Food Chemistry

14.4 Processing of Fats and Oils 661

crude lecithin (approx. 0.25%). Diet margarines
have higher levels of emulsifiers. Skim milk
or skim milk powder suspended in water (milk
proteins, 1%; 2% in semi-fat margarine) is added
in the production of high quality retail brands of
margarine. The casein assists the action of the
emulsifiers and, together with lactose, provides
the desired browning when heated.
The aqueous phase of the margarine acquires
apHof4.2–4.5 by addition of citric and lactic
acids. This not only affects the flavor, but protects
against microbial spoilage. In addition, traces
of heavy metal ions are complexed. Margarine
also contains the aroma substances typical of
butter, which can be produced by microbiological
souring (cf. 10.2.3.2). Readily available synthetic
compounds, such as diacetyl, butyric acid, lac-
tones of C 8 –C 14 hydroxy-fatty acids (cf. 5.3.1.4)
and(Z)-4-heptenal,mayalsobeusedforarom-
atization. Common salt (0.1–0.2%) is used to
round-off the flavor. Margarine is colored withβ-
carotene or with gentlyrefined, unbleached palm
oil. Attention is also given to maintaining the
presence of 1 mg ofα-tocopherol per g of linoleic
acid. High quality products are vitaminized by
the addition of about 25 IU/gvitaminAand
1IU/gvitaminD 2. The authenticity of margarine
is verified in some countries by an indicator sub-
stance added to it. This is required by legislation.
Gently refined sesame oil (for its detection, see
Table 14.22) is one of these substances.

14.4.5.2 Manufacturing

Margarine is manufactured continuously by
a process consisting essentially of three steps:

• Emulsification of water within the continuous
  oil phase.


• Chilling and mechanical handling of the emul-
  sion.


• Crystallization, preserving the type of w/o
  emulsion by efficient removal of the released
  heat of crystallization.

The triacylglycerols should preferentially crys-
tallize in theirβ′-forms (cf. 3.3.1.2). The higher
meltingβ-forms are not desired since they cause
a “sandy” texture. The transitioinβ′→β-form is
inhibited by addition of 1% saturated diacylglyc-
erols.

14.4.5.3 Varieties of Margarine

The characteristic features of some varieties of

margarine are summarized in Table 14.19.

14.4.6 Mayonnaise

Mayonnaise is an “oil in water” or o/w emulsion

(cf. 8.15.1) consisting of 50–85% edible oil,

5–10% egg yolk, vinegar, salt and seasonings

(cf. 11.4.2.3). The emulsion is stabilized by egg

yolk phospholipids. Products with a lower oil

content (<50%) may contain thickening agents

such as starch, pectin, traganth, agar-agar, algi-

nate, carboxymethylcellulose, milk proteins or

gelatin. Sorbic acid, benzoic acid or the ethyl

ester of p-hydroxybenzoic acid are added as

preservatives. The stable emulsion is produced

in a combinator with a homogenizer and then

packed.

14.4.7 Fat Powder

In contrast to fats and oils, fat powders have bet-

ter stability against autoxidation and, in some

food products such as dehydrated soup powders

or broths, are easier to handle. They are manufac-

tured from natural or hardened plant fats, some-

times with the addition of emulsifiers and protein

carriers. Butter and cream powders are also pro-

duced.

Two basic flow diagrams of the production of fat

powders are shown in Fig. 14.6.

In a cold-spray process, the melted fat is sprayed

under high pressure into a cooled (− 35 ◦C) air-

blast crystallization chamber, where the fat parti-

cles solidify. After being recrystallized, the parti-

cles are coated to avoid clumping.

In a spray-drying process, the fat is homogenized

with emulsifiers, water and skim milk, spray dried

and subsequently crystallized.

14.4.8 Deep-Frying Fats

Traditionally, the fats used for deep frying are

those whose stability against autoxidation have