.bmp)
Thursday, July 19, 2007
Wednesday, July 18, 2007
Package 2- Polymerase Chain Reaction (PCR)
Polymerase Chain Reaction (PCR) is the quick and easy method for generating unlimited copies of any fragment of DNA. This technique is used mainly in two areas: detection of infectious disease organisms & detection of variations and mutations in genes.
Why is PCR so useful?
The genetic material of each living organism (plant, animal, bacterium or virus) possesses sequences of its nucleotide building blocks (usually DNA, sometimes RNA) are uniquely and specifically present only in its own species. Complex organisms such as human beings possess DNA sequences that are uniquely and specifically present only in particular individuals. These unique variations make it possible to trace genetic material back to its origin, identifying with precision at least what species of organism it came from, and often which particular member of that species.
What PCR requires?
This technique requires a template molecule (the DNA or RNA you want to copy) and two primer molecules to get the copying process started. The primers are short chains of the four different chemical components that make up any strand of genetic material. These four components are like bricks or building blocks that are used to construct genetic molecules; also known as nucleotides or bases in laboratory. For PCR, primers must be duplicates of nucleotide sequences on either side of the piece of DNA of interest, which means that the exact same order of the primers’ nucleotides must be known already.
Procedures of PCR:
There are 3 basic steps in PCR.
1st step --> The target genetic material must be denatured, where the strands of its helix must be wound and separated by heating to 90-96°C.
2nd step --> Hybridization/annealing, where the primers bind to their complementary bases on the now single-stranded DNA.
3rd step --> DNA synthesis by a polymerase. Starting from the primer; the polymerase can read a template strand and match it with a complementary nucleotides very quickly.
The result is two new helixes in place of the first, each composed of one of the original strands plus its newly assembled complementary strand.
Quoted from: http://www.faseb.org/opa/bloodsupply/pcr.html
Why is PCR so useful?
The genetic material of each living organism (plant, animal, bacterium or virus) possesses sequences of its nucleotide building blocks (usually DNA, sometimes RNA) are uniquely and specifically present only in its own species. Complex organisms such as human beings possess DNA sequences that are uniquely and specifically present only in particular individuals. These unique variations make it possible to trace genetic material back to its origin, identifying with precision at least what species of organism it came from, and often which particular member of that species.
What PCR requires?
This technique requires a template molecule (the DNA or RNA you want to copy) and two primer molecules to get the copying process started. The primers are short chains of the four different chemical components that make up any strand of genetic material. These four components are like bricks or building blocks that are used to construct genetic molecules; also known as nucleotides or bases in laboratory. For PCR, primers must be duplicates of nucleotide sequences on either side of the piece of DNA of interest, which means that the exact same order of the primers’ nucleotides must be known already.
Procedures of PCR:
There are 3 basic steps in PCR.
1st step --> The target genetic material must be denatured, where the strands of its helix must be wound and separated by heating to 90-96°C.
2nd step --> Hybridization/annealing, where the primers bind to their complementary bases on the now single-stranded DNA.
3rd step --> DNA synthesis by a polymerase. Starting from the primer; the polymerase can read a template strand and match it with a complementary nucleotides very quickly.
The result is two new helixes in place of the first, each composed of one of the original strands plus its newly assembled complementary strand.
Quoted from: http://www.faseb.org/opa/bloodsupply/pcr.html
Saturday, July 14, 2007
Package 2- Immunoassays
Besides the conventional agar plate testing of foodborne pathogens, there are other methods such as Immunoassays, PCR, DNA hybridization etc.
Immunoassay refers to the qualitative or quantitative determination of antigen or antibody in a specimen by an immunological reaction. In addition, immunoassays are among the most commonly used techniques in clinical, food and environmental microbiology for rapidly detecting pathogenic bacteria.
