Lysine Bioavailability Research Articles

Milk protein glycation compromises post-prandial bioavailability of protein-derived lysine in vivo in men

Milk protein glycation compromises post-prandial bioavailability of protein-derived lysine in vivo in men

Digestible indispensable amino acid score (DIAAS): 10 years on.

The objective of the review is to revisit the findings of the 2011 Food and Agriculture Organization of the United Nations (FAO) Expert Consultation on Dietary Protein Quality Evaluation in Human Nutrition, and to report on progress on uptake of the findings. It is evident that since 2011 there has been a concerted research effort to enhance an understanding of the protein quality of foods. The validity of the growing pig ileal protein digestibility assay has been confirmed and numerous studies reported using the growing pig as a model to give true ileal amino acid digestibility values for foods as consumed by humans. This has allowed for the determination of digestible indispensable amino acid scores (DIAAS) for a range of foods. A new non-invasive true ileal amino acid digestibility assay in humans which can be applied in different physiological states, called the dual-isotope assay, has been developed and applied to determine the DIAAS values of foods. It is concluded that DIAAS is currently the most accurate score for routinely assessing the protein quality rating of single source proteins. In the future, the accuracy of DIAAS can be enhanced by improved information on: the ideal dietary amino acid balance including the ideal dispensable to indispensable amino acid ratio; dietary indispensable amino acid requirements; effects of processing on ileal amino acid digestibility and lysine bioavailability. There is a need to develop rapid, inexpensive in vitro digestibility assays. Conceptual issues relating DIAAS to food regulatory claims, and to holistic indices of food nutritional and health status are discussed. The first recommendation of the 2011 Consultation regarding treating each indispensable amino acid as an individual nutrient has received little attention. Consideration should be given to providing food label information on the digestible contents of specific indispensable amino acids.

Measuring bioavailability, utilization, and excretion of rumen-protected lysine in lactating cows using an isotope technique

Supplementing a diet with rumen-protected amino acids (AAs) is a common feeding strategy for efficient production. For a cost-effective use of rumen-protected AA, the accurate bioavailability of rumen-protected amino acids should be known and their metabolism after absorption needs to be well understood. The current study determined the bioavailability, absorption, utilization, and excretion of rumen-protected Lys (RP-Lys). Four ruminally cannulated cows in a 4 × 4 Latin square design (12 d for diet adaptation; 5 or 6 d for total collections) received the following treatments: L0, a basal diet; L25, the basal diet and L-Lys infused into the abomasum to provide 25.9 g/d L-Lys; L50, the basal diet and L-Lys infused into the abomasum to provide 51.8 g/d L-Lys; and RPL, the basal diet supplemented with 105 g/d (as-is) of RP-Lys to provide 26.7 g of digestible Lys. During the last 5 or 6 d in each period, 15N-Lys (0.38 g/d) was infused into the abomasum for all cows to label the pool of AA, and the total collection of milk, urine, and feces were conducted. 15N enrichment of samples on d 4 and 5 were used to calculate the bioavailability and Lys metabolism. We used a model containing a fast AA turnover (≤ 5 d) and slow AA turnover pool (> 5 d) to calculate fluxes of Lys. The Lys flux to the fast AA turnover pool (absorbed Lys + Lys from the slow AA turnover pool to fast AA turnover pool) was calculated using 15N enrichment of milk Lys. The flux of Lys from the fast AA turnover pool to milk and urine was calculated using 15N transfer into milk and urine. Then, absorbed Lys was estimated by the sum of Lys flux to milk and urine assuming no net utilization of Lys by body tissues. Duodenal Lys flow was estimated by 15N enrichment of fecal Lys. The bioavailability of RP-Lys was calculated from duodenal Lys flows and Lys absorption for RPL. Increasing Lys supply from L25 to L50 increased Lys utilization for milk by 9 g/d but also increased urinary excretion by 10 g/d. For RPL, absorbed Lys was estimated to be 136 g/d where 28 g of absorbed Lys originated from RP-Lys. In conclusion, 68% of bioavailability was obtained for RP-Lys. The Lys provided from RP-Lys was not only utilized for milk protein (48%) but also excreted in urine (20%) after oxidation.

