Oxidative Stability and Shelf Life of Foods Containing Oils and Fats

Min Hu, Charlotte Jacobsen

• Publisher: Academic Press and AOCS Press
• Year: 2016
• ISBN:
  9781630670573
• Topic: Technik & Maschinenbau
• Subtopic: Lebensmittelwissenschaft

Oxidative Stability and Shelf Life of Foods Containing Oils and Fats focuses on food stability and shelf life, both important factors in the improvement and development of food products. This book, relevant for professionals in the food and pet food industries, presents an evaluation of methods for studies on the oxidative stability and shelf life of bulk oils/fats, fried oils and foods, food emulsions, dried foods, meat and meat products, and seafood in food and pet food.

• Focuses on the application of various evaluation methods to studies of oxidative stability and shelf life in oils and fats and oils and fats-containing foods in the food and pet food industries
• Discusses oxidative stability and shelf life of low-moisture (dry) food, including dry pet food
• Discusses lipid co-oxidation with protein because a number of food products contain both lipids and proteins
• Directed mainly toward readers working in the food and pet food industries

Chapter 1

Analysis of Lipid and Protein Oxidation in Fats, Oils, and Foods

K.M. Schaich Department of Food Science, Rutgers University, New Brunswick, NJ, USA

Abstract

During nearly 20 years of the low-/no-fat era, lipid oxidation was essentially forgotten as a stability problem. Now, the era of healthy fats focuses on reformulating foods with highly unsaturated (polyunsaturated) fatty acids (PUFAs). PUFAs are essential – they cannot be synthesized by humans and they are required for many physiological processes – but also are extremely sensitive to oxidation and can very rapidly degrade food quality, function, and nutrition by production of off-flavors and odors, loss of essential fatty acids, and co-oxidation of proteins and vitamins. Thus, a need for accurate and sensitive tracking of lipid oxidation has once again moved to the forefront in food analyses and quality control. Old “rules” of how to measure lipid oxidation do not always provide accurate pictures of lipid oxidation. Most critically, they often underestimate total oxidation levels and misrepresent active pathways. This chapter argues for a new paradigm in analysis of lipid oxidation. The main focus is on analyses used or likely to be applied in the food industry. Highly specialized methods such as electron paramagnetic resonance, nuclear magnetic resonance, and mass spectrometry requiring expensive instrumentation are not included.

Keywords

Food industry; Healthy fats; Lipid oxidation; Polyunsaturated fatty acids

1.1. Introduction

During nearly 20 years of the low-/no-fat era, lipid oxidation was essentially forgotten as a stability problem. Now, the era of healthy fats focuses on reformulating foods with highly unsaturated (polyunsaturated) fatty acids (PUFAs). PUFAs are essential – they cannot be synthesized by humans and they are required for many physiological processes – but also are extremely sensitive to oxidation and can very rapidly degrade food quality, function, and nutrition by production of off-flavors and odors, loss of essential fatty acids, and co-oxidation of proteins and vitamins. Thus, the need for accurate and sensitive tracking of lipid oxidation has once again moved to the forefront in food analyses and quality control.

A book published by the American Oil Chemists’ Society, Lipid Oxidation: Challenges in Food Systems (Logan et al., 2013), addressed issues that pose stumbling blocks to understanding, analyzing, and stabilizing lipid oxidation. The current book moves forward to practical problems in dealing with lipid oxidation in foods. Chapter 2 in the preceding book presented a number of conceptual and practical challenges to analyzing lipid oxidation (Schaich, 2013b). Readers are referred to that chapter because it provides a critical base for this chapter, which moves forward to consider options in analyzing lipid oxidation.

Deciding how to measure lipid oxidation and its associated co-oxidations is much more complicated than just selecting an assay from a list or following procedures of standardized methods. The assay selected must match the chemistry of lipid oxidation, the information needed, and the equipment and time available. Some key questions that must be considered include:

• Are you measuring continuously over time, infrequently (weekly or monthly), or only once on isolated samples?

• Are you most interested in early or secondary degradation products, or do you need both for a more accurate picture?

• Do you need detailed data for research or just markers that correlate with sensory responses or known rejection points?

• How fast do you need the information?

• Are co-oxidations likely to re-route lipid oxidation radicals and secondary products to other molecules, particularly proteins, which must then also be monitored to determine system oxidation?

