Effect of storage conditions on virgin olive oil quality

Abstract

Virgin olive oil (VOO) quality depends on many factors, including duration of storage of the fruits before processing, olive oil color, and storage conditions. We characterized here a Souri virgin olive oil cultivar and evaluated some chemical and physical characteristics during 3 years in different storage conditions. Samples of VOO were collected from the first cold pressing of olives and stored in different storage containers: polyethylene, glass, and stainless steel. Samples (100 ml) were then subjected to colorimetric and chemical measurements. VOO stored in polyethylene containers for 3 years showed higher increases in acidity (2.43%) compared to 1.36 and 1.64% found in oil stored in glass bottle and stainless containers, respectively. VOO color represented by O.D. 450-600 nm, was diminished significantly in polyethylene containers (0.67) as compared to O.D. (1.41 and 1.72) in stainless steel and glass containers, respectively, during the storage period. The majority of volatile compounds detected were acids, alcohols, and aldehydes. The concentrations of hexanal, hexanol, E -2-hexanal, and E -2-hexen-l-ol decreased significantly after 12 months of storage in polyethylene containers as compared to fresh oil. These data led to the conclusion that color and acidity could be used as a marker for VOO quality and freshness. An unexpected volatile compound (styrene 2.4%) was detected only in olive oil samples stored in polyethylene containers. Styrene is an oily organic compound, widely used to make plastics and rubber, and considered to be harmful to human health. Therefore, VOO is not recommended to be stored in polyethylene containers.