Enzymic dephosphorylation of bovine casein to improve acid clotting properties and digestibility for infant formula

Gastrointestinal digestibility of micellar casein dispersions: Effects of caprine vs bovine origin, and partial colloidal calcium depletion using in vitro digestion models for the adults and elderly

In vitro coagulation and digestion of caprine and bovine micellar casein concentrate (MCC) with or without partial colloidal calcium depletion (deCa) were studied under simulated adult and elderly conditions. Gastric clots were smaller and looser for caprine than bovine MCC, and were further looser with deCa and under elderly condition for both caprine and bovine MCC. Casein hydrolysis and concomitant formation of large peptides was faster for caprine than bovine MCC, and with deCa and under adult condition for caprine and bovine MCC. Formation of free amino groups and small peptides were faster for caprine MCC, and with deCa and under adult condition. Upon intestinal digestion, proteolysis occurred rapidly, and was faster under adult condition, but showed less differences with increasing digestion between caprine and bovine MCC, and with and without deCa. These results suggested weakened coagulation and greater digestibility for caprine MCC and MCC with deCa under both conditions.

New Insights into Cheese Microstructure

Microscopy is often used to assist the development of cheese products, but manufacturers can benefit from a much broader application of these techniques to assess structure formation during processing and structural changes during storage. Microscopy can be used to benchmark processes, optimize process variables, and identify critical control points for process control. Microscopy can also assist the reverse engineering of desired product properties and help troubleshoot production problems to improve cheese quality. This approach can be extended using quantitative analysis, which enables further comparisons between structural features and functional measures used within industry, such as cheese meltability, shreddability, and stretchability, potentially allowing prediction and control of these properties. This review covers advances in the analysis of cheese microstructure, including new techniques, and outlines how these can be applied to understand and improve cheese manufacture.

Improvement of meat protein digestibility in infants and the elderly

Meat is a valuable protein source with a balanced composition of essential amino acids and various nutrients. This review aims to identify methods to improve digestion of meat proteins, as well as evaluate the digestive characteristics of infants and the elderly. Immature digestive conditions in infants, including a high gastric pH and low protease concentration, can hinder protein digestion, thus resulting in inhibited growth and development. Likewise, gastrointestinal (GI) tract aging and chronic health problems, including tooth loss and atrophic gastritis, can lead to reduction in protein digestion and absorption in the elderly compared with those in young adults. Moderate heating and several non-thermal technologies, such as aging, enzymatic hydrolysis, ultrasound, high-pressure processing, and pulsed electric field can alter protein structure and improve protein digestion in individuals with low digestive capacity.

Composition, Structure, and Digestive Dynamics of Milk From Different Species-A Review

Background: The traditional dairy-cattle-based industry is becoming increasingly diversified with milk and milk products from non-cattle dairy species. The interest in non-cattle milks has increased because there have been several anecdotal reports about the nutritional benefits of these milks and reports both of individuals tolerating and digesting some non-cattle milks better than cattle milk and of certain characteristics that non-cattle milks are thought to share in common with human milk. Thus, non-cattle milks are considered to have potential applications in infant, children, and elderly nutrition for the development of specialized products with better nutritional profiles. However, there is very little scientific information and understanding about the digestion behavior of non-cattle milks. Scope and Approach: The general properties of some non-cattle milks, in comparison with human and cattle milks, particularly focusing on their protein profile, fat composition, hypoallergenic potential, and digestibility, are reviewed. The coagulation behaviors of different milks in the stomach and their impact on the rates of protein and fat digestion are reviewed in detail. Key findings and Conclusions: Milk from different species vary in composition, structure, and physicochemical properties. This may be a key factor in their different digestion behaviors. The curds formed in the stomach during the gastric digestion of some non-cattle milks are considered to be relatively softer than those formed from cattle milk, which is thought to contribute to the degree to which non-cattle milks can be easily digested or tolerated. The rates of protein and fat delivery to the small intestine are likely to be a function of the macro- and micro-structure of the curd formed in the stomach, which in turn is affected by factors such as casein composition, fat globule and casein micelle size distribution, and protein-to-fat ratio. However, as no information on the coagulation behavior of non-cattle milks in the human stomach is available, in-depth scientific studies are needed in order to understand the impact of compositional and structural differences on the digestive dynamics of milk from different species.

