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Study Guide - Module 1
Food Technology (FDS308)
Charles Sturt University
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FDS
Food Technology
FACULTY OF SCIENCE
Module 1 201830
FDS308
Food Technology
FDS308 Module 1 Preservation principles
Faculty of Science
Originally written and compiled by Associate Professor Samson Agboola
Adapted for FDS308 by Dr Ester Khosa
iii
Contents
- Module profile Page
- Topic 1 Introduction to food technology
- Introduction
- Principles of food preservation
- Physical preservation
- Chemical preservation
- Biological preservation
- Unit operations and food processing
- Minimal processing methods
- The consumer and the process
- Topic 2 Heat processing
- Introduction
- Pasteurisation
- Checking pasteurisation efficiency
- Heat sterilisation
- Thermal inactivation of microorganisms
- Methods of heat sterilisation
- Hot pack or hot fill
- An overview of canning
- History
- Canning operations
- Double seaming
- HACCP and canning
- Topic 3 Concentration processes
- Introduction
- Evaporation
- Creation of vacuum
- Steam economy
- Membrane concentration
- Freeze concentration
- Topic 4 Food dehydration
- Introduction
- Drying mechanisms and drying curves
- Factors affecting drying
- Effects of food properties on drying
- Drying equipment
- Manufacture of instant milk powders
- What is an instant product?
- What is the mechanism for agglomeration?
- What other techniques?
- Any special treatment for fat-containing products? iv
- techniques? Can instant milk powder be produced by using non-agglomeration
- Any problems with instant products?
- Drying of thermoplastic foods
- Topic 5 Freezing of food
- Introduction
- Calculating refrigeration load
Topic 1 Introduction to food technology
Objectives
Upon successful completion of this topic, students should be able to:
review food preservation techniques;
highlight the requirements necessary for a good understanding of this subject;
introduce the socio-economic aspect of food technology, especially the role of the consumer;
give a synopsis of the subsequent topics; and
provide the basic concepts of process engineering, mass and energy balances.
Introduction
We are all familiar with the fact that food is a perishable commodity. Deterioration in food quality starts as soon as the plant is harvested or the animal slaughtered. Many factors contribute to this. These factors include biological deterioration and post-harvest (slaughter) loss from bacteria, yeasts, moulds, insect and rodents; chemical breakdown of food components catalysed by enzymes, light or oxygen; and physical loss of tissues due to harvesting or handling techniques. Deterioration manifests in food in the form of poor quality attributes like physical damage and poor appearance, flavour defects, and nutritional loss. Most importantly, food deterioration also leads to microbiologically unsafe food, ingestion of which could lead to health problems or even death. As a result of these, matching the supply of food as produced by the agricultural sector with the demand for food by the consumers in both time and space necessitates the use of a variety of preservation techniques. In this topic, we will review food preservation techniques, which are basically most of what you have learnt in Food Processing (FDS101) or equivalent subject. A summary of the principles behind these techniques are given below.
Principles of food preservation
Food preservation techniques can be divided into three (3) major groups; they are physical, chemical and biological techniques. Over the years, each of these techniques has been so developed that they are currently comprised of many processes and operations and these form the basis of this subject. Below is an overview of these techniques.
Physical preservation
Thermal methods
These include thermal methods which help extend the shelf life of foods by destroying or inactivating microorganisms and enzymes. Thermal methods comprise both heat- and cold-preservation of foods. The most intense heat preservation technique is sterilisation, which refers to a complete destruction of all microorganisms, including spoilage and pathogenic ones. Other methods such as pasteurisation and blanching are less severe since the objectives are different. In pasteurisation, the main objective is to eliminate organisms of public health concern (pathogens) while the objective of blanching is to inactivate enzymes. Low temperature preservation methods include refrigeration and freezing. Storage at temperatures below 15°C retards the growth of microorganisms, metabolic activities of plant tissues post-harvest and animal tissues post-slaughter, deteriorative chemical reactions such as oxidation and enzyme catalysed reactions, and moisture loss. Refrigeration is carried out normally at temperatures slightly above the freezing point of water (4 - 7°C) while freezing is carried out well below the freezing point (storage around -18°C). Unlike heating, cold-preservation does not destroy the microorganisms but only retards their growth and attendant biochemical activities; the product is thus still subject to fast deterioration under more favourable conditions. This emphasises the importance of packaging and proper storage conditions in these as in other food preservation methods. Table 1. shows the thermal methods of food preservation, including the purposes of each method.
