Metabolic Availability of the Limiting Amino Acids Lysine and Tryptophan in Cooked White African Cornmeal Assessed in Healthy Young Men Using the Indicator Amino Acid Oxidation Technique

Lysine from Whole Wheat Bread Consumed by Healthy Adult Males Has High Metabolic Availability When Assessed Using the Indicator Amino Acid Oxidation Method

BACKGROUND

The protein quality of wheat is limited by its low content of the indispensable amino acid (AA) lysine and the metabolic availability (MA) of lysine in wheat bread for humans is unknown.

OBJECTIVES

The study objective was to determine the MA of lysine in whole wheat bread.

METHODS

Five healthy young males (≤30 y, body mass index <25) were studied in a repeated-measures design using the indicator amino acid oxidation (IAAO) method, with L-[1-13C] phenylalanine as the indicator. Each received 7 levels of lysine intakes in random order; 4 levels of L-lysine; 5, 8, 12, and 15 mg/kg/d (reference diet), and 3 intakes of lysine from whole wheat bread (test diet). The MA of lysine in whole wheat bread was assessed by comparing the IAAO response to the test diet (whole wheat bread) with the IAAO response to the reference diet using the slope ratio method.

RESULTS

The MA of lysine from whole wheat bread was 90%.

CONCLUSIONS

Lysine has a high MA but it is still limiting in whole wheat bread due to its low concentration. A combination of wheat with a complementary protein source (that is, lentils which are sufficient in lysine) is recommended to meet the lysine requirement in a wheat-based diet for healthy young males. This trial was registered at clinicaltrials.gov as NCT03674736 and NCT03200652.

Post-prandial tracer studies of protein and amino acid utilisation: what can they tell us about human amino acid and protein requirements?

Nitrogen balance (NB), the principal methodology used to derive recommendations for human protein and amino acid requirements, has been widely criticised, and calls for increased protein and amino acid requirement recommendations have been made, often on the basis of post-prandial amino acid tracer kinetic studies of muscle protein synthesis, or of amino acid oxidation. This narrative review considers our knowledge of the homeostatic regulation of the FFM throughout the diurnal cycle of feeding and fasting and what can and has been learnt from post-prandial amino acid tracer studies, about amino acid and protein requirements. Within the FFM, muscle mass in well fed weight-stable adults with healthy lifestyles appears fixed at a phenotypic level within a wide range of habitual protein intakes. However homoeostatic regulation occurs in response to variation in habitual protein intake, with adaptive changes in amino acid oxidation which influence the magnitude of diurnal losses and gains of body protein. Post-prandial indicator amino acid oxidation (IAAO) studies have been introduced as an alternative to NB and to the logistically complex 24 h [13C-1] amino acid balance studies, for assessment of protein and amino acid requirements. However, a detailed examination of IAAO studies shows both a lack of concern for homeostatic regulation of amino acid oxidation and  major flaws in their design and analytical interpretation, which seriously constrain their ability to provide reliable values. New ideas and a much more critical approach to existing work is needed if real progress is to be made in the area.

Metabolic availability of amino acids in humans

Knowledge of amino acid bioavailability and the effect of combining complementary protein sources are required to determine how to best meet an individual's protein and indispensable amino acid needs. Traditionally, protein quality of foods has been assessed using digestibility data. Digestibility may overestimate bioavailability of some amino acids particularly those more susceptible to heat and processing. The indicator amino acid oxidation (IAAO) method has been validated and applied to determine amino acid bioavailability termed metabolic availability of the first limiting amino acid of a proteinaceous food. The metabolic availability of the limiting amino acid in the test protein is determined as a ratio of the indicator amino acid oxidation response to graded intakes of the test protein compared to the indicator response to a reference protein (crystalline amino acid patterned after egg protein). The IAAO method has also been applied to assess the effect of protein complementation directly in humans on the overall protein quality of the diet. The results demonstrate that protein complementation augments the limiting amino acid supply and increases protein synthesis.

