Introduction: The content of polar compounds (PC) and polymeric triglycerides build up in fried and recycled/reused oils and therefore, these undesirable components are often used as markers of deterioration in edible oil quality. Expert and authoritative agencies have recommended an upper limit of 25% for PC in fried/reused edible oils; beyond this level the oil is considered unsuitable for human consumption. The safety of recycled or repeatedly-heated oils is still very much a concern of both the health authorities and the general public.
Objective: The present study evaluates the safety of long-tern consumption of heated vegetable oils containing 25% of PC on growth, effect on major body organs and reproduction outcome, using the Sprague-Dawley rat model.
Methods: Refined, bleached and deodorised palm olein (PO) and partially hydrogenated soybean oil (HSBO) were repeatedly heated for 5 hours daily with no topping-up at Isoac until a polar compound (PC) content of25% was attained. Refined soybean oil was similarly heated up to 50% PC and used in the positive control diet. All five experimental oils, namely unheated PO (No PC), heated PO (25% PC), unheated HSBO (No PC), heated HSBO (25% PC), and positive control oil (50% PC) were separately incorporated at 30% energy (15% w/w) as the sole dietary fat into nutritionally-adequate purified diets. Each experimental diet was provided ad libitum to a different dietary group comprising 14 male and 20 female Swiss albino rats. After 13 weeks (90 days), 10 males were selected from each group and each male was paired with two females from the same dietary group for the reproductive study. After 4 weeks into the reproductive study (total of 17 weeks on the experimental diets), all 10 males in each group were sacrificed and the usual toxicity tests consisting of blood cell type counts, liver and kidney function tests, and examination (organ-to-body weight ratios and histology) of the liver, kidney, heart and spleen were performed.
Results: The heated PO and HSBO diets were well-tolerated by the animals. However, these heated test oils inhibited growth marginally (p>0.05), enlarged the liver, kidney and heart, and markedly raised serum alkaline phosphatase (liver function test) compared to the unheated oils (p