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stabilisation of B- and y-tocopherols was also evident (Table 1). The stabilising effect of the rosemary extract and the ascorbyl palmitate in reducing losses of a-tocopherol is particularly marked, and it is clear that the rosemary extract was slightly more active than the ascorbyl palmitate at the concentrations used.

Table 1 stabilisation of B- and y-tocopherols was also evident (Table 1). The stabilising effect of the rosemary extract and the ascorbyl palmitate in reducing losses of a-tocopherol is particularly marked, and it is clear that the rosemary extract was slightly more active than the ascorbyl palmitate at the concentrations used.

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Fig. 2. Relative change in tocopherol content during frying of potato chips in rapeseed oil containing 0-1% rosemary extract. The rapeseed oil with no additives showed clearly that the a-tocopherol was consumed significantly faster than the B- or y-tocopherol (Fig. 1). This difference in stability of the tocopherols was also evident in the oil samples containing rosemary extract and ascorbyl palmitate (Figs 2 and 3). However, both rosemary extract and ascorbyl palmitate increased the stability of the tocopherols by a considerable extent. A 50% reduc- tion in concentration of a-tocopherol occurred after about 4—5 frying operations for the control compared with values of 9-10 and about 8 for samples fried in rapeseed oil containing the rosemary extract at 0-1% and ascorbyl palmitate at 0-02%, respectively. Similar
Fig. 2. Relative change in tocopherol content during frying of potato chips in rapeseed oil containing 0-1% rosemary extract. The rapeseed oil with no additives showed clearly that the a-tocopherol was consumed significantly faster than the B- or y-tocopherol (Fig. 1). This difference in stability of the tocopherols was also evident in the oil samples containing rosemary extract and ascorbyl palmitate (Figs 2 and 3). However, both rosemary extract and ascorbyl palmitate increased the stability of the tocopherols by a considerable extent. A 50% reduc- tion in concentration of a-tocopherol occurred after about 4—5 frying operations for the control compared with values of 9-10 and about 8 for samples fried in rapeseed oil containing the rosemary extract at 0-1% and ascorbyl palmitate at 0-02%, respectively. Similar
Fig. 1. Relative change in tocopherol content during frying of potato chips in rapeseed oil. The concentrations of a-, B, y- and 6- tocopherols in rapeseed oil were found to be 215, 106, 401 and <13 ppm, respectively, based on the a-tocopherol calibration curve and using the same response factor for each toco- pherol. This may give a slight overestimate of the con- centration of B-, y- and 6-tocopherol since the response factors relative to a-tocopherol are reported to be 1: 1-29:1-1:1.22 (Thompson & Hatina, 1979) or 1:1-14: 1:18 (a: 8:4) (Duggan, 1959). However, these concen- trations are within the range of 180-280, 380-590 and 10-20 ppm reported respectively for a-, y- and 6-toco- pherols in rapeseed oil by Schuler (1990). Rahman (1990) reported 250, 157, 519 and 9 ppm for a-, B-, y. and &tocopherol, respectively. The 8-tocopherol level was near the limit of detection and therefore changes in this component are not discussed in this paper.
Fig. 1. Relative change in tocopherol content during frying of potato chips in rapeseed oil. The concentrations of a-, B, y- and 6- tocopherols in rapeseed oil were found to be 215, 106, 401 and <13 ppm, respectively, based on the a-tocopherol calibration curve and using the same response factor for each toco- pherol. This may give a slight overestimate of the con- centration of B-, y- and 6-tocopherol since the response factors relative to a-tocopherol are reported to be 1: 1-29:1-1:1.22 (Thompson & Hatina, 1979) or 1:1-14: 1:18 (a: 8:4) (Duggan, 1959). However, these concen- trations are within the range of 180-280, 380-590 and 10-20 ppm reported respectively for a-, y- and 6-toco- pherols in rapeseed oil by Schuler (1990). Rahman (1990) reported 250, 157, 519 and 9 ppm for a-, B-, y. and &tocopherol, respectively. The 8-tocopherol level was near the limit of detection and therefore changes in this component are not discussed in this paper.
Fig. 3. Relative change in tocopherol content during frying of potato chips in rapeseed oil containing 0-02% ascorbyl palmitate. Table 1. Number of frying operations before the tocopherol level falls by 50% (t1,)
Fig. 3. Relative change in tocopherol content during frying of potato chips in rapeseed oil containing 0-02% ascorbyl palmitate. Table 1. Number of frying operations before the tocopherol level falls by 50% (t1,)
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