The Microbiological Quality of Food

Foodborne Spoilers

Antonio Bevilacqua, Maria Rosaria Corbo, Milena Sinigaglia

• Publisher: Woodhead Publishing
• Year: 2016
• eBook ISBN: 9780081005033
• Topic: Technology & Engineering
• Subtopic: Microbiology
• Index: Technology & Engineering

The Microbiological Quality of Food: Foodborne Spoilers specifically addresses the role of spoilers in food technology and how they affect the quality of food. Food spoilers represent a great challenge in food quality, determining the shelf-life of many products as they impact consumer acceptability of taste, texture, aroma, and other perceptions.Divided into four sections, the first section defines microbial spoilage of food, with special emphasis on methods for the evaluation of spoiling phenomena and the status of their regulatory framework, examining both existing regulations and possible gaps. The second section examines spoiling microorganisms, covering a range of common spoilage microorganisms, including pseudomonas, yeasts, and molds and spore formers, as well as less-common spoilers, including lactic acid bacteria and specific spoilage organisms in fish.The third section highlights spoiling phenomena within certain food types. Chapters cover dairy, fish, meat, and vegetables, and other products. The final section investigates emerging topics which point to future trends in the research of food spoilers. There is insight into microorganisms resistant to preservation, the role of biofilms in food quality, and the link between food safety and food spoilage, with a special emphasis on certain spoiling microorganisms which could be opportunistic pathogens. Written by an international team of leading authors, this book provides state-of-the-art coverage of this topic, which is essential to the shelf-life and quality of food.- Provides in-depth coverage of the different spoilers which cause the deterioration of foods, including less common spoilers not covered in other publications- Includes dedicated chapters covering the spoilage of specific products, making this book ideal for those working in the food industry- Presents a framework for future research in the area of foodborne spoilers

Chapter 1

Microbial Spoilage of Foods

Fundamentals

Leonardo Petruzzi, Maria Rosaria Corbo, Milena Sinigaglia and Antonio Bevilacqua, University of Foggia, Foggia, FG, Italy

Abstract

Despite modern technological advances, spoilage of foods continues to occur. Excessive economic losses are due to microbial spoilage, resulting in final products with an inadequate shape or appearance. Understanding how different properties of a food, its environment and “history,” can influence the microbiota that develops in products, is a pivotal step to control quality and safety. The present chapter discusses the characteristics of microbial spoilage of foods with a focus on the major spoilage microorganisms and how they can be detected and controlled.

Keywords

Food spoilage; microbial contamination; enzymes; quality; safety; perishable foods

1.1 Introduction

Food spoilage results when microbiological, chemical, or physical changes occur, rendering the food product unacceptable to the consumer. Microbiological food spoilage is caused by the growth of microorganisms which produce enzymes that lead to objectionable by-products in the food. Chemical food spoilage occurs when different components in the food react with each other or with some added component which alter the food’s sensory characteristics. Examples of this include: oxidation; enzymatic browning; and nonenzymatic browning. Physical food spoilage results when moist foods are excessively dehydrated or dried foods absorb excessive moisture (Benner, 2014).

For years, safety (i.e., the exclusion or elimination of pathogens from food) has been studied separately from the prevention of spoilage. In most countries the legislation has tended to reinforce this concept. However, from a microbiological-ecological point of view the two areas cannot be distinguished. In spite of considerable efforts, microbiological safety assurance seems as remote as ever, even in advanced countries. Death, suffering, economic losses, and civil claims on behalf of victims of foodborne diseases are matched by the economic losses caused by food spoilage (Di Renzo et al., 2015).

Although exact figures of the total economic losses due to food spoilage are unknown, it is clear that it constitutes an enormous financial burden (Blackburn, 2006) estimated at 1.3 billion tons per year by FAO (Cichello, 2015). According to the USDA Economic Research Service estimates, about 96 billion pounds of food, or more than a quarter of the 356 billion pounds of edible food available for human consumption in the United States, were lost to human use at three marketing stages: retail, foodservice, and consumers. Fresh fruits and vegetables (19.6%), fluid milk (18.1%), grain products (15.2%), and sweeteners (12.4%), mostly sugar and high-fructose corn syrup, accounted for two-thirds of these losses (Nguyen Van Long et al., 2016).

