Chemistry Reference
In-Depth Information
blood cholesterol, and coronary disease. The majority of nutritionists, however, advocate balanced
fat intake as a proportion of the daily energy requirements with concomitant limitation of levels of
saturated fats in the diet. Current guidelines in many countries state that the total daily fat intake
should be no more than 30% of the total energy, with saturated fat constituting less than 10% of
calories. Intensive efforts from ingredient suppliers and product developers have reduced the use of
ingredients rich in saturated fats such as lard, beef tallow, butterfat, coconut oil, and palm oil and
increased the use of vegetable oils with higher percentages of monosaturated and polyunsaturated
fats.
The majority of the consumed fat comes from salad and cooking oils, as well as frying fats and
bakery shortenings. Furthermore, meat, poultry, ish, and dairy products (cheese, butter, and marga-
rine) also contribute substantially to fat consumption. The fat plays a unique functional role in each
food product; for example, in fried foods, oil serves as a heat conductor and, at the same time, is
incorporated into the food. Due to this dual role, the oil must meet several important requirements:
good thermal and oxidative stability, in addition to good lavor, good shelf life, and acceptable
cost. Fats and oils provide important textural qualities to certain foods. The physical properties of
food fats are inluenced primarily by three factors: (1) polymorphism (structural, solidiication, and
transformation behavior); (2) the phase behavior of fat mixtures; and (3) the rheological and textural
properties exhibited by fat crystal networks. In fat crystals, three main polymorphic forms, namely,
α, βʹ, and β, are deined in accordance with subcell structure. Transformation from polymorphic
form βʹ to polymorph β frequently results in the deterioration of the end product, mainly due to
changes in crystal morphology and network. Naturally occurring fats and lipids are mixtures of
different types of triacylglycerol (TG). The complex behavior of fats with regard to melting, crys-
tallization and transformation, and crystal morphology and aggregation is, in part, a result of the
physical properties of the component TGs and, more importantly, a result of the phase behavior of
the mixture. One of the most important macroscopic physical properties of food fats is rheology,
which governs a number of important attributes, including the spreadability of spreads, the brittle-
ness of chocolate, and the smoothness, mouthfeel, and stability of bulk fats and emulsion products
(deMan 1999). The rheological properties of food fats are governed by numerous factors, which
can be grouped as intrinsic, including the molecular compositions of fats (TGs, ingredients, and
additives), the polymorphism of crystals of the constituent TGs, and the microstructure of fat crys-
tals (morphology, crystal size distribution, and crystal network formation), and extrinsic, including
processing conditions, such as temperature, shear, and low velocity. Therefore, in order to replace
fat, all these properties must be considered, which ultimately means that fat replacement carries
many additional requirements than the fat itself. For example, additional ingredients are required
to address mouthfeel, texture, aeration or structure, color, lavor, handling characteristics, and shelf
stability. These are additionally accompanied by other factors such as cost, safety, and regulatory
concerns.
The traditional approach to fat substitution was to replace it with either water or air, for example,
using skim milk instead of whole milk in frozen dessert or alternative processing such as baking
instead of frying. Fat replacers indicate food ingredients that can take the place of all or some of the
fat in foods and yet give similar organoleptic properties to the foods (Akoh 1994, 1998). Depending
on their chemical structure, fat replacers are classiied into lipid-, protein-, and carbohydrate-based
fat replacers. Another well-accepted classiication is (1) fat substitutes and compounds, which are
mainly lipid based, physically and chemically resemble TGs, and are often chemically or enzymati-
cally synthesized, and (2) fat mimetics, constituting carbohydrate- and protein-based ingredients
that imitate the organoleptic or physical properties of TGs. Most carbohydrate-based fat mimetics
are hydrocolloids, which are mainly high-molecular-weight, hydrophilic biopolymers with a great
water-holding capacity. Due to this property, their unique physical functionalities such as thicken-
ing, gelling, and emulsifying properties allow them to mimic the mouthfeel and low properties
that resemble those of fat in aqueous systems. The increased viscosity of dispersions containing
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