E. coli biosensor based on modular GFP and luxI/luxR cyclic amplification circuit for sensitive detection of lysine.

In this study, an E. coli biosensor based on modular green fluorescent protein and luxI/IuxR cycle amplification circuit was constructed for sensitive detection of bioavailable lysine. The results indicated that the luxI/IuxR positive feedback circuit based on quorum sensing can be used as a signal amplifier to improve the sensitivity to lysine detection with the detection limit of 256 nM. The presented method was more sensitive than the previously reported whole-cell fluorescent microbial biosensors. In addition, the developed E. coli biosensor was specific for lysine detection, and other amino acids and proteins did not cause any interference. The constructed genetic engineered biosensor was accurate for lysine detection, the lysine content of 6.87 ± 0.36% in tryptone was successfully measured, and after adding 10, 30, and 50 μM lysine in tryptone, the recoveries of 109.98 ± 10.44%, 103.88 ± 7.66%, and 105.89 ± 6.34% were obtained, respectively. Furthermore, as the design of the genetic engineered biosensor is modular, it can conceivably be utilized as a component in the design of more complex synthetic gene circuits without any changes to the amplifier and reporter system.

129 Protein and Amino Acid Modifications During Extrusion

Abstract Extrusion cooking is a high-temperature, short-time process and the foremost technique to produce attractive, nutritious and safe pet foods. As extruded foods are often routinely fed throughout the entire life of pet dogs and cats, it is important to understand the factors that influence protein quality. Protein quality, i.e. the quantity and bioavailability of amino acids, depends on the ingredients and the combination of interrelated process parameters including moisture, temperature, pressure, and mechanical shear. Few studies on the effects of extrusion of pet foods are available and both positive and negative effects on the bioavailability of proteins and amino acids were noted. Effects can in part relate to changes in the food matrix rendering proteins available for digestive enzymes. Moreover, various molecular transformations and chemical reactions can occur including denaturation, aggregation, Maillard reaction, cross-linking, oxidation, and racemisation. Denaturation of proteins is likely not important for facilitating digestion, but denaturation of enzyme inhibitors is key for plant-based pet foods as well as the reduction or elimination of non-protein anti-nutritional factors. It is clear that both ingredient selection and extrusion process parameters impact changes in quantities of bioavailable lysine via the Maillard reaction. The supply of reactive lysine can be insufficient for growing dogs and should be monitored. Bioavailability of methionine and cysteine can also be compromised due to oxidation during processing but is currently understudied. As with studies on lysine, specific analytical procedures should be applied to prevent overestimation of methionine and cysteine in pet foods. In conclusion, the extrusion is a complex process that can impact protein quality in many ways and to various degrees and more studies are required to advance our understanding of the exact underlying molecular mechanisms and to assure the quality of pet foods.

Metabolic Fate Is Defined by Amino Acid Nature in Gilthead Seabream Fed Different Diet Formulations.

Simple SummaryThe maximisation of fish growth depends on amino acids’ availability in tissues at an optimum ratio since imbalances may lead to their utilisation for energy rather than growth. Amino acids may be catabolised in multiple pathways and be classified according to their metabolic fate: ketogenic and glucogenic. Ketogenic amino acids (e.g., lysine) are precursors of ketone bodies or long chain fatty acids and can be used in lipogenesis. Glucogenic amino acids (e.g., methionine) can be converted into glucose through gluconeogenesis. Some amino acids, such as tryptophan, can be ketogenic and glucogenic. This study aimed to evaluate how fish discriminate among different amino acids when they are fed different diets to attain the best utilisation of the feed. This trial was carried out in gilthead seabream juveniles fed experimental diets containing different levels of protein and/or distinct lipid levels. The metabolic fate and bioavailability of the indispensable amino acids lysine, methionine, and tryptophan were defined by their ketogenic and/or glucogenic nature rather than diet formulations. The optimisation of diets that consider the amino acids’ bioavailability will maximise protein retention in fish and is a viable solution to develop cost-effective fish diets.The sustainability of the Aquaculture industry relies on optimising diets to promote nitrogen retention and maximise fish growth. The aim of this study was to assess how different dietary formulations influence the bioavailability and metabolic fate of distinct amino acids in gilthead seabream juveniles. Amino acids (lysine, tryptophan, and methionine) were selected based on their ketogenic and/or glucogenic nature. Seabream were fed practical diets with different protein (44 and 40%) and lipid contents (21 and 18%): 44P21L, 44P18L, 40P21L, and 40P18L. After three weeks of feeding, the fish were tube-fed the correspondent diet labelled with 14C-lysine, 14C-tryptophan, or 14C-methionine. The amino acid utilisation was determined based on the evacuation, retention in gut, liver, and muscle, and the catabolism of the tracer. The metabolic fate of amino acids was mainly determined by their nature. Tryptophan was significantly more evacuated than lysine or methionine, indicating a lower availability for metabolic purposes. Methionine was more retained in muscle, indicating its higher availability. Lysine was mainly catabolised, suggesting that catabolism is preferentially ketogenic, even when this amino acid is deficient in diets. This study underpins the importance of optimising diets considering the amino acids’ bioavailability and metabolic fate to maximise protein retention in fish.