Impact of Processing Methods on the In Vitro Protein Digestibility and DIAAS of Various Foods Produced by Millet, Highland Barley and Buckwheat

Cereals are rich sources of dietary protein, whose nutritional assessments are often performed on raw grains or protein isolates. However, processing and gastrointestinal digestion may affect amino acid (AA) compositions, then change the protein quality. In this study, we determined the digestibility and AA compositions of various foods produced by whole grains (PG) or flour (PF) from three cereals (millet, highland barley and buckwheat) and analyzed the impact of processing methods on the digestible indispensable amino acid score (DIAAS) using the INFOGEST protocol. The in vitro protein digestibility of cereal-based foods was lower than raw grains, and PF showed a better digestion property than PG. The intestinal digestibility of individual AA within a food varied widely, and the digestibility of Cys and Ile was the lowest among all AAs. The DIAAS values of PG were lower than those of PF in each kind of cereal, and PF of buckwheat had the highest DIAAS value, followed by highland barley. The first limiting AA was still Lys for millet and highland barley compared to the raw grains; however, for buckwheat it was Leu. This study provided nutritional information on cereal products and helped to guide the collocation of different foods in diets.

Wool keratin as a novel alternative protein: A comprehensive review of extraction, purification, nutrition, safety, and food applications

The growing global population and lifestyle changes have increased the demand for specialized diets that require protein and other essential nutrients for humans. Recent technological advances have enabled the use of food bioresources treated as waste as additional sources of alternative proteins. Sheep wool is an inexpensive and readily available bioresource containing 95%-98% protein, making it an outstanding potential source of protein for food and biotechnological applications. The strong structure of wool and its indigestibility are the main hurdles to achieving its potential as an edible protein. Although various methods have been investigated for the hydrolysis of wool into keratin, only a few of these, such as sulfitolysis, oxidation, and enzymatic processes, have the potential to generate edible keratin. In vitro and in vivo cytotoxicity studies reported no cytotoxicity effects of extracted keratin, suggesting its potential for use as a high-value protein ingredient that supports normal body functions. Keratin has a high cysteine content that can support healthy epithelia, glutathione synthesis, antioxidant functions, and skeletal muscle functions. With the recent spike in new keratin extraction methods, extensive long-term investigations that examine prolonged exposure of keratin generated from these techniques in animal and human subjects are required to ascertain its safety. Food applications of wool could improve the ecological footprint of sheep farming and unlock the potential of a sustainable protein source that meets demands for ethical production of animal protein.

Evaluation of Protein Quality in Humans and Insights on Stable Isotope Approaches to Measure Digestibility - A Review

The recent Food and Agricultural Organization/World Health Organization/United Nations University expert consultations on protein requirements and quality have emphasized the need for the new Digestible Indispensable Amino Acid Score (DIAAS), as a measure of protein quality. This requires human measurements of the true ileal digestibility of individual indispensable amino acids (IAAs) until the end of the small intestine. Digestibility is measured using standard oro-ileal balance methods, which can only be achieved by an invasive naso-ileal intubation in healthy participants or fistulation at the terminal ileum. Significant efforts have been made over the last 2 decades to develop noninvasive or minimally invasive methods to measure IAA digestibility in humans. The application of intrinsically labeled (with stable isotopes like 13C, 15N, and 2H) dietary proteins has helped in circumventing the invasive oro-ileal balance techniques and allowed the differentiation between endogenous and exogenous protein. The noninvasive indicator amino acid oxidation (IAAO) technique, which is routinely employed to measure IAA requirements, has been modified to estimate metabolic availability (a sum of digestibility and utilization) of IAA in foods, but provides an estimate for a single IAA at a time and is burdensome for participants. The recently developed minimally invasive dual isotope tracer method measures small intestinal digestibility of multiple amino acids at once and is suitable for use in vulnerable groups and disease conditions. However, it remains to be validated against standard oro-ileal balance techniques. This review critically evaluates and compares the currently available stable isotope-based protein quality evaluation methods with a focus on the digestibility and metabolic availability measurements in humans. In view of building a reliable DIAAS database of various protein sources and subsequently supporting protein content claims in food labeling, a re-evaluation and harmonization of the available methods are necessary.

