Whole grain in manufactured foods: Current use, challenges and the way forward.

Some countries now incorporate recommendations for increased consumption of whole grain (WG) into local dietary guidelines. Cereal and pseudo-cereal grains are good sources of complex carbohydrates, dietary fiber, proteins, phytochemicals, vitamins and minerals. However, research shows that the large majority of consumers are still falling short of WG consumption goals. To address this, we are actively involved in research to help increase the WG content of processed foods without compromising on taste and texture. In order to ensure consumer trust, the advancement of process technologies in incorporating WG to produce tasty food has to go hand in hand with well designed clinical trials that confirm the health benefits resulting from diets rich in WG.

Mannans in tomato fruit are not depolymerized during ripening despite the presence of endo-ß-mannanase.

Cell walls of tomato fruit contain hemicellulosic mannans that may fulfill a structural role. Two populations were purified from cell walls of red ripe tomato tissue and named galactoglucomannan-glucuronoxylan I and II (GGM-GX I and II), respectively. Both polysaccharides not only consisted of mannose, glucose and galactose, indicating the presence of GGM, but also contained xylose and glucuronic acid, indicating the presence of GX. Treatment of both polysaccharides with xylanase or endo-ß-mannanase showed that the GX and the GGM were associated in a complex. The composition of GGM-GX II changed slightly during tomato ripening, but both GGM-GX I and II showed no change in molecular weight, indicating that they were not hydrolyzed during ripening. Ripe tomato fruit also possess an endo-ß-mannanase, an enzyme that in vitro was capable of either hydrolyzing GGM-GX I and II (endo-ß-mannanase activity), or transglycosylating them in the presence of mannan oligosaccharides (mannan transglycosylase activity). The lack of evidence for hydrolysis of these potential substrates in vivo suggests either that the enzyme and potential substrates are not accessible to each other for some reason, or that the main activity of endo-ß-mannanase is not hydrolysis but transglycosylation, a reaction in which polysaccharide substrates and end-products are indistinguishable. Transglycosylation would remodel rather than weaken the cell wall and allow the fruit epidermis to possibly retain flexibility and plasticity to resist cracking and infection when the fruit is ripe.

Exploring novel non-Leloir ß-glucosyltransferases from proteobacteria for modifying linear (ß1->3)-linked gluco-oligosaccharide chains.

Over the years several ß-glucan transferases from yeast and fungi have been reported, but enzymes with such an activity from bacteria have not been characterized so far. In this work, we describe the cloning and expression of genes encoding ß-glucosyltransferase domains of glycosyl hydrolase family GH17 from three species of proteobacteria: Pseudomonas aeruginosa PAO1, P. putida KT2440 and Azotobacter vinelandii ATCC BAA-1303. The encoded enzymes of these GH17 domains turned out to have a non-Leloir trans-ß-glucosylation activity, as they do not use activated nucleotide sugar as donor, but transfer a glycosyl group from a ß-glucan donor to a ß-glucan acceptor. More particularly, the activity of the three recombinant enzymes on linear (ß1 â†’ 3)-linked gluco-oligosaccharides (Lam-Glc(4-9)) and their corresponding alditols (Lam-Glc(4-9)-ol) was studied. Detailed structural analysis, based on thin-layer chromatography, matrix-assisted laser desorption ionization time-of-flight mass spectrometry, electrospray ionization mass spectrometry, and 1D/2D (1)H and (13)C nuclear magnetic resonance data, revealed diverse product spectra. Depending on the enzyme used, besides (ß1 â†’ 3)-elongation activity, (ß1 â†’ 4)- or (ß1 â†’ 6)-elongation, or (ß1 â†’ 6)-branching activities were also detected.

Re-interpreting the role of endo-beta-mannanases as mannan endotransglycosylase/hydrolases in the plant cell wall.

BACKGROUND: Mannans are hemicellulosic polysaccharides in the plant primary cell wall with two major physiological roles: as storage polysaccharides that provide energy for the growing seedling; and as structural components of the hemicellulose-cellulose network with a similar function to xyloglucans. Endo-beta-mannanases are hydrolytic enzymes that cleave the mannan backbone. They are active during seed germination and during processes of growth or senescence. The recent discovery that endo-beta-mannanase LeMAN4a from ripe tomato fruit also has mannan transglycosylase activity requires the role of endo-beta-mannanases to be reinterpreted. AIMS: In this review, the role of endo-beta-mannanases as mannan endotransglycosylase/hydrolases (MTHs) in remodelling the plant cell wall is considered by analogy to the role of xyloglucan endotransglucosylase/hydrolases (XTHs). The current understanding of the reaction mechanism of these enzymes, their three-dimensional protein structure, their substrates and their genes are reported. FUTURE OUTLOOK: There are likely to be more endohydrolases within the plant cell wall that can carry out hydrolysis and transglycosylation reactions. The challenge will be to demonstrate that the transglycosylation activities shown in vitro also exist in vivo and to validate a role for transglycosylation reactions during the growth and development of the plant cell wall.

Dietary fiber as a versatile food component: an industrial perspective.

The continued emphasis on the importance of dietary fibers to the Western diet and the need for products with a lower calorific content is pressuring food companies to allocate more resources to the development of fiber-enriched products. The challenge to the industry is to accomplish this goal without sacrificing the organoleptic appeal of some of their core offerings. As future research details specific nutritional benefits of individual components of dietary fiber, food companies will need flexible alternatives in order to validate new 'functional' food claims and to respond rapidly to emerging trends in fiber-enriched products. These objectives will be achieved by understanding the physicochemical basis for the biotechnical functionality of fibers and by developing, and making available fibers which provide a broad spectrum of bioactive and texture modulating properties.