Amino Acid Metabolism in Gilthead Seabream Is Affected by the Dietary Protein to Energy Ratios

The dietary protein to energy ratio (P/E) has proven to influence protein utilization and/or growth in several fish species. This study intended to unravel the bioavailability and metabolic fate of lysine and methionine in gilthead seabream (Sparus aurata) juveniles fed plant diets with different P/E ratios. Seabream juveniles were fed two isonitrogenous diets (45% crude protein) differing in crude lipids (20 and 14%): LowP/E ( P / E ratio = 20.0 mg protein k J − 1 ) and HighP/E ( P / E ratio = 21.4 mg protein k J − 1 ). After three weeks, fish ( 11.6 ± 4.3 g ) were tube-fed the respective diet labelled with 14C-protein (L-amino acid mixture), 14C-lysine, or 14C-methionine. Protein, lysine, and methionine utilization were determined based on the proportion of 14C-amino acid evacuated, retained in the free or protein-bound fraction of liver and muscle, or catabolized. This study revealed that a decrease in P/E ratio resulted in lower amino acid evacuation (p <0.05), contributing to a more efficient amino acid uptake. Results indicate that amino acids are retained as protein in the liver and not only temporarily available in the free pool. The amount of free amino acids retained in the muscle of LowP/E fed fish was significantly higher than in HighP/E fish ( p < 0.05 ) due to a simultaneous higher retention of lysine and methionine, without affecting the overall protein retention. Methionine catabolism was significantly lower than lysine or protein independently of the P/E ratio ( p < 0.05 ), reinforcing that this amino acid is preferentially spared for metabolic functions and not used as energy source. In contrast, increasing the dietary P/E ratio decreased lysine catabolism and increased its availability for growth. The bioavailability and metabolism of individual amino acids should be considered when optimizing P/E ratios in diets for gilthead seabream juveniles. Formulating diets with optimum P/E ratios will improve diet utilization and fish performance.

51 Supplemental Lysine in Finishing Cattle Diets

Abstract Smartamine ML (Adisseo), a bioavailable (80%) source of lysine and methionine was used to evaluate effects of increasing lysine supply on performance of beef cattle. Crossbred steers (n=120, initial BW 261 kg) were individually fed a diet of 15% modified distillers grains plus solubles (MDGS), 68% blend of high moisture and dried rolled corn, 12% corn silage, and 5% supplement with Smartamine ML top-dressed daily. Steers were assigned to 8 inclusions of lysine, 0 to 7 g/d in 1 g increments, with 15 steers per treatment. Data were analyzed with MIXED procedure of SAS as a generalized randomized design with animal as experimental unit and treatment as fixed effect. Orthogonal contrasts evaluated linear, quadratic, and cubic responses. Contrast statements compared the control with 1, 2, and 3 g/d treatments. Feeding increasing amounts of bioavailable lysine linearly decreased DMI (P = 0.04), final live BW (P = 0.04), and ADG (P = 0.02) with no effect on G:F (P ≥ 0.27). Numerical differences in DMI and ADG (P ≥ 0.26) led to a trend (P = 0.06) for improved live G:F for the 1 g/d treatment compared with control (0.188 and 0.176, respectively). During the Optaflexx feeding period (d 163-195), DMI linearly decreased (P = 0.01) as lysine increased in the diet with no differences in ADG (P ≥ 0.13) or G:F (P ≥ 0.12), with a trend (P = 0.08) for improved live G:F for 3 g/d compared with control (0.163 and 0.131, respectively). Hot carcass weight tended (P = 0.07) to linearly decrease as Smartamine ML increased in the diet, with no effect on other carcass measures including longissimus muscle area, 12th rib fat, and marbling score (P ≥ 0.18). In finishing beef cattle diets with 15% MDGS, more than 3 g/d of supplemental lysine did not improve performance.