Metabolic Availability of Methionine Assessed Using Indicator Amino Acid Oxidation Method, Is Greater when Cooked Lentils and Steamed Rice Are Combined in the Diet of Healthy Young Men

BACKGROUND

Lentil is considered a high protein source. However, it is low in sulphur amino acids (SAA) and their metabolic availability (MA) is further affected by antinutritional factors in lentils. The combination of lentils with grains such as rice can enhance the protein quality of a lentil-based meal but the MA of SAA in lentils must first be known.

OBJECTIVES

The objectives of the current study were to assess the MA of methionine in lentils and to test the effects of consumption of complementing lentils with rice in young adults.

METHODS

Five healthy young men [age <30 y, BMI <25 (in kg/m2)] were each studied at 8 or 10 intake amounts of methionine in random order; 4 daily intake amounts of l-methionine: 0.5, 1, 2, and 3 mg.kg-1.d-1 (reference diet), 3 daily intake amounts of methionine from lentils, and 3 daily intake amounts of the mixed meal of lentils + rice (test diets). The MA of methionine and the effects of complementation were assessed by comparing the indicator amino acid oxidation (IAAO) response to varying intakes of methionine in cooked Canadian lentils, and in rice + lentils combined, compared with the IAAO response to l-methionine intakes in the reference protein (crystalline AA mixture patterned after egg protein) using the slope ratio method. l-[1-13C] phenylalanine was used as the indicator. Data were analyzed using the procedure "MIXED" with subject as a random variable, and oxidation day as repeated measure.

RESULTS

The MA of methionine from lentils was 69%. Complementation of cooked lentils with rice decreased the oxidation of l-[1-13C] phenylalanine by up to 16% (P < 0.05).

CONCLUSIONS

The content and MA of methionine are low in lentils. However, combination of lentils with rice in a 1:1 ratio can improve the protein quality of lentil-based diets, resulting in increased protein synthesis in young healthy adults. This trial was registered at www.clinical trials.gov as NCT03110913.

Bioavailable Lysine Assessed Using the Indicator Amino Acid Oxidation Method in Healthy Young Males is High when Sorghum is Cooked by a Moist Cooking Method

BACKGROUND

Sorghum is the fifth most consumed cereal grain but limiting in the indispensable amino acid lysine. Complementing sorghum with lentils can improve the quality of sorghum-based diets. However, knowledge of lysine bioavailability in sorghum is lacking.

OBJECTIVES

The study objectives were to determine the bioavailability of lysine in sorghum and to assess the effect of complementation of sorghum and lentils in a mixed-meal format.

METHODS

We studied 5 healthy young men (≤30 years; BMI <25 kg/m2) in a repeated-measure design using the indicator amino acid oxidation (IAAO) method, with L-[1-13C] phenylalanine as the indicator. Each subject participated in 8 determinations in random order. On the reference diet, subjects received 4 amounts of L-lysine (5, 8, 12, and 15 mg. kg-1 . d-1) from a crystalline amino acid mixture patterned after egg protein. On the test diet, they received 3 levels of lysine (8.2, 12.5, and 15.7 mg. kg-1 . d-1) from sorghum, and on the complementation diet they received 1 level of lysine from a mixed meal of sorghum and lentils. The bioavailability of lysine in sorghum was estimated by comparing the IAAO response to the test diet with the IAAO response to the reference diet using the slope-ratio method. Effectiveness of complementation was assessed by comparing the IAAO response to the mixed meal to the IAAO response to the test protein.

RESULTS

The bioavailability of lysine from sorghum was 94%. Upon complementation with lentils, there was a decline in the oxidation of L-[1-13C] phenylalanine by 19% (P < 0.0495), reflecting an improvement in available lysine in the mixed meal due to increased lysine intake.

CONCLUSIONS

Although the bioavailability of lysine in sorghum is high, its lysine content is limiting. Complementation with lentils in a 1:1 ratio is recommended to achieve the lysine requirement for adult men consuming a sorghum-based diet. This trial was registered at clinicaltrials.gov as NCT03411005.