Research on mechanisms requires more detailed product analysis over longer time periods from initial to extended oxidation, whereas strategies to assess effects of processing or antioxidants on stability must follow changes rapidly, and quality control analyses are more often conducted as isolated analyses on samples with unknown extent of oxidation.

Now add to these issues new information indicating that lipid oxidation pathways and formation of lipid oxidation products may not follow the sequence that has dictated most oxidation analyses in current use (Schaich, 2005) but have addition, internal rearrangement, scission, and other reactions that compete with the well-known hydrogen abstractions. Research and industrial food laboratories alike have encountered situations in which standard lipid oxidation products such as hydroperoxides or carbonyls are measured but the results do not correlate with fatty acid loss, sensory evaluations, or off-odors and yellowing in the product. Further, products expected to be secondary frequently begin forming at the same time as conjugated dienes (CDs) and hydroperoxides rather than after observable hydroperoxide decomposition. Thus, old “rules” of how to measure lipid oxidation do not always provide accurate pictures of lipid oxidation. Most critically, they often underestimate total oxidation levels and misrepresent active pathways.

To address these challenges, this chapter argues for a new paradigm in analysis of lipid oxidation. Rather than focusing on single products, analytical strategies must move toward analyzing multiple classes of products to detect all active pathways, to avoid missing some oxidation, and to more accurately assess the extent and pathways of lipid oxidation. The main focus is on analyses used or likely to be applied in the food industry. Highly specialized methods such as electron paramagnetic resonance, nuclear magnetic resonance, and mass spectrometry (MS) requiring expensive instrumentation are not included.

1.1.1. Fundamental Processes of Lipid Oxidation

For more than 70 years, lipid oxidation has been viewed as a radical chain reaction driven by hydrogen abstractions. Hydroperoxides are the first stable product and their decomposition radicals serve as precursors for all secondary products that form at the end of oxidation chains (Figure 1.1). Many books and reviews have presented details of initiation processes, kinetics, and reactions leading to secondary products (Lundberg, 1961; Scott, 1965; Chan and Coxon, 1987; Frankel, 2005b; Schaich, 2005). In the context of oxidation analysis, a key characteristic of the chain reaction is that there is a specific sequence in formation of products – first CDs, then hydroperoxides, and secondary products only evolve after hydroperoxide decomposition. Assumptions also have been that lipid oxidation is relatively slow, so products need only be monitored weekly or monthly in shelf-life studies. Indeed, most analytical strategies have been designed to fit with this scenario.

Figure 1.1 Traditional free radical chain reaction of lipid oxidation. From Schaich (2005); used with permission.

However, experimental results for both kinetics and products often have been inconsistent with the traditional reaction scheme. Attempts to find explanations identified a number of reactions of peroxyl and alkoxyl radicals that compete with hydrogen abstraction and have the potential for greatly complicating lipid oxidation. These alternate reactions were combined with the traditional sequence of hydrogen abstractions to develop an integrated reaction scheme that may more fully and more accurately describe the complex reactions of lipid oxidation, show...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of Contributors
• Preface
• Introduction
• Chapter 1. Analysis of Lipid and Protein Oxidation in Fats, Oils, and Foods
• Chapter 2. Determination and Prediction of Shelf Life of Oils/Fats and Oil/Fat–Based Foods
• Chapter 3. Sensory Evaluation of Oils/Fats and Oil/Fat–Based Foods
• Chapter 4. Oxidative Stability and Shelf Life of Vegetable Oils
• Chapter 5. Oxidative Stability and Shelf Life of Fish Oil
• Chapter 6. Oxidative Stability and Shelf Life of Bulk Animal Fats and Poultry Fats
• Chapter 7. Oxidative Stability and Shelf Life of Frying Oils and Fried Foods
• Chapter 8. Oxidative Stability and Shelf Life of Food Emulsions
• Chapter 9. Oxidative Stability and Shelf Life of Low-Moisture Foods
• Chapter 10. Oxidative Stability and Shelf Life of Meat and Meat Products
• Chapter 11. Oxidative Stability of Seafood
• Chapter 12. Oxidative Stability and Shelf Life of Crackers, Cookies, and Biscuits
• Chapter 13. Packaging Technologies to Control Lipid Oxidation
• Index