Cooking and cholesterol oxides

Salmon was processed by three different culinary techniques: pan-frying with olive oil, pan-frying with soya oil, and roasting. Roasting did not modify the fat content from that of raw samples. Frying increased the fat content 2-fold, with no difference between samples fried with different oils. Total cholesterol oxidized products (COPs) were 0.74, 2.98, 3.35, and 7.38 μg/g fat in raw, fried with olive oil, fried with soya oil, and roasted salmon, respectively, which represent 0.01, 0.08, 0.09, and 0.15% of cholesterol. A significant correlation (r = 0.902, ≤ 0.01) was found between acidity index and total COPs. The most abundant COPs were 7-ketocholesterol, which appeared in all the samples, and cholestanetriol (one of the most citotoxic COP), which appeared only in cooked samples (1.05−1.33 μg/g fat). All cooked samples supplied more ω-6 polyunsaturated fatty acids (PUFAs) than raw samples and showed higher ω-6/ω-3 ratios. Roasted salmon showed the lowest ω-3 content and the highest PUFAs/(SFAs)-C18:0 and MUFAs+PUFAs/(SFAs-C18:0) ratios.

Table 3. Cholesterol oxides levels (µg.g

-1

, dry basis) in raw and grilled 

sardine and hake samples.

COPs Sardine Hake

Raw Grilled Raw Grilled

19-OH 15.18 ± 1.2

B

27.69 ± 1.3A

2.16 ± 0.1

b

3.84 ± 0.3

a

24(S)-OH 1.24 ± 0.2

B

3.45 ± 0.6A

0.37 ± 0.03

b

1.19 ± 0.1

a

22(S)-OH 1.37 ± 0.3

B

2.29 ± 0.6A

0.96 ± 0.05

b

1.53 ± 0.7

a

25-OH 1.17 ± 0.2

B

6.48 ± 0.1A

4.49 ± 0.2

b

10.84 ± 1.0

a

25(R)-OH 0.35 ± 0.04

B

0.69 ± 0.01A

0.81 ± 0.01

b

1.29 ± 0.3

a

7-keto 1.31 ± 0.6

B

2.68 ± 0.3A

- 0.66 ± 0.1

a

Tot al 20.62 ± 0.4

B

43.28 ± 0.4A

8.79 ± 0.1

b

19.35 ± 0.4

a

A,B

Mean and relative standard deviation (RSD) of the four analyses in sardine (two 

batches in duplicate); 

a,b 

Mean and relative standard deviation (RSD) of the four analyses 

in hake (two batches in duplicate); means in the same letter do not differ significantly 

(p > 0.02)

Merlu/colin = hake