Grains - a major source of sustainable protein for health

Cereal grains are the main dietary source of energy, carbohydrates, and plant proteins world-wide. Currently, only 41% of grains are used for human consumption, and up to 35% are used for animal feed. Cereals have been overlooked as a source of environmentally sustainable and healthy plant proteins and could play a major role in transitioning towards a more sustainable food system for healthy diets. Cereal plant proteins are of good nutritional quality, but lysine is often the limiting amino acid. When consumed as whole grains, cereals provide health-protecting components such as dietary fiber and phytochemicals. Shifting grain use from feed to traditional foods and conceptually new foods and ingredients could improve protein security and alleviate climate change. Rapid development of new grain-based food ingredients and use of grains in new food contexts, such as dairy replacements and meat analogues, could accelerate the transition. This review discusses recent developments and outlines future perspectives for cereal grain use.

Intestinal Exposure to Food-Derived Protease Inhibitors: Digestion Physiology- and Gut Health-Related Effects

Plant-derived protease inhibitors (PI), such as Bowman-Birk inhibitors and Kunitz-type inhibitors, have been suggested to negatively affect dietary protein digestion by blocking the activity of trypsin and chymotrypsin in the human gastrointestinal system. In addition, some PIs may possess proinflammatory activities. However, there is also scientific evidence on some beneficial effects of PIs, for example, gut-related anti-inflammatory and chemopreventive activities in vitro and in vivo. Some PIs are sensitive to processing and digestion; thus, their survival is an important aspect when considering their positive and negative bioactivities. The aim of this review was to evaluate the relevance of PIs in protein digestion in humans and to discuss the potential of PIs from whole foods and as purified compounds in decreasing symptoms of bowel-related conditions. Based on the reviewed literature, we concluded that while the complex interactions affecting plant protein digestibility and bioavailability remain unclear, PI supplements could be considered for targeted purposes to mitigate inflammation and gastric pain.

Multinutrient Biofortification of Maize (Zea mays L.) in Africa: Current Status, Opportunities and Limitations

Macro and micronutrient deficiencies pose serious health challenges globally, with the largest impact in developing regions such as subSaharan Africa (SSA), Latin America and South Asia. Maize is a good source of calories but contains low concentrations of essential nutrients. Major limiting nutrients in maize-based diets are essential amino acids such as lysine and tryptophan, and micronutrients such as vitamin A, zinc (Zn) and iron (Fe). Responding to these challenges, separate maize biofortification programs have been designed worldwide, resulting in several cultivars with high levels of provitamin A, lysine, tryptophan, Zn and Fe being commercialized. This strategy of developing single-nutrient biofortified cultivars does not address the nutrient deficiency challenges in SSA in an integrated manner. Hence, development of maize with multinutritional attributes can be a sustainable and cost-effective strategy for addressing the problem of nutrient deficiencies in SSA. This review provides a synopsis of the health challenges associated with Zn, provitamin A and tryptophan deficiencies and link these to vulnerable societies; a synthesis of past and present intervention measures for addressing nutrient deficiencies in SSA; and a discussion on the possibility of developing maize with multinutritional quality attributes, but also with adaptation to stress conditions in SSA.

Values for Digestible Indispensable Amino Acid Score (DIAAS) Determined in Pigs Are Greater for Milk Than for Breakfast Cereals, but DIAAS Values for Individual Ingredients Are Additive in Combined Meals

BACKGROUND

Breakfast cereals contain low-quality proteins and are often consumed with milk. The digestible indispensable amino acid score (DIAAS) has been used to evaluate protein quality, but it is not known if DIAAS obtained in individual foods is additive in combined meals.

OBJECTIVES

The following hypotheses were tested: amino acids (AAs) in milk complement AAs in breakfast cereals to provide a balanced meal, and DIAAS in individual foods is additive in combined meals.

