1
Control of Biodeteriorationin Food
1.1 OVERVIEW
All food undergoes deterioration to some degree once harvested or slaughtered. The deterioration may include loss of nutritional value, organoleptic and colour changes, and most importantly, safety may become compromised. It is the challenge of the food industry to control this deterioration and maintain the safety of the food, while making sure that the food is as convenient, nutritious and available as it can possibly be.
Biodeterioration is defined as any undesirable change in the property of a material caused by the vital activities of organisms [1]. It is applicable to many materials for example food, wood, paper, leather, fuels, cosmetics, building materials and building structures. Biodeterioration may be a result of the metabolic processes of one of many microorganisms, or it can be caused by insect, rodent or bird damage. As an incredibly broad and diverse field, all biodeterioration has as a common theme in that it affects materials and substances that we need and value, and that it can largely be controlled by proper understanding of the materials and the possible spoilage organisms and their mechanisms of decay.
Biodeterioration is also specifically different from biodegradation in that the changes are ‘undesirable’. Biodegradation occurs when complex materials are broken down by microorganisms to form simple end-products. Within a biological ecosystem, there are microorganisms that produce a host of enzymes that can biodegrade natural as well as some synthetic products; this is very important for maintaining the stability of the ecosystem and is extremely important for water purification and sewage treatment. It is also widely used in the food industry. The main differences between biodeterioration and biodegradation are the undesirability and uncontrollability of the former [2].
Another important feature of biodeterioration is that it is caused by organisms. According to the definition, it is not the degradation that occurs naturally in some organic materials or foods caused by intrinsic enzymes. These enzymes are present in the product and cause degradation or decay after death. Loss of food quality by intrinsic enzymes is an important topic as it can cause quality deterioration and render food unacceptable. Reactions due to these enzymes will not be considered in detail in this text, but are important to bear in mind as their activities can make nutrients from the product available and accessible to microorganisms so that biodeterioration reactions can follow [2, 3].
1.2 A SUMMARY OF THE DIFFERENT KINDS OF BIODETERIORATION
1.2.1 Chemical biodeterioration
There are two modes of chemical biodeterioration. Both have a similar result, that is the material becomes spoilt, damaged or unsafe (see Table 1.1 and Fig. 1.1), but the cause or biochemistry of the two is quite different [2, 4]:
- Biochemical assimilatory biodeterioration – the organism uses the material as food or an energy source. Growth of mould on bread is an example of this type of biodeterioration.
- Biochemical dissimilatory biodeterioration – the chemical change in the food is as a result of waste products from the organisms in question. Examples of this are pH changes in food that arise from acids generated from the metabolic action of microorganisms such as bacteria, yeast and mould.
Table 1.1 Examples of the diversity of biodeterioration.
| Affected material | Example | Type of biodeterioration |
| Stone, marble, concrete | Deterioration of stone monuments | Chemical assimilatory: where calcium and other minerals are used as a food source Chemical dissimilatory: where acid by-products dissolve the surfaces Mechanical: where root damage can undermine and weaken structures
Fouling: where biofilms can affect the aesthetics of the structure |
| Wood | Rotting of wooden floorboards and timber structures | Chemical assimilatory: where the cellulose and lignin in the wood are used as food by fungi and other organisms
Dissimilatory: where acid and other by-products result in breakdown of the structure |
| Leather | Loss of strength and structure of leather objects | Chemical assimilatory: by proteolytic bacteria, which break down the proteins |
| Paper | Degradation of books | Chemical assimilatory: most commonly by fungi |
| Paint | Water-based paints | Chemical assimilatory: by bacteria and fungi, results in thinning of the paint and production of off odours |
| Museum artefacts | Discoloration and degradation of valuable relics | Chemical assimilatory and chemical dissimilatory: by bacteria and mould, resulting in weakening of structures and discoloration of the objects |
| Food | All foods: animal matter and vegetable based | The most important is chemical assimilatory: the food is used as a food source as it is nutritionally compromised and can have toxins associated with it as by-products of the microbial activity |
| Metal | Biodeterioration of the wreck of the RMS Titanic | Chemical assimilatory: attack on the steel by communities of bacteria and fungi |
| Fuels | Fuels in tanks | Chemical assimilatory: most commonly the C-10 to C-18 hydrocarbons are broken down to form shorter chain hydrocarbons that, together with the biofilms, can clog fuel lines |
| Lubricants | Lubricants in metal working lines | Chemical assimilatory: resulting in the loss of lubricating properties and therefore functionality |
| Teeth | Tooth decay | Chemical dissimilatory: waste products from oral acidogenic bacterial growth cause tooth decay |
| Glass | Leaching, staining of stained glass windows | Chemical dissimilatory: by waste products from growth of fungi and Cyanobacteria
Mechanical: filamentous organisms can cause stress cracking |
Fig. 1.1 Some common biodeterioration problems. (a) Mouldy bread; (b) mould on antique book; (c) rotten floorboards; (d) soft rot on apples.
1.2.2 Physical biodeterioration
- Mechanical biodeterioration – this occurs when the material is physically disrupted or damaged by the growth or activities of the organisms. Examples of physical damage can be seen as yeast and mould break down the surfaces of biological materials over time.
- Soiling or fouling – with this kind of biodeterioration the material or product is not necessarily unsafe, but as its appearance has been compromised, it is rendered unacceptable. An example is the building up of biofilms on the surface of a material that can affect the performance of that material.
Living organisms can be divided on the basis of their nutritional requirements into autotrophs and heterotrophs (see Table 1.2). Autotrophic organisms see all inorganic materials as a potential source of nutrients, while heterotrophic organisms can only use organic matter. The organisms responsible for biodeterioration of food are usually chemoheterotrophs; however, it is important to realize that even the packaging that the food is stored in, and the warehouses themselves, can be a source of nutrients for some microorganisms, and it is therefore important to control the humidity, temperature and duration of storage of food, as far as possible [4].
Table 1.2 Classification of microorganisms on the basis of their nutritional requirements.
| Nutritional classification | Source of energy | Source of carbon | Examples of organisms |
| Photoautotroph (photolithotroph) | Sunlight (light energy) | Carbon dioxide (CO2) | Aerobic |
| Chemoautotroph (chemolithotroph) | Redox reactions (chemical energy) | Carbon dioxide (CO2) | Aerobic |
| Sulphur-oxidizing bacteria |
| Photoheterotroph (photo-organotroph) | Sunlight (light energy) | Organic carbon or carbon dioxide (CO2) | Aerobic |
| Purple non-sulphur bacteria |
| Chemoheterotroph (chemo-organotroph) | Redox reactions (chemical energy) | Organic... |
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