There are 5 types of immunoassays techniques:
1) Immunofluorescence
This technique is the first type of immunoassay used to detect bacteria in biological specimens. Immunofluorescence kits for detecting Salmonella in food have been commercially available. In this method, bacteria from an enrichment culture are fixed to a microscope slide and the fixed cells are treated with fluoresin-conjugated somatic and flagellar antibodies specific for Salmonella. After excess reagent is removed, the slide is observed under fluorescence microscope for cells with fluorescent cell wall and/or flagella. Although immunofluorescence is a useful tool in the research laboratory, it is not used in most food microbiology laboratories because final evaluation of the reaction is performed by microscopic examination, which is tedious. Furthermore, trained and experienced personnel are needed to obtain reliable results.
2) Coagglutination (agglutination-enhancement)
This technique is popular in clinical microbiology because it is simple, rapid, moderately sensitive and does not require instrumentation. The most common type of antigen can be immobilized on inert latex particles by either passive adsorption or covalent bonding. Latex reagents prepared in this manner are stable for as long as 1 year when stored at 4°C. The test is performed as follows:
· After centrifugation of an enrichment culture, the pellet containing bacteria of interest is re-suspended in an appropriate buffer.
· A drop of the bacterial suspension is placed on a slide.
· A drop of the sensitized latex reagent is added and mixed thoroughly with the specimen.
· The slide is rocked for 1-5minutes and then visually examined under a high-intensity lamp for agglutination. The sensitivity of the latex agglutination test for bacteria is generally in the range 10^7-10^8 cells per ml.
It is important to perform appropriate controls each time to ensure that the senitized latex has retained reactivity and to detect false-positives caused by spontaneous agglutination of the senitized latex.
3) Immunoaffinity Chromatography
A monoclonal or polyclonal antibody to the target molecule- for example: aflatoxin B1, is immobilized on a solid inert support contained in a mini-column. A sample is suspected to contain the target antigen is allowed to flow through the column. The target molecule is retained while other materials are removed by extensive washing. The retained target molecule is eluted by changing the composition of the mobile phrase and quantitated by an appropriate method (for example: fluorometry).
4) Immunoimmobilization
Immunoimmobilization is a procedure that takes advantage of the immobilization of motile bacteria cells in a semisolid medium by a specific antibody directed against the flagella of the bacteria. Motile bacteria traverse the semi-solid medium until they meet the antiflagellar antibody diffusing from the opposite direction. A visible arc of immobilization forms at the antibody/bacterial interface; this arc indicated that target bacteria are present.
5) Enzyme Immunoassays
Enzyme immunoassays (EIA) also know as Enzyme-Linked-Immunosorbent Assay (ELISA), is the most commonly used format for the immunological detection of microorganisms and their metabolites (toxins). EIA depends on 3 principles:
Ø The exquisite specifity of antigen-antibody reactions
Ø Biological amplification of the antigen-antibody reaction by an enzyme
Ø The antibody’s ability to retain its immunoreactivity after conjugation with an enzyme.
Traditional immunoassays that used polyclonal antibodies often suffered from shortcoming caused by the presence of antibodies cross-reactive to bacteria other than the target organism and from batch-to-batch variations in antibody specificity.
Wednesday, July 11, 2007
Package 2- GM Labeling
GM Labeling
According to an article in the Food Standards Agency:
In the EU, if a food contains or consists of genetically modified organisms (GMOs), or contains ingredients produced from GMOs, this must be indicated on the label. For GM products sold 'loose', information must be displayed immediately next to the food to indicate that it is GM.
On 18 April 2004, new rules for GM labelling came into force in all EU Member States.
The GM Food and Feed Regulation (EC) No. 1829/2003 lays down rules to cover all GM food and animal feed, regardless of the presence of any GM material in the final product.
This means products such as flour, oils and glucose syrups will have to be labelled as GM if they are from a GM source.
Products produced with GM technology (cheese produced with GM enzymes, for example) will not have to be labelled.
Products such as meat, milk and eggs from animals fed on GM animal feed will also not need to be labelled. Details on the labelling rules can be found on the table below.
