Food Preservation Techniques

Peter Zeuthen, Leif Bøgh-Sørensen

• Publisher: Woodhead Publishing
• Year: 2003
• ISBN:
  9781855737143
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

Extending the shelf-life of foods whilst maintaining safety and quality is a critical issue for the food industry. As a result there have been major developments in food preservation techniques, which are summarised in this authoritative collection. The first part of the book examines the key issue of maintaining safety as preservation methods become more varied and complex. The rest of the book looks both at individual technologies and how they are combined to achieve the right balance of safety, quality and shelf-life for particular products.

• Provides an authoritative review of the development of new and old food preservation technologies and the ways they can be combined to preserve particular foods
• Examines the emergence of a new generation of natural preservatives in response to consumer concerns about synthetic additives
• Includes chapters on natural antimicrobials, bacteriocins and antimicrobial enzymes, as well as developments in membrane filtration, ultrasound and high hydrostatic pressure

1

Introduction

One of the major advances in human history was the ability to preserve food. It was the prerequisite to man settling down in one place, instead of moving from place to place in the never ending hunt for fresh food. The earliest preservation technologies developed were drying, smoking, chilling and heating. Later on the art of controlling these technologies was developed. The work of Pasteur in the nineteenth century then made it possible to understand the real mode of operation of preservation techniques such as heating, chilling and freezing, providing the basis for more systematic monitoring and control.

The use of various compounds such as salt and spices to preserve foods was also used in ancient times. Unfortunately, the gradual use of a wider range of chemicals for preservation such as boron or cumarine sometimes led to misuse. Consumers have developed some suspicion of the use of chemical additives, sometimes with good reason in such cases as antibiotics and materials such as hexamethyltetramine (which during processing and storage develops into formaldehyde).

Consumers have fewer reservations about physical treatments, although one of the oldest technologies, smoking, is now suspected of being carcinogenic. Another more recent physical treatment which is also much under debate is irradiation. Many studies have shown it to be safe and it has been approved for use in food processing in several countries, e.g., the USA, because it has proved to be the best way to kill Salmonella and other pathogenic bacteria. However, irradiation of foods is not used in practice in most countries in Europe because of continuing consumer concerns about the safety of the technology.

Recent debate about preservation techniques has focused on ways of preserving foods in a way that is both safe but also preserves the intrinsic nutritional and sensory qualities present in raw and fresh food by minimising the amount and severity of subsequent processing operations. This is why minimally processed foods have gained such great popularity, although they raise new safety risks. As an example, they often rely on an effective cold chain during storage and distribution to prevent microbial growth. This book describes both established and new preservation methods which embrace biotechnology and physics. Both methods offer the possibility of preserving food safely with a minimal impact on quality. The book describes the principles behind individual preservation methods, the foods to which they can be applied, their impact on food safety and quality, their strengths and limitations. It also shows how individual techniques have been combined to achieve the twin goals of food safety and quality. The book tries to describe a status quo of where we are in the development of food preservation techniques at the beginning of a new millennium, and some of the things we still need to do.

Part I

Ingredients

2

The use of natural antimicrobials

P.M. Davidson; S. Zivanovic University of Tennessee, USA

2.1 Introduction

Food antimicrobials are chemical compounds added to or present in foods that retard microbial growth or kill microorganisms. The functions of food antimicrobials are to inhibit or inactivate spoilage microorganisms and pathogenic microorganisms. The latter function has increased in importance in the past 10–15 years as food processors search for more and better tools to improve food safety (Davidson, 2001). Prior to recent approvals of certain compounds to control foodborne pathogens by worldwide regulatory agencies, one of the only uses of antimicrobials to control a pathogen was nitrite or nitrate against Clostridium botulinum in cured meats.

