Antioxidants in Food

Practical Applications

J. Pokorný, N Yanishlieva, Michael Gordon

• Publisher: Woodhead Publishing
• Year: 2001
• Print ISBN: 9781855734630
• eBook ISBN: 9781855736160
• Topic: Technik & Maschinenbau
• Subtopic: Lebensmittelwissenschaft

Antioxidants are increasingly important additives in food processing. Their traditional role is, as their name suggests, in inhibiting the development of oxidative rancidity in fat-based foods, particularly meat and dairy products and fried foods. However, more recent research has suggested a new role in inhibiting cardiovascular disease and cancer. Antioxidants in food provides a review of the functional role of antioxidants and discusses how they can be effectively exploited by the food industry.Part one of the book looks at antioxidants and food stability with chapters on the development of oxidative rancidity in foods, methods for inhibiting oxidation and ways of measuring antioxidant activity. Part two looks at antioxidants and health, including chapters on antioxidants and cardiovascular disease, their antitumour properties and bioavailability. A major trend in the food industry, driven by consumer concerns, has been the shift from the use of synthetic to natural ingredients in food products. Part three looks at the range of natural antioxidants available to the food manufacturer. Part four of the book looks at how these natural antioxidants can be effectively exploited, covering such issues as regulation, preparation, antioxidant processing functionality and their use in a range of food products from meat and dairy products frying oils and fried products, to fruit and vegetables and cereal products.Antioxidants in food is an essential resource for the food industry in making the best use of these important additives.- Provides a review of the functional role of antioxidants- Discusses how antioxidants can be effectively exploited by the food industry

1

Introduction

Professor Jan Pokorný    Prague Institute of Chemical Technology

Fats, oils and lipid-based foods deteriorate through several degradation reactions both on heating and on long term storage. The main deterioration processes are oxidation reactions and the decomposition of oxidation products which result in decreased nutritional value and sensory quality. The retardation of these oxidation processes is important for the food producer and, indeed, for all persons involved in the entire food chain from the factory to the consumer. Oxidation may be inhibited by various methods including prevention of oxygen access, use of lower temperature, inactivation of enzymes catalysing oxidation, reduction of oxygen pressure, and the use of suitable packaging.

Another method of protection against oxidation is to use specific additives which inhibit oxidation. These are correctly called oxidation inhibitors, but nowadays are mostly called antioxidants. These inhibitors represent a class of substances that vary widely in chemical structure, and have diverse mechanisms of action (Table 1.1). The most important mechanism is their reaction with lipid free radicals, forming inactive products. Additives with this mechanism are antioxidants in the proper sense. Usually, they react with peroxy or alkoxy free radicals, formed by decomposition of lipid hydroperoxides. Other inhibitors stabilise lipid hydroperoxides, preventing their decomposition into free radicals. Decomposition of hydroperoxides is catalysed by heavy metals, and consequently metal chelating agents also inhibit oxidation. Some substances called synergists demonstrate no antioxidant activity in themselves, but they may increase the activity of true antioxidants. Another group of substances decompose lipid hydroperoxides by a non-radical pathway, thereby reducing free- radical content. Finally, singlet oxygen oxidises lipids many times faster than the common triplet oxygen, and consequently singlet oxygen quenchers also have an important inhibitory effect on lipid oxidation. In this book, we shall discuss all the above groups of inhibitors, calling all of them antioxidants.

Table 1.1

Mechanisms of antioxidant activity

Antioxidant class	Mechanism of antioxidant activity	Examples of antioxidants
Proper antioxidants	Inactivating lipid free radicals	Phenolic compounds
Hydroperoxide stabilisers	Preventing decomposition of hydroperoxides into free radicals	Phenolic compounds
Synergists	Promoting activity of proper antioxidants	Citric acid, ascorbic acid
Metal chelators	Binding heavy metals into inactive compounds	Phosphoric acid, Maillard compounds, citric acid
Singlet oxygen quenchers	Transforming singlet oxygen into triplet oxygen	Carotenes
Substances reducing hydroperoxides	Reducing hydroperoxides in a non-radical way	Proteins, amino acids

Antioxidant activity depends on many factors such as the lipid composition, antioxidant concentration, temperature, oxygen pressure, and the presence of other antioxidants and many common food components, e.g. proteins and water. Antioxidants were first used before World War II for food preservation. These early antioxidants were natural substances. They were, however, soon replaced by synthetic substances, which were cheaper, of more consistent purity, and possessed more uniform antioxidant properties. They were tested for toxicity by a range of methods in concentrations at 100-200 times the level actually consumed, to confirm their safe use as additives. The increased use of various synthetic food additives was then challenged by consumer groups. Consumers wished to have these additives replaced by natural materials, which were considered to be more acceptable as dietary components. Industrial producers have tried to comply with consumers’ wishes, and have moved to increased use of natural antioxidants. Most natural antioxidants are common food components, and have been used in the diet for many thousands of years so that humans have adapted to their consumption. In our book we place more emphasis on natural antioxidants than on synthetic antioxidants.

In the first part of this book we discuss the oxidation of lipids and its inhibition by antioxidants generally. The second part is devoted to health aspects and current research on the role of antioxidants in inhibiting the development of cardiovascular diseases and of cancer. In the third part, sources and properties of natural antioxidants are discussed. The emphasis is on substances present in plant foods which are frequently consumed in the human diet. In the last part of the book, practical aspects of antioxidant use in food processing are discussed, such as their regulation, preparation, changes during food processing, and application in food products.

Part 1

Antioxidants and food stability

2

The development of oxidative rancidity in foods

Dr Michael H. Gordon The University of Reading

2.1 Introduction

2.1.1 Lipids in foods

Lipids occur in nearly all food raw materials with the major classes being triglycerides (also known as triacylglycerols), which occur in fat storage cells of plants and animals, and phospholipids, which occur in biological membranes. In the processing of a wide range of foods, fats may be added as part of the food formulation. The added fats are a major component of many foods including mayonnaise, margarine, and frying oils. These fats are almost completely triglycerides, and it is these components that are of most significance as potential sources of oxidative off-flavours in these foods. In plant or animal tissues used as foods, the phospholipids present in all biological membranes may be an important substrate for oxidative deterioration.

2.1.2 Pathways to lipid oxidation

The spontaneous reaction of atmospheric oxygen with lipids, known as autoxidation, is the most common process leading to oxidative deterioration. Polyunsaturated fatty acids have the potential for decomposing by this process, whether they are present as free fatty acids or whether they are present in triglycerides (or diglycerides or monoglycerides) or phospholipids. When light and a sensitiser such as chlorophyll are present, activation of oxygen to singlet oxygen may play a role in the initiation of oxidative deterioration. Alternatively, metals including iron or copper, or the enzyme lipoxygenase, may play a role in the process by which oxidative deterioration is initiated. Lipoxygenase is present in plant tissues including those of soybean, pea and tomato. The enzyme may cause oxidative deterioration of lipids during isolation of oils from oilseeds, but it also plays a role in the formation of positive flavours in vegetables during mastication.

2.1.3 Lipid oxidation products

The components formed in the initial stage of autoxidation are the hydroperoxides, and these are also the products formed in lipoxygenasecatalysed oxidation. Although hydroperox...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• List of contributors
• 1: Introduction
• Part 1: Antioxidants and food stability
• Part 2: Antioxidants and health
• Part 3: Natural antioxidants
• Part 4: Practical applications
• Index