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

BackgroundSorghum 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. ObjectivesThe 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. MethodsWe 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. ResultsThe 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. ConclusionsAlthough 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 http://www.clinicaltrials.gov clinicaltrials.gov as NCT03411005.

Determination of Isothiocyanate-Protein Conjugates in a Vegetable-Enriched Bread.

Vegetables of the plant order Brassicales are believed to have health-promoting properties, as they provide high contents of glucosinolates (GLS) and deriving from these, enzymatically and heat-induced breakdown products, such as isothiocyanates (ITC). Besides their positive physiological effects, ITC are electrophilic and can undergo reactions with food components such as proteins. Following the trend of improving traditional food products with GLS-rich ingredients, interactions of ITC with proteins can diminish the properties of both components—protein’s value and functionality as well as ITC’s bioactivity. In vegetable-enriched bread, where cresses (Lepidium sativum L. or Tropaeolum majus L.) are added to the initial dough, together with benzyl cyanide, benzyl isothiocyanate (BITC) is formed during the baking process. The aim of the present study was to investigate the possible migration behavior of the GLS breakdown products and the formation of ITC-wheat protein conjugates. After the baking process, the breads’ proteins were enzymatically hydrolyzed, and the ITC-amino acid conjugates analyzed using a LC-ESI-MS/MS methodology. In all samples, BITC-protein conjugates were detected as thiourea derivatives, while formation of dithiocarbamates could not be detected. The study showed that GLS and their breakdown products such as ITC migrate into the surrounding food matrix and undergo reactions with proteins, which could in turn lead to modified protein properties and reduce the bioavailability of ITC and lysine.

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

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. 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. 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±0.98y 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. 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. 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

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. 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. 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. 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. 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.

Bioavailability of rumen-protected methionine, lysine and histidine assessed by fecal amino acid excretion

The objective of this experiment was to assess a new method to determine the bioavailability (BA) of rumen-protected (RP)His, RPLys and RPMet products by determining rumen escape (RE) and fecal excretion of undigested AA from RPAA. Eight lactating Holstein cows (79 ± 21 days in milk, 53.0 ± 7.0 kg/d milk yield), four of which rumen-cannulated, were used in a replicated 4 × 4 Latin square design experiment with four, 26-day experimental periods and a preceding 22-day background (BG) period. Four combinations of nine commercial and experimental RPAA (HisA, HisB, LysA, LysB, LysC, MetA, MetB, MetC, MetD) were fed daily to supply 20, 25, and 35 g/day of digestible (d)His, dLys and dMet, respectively. The following treatment combinations were used: (1) HisALysAMetA, (2) HisBLysBMetB, (3) LysCMetC and (4) LysCMetD. Spot sampling of feces was performed during the BG period to establish basal levels of AA in feces. Total fecal collection and blood sampling were performed during the last three days of each experimental period. Rumen escape fraction of each RPAA product was determined in situ and was greater for HisA (0.90) than for HisB (0.64), ranged from 0.33 to 0.85 (SEM = 0.017) for RPLys and from 0.53 to 0.95 (SEM = 0.017) for RPMet. Apparent post-ruminal digestibility of AA from RPAA was calculated as [(RE of AA, g/day – BG corrected fecal AA output, g/day) ÷ RE of AA, g/day]. Digestibility was similar between the two RPHis products (0.85 and 0.90). Apparent post-ruminal digestibility of Lys from RPLys products varied from 0.30 to 0.79 and digestibility for RPMet varied from 0.85 to 0.96. Bioavailability was calculated as: (RE, g/g × AA digestibility, g/g) × 100 and was greater for HisA compared with HisB (76.1 and 57.9 % respectively), varied from 9.63 (LysC) to 67.0 % (LysA) for the RPLys and was lowest for MetC (49.3 %) and greatest for MetD (91.9 %) among the RPMet products. Plasma His concentration was greater for HisA than for HisB and plasma Met concentration was greater for MetD compared with the other three RPMet products, reflecting estimated BA of the RPAA products. In contrast, plasma Lys concentration did not differ among RPLys products. This study showed that a method using fecal AA output in combination with RE of RPAA can reveal differences in BA between RPAA products. This is a first step in establishing the fecal AA excretion technique for determination of BA of RPAA and warrants further validation.