A number of compounds are approved by international regulatory agencies for use as direct food antimicrobials (Table 2.1). The question arises as to why, with so many compounds already approved for use in foods, would the food processing industry need a greater number of food antimicrobials? The primary incentive for searching for effective antimicrobials among naturally occurring compounds is to expand the spectrum of antimicrobial activity over that of the regulatory-approved substances. Most of the traditional, currently approved food antimicrobials have limited application due to pH or food component interactions. For example, organic acids function at low concentrations only in high acid foods (generally less than pH 4.5–4.6). This is because the most effective antimicrobial form is the undissociated acid which exists in majority only at a pH below the pK_a of the compound. All regulatory-approved organic acids used as antimicrobials have pK_a values less than 5.0 (Table 2.2) which means their maximum activity will be in high-acid foods. For food products with a pH of 5.5 or greater, there are very few compounds that are effective at low concentrations. Another factor leading to reduced effectiveness among food antimicrobials is food component interactions. Most food antimicrobials are amphiphilic. As such, they can solubilize in or be bound by lipids or hydrophobic proteins in foods making them less available to inhibit microorganisms in the food product.

Table 2.1

Current regulatory-approved compounds for use as direct addition food antimicrobials

Compound or group of compounds

Alkyl esters of p-hydroxybenzoic acid (Parabens; methyl, ethyl, propyl, butyl and heptyl)

Acetic acid and acetate salts, diacetates, dehydroacetic acid

Benzoic acid and benzoate salts

Dimethyl dicarbonate, diethyl dicarbonate

Lactic acid and lactate salts

Lysozyme

Natamycin

Nisin

Nitrites and nitrates

Phosphates

Propionic acid and propionate salts

Sorbic acid and sorbate salts

Sulfite derivatives

Table 2.2

pK_a of regulatory-approved organic acids

Compound or group of compounds	pKa
Acetic acid	4.75
Benzoic acid	4.19
Lactic acid	3.79
Propionic acid	4.87
Sorbic acid	4.75

Interest in natural antimicrobials is also driven by the fact that international regulatory agencies are generally very strict about requirements for toxicological evaluation of novel direct food antimicrobials. In many parts of the world, toxicological testing of new synthetic compounds could take many years and many millions of dollars to obtain approval. For some types of food additives a payback may be possible (e.g., artificial sweeteners), but for food antimicrobials it is less likely that obtaining approval would be profitable.

An argument often used to justify natural antimicrobials is that they will produce ‘green’ labels, i.e., one with few or no ‘synthetic’ additives in the ingredient list. While this rationale may be true, it must be remembered that many of the antimicrobial compounds approved for use in foods today come from natural sources (Table 2.3). If a truly effective antimicrobial was discovered from a natural source, it may be more economically feasible to synthesize it than to extract it from a natural source. This justification also leads consumers to the mistaken belief that food additives currently in use are potentially toxic and should be avoided.

Table 2.3

Natural sources for antimicrobials

Compound or group of compounds	Natural source
Acetic acid	Vinegar
Benzoic acid	Cranberries, plums, prunes, cinnamon, cloves, and most berries
Lactic acid	Lactic acid bacteria
Propionic acid	Swiss cheese (Propionibacterium freudenreichii ssp. shermanii)
Sorbic acid	Rowanberries

In addition to potential benefits associated with natural antimicrobials in foods, there are a number of potential concerns that need to be examined with respect to food safety. For example, if an antimicrobial is to be used exclusively to inhibit a pathogenic microorganism, it must be uniformly effective, stable to storage, and stable to any processes to which it is exposed. Standardized assays for activity need to be developed to ensure that the antimicrobial compounds retain potency. Finally, producers and users of natural antimicrobials that make claims for efficacy of use will be likely to be liable for any claims they make. In short, natural antimicrobials have excellent potential but probably will not produce miracles.

2.2 Natural antimicrobials from animal sources

Naturally occurring antimicrobials may be classified by source. There are compounds from animal, plant and microbial sources. As stated above, some naturally occurring antimicrobials have been approved for di...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• Contributor contact details
• 1: Introduction
• Part I: Ingredients
• Part II: Traditional preservation technologies
• Part III: Emerging preservation techniques
• Part IV: Assessing preservation requirements
• Index