Food Structure for Nutrition - Food Colloids: Self-Assembly and Material Science - page 6

1.5 Milk as a Model of Food Structure and Nutrition
Milk is the only biomaterial that has evolved for the purpose of nourishing
growing mammals. Survival of mammalian offspring has exerted a strong
selective pressure on the biochemical evolution of the lactation process. Just
as for evolution of any biological process, the strong survive at the expense of
the weak, which leads to the appearance of new traits that promote health,
strength, and, ultimately, survival. The same is true of milk. The role of milk was
to produce the molecules that would ensure the survival of the mammalian
offspring. The various processes of lactation have been described: the immature
gland, the developing gland, 14 colostrum formation, 15 secretory activation
(lactogenesis), 16-18 and involution and senescence. 19 The overall process of
lactation requires extensive physiological, structural, and metabolic remodelling
of the mammary tissue to enable it to acquire milk-forming capabilities.
This evolutionary pressure led to the elaboration of a whole food that
contains proteins, peptides, complex lipids, and oligosaccharides in higher
order structures, and all coming together as a complex, multicomponent -
yet highly organized - food. In simple terms, milk is an obligate liquid. The
basic mammary tissue constraints and the early evolutionary direction led to a
liquid emulsion that had to stay in the liquid form to exit the ductal tissue and
flow to the infant. Table 1 shows that the variation in milk composition is
significant across mammals. 20 The composition of all of the macronutrients
(protein, fat, and carbohydrate) vary significantly, with the extremes of protein
being from 11 g per 100 g of fresh milk.

As milk has been studied more intensively, it has become evident that it is
more than a simple repository of essential nutrients in a protein/fat/lactose
'broth'. Milk contains many compounds that exhibit properties associated with
biological functions beyond simple provision of essential building blocks. Milk
compounds and their configurations act as growth factors, toxin-binding
factors, antimicrobial peptides, prebiotics, and immune regulatory factors
within the mammalian intestine. 21 Gradually, science has found that these
macromolecules deliver biological advantages to the intestine and throughout

1to

B B

Table 1 Protein, fat, and carbohydrate composition of milk from different
mammalian species (per 100 g fresh milk) (data taken from Ref. 20)

Species Protein (g) Fat (g) Carbohydrate (g)

Human 1.1 4.2 7.0

Monkey (rhesus) 1.6 4.0 7.0

Donkey 1.9 0.6 6.1

Goat 2.9 3.8 4.7

Cow 3.2 3.7 4.6

Elephant 4.0 5.0 5.3

Water buffalo 4.1 9.0 4.8

Mouse 9.0 13.1 3.0

Seal 10.2 49.4 0.1

Whale 10.9 42.3 1.3