Effect of fish meal replacement with CarinataBrassica carinatain low animal protein diets of rainbow troutOncorhynchus mykiss(Walbaum) on trypsin activity, protein and amino acid digestibility and bioavailability

Replacement of >25% of fish meal (FM) with aerobically converted carinata meal (ACCM) in low (200g/kg) animal protein (reference = 200g/kg FM) diets of rainbow trout Oncorhynchus mykiss resulted in reduced growth, partly due to reduced feed consumption and protein utilization. In this study, we determined the effect of FM replacement with ACCM on trypsin activity, apparent digestibility coefficients (ADCs) of protein, and essential amino acid (EAA) or conditionally essential amino acid (CEAA) ADCs and bioavailability. Replacement of FM did not alter protein ADCs or trypsin activity. Replacement of >25% FM reduced all EAA and CEAA ADCs except for arginine and leucine which were only reduced by 75% FM replacement. Only serum free lysine and muscle free histidine were reduced by >25% FM replacement. Muscle free lysine was only reduced by 75% FM replacement. Replacement of FM reduced EAA peak concentrations and resulted in slower release of EAAs in serum. Cumulative total EAAs in serum and muscle decreased with FM replacement. Ratios of EAAs to lysine showed that tryptophan was the most limiting EAA. However, isoleucine, leucine, methionine and phenylalanine were also inadequate for muscle synthesis for the first 9–12 hr following force‐feeding. Optimal time for protein synthesis was ≥36 hr. Although any level of FM replacement did not reduce protein ADCs and trypsin activity, replacement of ≥25% FM reduced EAA ADCs and bioavailability of lysine and histidine, which partly contributed to the observed differences in growth.

Quantification of nitrogen in the liquid fraction and in vitro assessment of lysine bioavailability in the solid fraction of soybean meal hydrolysates

ABSTRACTSoybean meal (SBM) is a product generated from the manufacture of soybean oil and has the potential for use as a source of fermentable sugars for ethanol production or as a protein source for animal feeds. Knowing the levels of nitrogen available from ammonium is a necessary element of the ethanolic fermentation process while identifying the levels of essential amino acids such as lysine is important in determining usage as a feed source. As such the purpose of this study was to quantify total nitrogen and ammonium in the liquid fraction of hydrolyzed SBM and to evaluate total and bioavailable lysine in the solid fraction of the hydrolyzed SBM. The effects of acid concentration, cellulase and β-glucosidase on total and ammonium nitrogen were studied with analysis indicating that higher acid concentrations increased nitrogen compounds with ammonium concentrations ranging from 0.20 to 1.24 g L−1 while enzymatic treatments did not significantly increase nitrogen levels. Total and bioavailable lysine was quantified by use of an auxotrophic gfpmut3 E.coli whole-cell bioassay organism incapable of lysine biosynthesis. Acid and enzymatic treatments were applied with lysine bioavailability increasing from a base of 82% for untreated SBM to up to 97%. Our results demonstrated that SBM has the potential to serve in ethanolic fermentation and as an optimal source essential amino acid lysine.

Lysine bioavailability among 2 lipid-coated lysine products after exposure to silage1

We conducted 2 experiments to determine lysine bioavailability from 2 lipid-coated lysine products. In an in vitro experiment we mixed each lipid-coated lysine product with either alfalfa- or corn-silage at different amounts of acidity. Scanning electron micrographs indicated that surface structure of each lipid-coated lysine particle was eroded after mixing with silage. Additionally, visual evaluation of scanning electron micrographs suggested that peripheral surface abrasion of lipid-coated lysine may be greater when lipid-coated lysine was mixed with alfalfa silage in comparison to corn silage. In a corresponding experiment, in vivo measures of lysine bioavailability to sheep from 2 lipid-coated lysine products and lysine-HCl were determined after mixing in corn silage. Plasma lysine concentrations increased linearly (P < 0.01) in response to abomasal lysine infusion indicating that our model was sensitive to increases in metabolizable lysine flow. Bioavailability of each lipid-coated lysine source and dietary lysine-HCl were calculated to be 23, 15, and 18%, respectively. Even though each dietary source of lysine increased plasma lysine, rates of increases in plasma lysine from one lipid-coated lysine source (linear; P = 0.20) and lysine-HCl (linear; P = 0.11) were not different from plasma lysine levels supported by diet alone. However, the rate of plasma lysine increase in response to lysine from the other lipid-coated lysine source was greater (P = 0.04) than plasma lysine from feed alone. Nonetheless, the rate of plasma lysine increase in response to lipid-coated lysine did not differ (P ≥ 0.70) from the rate of plasma lysine increase from lysine-HCl. Clearly, methods of manufacture, together with physical and chemical characteristics of diet, can impact amounts of metabolizable lysine provided from lipid-coated lysine products. Direct measures of lysine bioavailability from lipid-coated lysine products after mixing with diets should be based on measurements with the products treated similarly to the method of feeding.