A significant proportion of the loss is due to spoilage by microorganisms, resulting in final products with an inadequate shape or appearance (Dousset et al., 2016). It has been estimated that about 25% of all foods produced globally are lost due to microbial spoilage (Bondi et al., 2014).

The food industry is continually creating new microbial habitats, either by developing new products and reformulating traditional ones, or by chance, as a result of the composition of raw materials or in production (Argyri et al., 2014). Also, the modern consumers’ preference for fresh foods with extended shelf life and products that are free of chemical pesticides leave foods more vulnerable to spoilage, as well as increasing the diversity of spoilage species (Blackburn, 2006; Brandelli, 2015).

Understanding how different properties of a food, its environment and “history,” can influence the microbiota that develops in products, is an important first step toward control quality and safety (Argyri et al., 2014).

The present chapter discusses the characteristics of microbial spoilage of foods with a focus on the major spoilage microorganisms and how they can be detected and monitored.

1.2 Microbial Food Spoilage: Overview

The range of spoilage microorganisms is wide. Bacteria are responsible for some of the most rapid and evident spoilage events of proteinaceous foods such as meat, poultry, fish, shellfish, milk, and some dairy products. The growth of yeasts and molds is generally slower than that of bacteria, but the wide variety of ecological niches they can exploit, the ability to utilize a variety of substrates, and tolerance of more extreme conditions than (vegetative) bacteria makes them formidable spoilage agents (Blackburn, 2006).

The spoilage flora of perishable products is comprised on the one hand of the natural flora from the product itself, which is mainly influenced by its environmental conditions. For example, the natural microflora of fish is influenced by the habitat, the geography (tropical or arctic water), and the fishing season, whereas the natural flora of fruits and vegetables is influenced by the soil, air, irrigation water, insects, and animals. On the other hand, microorganisms will be transferred to food by cross contamination during or after processing via surfaces, machines, humans, or the surrounding atmosphere (Kreyenschmidt and Ibald, 2012).

The microbiological flora is not static, so the initial flora differs from the flora at the end of shelf life. Furthermore, only a small number of microorganisms are often responsible for the loss of quality based on food characteristics, environmental conditions, and interactions between the microorganisms. Those organisms mainly responsible for spoilage are known as specific spoilage organisms (SSOs) (Kreyenschmidt and Ibald, 2012).

The many kinds of microorganisms that can grow on food have evolved biochemical mechanisms to digest components of the food, thereby providing energy sources for their own growth (Sperber, 2009). Transformation of the available compounds gives a wide range of end products that affect the food’s sensory, chemical, and physical properties (Howell, 2016). The range of possible compounds produced is dependent on not only the genetic capability of the microorganism in question but also the intrinsic characteristics of the product and the extrinsic characteristics of handling and the storage environment that can vastly change biochemical pathways (Benner, 2014; Howell, 2016).

1.3 Factors Affecting Microbial Spoilage

1.3.1 Food Structure

Raw food is often protected from attack by microorganisms by means of structures that are not easily degradable (fruit skin, nut shells, bran, collagen muscle tissue, egg shells, etc.). Only microbial species with appropriate enzymes (cellulase, pectinase, protease, etc.) can attack these structures. As a result, raw food prior to harvest is often only contaminated on the surface. However, as soon as the processing stage begins, this protection ceases and the food becomes more vulnerable to the spread of microorganisms (Baron and Gautier, 2016).

In general, fluid foods spoil rapidly because the organisms can easily spread throughout the food by means of their own motility or by convection currents. Semi-solid foods such as meat stews, soup, and tinned fruits can spoil as rapidly as fluid foods. Solid foods tend to spoil from their outside surfaces inwards, these being the first surfaces to become contaminated (Modi, 2009).

1.3.2 Food Composition

The nutrient composition of food also influences the growth of the most suitable species of microorganisms. Protein foods such as meat, fish, and eggs are liable to be attacked by proteolytic organisms; “carbohydrate” foods such as bread, flour, pasta, syrups, and jams are more liable to attack by fermentative organisms; fats are liable to be attacked by lipolytic organisms (Modi, 2009).

Lipids can be degraded enzymatically to produce free fatty acids that have rancid and unpleasant off-aromas. Breakdown of lipids is important in meat, dairy, and olive oil systems (Howell, 2016).