Low Protein Digestibility of Beef Puree in Infant In Vitro Digestion Model

This study investigated protein digestibility of beef puree in infant and adult in vitro digestion models. The simulated digestive juices for infant and adult were prepared. Protein digestibility of beef puree was calculated in the gastric and gastrointestinal compartments. The 10% trichloroacetic acid soluble nitrogen and α-amino group contents of gastric digesta were lower in the infant in vitro digestion model than those in the adult in vitro digestion model (p<0.05). In addition, the gastrointestinal digesta from the infant in vitro digestion model had lower value of the 10% trichloroacetic acid soluble nitrogen and α-amino group contents than those of the adult in vitro digestion model (p<0.05). The results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the remarkable bands of actin and myosin light chain B were found in the digesta of beef puree from the infant in vitro digestion model. The results of this study revealed the lower protein digestibility of beef puree in infants compared to that in adults. Therefore, the development of ways to increase digestibility of meat protein can improve the nutritional quality of meat products for infants.

Crosslinking with transglutaminase does not change metabolic effects of sodium caseinate in model beverage in healthy young individuals

Background

Postprandial metabolic and appetitive responses of proteins are dependent on protein source and processing technique prior to ingestion. Studies on the postprandial effects of enzymatic crosslinking of milk proteins are sparse. Our aim was to study the effect of transglutaminase (TG)-induced crosslinking of sodium caseinate on postprandial metabolic and appetite responses. Whey protein was included as reference protein.

Methods

Thirteen healthy individuals (23.3 ± 1.1 y, BMI 21.7 ± 0.4 kg/m²) participated in a single-blind crossover design experiment in which the subjects consumed three different isovolumic (500 g) pourable beverages containing either sodium caseinate (Cas, 29 g), TG-treated sodium caseinate (Cas-TG, 29 g) or whey protein (Wh, 30 g) in a randomized order. Blood samples were collected at baseline and for 4 h postprandially for the determination of plasma glucose, insulin and amino acid (AA) concentrations. Gastric emptying (GE) was measured using the ¹³ C-breath test method. Appetite was assessed using visual analogue scales.

Results

All examined postprandial responses were comparable with Cas and Cas-TG. The protein type used in the beverages was reflected as differences in plasma AA concentrations between Wh and Cas, but there were no differences in plasma glucose or insulin responses. A tendency for faster GE rate after Wh was detected. Appetite ratings or subsequent energy intake did not differ among the protein beverages.

Conclusions

Our results indicate that the metabolic responses of enzymatically crosslinked and native sodium caseinate in a liquid matrix are comparable, suggesting similar digestion and absorption rates and first pass metabolism despite the structural modification of Cas-TG.

Intestinal alkaline phosphatase detoxifies lipopolysaccharide and prevents inflammation in zebrafish in response to the gut microbiota

Vertebrates harbor abundant lipopolysaccharide (LPS) in their gut microbiota. Alkaline phosphatases can dephosphorylate and detoxify the endotoxin component of LPS. Here, we show that expression of the zebrafish intestinal alkaline phosphatase (Iap), localized to the intestinal lumen brush border, is induced during establishment of the gut microbiota. Iap-deficient zebrafish are hypersensitive to LPS toxicity and exhibit the excessive intestinal neutrophil influx characteristic of wild-type zebrafish exposed to LPS. Both of these Iap mutant phenotypes are dependent on Myd88 and Tumor Necrosis Factor Receptor (Tnfr), proteins also involved in LPS sensitivity in mammals. When reared germ-free, the intestines of Iap-deficient zebrafish are devoid of neutrophils. Together, these findings demonstrate that the endogenous microbiota establish the normal homeostatic level of neutrophils in the zebrafish intestine through a process involving Iap, Myd88, and Tnfr. Thus, by preventing inflammatory responses, Iap plays a crucial role in promoting mucosal tolerance to resident gut bacteria.

Camel's milk and gastric emptying

BACKGROUND & AIM

Gastric emptying is determined by food consistency, pH, osmolality, lipid and calorie content as well as the presence of different nutrients in the duodenal lumen. Control of gastric emptying is essential for ensuring optimal digestion. The present study tested the hypothesis that due to its different precipitation properties, gastric emptying of camel's milk may be quicker than that of bovine's milk with the same caloric and fat content.

METHODS

Gastric emptying was studied by a scintigraphic technique in a randomized, double blind fashion in 8 volunteers after drinking 450 mL of either cow's milk or camel's milk.

RESULTS

No differences in gastric emptying rates were found between the two types of milk. The percentage of retention of the meal after 60 min was 74.6+/-13.2% for cow's milk and 79.8+/-10.8% for camel's milk. The 50% emptying time (T(1/2)) was 131.8+/-37.4 min for cow's milk and 136.8+/-55.8 min for camel's milk.

CONCLUSIONS

Camel's milk is most probably not a useful substitute for other types of milk to shorten gastric emptying.

