Harry Gruppen

Sorghum grain as human food in Africa: relevance of content of starch and amylase activities

Sorghum is a staple food grain in many semi-arid and tropic areas of the world, notably in Sub-Saharan Africa because of its good adaptation to hard environments and its good yield of production. Among important biochemical components for sorghum processing are levels of starch (amylose and amylopectin) and starch depolymerizing enzymes. Current research focus on identifying varieties meeting specific agricultural and food requirements from the great biodiversity of sorghums to insure food security. Results show that some sorghums are rich sources of micronutrients (minerals and vitamins) and macronutrients (carbohydrates, proteins and fat). Sorghum has a resistant starch, which makes it interesting for obese and diabetic people. In addition, sorghum may be an alternative food for people who are allergic to gluten. Malts of some sorghum varieties display

Peptides are Building Blocks of Heat-Induced Fibrillar Protein Aggregates of β-Lactoglobulin Formed at pH 2

The proteinaceous material present in beta-lactoglobulin fibrils formed after heating (20 h at 85 degrees C) at pH 2 was identified during this study. Fibrils were separated from the nonaggregated material, and the fibrils were dissociated using 8 M guanidine chloride and 0.1 M 1,4-dithiothreitol (pH 8). Characterization of the different fractions was performed using thioflavin T fluorescence, high-performance size-exclusion chromatography, reversed-phase HPLC, and mass spectrometry (MALDI-TOF). Beta-lactoglobulin was found to be hydrolyzed into peptides with molecular masses between 2000 and 8000 Da, and the fibrils were composed of a part of these peptides and not intact beta-lactoglobulin. The majority of the peptides (both aggregated and nonaggregated) were a result from cleavage of the peptide bonds before or after aspartic acid residues. Explanations for the presence of certain peptide fragments in the fibrils are the hydrophobicity, low charge, charge distribution, and capacity to form beta-sheets.

Optimisation of the angiotensin converting enzyme inhibition by whey protein hydrolysates using response surface methodology

Protein hydrolysates inhibiting the angiotensin converting enzyme (ACE) in vitro, are potentially interesting constituents for blood pressure decreasing products. To minimise the amount of hydrolysate needed, the ACE inhibitory activity should be maximised. The total peptide composition of a hydrolysate determines its ACE inhibitory ability and depends on the specificity of the proteolytic enzyme and the process conditions used for the production of the hydrolysate. In the present research, the effect of process conditions on the ACE inhibitory activity of whey protein concentrate hydrolysed with a pancreatic enzyme mixture was investigated systematically using response surface methodology. It was shown that ACE inhibitory activity of the whey hydrolysates could be controlled by regulation of five process conditions. Hydrolysis conditions for optimal ACE inhibition were defined using a response surface model.

Characterisation by 1H NMR spectroscopy of enzymically derived oligosaccharides from alkali-extractable wheat-flour arabinoxylan.

Abstract Oligosaccharides obtained from alkali-extractable wheat-flour arabinoxylans by digestion with endo-(1 → 4)-β- d -xylanase from Aspergillus awamori were fractionated by size-exclusion chromatography on Bio-Gel P-2 followed by high-performance anion-exchange chromatography, and subjected to monosaccharide analysis and 1 H NMR spectroscopy. The results revealed (1 → 4)-linked β- d -xylopyrano-oligosaccharides partly 3- and/or 2,3-substituted with single α- l -arabinofuranosyl groups. The structures of 12 such arabinoxylan oligosaccharides were established.

Mode of action of the xylan-degrading enzymes from Aspergillus awamori on alkali-extractable cereal arabinoxylans

Alkali-extractable cereal arabinoxylan and oligosaccharides of known structure derived from it by enzymic hydrolysis were treated with endo-(1-->4)-beta-D-xylanases I and III from Aspergillus awamori CMI 142717 and the digests subjected to analysis by high performance anion-exchange chromatography. Clear differences in the mode of action of the two endo-(1-->4)-beta-D-xylanases were observed. When counting from the reducing end, at least one unsubstituted xylopyranosyl residue adjacent to singly substituted xylopyranosyl residues or two unsubstituted xylopyranosyl residues adjacent to doubly substituted xylopyranosyl residues cannot be removed by endo-(1-->4)-beta-D-xylanase I. At least two unsubstituted xylopyranosyl residues adjacent to singly or doubly substituted xylopyranosyl residues cannot be removed by endo-(1-->4)-beta-D-xylanase III. beta-D-Xylosidase from the same xylanolytic system was able to remove terminal xylopyranosyl residues from the nonreducing end of branched oligosaccharides only when two contiguous unsubstituted xylopyranosyl residues were present adjacent to singly or doubly substituted xylopyranosyl residues.

