Butter and Butter Products 219ity evaluation (chemical, physical, micro-
biological, and sensory) of milk and milk
products. A list of reference methods from
the International Standards Organization
(ISO) and International Dairy Federation
(IDF) to evaluate milk and milk product
quality are detailed (Table 9.5 ). Other analy-
ses for which no reference method exists, for
example, sensory evaluation of butter (Tables
9.6 and 9.7 ), are described in detail in the
regulation (Regulation No. 273/2008). Com-
positional standards such as fat, solids - not -
fat, and moisture levels are set down, as are
tests and standards for quality parameters
such as fat purity (using gas chromato graphy)
or fat deterioration (by determining peroxide
value and fat acidity levels). Determination
of fat and moisture in butter and spreads is
now often accomplished using infrared (IR)
and near infrared (NIR) absorption tech-
niques, which can respond rapidly to the
turnaround needed with continuous produc-
tion, product composition ranges, and physi-
cal form.
Off Flavor Development
Some aspects of quality are less straightfor-
ward to monitor than composition. Milk fat
fl avor comes from approximately 120 differ-
ent compounds, of which the main fl avor
components are free fatty acids, lactones, and
methyl ketones. The microbiological quality
of the raw cream and thermal treatments
applied during processing has a signifi cant
effect on fl avor development (Chapter 12 ).
Heating encourages formation of fl avor
precursors and promotes Maillard reactions
and associated protein/carbonyl interactions.
The high temperatures applied in the manu-
facture of ghee, for example, encourage
development of a “ cooked ” fl avor due to
formation of methyl ketones, while some
oxidation of the fat and lactone formation
also contribute to the characteristic ghee
fl avor. The use of cultured products to manu-
facture ghee introduces another characteristic
fl avor compound, diacetyl, generated by the
action of starter cultures used for lactic acid
production.
In concentrated milk fat products fl avor
deterioration may occur via oxidation, lipoly-
sis, or heat - induced breakdown of fl avor
precursors.Oxidation and Lipolysis
Although cream for butter or AMF manufac-
ture is used fresh, butter itself or AMF may
be stored for some time before repackaging
for market, refi ning, or incorporation into a
product. Butter is often stored as 25 - kg
blocks for extended periods of time (four to
nine months) in refrigerated or - 20 ° C ( - 4 ° F)
storage. It has been shown that butter stored
at refrigerator temperatures exhibits a stale
off fl avor and increased levels of oxidation
more rapidly than butter stored at - 20 ° C
( - 4 ° F) (Krause et al. 2008 ). AMF is com-
monly held in 200 - kg drums or 20 - liter small
metal containers at ambient temperatures for
several months or at - 20 ° C ( - 4 ° F) in plastic -
lined cartons. High ambient temperatures
(30 ° C; 86 ° F or greater) as occur in tropical
countries reduce shelf life by causing more
rapid deterioration of the milk fat and devel-
opment of stale, oxidized fl avor (Wilbey
1991 ).
Oxidation is the reaction between oxygen
and the unsaturated fatty acids in the triacyl-
glycerols. It may be catalyzed by light and
metals such as copper and iron and the rate
of oxidation increases with temperature.
Oxidation is the main cause of fl avor deterio-
ration in AMF but it may be inhibited by
reducing dissolved oxygen and headspace
oxygen during manufacture and packing and
eliminating contact with copper and iron.
Oxidation may be assessed by measuring the
peroxide value (PV), with a standard of less
than 0.5 mEq oxygen/kg fat (Commission
Regulation (EC) No. 273/2008) (Table 9.5 ).
Compared with many fats, milk fat is rela-
tively stable toward oxidation, although it
has been reported that milk fat with a PV of
0.3 to 0.4 mEq oxygen/kg fat had an oxidized