Food preservation methods history
Food preservation methods history
Some foods are even dangerous if eaten without proper processing. Food processing is “a variety of operations by which raw food is made suitable for consumption, cooking or storage”.
In large-scale food manufacture, processing involves applying scientific and technological principles to preserve foods by slowing down or stopping the natural processes of decay.
Food processing also uses the creative potential of the processor to change basic raw materials into a range of tasty attractive foods that provide interesting variety in the diets of consumers. Without food processing it would not be possible to sustain the needs of modern urban populations, and the choice of foods would be limited by seasonality.
Processed foods
Processing spans the whole food chain from harvesting on the farm to different forms of culinary preparation in the home, and it greatly facilitates provision of safe food to populations around the globe.
Need for Processing
Food processing can lead to improvements and prevent damage to the nutritional value of foods. Extend shelf life and quality of foods.Avoid lot of food from spoiled.
Fulfill the population needs.Food processing methods (e.g. food additives and advances in technology) help to make this possible. Food additives are added for a particular purpose whether it is to ensure food safety, to add nutritional value or to improve food quality.
They play an important role in preserving the freshness, safety, taste, appearance and texture of foods. For example, antioxidants prevent fats and oils from becoming rancid whereas emulsifiers stop peanut butter from separating into solid and liquid fractions. Food additives keep bread free of mold for longer and allow fruit jams to "gel" so they can be spread onto bread.
History
Humans have been processing foods for centuries. The oldest traditional techniques included sun-drying, the preservation of meat and fish with salt, or fruit with sugar (what we now call jamming). These all work on the premise that reduction of water availability in the product increases shelf-life. More recently, technological innovations in processing have transformed our food supply into the rich variety that is available in supermarkets today. In addition, food processing enables manufacturers to make nutritionally enhanced products (‘functional foods’) with added ingredients that provide specific health benefits beyond basic nutrition.
The canning story
Canning originated in the early 19th century as Napoleon’s troops faced a serious food shortage. In 1800, Napoleon Bonaparte offered an award of 12,000 francs to anyone who could devise a practical method for food preservation for armies on the march; he is widely reported as saying "An army marches on its stomach". After years of experiment, Nicolas Appert submitted his invention of sealing foods in glass jars and cooking them, and won the prize in 1810. The following year, Appert published L'Art de conserver les substances animales et végétales (or The Art of Preserving Animal and Vegetable Substances), which was the first cookbook of its kind on modern food preservation methods. Also in 1810, the Englishman Peter Durand applied the Appert process using various vessels made of glass, pottery, tin or other metals and obtained the first canning patent from King George III. This can be considered the origin of the modern can.
The history of freezing
The modern frozen food industry was started by Clarence Birdseye in America in 1925. He was a fur trader in Labrador, and noticed that fillets of fish left by the natives to freeze rapidly in arctic winters retained the taste and texture of fresh fish better than fish frozen in milder temperatures at other times of the year. The key to Birdseye’s discovery was the importance of the speed of freezing, and he pioneered industrial equipment to freeze foods rapidly. We know today that, coupled with appropriate treatment prior to freezing, this rapid freezing has the potential to ensure excellent preservation of nutritional value for a wide range of foods.
Main benefits of processed foods
Palatable and sensory improvements
Almost all foods undergo some form of processing before they are ready to eat. At its most simple, this could be peeling a banana or boiling a potato. However, with some products such as wheat, it requires quite elaborate processing before it becomes palatable. First there is grain harvesting, then removal of the husk, stalk, dirt and debris. The cleaned up grain is usually cooked or milled into flour and then it is often made into another product such as bread or pasta.
The organoleptic (sensory) quality of some foodstuffs benefits directly from processing techniques. For example, baked beans derive their creamy texture from the heat treatment during canning. Extruded and puffed products like breakfast cereals or crisps would be almost impossible to make without large scale modern food processing equipment.
Preserved and improved nutritional quality
Processing such as freezing preserves the nutrients that are naturally present in foods. Other processes, like cooking, can sometimes improve the nutritional value by making nutrients more available. For example, cooking and canning tomatoes to make tomato paste or sauce renders the bio-active compound lycopene more available to the body. When processed carefully, cocoa and chocolate processing preserves the levels of flavonoids like epicatechin and catechins, but their contents can be reduced with poor processing conditions. Lycopene and flavoring have antioxidant properties which, according to some research, contribute to maintenance of heart health and may reduce the risk of certain cancers.
