Application of Biotechnology to Food Production and Preservation
Microorganism such as bacteria and fungi in collaboration with worms play vital roles in creating and maintaining soil fertility. When animals, plants or other organisms die, the remains are broken down by decomposers, especially fungi, bacteria and earthworms.
Decomposition recycles important nutrients such as nitrogen and phosphorus into the soil to make them available for plants. Insects play a secondary role in this process, because both their remains and their faeces are recycled in the same manner.
Some fungi colonise plant roots and act as symbionts, providing nutrients such as phosphorus and nitrogen to the plant in exchange for carbon.
Nitrogen-fixing and nitrifying bacteria play a more important role by capturing atmospheric nitrogen and converting it to compounds plants can use. Earthworms also help mix the soil, carrying organic compounds from higher soil to lower layers and increasing porosity, which increases the rate of nutrient and water flow.
Some species of fungi can help clump or bind soil particles, increasing the amount of water the soil can hold. Not only do bacteria, fungi and earthworms help sustain plant life, they lend soil its characteristic odor.
These activities increase soil fertility, which generally is a function of available nutrients in the soil. Plant growth in any soil therefore depends on the availability of nutrients and ability of plants to take them up.
Application of biotechnology to plant growth is usually directed at either optimising the activities of soil microorganisms to enhance soil nutrients or the ability of plants to take up nutrients, or both.
Specifically, it involves a genetic modification of plant seedlings for better crop yield and to make them more resistance to pests, reduce weed and pest effects.
Genetically-modified foods are therefore foods produced by altering the genetic materials either in plants or animal to enable them grow better or withstand pests or pathogens of diseases in the environment.
Conventional plant breeding to improve plant characteristics involves selecting and breeding individuals with desired characteristics. Consequently, modern plants evolving in the last millennium differ substantially from their ancestors.
Plant breeding is carried out by crossing breeds of two individuals of the same or of two very closely related species. Each parent contributes half of its genetic material (DNA) to its offspring (equivalent to sexual reproduction).
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This means a wholesome transfer of both beneficial and non-beneficial characteristics. Progressive selection may subsequently eliminate all or some of the non -beneficial characteristics, but there is never a full proof assurance that this will ever happen.
This is because, this conventional method is slow to act and takes very long time, often many generations to take place.
Modern biotechnology has changed all these. By using genetic engineering methods, it is now possible to identify those genes encoding beneficial characteristics, isolate them and incorporate them into another plant at the expense of non-beneficial threats. This gives rise to a new, better and beneficial crop.
This is the genetically-modified or engineered crop (commonly known as GM crops). Several methods are used to accomplish genetic modification of crops.
(1) Cisgenesis which involves the insertion or deletion of genes. In this process, genes are artificially transferred between organisms that could be conventionally bred.
(2) Transgenesis in which genes from a different species are inserted into another plant (a form of horizontal gene transfer).
Transgenesis may also occur in nature when exogenous DNA (foreign DNA) penetrates the cell membrane of another plant species for any reason. Artificially, gene transfer can be carried out using different methods
(1) As part of an attenuated virus genome,
(2) By physically inserting the extra DNA into the nucleus of the intended host using a microsyringe (requiring a highly technical skill),
(3) By coating the gene on gold nanoparticles and firing from a gene gun. Naturally, transfer between plant cells is carried out by vector bacteria such as Agrobacterium and between animal cells by vector virus such as lentiviruses.
Introducing new genes into plants requires a promoter specific to the area where the gene is to be expressed. For instance, if we want the gene to be expressed only in rice grains and not in leaves, then an endosperm- specific promoter gene would be used.
The codons (a sequence of three adjacent nucleotides constituting the genetic code that determines where specific amino acids are inserted in a polypeptide chain during protein synthesis or the signal to stop protein synthesis) of the gene being transferred must also be optimised for the organism because every gene determines what codon it uses in each organism.
The transgenic gene products should also be able to be denatured by heat so that they are destroyed during cooking.
Growth of genetically- modified plants is growing by the day. It started in the industrialised countries but is now spreading in many developing countries. In 2006, 252 million acres of transgenic crops were planted in 22 countries by 10.3 million farmers.