The nearly complete removal of water from both solid and liquid foods is known as drying or dehydration. The food can be consumed dried, e., dried fruits and meats, or after reconstitution with water as in dried milk, potato flakes or instant coffee. There are many methods available for dehydrating foods, the major ones involve the use of dry hot air.
Oxygen control
Oxygen control is also a major physical preservation technique in foods. This is important because of the strict oxygen requirements for the growth of many microorganisms (aerobes) and the participation of oxygen in a number of chemical reactions that deteriorate foods. Control or modified atmosphere storage in fruits and vegetable is an excellent example. Closely related to oxygen control is the protection offered by packaging materials which serve as barriers against the action of biological organisms as well as oxygen. In fact, packaging of some dried products should be done in the absence of oxygen (usually in the presence of the inert nitrogen).
Radiation
The final physical preservation technique is radiation. The use of ionising radiation (irradiation) and electromagnetic energy (microwave and infra red heating) in food preservation is relatively newer than the other physical methods. Irradiation involves exposing the food material to an even distribution of the penetrating gamma (γ) rays (from radio-isotopes) in an enclosed chamber for the time necessary to accomplish microorganism inactivation. Several processes have been developed which are equivalent to some of the thermal processes. Microwave and infra-red radiation are also used in food processing for heating and microbial inactivation.
Chemical preservation
Preservation of foods by adding or developing chemicals in the food has been practised for a very long time. These include direct addition of chemicals like salts, smoke, acids and sugars to enhance microbial inactivation. Common salt and sugars act by absorbing water that would have otherwise been available for the microbial cell, causing partial dehydration of the cell (plasmolysis) and destroying its viability. Foods containing sugars and other humectants (e., glycerol, sorbitol) which are eaten as is without rehydration and yet shelf stable without refrigeration or thermal processing are collectively known as intermediate moisture foods (IMFs). Examples of IMFs are jams and jellies, fruit cakes and sweetened condensed milk. Acids provide an environment which is conducive only to very few microorganisms (acidophiles). Other chemical preservatives like sodium benzoate, sorbates, nitrites and sulphites act by possessing bactericidal effects and they are added to both liquid and solid foods in regulated amounts. This regulation is necessary in order to prevent abuse by manufacturers and thus reduce possible chronic or acute effects in consumers. In this subject we will discuss some of these chemical preservative methods in detail, especially as they relate to the technology of liquid foods.
Biological preservation
Unlike other preservation methods, biological preservation is obtained by increasing the number of microorganisms present in the food. The major process is fermentation which is a historically important means of food preservation. Here, the food constituents, especially carbohydrates (and to a lesser extent proteins and lipids) are broken down into simpler substances like acids, alcohols and carbon dioxide. These breakdown products are usually responsible for the flavour of these foods. This is effected by the action of a particular organism or a group of similar organisms. The conditions of fermentation favour the growth of the desirable organism(s) which is added in the form of a pure culture, and cause the competitive disappearance of undesirable spoilage and pathogenic organisms. Examples of food fermentation include the production of alcohols by yeasts in wine and beer, and the production of lactic acid by bacteria in fermented milks, yoghurt and pickles. Some of these products will be examined in greater detail later on in the subject.
Unit operations and food processing
A process is any activity or collection of activities that takes inputs, transforms and adds value to them, and then delivers an output to a customer. The study of process engineering is an attempt to analyse all forms of physical processing into smaller number of basic operations called unit operations. In food technology, a process usually involves both physical and chemical changes while unit operations primarily involve physical changes but sometimes physico-chemical changes as well. A process can be represented by a flowchart made up of several unit operations. Examples of unit operations are fluid flow (e. pumping), heat transfer, drying, evaporation, extraction, crystallisation, size reduction, filtration, centrifugation, sieving, and mixing. More information about these unit operations are given in the first few chapters of Fellows (2009). Beer making from barley malt is an example of a process.
From the examples above, it can be seen that operations deal with mass and energy transfers. Therefore, all unit operations must obey the law of conservation of mass and the law of conservation of energy. Although these materials are not directly examinable, it is important for you to know them very well since they form the foundation for subsequent topics. You should be familiar with material and energy balances, calculations relating to them, the use of steam tables and psychrometric charts.
Since microorganisms are the major culprits in the battle for food preservation, some knowledge about their nature is very important. You should be familiar with the major types of microbes that are important in food processing and spoilage, and of course, public health and safety. A revision of basic microbiology is therefore in order.
