Quality evaluation of cold-pressed edible oils from Macedonia
The chemical composition and quality of eight pure cold-pressed oils and two blend oils from Macedonia were examined in this work. The highest level of oleic acid was determined in apricot kernel oil and rapeseed oil with abundance of 70.9 and 59.2 %, respectively. The highest level of polyunsaturated fatty acids had flaxseed and hemp seed oil with abundance of α-linolenic acid of 55.1% for flaxseed oil and linoleic acid of 57.4% for hemp seed oil. Apricot kernel oil and roasted sesame seed oil had the highest oxidative stability with induction times of 7.6 and 10.9 h. Apricot oil, hemp seed oil and flaxseed oil had the highest level of total vitamin-E-active compounds with 58.8 mg, 58.1 mg and 69.7 mg per 100 g of oil with predomination of γ-tocopherol. The highest peroxide number was detected in blend oils (oil 2 and oil 8) with values over 10 meq O2/kg of oil. The highest FFA was detected in rapeseed oil (1.57 %). Roasted and unroasted sesame seed oils had relatively high specific extinction (K232 values 3.55 and 3.33 respectively). However, the highest UV extinction had a blend of pumpkin seed oil and sunflower oil with a value of 3.84. Practical applications: The results of this study can be applied for determination of the most important major and minor components responsible for quality evaluation of cold-pressed oils. Statistical results indicated strong relationship between the level of monounsaturated fatty acids in the oil and their oxidative stability. The level of tocopherols and other vitamin-E-related compounds was in strong relationship with the antioxidant activity of the oils measured by DPPH method. Phytosterols, as minor compounds present in the oils, did not contribute significantly to the total antioxidant potential of the oils but, their levels in particular oils, together with fatty acids, can be useful and reliable markers for the purity of the oils and determination of the composition of blends.