Any intentional use of GM ingredients at any level must be labelled. But there is no need for small amounts of GM ingredients (below 0.9% for approved GM varieties and 0.5% for unapproved GM varieties that have received a favourable assessment from an EC scientific committee) that are accidentally present in a food to be labelled.
The above article is quoted from: http://www.food.gov.uk/gmfoods/gm_labelling
According to an article in the Food Standards Agency:
In the EU, if a food contains or consists of genetically modified organisms (GMOs), or contains ingredients produced from GMOs, this must be indicated on the label. For GM products sold 'loose', information must be displayed immediately next to the food to indicate that it is GM.
On 18 April 2004, new rules for GM labelling came into force in all EU Member States.
The GM Food and Feed Regulation (EC) No. 1829/2003 lays down rules to cover all GM food and animal feed, regardless of the presence of any GM material in the final product.
This means products such as flour, oils and glucose syrups will have to be labelled as GM if they are from a GM source.
Products produced with GM technology (cheese produced with GM enzymes, for example) will not have to be labelled.
Products such as meat, milk and eggs from animals fed on GM animal feed will also not need to be labelled. Details on the labelling rules can be found on the table below.
Any intentional use of GM ingredients at any level must be labelled. But there is no need for small amounts of GM ingredients (below 0.9% for approved GM varieties and 0.5% for unapproved GM varieties that have received a favourable assessment from an EC scientific committee) that are accidentally present in a food to be labelled.
The above article is quoted from: http://www.food.gov.uk/gmfoods/gm_labelling
Thursday, July 5, 2007
Package 2- Genetically Modified (GM) Food
What is GM food?
GM food stands for Genetically Modified Food. It is the altering of the genetic make-up of a living organisms/food by using a particular method to transfer one or more genes from one organism to another. Usually, through this process, the nutrient value, yield or resistant against pest of the crops will increase. Thereby, increasing the food supply.
Definition of genes:
Genes are the instruction code for all characteristics that are inherited from one generation to the next and are found in nucleus in every cell in every living organism.
Difference between GM and biotechnology:
Genetically Modified Process is different from biotechnology. Genetically Modified Process involves the altering of genes whereas biotechnology makes use of the natural process/products of living things for medical, industrial and environmental.
Example of GM food:
· Tomatoes --> modified to ripen slowly to improve flavour and shelf life.
· Soybeans --> modified to resist herbicide to improve crop yields.
· Canola Oil --> modified to have a higher content of monounsaturated fatty acids, which is healthier.
· Rice --> modified to produce beta-carotene to prevent vitamin A deficiency in developing countries.
GM food stands for Genetically Modified Food. It is the altering of the genetic make-up of a living organisms/food by using a particular method to transfer one or more genes from one organism to another. Usually, through this process, the nutrient value, yield or resistant against pest of the crops will increase. Thereby, increasing the food supply.
Definition of genes:
Genes are the instruction code for all characteristics that are inherited from one generation to the next and are found in nucleus in every cell in every living organism.
Difference between GM and biotechnology:
Genetically Modified Process is different from biotechnology. Genetically Modified Process involves the altering of genes whereas biotechnology makes use of the natural process/products of living things for medical, industrial and environmental.
Example of GM food:
· Tomatoes --> modified to ripen slowly to improve flavour and shelf life.
· Soybeans --> modified to resist herbicide to improve crop yields.
· Canola Oil --> modified to have a higher content of monounsaturated fatty acids, which is healthier.
· Rice --> modified to produce beta-carotene to prevent vitamin A deficiency in developing countries.
Sunday, May 20, 2007
Package 1 - What are the potential hazards in fruits & vegetables?
1) Water/ Agriculture water (for growing the vegetables)
Water of inadequate quality has the potential to be a direct source of contamination and a vehicle for spreading localized contamination in the field, facility, or transportation environments. Wherever water comes in contact with fresh produce such as vegetables, its quality dictates the potential for pathogen contamination. If pathogens survive on the produce, they may cause foodborne illness.
