Ian M. Morrison

Starch production and industrial use

This review of starch is concerned with its industrial uses, origins and structure. The current demand for starch is met by a restricted range of crops, the most important of which are potatoes, maize, wheat and tapioca. Improvements in the properties of starches for industrial uses can be achieved through chemical and physical modification of extracted starch and through the manipulation of starch biosynthesis in the plant itself. We examine starch structure and composition in relation to its use and exploitation by industry. The current understanding of physiological and biochemical mechanisms influencing starch formation in higher plants is described. This information is set in the context of the need to know the physical/chemical specification for each individual starch and to understand the genetic control of these characteristics in order to identify target genes for manipulation.

Plant cell walls as dietary fibre : range, structure, processing and function

The ingestion of dietary fibre has been correlated with the prevention of many health-threatening diseases and cancers. Plant cell walls are the major source of dietary fibre and this review investigates the relationship between the structure of different types of plant cell walls and their beneficial effects. The effects of processing and cooking on dietary fibre are also examined. Structure-function relationships between individual cell wall components and the beneficial effects of dietary fibre are not well defined and it may be that the physical, physiochemical and topochemical properties of plant cell walls and their components are also important.

Hydrolysis of plant cell walls with trifluoroacetic acid

Abstract A method is presented for the determination of the neutral monosaccharide units present in plant cell walls. The cell wall sample is dissolved by stirring for 18 hr at 37° with trifluoroacetic acid. The cellulosic component is hydrolysed by the addition of small amounts of water during heating at 100° so that the cellulose, during depolymerisation, stays in solution. The hemicellulosic component is hydrolysed under more dilute conditions at 100° such that the hemicellulosic pentose units undergo minimum degradation. The stability of the monosaccharide units under the different hydrolytic conditions is presented. The reproducibility of the method is demonstrated by comparing results of the new method with those from more established methods using samples of Italian ryegrass leaf and stem, lucerne stem, sainfoin leaf, birch sawdust and barley straw.

ISOLATION AND ANALYSIS OF LIGNIN-CARBOHYDRATE COMPLEXES FROM LOLIUM MULTIFLORUM

Lignin-carbohydrate complexes were extracted from grass cell walls by a variety of solvents. The yield of complexes was greatly enhanced if the sample was finely milled in a ball mill; dimethyl sulphoxide and N alkali extractions gave the highest yields. Hydrolysis showed that the carbohydrate fraction of the alkali-extracted complex contained mainly xylose (ca. 70%) and arabinose (ca. 20 %) whereas the dimethyl sulphoxide extracted complex contained glucose (ca. 50 %), xylose (ca. 30%), arabinose (ca. 12 %) and galactose (ca. 5 %). The UV spectrum of the dimethyl sulphoxide extracted complex showed lignin absorbance at 280 nm, but, in addition, ester bonding was also observed by the presence of a secondary absorbing region near 325 nm. This secondary absorbing region was absent from the spectrum of the alkali-extracted complexes. Fractionation of the complexes by ethanol precipitation gave a major component which appeared homogeneous by molecular sieve chromatography and had a MW of ⩾ 150,000.

Cell wall-bound oxidases from tobacco (Nicotiana tabacum)xylem participate in lignin formation

A band of cells closest to the cambium in the xylem of tobacco (Nicotiana tabacum L. cv. Samsun) stems oxidized 2,2-azinobis-(3-ethylbenzo-thiazoline-6-sulphonate) (ABTS), o-dianisidine and syringaldazine in the absence of exogenously added hydrogen peroxide. The oxidation was not prevented by catalase which suggests that the oxidation is not dependent on the production and utilisation of endogenous hydrogen peroxide by cell-wall peroxidases. Cell walls, isolated from tobacco xylem, also oxidized these substrates in the absence of added hydrogen peroxide. The cell walls consumed molecular oxygen whilst oxidizing a range of compounds including coniferyl alcohol. The substrate preference and sensitivity to inhibitors suggest the presence of laccasetype polyphenol oxidases (p-diphenol:O2 oxidoreductase EC 1.14.18.1) which are covalently bound to the wall. The oxidation of coniferyl alcohol by the xylem cell walls was confirmed by assays based on the disappearance of coniferyl alcohol and was not affected by the presence of 500 units·mi-1 catalase or Superoxide dismutase. Prolonged incubation of cell walls with coniferyl alcohol led to the production of a yellow-orange water-insoluble material that precipitated with the cell walls. Although a proportion of this material was soluble in methanol, the majority was tightly associated with the cell walls. These coloured cell walls had elevated lignin contents when assayed by the acetyl-bromide method. Fourier transforminfrared spectroscopic analysis of the coloured cell walls indicated that the increased lignin content is due to the deposition of guaiacyl-type lignin. Digestion of the xylem cell walls with Driselase, a mixture of fungal glycases, produced a wall residue that had a dramatically reduced ability to oxidize ABTS in the absence of added H2O2. However, oxidase activity could not be detected in the Driselase-solubilized extract, although small amounts of oxidase activity could be recovered from the Driselaseresistant wall residue by extraction in 3 M CaCl2.