The majority of these crops were herbicide- and insect-resistant soybeans, corn, cotton, canola, and alfalfa. Other crops grown commercially or field-tested are a sweet potato resistant to a virus that could decimate most of the African harvest, rice with increased iron and vitamins that may alleviate chronic malnutrition in Asian countries, and a variety of plants able to survive weather extremes.
On the horizon are bananas that produce human vaccines against infectious diseases such as hepatitis B; fish that mature more quickly; cows that are resistant to bovine spongiform encephalopathy (mad cow disease); fruit and nut trees that yield years earlier, and plants that produce new plastics with unique properties.
In the same year 2006, countries that grew 97 per cent of the global transgenic crops were the United States (53 per cent), Argentina (17 per cent), Brazil (11 per cent), Canada (six per cent), India (four per cent), China (three per cent), Paraguay (two per cent) and South Africa (one per cent).
Although growth is expected to stabilise industrialised nations, it is increasing in developing countries. By the year 2020, it is expected that rate of genetically-modified crops will grow exponentially in the developing nations as researchers gain increasing and unprecedented access to genomic resources that are applicable to a wide range of organisms.
A genetically- engineered or “transgenic” animal is an animal that carries a known sequence of recombinant DNA in its cells, and which passes that DNA onto its offspring. Recombinant DNA refers to DNA fragments that have been joined together in a deliberate pattern.
The resultant recombinant DNA “construct” is usually designed to express the protein(s) that are encoded by the gene(s) included in the construct, when present in the genome of a transgenic animal. Because the genetic code for all organisms is made up of the same four deoxynucleotide building blocks, this means that a gene makes the same protein whether it is made in an animal, a plant, or a microbe.
Transgenic animals look and behave normally, and differ from their non-modified counterparts only in the expression of an additional protein produced by the extra DNA encoded in its genome.
Some examples of proteins that have been expressed in transgenic animals include therapeutic proteins for the treatment of human diseases, proteins that enable animals to better resist disease and proteins that result in the production of more healthful animal products (milk, eggs, or meat) for consumers.
A variety of techniques have been used to produce transgenic livestock with varying degrees of success. Microinjection of foreign DNA into newly fertilized eggs has been the predominant method used for the generation of transgenic livestock over the past 20 years. This technology is inefficient (3-5 per cent of animals born carry the transgene) and this results in an animal welfare concern because it requires the use of many more animals than would be needed if success rates were higher.
Additionally, this technique results in random integration and variable expression levels of the target gene in the transgenic offspring. Thus, the level of expression of the introduced gene is generally very poor. This has sometimes resulted into significant growth abnormalities.
Newer methods of making transgenic animals have been developed that employ somatic cell nuclear transfer cloning. The cloning process was first made famous by Dolly the sheep.
Cloning offers the opportunity to produce 100 percent transgenic offspring from cell lines that are known to contain the transgene, and further also allows gene targeting whereby researchers are able to integrate the foreign DNA at a specific location in the genome, and thereby have more control over the expression level of the transgene.
There have been published reports of the following species being cloned: carp, sheep, mice, cattle, goats, pigs, cats, rabbits, mules, horses, rats, and a deer. Some closely related species have also been cloned (a banteng, a wild cow, and a mouflon, a kind of sheep). A gaur, a wild ox, was cloned but died within two days.
Attempts have also been made, without success, to clone monkeys, dogs, pandas, chickens, and at least two extinct species: the Tasmanian tiger and the woolly mammoth. The mammoth experiment used an elephant surrogate and tissue found in permafrost.
Genetic engineering is a useful technology because it enables animals to produce extra and beneficial proteins.
Conventional animal breeding is constrained to selection based on naturally-occurring variations in the proteins that are present in a species, and this limits the range and extent of genetic improvement.
Genetically-engineered animals are being produced for two distinct applications: human medicine and agriculture.
Most commercial transgenic animal research is in the field of human medicine. Many therapeutic proteins for the treatment of human diseases require that animal cells are specifically modified in a specific way. This can only be done using the genetic engineering techniques, in most cases using the mammalian cell-based bioreactors.
