Understanding the Science of Food

From molecules to mouthfeel

Sharon Croxford

• Editorial: Routledge
• Año: 2020
• ISBN:
  9781000248296
• Edición: 1
• Categoría: Medizin
• Categoría: Ernährung, Diätetik & Bariatrie

Being able to understand the principles of food science is vital for the study of food, nutrition and the culinary arts. In this innovative text, the authors explain in straightforward and accessible terms the theory and application of chemistry to these fields.The key processes in food preparation and the chemistry behind them are described in detail, including denaturation and coagulation of proteins, gelatinisation, gelation and retrogradation of starches, thickening and gelling, browning reactions, emulsification, foams and spherification, chemical, mechanical and biological leaveners and fermentation and preservation. The text also describes the science of key cooking techniques, the science of the senses and the experience of food, food regulations and the future of healthy food. The origins of food are explored through a focus on the primary production of key staples and their journey to the table. Tips and advice from leading chefs as well as insights into emerging food science and cutting-edge nutrition research from around the world are included throughout, and reveal both the practical application of food chemistry and the importance of this field. Featuring explanatory diagrams and illustrations throughout, Understanding the Science of Food is destined to become an essential reference for both students and professionals.
'An innovative and informative text that will address the need for a food science text suitable for nutrition and dietetics students in Australia.' - Katherine Hanna, Faculty of Health, Queensland University of Technology.'A unique and timely text that will be welcomed by students, instructors, and scientists in multiple disciplines. I am thrilled to see such a modern take on the subject, blending the fundamentals of food science and chemistry with the insights and experience of practitioners from the culinary arts.' - Patrick Spicer, lecturer and researcher in food science

Part 1
FOOD COMPONENTS,
INTRODUCTORY CHEMISTRY
AND FOOD SAFETY

Chapter 1
Introductory chemistry

LEARNING OUTCOMES

After completing this chapter, you should be able to:

• describe atoms, elements, molecules, compounds and ions
• explain chemical bonding, including the different bonding types and their relative strengths
• outline the periodic table, including how periods, groups and blocks of elements are arranged and the reasons for these arrangements
• identify, name and draw key organic compounds found in food in a range of formats
• explain oxidation and reduction reactions
• explain acid–base reactions and how buffers work.

Foundations

This chapter provides an introduction to chemistry and works through the key concepts required for a good foundation knowledge of the subject before launching into some more specific food science. A sound understanding of the foundation concepts described is important for a full appreciation of the fascinating world of food science and its application in food preparation and cooking, nutrition and dietetics, and food technology and production. Foods are, after all, complex chemicals, and they undergo a range of physical and chemical changes when they are subjected to manipulations in the laboratory and kitchen.

Atoms, elements, molecules and compounds

Atoms

Atoms are the building blocks of all things. They are made up of protons, electrons and neutrons. Protons have a positive charge and electrons a negative charge, while neutrons have a neutral charge. Each atom has the same number of protons as it does electrons. There are usually the same number or more neutrons as there are protons. Atoms of one element can have different numbers of neutrons; such atoms are called isotopes.

Protons and neutrons are concentrated towards the centre of the atom, the nucleus. Electrons arrange themselves around the nucleus in pathways called shells, which contain subshells; these in turn contain orbitals. Each shell can have only a set number of electrons. Electrons’ negative charge means they are attracted to the nucleus of the atom; therefore, electrons typically take up the inner (lowest energy) before the outer (highest energy) shells. The Aufbau principle (from the German for ‘building up’) states that electrons fill the lowest energy shells before filling the highest energy shells, in order to promote stability.

Table 1.1 shows shells and subshells with their maximum numbers of electrons. An atom with eight electrons has two in subshell 1s, two in subshell 2s and four in subshell 2p. This leaves two places in subshell 2p to complete the 2 shell. The atom is not completely stable, as the outermost shell, or valence shell, is not full. This principle is referred to as the octet rule, which states that stability comes with full s and p electron subshells (eight electrons), which brings the electron arrangement of elements in the main group of the periodic table closest to the noble gases. When applying the Aufbau principle it is important to note that the subshell 4s is lower in energy than the subshell 3d. Subshells theoretically fill in the following order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, and so on. This order for filling electron subshells is called the Madelung rule, after the German physicist Erwin Madelung.

Noble gases, which include helium and neon, in group 18 of the periodic table (see Figure 1.3), have full valence shells. Fluorine, in group 17, has nine electrons, with seven in its valence shell. It is highly reactive as it readily

Table 1.1 Maximum number of electrons in the first five shells and their subshells

	Shell		Subshell
Number	Name	Max. electrons	Name	Max. electrons
1	K	2	1s	2
2	L	8	2s	2
			2P	6
3	M	18	3s	2
			3p	6
			3d	10
4	N	32	4s	2
			4p	6
			4d	10
			4f	14
5	O	50	5s	2
			5p	6
			5d	10
			5f	14
			5g	18

participates in chemical reactions, bonding with other elements to fill its outer shell and become more stable. Chemical reactions involve the rearrangement of the molecular or ionic structure of substances to produce different substances. Bonds are broken in reactants and re-formed to create products. Figure 1.1 shows electron shells and their arrangements in potassium, and Figure 1.2 shows key elements and their arrangements of electrons, highlighting those that are stable and unstable.

Figure 1.1 Atomic arrangement of potassium
Note: This figure is not to scale, and the electrons are in constant motion.

Figure 1.2 Atomic arrangements of key elements

Elements

An element is a pure substance made up of a single type of atom; it cannot be broken down chemically. Elements are classified as metals or nonmetals. Most elements are metals. Metals conduct heat and electricity well, are mostly solid at room temperature and form positive ions (see belo...