The kinetics of peptide release during in vitro digestion of 4 protein sources (casein, cod protein, soy protein, and gluten) were investigated. Samples were sequentially hydrolyzed with pepsin (30 min) and pancreatin (2, 4, or 6 h) in a dialysis cell with continuous removal of digestion products. Nondialyzed digests were fractionated by ion-exchange chromatography and ultrafiltration. Animal proteins were digested at a greater rate than plant proteins. Target amino acids of specific enzymes appeared more rapidly in the dialyzed fractions when compared to other amino acids. Throughout the hydrolysis, nondialyzed digests contained a higher proportion of peptide mixtures with basic-neutral properties. Except for gluten, peptide fractions with molecular weights that exceeded 10 kDa (basic-neutral, BN > 10) were rapidly hydrolyzed during the first 2 h of pancreatin digestion. The kinetics of release and the composition of peptide fractions were different when the protein sources were compared. The analysis of amino acids revealed that threonine and proline proportions were relatively high in BN > 10 and in peptide fractions with molecular weight between 10-1 kDa (BN 10-1), while tyrosine, phenylalanine, lysine, and arginine predominated in the low molecular weight (<1 kDa) fractions. More resistant peptides were generally rich in proline and glutamic acid. The role of in vitro digestion assays in dietary protein quality evaluation is discussed.

The charges and sizes of peptides released during in vitro casein digestion were investigated. Casein was hydrolysed sequentially by pepsin and pancreatin and, during hydrolysis, the products of digestion were removed by dialysis. The undigested residues were separated by ion-exchange chromatography into basic-neutral (BN), lightly acid (LA) and acid (A) fractions. Each of these fractions was further resolved by sequential ultrafiltration (MWCO 10 and 1 kDa) into two retentates (>10 and 10-1 kDa) and one permeate (<1 kDa). The polypeptides (>10 kDa) produced by pepsin hydrolysis were degraded into small molecules during the first 2 h of pancreatin hydrolysis; less than 100 mg g −1 of the total N remained undigested. Most of the material produced was in the BN10-1 (ie basic-neutral, 10-1 kDa) fraction, with three times as much N as the A10-1 fractions. As digestion progressed a decrease in the proportion of N in the residues retained by the dialysis membrane was observed. This decrease was particularly rapid in the BN10-1 fraction. Large proportions of leucine (Leu), lysine (Lys), arginine (Arg), phenylalanine (Phe) and tyrosine (Tyr) were found as peptides smaller than 1 kDa, both in the dialysates and retentates, while glutamine (Glu), threonine (Thr), serine (Ser) and asparagine (Asp) appeared mostly in the A10-1 and A >10 fractions. After 6 h of pancreatin hydrolysis most of the proline (Pro) content was in the BN10-1 fractions. The mechanisms behind and the implications of these results are discussed.

Este trabajo presenta un estudio cuantitativo en la subcuenca río alto Bogotá con relación a las condiciones de calidad químicas y biológicas en las que se encuentra el tramo del río estudiado y su estado en cuanto a calidad del recurso hídrico, para lo cual, se analizaron los parámetros de temperatura del agua (T° Agua), demanda biológica de oxígeno (DBO) y oxígeno disuelto (OD). El estudio se fundamentó en la recolección y análisis de información, para ser aplicado en el software libre HEC-RAS (ver. 5.0.4.). Se llevó a cabo la calibración del modelo hidrodinámico a partir de las velocidades tomadas en campo, alcanzándose una diferencia entre los valores reales y los valores de salida del 22.58%. Una vez calibrado el modelo hidrodinámico, se efectuó la simulación de calidad de agua a partir de las condiciones de mayor vulnerabilidad del recurso hídrico en el periodo 2014-2016 y posterior a ello, su calibración en donde se ajustaron los valores de los parámetros de nutrientes y la radiación solar obteniéndose así una variación promedio de error del 1-5%. Seguido a la calibración, se representaron cartográficamente los resultados para facilitar el entendimiento de los parámetros simulados y evidenciar el comportamiento en el río. Estos se compararon contra los objetivos de calidad del agua propuestos por la autoridad ambiental para la clase I y II (Acuerdo CAR No 43/2006) encontrándose que con respecto a DBO y OD las altas cargas contaminantes recibidas por el río no permiten alcanzar los objetivos de calidad hídrica.