Food Safety
Many processing techniques ensure the safety of foods by reducing the numbers of harmful bacteria that can cause illness (e.g. pasteurization of milk). Drying, pickling and smoking reduce the water activity (i.e. water available for bacterial growth) and alter the pH of foods and thereby restrict the growth of pathogenic and spoilage micro-organisms and retard enzyme reactions. Other techniques such as canning, pasteurization and Ultra-High Temperature (UHT) destroy bacteria through heat treatment.
Another benefit of processing is destruction of anti-nutritional factors. For example, cooking destroys protease inhibitors such as trypsin inhibitors found in peas, beans or potatoes. Trypsin inhibitors are small globular proteins which inhibit the action of the human digestive enzymes trypsin and chymotrypsin required to break down dietary proteins. If present in foods, they can reduce the nutritional value of the food and in high doses they have been shown to be toxic in animal studies, with some human evidence showing similar results.
Prolonged boiling also destroys the harmful lectins present in legumes such as red kidney beans. Lectins make red blood cells clump together and if not degraded prior to consumption cause severe gastro-enteritis, nausea and vomiting.
Preservation, convenience and choice
Food processing enables extension of the shelf-life of foods (e.g. perishable foods such as meat, milk and products thereof).
Food processing enables us to enjoy a varied diet that fits with the fast pace and pressures of our modern day society. People are increasingly travelling abroad for their holidays, thus they are exposed to a wider selection of flavors and styles of foods.
In the Western world, our foods are predominantly based on five staple crops – rice, wheat, maize, oats and potatoes. The array of characteristics we are used to in our foods are derived from these five simple staples combined with modern food processing techniques. Therefore, it can be said that today we have become accustomed to a diversity of foods, made from a narrow range of plant species, to provide our nutrition. This transformation of staple foods into processed foods would not be possible without modern food technology.
Reducing health concerns
The people living on a low income have a less varied diet and this is reflected in poorer nutrient intake and poorer nutritional status. Processing such as fortification of certain products like flour, bread and breakfast cereals has reduced the number of people in Europe with a low nutrient status.
Chronic diseases such as heart disease, obesity and diabetes can be managed, in part, through dietary strategies. In response to this, manufacturers have applied food processing techniques to offer consumers the choice of low fat or fat-free versions of many foods and meals.
In addition to low fat products, food processing now enables production of low salt, low sugar and high fiber versions of many foods, enabling consumers to make food choices suitable for their individual health requirements.
Different processing methods
Traditional
Heating
The temperature of the food is raised to a level which inhibits the growth of bacteria, inactivates enzymes or even destroys viable bacteria. Traditional wet cooking methods include blanching, boiling, steaming and pressure cooking.
Dry cooking methods include baking, frying and roasting. In newer techniques, heat is applied by electro-magnetic radiation such as microwaves.
Ultra-High Temperature (UHT) techniques are used widely across the food industry. This involves heating the food to ≥135 °C for at least 1 second followed by rapid cooling in order to destroy all microorganisms.
Pasteurization is when the food is heated to at least 72 °C for at least 15 seconds to kill most food-borne pathogens, then cooled rapidly to 5 °C.
Cooling
The temperature of the food is reduced to slow deterioration of the food either through bacterial growth retardation or inactivation of enzymes with deteriorative effects. Traditional cooling methods include refrigeration where temperatures are around 5 °C, and freezing, where temperatures are reduced to below -18 °C (even down to -196 °C in commercial deep freezers).
The lower the temperature, the longer foods can be stored safely. However, severe temperature changes over prolonged time periods can lead to nutrient losses and breakdown of integral food structures such that the nature and nutritional value of that food is significantly reduced.
Drying
In drying, the water content of plant foods is reduced to the level where biological reactions (like enzyme activity and microbial growth) are inhibited and the likelihood of food spoilage is thus lowered. Drying may be in the form of freeze-drying (e.g. herbs and coffee), spray-drying (e.g. milk powder), sun-drying (e.g. tomatoes, apricots) or tunnel-drying (e.g. vegetable pieces).
Salting
The addition of salt to foods has been used for centuries as a method of food preservation. This method works on the premise that the salt reduces the water activity of the food being preserved, which prevents growth of spoilage organisms. Depending on the type of food, similar effects may be achieved with sugar.
In brining the food is put in brine, water saturated, or nearly saturated with salt, a method which has been a common way to preserve meat, fish and vegetables. Today, brining of foods is a less pertinent preservation method.