Sisal fibres and their constituent non-cellulosic polymers

Abstract To characterise the constitutive non-cellulosic components sisal fibres were sequentially extracted with CDTA, Na2CO3 and increasing concentrations of NaOH. Gel permeation chromatography (GPC) of the CDTA extract suggested that a pectic polysaccharide similar to rhamnogalacturonan II (RG II) and glucuronoxylan were present. Diffuse reflectance infrared (DRIFT) and solid state NMR spectroscopies indicated that these polysaccharides were attached to esterified cinnamic acids and/or oligo-lignins. Treatment with Na2CO3 also extracted a RG-I-like polysaccharide and glucuronoxylan and reduced the degree of esterification in the residue as confirmed by both DRIFT and NMR spectroscopies. Extraction with 0.1–4.0 M NaOH reduced lignin and non-cellulosic polysaccharide (NCP) contents with glucuronoxylan as the main extracted NCP. Small amounts of pectin and mannan-derived fragments were also identified in the 0.1 M and 1.0 M NaOH extracts. Treatment with 4 M NaOH 50 mM H3BO3 dramatically altered the structure of the fibre, reducing the proportion of crystalline cellulose, as demonstrated by DRIFT and NMR spectroscopies. GPC of the extract revealed that xylan, amorphous cellulose and a glucomannan had been extracted. DRIFT spectroscopy also indicated that, despite extensive washing, the residue contained bound-borates. The NMR spectrum revealed that the lignin remaining after extraction with 4 M NaOH was almost exclusively guaiacyl.

Tyrosine residues enhance cross-linking of synthetic proteins into lignin-like dehydrogenation products

Synthetic proteins composed of lysine (polylysine, PL) and a random co-polymer of lysine and tyrosine (polylysine/tyrosine, PLT) were incorporated into lignin-like dehydrogenation polymers (DHPs) formed by the peroxidase-catalysed polymerisation of coniferyl alcohol. The yield of water-insoluble DHPs was greater in the presence of the tyrosine-containing PLT than PL. Indeed, the increase in total yield with PLT was often greater than could be accounted for if all the protein added had become incorporated into the DHPs. A comparison of the Fourier transform infra-red spectra of the DHPs formed in the absence and presence of synthetic proteins provided evidence that the presence of PLT had enhanced the incorporation of coniferyl alcohol, albeit in a less cross-linked form, into DHPs. The insolubilisation of PL and PLT was suggested by the presence of absorption bands in the infra-red spectra of their respective DHPs that are characteristic of protein/amide moieties. The insolubilisation of PLT was confirmed by the release of material from PLT-DHPs by digestion with trypsin. Therefore, this study provides evidence that the presence of tyrosine residues may enhance the cross-linking of proteins into lignin.

Lignin-carbohydrate complexes from Lolium perenne.

Abstract Lignin-carbohydrate and lignin-hemicellulose complexes were extracted sequentially from four varieties of Lolium perenne which had previously been

Phenolic-carbohydrate complexes in the cell walls of Lolium perenne

Abstract Two classes of phenolic-carbohydrate complexes were purified from the water-soluble products obtained from the digestion of ryegrass cell walls with a cellulase preparation. They contained D -glucose, D -xylose, L -arabinose, D -galactose and D -mannose residues in the ratios 3.6:10:6.3:1.4:2.3 and 5.3:10:3.0:1.1:2.1, respectively, and contained ca one ferulic acid residue to every 50–100 neutral sugar residues. The complexes were based on (1 » 4)β- D -xylan chains to which were attached residues of L -arabinofuranose and D -galactopyranose. Mixed linkage (1 » 3), (1 » 4)-β- D -glucan chains also appeared to be integral components of these complexes. Phenolic-carbohydrate complexes could also be solubilized from the enzyme-resistant residue on hydrolysis under mildly acidic conditions. Two complexes were purified and found to contain the neutral sugar residues listed above, along with small amounts of L -rhamnose, in the ratios 3.5:10:4.9:1.1:3.0 and 3.3:10:3.7:2.8:1.1:2.0, respectively. These latter complexes were also based on galacto-arabinoxylans associated with (1 » 3), (1 » 4)-β- D -glucans and also contained ferulic acid residues which could be released on saponification.

Potato starches: variation in composition and properties between three genotypes grown at two different sites and in two different years

Starch granules were isolated from three distinct potato (Solanum tuberosum L) genotypes, cvs Glamis and Record and line 86Q35(8), grown at two different sites in 1996 and 1997. Differences in the chemical compositions of the granules were investigated using blue values of the starch–iodine complexes as indicators of amylose contents and from phosphorus contents. The physical properties determined were starch damage, swelling power, turbidity, granule size distribution, viscosity data and profile, and gelatinisation temperatures as well as enthalpy of gelatinisation. The differences in the blue values of the starch–iodine complexes were significant for genotype (P < 0.001) but not for site or year. Highly significant differences in starch granule phosphorus contents were found both between genotypes (P < 0.001) and between sites (P < 0.001), but the differences between years were less significant (P < 0.01). Genotype 86Q35(8) had nearly twice the starch phosphorus content of the other two genotypes. Significant differences were also found between genotypes in terms of granule size distributions (P < 0.01), with 86Q35(8) having a modal granule size smaller than that of the other two genotypes. The viscosity data and profiles, measured at 48 g l−1, showed that samples of starch granules isolated from genotype 86Q35(8), irrespective of the site or year, behaved similarly to each other. However, the profiles obtained from starch granules derived from Glamis and Record depended on the site and year and were distinctly different from the profiles obtained from starch granules isolated from 86Q35(8). On the other hand, the differential scanning calorimetric data recorded no consistent differences in the gelatinisation temperatures and enthalpy of gelatinisation between genotype, site and year. The prospects of using specific potato genotypes as sources of starch for particular uses are discussed. © 2000 Society of Chemical Industry