www.BioTopics.co.uk
Site author Richard Steane
The BioTopics website gives access to interactive resource material, developed to support the learning and teaching of Biology at a variety of levels.

Functional foods

Functional foods are more than fuel for our bodies’ processes, and raw materials to be built up for use in growth and repair.
They contain extra ingredients which are intended to promote good health.

Prebiotic foods

These contain substances which are used by certain “useful” bacteria which exist naturally in the gut and when they are encouraged to grow they suppress the growth of other less useful bacteria.
Prebiotics are generally carbohydrates – oligosaccharides - often composed of unusual sugars linked by bonds which human digestive enzymes cannot usually break – so the beneficial bacteria have a food source that is selective and puts them at an advantage over other (non beneficial?) bacteria.
This is a picture of a molecule of nystose - a fructo-oligosaccharide (FOS) which is composed of 3 fructose units linked by β 2,1 bonds to a glucose unit. It cannot be broken down by human enzymes, but which acts as food for beneficial bacteria such as Lactobacillus acidophilus and Bifidobacteria in the colon.

Certain food sources appear to be good sources of these compounds, but an industry has sprung up to provide these substances as supplements, and food products which contain them. Unrefined cereals like oats, wheat, barley (and similar cereal products), and certain vegetables – soybeans, onions and garlic – contain some of these compounds, perhaps at insignificant levels.
Then of course manufacturers need to market these products and not all the claims that are made are necessarily fully supported by scientific research.

Probiotic foods

These contain living bacteria, which may affect the balance of bacteria in the human gut (its microflora). For instance yoghurt contains lactic acid bacteria Lactobacillus spp and there are a variety of different strains which are subject to commercial claims.
Lactobacillus acidophilus Bifidobacterium spp

These are produced by fermentation.

Plant stanol esters

e.g Benecol®, Flora Pro-activ®

Using these compounds in diet, e.g. as margarine/spreads or added to yoghurts or milk drinks, is said to reduce the level of low-density lipoprotein (LDL) cholesterol in blood – which may build up and cause heart attacks, strokes, and other circulatory problems etc. The starting material is sterols from plants, which are very similar in structure to cholesterol, which are then converted to the stanol form, and these are reacted with fatty acids to produce stanol esters.
The recommended consumption of 2-2.5 grams of plant sterol per day is said to be optimal for lowering cholesterol.
It is said that this may provide a reduction in LDL cholesterol of about 10%. The compound itself passes through the gut without entering the the blood stream or lymph. Its presence, however, reduces both the amount of cholesterol the body absorbs from food and the reabsorption of the cholesterol component of bile.

sterol&stanol structures
sitostanyl oleate.
These images (from the Benecol site) show simplified versions of the molecular structure of cholesterol, and the plant sterol sitosterol and its derivative sitostanol. Most of the hydrogen atoms are not displayed, and the position of carbon atoms is at the end of each line section.

You can also see 3-dimensional structures of these molecules on this website.

What difference can you see between the cholesterol molecule and the sitosterol molecule?
> extra branch on chain on the top section - actually C2H5-

What difference can you see between the sitosterol molecule and the sitostanol molecule?
> No double bond in one of the rings (i.e. it is fully saturated).

What difference can you see between the sitostanol molecule and the sitostanyl oleate molecule?
> Long chain (oleic acid residue) attached to OH at bottom ring section.

How many extra carbons have been added?
>18 (17 in the chain, and one with =O group)


Why does the label on a yoghurt state "Plant sterol esters (1%)*", and underneath "* equivalent to plant sterols (0.6%)" ?
> Plant sterol ester is 60% sterol and 40% fatty acid.

Web references

Stanol ester From Wikipedia, the free encyclopedia
Properties of Plant Stanol Esters from Benecol

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