The consumer therefore dictates the quality of the food product. Nowadays, consumer preferences in food products are increasing and food processors must study and understand the consumer. These studies often involve demographics and psychographics. Demography refers to the statistical makeup of the population by age, wealth, sex, etc., while psychography refers to the attitudes, interests and opinions of the population. We are faced not just with the task of preserving the food, but of preserving it in the way consumers want it and at the price they can afford. This is a note that will sound throughout this subject and will be important for you to keep in mind as you continue to develop your career in food science and technology.
Study tasks
Revise unit operations in food processing (from FDS101 or from your text - Fellows).
Study laws of conservation of mass and energy.
Revise microbiology of bacteria, yeasts and moulds (any basic microbiology text would suffice).
Recommended readings (available online at CSU library eReserve)
Textbook: Fellows, P. J. (2009). Properties of food and processing (pp. 11-49).
Textbook: Fellows, P. J. (2009). Properties of food and processing (pp. 50-88).
Ramaswamy, H. S., & Marcotte, M. (2006). Background basics. In Food Processing: Principles and Applications (pp. 7-27). Boca Raton: CRC Press.
Topic 2 Heat processing
Objectives
Upon successful completion of this topic, students should be able to:
understand the meaning of pasteurisation, its purpose(s), the equipment (methods) commonly used in the industry, and how to ensure the efficiency of pasteurisation;
understand the meaning of sterilisation and commercial sterility; in- container sterilisation and factors influencing process time for foods; ultra- high temperature (aseptic) technology;
understand the concept of D, z and F values as indices of heat process requirements for commercial sterility; calculations of process lethality; and
have an overview of canning technology.
Introduction
We will look at the major heat processing operations in this topic. Basically, we will study pasteurisation and sterilisation. Although heat processing is a large part of concentration processes, we will study that separately in the next topic.
Pasteurisation
This process is named after Frenchman Louis Pasteur. He was the first to use this mild heat treatment (50-60°C for a few minutes) to control wild yeasts and bacteria responsible for the spoilage of wine in 1864. Pasteur applied the method to beer as well. The method was later applied to market milk in order to primarily destroy the pathogens. There are different purposes for which this process is used in different foods. The safety and public health concerns have also necessitated the specifications of pasteurising procedures for some foods. These legal standards must be taken into considerations by food manufacturers. Because the heat treatment is mild, pasteurisation alone will not preserve the food for a very appreciable length of time.
very severe; not only are vegetative cells and spores of microorganisms destroyed, some of the food nutrients like proteins and vitamins are also lost. Thus, commercially sterile products may contain heat-resistant spores of microorganisms (usually present in very low numbers), but these spores will not normally multiply under normal conditions of handling and storage. However, if these spores were isolated from the food and given favourable environmental conditions, they could be shown to be alive.
Most canned and bottled food products are commercially sterile and have a shelf life of 2 years or more. Even after longer periods, so-called deterioration is generally due to texture or flavour changes rather than the growth of microorganisms. An overview of canning is given later in this topic.
Thermal inactivation of microorganisms
Bacteria and their spores are killed by heat at a rate that is nearly proportional to the number present in the system being heated. The same percentage of the bacterial population will be destroyed in a given time interval. This is known as the thermal death rate and can be graphically represented in what is known as the thermal death rate curve, i., number of surviving microorganisms vs. heating time at a particular temperature. The time needed for a 90% reduction (1 log cycle) in the number of microorganisms is known as the decimal reduction time or simply the D-value. Thus, the higher the D-value of a particular microorganism at a specific temperature, the higher its thermal resistance.
A plot of D-values against temperature for a specific organism will give us a thermal death time curve. The change in temperature for a 90% reduction in the D-value gives us another index of heat resistance known as the z-value. Details of these curves are given in your book.
Read (available online at CSU library eReserve)
Textbook: Fellows (2009). Properties of foods and processing (pp. 11-88).
Be familiar with the concepts of D- and z-values.
Heat sterilisation
Sterilisation can be effected in or outside containers. In-container sterilisation could be done in different containers including cans, glass containers, rigid polymers or flexible pouches and various heating media can be used, including saturated steam, hot water and flames. Many factors affect the heat process requirements for sterilisation, notable among which is the nature of the food (acidity).
