic waves such as X-rays and ultraviolet light readily denature proteins. Food-processing plants exploit this mechanism for sterilization, while in home kitchens, microwave ovens serve this purpose. Strictly speaking, microwaves primarily cause polar small molecules—like water—to rotate rapidly, generating heat that subsequently denatures proteins. Thus, this process still falls under thermal denaturation—but its effects differ markedly from conventional heating. First, microwave heating occurs simultaneously throughout the food’s interior and exterior. Consequently, volume changes (typically contraction) accompanying protein denaturation proceed uniformly, yielding a tenderer texture. By contrast, conventional heating proceeds inward from the surface, often overcooking outer layers and rendering them tough and dry—though extreme techniques like pan-frying, roasting, or deep-frying produce a contrasting ‘crispy outside, tender inside’ effect, accentuating Maillard reaction aromas. Microwave heating, however, delivers comparatively milder flavor development. Second, microwaving somewhat resembles reverse steaming: moisture content actually decreases rather than increases during the process, thereby affecting texture to some degree.

The beauty of chemical structures surpasses your imagination!

Proteins, water molecules, DNA… When encountering these familiar terms, have you ever considered appreciating them through the lens of chemistry? What microscopic structures do they truly possess within the chemical world? The popular science project ‘Beautiful Chemistry’, jointly launched by the Advanced Technology Research Institute of the University of Science and Technology of China and Tsinghua University Press, presents these rarely seen chemical structures using exquisitely detailed imagery—including screenshots from computer-generated animations of molecular structures. Get ready—step into the wondrous microscopic world of chemistry and marvel at these astonishingly beautiful structures! 1. Molecules Elements and Compounds White: hydrogen, gray: carbon, red: oxygen, yellow: sulfur Common Organic Molecules in Daily Life White: hydrogen, gray: carbon, red: oxygen, blue: nitrogen Molecular models generated using Chem3D software 2. Supramolecules and Self-Assembly Molecular Flask Containing a Guest Molecule White: carbon, gray: nitrogen, yellow: palladium, green: guest molecule; hydrogen atoms omitted Science 312, 251 (2006) Supramolecular Cage White: carbon, gray: oxygen, sulfur, nitrogen, green: palladium; hydrogen atoms omitted Science 328, 1144 (2010) 3. Interlocked Molecules Molecular Solomon Link Orange: copper, yellow: zinc; within molecular rings: light-colored atoms = carbon, dark-colored atoms = nitrogen/oxygen; hydrogen atoms omitted Angew. Chem. Int. Ed. 46, 218 (2007) Molecular Borromean Rings Yellow: zinc; within molecular rings: light-colored atoms = carbon, dark-colored atoms = nitrogen/oxygen; hydrogen atoms omitted Science 304, 1308 (2004) 4. Proteins Human Apoptosome Complex Protein surface structure rendered using Molecular Maya software PDB ID: 3J2T; Biochemistry 52, 2319 (2013) Earthworm Hemoglobin

Chemistry in Pictures: Practice Makes Perfect Proteins

2 days ago

Saacnicteh Toledo-Patiño has joined the National Autonomous University of Mexico to lead a lab focused on protein engineering and enzyme evolution. Her work utilizes protein crystallization and X-ray analysis to study how structural changes affect function.

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2026-10-21

Chemistry in Pictures: Practice Makes Perfect Proteins

Chemistry in Pictures: Practice Makes Perfect Proteins

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