In general, esterified PS
are preferred than their free forms (205). It is
highly important to find a food-grade method for producing PS esters of PUFA
that could be commercial available (206, 207). Esterification
of sterols and stanols was initially used for fat spreads because the esters
are readily lipid soluble, whereas free sterol is not particularly soluble in
either fat or water. Free sterols are found at levels of up to 400 mg/100 g in
seed oils. Esterified sterols are also found naturally in plant oils and may be
up to 70% of total sterols. The advantage of free sterols is a lower added mass
(30% less without the fatty acid) and lower calories, no requirement for fat in
the product, and no additional processing required prior to micro-emulsification.
Free sterols have been used in juice, bread, meat, jam, chocolate, snack bars,
yogurt, low fat cheeses, etc., but sterols and stanol esters have also been
used in these foods (208). Microencapsulation of PS by spray
drying is an alternative technique to facilitate their usage in different food
products (209, 210),
and provide oxidative stability (211). It should be considered that addition of phytosterol esters to
the fat phase of food products may influence its crystallization behavior and
may thus lead to problems occurring during the production process or with the macroscopic
properties of the end product (212).
Better stability of PS is
observed when oils are stored in the dark (or in opaque bottles) and at a
temperature lower than room temperature. During cooking of foods which contain
PS at a temperature lower than 100 ?C, PS will not be affected. However,
heating at about 140–170 ?C and at 200 ?C, more than one-half of the sterols may
be modified (213). The rate of thermo-oxidative changes may be reduced by
application of natural and synthetic antioxidants (214).
Mixtures of plant sterols (e.g., ?-oryzanol
and ?-sitosterol) can be potentially used as an alternative to crystalline fats
like triacylglycerols for structuring the oil phase of some food products (215).
Mixtures of ?-oryzanol and ?-sitosterol are able to form transparent organogels
in edible oils. It was found that ?-oryzanol and ?-sitosterol self-assemble
into hollow double-walled tubules (ca. 7 nm in diameter and just under 1 nm wall thickness) forming a
transparent and firm organogel (216-220). It has been demonstrated that ?-oryzanol + ?-sitosterol-structured
organogel can suppress or prevent oil migration in filled chocolate products (221).
In addition, a newly conducted study indicated the possibility of preparing
edible fat-like oleogel from sunflower oil with a specific combination of ?-sitosterol
and stearic acid (222).
It is also possible to replace 50% of the pork
backfat in frankfurter sausages with monoglycerides and phytosterols-structured
sunflower oil (223).
The major sources of phytosterols for
current functional foods and dietary supplements are tall oil and vegetable oil
deodorizer distillate (Table 18). Tall oil is a by-product of the kraft pulping
of wood to make paper. Tall oil contains a mixture of phytosterols and
Deodorizer distillates from soybean oil and other vegetable oils could
potentially be used as a source of phytosterols (224).