METHODS

Six ileal cannulated gilts [body weight mean: 55.6 ± 3.7 (SD) kg] were allotted to a 6 × 6 Latin square with six 7-d periods. Ileal digesta were collected for 9 h on days 6 and 7 of each period. Three diets contained a breakfast cereal (i.e., cornflakes or quick oats) or dry milk as the sole source of AAs. Two additional diets contained a combination of dry milk and cornflakes or quick oats. A nitrogen-free diet was also used, and DIAAS was calculated for cornflakes, quick oats, dry milk, and the 2 combined meals for children aged 6 to 36 mo and individuals older than 36 mo through adulthood. For the combined meals, DIAAS was also predicted from the individual ingredient DIAAS.

RESULTS

Dry milk had greater (P < 0.05) DIAAS (123 and 144) than quick oats (57 and 67), but cornflakes had less (P < 0.05) DIAAS (16 and 19) than the other ingredients. Both breakfast cereal-dry milk meals had DIAAS close to or greater than 100 for children aged 6 mo to 3 y and for older children, adolescents, and adults, but there were no differences between measured and predicted DIAAS.

CONCLUSIONS

The combination of milk and breakfast cereals results in a meal that is balanced in indispensable AAs for humans, and DIAAS obtained from individual ingredients is additive in mixed meals.

Determinants of amino acid bioavailability from ingested protein in relation to gut health

PURPOSE OF REVIEW

The current review provides an update on the recent research developments regarding amino acid bioavailability in conditions of both good health and gut disorders.

RECENT FINDINGS

Determination of amino acid bioavailability is complex and invasive. Minimally invasive methods using stable isotopes have been developed for humans. Data were collected in different models - humans, pigs and rats with various procedures - leading to interstudy variability. They mainly focused on either plant protein or the effect of food processing on animal protein. Plant protein in their original food matrix (legumes, grains, nuts) are generally less digestible (about 80%) than animal protein (meat, egg, milk; about 93%). Food processing has a limited impact on animal protein but its effect might be higher on plant protein. Few studies have documented the effect of gut disorders on protein digestibility, except in gastric bypass where paradoxical effects were reported. Data are needed to identify the amplitude of protein malabsorption in diseases such as inflammatory bowel disease or environmental enteric dysfunction.

SUMMARY

The past 5 years have seen a renewed interest in amino acid bioavailability in view of assessing protein quality to support current shifts in protein sourcing. Methodological developments have been performed and several studies have reported values in various models. The question of protein digestibility in gut disorders remains poorly addressed.

Lysine Bioavailability in School-Age Children Consuming Rice Is Reduced by Starch Retrogradation

BACKGROUND

Rice is one of the most commonly consumed cereal grains and is part of staple diets in the majority of the world. However, it is regarded as an incomplete protein, with lysine being a limiting amino acid.

OBJECTIVES

Our objectives were to determine the bioavailability of lysine in school-age children consuming cooked white rice and to assess the effect of rice starch retrogradation.

METHODS

Bioavailability or metabolic availability (MA) of lysine was determined using the indicator amino acid oxidation (IAAO) method in a repeated-measures design. Six healthy school-age children (3 boys, 3 girls) with a mean ± SD age of 6.8 ± 0.98 y randomly received 4 crystalline l-lysine intakes (2, 6, 10, 14 mg · kg-1 · d-1), and 5 rice intakes to provide lysine at 8, 11, or 14 mg · kg-1 · d-1. The 14 mg · kg-1 · d-1 intakes were measured twice as warm rice and once as cold rice (to assess the impact of starch retrogradation on MA). Diets provided protein at 1.5 g · kg-1 · d-1 and calories at 1.7 times the participant's measured resting energy requirement, and were isonitrogenous. Breath samples were collected at baseline and during an isotopic steady state for 13C enrichment measurement. The MA of lysine from rice was determined by comparing the IAAO response of rice with l-lysine using the slope-ratio and single intake methods. Starch retrogradation was characterized using differential scanning calorimetry.

RESULTS

MA of lysine in warm rice measured in school-age children was 97.5% and was similar to a repeated rice study (97.1%) within the same study population. MA of lysine was reduced significantly (P < 0.05) to 86.1% when the cooked rice was consumed cold, which corresponded to detectable starch retrogradation.