Sterilisation can be carried out, usually in liquid or particulate foods outside the containers. This brings on the added requirement that packaging of the food be done under sterile conditions in order to prevent recontamination. This process is usually carried out under ultrahigh temperature (UHT) and for a short period of time (usually measured in seconds) and it is known as UHT or aseptic processing.
Read (available online at CSU library eReserve)
Textbook: Fellows (2009). Heat sterilisation (pp. 396-425).
This is a chapter on heat sterilisation and deals with both in-container sterilisation, e., canning and aseptic processing of foods. With respect to in-container sterilisation, you must be familiar with factors influencing the rate of heat penetration, development of heat penetration curves, the graphical method of calculating process times, the meaning of F values and the significance of F 0 values, heat exchangers, and methods of retorting. The formula method for calculating process time may be read for general knowledge but will not be examined. We will also be doing some laboratory work on retorting and will use the graphical method to calculate process lethality. You should also be familiar with the theory and equipment used for aseptic processing (UHT sterilisation) of liquid foods.
Hot pack or hot fill
These terms refer to the packing of previously pasteurised or sterilised food, while still hot, into clean but not necessarily sterile containers. The heat of the food and some holding period before cooling is used to render the container commercially sterile, i. although it may still contain a very low number of microorganisms, it would still be shelf-stable and would not cause any harm to the consumer.
This is usually carried out with high acid foods (pH <4), since the increased acidity will prevent the growth of Clostridium botulinum or the production of its fatal toxin. For products with pHs higher than 4, the use of this technology is not feasible unless there will be an additional means of preservation e., refrigeration or addition of chemical preservatives like salt and sugar. This is because residual heat of the food is not enough to guarantee the destruction of spores that may be present on the containers.
Examples of foods that could be hot filled (packed) include acid juices like orange, grapefruit, grape and tomato. They are usually hot packed following pasteurisation or sterilisation (these terms can be used interchangeably for acid foods). Typically they are first heated in the temperature range 77-100°C for about 30-60 seconds, hot filled at not lower than 77°C and often closer to 93°C, and held at this temperature for 1-3 min, including an inversion of the container before cooling. This inversion is necessary in order for the heat to contact all surfaces before cooling. Definite conditions must be determined for specific products mainly by experimentation.
Figure 2: Double seaming operations: a. first operation; b. second operation.
Source: Bell packaging Products (1989). Double seam inspection and evaluation.
Making consistently good seams requires careful closing machine maintenance; frequent regularly scheduled seam evaluation; keeping of complete and accurate seam records; and immediate correction of seam conditions which are outside of established tolerances. The use of microscopy and image analysis greatly assists the quality inspection aspects of the seaming operation. However, experienced canners can spot most can defects by visual examinations.
HACCP and canning
The Hazard Analysis and Critical Control Point (HACCP) system has been devised to assure safety and quality of food products. The basic premise of this program is to identify possible hazards in advance and set up a system of procedures, inspections and record keeping to minimise the possibility of the hazards causing unsafe or poor quality end products. First, the sequence of operations is listed (usually with a flowchart) and the critical control points where hazards are likely to occur are identified. The general categories of hazards include microorganisms and their toxic products, chemicals and foreign matter. The various steps and probable concerns are listed in Table 2. Please note that these concerns are also applicable in other heat preservation techniques.
Table 2: HACCP applied to canning
Step Concerns
Raw Products and Ingredients Set up purchase specifications and sampling procedures and record keeping, check use of agricultural chemicals; establish in-plant ingredient storage and handling (first in- first out) Handling Set up inspection program Washing Check water quality, water pressure Product preparation Institute quality control tests Filling operations Check fill weights and temperature, set up control charts Containers, closures Examine for defects using statistical sampling plan, check integrity of seals Processing operation e. retorting Proper design and control of the thermal processing operation is the most important critical control point in the canning process. Many government regulations are to be adhered to, especially Good Manufacturing Practice (GMP) Act. Proper record keeping critical Post-processing Careful handling necessary to guard can seams Warehousing Control of temperature, infestations Coding All sealed containers must be coded so that product can be traced Clean-up, sanitation Prepare manual and check list for equipment and general cleaning Recall procedure Careful record keeping and coding, shipping records
nullReview questions: Heat processing-pasteurisation and sterilisation
- What is the main objective of pasteurisation in the manufacture of the following:
a. homogenised milk;
b. beer; and
Study Guide - Module 1
Course: Food Technology (FDS308)
University: Charles Sturt University
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