The effect of thermal processing on the in vitro digestibility of pork proteins was studied. Raw samples were considered the control group, while the thermal treatments included 58, 80, 98 and 160 °C ...for 72 min, 118 °C for 8 min and 58 °C for 17 h, resembling a range of different cooking procedures. Samples were subsequently subjected to pepsin digestion at pH 3.00 in the gastric phase followed by trypsin and α-chymotrypsin at pH 8.00 in the intestinal phase. Pork cooked at 58 °C for 72 min had a significantly higher pepsin digestibility rate than meat cooked at 80 °C or 160 °C. The trend was similar in the intestinal phase, with samples cooked at 58 °C for 72 min having enhanced digestion rate over other treatments after 120 min of digestion. A PLS model pointed out to an inverse relationship between in vitro proteolysis rate and variables like Maillard reaction compounds or protein structural changes.
•In vitro protein digestibility in pork under different heat treatments was studied.•Protein digestion rate decreased with higher cooking temperature and time.•Structural and chemical modifications of pork proteins were related to change in digestion rate.•Maillard reactions, protein aggregation and % beta sheet negatively affected protein digestion.
The nutritional value of proteins was investigated after the storage and cooking of rhea
M. Gastrocnemius pars interna. Oxidation of basic and aromatic amino acids, surface hydrophobicity and ...aggregation state of proteins, were determined in raw and cooked meat. In addition, myofibrillar proteins were exposed
in vitro to proteases of the digestive tract. Cooking markedly affected the protein surface hydrophobicity. The BBP bound content was three times greater in cooked than in fresh rhea meat. A small increment in tryptophan content after cooking was observed. Storage influenced Schiff bases formation indicating the presence of protein–aldehyde adducts after cooking. High content of Schiff bases was found after cooking of samples stored for 5
days, demonstrating a probable implication of free amino groups, most likely from lysine. Cooking decreased the myofibrillar protein susceptibility to pepsin activity. After cooking, the proteolysis rate by pancreatic enzymes increased. Our findings support the importance of protein aggregation in the nutritional value of meat proteins.
A new enzyme （alkaline protease 894） obtained from the marine extremophile Flavobacterium yellowsea （YS-80-122） has exhibited strong substrate-binding and catalytic activity, even at low temperature, ...but the characteristics of the hydrolysis with this enzyme are still unclear. The pearl oyster Pinctada martensii was used in this study as the raw material to illustrate the kinetic properties ofprotease 894. After investigating the intrinsic relationship between the degree of hydrolysis and several factors, including initial reaction pH, temperature, substrate concentration, enzyme concentration, and hydrolysis time, the kinetics model was established. This study showed that the optimal conditions for the enzymatic hydrolysis were an initial reaction pH of 5.0, temperature of 30~C, substrate concentration of 10% （w/v）, enzyme concentration of 2 500 U/g, and hydrolysis time of 160 min. The kinetic characteristics of the protease for the hydrolysis ofP. martensii were obtained. The inactivation constant was found to be 15.16/min, and the average relative error between the derived kinetics model and the actual measurement was only 3.04%, which indicated a high degree of fitness. Therefore, this study provides a basis for the investigation of the concrete kinetic characteristics of the new protease, which has potential applications in the food industry.
The transition curves of soybean glycinin egg lysozyme, bovine serum albumin (BSA) denaturation under the action of increasing urea concentration were monitored by determination of the increase in ...rate constants of cooperative enzymatic proteolysis. The results were compared with those obtained using intrinsic fluorescence and the number of accessible tyrosine. It was shown that the determination of the changes of proteolysis rate permits to disclose conformation changes not detected by other methods.
Acute deviations in protein intake before the quantification of protein kinetics in older humans may explain the controversy over the effects of older age on muscle protein synthesis and proteolysis ...rates.
We hypothesized that an acute decrease in protein intake from the habitual intake is associated with lower muscle protein synthesis and higher proteolysis rates, whereas an acute increase in protein intake from the habitual intake is associated with higher muscle protein synthesis and lower proteolysis rates.
In 112 community-dwelling healthy men aged 65-90 y, we quantified resting whole-body 1,2-(13)C(2)leucine kinetics, muscle mixed protein fractional synthesis rates (FSRs), and muscle proteasome proteolytic enzyme activities after participants consumed for 3 d controlled research meals (0.9-1.1 g protein · kg(-1) · d(-1)) that contained more or less protein than that habitually consumed and that induced alterations in nitrogen balance.
Protein kinetic parameters were not significantly different between the groups, despite controlled research protein intakes that were lower (-0.2 to -0.3 g · kg(-1) · d(-1)) or higher (+0.2 g · kg(-1) · d(-1)) than habitual intakes and that induced negative (-22 to -25 mg · kg(-1) · d(-1)) or positive (22-25 mg · kg(-1) · d(-1)) nitrogen balance. Within these acutely altered protein intake and nitrogen balance boundaries, a reduction in protein intake from habitual intake and induction of negative nitrogen balance were not associated with higher proteolysis or lower muscle FSR, and an acute increase in protein intake from habitual intake and induction of positive nitrogen balance were not associated with lower proteolysis or higher muscle FSR. A higher quantitative insulin sensitivity check index was associated with lower whole-body proteolysis rates.
The practice of acutely controlling protein intake, even at intakes lower than habitual intakes that induce negative nitrogen balance, before quantifying human protein kinetics does not significantly reduce muscle protein synthesis or increase proteolysis. Factors other than protein intake explain lower muscle protein synthesis rates with advanced age. This trial is registered at clinicaltrials.gov as NCT00183040.
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