Ambroxol reduces LPS toxicity mediated by induction of alkaline phosphatases in rat lung

Alkaline phosphatases (APs) have been suggested to detoxify lipopolysaccharide (LPS) by dephosphorylation. Ambroxol, a bronchial expectorant, is known to accelerate the secretion of pulmonary surfactant particles including AP molecules as a pharmacological action. In the present study, some beneficial effects of ambroxol on LPS toxicity in the rat lung were investigated. In an experiment using the rat lung organ culture, AP activities were enhanced in a time-dependent manner by incubation with 25 microM of ambroxol in both the tissue and the medium. Western blot analysis indicated that AP activity was elevated by the treatment with ambroxol, due to the induction of surfactant proteins (SPs) and AP molecules. In the in vivo experiment, the serum LPS content was markedly increased after LPS administration to rats by intratracheal instillation of 20 mg/kg. However, when the rats were pretreated with oral ambroxol (1.0 mg/kg) at 1 h before LPS challenge, the area under the concentration--time curve (AUC) of serum LPS was significantly decreased. These results suggest that ambroxol inhibits the translocation of LPS from the lung into the circulation as well as its detoxification effect via the elevation of AP activity. Bromhexine, another expectorant, is less effective than ambroxol as an LPS detoxificant. Maintenance of high AP activity level in the lung suggests APs to have physiological significant effects against the inflammatory events induced by LPS.

Dietary protein precipitation properties have effects on gastric emptying in healthy volunteers

BACKGROUND & AIMS

Strategies that reduce the size of particles in the stomach accelerate gastric emptying. Partial dephosphorylation of casein reduces the size of protein precipitates (curds) in acid conditions and facilitates peptic digestion. We hypothesized that changing the precipitation properties of casein by partial dephosphorylation would accelerate gastric emptying.

METHODS

Eight healthy male volunteers entered a prospective, double blind, randomized study with crossover design. Gastric emptying of milk based formula containing either unmodified or dephosphorylated casein was assessed by scintigraphy. Gastric pH measurements were acquired concurrently.

RESULTS

A trend to faster gastric emptying was observed for the unmodified preparation, with lower median half time (unmodified 133; dephosphorylated 214 min, P = 0.09) and area under the curve (unmodified 8425 min%; dephosphorylated 9135 min%, P = 0.08). A positive correlation was found between half time for the dephosphorylated preparation and the treatment effect (r2 = 0.81, P < 0.02). Gastric pH was unaffected.

CONCLUSIONS

The study hypothesis was rejected; indeed gastric emptying tended to be faster for the unmodified than the dephosphorylated protein. This effect was more pronounced in subjects with slow gastric emptying on the dephosphorylated preparation. Properties other than the size of protein precipitates determine the rate of gastric emptying for milk based formula.

Effect of pH and ionic strength on competitive protein adsorption to air/water interfaces in aqueous foams made with mixed milk proteins

Quantitative analysis of competitive milk protein adsorption to air/water interfaces in aqueous foam was performed by capillary electrophoresis (CE). Foams were made by whipping protein solutions, in which skim milk powder (SMP) and whey protein isolate (WPI) were mixed at 0.5% protein in different proportions at different pH values and NaCl concentrations. Preferential adsorption of beta-casein into foam phases occurred under most solution conditions, if partial dissociation of the casein micelles had occurred. Preferential adsorption of beta-casein was not observed with added Ca2+, due to the re-association of casein micelles. Enrichment of caseins into the foam phase was more apparent than that of whey proteins. The foamability of SMP demonstrated a continuous improvement due to the gradually increasing dissociation of casein micelles when the concentration of NaCl increased from 0 to 0.8 M. The foamability of WPI increased when NaCl concentration rose from 0 to 0.1 M, and decreased with further increase in NaCl concentration. NaCl at low concentration (I < or = 0.4) did not show a significant effect on the competitive adsorption among milk proteins, indicating that electrostatic interactions do not play a key role in competitive adsorption. NaCl at higher concentration, e.g., 0.6 M, caused less whey protein to be adsorbed to the air/water interfaces. The whippability of WPI was highest at pH 4.5 and lowest at pH 3, and that of SMP was the opposite. The proportions of beta-lactoglobulin and alpha-lactalbumin in the foam phase were lower at acidic pH and higher at basic pH, compared with that at natural pH of WPI.