Curing is a common name for food processing methods, mainly used for fish and meat, in which combinations of salt and sugar and also sometimes nitrates or nitrite (which prevents the growth of the harmful bacteria Clostridium botulinum and gives the meat an appealing pink colour) are added to food. In curing the food is sometimes also smoked.
Fermentation
In fermentation, specific yeasts or bacteria are used to give a food its desired flavour and texture, but it is also a way of altering the biochemical characteristics of foods and thereby prevent growth of spoilage micro-organisms.
In aerobic conditions, i.e. when oxygen is available, the yeast converts sugars and other carbohydrates to carbon dioxide and water. This is what makes dough leaven; the yeast produces carbon dioxide, which forms gas bubbles in the dough and makes it expand. When baked, the spongy structure is fixated by the heat and the bread gets its soft texture. The yeast is killed off by the heat.
In the production of beer, wine and other alcoholic beverages the role of the yeast is to form alcohol and partly also to carbonate the beverage. Under anaerobic (oxygen-free) conditions, yeast transforms sugar or other carbohydrates to alcohol (ethanol) and carbon dioxide. If the carbon dioxide is not eliminated, it will make the beverage fizzy. In the manufacture of alcoholic beverages it is common to add specific yeast cultures, but in certain production processes the beverage undergoes spontaneous fermentation, meaning that the fermentation is driven by yeast and other micro-organisms naturally occurring on the grapes or in the production environment. In baking, ethanol is formed as a by- product. The fermentation process alters from being aerobic to anaerobic along the leavening as the oxygen is consumed by the yeast. However, the alcohol evaporates during baking and thus, bread does not contain any alcohol. Fermentation is of great importance for the taste of beer, wine etc. as the yeast, besides ethanol and carbon dioxide, produces a number of other compounds, that give these beverages their specific aromatic characteristics.
In addition to the taste and texture, durability and safety of foods, fermentation may enhance the nutritional value of foods. Micro-organisms do produce amino acids, fatty acids and certain vitamins which are absorbed and made use of as we eat the foods.
The microbial activity may also reduce the content of antinutrients, substances present in certain foods (e.g. pulses, cereals, vegetables), which interfere with the absorption of nutrients. Reducing the content of such components enhances absorption of nutrients from the food and thereby increases its nutritional value.
Food additives
Food additives are substances that are added to foods to serve specific technical purposes, and are grouped depending on the function they perform when added to foods, e.g. preservatives, antioxidants, stabilisers, anti-caking agents, or packaging gases. Only substances that are not normally consumed as a food in itself and that are not normally used as a characteristic ingredient of food, qualify as additives.
The advantages of new technologies
Many of the traditional methods of preservation cause inevitable losses in nutrient levels and can adversely affect the nature and quality of the produce following processing.
Microwaving
Microwave processing is heating by radiation as opposed to the more traditional convection or conduction techniques. Microwaves are transmitted efficiently in water but not by plastics or glass, and are reflected by metals. It is oscillation of the water molecules in food which leads to the heating of that food. Since the water is usually distributed unevenly in a food, occasional stirring is required for proper heating and safe food handling. Microwaving food is a fast method of heating which requires little addition of water and thus leads to less nutrient losses than other forms of cooking.
Modified atmosphere preparation (MAP)/storage/packaging
It may be defined as ‘the enclosure of food products in gas-barrier materials in which the gaseous environment has been changed’. It refers to controlled alterations of the atmosphere in which foods are prepared, packaged or stored, which together inhibit the growth of bacteria. Usually oxygen, carbon dioxide and nitrogen are the gases employed. MAP can be vacuum packaging or the introduction of a gas during packing. Most recently, MAP has evolved into active packaging where the atmosphere continuously changes during the shelf-life of the product. For example, oxygen absorbers or carbon dioxide emitting films may be used. Reduction of oxygen levels and increase in carbon dioxide levels both lead to microbial growth inhibition.
Irradiation
Processing by ionising radiation is a particular kind of energy transfer with the portion of energy transferred per treatment being high enough to cause ionisation. It is used to control and disrupt biological processes in order to extend the shelf-life of fresh products, and it can be applied to sterilise packaging materials.
Beneficial biological effects of irradiation include sprouting inhibition, ripening delay and insect disinfestations. Microbiologically, irradiation suppresses pathogenic and other spoilage-causing microorganisms. The major advantage of irradiation is that it passes through the food, kills microorganisms but because it does not heat the food it has a marginal effect on the nutritional composition. Proteins and carbohydrates may be broken down to some degree but their nutritional value is little affected.
