Determination of the lysine bioavailability from cereal food sources in healthy school-aged children

Background: Cereal grains provide essential nutrients and dietary energy (38-80% daily) as part of staple diets globally. Proteins in cereals contain relatively low amounts of lysine, an essential amino acid, which can potentially limit growth in children. Losses within digestion, absorption and utilization combined with losses from cooking may further decrease bioavailable lysine. Objectives: To assess lysine bioavailability from commonly consumed foods (white rice, oats, corn, black beans, and whole milk) in healthy school-aged children; and to determine the effects of food matrix and cooking techniques on lysine bioavailability. Methods: Using a repeated-measured design and a stable isotope-based technique (Indicator Amino Acid Oxidation, IAAO), three experiments were conducted where 5-6 children aged 6-10y participated per experiment (totaling 143 study days) to evaluate lysine bioavailability from test foods. The effects of food matrix and cooking techniques were analyzed using in-vitro assays - Differential Scanning Calorimeter (DSC) for starch retrogradation and colorimeter for Maillard Reaction Products (MRPs) formation. Results: Lysine bioavailability from rice was high (97%), but consuming rice cold reduced it to 86.1%. DSC analysis showed that cold rice samples had retrograded starch within their food matrix. Lysine bioavailability was high in milk (103.7%) compared to black beans (81.5%). When oats were consumed as oatmeal (moist-heat cooking), lysine bioavailability was 92.7%; when the same oats were prepared as granola (dry-heat cooking), lysine bioavailability was reduced to 43.2%. A similar pattern was observed for corn atole (moist-heat cooking) had a higher lysine bioavailability (96.8%) than corn tortillas (dry-heat cooking) (75.4%). Color change analysis showed a higher magnitude of browning for granola (68%) compared to oatmeal, and for tortilla (17%) compared to atole, suggesting possible formation of reaction compounds and brown pigments derived from Maillard reaction leading to reduced bioavailability. Conclusion: Lysine was highly bioavailable within warm and moist-heat cooked foods, whereas reduced bioavailability was observed when foods were consumed cold and cooked using dry-heat. With the lysine bioavailability data obtained from this dissertation, improved dietary recommendations that meet lysine requirements from foods can be developed for children who consume a predominantly cereal/plant-based diet.Land and Food Systems, Faculty ofGraduat

Protein quality and glycemic indexes of mango drinks fortified with a soybean/maize protein isolate with three levels of urease activity fed to weanling rats

Introduction: Public health professionals established a direct link between obesity and the rise in high caloric beverage intake. Current recommendations promote the elimination of sweet fruit drinks from the population’s diet. One way of evading this is by modifying the drink’s nutritional characteristics regarding nutrient uptake and utilization. Objectives: evaluate the protein quality of a soy/maize protein (SMP) and its physiological effects on nutrient intake and to assess glycemic indexes (GIs) of mango based drinks prepared with sucrose or stevia. Materials and methods: Mango drinks were supplemented with different sources of protein (three SMP thermally treated to contain different urease activities (UA) or whey protein concentrate (WPC)) that were sweetened with sucrose or stevia/sucralose. The protein digestibility, net protein absorption (NPA), biological value (BV), net protein utilization (NPU) value and protein efficiency ratio (PER) were assessed with weanling rats. Moreover, the GIs of the mango drinks were measured in the same animal model. Results: PER and NPA evaluated in a rat model showed that increased levels of UA decreased Biological (BV) and Net Protein Utilization (NPU) values. The GIs of the mango drinks significantly diminished with the addition of 3.5% of SMP, but unexpectedly the substitution of sucrose by stevia/sucralose did not significantly change the glycemic response. Conclusion: the SMP isolate can be used to improve the nutritional profile and lower GIs of mango drinks