From http://www.scielo.cl/scielo.php?pid=S0716-97602003000300002&script=sci_arttext

A newer report with levels of oxidized cholesterol:

OXYSTEROLS IN COMMONLY CONSUMED FOODS

It has been estimated that approximately 1% of the cholesterol
consumed in a mixed Western diet is oxidized cholesterol (van de
Bovenkamp et al., 1988). Dietary sources of oxysterols are cholesterol-
rich foods, such as dairy, processed eggs, and meat products.
Cholesterol containing foods, when subjected to high temperatures
during manufacture and/or processing may form variable amounts of
oxysterols, depending on the analytical method applied for their
identification, as was discussed above. The most commonly detected
oxysterols in foods are the major products of cholesterol oxidation: 7
a-hydroxycholesterol, 7 ß-hydroxycholesterol, a-epoxycholesterol, ß-
epoxycholesterol, and 7-ketocholesterol, which can be found in amounts
ranging from nano gr to mg/gr of sample (Sander et al., 1989;
Paniangvait, et al., 1995).

Eggs and egg-derived products
Foods that are naturally characterized by high cholesterol content are
major sources of oxysterols when processed, such as eggs and egg-
derived products. An average egg contains 200-220 mg cholesterol,
which is about twice the cholesterol content of butter and freeze-
dried meat products, and about 5-10 times more cholesterol than is
found in most dairy products. Dried whole egg or dried egg yolk, but
not fresh egg yolk, are significant sources of oxysterols when used in
the manufacture of convenience foods (Missler et al., 1985; Galobart
et al., 2002). Oxysterol content of eggs (dehydrated, dried) are in
the range of 0.05-1.50 ug/g, and for egg-yolk (dehydrated or dried)
amounts are 15-120 ug/g (Morgan & Armstrong, 1992). Irradiation
applied to the control of Salmonella considerably increases the amount
of oxysterols in egg yolk powder from 10 ug/g to 470 ug/g on average
(Du & Ahn, 2000).

Dairy products
Several dairy products and milk powder are reported to contain
oxidized cholesterol after processing (Dionisi et al., 1998). The
oxysterols found in these products are the same as those in processed
eggs. However, fresh milk contains 0 or only trace amounts of
cholesterol oxides, which means that processing (e.g high temperature)
is the main source of oxysterols (Angulo et al., 1997). Other milk-
derived products such as cheeses, yogurt, and evaporated milk, contain
very low amounts of cholesterol oxides. The oxysterol content of milk
powder is in the range 1.0-2.5 ug/g. Dehydrated cheese has 8-15 ug/g;
skimmed milk powder, 0.01-0.1 ug/g; and whole milk powder, 0.2-0.8 ug/
g (Paniangvait et al., 1995). The amount of oxysterols present in
these products depends on the processing temperature and the length of
the storage period (Nourooz-Zadeh & Appelqvist, 1988).

Meat and meat-derived products
The mean lipid content of lean meat is 10%, wet weight basis, of which
triglycerides and phospholipids are major components and cholesterol
is a lesser component, ranging from 50 to 89 mg. The main source of
oxysterols in meats (from bovine, poultry and porcine origin) is heat
processing, mainly over-heating. Fresh meat and fresh meat products
contain 0 or trace amounts of cholesterol oxides. Oxysterols contained
in cooked meat range from 180-1900 ug/g (Paniangvait et al., 1995).

Other food products
It has been proposed that frying in animal/vegetable oils is an major
source of oxysterol in the Western diet. The primary target are French
fried potatoes, which together to other deep-fried foods cooked in
animal/vegetable fat are considered the main source of oxysterols in
the U.S. and Latin America. The oxysterol content of potatoes fried in
tallow or vegetable/animal oil may be in the range of 1.4 mg/g to 16.7
mg/g, depending on the origin and/or the animal fat content of the
frying oil (Paniangvait et al., 1995).

Oxidation of Cholesterol in Mayonnaise During Storage
Department of Foods and Experimental Nutrition,
University of São Paulo, May 2004.

