Understanding and Measuring the Shelf-Life of Food

R. Steele

• Publisher: Woodhead Publishing
• Year: 2004
• Print ISBN: 9781855737327
• eBook ISBN: 9781855739024
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

The shelf-life of a product is critical in determining both its quality and profitability. This important collection reviews the key factors in determining shelf-life and how it can be measured.Part one examines the factors affecting shelf-life and spoilage, including individual chapters on the major types of food spoilage, the role of moisture and temperature, spoilage yeasts, the Maillard reaction and the factors underlying lipid oxidation. Part two addresses the best ways of measuring the shelf-life of foods, with chapters on modelling food spoilage, measuring and modelling glass transition, detecting spoilage yeasts, measuring lipid oxidation, the design and validation of shelf-life tests and the use of accelerated shelf-life tests.Understanding and measuring the shelf-life of food is an important reference for all those concerned with extending the shelf-life of food. - Reviews the key factors in determining shelf-life and how they can be measured - Examines the importance of the shelf-life of a product in determining its quality and profitability - Brings together the leading international experts in the field

Part I

Factors affecting shelf-life and spoilage

1

The major types of food spoilage: an overview

R.P. Singh; B.A. anderson University of California, USA

1.1 Introduction

All food products are composed of biological raw materials. Biological products inherently spoil and deteriorate over time. This spoilage and deterioration cannot be completely stopped; however, it is the desire of food processors to slow this rate of deterioration as much as possible through formulation, processing, packaging, storage and handling. To properly address this problem of spoilage it is first important to understand what is meant by food spoilage and by what various modes can it take place.

Food spoilage can be defined in several different ways. Generally, a food is considered spoiled when it is no longer acceptable to the consumer. The worst case of spoilage is when it becomes a food safety issue, where the food product may cause the consumer illness or even death. However, less serious cases of food spoilage can simply be that the color, flavor, texture, or aroma of the food has deteriorated to the point that it is no longer acceptable. Another case of spoilage could be that the nutrients (e.g. vitamin content) in the food have deteriorated to the point that the food product no longer meets its declared nutritional value. The time it takes for a food product to reach one of these spoilage conditions is generally termed the product's shelf-life.

Many food products have some variation of open shelf-life dating marked on their containers. Open shelf-life dating varies widely by product, region, and manufacturer. Common open shelf-life dates include a ‘sell-by-date’, a ‘best-if-used-by-date’, or a ‘better-if-used-by-date’. These dates help the consumer to decide how long the product may be stored prior to consumption and also help with stock rotation in grocery stores. Hopefully the food manufacturer conducted studies to properly determine the shelf-life of their product; however, often the date given assumes proper storage conditions of the product prior to consumption. It is important to understand what types of spoilage may occur in a product, how to best reduce the rate of deterioration of the product, and how to properly measure or detect its occurrence.

The three main categories of food spoilage that can occur are physical spoilage, chemical spoilage, and microbiological spoilage. There are some overlaps between the three categories, and often spoilage in one category can help to promote spoilage in another category. Table 1.1 lists the major mechanisms for spoilage or deterioration of various food categories. There are several main factors that influence most types of spoilage. These factors include temperature, pH, water activity, exposure to oxygen and light, and nutrients or chemicals available in the food product. Figure 1.1 shows graphically how one of these factors, water activity, affects various chemical and microbiological changes in typical food products. Each of the three main categories of spoilage is briefly reviewed in this chapter.

Table 1.1

Deterioration/spoilage mechanisms and critical variables for various food products (Kilcast and Subramaniam, 2000; Labuza and Szybist, 2001)

Food product/category	Type of spoilage/deterioration	Critical storage variables
Milk	Oxidation, hydrolytic rancidity, bacterial growth	Oxygen, temperature
Milk powder	Oxidation, browning, caking	Oxygen, humidity, temperature
Dairy products	Oxidation, rancidity, lactose crystallization	Oxygen, temperature
Ice cream	Ice crystal or lactose crystal formation, oxidation	Temperature (freeze/thaw), oxygen
Fresh beef	Microbial (bacterial) growth, oxidation, moisture loss	Temperature, oxygen, light, humidity
Fresh poultry	Microbial growth	Temperature, oxygen
Fresh fish and seafood	Microbial growth, oxidation	Temperature, oxygen
Fruit	Enzymatic softening, microbial growth, bruising, moisture loss	Temperature, light, oxygen, handling, humidity
Leafy vegetables	Enzymatic activity, moisture loss/wilting, microbial growth	Temperature, light, oxygen, humidity
Crisp vegetables	Enzymatic softening, microbial growth, bruising, moisture loss	Temperature, light, oxygen, handling, humidity
Bread	Moisture migration (staling), starch retrogradation, microbial (mold) growth	Humidity, temperature, oxygen
Cereals	Moisture migration (softening), starch retrogradation, oxidation, breakage	Humidity, temperature, oxidation, handling
Soft bakery products	Moisture migration (staling), microbial (mold) growth, starch retrogradation	Humidity, temperature, oxygen
Crisp bakery/fried products (cracker, etc.)	Moisture migration (softening), oxidation, breakage	Humidity, temperature, oxygen, handling, light
Chocolate	Sugar crystallization (sugar bloom), fat crystallization (fat bloom), oxidation	Humidity, temperature, oxidation
Candy	Moisture migration (stickiness), sugar crystallization	Temperature, humidity
Beer	Oxidation, microbial growth	Oxygen, light, temperature
Coffee/tea	Oxidation, volatile loss	Oxygen, light, moisture
Frozen meats	Oxidation, freezer burn (drying)	Oxygen, temperature, humidity
Other frozen foods	Oxidation, ice crystal formation, texture change	Oxygen, temperature

Fig. 1.1 Relative water activity stability map (from Labuza et al., 1970).

1.2 Physical instability

The first type of spoilage that can occur is due to physical changes or instability. This can include physical damage such as bruising of fresh fruits and vegetables or breaking of dry, brittle products such as potato chips and breakfast cereals. Bruising of fruits and vegetables can occur during transportation and distribution or by dropping the products. If the physical damage is severe, the product may become unacceptable to the consumer. There can be color changes due to enzymatic browning as cells are ruptured and there is often loss of water content at the bruise. In addition, bruising causes damage to cells and allows microbial growth to occur more readily. Breaking of dry, brittle products can make many products such as crackers, potato chips, ready-to-eat cereals, piecrusts, and many frozen foods unacceptable. The use of well-designed packaging systems that protect the products from vibrations and mechanical damage during distribution and handling can minimize the effects of bruising and breakage.

Most other physical changes or instabilities involve moisture or mass transfer of components in the food. A frequent cause of degradation of food products is a change in their water content (water loss, gain, or migration). The change in moisture alone may cause the product to become unacceptable, though frequently it also leads to other problems such as microbial or chemical degradation, which will be discussed in later sections. Moisture transfer occurs in foods due to gradients in chemical potential, which is directly related to the food's water activity (a_w). Water activity is defined as the equilibrium relative humidity for a produ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• Contributor contact details
• Part I: Factors affecting shelf-life and spoilage
• Part II: Measuring shelf-life and spoilage
• Index