In 2006, the first human therapeutic protein, Antithrombin III (ATryn®, GTC Biotherapeutics, Framingham, Mass.), derived from the milk of genetically-engineered goats was approved by the European Commission for the treatment of patients with hereditary antithrombin deficiency.
Transgenic animals are also being used to produce serum biopharmaceutical products, such as antibodies that can be used for the treatment of infections, cancer, organ transplant rejections and autoimmune diseases such as rheumatoid arthritis.
Transgenic mice have also become increasingly important for biological and biomedical research and have generated a vast amount of vital information about human diseases.
Other transgenic animals, including livestock species, are being produced specifically as biomedical research models for various human afflictions including Alzheimer’s disease, eye disease, and the possible xenotransplantation of cells, tissues, and organs from genetically-engineered animals into human organ-transplantation patients.
Transgenic animals are also being used to study animal diseases such as “mad cow” disease (BSE, bovine spongiform encephalopathy), and infection of the udder (mastitis).
Transgenic livestock for agricultural applications have also been produced but not at a commercial scale. These animals have enhanced production traits (e.g. egg-laying), are environmentally beneficial (produce less waste) and are disease resistant.
Quality and Safety of Genetically-modified Foods
The use of genetic engineering in agriculture and food production has impacts, not only on the environment and biodiversity, but also on human health. Therefore, thorough bio-safety assessment requires, not only evaluation of environmental impacts of genetically- engineered organisms, but also assessment of the risks that genetically- engineered foods may pose to the health of consumers.
There are three hazards that may arise from genetic engineering of foods. These are (1) allergens, (2) toxins, and (3) reduced nutritional quality. The genetic engineering of foods involves the introduction of new genetic information into a food-producing organism.
Some of the health risks associated with genetically-engineered foods can therefore come from the organism being modified (unmodified organism UMO) or from the donor organism (gene source, GS) from where the genetic material being transferred was taken.
For instance, if a gene derived from peanuts is introduced into a tomato, food produced from the resulting genetically-engineered tomato might cause allergic reactions in people that are allergic either to tomatoes (UMO) or to peanuts (GS).
A third source of hazard is the procedure of genetic engineering itself. Current recombinant DNA methods and those likely to be developed in the future are all capable of accidentally introducing unintended changes in the function and structure of the food producing organism.
As a result, the genetically-engineered food may have characteristics that were not intended by the genetic engineer, and that cannot be foreseen on the basis of the known characteristics of the unmodified organism or gene source.
To assure the safety of genetically-engineered foods, it is essential to test for health hazards derivable from all three sources of risk above.
As already stated the three most important hazards of genetically- engineered foods are allergens, toxins and reduced nutritional quality. Although there are several ways by which allergens could develop in genetically-engineered foods empirical evidence of its rate is sparse probably because only few of these foods have been tested for allergenicity.
However, evidence that it exists was provided by Pioneer Hybrid (a biotech company), which developed genetically-modified soybeans that contain proteins which turn out to be allergenic to a significant proportion of the population. The company subsequently terminated plans to commercialize this product.
Most substances that will occur in foods as a result of genetic engineering will be proteins that will be present in only trace concentrations. Nevertheless, those added components, in even trace amounts, may substantially alter either the nutritional or other biological characteristics of the food.
In addition to allergenicity, recombinant proteins could manifest a variety of other biological activities, and, in the case of recombinant enzymes, could catalyze the production of other compounds with biological activities not normally present in a particular food.
Such substances could act as toxins, irritants, hormone mimetic (imitation), etc., and could act at the biochemical, cellular, tissue, or organ levels to disrupt a range of physiological functions.
An example of a class of genetically-engineered foods that are of particular concern are those that have been modified to produce biological control agents, such as the family of insecticidal Bt enterotoxins.
Each of the Bt toxins is specific for a certain class of insects. Although the Bt toxin has been used topically in organic farming for many years without unexpected effects, concern still remain of its long term effect.
The greatest concern however, is the underlying fact that it is impossible to carry out laboratory experiments that will exhaustively, thoroughly, and conclusively establish that a genetically- engineered food is free of such toxins, and therefore absolutely safe.