Water can be a carrier of many microorganisms including pathogenic strains of Escherichia coli, Salmonella spp., Vibrio cholerae, Shigella spp., Cryptosporidium parvum, Giardia lamblia, Cyclospora cayetanensis, Toxiplasma gondii, and the Norwalk and hepatitis A viruses. Even small amounts of contamination with some of these organisms can result in foodborne illness.
Agricultural water quality will vary, particularly surface waters that may be subject to intermittent, temporary contamination, such as waste-water discharge or polluted runoff from upstream livestock operations.
*Factors to consider/take note:
- Identify the source and distribution of water used and be aware of its relative potential for
being a source of pathogens.
- Maintain wells in good working condition
- Review existing practices and conditions to identify potential sources of contamination.
- Be aware of current and historical use of land.
- Consider practices that will protect water quality.
- Consider irrigation water quality and use.
2) Anti-microbial chemicals
Anti-microbial chemicals are usually added in processing water (water used during the post-harvest handling of fruits and vegetables). The effectiveness of an anti-microbial agent depends on its chemical and physical state, treatment conditions (such as water temperature, acidity [pH], and contact time), resistance of pathogens, and the nature of the fruit or vegetable surface. Example of anti-microbial agents:
Chlorine
Commonly added to water at 50 - 200 ppm total chlorine, at a pH of 6.0 - 7.5, for post-harvest treatments of fresh produce, with a contact time of 1 - 2 minutes.
Ozone
Used to sanitize wash and flume water in packinghouse operations. Ultraviolet radiation may also be used to disinfect processing water.
Quoted from: http://www.foodsafety.gov/~dms/prodguid.html
All chemical substances used, which is in direct/indirect contact with foods must be in accordance with the local authorities (AVA – in Singapore, FDA- in USA). Anti-microbial chemical levels should also be routinely monitored and recorded to ensure that they are maintained at appropriate concentrations. Washing of vegetables & fruits (before packing) with some anti-microbial chemicals needs to be followed by a clean water rinse to remove any treatment residues.
3) Pesticides
Pesticides are use to prevent pests from growing in vegetables farms. However, pesticides also contain chemicals that can be harmful to human’s health if the amount of pesticides used is over-concentrated or vegetable surfaces are not thoroughly washed where residues of pesticides are still present. Therefore, it is important that vegetables are thoroughly washed clean before they are being packed.
Water of inadequate quality has the potential to be a direct source of contamination and a vehicle for spreading localized contamination in the field, facility, or transportation environments. Wherever water comes in contact with fresh produce such as vegetables, its quality dictates the potential for pathogen contamination. If pathogens survive on the produce, they may cause foodborne illness.
Water can be a carrier of many microorganisms including pathogenic strains of Escherichia coli, Salmonella spp., Vibrio cholerae, Shigella spp., Cryptosporidium parvum, Giardia lamblia, Cyclospora cayetanensis, Toxiplasma gondii, and the Norwalk and hepatitis A viruses. Even small amounts of contamination with some of these organisms can result in foodborne illness.
Agricultural water quality will vary, particularly surface waters that may be subject to intermittent, temporary contamination, such as waste-water discharge or polluted runoff from upstream livestock operations.
*Factors to consider/take note:
- Identify the source and distribution of water used and be aware of its relative potential for
being a source of pathogens.
- Maintain wells in good working condition
- Review existing practices and conditions to identify potential sources of contamination.
- Be aware of current and historical use of land.
- Consider practices that will protect water quality.
- Consider irrigation water quality and use.
2) Anti-microbial chemicals
Anti-microbial chemicals are usually added in processing water (water used during the post-harvest handling of fruits and vegetables). The effectiveness of an anti-microbial agent depends on its chemical and physical state, treatment conditions (such as water temperature, acidity [pH], and contact time), resistance of pathogens, and the nature of the fruit or vegetable surface. Example of anti-microbial agents:
Chlorine
Commonly added to water at 50 - 200 ppm total chlorine, at a pH of 6.0 - 7.5, for post-harvest treatments of fresh produce, with a contact time of 1 - 2 minutes.
