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New approaches to the assessment
of protein quality: Whey proteins
Paul Moughan
Riddet Institute, Massey University, New Zealand
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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)
1. 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.
How should ileal amino acid/
“reactive lysine” digestibility
be determined?
In humans:
> 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.
Terminal
ileum
Ref: Wrong OM, Edmonds CJ and Chadwick VS (1981) Comparative
anatomy and physiology In:
The Large Intestine, p 5, MTP Press Ltd, England.
10
Growing pig (a meal-eating omnivore) is preferred model:
Need to
collect ileal
digesta
(Moughan, unpublished)
True N digestibility in human (%)
True ileal AA digestibility in the adult human and
growing pig
True N digestibility in pig (%)
Conventional digestible lysine can be higher than
available lysine
Digestible reactive1 (available) lysine versus digestible total lysine (gKg-1 DM)
Lysine
Digestible Total
Available
Difference %
Shredded Wheat
Dried corn
1.8
2.6
1.6
1.9
11
27
Unleavened bread2
Puffed Rice
6.5
1.1
4.9
0.6
25
45
Rolled Oats
3.7
2.8
24
Wheat Bran
Corn
1.1
0.4
0.7
0.2
36
50
1Based
on -methylisourea assay; 2P Pellett, N Scrimshaw and P Moughan (unpublished data).
But not so in dairy:
Ileal digestible total and “available” lysine contents (g/kg air-dry) for 12
dairy protein sources
Lysine
Digestible
Availablea
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
Whole milk protein
aBioavailable
lysine; minimal difference between total lysine and reactive lysine denotes minimal Maillard damage.
Adapted from Rutherfurd & Moughan (2005), with permission of the publisher.
14
Amino acids in whey proteins are generally highly
digestible
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
2. 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)
Non truncation is significant
DIAAS
Milk Protein
Concentrate
Whey Protein
Isolate
Whey Protein
Concentrate
Red meat
Non-truncated
1.31
1.25
1.10
1.10
Truncated
1.0
1.0
1.0
1.0
DIAAS and PDCAAS values1 are different.
PDCAAS often overestimates for lower
quality proteins
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
1(Rutherfurd
and Moughan, unpublished data).
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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
Whey
Protein
Concentrate
2.53
Milk Protein
Concentrate
Soya
Protein
Isolate A
Soya
Protein
Isolate B
1.56
1.30
1.13
2.29
1.21
2.22
2.57
1.71
1.71
1.29
2.35
1.93
1.43
1.18
1.55
1.81
1.77
2.39
0.90
1.11
1.59
1.29
1.85
0.91
1.02
1.38
1.13
1.65
1.09
3.35
2.51
0.97
2.74
2.03
1.60
1.94
1.77
1.37
1.67
1.16
1.18
1.69
0.99
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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)