CONCLUSIONS

To our knowledge, this is the first study to measure the MA of lysine from rice in school-age children. Although the bioavailability of lysine from rice is high, it can be reduced by retrogradation of its starch component.This trial was registered at clinicaltrials.gov as NCT04135040.

Bioavailable Lysine, Assessed in Healthy Young Men Using Indicator Amino Acid Oxidation, is Greater when Cooked Millet and Stewed Canadian Lentils are Combined

BACKGROUND

Pearl millet is the chief source of energy in the diet in some developing regions, but has a limited amount of indispensable amino acid lysine. Complementation with pulses like lentils can improve the protein quality of millet diets, but the knowledge of lysine bioavailability (BA) in millet and lentils is lacking.

OBJECTIVES

The study objectives were to determine the BA of lysine in millet and lentils separately and to assess the effect of complementation of millet and lentils in a mixed meal format.

METHODS

We studied 9 healthy young men (≤30 y; BMI <25) in a repeated-measure design using the indicator amino acid oxidation (IAAO) method, with L-[1-13C] phenylalanine as the indicator. Each subject completed 7 or 8 experiments in random order. On the reference diet, subjects received 4 graded levels of L-lysine (5, 8, 12, and 15 mg·kg-1.d-1) from a crystalline amino acid mixture patterned after egg protein; on the test diets, they received 3 levels of lysine (10, 12, and 15 mg·kg-1.d-1) from either steamed millet or stewed lentils; and on the complementation diet, they received 1 level of lysine from a mixed meal of steamed millet and stewed lentils. The BA of lysine and the effect of complementation were assessed by comparing the IAAO responses to the test diets and the complementation diet with the IAAO response to L-lysine intakes in the reference protein, using the slope ratio method.

RESULTS

The BA of lysine was 97% from millet and 80% from lentils. Complementation of steamed millet with stewed lentils decreased the oxidation of L-[1-13C] phenylalanine by 27% (P < 0.05), signifying improved quality of the combined millet and lentil protein.

CONCLUSIONS

Lysine has high BA but is still limiting in steamed pearl millet. Complementation with lentils in a 2:1 ratio is recommended to meet the lysine and protein requirements for adult men consuming a millet-based diet. This trial was registered at clinicaltrials.gov as NCT03674736 and NCT03339167.

Metabolic Availability of Lysine in Milk and a Vegetarian Cereal-Legume Meal Determined by the Indicator Amino Acid Oxidation Method in Indian Men

BACKGROUND

Lysine rich foods such as milk and legumes serve as important food additions to the lysine deficient cereal-based diets of vegetarian populations in low- and middle-income countries (LMICs) to alleviate the risk of quality corrected dietary protein inadequacy. Dietary protein quality can be determined by estimating the metabolic availability (MA) of lysine.

OBJECTIVES

The study aimed to estimate the MA of lysine in spray-dried cow milk powder (SMP), heat-treated spray-dried cow milk powder (HSMP), and a habitually consumed cereal-legume based vegetarian meal (VM), using the indicator amino acid oxidation (IAAO) slope-ratio method.

METHODS

The MA of lysine in SMP, HSMP, and VM was estimated in 7 healthy young men aged 19-24 y with BMI of 21.5 ± 0.5 kg/m2 in a repeated measures design. The IAAO response slopes with 2 graded lysine intakes (10.5 and 15.0 mg·kg-1·d-1) from the SMP and VM were compared with the response slope generated with 3 graded crystalline lysine intakes (6.0, 10.5, and 15.0 mg·kg-1·d-1) at the subrequirement level. To produce HSMP, pasteurized cow milk was heat treated and spray dried. The MA of lysine in HSMP was tested at a single level of lysine intake (15 mg·kg-1·d-1). A total of 8 IAAO experiments were conducted on each participant in randomized order. The IAAO slopes were estimated using a linear mixed-effect regression model.

RESULTS

The MA of lysine in SMP, HSMP, and VM was 91.9%, 69.9%, and 86.6% respectively.