This fact was clearly illustrated by the tragic case of L-tryptophan (an essential amino acid in the human diet). The company Showa Denko genetically-engineered a microorganism to produce L-tryptophan at high levels.
The enzymes expressed in this bacterium through genetic manipulations were not present in massive amounts, but they altered the cellular metabolism substantially, leading to greatly increased production of tryptophan.
This organism was immediately used in commercial production of L-tryptophan, and the product placed on the market in the USA. Within two months, 37 people died and 1500 were permanently disabled from using this product.
Apparently, this may have been due to the presence of traces of powerful toxic contaminants in the product. This contaminant was extremely powerful, since the preparation was at least 98.5% tryptophan.
Nutritionally, genetically-modified foods are of high quality and taste and nutritionally rich. It improves yield and shortens production cycles. Genetic modification also endows crops with greater resistance to common diseases and harsh weather conditions.
Genetic modification of animals, likewise, improves animal health, minimizing their chances of being affected with common infections. Naturally, the improved breeds give better yields of eggs, meat and milk.
Genetically-modified foods were first introduced to the market in the early 1990s. The first was the tomato called FlavrSavr (created by Calgene in 1992). It was released in the US market post FDA approval in 1994.
A slightly different variant of the FlavrSavr was introduced in Europe in a paste form in 1996.
Other GM food crops in the market are herbicide and insecticide- resistant soybeans, canola, corn, cotton, sweet potato (resistant to a virus that has been destroying most of the African harvest), an iron and vitamin-enriched rice variety (to combat widespread malnutrition in Asian nations).
Application of Biotechnology to Food Production and Preservation
A variety of plants able to withstand extreme weather conditions are being field-tested prior to being launched in the market. Genetically-modified fruit and nut varieties that attain maturity early and bear fruits for long (or twice a year) have also been introduced.
Finally, genetic modification has also been used to develop fast maturing varieties of fish and poultry and milk production.
Preserving food to extend its shelf-life, whilst ensuring its safety and quality, is a central concern of households and food industries.
Preservation usually involves preventing the growth of bacteria, fungi (such as yeast), and other micro-organisms (although some methods work by introducing benign bacteria or fungi to the food), as well as retarding the oxidation of fats.
Food preservation can also include processes which inhibit visual deterioration, such as the enzymatic browning reaction in apples after they are cut, which can occur during food preparation.
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Many processes designed to preserve food will involve a number of food preservation methods. Preserving fruit by turning it into jam, for example, involves boiling (to reduce the fruit’s moisture content and to kill bacteria, yeasts, etc.), sugaring (to prevent their re-growth) and sealing within an airtight jar (to prevent recontamination).
There are many traditional methods of preserving food that limit and reduce carbon footprint (“the total set of greenhouse gas (GHG) emissions caused by an organization, event, product or person.).
There are several traditional methods of food preservation and a few emerging biotechnology ones.
The traditional methods include but not limited to sun drying, refrigeration, freezing, vacuum packing, salting, sugaring, smoking, artificial food additives, pickling, lye (sodium hydroxide that makes food too alkaline for bacteria to act on, canning and bottling (to prevent microbial access), jellying (cooking in a material that solidifies to gel also to prevent microbial access), jugging (a process of stewing the meat in a covered earthenware jug or casserole).
Irradiation (exposure to ionizing radiation such as high- energy electrons, X-ray from accelerators, gammar rays emmitted from radioactive sources as Cobalt-60 or Caesium-137), pulsed electric field processing (a method of processing cells using brief pulses of a strong electric field, a type of low temperature alternative pasteurization process for sterilizing food products), modified atmosphere (environmental manipulation), hih pressure (exposure to high pressure) and burial in the ground (exposure to low temperature, low oxygen etc.).
The emerging biotechnology methods include controlled use of microorganisms, biopreservation and hurdle technology.
Controlled use of microorganisms is based on the principle that some foods, such as many cheese, wines and beers will keep for a long time because their production involved the use of specific micro-organisms that combat spoilage from other less benign organisms.