Ozone
Used to sanitize wash and flume water in packinghouse operations. Ultraviolet radiation may also be used to disinfect processing water.
Quoted from: http://www.foodsafety.gov/~dms/prodguid.html
All chemical substances used, which is in direct/indirect contact with foods must be in accordance with the local authorities (AVA – in Singapore, FDA- in USA). Anti-microbial chemical levels should also be routinely monitored and recorded to ensure that they are maintained at appropriate concentrations. Washing of vegetables & fruits (before packing) with some anti-microbial chemicals needs to be followed by a clean water rinse to remove any treatment residues.
3) Pesticides
Pesticides are use to prevent pests from growing in vegetables farms. However, pesticides also contain chemicals that can be harmful to human’s health if the amount of pesticides used is over-concentrated or vegetable surfaces are not thoroughly washed where residues of pesticides are still present. Therefore, it is important that vegetables are thoroughly washed clean before they are being packed.
Package 1 - What are the potential hazards in fats/oil?
Fat is an important ingredient in many foods because of its functional properties. In many recipes, fat enhances the taste, aroma and texture of the food. It is also digested more slowly than protein or carbohydrates and plays an important role in satiety, providing a sense of fullness after eating.
WHAT IS RANCID OIL?
Rancid oils are a major source of destructive free radicals in our diet. Exposure to air, heat, and light cause oils to oxidize, become rancid, and form free radicals.
Saturated fats are not affected much by oxidation because they are very stable and have a high degree of resistance to oxidation. Monounsaturated fats, since they have a pair of missing hydrogen atoms are somewhat vulnerable to oxidation. Polyunsaturated oils, which are missing several pairs of hydrogen atoms, are very unstable and highly reactive to oxidation.
Signs of Deteriorated Oil
- Oil darkens with use because the oil and food molecules burn when subjected to high/prolonged heat.
- The more you use an oil, the more slowly it will pour. Its viscosity changes because of changes to the oil's molecular structure.
- Loose absorbent particles accumulate as sediment at the bottom of the storage container or are suspended in the oil.
- When smoke appears on the oils' surface before the temperature reaches 190 degrees C (375 degrees F), your oil will no longer deep-fry effectively.- If the oil has a rancid or "off" smell or if it smells like the foods you've cooked in it, it should be discarded.
Prolonging The Shelf-Life of Oil
The longer an oil is heated, the more quickly it will decompose. Avoid preheating the oil any longer than necessary. If you're cooking more than one batch of food, quickly add each new batch, unless time is needed to adjust the cooking temperature. Turn off the heat as soon as you've removed the last food batch from the oil. Cool.
Use a quality deep-fat frying thermometer, even if you're using an electric deep fryer.
Shake off loosely attached break crumbs from breaded food before adding the food to the oil. Loose crumbs and other particles scorch quickly and pollute your oil. Use a small strainer or slotted spoon to remove as many crumbs as possible.
When the oil has cooled enough that it is safe to handle, strain it through paper towels, coffee filters or cheesecloth into its original empty container or a clear glass jar. Do not mix it with unused oil.
Store the oil, tightly sealed, in a cool, dark place or in the refrigerator. The oil may cloud in the refrigerator, but it should become clear again at room temperature with no ill effects.
HYDROGENATED FATS
Hydrogenated fats is one of the fats that is least prone to oxidation, which can lead to rancidity. Hydrogenation is used to convert liquid oils to a semi-solid form for greater utility. For example, vegetable oils are often hydrogenated to produce shortenings or margarines. Hydrogenation also is used to increase the stability of a fat or oil, which is important in cooking and extending a product's shelf-life.All fats, particularly polyunsaturated fats, have a tendency to break down or oxidize when exposed to air. Oxidized fats impart an undesirable rancid flavor and odor. By adding hydrogen molecules, the fatty acids become more stable and resistant to oxidation. This is especially important for fats used in deep-fat frying.
