472 Handbook of herbs and spices
Herbs, regardless of the purpose they serve, are used fresh or dried. Enzymatic
processes during drying fresh plant tissues may lead to significant changes in the
composition of phytochemicals. The evaluation of antioxidant properties of the raw
material allows the determination of its suitability as high-quality food beneficial for
human health and therefore is of considerable importance. Capecka et al. (2004) has
presented the results of two assays of antioxidant capability and the content of total
phenolics, ascorbic acid, and carotenoids in the fresh and air-dried herbs of peppermint.
The highest antioxidant ability, expressed as inhibition of LA peroxidation (TAA),
was found for extracts from both fresh and dried oregano. The TAA value for peppermint
and lemon balm was significantly lower. In the case of these two species, the process
of drying decreased their total antioxidant activity. The ability of scavenging DPPH
- free radical measured after five minutes was very high in the extracts from all the
tested herbs, exceeding 90%. Comparison of RSA measurements after one and five
minutes allowed estimation of the rate of DPPH neutralization. In the case of peppermint
and lemon balm extracts, obtained both from fresh and dried plant material, this
parameter reached its maximum level after one minute. The content of total soluble
phenolics was very high (2600 mg GA 100 g–1 f.m.) in dried peppermint. Drying
resulted in a considerable increase of total phenolics in the case of oregano and
peppermint. A very important compound in herbs of Lamiaceae family is rosmarinic
acid, showing a high scavenging DPPH potential. The rosmarinic acid content in
peppermint was about 30,000 ppm.
To find the most suitable antioxidant for the stabilization of sunflower oil, the
kinetics of peroxide accumulation during oxidation of sunflower oil at 100 ∞C in the
presence of different concentrations of hexane, ethyl acetate and ethanol extracts of
six herbs including M. piperita was studied by Marinova and Yanishlieva (1997). The
strongest action in retarding the autoxidation process was exhibited by the ethanol
extracts from Saturejae hortensis, followed by the ethanol extracts from M. piperita
and Melissa officinalis. The stabilization factor F for the ethanol extracts (0.1–0.5%)
from Saturejae hortensis was 1.8–2.3, which is higher than F for 0.02% butylated
hydroxytoluene (BHT, F = 1.2).
The effect of different concentrations (0–1.2% v/v) of peppermint oil on the growth
and survival of Salmonella enteritidis and Staphylococcus aureus was studied in
nutrient broth by Tassou et al. (2000). The addition of mint essential oil reduced the
total viable counts of S. aureus about 6–7 logs while that of S. enteritidis only about
3 logs. The percentage of glucose utilization in the growth medium of both pathogens,
was reduced drastically with the addition of essential oil and as a consequence, the
assimilation or formation of different compounds, such as lactate, formate and acetate
in the growth medium was also affected.
Despite the beneficial effects of M. piperita in digestion, we should also be aware
of the toxic effects when the herb is not used in the recommended fashion or at the
recommended dose. To justify the effects of M. piperita herbal teas on plasma total
testosterone, luteinizing hormone, and follicle-stimulating hormone levels and testicular
histologic features, Akdogan et al. (2004) performed a study an its adverse effects on
the male reproductive function and found that the follicle-stimulating hormone and
luteinizing hormone levels increased and total testosterone levels decreased in the
experimental groups compared with the control group; and the differences were
statistically significant.
Whole plants of peppermint after etheric oil distillation were tested for in situ
degradability and in vitro gas production (Djouvinov et al., 1997). Digestibility of