Improved Milk

When milk is evaluated as a nutrient source, there are several facts and opinions that we need to consider when thinking about redesigning milk. Some of the facts about milk include: It is a nutritious and tasty food; it is high in fat, especially triacylglycerol; it is rich in saturated fatty acids; it is rich in CLA compared with other foods; it is a good source of calcium and an excellent source of dietary protein; and it causes intolerances for some individuals. Key features to incorporate into redesigned milk include making its fat contain an ideal fatty acid composition, converting lactose to its constituent sugars, increasing the solids in skim milk for better mouth feel, increasing the iron content, lessening the total fat content, and using milk as a carrier for specific nutrients. In 1989, a group of nutritionists, food scientists, animal scientists, producers, and processors proposed that the ideal milk fat is one in which the saturated fatty acids were decreased by being moved to the monounsaturated fatty acid category with a slight increase in the amount of polyunsaturated fatty acids (Fig. 1). These considerations did not take into account processing issues, but rather focused solely on the idealized fatty acid composition from a human health perspective.

One way of evaluating the healthfulness of the fatty acid composition of foods is by grouping the constituent fatty acids and calculating an atherogenic index (AI). The AI is calculated by summing the concentration of saturated fatty acids (omitting stearic acid) and four times the concentration of C-14 and using that sum as the numerator that is divided by the sum of unsaturated fatty acids in the product.[2] To illustrate the potential of producing a more idealized milk by genetic means, milk

Saturated

Monounsaturated

Polyunsaturated

Typical Ideal

Milk Type

Fig. 1 Idealized milk fat. (Data are adapted from Ref. [1].)

Table 1 Variation in atherogenic index (AI) and fatty acid composition of milk

Saturated

Monounsaturated

Polyunsaturated

Typical Ideal

Milk Type

Table 1 Variation in atherogenic index (AI) and fatty acid composition of milk

Measurement

Low 5%a

Mid 5%b

High 5%b

AI

1.06

2.30

3.31

Fatty acid

(wt. %)

14:0

5.2

10.l

12.6

16:0

25.3

28.0

36.2

18:0

14.4

13.9

9.l

18:1

3l.8

25.8

20.3

18:2

3.3

3.0

2.3

aLow 5% refers to the 5% of cows within a 180 cow herd that had the lowest AI.

bMid 5% and high 5% refer to the 5% of cows with mid and high AIs. (Data from Ref. [3].)

aLow 5% refers to the 5% of cows within a 180 cow herd that had the lowest AI.

bMid 5% and high 5% refer to the 5% of cows with mid and high AIs. (Data from Ref. [3].)

samples with a low, medium, and high AI from a Holstein herd are described in Table 1. With the AI ranging from 1.06 to 3.31, we observed a wide variation in fatty acid composition of individual milks. When the largest and smallest AIs of milk samples are compared with other foods, the milk with the smallest AI fits in the range of AIs for margarine. On the other hand, the greatest AI for milk does not approach that of coconut oil (AI=15.9), which is at the atherogenic extreme of common foods and food components.

A specific group of fatty acids that are enriched in ruminant-derived foods is CLA. Conjugated linoleic acid has been touted as a nutraceutical for several reasons because it benefits human health. For example, a study conducted by Ip et al.[4] clearly demonstrates that CLA, when incorporated into butter by preharvest or postharvest means, decreases tumor incidence in rats.

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