Paul MoughanRiddet Institute, Massey University, New Zealand

New approaches to the assessment of protein quality: Whey proteins

See display copy at Elsevier stand.

“Not all proteins are created equal nutritionally”

> Milk

> Meat

> Egg

> Soya

> Bean

In particular vegetable-based proteins are of lower quality than dairy based proteins

> fibre

> anti-nutritional factors

> different structures

An accurate description of Dietary Protein Quality is of fundamental importance:

> Dietary Assessment

> Nutritional Planning

> Regulatory Environment

> Trade

How then should Protein Quality

be determined?

> In the past PDCAAS (protein digestibility corrected amino acid score) has been the recommended scoring method (FAO 1989)

> There are a number of shortcomings of PDCAAS.

> New Recommendations (FAO, 2013)

Emphasis on individual digestible amino acid contents rather than a single score (ie treat each amino acid as an individual unit). This maximises the information on the nutritional (protein) value of food.

> Amino acid digestibility is determined at the end of the small intestine (True ileal digestibility).

> For processed foods ‘reactive lysine’ is determined in diet and ileal digesta rather than ‘total lysine’ to give lysine availability measures.

1.

How should ileal amino acid/ “reactive lysine” digestibility

be determined?

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> Digesta can be collected using ileostomates

> Digesta can be collected using a naso-ileal tube

> Both methods have drawbacks and are not routine

Need for an animal model.

Ref: Wrong OM, Edmonds CJ and Chadwick VS (1981) Comparative anatomy and physiology In:The Large Intestine, p 5, MTP Press Ltd, England.

Terminal ileum

In humans:

Growing pig (a meal-eating omnivore) is preferred model:

Need to collect ileal digesta

True ileal AA digestibility in the adult human and growing pig

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True N digestibility in pig (%)

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Digestible reactive1 (available) lysine versus digestible total lysine (gKg-1 DM)

Lysine

1Based on -methylisourea assay; 2P Pellett, N Scrimshaw and P Moughan (unpublished data).

Digestible Total Available Difference %

Shredded Wheat 1.8 1.6 11

Dried corn 2.6 1.9 27

Unleavened bread2 6.5 4.9 25

Puffed Rice 1.1 0.6 45

Rolled Oats 3.7 2.8 24

Wheat Bran 1.1 0.7 36

Corn 0.4 0.2 50

Conventional digestible lysine can be higher than available lysine

Lysine

Digestible Availablea

Whole milk protein 26.2 24.0

Infant formula A 8.3 8.6

Infant formula B 9.1 9.2

Infant formula C 11.1 11.7

Whey protein concentrate 79.9 77.5

UHT milk 31.7 31.4

Evaporated milk 23.4 20.5

Sports formula 20.4 19.1

Elderly formula 11.7 11.8

Hydrolysed lactose milk powder 27.2 25.1

aBioavailable lysine; minimal difference between total lysine and reactive lysine denotes minimal Maillard damage.Adapted from Rutherfurd & Moughan (2005), with permission of the publisher.

Ileal digestible total and “available” lysine contents (g/kg air-dry) for 12 dairy protein sources

But not so in dairy:

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Whey Protein Concentrate (n = 4)

Whey Protein Isolate (n = 1)

Whey Protein Hydrolysate (n = 1)

Lysine 98 100 94

Methionine 99 100 80

Cysteine 100 100 94

Leucine 99 100 96

Isoleucine 99 100 96

Valine 98 100 96

Tryptophan 100 100 -

Histidine 93 100 90

Threonine 94 100 93

Amino acids in whey proteins are generally highly digestible

When a single score of Protein Quality is needed DIAAS replaces PDCAAS.

With DIAAS (FAO, 2013):> Ileal AA digestibility replaces faecal CP digestibility> Reactive lysine replaces total lysine (conventional AA

analysis)> Scores are not truncated (unless diet or sole-source

food)> AA Reference Pattern (for regulatory purposes):

Infants: AA composition human milk

All others: AA requirement pattern for child (6 months – 3 years)

2.

DIAAS Milk Protein Whey Protein Whey Protein Red meatConcentrate Isolate Concentrate

Non-truncated 1.31 1.25 1.10 1.10 Truncated 1.0 1.0 1.0 1.0

Non truncation is significant

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1(Rutherfurd and Moughan, unpublished data).

Milk Protein Concentrate

Whey Protein Isolate

Soya Protein Isolate

Pea Protein

Cooked Beans

Cooked Rolled Oats

Wheat Bran

Roasted Peanuts

Rice Protein

Cooked Peas

PDCAAS 1.00 1.00 1.00 0.89 0.65 0.67 0.53 0.51 0.42 0.60

DIAAS 1.18 1.10 0.97 0.82 0.58 0.54 0.41 0.43 0.37 0.58

DIAAS and PDCAAS values1 are different. PDCAAS often overestimates for lower quality proteins

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But single scores omit much useful information: (eg leucine supply for optimal muscle function versus body protein maintenance).

Threonine

Met + Cys

Valine

Isoleucine

Leucine

Tyr + Phe

Histidine

Tryptophan

Lysine

Whey Protein Isolate

1.80

2.29

1.21

2.22

2.57

1.71

1.09

3.35

2.51

Whey Protein Concentrate

2.53

1.71

1.29

2.35

1.93

1.43

0.97

2.74

2.03

SoyaProtein Isolate B

1.13

0.91

1.02

1.38

1.13

1.65

1.18

1.69

0.99

Milk Protein Concentrate

1.56

1.18

1.55

1.81

1.77

2.39

1.60

1.94

1.77

SoyaProtein Isolate A

1.30

0.90

1.11

1.59

1.29

1.85

1.37

1.67

1.16

Conclusions

1. Considering amino acids as individual nutrients gives maximum information.

2. DIAAS incorporates recent scientific advances, and is an improvement over PDCAAS.

3. Before DIAAS can be implemented we need more data on the true ileal amino acid digestibility of foods.

4. Establishment of such a world food data-set is greatly needed.

5. This is an important step in the fight against malnutrition.

“Protein/Energy malnutrition affects every fourth child

world-wide”WHO/NHD (2000)