Mannan transglycosylase: a novel enzyme activity in cell walls of higher plants.

Mannan transglycosylase is a novel cell wall enzyme activity acting on mannan-based plant polysaccharides in primary cell walls of monocotyledons and dicotyledons. The enzyme activity was detected by its ability to transfer galactoglucomannan (GGM) polysaccharides to tritium-labelled GGM-derived oligosaccharides generating tritium-labelled GGM polysaccharides. Mannan transglycosylase was found in a range of plant species and tissues. High levels of the enzyme activity were present in flowers of some kiwifruit (Actinidia) species and in ripe tomato (Solanum lycopersicum L.) fruit. Low levels were detected in mature green tomato fruit and activity increased during tomato fruit ripening up to the red ripe stage. Essentially all activity was found in the tomato skin and outermost 2 mm of tissue. Mannan transglycosylase activity in tomato skin and outer pericarp is specific for mannan-based plant polysaccharides, including GGM, galactomannan, glucomannan and mannan. The exact structural requirements for valid acceptors remain to be defined. Nevertheless, a mannose residue at the second position of the sugar chain and the absence of a galactose substituent on the fourth residue (counting from the non-reducing end) appear to be minimal requirements. Mannan-based polysaccharides in the plant cell wall may have a role analogous to that of xyloglucans, introducing flexibility and forming growth-restraining networks with cellulose. Thus mannan transglycosylase and xyloglucan endotransglycosylase, the only other known transglycosylase activity in plant cell walls, may both be involved in remodelling and refining the cellulose framework in developmental processes throughout the life of a plant.

Changes to the galactose/mannose ratio in galactomannans during coffee bean ( Coffea arabica L.) development: implications for in vivo modification of galactomannan synthesis.

Endosperm was isolated from Arabica Caturra coffee beans 11, 15, 21, 26, 31 and 37 weeks after flowering, and the chemical composition and relative solubility of its component polysaccharides determined at each growth stage. Chemical analysis of the total mannan content of the cell wall material was done after solubilisation of galactomannans by alkaline extraction of the cell wall material followed by enzymatic digestion of the alkali-insoluble residue with a mixture of endo-mannanse and endo-glucanase. Eleven weeks after flowering, galactomannans accounted for approximately 10% of the polysaccharides but were highly substituted, with galactose/mannose ratios between 1:2 and 1:7. As the bean matured, galactomannan became the predominant polysaccharide, until 31 weeks after flowering it accounted for approximately 50% of the polysaccharides. However, it was less substituted, possessing galactose/mannose ratios between 1:7 and 1:40. Early in bean growth, up to 50% of the cell wall polysaccharides were extractable but as the galactomannan content of the bean increased there was a reduction in the extractability of all polysaccharides. The decrease in the galactose/mannose ratio of the galactomannans commenced between 21 and 26 weeks after flowering and was in synchrony with a rise in the concentration of free galactose in the beans. The results indicated that the degree of substitution of the galactomannans in coffee beans is developmentally regulated and may result, in part, from the modification of a primary synthetic product by the action of an alpha-galactosidase.

Effect of roasting on degradation and structural features of polysaccharides in Arabica coffee beans.

The degree and nature of polysaccharide degradation at different roasting levels was determined for three Arabica (Coffea arabica) bean varieties. Between 12 and 40% of the bean polysaccharides were degraded depending on the roasting conditions. The thermal stability of the arabinogalactans, (galacto)mannans and cellulose was markedly different. The arabinogalactans and mannans were degraded up to 60 and 36%, respectively, after a dark roast, while cellulose showed negligible evidence of degradation. Roasting led to increased solubility of both the arabinogalactans and (galacto)mannans from the bean but the structural modifications, which accompanied this change in solubility, were different for each polysaccharide. Despite the moderate degradation of the (galacto)mannans, those remaining in the bean after roasting showed no evidence of change to their molecular weight even after a dark roast. In contrast, arabinogalactans were depolymerised after a light roast both by fission of the galactan backbone and loss of arabinose from the sidechains. The recently discovered covalent link between the coffee bean arabinogalactans and protein survived roasting. The glucuronic acid component of the AG was degraded markedly after a dark roast, but approximately 30% of the original content remained as part of the AG polymer. The results show that polysaccharide degradation during roasting is more marked than previously documented, and points to roasting induced changes to the polysaccharides as major factors in the changing physicochemical profile of the coffee bean during processing.

Coffee bean arabinogalactans: acidic polymers covalently linked to protein.

The arabinogalactan content of green coffee beans (Coffea arabica var. Yellow Caturra) was released by a combination of chemical extraction and enzymatic hydrolysis of the mannan-cellulose component of the wall. Several arabinogalactan fractions were isolated, purified by gel-permeation and ion-exchange chromatography and characterised by compositional and linkage analysis. The AG fractions contained between 6 and 8% glucuronic acid, and gave a positive test for the beta-glucosyl-Yariv reagent, a stain specific for arabinogalactan-proteins. The protein component accounted for between 0.5 and 2.0% of the AGPs and contained between 7 and 12% hydroxyproline. The AG moieties displayed considerable heterogeneity with regard to their degree of arabinosylation and the extent and composition of their side-chains. They possessed a MW average of 650 kDa which ranged between 150 and 2000 kDa. An investigation of the structural features of the major AG fraction, released following enzymatic hydrolysis of the mannan-cellulose polymers, allowed a partial structure of coffee arabinogalactan to be proposed.