Some foods also have inhibitory substances or naturally occurring antimicrobials present (Davidson and Critzer, 2012). Such substances can inhibit or slow the growth of some microorganisms (Kreyenschmidt and Ibald, 2012). For example, egg albumin contains the enzyme lysozyme, which disrupts the cell walls of Gram-positive bacteria by hydrolyzing the glycosidic bonds of N-acetylmuramic acid and N-acetylglucosamine in the peptidoglycan layer, avidin, which ties up the vitamin biotin, conalbumin, which ties up iron, and protease inhibitors, which inhibit protein degradation. All of these compounds act in concert to inhibit microbial growth. Raw milk also contains lysozyme and the lactoperoxidase system, which requires the interaction of the enzyme lactoperoxidase, thiocyanate, and hydrogen peroxide to produce the antimicrobial hypothiocyanate (Davidson and Critzer, 2012).

Lactoferrin is also present, which sequesters the iron necessary for microbial growth similar to conalbumin found in eggs (Davidson and Critzer, 2012).

In general, Gram-positive bacteria are sensitive to many molecules such as citrate, nisin, butylated hydroxyanisol or butylated hydroxytoluene, as well as molecules known for their antifungal activity, such as sorbates or benzoates. Gram-negative bacteria are more resistant than Gram-positive bacteria, but are still susceptible to a broad spectrum of additives as well as SO₂ (Baron and Gautier, 2016).

There are some yeast species that are tolerant to ethanol at high concentrations, although their metabolism may be affected, and these include Zygosaccharomyces, Dekkera, Pichia, and Saccharomycodes. Many yeast species have evolved resistance to weak organic acids and include Zygosaccharomyces, along with some strains of Candida krusei and Pichia membranifaciens (Howell, 2016).

Foods with low sugar content, such as juices, jellies, and jams, contain acids, sweeteners, and hydrocolloids. These additives are needed for sensory purposes. Aspartame is among the most used sweeteners, though the use of the natural sweetener stevia is increasing in recent years. The presence of mentioned additives affects the growth of Zygosaccharomyces bailii (Campos et al., 2015).

Some yeasts are able to grow in media or substrates with high salt or sugar concentrations. For example, Debaryomyces hansenii is very salt tolerant, and some strains can tolerate up to 24% (w/v) NaCl. Saccharomyces cerevisiae also exhibits significant salt tolerance, but this is strain-dependent and is also influenced by pH of the food or beverage in question (Howell, 2016). Some species such as Hemimysis anomala and Candida pseudotropicalis may grow at NaCl up to 11% (Campos et al., 2015). Zygosaccharomyces rouxii is exceptionally tolerant to high sugar concentrations (up to 70% w/v sucrose) (Howell, 2016). Similarly, molds are tolerant to high concentrations of sugar or salt (Modi, 2009).

1.3.3 Water Activity

The water activity (a_w), which is the ratio of the vapor pressure of the food to the vapor pressure of pure water, has an important influence on the growth of the microorganisms since an aqueous phase is a main requirement for their metabolic activity. The optimum a_w for most microorganisms is in the range 0.995–0.980. Lowering the a_w (e.g., due to salt, sugar, drying, or curing) inhibits microbiological growth or results in an increased lag phase and a decreased growth rate and thus leads to a longer shelf life. Since microorganisms have different demands with regard to water activity, the composition of the microflora is influenced by the prevalent a_w (Kreyenschmidt and Ibald, 2012).

Bacteria require a high a_w and cannot therefore contribute to the spoilage of dry foods while they remain dry (Modi, 2009). With a few exceptions, the bacterial growth continues up to a ≥0.88 (Kreyenschmidt and Ibald, 2012). Some bacteria produce molecules called osmoprotectants (ectoine produced by Brevibacterium linens) that can keep water inside the cytoplasm (Baron and Gautier, 2016).

Generally, yeasts must have an a_w above 0.87–0.94, but some osmotolerant species grow in an a_w as low as 0.60. Molds can grow in foods with t...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of Contributors
• Woodhead Publishing Series in Food Science, Technology and Nutrition
• Food Spoilage: A New Threat?
• Chapter 1. Microbial Spoilage of Foods: Fundamentals
• Part I: The Spoilers
• Part II: A Focus on Food Spoilage
• Part III: Future Trends in Food Spoilers
• Index