Effect of frying oil quality and TBHQ on the shelf-life of potato crisps

Three different systems were used for the evaluation of the effect of frying oil quality and tertiarybutyl hydroquinone (TBHQ) on the shelf-life of fried potato crisps. Batches of potato slices were fried for 4 min at 30 min intervals over a period of 5 h day^?1 for eight consecutive days in refined, bleached and deodorised palm olein (RBD olein) without antioxidant (system 1); RBD containing 200 μg g^?1 TBHQ at the start of the experiment (system 2) and RBD olein which had TBHQ topped up to a level of 200 μg g^?1 at the start of each frying day (system 3). Sensory evaluation of crisps showed that there is an initial rapid decrease in shelf-life with increase in fry number in all systems. There was only a comparatively smaller effect on shelf-life with increase in fry number in later fryings. When the shelf-life of crisps was related to the quality of oil in the frying medium, it was found that the shelf-life of the product is only slightly affected when the oil had deteriorated beyond the acceptable limit of quality of frying oil, where the acceptable limit was taken as 27-30% polar components and 1–2 mg potassium hydroxide g^?1 oil. TBHQ does have a protective carry-through effect. The protective effect is more pronounced when TBHQ is topped up to a level of 200 μg g^?1 at the beginning of each frying day.     

Effect of TBHQ on quality characteristics of RBD olein during frying

The changes in quality characteristics of refined, bleached and deodorized palm olein (RBD olein) during heating with intermittent frying for 5 hr/day for weight consecutive days in three systems were compared. The systems were (i) RBD olein without antioxidant (system 1); (ii) RBD olein to which 200 ppm of tertiary butylhydroquinone (TBHQ) had been added prior to frying on the first day (system 2), and (iii) RBD olein which had TBHQ added to a level of 200 ppm at the start of each day. The addition of TBHQ reduced the level of polar components and polymers in the oil, decreased the rates of change in iodine value and dielectric constant and decreased the rate of oxidation of C18:2. The reduction in the rates of these undesirable changes was more pronounced when the TBHQ was added to the system on each day of frying than when there was a single addition of TBHQ prior to frying on the first day. The undesirable effect of adding TBHQ was that it darkened the oil.     

Relationships between measurements of fat deterioration during heating and frying in RBD olein

The relationships between measurements of fat deterioration during static heating and heating with intermittent frying of potato crisps in RBD olein in the presence and absence of TBHQ were evaluated. Significant linear relationships were found between iodine value, C18:2/C16:0 ratio, polar components and dielectric constant. Nonlinear relationships were found between smoke point, acid value and polar components. The relationships between polymer content and polar components, E _{1 cm} ^1% at 232 nm and wavelength (λ) for which E _{1 cm} ^10% =1 also were found to be nonlinear.