Handbook of Antioxidants for Food Preservation (eBook)

eBook Download: PDF | EPUB

2015 | 1. Auflage
514 Seiten
Elsevier Science (Verlag)
978-1-78242-097-2 (ISBN)

Lipid oxidation in food leads to rancidity, which compromises the sensory properties of food and makes it unappealing to consumers. The growing trend towards natural additives and preservatives means that new antioxidants are emerging for use in foods. This book provides an overview of the food antioxidants currently available and their applications in different food products. Part one provides background information on a comprehensive list of the main natural and synthetic antioxidants used in food. Part two looks at methodologies for using antioxidants in food, focusing on the efficacy of antioxidants. Part three covers the main food commodities in which antioxidants are used. - Reviews the various types of antioxidants used in food preservation, including chapters on tea extracts, natural plant extracts and synthetic phenolics - Analyses the performance of antixoxidants in different food systems - Compiles significant international research and advancements

Lipid oxidation in food leads to rancidity, which compromises the sensory properties of food and makes it unappealing to consumers. The growing trend towards natural additives and preservatives means that new antioxidants are emerging for use in foods. This book provides an overview of the food antioxidants currently available and their applications in different food products. Part one provides background information on a comprehensive list of the main natural and synthetic antioxidants used in food. Part two looks at methodologies for using antioxidants in food, focusing on the efficacy of antioxidants. Part three covers the main food commodities in which antioxidants are used. - Reviews the various types of antioxidants used in food preservation, including chapters on tea extracts, natural plant extracts and synthetic phenolics- Analyses the performance of antixoxidants in different food systems- Compiles significant international research and advancements

Antioxidants

Principles and applications

F. Shahidi Memorial University of Newfoundland, St. John’s, NL, Canada

Abstract

Antioxidants are used in food to protect it from deleterious effects of oxidation and are also employed as dietary supplements to neutralize the adverse effects of oxidative stress. Many of the natural antioxidants of interest are of plant origin and belong to the phenolic and polyphenolic class of compounds as well as carotenoids and antioxidant vitamins, among others. The activity of antioxidants and their mechanism of action is dictated by the structural features of the molecules involved, the system in which they are present as well as processing and storage conditions, among others. While much research has been carried out on natural sources of antioxidants, their widespread use is hindered by regulations, which only permits the use of those that have an RDI (required daily intake) such as vitamins. However, green tea, rosemary and other spices or their extracts thereof, and mixed tocopherols are often used in foods as flavouring agents or under other disguised forms to bypass these unwarranted regulatory issues.

Keywords

Antioxidants; Carotenoids; Chemical structures; Green tea; Legal status; Phenolics; Polyphenolics; Rosemary; Spices; System dependencyTocopherols

1.1. Introduction

Use of antioxidants in food was unintentionally practiced since antiquity, when populations living in hot climates in countries like India, Thailand, and certain parts of China (such as Sichuan Province) learned from experience that addition of spices to foods extended their shelf life and prevented spoilage (Shahidi, unpublished work). Of course, this was not only due to the action of spices as antioxidants, but also due to their antimicrobial action. As time progressed, and in more recent history, intentional use of antioxidant spices became commonplace.

Antioxidants may be defined as substances that, when present in food, delay, control, or inhibit oxidation and deterioration of food quality. In the body, antioxidants reduce the risk of degenerative diseases arising from oxidative stress. This definition extends that originally coined by Halliwell in 1999. The antioxidants used in food or present in it could be either primary or secondary in nature. The primary antioxidants are those that neutralize free radicals by either donating a hydrogen atom (hydrogen atom transfer or HAT) or by a single electron transfer (ET) mechanism. Meanwhile, secondary antioxidants are those that neutralize prooxidant catalysts. These include chelators of prooxidant metal ions (e.g., iron and copper), exemplified by ethylenediaminetetraacetic acid (EDTA) and citric acid (CA) or deactivate reactive species such as singlet oxygen (e.g., beta-carotene).

Synthetic antioxidants such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate (PG), and tertbutylhydroquinone (TBHQ) have been used as primary antioxidants to arrest free radicals and control oxidation and off-flavour development. However, more recent interest has focused on studying natural antioxidants due to the toxicity and carcinogenic effects of some synthetic antioxidants in animals at high concentrations. To this end, the number of publications on food phenolics, which are considered potential antioxidants, has increased dramatically in the past 20 years, and from 1989 until 2011 total over 24,000. However, very few antioxidants from natural sources have reached the market due to problems associated with regulatory issues, among others. This chapter provides a brief summary of the different classes of food phenolics and some structural characteristics that affect their antioxidant potential. In addition, antioxidants that are commonly used in foods are considered and appraised in terms of using them as natural sources of antioxidants in food to extend shelf life. Needless to say, some of these natural sources of antioxidants may also be very important in rendering health benefits and reducing the risk of certain diseases (Shahidi & Wanasundara, 1992).

