132 Handbook of herbs and spices
to a reactive oxygen or reactive nitrogen species then the oxidant radical which is
formed in the reaction may then activate the gene expression of the phase 2 enzymes
(Moskaug et al., 2004).
8.4 Measurement of antioxidants.........................................................
A number of methods have been developed to measure the antioxidant concentration
or capacity in dietary plants including herbs (Halvorsen et al., 2002). These are the
6-hydroxy-2,5,7,8-teramethylchroman-2-carboylic acid (Trolox) equivalent antioxidant
capacity (TEAC) assay of Miller and Rice Evans (1996), the oxygen radical absorbance
capacity (ORAC) assay of Delange and Glazer (1989) and the ferric reducing ability
of plasma (FRAP) assay of Benzie and Strain (1996). The TEAC and the ORAC
assays are based on the antioxidants’ ability to react with free radicals while the
FRAP assay measures the reduction of Fe+++ (ferric iron) to Fe++ (ferrous iron). The
FRAP assay is the least selective and is therefore a good method for estimating the
total antioxidant capacity of herbs in both water and fat soluble extracts. Using this
method particularly it has been possible to draw up a table of anti-oxidant values for
many types of foods including herbs and spices. Values of total anti-oxidant values
in foods as determined by the ferric-reducing ability of plasma assay (mmol/100g)
for cinnamon was 98.4, rosemary 66.9 and oregano 45.0 compared to the highest
berries, dog rose 39.5 and blueberry 5.1, the highest nut, walnut 21.0, the highest
fruit, pomegranate 11.3, the highest vegetable, kale 2.3 and fruit juice, blue grape 1.6
show that the herbs and spices are by far the richest source of anti-oxidants (Blomhoff,
2005).
Supplementing the bodies’ defence mechanism by taking antioxidant supplements
or eating a diet rich in anti-oxidants is regarded as a means of reducing the risk of
cardiovascular disease. Support is sought for this approach by experimental modelling
using organic molecules, cells and animals, epidemiological studies and finally by
randomised intervention trials on human volunteers.
8.4.1 Model systems
Model systems are a direct method of establishing the anti-oxidant potential of herbs
and spices. However, the experiments may only indicate an anti-oxidant effect, rather
than one specifically related to cardiovascular disease. The anti-oxidant properties of
seven dessert spices (anise, cinnamon, ginger, liquorice, mint, nutmeg, and vanilla)
were compared with those of the common food anti-oxidants butylated hydroxyanisole
(BHA) and butylated hydroxytoluene (BHT) and propyl gallate. Mint and cinnamon
exhibited a higher percentage of inhibition of oxidation than the other spices and
the food anti-oxidants analysed, as tested by the lipid peroxidation assay (Murcia
et al., 2004).
Many cellular lipids and especially polyunsaturated fatty acids are vulnerable to
attack by reactive oxygen species resulting in the formation of lipid peroxidases. The
peroxidised lipids can cause cellular damage such as cross-linking of proteins and
DNA. Also oxidised low-density lipoproteins can contribute to the formation of
atheroslerotic plaques. Water and alcohol extracts of ginger have been shown to
possess anti-oxidant activity on fats and oils and prevent lipid oxidation (Hirahara,
1974). In addition zingerone functioned as an effective scavenger of superoxide