Term
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Definition
| The term dietary fibre is loosely used to include any unavailable polysaccharide and lignin, which is not a carbohydrate. |
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Term
| The 2 sources of dietary fibre |
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Definition
- Unavailable polysaccharides that are the storage forms of some seeds that do not use starch.
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Term
| Describe the development of the cell plate |
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Definition
At cell division growing point they become separated by a newly sysnthesised partition, the cell plate. Each cell deposits material on the shared portion and it is now called the middle lamella. It remains as an intracellular cement. The material deposited on the middle lamella forms the primary cell wall. |
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Term
| The composition of the middle lamella (the artist formerly known as the cell plate) |
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Definition
It consists mostly of pectins ( the simplest of which is polygalacturonic acid.) Many of the acid groups are esterified with methyl groups. Others are free to bind calcium which links 2 pectin molecules together as a gel. |
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Term
| What provides the primary cell wall of dietary fibre? |
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Definition
| The material deposited on the middle lamella forms the primary cell wall which has to be able to stretch as the cell grows in length. |
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Term
| What does the cell wall consist of? |
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Definition
| The cell wall consists of pectin substances with cellulose, hemicellulose and some glycoproteins. |
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Term
| What is cellulose composed of? |
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Definition
| Cellulose is made up of beta-linked glucose units which are linked by hydrogen bonds lengthways in section that are highly crystalline. |
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Term
List the components of the: Primary cell wall Middle Lamella Seconday cell wall |
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Definition
Primary cell wall: Pectins, cellulose, hemicellulose Middle lamella: Pectins, polygalacturonic acid Secondary cell wall: Lignin, cellulose, hemicellulose. |
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Term
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Definition
Hemicellulose is a term for a very complex mixture of polysaccharides, frequently containing 5-carbon sugars They are linked to cellulose by hydrogen bonds in the plant cell wall. |
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Term
| How do you separate hemicellulose and cellulose? |
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Definition
| Hemicellulose is more easily dissolved by acid than cellulose this is the main method of separating them. |
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Term
| Describe the oldest method of estimating fibre |
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Definition
It involved treating food with hot strong acid followed by alkali and the remainder was called crude fibre. Crude fibre includes about 60% of the cellulose, 20% of the hemicellulose and 10-40% of the lignin. It estimates only a small and variable fraction of dietary fibre. |
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Term
| Describe analysis of dietary fibre using detergents. |
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Definition
Fibre may be analysed using detergents that dissolve other components of food, leaving the fibre. Neutral detergent residue gives a rough estimate of cell wall material, excluding only pectin. Acid detergent residue estimates cellulose and lignin since the hemicellose is dissolved by acid. |
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Term
| Describe the pros and cons of Neutral Detergend analysis of food. |
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Definition
Neutral detergent residue gives a rough estimate of cell wall material, excluding only pectin, which has to be analysed separately becasue it is soluble. NDR figures may overestimate fibre if there is some starch that resists dissolution so amylase is usually employed. In fruits and vegetables NDR underestimates because some soluble fibre is not included. |
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Term
| Give details of Acid Detergent analysis of foods and its pros and cons. |
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Definition
| Acid Detergent Residue estimates cellulose and lignin since the hemicellulose is dissolved by the acid. Lignin is then oxidised by potassium permanganate so that the remainder is cellulose. |
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Term
| Describe analysis of food with enzymes to estimate dietary fibre. |
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Definition
It is possible to treat foods with the enzymes found in the gut and estimate the remainder as fibre. This metho also suffers from the problem of incomplete starch digestion in some samples and does not fractionate the sample into different types of fibre. |
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Term
| Name the most indepth method of analysing food to estimate dietary fibre. |
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Definition
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Term
| Describe the southgate method which analyses all the sugar derived from each fraction of fibre separately. |
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Definition
| The method involves a step-by-step extraction and separation of fibre into cellulose, water soluble non-cellulosic polysaccharides, water insoluble non-cellulosic polysaccharides and lignen. |
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Term
| Provide a step-by-step flow diagram of the Southgate method |
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Definition
100mg sample* Add 10ml enzyme solution in buffer (pH6.9); pancreatic alph-amylase (500U); 0.1M tris-maleate buffer solution (calcium chloride 4mM) | Mix 16 hours @ 37˚c then add 40ml ethanol | Leave for 1 hour, then centrifuge | Wash residue twice with 80% EtOH, dry at 60˚c. Add 1.56ml H20 then add 1.5ml 4M KOH | Mix 0.5 hours at room temp. Add 12ml H2O | To 1.5ml dispersion, add approximately 0.65ml 2M acetic acid (to obtain pH 4.5) and 0.1ml amyloglucosidase (20U/0.1ml 0.1M Na acetate buffer pH 4.5) Shake 90 min at 65˚c | Determine glucose using glucose oxidase assay. The result is resistant starch |
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Term
| Gravimetric AOAC method for analysing food and estimating fibre is similar to which other method? |
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Definition
| The southgate method -Englyst |
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Term
| What is the average intake of fibre/day using the southgate method of analysis? |
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Definition
| 20g fibre/day but ranging widely from one individual to another. |
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Term
| What type of fibre make up the main component of the average 20g of dietary fibre? |
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Definition
Cereal fibre make us over a third. THis rose to nearly 2/3 during the 2nd world war. |
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Term
| What is the average amount of non-polysaccharide fibre? |
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Definition
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Term
| Give the composition in % of the sources of Britain's 12g daily non-starch polysaccharide fibre. |
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Definition
Vegetables - 48% Fruit - 10% Cereals - 38% |
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