Handbook of Food Science and Technology 3

Food Biochemistry and Technology

Romain Jeantet, Thomas Croguennec, Pierre Schuck, Gérard Brule

• Publisher: Wiley-ISTE
• Year: 2016
• ISBN:
  9781119296232
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

This third volume in the Handbook of Food Science and Technology Set explains the processing of raw materials into traditional food (bread, wine, cheese, etc.). The agri-food industry has evolved in order to meet new market expectations of its products; with the use of separation and assembly technologies, food technologists and engineers now increasingly understand and control the preparation of a large diversity of ingredients using additional properties to move from the raw materials into new food products.

Taking into account the fundamental basis and technological specificities of the main food sectors, throughout the three parts of this book, the authors investigate the biological and biochemical conversions and physicochemical treatment of food from animal sources, plant sources and food ingredients.

PART 1
Food from Animal Sources

1
From Milk to Dairy Products

Secreted from the mammary glands of mammals, milk is a complete food designed to provide newborns with energy, compounds necessary for growth, immunological protection, and so forth, which are all vital in the early stages of life. From a physicochemical point of view, milk is complex in terms of its structure, the interactions between its various components and its variability in composition based on species, breed, diet and lactation period. It is a dynamic system due to the presence of endogenous enzymes and microorganisms as well as ionic equilibria, which depend on pH and temperature, and determine the stability of dispersed elements. These physical, physicochemical and biological changes lead to instability in milk, which can be exploited during processing into a variety of dairy products, such as fermented products, cheese, cream, butter, and so on.

1.1. The biochemistry and physical chemistry of milk

Milk is a natural emulsion. Fat, which represents approximately 4% of the overall composition of cow’s milk (w/w), is present in the form of fat globules dispersed in the skimmed milk phase.

The non-fat phase of cow’s milk (skimmed milk) is composed mainly of water (90% (w/w) of the overall composition) in which the following are dispersed or dissolved:

1. – lactose (4.8 – 5% (w/w) of overall composition);
2. – protein (3.2 – 3.5% (w/w));
3. – non-protein nitrogen (NPN) consisting of urea, amino acids and peptides, representing about 5% of the nitrogen fraction of milk;
4. – inorganic minerals (calcium, phosphate, chloride, potassium, sodium) and organic acids (mainly citric acid in fresh milk);
5. – water-soluble vitamins.

1.1.1. Milk fat

The fat content of cow’s milk varies between about 3.3 and 4.7% (w/w) depending on breed, lactation stage, season, and so forth. Milk fat is mostly present in the form of fat globules measuring between 0.2 and 15 µm in diameter. Around 75% of fat globules are smaller than 1 µm, but they represent less than 10% of the total volume of milk fat. Similarly, there are very few fat globules larger than 8 µm; they represent less than 3% of the overall volume. Thus, almost 90% of milk fat is in the form of milk globules measuring between 1 and 8 µm in diameter. The average diameter of fat globules is approximately 4 µm. The core of the fat globule almost exclusively consists of neutral lipids, while the fat globule membrane is composed of complex lipids and proteins. The amphiphilic properties of these complex lipids and proteins facilitate the creation of interfaces and help keep the fat in the dispersed state (Figure 1.1).

Figure 1.1. Composition and main characteristics of milk fat globules

1.1.1.1. Composition and characteristics of milk fat

Table 1.1 shows the average lipid composition of cow’s milk. Triacylglycerols represent approximately 97.5% of the total lipids. Diacylglycerols, monoacylglycerols and free fatty acids are naturally present in small amounts but their proportion can increase with lipolysis. The many other compounds (cholesterol, steroid hormones, vitamins, flavorings and flavor substrates, etc.), even though low in number, play a crucial nutritional and sensory role.

Table 1.1. Average lipid composition of cow’s milk (Source: [CHR 95])

Class of lipids	Percentage of total lipids (w/w)
Triacylglycerols	97.5
Diacylglycerols	0.36
Monoacylglycerols	0.027
Free fatty acids	0.1
Cholesterol	0.31
Hydrocarbons	Traces
Carotenoids	0.008
Phospholipids	0.6

Milk triacylglycerols are made up of more than 400 different fatty acids, which makes milk fat a very complex lipid source, as each fatty acid can be esterified to one of the three hydroxyl groups of glycerol (Table 1.2). However, only 12 fatty acids are present in quantities of more than 1% (mol/mol). Fatty acids are either synthesized in the secretory cells in the udder or taken from the bloodstream (body fat or food origin). Thus, milk fat varies depending on the season, the cow’s diet and the energy level of the food intake, which could determine the ratio of de novo synthesis with regard to plasma uptake.

Table 1.2. Fatty acid composition of milk and distribution on the three positions of glycerol (adapted from [CHR 95])

Fatty acids	Symbol	% mol	Distribution on the glycerol sites (% mol)			Melting point (°C)
			Sn1	Sn2	Sn3
Butyric	4:0	4.8	-	-	35.4	-7.9
Caproic	6:0	2.2	-	0.9	12.9	-1.5
Caprylic	8:0	1.3	1.4	0.7	3.6	+16.5
Capric	10:0	2.9	1.9	3.0	6.2	+31.4
Lauric	12:0	3.3	4.9	6.2	0.6	+43.6
Myristic	14:0	10.8	9.7	17.5	6.4	+53.8
Palmitic	16:0	26.1	34.0	32.3	5.4	+62.6
Palmitoleic	16:1	1.4	2.8	3.6	1.4	-0.5
Stearic	18:0	10.8	10.3	9.5	1.2	+69.3
Oleic	18:1	24.1	30.0	18.9	23.1	+14.0
Linoleic	18:2	2.4	1.7	2.5	2.3	-5.0
Linolenic	18:3	1.1	-	-	-	-11.0

Milk fat is characterized by:

1. – a high proportion of short-chain fatty acids (chain lengths of four to ten carbons) synthesized from acetate and β-hydroxybutyrate produced by microorganisms during cellulose degradation in the rumen. These fatty ...

Table of contents

• Cover
• Table of Contents
• Title
• Copyright
• Introduction
• PART 1: Food from Animal Sources
• PART 2: Food from Plant Sources
• PART 3: Food Ingredients
• Bibliography
• List of Authors
• Index
• End User License Agreement