Agriculture Reference
In-Depth Information
Table 17.8
Heat treatment classifi cation for SMP
Classifi cation
Skimmed milk heat treatment
Undenatured whey protein
nitrogen (mg/g powder)
Low heat
Cumulative heat treatment not over
71.1°C for 2 minutes
Over 6.0
Medium heat
Preheat to 71.1-79.4°C for 20 minutes
1.51-5.99
High heat
Preheat to 87.8°C for 30 minutes
Under 1.5
Source: Adapted from ADPI (2002).
and casein. The nature and degree of the interactions depends on the heat treatment
conditions. ADPI (2002) gives three heat treatment classifi cations: low heat,
medium heat and high heat. These relate to levels of undenatured whey protein in
the different grades of powder (Table 17.8). Low heat SMP is used as an ingredient
in chocolate, sugar confectionery and milk based beverages. It is also used as an
ingredient in the production of cheese starter culture media, as the absence of
whey protein denaturation and casein interactions allows the casein to precipitate
fully during acidifi cation. Medium heat and high heat SMP are used as ingredients
in ice cream, soups and sauces (wet and dry mix), confectionery and meat
products.
An additional category of SMP, known as High Heat Heat-Stable (HHHS)
SMP, can be made by pre-heating skimmed milk in excess of 95°C for 15-30
seconds to maximise whey protein-casein interactions. This powdered ingredient
is used particularly in the manufacture of recombined milks that are UHT
processed. The heat-stable SMP is reconstituted in water with butteroil to produce
a 'double strength' milk, i.e. a milk with twice the NFMS and fat content as fresh
milk, which is UHT processed and aseptically packaged. Consumers can mix the
double strength milk 1:1 with water to give a liquid milk of standard composition.
By inducing whey protein-casein interactions in skimmed milk, the whey proteins
are protected from gelation during UHT processing and the occurrence of product
defects (e.g. protein fl ocs) and increased recombined milk viscosity.
WMP and SMP are the products of spray-drying processes, although roller (or
drum) drying is still relevant. Spray drying allows the creation of powder properties
of use to food manufacturers, such as cold water dispersable powders (Palzer and
Fowler 2010). The production of milk powders is essentially a two-step process:
1 Removal of most of the water from the material to be dried, usually by multiple
effect vacuum evaporator (Fig. 17.1)
2
Spray drying.
In the production of SMP, skimmed milk at 8.7% solids is pasteurised and
evaporated to a concentrate of 45-50% solids and around 90% of the water is
removed. The concentrate is atomised (usually by means of a rotary atomiser or
high pressure nozzle) into a drying chamber (Fig. 17.2) fed with air at 180-250°C.
The fi ne droplets, or primary particles, fall through the hot air and evaporation
Search WWH ::
Custom Search