Alkaline phosphatases reduce toxicity of lipopolysaccharides in vivo and in vitro through dephosphorylation

Intestinal alkaline phosphatase (AP), as a host defense factor, was first investigated in vivo using rats orally exposed to lipopolysaccharide (LPS). After the oral administration of LPS to rats, serum LPS content was increased within 2 hr and then decreased to 6 hr. In contrast, when L-phenylalanine (L-Phe), an inhibitor of intestinal-type AP isozymes, was simultaneously administered with LPS, serum LPS content significantly increased from 1 hr and the area under the concentration-time curve of serum LPS was augmented approximately 2-fold, suggesting that APs in the gastrointestinal tract reduced serum LPS content. In addition, LPS toxicity diminished by a treatment in vitro with intestinal APs, were recovered by the treatment in the co-presence of L-Phe. In the experiment using human aortic endothelial cells (HAECs), we observed that the cell viability decreased in a dose-dependent manner of LPS-exposure, and the LPS dose, exhibiting 50% viability of the cells, was 0.05 microg/ml. When the cells were exposed to LPS pretreated with 50 nIU/ml of intestinal AP at pH 10.0 and 8.0, the 50% viability was at 2.0 microg/ml of LPS. These results strongly suggest that the APs reduced the toxicity of LPS, as a host defense factor against LPS.

Dephosphorylation of sodium caseinate, enzymatically hydrolyzed casein and casein phosphopeptides by intestinal alkaline phosphatase: implications for iron availability

Clusters of phosphoserine residues in casein bind iron with high affinity. Casein inhibits iron absorption in humans but partial hydrolysis of casein prior to ingestion diminishes this inhibition. The objective of this study was to test two hypotheses: 1. Partial hydrolysis of the peptide bonds in casein exposes phosphoserine residues to attack by intestinal alkaline phosphatase (IAP). 2. Hydrolysis of the phospho-ester linkage in phosphoserine residues in casein by IAP releases bound iron or inhibits iron chelation, thereby allowing its absorption. Test of hypothesis 1: Suspensions of sodium caseinate (SC), enzymatically hydrolyzed casein (EHC), and casein phosphopeptides (CPP) were subjected to an in vitro pepsin/pancreatin digestion and subsequently incubated in the presence of calf IAP. The rate of release of inorganic phosphate was measured with the following results (expressed as &mgr;mol phosphate released/unit of IAP/min): 0.081, 0.104, 0.139 for SC, EHC, and CPP, respectively. These results are consistent with hypothesis 1. Test of hypothesis 2: (59)Fe-citrate or (59)Fe-citrate + CPP in minimum essential media were spiked with a Na(2)WO(4) solution or water (Na(2)WO(4) is a known inhibitor of IAP) and placed on Caco-2 cell monolayers. Uptake of (59)Fe by the cells was used as an index of iron bioavailability. Na(2)WO(4) did not affect (59)Fe uptake from samples containing only iron but did slightly inhibit (by 10%) uptake from samples containing iron + CPP. These results are consistent with hypothesis 2 and provide a possible explanation for the observation that partial hydrolysis of casein improves iron bioavailability.

Post-translational phosphorylation affects the IgE binding capacity of caseins

IgE response specific to those molecular regions of casein that contain a major phosphorylation site was analyzed using native and modified caseins and derived peptides. This study included (i) the naturally occurring common variants A1 and A from beta- and alphas2-caseins, respectively, which were purified in the native form and then dephosphorylated, (ii) a purified rare variant D of alphas2-casein which lacks one major phosphorylation site, and (iii) the native and dephosphorylated tryptic fragment f(1-25) from beta-casein. Direct and indirect ELISA using sera from patients allergic to milk showed that the IgE response to caseins is affected by modifying or eliminating the major phosphorylation site.

Overphosphorylation of milk caseins by a recombinant protein kinase CK2 catalytic subunit

Milk caseins have been phosphorylated by a recombinant protein kinase CK2 catalytic subunit from Schizosaccharomyces pombe (rspCK2alpha). Phosphate incorporation stoechiometries into purified caseins and into native phosphocaseinate, a substrate exhibiting a micellar-like structure, were determined. We incorporated 2.01 mol of P/mol of alpha-casein, 6.46 mol of P/mol of beta-casein, up to 0. 29 mol of P/mol of kappa-casein in 4 h, and more than 1.36 mol of P/mol of casein into phosphocaseinate under optimized conditions. Phosphocaseinate was sequentially phosphorylated; beta-caseins being labeled at first; alpha-caseins being labeled later; and to a lower extend, kappa-caseins were the last to be phosphorylated. The solubility of phosphocaseinate micelles increased by 1.34 from 65 to 87%, and its rennetting time was increased 2.88 times. These results are discussed in terms of plausible structural organization of caseins micelles and the effect of phosphorylation on their structure.