CONCLUSIONS

Heat treatment reduced the MA of lysine by 22% in HSMP compared with SMP in healthy Indian adults. The lysine MA estimates can be used to optimize lysine limited cereal-based diets, with the addition of appropriately processed legumes and milk powder, to meet the protein requirement. This trial was registered at Clinical Trials Registry of India (http://ctri.nic.in) as CTRI/2019/08/020568.

Methionine Nutrition and Metabolism: Insights from Animal Studies to Inform Human Nutrition

Methionine is a nutritionally indispensable amino acid, and is unique among indispensable amino acids due to its sulfur atom. Methionine is involved in cysteine synthesis via the transsulfuration pathway, which is rate limiting for the key antioxidant molecule, glutathione. Methionine is also the primary methyl donor in the body through S-adenosylmethionine via the transmethylation pathway, which is involved in the synthesis of several key metabolites including creatine and phosphatidylcholine. Methionine can also be remethylated from homocysteine, in the presence of betaine via choline and/or folate. Thus methionine demands from a dietary perspective are regulated not only by the presence of cysteine in the body, but also by the demands in vivo for the various metabolites formed from it, and also by the presence of these compounds in foods. Indeed, methionine, cysteine, and the various methyl donors/acceptors vary in human foods, and thus regulate methionine availability, especially under conditions of growth and development. Much of our understanding of methionine nutrition and metabolism arises from experiments in animal models. This is because most animal feed formulations are plant-based and plant sources are relatively low in methionine and cysteine amounts. Thus, this brief review will touch on some broad aspects of human methionine nutrition, including requirements in different life stages, disease, and bioavailability, with some examples from the insights/lessons learned from experiments initially conducted in animals.

Bioavailable Methionine Assessed Using the Indicator Amino Acid Oxidation Method Is Greater When Cooked Chickpeas and Steamed Rice Are Combined in Healthy Young Men

BACKGROUND

In general, pulse protein is limiting in the indispensable amino acid methionine, and antinutritional factors in pulses can affect methionine bioavailability. Complementation with grains such as rice can improve pulse protein quality, but knowledge of methionine bioavailability in pulses and grains is necessary to correct for available methionine when planning and assessing dietary protein intake.

OBJECTIVES

The study objectives were to determine the bioavailability of methionine in rice and chickpeas separately and to assess the effect of complementation of chickpeas and rice.

METHODS

Eleven healthy young men (<30 y, BMI <25 kg/m2) were studied in a repeated-measures design using the indicator amino acid oxidation (IAAO) method, with l-[1-13C]phenylalanine as the indicator. Each received 7 or 10 methionine intakes in random order: 4 intakes of l-methionine-0.5, 1, 2, and 3 mg⋅kg-1⋅d-1 (reference diet); 3 intakes of methionine from rice and from chickpeas; and 3 intakes from the mixed meal of chickpeas plus rice (test diets). The bioavailability of methionine and the effect of complementation were assessed by comparing the IAAO response to varying intakes of methionine in rice, in cooked Canadian chickpeas, and in rice plus chickpeas combined compared with the IAAO response to l-methionine intakes in the reference protein (crystalline amino acid mixture patterned after egg protein) using the slope ratio method.

RESULTS

The bioavailability of methionine from rice and from chickpeas was 100% and 63%, respectively. Complementation of cooked chickpeas with rice decreased the oxidation of l-[1-13C]phenylalanine by up to 14% (P < 0.05), suggesting an improved protein quality of the combined chickpeas plus rice protein.

CONCLUSIONS

When chickpeas are the main protein source in the diet of young adult men, the combination of rice and chickpeas in a 3:1 ratio is recommended to improve dietary protein quality. This trial was registered at clinicaltrials.gov as NCT03339154 and NCT03674736.

