Assessing protein quality

Transcription

1 Assessing protein quality Toon van Hooijdonk IDF/ISO Analytical Week June 5, 2013, Rotterdam

2 Food security: a massive challenge UN Food & Agriculture Organisation (FAO) Int Energy Agency (IEA) Int Food Policy Research

3 Outlook towards billion people more in 2050 Food demand increases by more than 50% (1.1 %/year) Undernourishment is still at a level 300 million people There is a shift towards more animal products in the diet Milk demand increases from 704 billion kg in 2012 to 1077 billion kg in 2050

4 Importance of protein for food security Protein: the limiting macronutrient for food security FAO 2013 As the world s population increases rapidly and against the constraints of limiting land, water and food resources, it is more important than ever to be able to define accurately the amount and quality of protein required to meet human nutritional needs

5 Protein intake per capita is rising Protein consumption kg/per person/year Animal protein Total protein Area Incr Incr. World % % Developed countries % % Latin America % % Near east % % Sub-Saharan Africa % % Developing Asia % % Source: FAO 2006

6 Animal products are a part of the nutrient security solution On a global basis, livestock products provide 17% of the energy and 35% of the protein in the human diet But, large variation per region: More animal products in the diet of low intake countries leads to an improved growth, cognitive development and health In high intake countries animal products also contribute to adverse effects, mainly caused by excessive energy intake

7 Animal products are an important source of protein Energy and protein supply by Animal products Dairy and meat products in the Dutch diet 70% developed countries developing countries Dairy meat 60% 50% 40% 30% 27% 56% 26% 70% 60% 50% 40% 30% 34% 20% 10% 0% 11% Energy Protein 20% 10% 0% 13% 15% Energy 25% Protein Source: FAO, 2011 Source: Voedingscentrum, VCP 2003

8 Protein requirements The human body does not have significant stores of protein and the food needs to provide protein daily Protein intake should be sufficient to sustain growth and maintenance Protein requirement is depended on age and physiological condition Infants, pregnant women, recovering people and elderly have higher requirements due to growth and tissue repair Protein requirement is based on nitrogen balance studies and expressed per kg body weight

9 Protein requirements: input and output in balance Negative N balance: => tissue breakdown Positive N balance: => tissue build-up Not all amino acids are equal Source: WHO Technical Report Series 935

10 A one way input and a multiple way output Source: FAO Food and Nutrition Paper 92

11 Protein quality counts The amount of protein needed to obtain a N-balance and optimal growth/recovery depends on the quality of the protein The main determinant for nutritional quality is the amount of indispensible amino acids (IAA s) in a dietary protein. The closer the IAA pattern of a protein resamples the human IAA requirements the higher its quality is. Different methods to asses protein quality as been adopted over the years Biological assays Chemical assays Mixed assays (chemical + biological)

12 Methods to assess protein quality Biological assays Biological Value (BV): based on N-retention Net Protein Utilisation (NPU): based on N-retention Protein Efficiency ratio (PER): based on growth rate of rats Chemical assays Chemical score (CS): based on the most limiting IAA against egg protein. Amino Acid Score (AAS): based on the most limiting IAA against a human reference requirement pattern Mixed assays Protein digestibility corrected amino acid score (PDCAAS) Digestible indispensible amino acid score (DIAAS)

13 From PDCAAS to DIAAS Since 1991 the PDCAAS has been proposed by the FAO/WHO as the preferred method to assess protein quality From a regulatory perspective, both public needs and the economic impact of protein quality characterization are important in the selection and approval of methods for assessing protein quality Early 2013 an expert consultation of the FAO recommended to implement DIAAS as the replacement for PDCAAS...the DIAAS approach is more likely to enable accurate prediction of dietary protein quality than PDCAAS....

14 Human protein and IAA requirements are the basis of the reference patterns for PDCAAS and DIAAS Protein and IAA requirements are age depended The IAA reference pattern for a particular age category is obtained by dividing the IAA requirements (mg/per kg body weight/day) with the total protein requirement (g/per kg body weight/day) and expressed as mg/g protein The IAA reference pattern for infants is based on the composition of human milk The overall quality of a protein is determined by the most limiting IAA compared to a reference pattern = AAS AAS is corrected for digestibility which is based on a biological assay

15 PDCAAS of different food proteins Amino acid mg/g protein Reference pattern Milk Beef Soy Wheat Egg Isoleucine Leucine Lysine Methionine + Cystine Phenylalanine + Tyrosine Threonine Tryptophan Valine AAS Digestibility (faecal) , PDCAAS (D x AAS) Reference pattern: all other ages AAS = limiting AA divided by reference PDCAAS values above 1 are truncated to 1.00

16 Differences between assay types In all assays animal proteins have a higher quality than plant proteins Protein BV NPU PER D AAS PDCAAS* PDCAAS Egg Cow s milk Beef Soy Wheat * Not truncated Source: Schaafsma (2000) J Nutr

17 Amino acid reference requirements patterns are not the same for PDCAAS and DIAAS Protein and amino acid requirements are determined by N- balance studies in humans. Protein requirement is based on the minimal amount of a complete high quality protein (mostly egg protein) to obtain N-balance In the case of PDCAAS the average protein requirement is increased by the SD to the so called safe level of protein intake (0.75 g/kg for adults) => this lowers the values of all IAA in the reference requirement pattern. DIAAS uses the mean level of protein intake (0.66 g/kg for adults)

