Page 63 - Zbornik_Konf_2019

https://doi.org/10.15414/2019.9788055220703

4 International Scientific Conference Abstracts Book
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EFFECT OF CHANGES IN POLYUNSATURATED FATTY ACIDS ON THE QUALITY
OF WALNUT OIL
Pavel Tatarov , Elisaveta Sandulachi , Raisa Ivanova 2
1
1
1 Technical University of Moldova, Chisinau, Republic of Moldova;
E-mail.: p_tatarov@yahoo.com
2 Institute of Genetics, Physiology and Plant Protection, Chisinau, Republic of Moldova

The walnut oil obtained by the cold pressing of Juglans regia L. kernels is a food of high
quality because of dominated content of polyunsaturated essential fatty acids: linolenic,
linoleic, docosahexaenoic, eicosapentaenoic (ω-6, ω-3). The quality and shelf life of walnut oil
depend on several factors, among which the physicochemical changes in polyunsaturated
fatty acids play an important role. The processes of polyunsaturated fatty acids auto-oxidation
under the action of enzymes, atmospheric oxygen and light have a strong influence on the
quality decreasing of walnut oil.
The purpose of this investigation was to study the dynamics and kinetics of the
polyunsaturated fatty acid oxidation processes; and analysis of the formation of primary and
secondary oxidation compounds. Experimental researches were carried out during 2014–
2018 years using walnuts of Cogalniceanu variety, harvested in Calarasi area (Republic of
Moldova). Walnut oil was obtained by cold pressing of the walnut kernels and oil yields were
determined. The analysis of walnut lipids, reactions kinetic of polyunsaturated fatty acids
oxidation, and accumulation of primary and secondary oxidation compounds was studied.
Changes in physicochemical and sensory quality of the walnut oil were determined. Freshly
obtained walnut oil had the followed indexes of quality: acidity – 0.38±0.07mg KOH/g; iodine
value – 148.0±0.6g per100 g of lipids; saponification index – 188.0±1.3mg KOH/g; water
content – 0.1 %. The content of polyunsaturated fatty acids (ω-6, ω-3) in walnut oil ranged
from 8.0 to 13.0 % of total fatty acids. During storage, the walnut oil changed permanently
with losses of nutritional quality. The reaction of hydroperoxides formation as the primary
oxidation compounds had zero order, but the rate of reaction was variable. Take into account
that the molecular mechanism of lipid oxidation-reduction reactions is complex; the kinetic
model of the lipid oxidation process was developed.
During storage, the variability of constant (K, days ) of reaction rate for hydroperoxides
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formation was evaluated depending on temperature and storage duration. At the initial stage
of storage, an increase in storage temperature from 3 to 60 °C led to a rise in reaction rate
constant by 17.8–35.0 times (from 0.052 to 1.821 days ). At the second stage, the process of
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hydroperoxides decomposition began, but the rate of this process was 2.15 times less than the
reaction of their formation. After 180 days of storage, the concentrations of hydroperoxides
stabilized at values of 1.7–3.0µmol/kg. It was shown that the changes in the acidity of walnut
oil were significantly slower and ranged from 0.38 to 0.53mg KOH/g.

Keywords: walnut oil, polyunsaturated fatty acid, hydroperoxides, acidity.
Acknowledgments
The authors R. Ivanova and P. Tatarov express their deepest gratitude, the International Visegrad
Scholarship Fund (51910230) and the Erasmus plus Programme provided the opportunity to conduct
research and teach in Nitra.

4 International Scientific Conference Agrobiodiversity Nutrition, Health and Quality of Human and Bees Life |63
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September 11–13, 2019