These micro- organisms keep pathogens in check by creating an environment toxic for themselves and other micro-organisms by producing acid or alcohol.
Starter micro-organisms, salt, hops, controlled (usually cool) temperatures, controlled (usually low) levels of oxygen and/or other methods are used to create the specific controlled conditions that will support the desirable organisms that produce food fit for human consumption.
Biopreservation is the use of natural or controlled microbiota or antimicrobials to preserve food and extend its shelf life. Beneficial bacteria or the fermentation products produced by these bacteria are used in biopreservation to control spoilage and render pathogens inactive in food.
One of such beneficial bacteria are lactic acid bacteria (LAB). Lactic acid bacteria have antagonistic properties which make them particularly useful as biopreservatives. When LABs compete for nutrients, their metabolites often include active antimicrobials such as lactic and acetic acid, hydrogen peroxide, and peptide bacteriocins.
Some LABs also produce the antimicrobial nisin which is a particularly effective preservative. LAB bacteriocins are now used as an integral part of hurdle technology for maximum effect.
Using them in combination with other preservative techniques can effectively control spoilage bacteria and other pathogens, and can inhibit the activities of a wide spectrum of organisms, including inherently resistant gram negative bacteria.
Hurdle technology is combination of preservative methods with an objective of total eliminating of pathogens in food products. This method can be thought of as an assemblage of “hurdles” pathogens have to overcome if they wish to remain active in the food.
The right combination of these hurdles ensures that none of the pathogens ever is a able to overcome all and subsequently all are eliminated or rendered too weak to be harmful.
Accordingly, Leistner (2000) defined hurdle technology as ‘an intelligent combination of hurdles which secures the microbial safety and stability as well as the organoleptic and nutritional quality and the economic viability of food products. The organoleptic quality of the food refers to its sensory properties, that is its look, taste, smell and texture.
Examples of hurdles in a food system are high temperature during processing, low temperature during storage, increasing the acidity, lowering the water activity or redox potential, or the presence of preservatives or biopreservatives.
According to the type of pathogens and how risky they are, the intensity of the hurdles can be adjusted individually to meet consumer preferences in an economical way, without sacrificing the safety of the product. The basic well tested hurdle options available are presented in
|Table: Principal Hurdles Used for Food Preservation (after Leistner,1995)|
|Low temperature||T||Chilling, freezing|
|Reduced water activity||aw||Drying, curing, conserving|
|Increased acidity||pH||Acid addition or formation|
|Reduced redox potential||Eh||Removal of oxygen or addition of ascorbate|
|Biopreservation||Competitive flora such as microbial fermentation|
|Other preservatives||Sorbates, sulfites, nitrites|
In summary, genetically- modified foods are crops and animals produced by a deliberate alteration of their genetic constitution to enable them grow better and withstand environmental adversities such as pest infestation and / or disease infection.
Specifically, genetically-modified crop or genetically-engineered crop (abbreviated to GM or GE crop) involved a deliberate alteration of the genetic makeup of a plant species to increase productivity, withstand insect pest, weeds and improve on the nutritional quality of its products.
The alteration is carried out either through cisgenesis (insertion or deletion of genes involving artificial transfer between organisms that could be conventionally bred) or transgenesis (inserted into another plant of different species).
Most genetically-engineered crops grown around the world are herbicide- and insect-resistant and included soybeans, corn, cotton, canola, alfalfa, sweet potato and rice. The United States of America is leading other 21 nations known to grow genetically-modified crops.
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Although several concerns were expressed about the safety of genetically-modified foods, acceptance is increasing so is the proportion of genetically-modified foods in the market.
Biotechnology methods can be used to improve on food production, processing and preservation and biotechnology techniques such as genetic engineering is being used to make crops better by developing insect and disease resistant crops, herbicide resistant crops and high yielding seedling and cultivars for the production of genetically-modified foods (GM foods) also known as genetically-engineered foods (GE foods).
Genetic engineering is also used to reduce the time it takes crops to begin production and to make tastier and better looking crops and fruits. In the next unit, we will continue the discussion by looking at the application of biotechnology to pollution control and abatement.
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