Tips for saving frying oil:
Usually, after frying food such as chicken wings, fish, prawns etc, people used to store the leftover frying oil again to re-use for another time. Frying oil CAN be saved for further frying but it is recommended to do the following:
- Let the oil cool.
- Using a fine strainer, remove any large pieces of debris.
- Using cheese cloth, filter again to remove fine particles of debris.
- Pour into a covered container and refrigerate to prevent rancidity.
-Frying oil can be used 3-4 times before discarding. But refrain from using more than 4 times as rancidity might have occured.
WHAT IS RANCID OIL?
Rancid oils are a major source of destructive free radicals in our diet. Exposure to air, heat, and light cause oils to oxidize, become rancid, and form free radicals.
Saturated fats are not affected much by oxidation because they are very stable and have a high degree of resistance to oxidation. Monounsaturated fats, since they have a pair of missing hydrogen atoms are somewhat vulnerable to oxidation. Polyunsaturated oils, which are missing several pairs of hydrogen atoms, are very unstable and highly reactive to oxidation.
Signs of Deteriorated Oil
- Oil darkens with use because the oil and food molecules burn when subjected to high/prolonged heat.
- The more you use an oil, the more slowly it will pour. Its viscosity changes because of changes to the oil's molecular structure.
- Loose absorbent particles accumulate as sediment at the bottom of the storage container or are suspended in the oil.
- When smoke appears on the oils' surface before the temperature reaches 190 degrees C (375 degrees F), your oil will no longer deep-fry effectively.- If the oil has a rancid or "off" smell or if it smells like the foods you've cooked in it, it should be discarded.
Prolonging The Shelf-Life of Oil
The longer an oil is heated, the more quickly it will decompose. Avoid preheating the oil any longer than necessary. If you're cooking more than one batch of food, quickly add each new batch, unless time is needed to adjust the cooking temperature. Turn off the heat as soon as you've removed the last food batch from the oil. Cool.
Use a quality deep-fat frying thermometer, even if you're using an electric deep fryer.
Shake off loosely attached break crumbs from breaded food before adding the food to the oil. Loose crumbs and other particles scorch quickly and pollute your oil. Use a small strainer or slotted spoon to remove as many crumbs as possible.
When the oil has cooled enough that it is safe to handle, strain it through paper towels, coffee filters or cheesecloth into its original empty container or a clear glass jar. Do not mix it with unused oil.
Store the oil, tightly sealed, in a cool, dark place or in the refrigerator. The oil may cloud in the refrigerator, but it should become clear again at room temperature with no ill effects.
HYDROGENATED FATS
Hydrogenated fats is one of the fats that is least prone to oxidation, which can lead to rancidity. Hydrogenation is used to convert liquid oils to a semi-solid form for greater utility. For example, vegetable oils are often hydrogenated to produce shortenings or margarines. Hydrogenation also is used to increase the stability of a fat or oil, which is important in cooking and extending a product's shelf-life.All fats, particularly polyunsaturated fats, have a tendency to break down or oxidize when exposed to air. Oxidized fats impart an undesirable rancid flavor and odor. By adding hydrogen molecules, the fatty acids become more stable and resistant to oxidation. This is especially important for fats used in deep-fat frying.
Tips for saving frying oil:
Usually, after frying food such as chicken wings, fish, prawns etc, people used to store the leftover frying oil again to re-use for another time. Frying oil CAN be saved for further frying but it is recommended to do the following:
- Let the oil cool.
- Using a fine strainer, remove any large pieces of debris.
- Using cheese cloth, filter again to remove fine particles of debris.
- Pour into a covered container and refrigerate to prevent rancidity.
-Frying oil can be used 3-4 times before discarding. But refrain from using more than 4 times as rancidity might have occured.
Subscribe to:
Posts (Atom)