The oxidative stability of cholesterol in commercial mayonnaise under
different storage conditions was evaluated by measuring cholesterol
oxides (COs), 7-ketocholesterol (7-Keto), 25-hydroxycholesterol (25-
OH), 7α-hydroxycholesterol (7α-OH) and 7β-hydroxycholesterol (7β-OH)
using HPLC. Oxidation of cholesterol was indicated within about 15
days after manufacture by the presence of 7-Keto. Oxidation increased
during storage at 4 and 25 °C (being greater at 25 °C) for 165 days in
darkness, as indicated by the presence of 7-Keto, 25-OH, 7α-OH and 7β-
OH. There was a strong correlation between COs and PV (peroxide value)
[r2=0.95 (4 °C) and r2=0.96 (25 °C)] during the process of oxidation.
The pattern of fatty acids was not affected during the period of the
experiment. Temperature and time were important factors in the
oxidative stability of cholesterol. Total formation of COs during 165
days was 20.3 μg/g at 4 °C and 30.2 μg/g at 25 °C.

Fatty acid contents evolution and cholesterol oxides formation in
Brazilian sardines (Sardinella brasiliensis) as a result of frozen
storage followed by grilling. Sept 2007.

Brazilian sardines (Sardinella brasiliensis) are the main fishery
resource commercialized in Brazil. The traditional forms of storage
and cooking (frozen and grilling) and its relation to changes of the
fatty acids, cholesterol and cholesterol oxidation products (COP)
formation were evaluated. Fresh sardines presented an important
content of PUFA n-3 fatty acids (11.4±0.5 of eicosapentaenoic acid
(EPA) and 16.7±0.3 of docosahexaenoic acid (DHA), g/100 g of the oil),
that decreased significantly during processing, as well as the total
cholesterol amount, with concomitant formation of cholesterol oxides.
The cholesterol oxides determined in sardine samples were 19-
hydroxycholesterol, 22(S)-hydroxycholesterol, 24(S)-
hydroxycholesterol, 25-hydroxycholesterol, 25(R)-hydroxycholesterol
and 7-ketocholesterol, being the main product the 19-
hydroxycholesterol. High variations of the total COP contents
(19.4±0.4-177.9±1.2 μg/g) was found during the experiment. Cholesterol
oxides levels showed a negative correlation (r0.84) with cholesterol,
DHA and EPA content by principal components analysis, whereas
cholesterol oxides levels increased while cholesterol, EPA and DHA
values decreased in sardines grilled or storage for 120 days.

Effect of anhydrous milk fat on lymphocytes in rats
October 2001

Lymphocytes are important components of the immune system. Dietary
lipids affect the functioning of the immune system. Changes in the
lipid composition of the lymphocyte membrane is a case in point.
Membrane structural changes are reflected in the altered function of
the cell. Lymphocyte proliferation and lymphocyte rosetting are
membrane associated phenomena. Ghee, is a clarified butter product,
commonly used in the Indian diet. It is rich in saturated fatty acids
and also contain oxysterols which are generated on prolonged heating
of ghee. Male weanling rats were fed 2.5% (of the total fat levels) of
fresh or thermally oxidized ghee for a period of 8 weeks. The control
rats were fed groundnut oil. Lipid composition of lymphocytes in ghee
fed rats showed changes. In vitro lipid peroxidation of lymphocyte
membranes increased by 26% in oxidized ghee fed rats. Na+K+ ATPase
activity was decreased in oxidized ghee fed rats (18%). Lymphocyte
proliferation was reduced in ghee fed rats (32%), compared to the
controls, irrespective of the mitogens used (Con-A or PHA), or the
tissue (splenocytes or peripheral blood lymphocytes). Oxysterols
present in oxidized ghee are the likely agents inhibiting
lymphoproliferation. Rosetting of lymphocytes decreased in the fresh
ghee fed rats by 16% and in oxidized ghee fed rats by 25%. Membrane
fluidity declined in the oxidized ghee fed rats. It is concluded that
feeding ghee results in decreased proliferation of lymphocytes. Also,
feeding oxidised ghee results in decreased proliferation of
lymphocytes through alterations in the structure of the lymphocyte
membranes in the rat.