EVALUATING ANTIOXIDANT POWER OF NETTLE

1
EVALUATING ANTIOXIDANT POWER OF NETTLE (Urtica
dioica) IN OLIVE OIL DURING STORAGE ESRA
ÇAPANOGLU, DILARA NILÜFER AND DILEK
BOYACIOGLU E-mail capanogl_at_itu.edu.tr Istanbul
Technical University, Food Engineering
Department, Istanbul, Turkey. ISF 26th World
Congress and Exhibition, 25-28 September, Prague,
Czech Republic.
Natural antioxidants with the advantage of
having positive effects on health, such as
reducing the risk of chronic diseases besides
their non-toxic characteristics, became an
important concern for the researchers. In this
study, the antioxidative effects of nettle
(Urticae herba) in a model system was
investigated. As a model system olive oil was
selected. Dried and ground nettle (25 g/500 g
olive oil) was added into olive oil and stored in
glass bottles at two different temperatures (25C
and 50 C) for 6 weeks. The control sample and
synthetic antioxidant involving olive oil was
prepared with addition of Butylated Hydroxy
Toluene, BHT, (0.02) and stored under same
conditions. Peroxide values, free fatty acid
(FFA) contents, and Rancimat analysis were
performed to follow the rate of oxidation. Also,
total phenolics by using Folin-Ciocalteu method
and antioxidant assay (2,2 diphenyl-1-picryl-hydra
zyl (DPPH) radical scavenging activity analysis)
were carried out in order to evaluate the
antioxidative power of the sample. As a result,
the effect of nettle on olive oil is quite
questionable and more data is required to
understand its action mechanism as a natural
antioxidant during storage of olive oil.
RESULTS
ABSTRACT
Figure 1. Results of Peroxide Value Analysis
INTRODUCTION Recently, various phytochemicals and
theirs effects on health, especially the
supression of active oxygen species by natural
antioxdants from teas, spices and herbs, have
been intensively studied. However, almost all
these studies were based on hydrophilic models
and included only phenolic compounds or
ascorbate. Aqueous infusions of Mediterranean
herbs including Urtica dioica, exhibit
antioxidant activity towards iron-promoted
oxidation of phospholipids, linoleic acid, and
deoxyribose. Urtica dioica herbs are used to
treat stomachache in Turkish folk medicine. In
addition, this herb is used to treat rhematic
pain and for colds and cough and is used against
liver insufficiency (Gülçin, et.al., 2004 Toldy,
et.al., 2005). Olive oil is a product widely
used throughout the ages in the Mediterranean
cuisine and is highly appreciated for its
delicious taste and aroma, as well as for its
nutritional properties (Kiritsakis, 1990
Moldao-Martins, 2004). Aromatic plants have also
been used since ancient times, in food
flavouring, pharmaceutical, cosmetic and
perfumery due to the presence of essential oils.
Several biological activities, including
antimicrobial and antioxidant properties are
usually assigned to these oils or essential oils
as a flavouring agent instead of the whole plant.
There have been many studies on investigating the
antioxidant properties of such aromatic plants
including thyme, basil, rosemary, chamomile,
lavender and cinnamon (Özcan and Akgül, 1995
Pokorny et al., 2001 Lee and Shibamoto, 2002
Tanabe et al., 2002 Moldao-Martins, 2004).
Flavoured olive oils are usually prepared by
macerating the aromatic plants in the oil. Market
studies have demonstrated that consumers are
interested in this kind of product
(Moldao-Martins, 2004). The objective of the
study was to investigate the antioxidative
effects of intact nettle in an olive oil model
system.
Figure 2. Results of Free Fatty Acid Analysis
Figure 3. Results of Rancimat Analysis

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REFERENCES
CONCLUSION

• The peroxide values were in a fluctuating manner
  from week to week for nettle-involving olive oil
  sample for both storage temperatures.
• FFA values were in increasing trend and highest
  values were obtained for the nettle-containing
  samples for all weeks.
• However, from rancimat analysis it was seen that
  induction period was extended with respect to
  control samples, by the addition of nettle. The
  protection factor of nettle was found to be as
  high as BHT at 25C, however its efficiency
  decreases as the temperature increases.
• The total phenolic content of the nettle was
  found to be 22.63 mg GAE/g sample by using
  Folin-Ciocalteu method. Scavenging activities of
  the nettle at 1,666 mg/ml concentration on DPPH
  radical was 52.57, which shows that nettle has
  an antioxidative power.
• Owing to variations in the solubility and
  antioxidative mechanism of phytonutrients, it is
  necessary to perform antioxidant assays in both
  hydrophilic and lipophilic models in which the
  antioxidative effects of different antioxidants
  can be measured.
• Previous studies show that nettle leaves have an
  antioxidant, antiinflammatory, immune-suppresive,
  and anti-rheumatoid effect. The antioxidative
  effect of nettle was also observed during this
  study. However, the effect of nettle in olive oil
  model system is quite questionable and more data
  is required to understand its action mechanism as
  a natural antioxidant during storage.
• Future studies are necessary to evaluate the
  application of these herbs in the food industry.
  Also, synergistic effects while using two or more
  herbs together, should be investigated. It is
  noteworthy that several herbs and plants can take
  place of synthetic antioxidants in the future.

MATERIALS METHODS

• Total phenolic content
• (Folin-Ciocalteu method)
• Antioxidant activity
• (DPPH method)

Dry ground nettle (25 g/500 g olive oil)
Free Fatty Acid Analysis
Flavoured olive oil
Stored at 25C and 50 C for 8 weeks