Harnessing Microbes for Sustainable Development: Food Fermentation as a Tool for Improving the Nutritional Quality of Alternative Protein Sources

In order to support the multiple levels of sustainable development, the nutritional quality of plant-based protein sources needs to be improved by food technological means. Microbial fermentation is an ancient food technology, utilizing dynamic populations of microorganisms and possessing a high potential to modify chemical composition and cell structures of plants and thus to remove undesirable compounds and to increase bioavailability of nutrients. In addition, fermentation can be used to improve food safety. In this review, the effects of fermentation on the protein digestibility and micronutrient availability in plant-derived raw materials are surveyed. The main focus is on the most important legume, cereal, and pseudocereal species (Cicer arietinum, Phaseolus vulgaris, Vicia faba, Lupinus angustifolius, Pisum sativum, Glycine max; Avena sativa, Secale cereale, Triticum aestivum, Triticum durum, Sorghum bicolor; and Chenopodium quinoa, respectively) of the agrifood sector. Furthermore, the current knowledge regarding the in vivo health effects of fermented foods is examined, and the critical points of fermentation technology from the health and food safety point of view are discussed.

Protein Quality Assessment of Follow-up Formula for Young Children and Ready-to-Use Therapeutic Foods: Recommendations by the FAO Expert Working Group in 2017

The FAO of the UN convened an Expert Working Group meeting to provide recommendations related to protein quality evaluation of Follow-up Formula for Young Children (FUF-YC) and Ready-to-Use Therapeutic Foods (RUTFs). The protein and amino acid (AA) scoring patterns for the target age groups were defined and recommendations provided on the use of currently available protein and indispensable AA digestibility data. For FUF-YC, an age category of 1-2.9 y was identified, and a matching protein requirement of 0.86 g · kg-1 · d-1 with corresponding AA requirements were recommended. For RUTF, the protein requirement recommended was 2.82 g · kg-1 · d-1, to achieve a catch-up weight gain of 10 g · kg-1 · d-1 in children recovering from severe acute malnutrition. The AA requirements were factorially derived based on the adult protein requirement for maintenance and tissue AA composition. A flowchart was proposed for the best available methods to estimate digestibility coefficients (of either protein or AAs), in the following order: human, growing pig, and rat true ileal AA digestibility values. Where this is not possible, fecal protein digestibility values should be used. The Expert Working Group recommends the use of the Protein Digestibility Corrected Amino Acid Score (PDCAAS), with existing protein digestibility values, or the Digestible Indispensable Amino Acid Score provided that individual AA digestibility values are available for protein quality evaluation using the latter score. The Group also recommends the use of ileal digestibility of protein or of AAs for plant-based protein sources, recognizing the possible effects of antinutritional factors and impaired gut function. A PDCAAS score of ≥90% can be considered adequate for these formulations, whereas with a score <90%, the quantity of protein should be increased to meet the requirements. Regardless of the protein quality score, the ability of formulations to support growth in the target population should be evaluated. Future research recommendations are also proposed based on the knowledge gaps identified.

Protein quality & amino acid requirements in relation to needs in India

The relevance of protein and its constituent amino acids (AAs) in the structure and function of the human body is well known. Accumulating evidence has conferred specific functional and regulatory roles for individual AAs, adding relevance to their requirements across different age groups. The methods for measuring AA requirements have progressed from the classical nitrogen balance to the current stable isotope-based AA balance methods. Requirements of most of the indispensable AA (IAA) have been estimated in healthy Indian population by the best available balance method and has shown to be higher than earlier 1985 WHO/FAO/UNU (World Health Organization/Food and Agriculture Organization/United Nations University) recommendations. In addition, potential changes in the requirement, through adaptation to chronic undernutrition or to infection, have also been evaluated. In 2007, the WHO/FAO/UNU released a recommendation that increased the daily IAA requirement, based on primary evidence from Indian balance studies. This meant that to ensure that the new IAA requirements were met, individual foods or mixed diets needed to be assessed for their protein quality, or their ability to deliver the required amount of IAA. The recent FAO report on protein quality evaluation recommends the use of a new chemical AA score, the digestible IAA score (DIAAS), to replace the earlier protein digestibility corrected AA score. The DIAAS requires the determination of individual AA digestibility at the ileal level. A minimally invasive dual stable isotope tracer-based approach has been developed in India and has been used to determine digestibility of various foods in Indian adults and children. The increase in IAA requirements and subsequent protein quality requirements have implications for national regulatory frameworks, growth and development, and in turn, for economic and agricultural policy.