Evaluation of standardized ileal digestibility of amino acids and metabolic availability of methionine, using the indicator amino acid oxidation method, in black soldier fly larvae (Hermetia illucens) meal fed to growing pigs

Standardized ileal digestibility (SID, %) of crude protein (CP) and amino acid (AA) and the metabolic availability (MA) of Met using the indicator amino acid oxidation (IAAO) method, in partially defatted black soldier fly larvae (PD-BSFL) meal were determined in growing pigs in 2 experiments. The Met SID value was then compared numerically with the Met MA to understand how different SID is compared with its MA value. In Exp. 1, 6 ileal-cannulated barrows (initial body weight [BW] = 18.03 ± 0.34 kg) were used in a 2-period switch back design and fed either a nitrogen-free diet (NFD) or test diet, with PD-BSFL meal as the sole source of AA, over two 11-d experimental periods, at a feeding level of 2.8 × estimated maintenance digestible energy requirement. Barrows were adapted for 9-d to the diet, followed by continuous 8-h ileal digesta collection on day 10 and 11. Digesta were pooled per pig within period. The SID of CP and Met of PD-BSFL meal were 76.1 ± 6.2% and 90.4 ± 3.9%, respectively. In Exp. 2, 7 barrows (initial BW = 18.77 ± 0.69 kg) were used in a 7 × 7 Latin square design with L-[1-13C]-Phe as the indicator AA. Each pig was randomly assigned to 1 of 7 dietary treatments over seven 3-d experimental periods. Two diet types were studied including reference (crystalline AA) and PD-BSFL test diets, each supplying graded intakes of Met at 55, 65, and 75% of the estimated SID requirement (NRC, 2012). The MA of Met was determined by comparing the IAAO response between the reference and PD-BSFL test diet using the slope-ratio method. Linear regression determined a negative slope of the best fit line for both the reference and test diets (P < 0.05). The MA of Met in PD-BSFL meal was 53.3%, which is as expected lower than the SID value. While it is generally appreciated that MA will be less than SID, the use of SID is more practical. In cases where SID cannot explain physiological outcomes of feeding a novel ingredient, IAAO may provide additional insight into whether MA should be explored.

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.

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.

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.

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.

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.