- there is a reasonable technological need
- it presents no health hazard
- it is of benefit to the consumers or
- it is not used as a substitute for hygiene and health practices or for good manufacturing or agricultural practice.
Ohmic heating
This is a thermal process in which heat is internally generated by the passage of alternating electrical currents through the food which acts as electrical resistance. Ohmic heating is also known as ‘resistance heating’, or ‘direct resistance’ heating. It is not reliant on transfer of energy by water particles so it is an important development for the efficient heating of low water, low particulate foods. It is a high-temperature short-time (HTST) method, thus decreasing the possibility of high-temperature over-processing and its likely associated loss of nutrients. Another advantage of Ohmic heating is that it keeps delicately structured foods such as strawberries intact.
4.2.5 Ultra-high pressure
High pressure technology subjects foods to pressures of 100 – 1000 Megapascal usually for 5 – 20 minutes. It has a number of key attributes including micro-organism inactivation, modification of biopolymers such as gel formation and quality retention such as colour, flavour and nutrients. This is because of its unique ability to directly affect non-covalent bonds (such as hydrogen, ionic and hydrophobic bonds) whilst leaving covalent bonds intact, and both without employing heat. As a consequence, it offers the possibility of retaining vitamins, pigments and flavour components while inactivating microorganisms or enzymes that could otherwise negatively affect food functionality through food spoilage.
Light pulses
This method uses intermittent flashes of white light (20% UV, 50% visible and 30% infra-red) with an intensity claimed to be 20,000 times that of the sun at the earth’s surface. One to twenty flashes per second are typical pulse rates which lead to significant surface reductions in micro-organisms when used on meat, fish and bakery products. This technique is ideal for surface decontamination of packaging materials and works best on smooth, dust-free surfaces.
Pulsed electric fields (PEF)
This process involves applying repeated short pulses of a high-voltage electric field (10 – 50kV/cm) to a pumpable fluid flowing between two electrodes. It does not use electricity to generate heat, but instead it inactivates micro-organisms by disrupting the walls and membranes of cells exposed to the high-voltage pulses. PEF is mostly used in refrigerated or ambient products and because it is applied for just one second or less, it does not result in heating of the product. It is for this reason that it has nutritional advantages over more traditional thermal processes which degrade heat-sensitive nutrients.
Effects of processing on nutritional quality
Food processing can lead to improvements in, or damage to, the nutritional value of foods. Simple food preparation processes in the domestic kitchen lead to inevitable damage to the cells of plant foods, leading to leaching of essential vitamins and minerals. However, if we are careful in the way we process foods, and choose a variety of processed foods, they can play an important role in a nutritious and balanced diet. Unlike the domestic environment, food manufacturers have access to commercial scale, fast processing methods which cause minimal nutrient losses, and they utilise processes which actually help to release positive nutrients (like lycopene in the cooking of tomatoes) or eradicate compounds of concern (like lectins in legumes).
Vitamins and minerals
There are 13 vitamins, required by the body in small amounts, but nonetheless essential. Four are fat soluble (A, D, E, and K) and the remaining nine are water soluble (C, B group vitamins). No single food contains all the vitamins so a balanced and varied diet is necessary for an adequate intake. Processing affects different vitamins in different ways. For example, the water soluble vitamins tend to be more sensitive to processing and are often partially lost during boiling and heat treatment. However, newer ‘non-thermal’ processes such as Ohmic heating or ultra-high pressure treatment can help to retain vitamins because they subject the food to lower temperatures (if any) and the processes occur for a very short time. In some situations, processed foods actually contain more vitamins than fresh products. For example, frozen vegetables picked and frozen within hours retain more vitamin C than their fresh counterparts because more vitamin C is lost over time during chilled storage compared to frozen storage.
Minerals are inorganic elements which our body needs in small amounts, usually obtained sufficiently by consuming a conventional mixed diet. Food processing can have important beneficial effects on the availability of minerals from foods. For example, phytates in wholegrain cereals inhibit iron and zinc absorption but during fermentation, enzymes are released which degrade the phytates and increase the iron and zinc availability in the dough.
Carbohydrates and fibre
For mono- and oligosaccharides, little degradation occurs at temperatures right up to those used in UHT processing but there are several reactions that may affect nutritional quality. For example, some sugars could change their molecular structure during heating, which may affect digestibility. This could be advantageous in reducing the presence of indigestible oligosaccharides (like stachyose or raffinose present in legumes and some other foods) that cause flatulence if over-consume.
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