144 Chapter 6
have been also suggested as alternative mea-
sures of the extent of heat treatment for skim
milk powders (Table 6.2 ). However, the
WPNI method remains the guide that many
manufacturers use for classifying skim milk
powders.Other indicators of the extent of whey pro-
tein denaturation, such as the casein number,
heat number, thiol number, cysteine number,
and furosine content (Wilcek, 1990 ; Tong,
2001 ), and sulphydryl content and absor-
bance at 340 nm (Guingamp et al., 1999 )
Table 6.2. Heat classifi cation of skim milk powder.
Milk powder class Whey protein
nitrogen indexCysteine
number bThiol
number bHeat
number b
Extra - low heat 24 – 31
Low heat ≥ 6 31 – 38 ≤ 7.5 ≤ 80
Medium heat 1.51 – 5.99 38 – 62 7.5 – 13.3 80.1 – 88
High heat ≤ 1.5 ≥ 62 ≥ 13.3 ≥ 88.1a From Standards for Grades of Dry Milks Including Methods of Analysis, American Dry Products Institute, Bulletin
916 (2002)
b IDF specifi cations, Wilcek (1990)
Table 6.1. Specifi cations for dry milk products.
Product ADPI a Codex Alimentarius
Skim milk powder
Fat Max. 1.25% Max. 1.5%
Water Max. 4.0% Max. 5.0%
Protein Min. 34% c
Titratable acidity Max. 0.15% Max. 18 b
Solubility index Max. 1.2 ml Max. 1.0 ml
Bacterial estimate c Max. 10,000/g
Scorched particles Max. Disc B (15.0 mg) Max. Disc B
Full - cream milk powder
Fat Min. 26%, Max. 40% Min. 26%, Max. 42%
Water Max. 4.5% d Max. 5.0%
Protein Min. 34% e
Titratable acidity Max. 0.15% Max. 18 b
Solubility index Max. 1.0 ml Max. 1.0 ml
Bacterial estimate Max. 10,000/g
Scorched particles Max. Disc B (15.0 mg) Max. Disc B
Buttermilk powder
Fat Min. 4.5%
Water Max. 4.0%
Protein Min. 30%
Titratable acidity 0.10% – 0.18%
Solubility index Max. 1.25 ml
Bacterial estimate e Max. 20,000/g
Scorched particles Max. Disc B (15.0 mg)
Cream powder
Fat Min. 42%
Water Max. 5.0%
Protein Min. 34% c
a ADPI (2002) specifi cations for Extra Grade
b As ml 0.1 N NaOH/10 g solids - not - fat
c With coliforms not greater than 10/g
d As determined by weight of moisture on a milk - solids - not - fat basis
e As a proportion of milk solids - not - fat