1.2. Phenolic compounds in plant foods and natural health products and their structural features

Phenolic and polyphenolic compounds are secondary metabolites occurring in plants and are produced via shikimic acid pathway. The precursors to phenolic compounds are phenylalanine and, to a lesser extent, tyrosine. The removal of an ammonia molecule from these amino acids occurs via the action of phenylalanine ammonia lyase (PAL) or tyrosine ammonia lyase (TAL), respectively. The cinnamic acid molecules so produced may further be derivatized to different phenylpropanoids or hydroxycinnamic acids (Figure 1.1). Loss of a two-carbon moiety from the latter class of compounds leads to the formation of the hydroxybenzoic acid family of food phenolics that are dominant in cereals, grains, and legumes (Figure 1.1). Furthermore, phenylpropanoids may react with three molecules of malonyl coenzyme A to produce chalcones that can subsequently cyclize to afford different subclasses of flavonoids (Figures 1.2 and 1.3). Condensation of phenolics may lead to the formation of tannins, both hydrolyzable and condensed/nonhydrolyzable (Figure 1.4).

The antioxidant potency of the aforementioned phenolics, the main phenolics in food, is dictated by their structural characteristics as well as the medium in which they are used. In the latter case, polar antioxidants are generally more effective in bulk oil while nonpolar antioxidants are superior in their action in oil-in-water emulsions, as explained by polar paradox theory (Porter, 1980). A critical reevaluation of this theory has recently been provided (Shahidi & Zhong, 2011). Meanwhile, the antioxidant activity of phenolic acids and their esters depends on the number of hydroxyl groups in the molecule, and this would be strengthened by steric hindrance (Shahidi & Naczk, 2004). Hydroxylated cinnamic acids with extended conjugation are more effective than their corresponding benzoic acid counterparts. Furthermore, within each class or subclass, the special arrangement of hydroxyl groups or hydroxyl and keto groups, as exists for 3-hydroxy-4-keto group and/or 5-hydroxy-4-keto group (when the A-ring is hydroxylated at the 5th position) in flavonols, allows chelation of prooxidant metal ions. An o-quinol group at the B-ring can also demonstrate metal chelating activity (Pratt & Hudson, 1990). Hence, the antioxidant efficacies can be rendered by one or more mechanisms. Of course, the reducing power of phenolics present also provides another mechanism by which antioxidant effects of food phenolics may be experienced.

1.2.1. Oxidative processes, natural antioxidants and their mechanism of action

Autoxidation of polyunsaturated lipids in food involves a free radical chain reaction that is generally initiated by exposure of lipids to light, heat, ionizing radiation, metal ions, or metalloprotein catalysts. Enzyme lipoxygenase can also initiate oxidation. Under exposure to light, photooxidation may proceed, and high temperature thermal oxidation, under high temperatures of cooking, grilling, or frying, produces polar and polymeric products. The most common oxidation occurring in foods is autoxidation. The classical route of autoxidation includes initiation (production of lipid free radicals), propagation, and termination (production of nonradical products) reactions [reactions (1.1) to (1.4)]. Figure 1.5 represents a general scheme for autoxidation of polyunsaturated lipids and its consequence in quality deterioration of food.

Figure 1.1 Production of phenolic acids from phenylalanine and tyrosine.

Figure 1.2 Production of flavonoids from phenyl propanoids.

Figure 1.3 Chemical structures of different flavonoids.

Figure 1.4 Chemical structures of typical tannins.

RH→R•+H•

(1.1)

R•+O2→ROO•

(1.2)

O•+RH→R•+ROOH

(1.3)

(1.4)

Meanwhile, some plant phenolic compounds have been considered as antioxidants and are being commercially produced. These include specific spices such as rosemary extract, as well as green tea and mixed tocopherols, in addition to materials that may be used as process adjuncts. These latter materials include protein binders and other processing aids such as liquid smoke used in preparation of certain processed meats. Phenolic compounds with antioxidant potential can also seep into wine from the wood barrels used in storage and aging.

The mechanism by which antioxidants exert their effects may vary depending on the compositional characteristics of the food, including its minor components. Furthermore, the beneficial health effects of consuming plant foods have been ascribed, in part, to the presence of phenolics, which are associated with counteracting the risk of cardiovascular diseases, cancer, and cataracts, as well as a number of other degenerative diseases. This is achieved by preventing lipid oxidation, protein cross linking, and DNA mutation, and at later stages tissue damage. However, there are many...

Erscheint lt. Verlag	25.2.2015
Sprache	englisch
Themenwelt	Technik ► Lebensmitteltechnologie
ISBN-10	1-78242-097-5 / 1782420975
ISBN-13	978-1-78242-097-2 / 9781782420972

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