Relative lysine bioavailability of hydrolyzed porcine mucosal tissue compared with acid casein in weaned piglets

Relative lysine bioavailability of hydrolyzed porcine mucosal tissue compared with acid casein in weaned piglets

Blocked Lysine in Dairy Products: Formation, Occurrence, Analysis, and Nutritional Implications

Lysine residues in milk proteins become "blocked" when they react with reducing sugars, particularly lactose, in the Maillard reaction. The blocked or glycated lysines reduce the biological availability of the lysine to metabolic processes and also hinder hydrolysis of the parent protein by digestive enzymes. Heating and storage of milk and milk products are the major promotants of the Maillard reaction and resulting chemical damage to the proteins. Several methods have been proposed to estimate the extent of this protein damage. Two major compounds, furosine, a product of acid hydrolysis of lactulosyl-lysine, the 1st stable product of the Maillard reaction, and carboxymethyl-lysine are used for assessing the early and advanced stages of the Maillard reaction, respectively. In addition, several methods are used for assessing the bioavailability of lysine in a protein; these include chemical, enzymic, and animal-based methods. This review discusses the Maillard reaction and its significance in milk and dairy products, methods of assessing the extent of the reaction and of the bioavailability of lysine, and the nutritional significance of blocked lysines and associated Maillard reaction products in milk proteins.

Use of the guanidination reaction for determining reactive lysine, bioavailable lysine and gut endogenous lysine.

Determining the bioavailability of lysine in foods and feedstuffs is important since lysine is often the first limiting indispensable amino acid in diets for intensively farmed livestock (pigs and poultry) and also in many cereal-based diets consumed by humans. When foods or feedstuffs are heat processed, lysine can undergo Maillard reactions to produce nutritionally unavailable products. The guanidination reaction, the reaction of O-methylisourea with the side chain amino group of lysine that produces homoarginine, has been used to determine the unmodified lysine (reactive lysine) in processed foods and feedstuffs and also true ileal digestible reactive lysine (bioavailable lysine). The advantages of the guanidination method in comparison with other reactive lysine methods such as the fluorodinitrobenzene, trinitrobenzenesulphonic acid and dye-binding methods are that it is very specific for reactive lysine and also that the method is relatively straightforward to conduct. The specificity of the guanidination reaction for the lysine side chain amino group is particularly important, since ileal digesta will contain N-terminal groups in the form of free amino acids and peptides. The main disadvantage is that complete conversion of lysine to homoarginine is required, yet it is not straightforward to test for complete guanidination in processed foods and feedstuffs. Another disadvantage is that the guanidination reaction conditions may vary for different food types and sometimes within the same food type. Consequently, food-specific guanidination reaction conditions may be required and more work is needed to optimise the reaction conditions across different foods and feedstuffs.

Mass spectrometry for the analysis of protein lactosylation in milk products

Milk and dairy products are usually submitted to thermal procedures in order to preserve microbiological safety and to prolong their shelf-life; these actions may eventually induce structural modifications of several components. In particular, milk proteins undergo a non-enzymatic glycation, known as the Maillard reaction, in which reducing sugars (such as lactose) mainly react with the ε-amino group of Lys residues, leading to the formation of the Amadori product lactulosyl-lysine. Protein lactosylation leads to a decrease of milk nutritional value as it reduces the bioavailability of the essential amino acid lysine and to a potential increase of the specific allergen activity, due to the formation of new hapten-like antigens. These aspects are of particular importance in products intended for infant diet, such as milk powders and infant milk formulas; accordingly, a detailed structural characterization of the extent and site-specificity of milk protein lactosylation is mandatory. Analytical methodologies based on mass spectrometry and more recently proteomics have been thoroughly applied to the structural analysis of milk proteins and their modified forms, including glycation products. This review highlights the contribution of mass spectrometry to the extensive investigation of lactosylation events in milk proteins, with a particular focus on the most up-to date technological improvements.