18 Slightly different IAA patterns for PDCAAS and DIAAS PDCAAS IAA patterns Amino acid mg/g protein Infants Reference patterns All other ages His 26 (19) Ile Leu Lys Met + Cys Phe + Tyr Thr Trp Val Source: FAO 1991, report 51 DIAAS IAA patterns Amino acid mg/g protein Infants Reference patterns* All other foods** His Ile Leu Lys Met + Cys Phe + Tyr Thr Trp Val *patterns for regulatory purposes ** = pattern for age 0,5 3 y Source: FAO 2013, report 92

19 Other important differences between DIAAS and PDCAAS Digestibility assay Correction in PDCAAS is for true faecal digestibility of crude protein in rats, whereas in DIAAS the correction is for true ileal digestibility of individual amino acids in humans or pigs No truncation for ingredients DIAAS values are not truncated to 1.00 showing the excess quality of animal proteins Effect of processing Available lysine is basis for content and digestibility calculations Calculation procedure PDCAAS = D x Lim-AA/Ref-AA DIAAS = Lim-DxAA/Ref-AA

20 Correction for digestibility is the most serious shortcoming in the PDCAAS method Amino acids are absorbed in the small intestine and should be measured at the end (ileum). No absorption in the hindgut Crude protein digestibility is not the same as IAA digestibility For many processed foods conventionally determined lysine are in error leading to wrong digestibility values Microbial N losses are interfering with faecal digestibility determination

21 Rationale: digestive AA are absorbed before the ileum In humans digesta can be collected using: Ileostomates naso-ileal tube Both have drawbacks and are not routine An animal model needed Source: WikiCommons

22 The pig is the best model for humans Source: Stein Monogastric Nutrition Laboratory, University of Illinois at Urbana-Champaign

23 Differences between ileal and faecal digestibility Digestibility in humans Amino acid Ileal Faecal Difference Glycine ** Serine ** Methionine ** Tryptophan * * p<0.01 ** p<0.001 Source: Rowan et al (1994) Br J Nutr

24 Variability in ileal digestibility Source: subcommittee report Protein Quality Evaluation in Human Nutrition FAO, 2011

25 Source: Rutherfurd (2006) J Agric Food Chem & Moughan, IDF world dairy summit 2012 Effect of processing on lysine digestibility Total digestible and reactive available digestible lysine in different processed products Product Digestible Lysine Available Lysine Difference (%) Shredded wheat Puffed rice Rolled Oats Wheat Bran Corn Whole milk protein WPC UHT milk

26 DIAAS for whole milk powder Amino acid mg/g protein DIAAS Reference patterns Infants Others* Milk powder IAA D digestibility D x IAA DIAAS Child Infants His Ile Leu Lys Met + Cys Phe + Tyr Thr Trp Val * Regulatory pattern to be used for all ages except infants Source: FAO 2013, report 92

27 PDCAAS versus DIAAS, some first results PDCAAS and DIAAS values for some protein sources Product PDCAAS DIAAS Wheat Beans Milk Source: FAO Food and Nutrition Paper 92 & Schaafsma (2000) Br J Nutr.

28 DIAAS and nutritional labelling Both quantity and quality counts. Quantity: Nutrient reference value (NRV) for protein is 50 g Source 10% of NRV per 100 g solids and 5% of NRV per 100 ml liquids; 5% of NRV per 100 kcal or 10 of NRV per serving High two times the value for source Quality: thresholds/statements for protein quality DIAAS cut-off values for source (75-99) and high (>100) No claims for DIAAS below (e.g.75) Quality Statement allowed source of quality protein DIAAS substitute foods not lower than the real food Source: FAO Food and Nutrition Paper 92 & Schaafsma (2000) Br J Nutr.

29 DIAAS and nutritional labelling Product Amount Protein g/100g DIAAS Judged quality Eligible for claim based on quantity Wheat 100 g Low Yes, high Peas 100 g Low Yes, high WMP 100 g High Yes, high Eligible for claim based on quantity and quality No, none No, none Yes, high Source: FAO, protein quality evaluation in human nutrition

30 DIAAS favourable for animal proteins Advantages for dairy proteins No truncation better shows the ability of dairy proteins to complement low quality proteins More emphasis on all essential amino acids, where dairy is providing relatively large amounts of several essential amino acids True ileal digestibility better shows the high bio-availability of dairy proteins Room for nutritional claims

31 Recommendations by the FAO 2013 Consultation 1. In dietary protein quality evaluation, dietary amino acids should be treated as individual nutrients and wherever possible data for digestible or bioavailable amino acids should be given in food tables on an individual amino acid basis. 2. A new protein quality measure (digestible indispensable amino acid score; DIAAS) is recommended to replace PDCAAS. 3. That for foods susceptible to damage from processing, reactive lysine content for content and the true ileal digestibility in the calculation of DIAAS. 4. DIAAS to be used for regulatory purposes with two scoring patterns as reference: infants and other ages (= pattern for young child)

32 For DIAAS implementation the Consultation recommended 1. To develop the experimental protocol of assessing ileal digestibility 2. To review AA analysis methodologies and to guide international standardisation 3. To undertake research for the development of a DIAAS data set. Research to be funded by private sector and governmental agencies 4. Until a sufficient data set on ileal digestibility is available, protein quality should be assessed by DIAAS using faecal digestibility 5. To formulate guidelines for nutrition claims

33 Thank you for your attention! Thanks to Kasper Hettinga for his contribution