Procyanidin Dimers A1, A2, and B2 Are Absorbed without Conjugation or Methylation from the Small Intestine of Rats

Intervention studies with procyanidin (PC)-rich extracts and products such as cocoa and wine suggest protective effects of PC against cardiovascular diseases. However, there is no consensus on the absorption and metabolism of PC dimers. Interestingly, nothing is known about the absorption of A-type PC. In this study, the absorption and metabolism of purified PC dimers A1 [epicatechin-(2-O-7, 4-8)-catechin], A2 [epicatechin-(2-O-7, 4-8)-epicatechin], and B2 [epicatechin-(4-8)-epicatechin], A-type trimers, a mixture of A1, B2, and a tetrameric A-type, and monomeric epicatechin were compared by in situ perfusion of the small intestine of rats for 0-30 min. The rats had their bile duct, portal vein, and small intestine cannulated. Unmodified and methylated metabolites were distinguished from their conjugates by differential beta-glucuronidase treatment. A1 and A2 dimers were absorbed from the small intestine of rats and they were better absorbed than dimer B2. Absorption of the A-type dimers was only 5-10% of that of monomeric epicatechin. Dimers were not conjugated or methylated in contrast to epicatechin, which was partly methylated and 100% conjugated. A-type trimers were not absorbed. Furthermore, the presence of tetrameric PC enhanced the absorption of B2 but not that of A1. Epicatechin, methylated epicatechin, and their conjugates were not found as metabolites of the PC tested. In conclusion, dimers A1, A2, and B2 are slightly absorbed but are not conjugated or methylated, thus conserving their biological activity after absorption. Because PC contents of foods are relatively high, dimers may contribute to systemic effects of PC.

Isolation and characterization of soluble protein from the green microalgae Tetraselmis sp.

Extraction of high-value protein fractions for techno-functional applications in foods can considerably increase the commercial value of microalgae biomass. Proteins from Tetraselmis sp. were extracted and purified after cell disintegration by bead milling, centrifugation, ion exchange chromatography using the absorbent Streamline DEAE, and final decolorization by precipitation at pH 3.5. The algae soluble isolate was free from the intense color typical for algae products and contained 64% (w/w) proteins and 24% (w/w) carbohydrates. The final isolate showed solubility independent of ionic strength and 100% solubility at and above pH 5.5. Since most plant proteins used in foods show poor solubility in the pH range 5.5-6.5, the algae soluble protein isolate could be useful for techno-functional applications in this pH range.

Efficacy of Food Proteins as Carriers for Flavonoids

Enrichment of flavonoids in food is often limited by their off-tastes, which might be counteracted by the use of food proteins as carriers of flavonoids. Various milk proteins, egg proteins, and gelatin hydrolysates were compared for their binding characteristics to two flavan-3-ols. Among the proteins tested for their affinities toward epigallocatechin gallate (EGCG), β-casein and gelatin hydrolysates, in particular fish gelatin, were found to be the most promising carriers with an affinity on the order of 10(4) M(-1). A flexible open structure of proteins, as present in random coil proteins, was found to be important. The saturation of binding observed at high flavonoid/protein ratios was used to estimate the maximal binding capacity of each protein. To reach a daily intake of EGCG that has been associated with positive health effects, only 519 mg of gelatin B and 787 mg of β-casein were required to complex EGCG on the basis of their maximal binding capacity. When the absence of turbidity is taken into account, β-casein prevails as carrier. Three selected proteins were further investigated for their binding potential of representative flavonoids differing in their C-ring structure. An increase in hydrophobicity of flavonoids was related to a higher affinity for proteins, and the presence of a gallic acid ester on the C-ring showed an overall higher affinity.

Some phenolic compounds increase the nitric oxide level in endothelial cells in vitro

The vasorelaxing properties of chocolate and wine might relate to the presence of phenolic compounds. One of the potential mechanisms involved is stimulation of endothelial nitric oxide (NO) production, as NO is a major regulator of vasodilatation. This study aimed to develop an in vitro assay using the hybrid human endothelial cell line EA.hy926 to rapidly screen phenolic compounds for their NO-stimulating potential. The assay was optimized, and a selection of 33 phenolics, namely, procyanidins, monomeric flavan-3-ols, flavonols, a flavone, a flavanone, a chalcone, a stilbene, and phenolic acids, was tested for their ability to enhance endothelial NO level. Resveratrol, a well-known enhancer of NO level, was included as a positive control. Of the 33 phenolics tested, only resveratrol (285% increase in NO level), quercetin (110% increase), epicatechingallate (ECg) (85% increase), and epigallocatechingallate (EGCg) (60% increase) were significant (P <or= 0.05) enhancers. Procyanidins showed a nonsignificant tendency to elevate NO level. Concentration-dependent correlations between enhanced NO level and endothelial nitric oxide synthase (eNOS) expression were demonstrated for the three polyphenols tested (resveratrol, ECg, and EGCg). Thus, an easy screening tool for change in cellular NO level was developed. Use of this assay showed that only a limited number of phenolic compounds might enhance NO level with an increased amount of eNOS enzyme as a possible contributing mechanism.

Characterization of Oligomeric Xylan Structures from Corn Fiber Resistant to Pretreatment and Simultaneous Saccharification and Fermentation

Corn fiber, a byproduct from the corn industry, would be a good source for bioethanol production if the hemicellulose, consisting of polymeric glucoronoarabinoxylans, can be degraded into fermentable sugars. Structural knowledge of the hemicellulose is needed to improve the enzymatic hydrolyses of corn fiber. Oligosaccharides that resisted a mild acid pretreatment and subsequent enzymatic hydrolysis, representing 50% of the starting material, were fractionated on reversed phase and size exclusion material and characterized. The oligosaccharides within each fraction were highly substituted by various compounds. Oligosaccharides containing uronic acid were accumulated in two polar fractions unless also a feruloyl group was present. Feruloylated oligosaccharides, containing mono- and/or diferulic acid, were accumulated within four more apolar fractions. All fractions contained high amounts of acetyl substituents. The data show that complex xylan oligomers are present in which ferulic acid, diferulates, acetic acid, galactose, arabinose, and uronic acids were combined within an oligomer. Hypothetical structures are discussed, demonstrating which enzyme activities are lacking to fully degrade corn glucuronoarabinoxylans.