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Active-Italia: Long-Term Preservation of Total Phenolic Content and Antioxidant Activity in Extra Virgin Olive Oil: A Physico-biochemical Approach

Long-Term Preservation of Total Phenolic Content and Antioxidant Activity in Extra Virgin Olive Oil: A Physico-biochemical Approach

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The preservation of Extra Virgin Olive Oil (EVOO) quality is of uttermost economic and health importance, as EVOO is prone to oxidation both during production and storage. In particular, the storage conditions of EVOO are very important for avoiding or reducing the negative effects by autoxidation on the qualitative characteristics of the packaged product.

The level of oxidation degradation is greatly affected by the EVOO storage conditions; temperature; exposure to light and oxygen, mainly singlet oxygen O2, free fatty acids; chemical composition; saturated to unsaturated fatty ratio; total phenol content (TPC), etc.

Moreover, the existence of unsaturated fatty acids in oils and fats is the intrinsic reason for lipids oxidation. As reported by Di Giovacchino the TPC of EVOO decreases during storage because its oxidation protects the oils from autoxidation, especially where the initial content of total phenols is higher than 150 mg/L.

This phenolic antioxidant mechanism has been confirmed. According to Bendini the phenols in EVOO are very sensitive to interfacial physicochemical reactions (e.g., at air-oil or oilwater interfaces), which significantly affect their relative activities in different lipidic systems. Moreover, the EVOO remains in good state for a long time when stored in a fully filled bottle at room temperature (commercial conditions 20-25°C), where tyrosol derivatives are more stable than LH-ROH compounds. Moreover, the storage of EVOO is sensitive to temperature changes. Previous research showed that the degradation of secoiridoid phenolic during storage displayed pseudo-firstorder kinetics and depended on the initial phenolic content. In particular, the initial degradation rate was similar at 5 and 15°C but increased considerably at 25°C and was even faster at 50°C. Within this context, as reported by Krichene the increase in the content of simple phenolics, the decrease of their secoiridoid derivatives, or the ratio of simple to secoiridoid phenolics could be used as indices of the oxidative and hydrolytic degradation of phenolics.  Additionally, when EVOOs were stored in the light had significantly lower tocopherol, carotenoid and chlorophyll content, while EVOO colour values changed from green to yellow versus in comparison to a 12-month storage in the dark. As reported by Caponio oils stored in the dark contained mainly  primary  oxidation  products,  whilst  oils  stored  in  the  light  contained  secondary  oxidation  products  as  confirmed  by  the  K270,  K232 and ΔKUV-absorptionvalues.

In another treatment approach,  N2  has  been  utilized  as  a  conditioner  gas to study the possibility of improving the stability of EVOO. Studies showed that the presence of N2 in the bottle headspace can increase the EVOO shelf-life,  preserving  its  organoleptic  and  functional  features;  whilst another study showed that free radical production was markedly reduced  by  N2 bubbling.

Moreover, the effects of a storage up to 18 months after bottling of  Tuscan  EVOOs  filtered  and  frozen  at  −23°C in  comparison  to  same  samples  maintained  at  room  temperature  in  the  dark,  were  evaluated  by  monitoring  the  evolution  of  their  phenolic  composition and aromatic profile. The results showed that an increase of tyrosol, hydroxytyrosol (LH-ROH) and % of hydrolysis was observed in EVOOs stored at room temperatures starting from 3-months storage and increased thereafter,  whilst  all  frozen  EVOOs  showed  negligible  differences in aromatic profile up to a 12-month storage. In addition, the filtering step allows the suspended particles to be separated, thus avoiding the formation of deposits and  mucilage.  This significantly improves the preservation of the product.

In fact, if the storage temperature decreases, for instance to -6°C, the oil will change its physical state. That might imply a loss of the total availability by the antioxidant compounds, reducing its natural protection against lipid oxidation. In conclusion, the effect of storage temperature, especially below 0°C, requires much more attention from a technological  point  of  view  because,  in  some  way,  it  appears  to  affect  the  oil  shelf  life.

Thus, controlled freezing  provides  a  promising method for longer life than any other preservation technique used  for  olive  oil.  At present, this method  has  to  be  optimized  and  parameterised with regard to the preservation of phenols in olive oil and mostly in the higher quality grades, such as EVOO. This study  aims  to  evaluate  a  novel  methodology  for  the  stabilisation  of  TPC  in  EVOO.  The  goal  is  to  determine  the  optimal  cost-effective  freezing-temperature zone where the phenolic content will be preserved. The proposed research is investigated by studying four Quality Indexes (QIs)of olive oil  under  controlled  O2  and  light  at  various  storage  temperatures  (25,  4,  -20  and  -80°C).  These Qis are:  free  acidity,  as  %  of oleic acid (1st-QI); UV-absorption values; K272, K232 and ΔK (2nd-QI); TPC  as  gallic  acid  equivalence  (GAE)  (3rd-QI);  and  lipid  peroxidation,  as  free  malondialdehyde  (MDA)  (4th-QI).  These  QIs  are  monitored  by  analytical  and  spectroscopic  methodologies.  Expected  outcomes  of  this  study’s  aims  are:  development  and  evaluation  of  a  methodology  (freeze  controlled  treatment)  for  the  long-term  preservation  of  EVOO  quality,  understanding the physicochemical mechanism and factors determining  EVOO  quality and ready-to-use  technology  for  the  local and international market.

Source of the Article

By E. Giannakopoulos, Georgios Salachas, D. Zisimopoulos, S. Barla, Electra Kalaitzopoulou, Polyxeni Papadea, Marianna Skipitari, C. Georgiou

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