Carol M. Duffus

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.

The effect of storage temperature on reducing sugar concentration and the activities of three amylolytic enzymes in tubers of the cultivated potato, Solanum tuberosum L.

SummaryReducing sugar content, and activities of three starch hydrolysing enzymes, alpha-amylase, beta-amylase and debranching enzyme were measured over several months in tubers of five cultivars stored at 4°C or 10°C. Cultivars differed in their sensitivity to storage temperature. Reducing sugar content of tubers and the activities of three starch hydrolysing enzymes increased sharply during the first weeks of storage at 4°C. At 10°C, reducing sugar content, and the activity of the three enzymes remained constant or increased only slightly.

Amylolytic activity in stored potato tubers. 2. The effect of low-temperature storage on the activities of α-and β-amylase and α-glucosidase in potato tubers

SummaryTubers of the potato cultivars Record, Wilja, Pentland Dell and Brodick (formerly clone 137371) were sampled before and after storage at either 4°C or 10°C. Reducing sugar content stayed constant during storage at 10°C in all four cultivars but rose greatly during the first 6–12 weeks of storage at 4°C in Record, Wilja and Pentland Dell but not in Brodick. Amylolytic activity was determined after 5 weeks storage using blockedp-nitrophenyl maltoheptaoside as substrate for α-amylase,p-nitrophenyl maltopentaoside as substrate for β-amylase, andp-nitrophenylglucopyranoside as substrate for α-glucosidase. The values obtained from tubers stored at 4°C were higher than those from tubers stored at 10°C, the differences being much less in Brodick than in the other three cultivars.

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 (Pu2005<u20090.001) but not for site or year. Highly significant differences in starch granule phosphorus contents were found both between genotypes (Pu2005<u20090.001) and between sites (Pu2005<u20090.001), but the differences between years were less significant (Pu2005<u20090.01). 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 (Pu2005<u20090.01), with 86Q35(8) having a modal granule size smaller than that of the other two genotypes. The viscosity data and profiles, measured at 48u2009gu2009l−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. n n© 2000 Society of Chemical Industry

Involvement of polyamines, diamine oxidase and polyamine oxidase in resistance of barley to Blumeria graminis f. sp. hordei

Polyamine levels and diamine and polyamine oxidase activities have been investigated in the first leaves of barley (Hordeum vulgare L.) in the absence of or following inoculation with conidia of powdery mildew (Blumeria graminis f. sp. hordei). Two cultivars with varying sensitivity to powdery mildew, viz., Chariot (resistant) and Golden Promise (susceptible) were used. The levels of putrescine, spermidine and spermine were found to be higher in the leaves of Chariot than in the leaves of Golden Promise and, with the exception of spermine, were generally higher in both cultivars after inoculation. In inoculated leaves of Chariot, levels of putrescine and spermidine peaked at 9 days and 12 days, respectively. In controls (uninoculated leaves), the activities of these enzymes, and putrescine and spermidine levels also increased but not to the same extent as in inoculated leaves. With Golden Promise, the levels of putrescine and spermidine in the inoculated leaves changed very little over sampling times but were always higher than in the controls. In this cultivar, there was little difference between inoculated leaves and the controls in diamine oxidase activity which reached a maximum value at 9 days post-inoculation. Activity of the bound form of diamine oxidase was low in both the cultivars. Polyamine oxidase was not detected at 3 days after inoculation in either cultivar but activity at fairly low levels was recorded at later times, usually reaching a maximum value at 9 days. The results suggest that polyamine metabolism and diamine oxidase activity in particular may be involved in the mechanism conferring resistance to barley powdery mildew in Chariot.

Changes in the surface morphology of starch granules of the cultivated potato,Solanum tuberosum L. during storage

SummaryLow temperature sweetening is a major problem to chip and crisp manufacturers as it results in the production of unacceptably dark fry products. Cryo-electron microscopy was used to examine the changes which occur to the surface morphology of starch granules from tubers of cultivars Record and Brodick stored at 4°C and 10°C. At harvest, the surface of the starch granules was smooth but during storage the surface of the granules became progressívely more pitted. The feasibility of using this technique to determine whether increased starch breakdown occurs at low storage temperatures is discussed.

Amylolytic activity in stored potato tubers. 1. Estimation usingp-nitrophenyloligosaccharides

SummaryMethods for the estimation of amylolytic activity are reviewed. A procedure for the routine extraction of amylolytic activity from freeze-dried powder prepared from potato tubers is described. The extraction medium is buffered at pH 7.0 and contains glycerol, dithiothreitol, calcium chloride and the non-ionic detergent, nonidet P-40. α-Amylase activity and exoamylolytic activity were estimated in crude extracts of potato tubers using the substrates, blockedp-nitrophenyl-maltoheptaoside andp-nitrophenyl-maltopentaoside respectively. These substrates are included in kits supplied by Biocon, (UK) Ltd to measure the α- and ß-amylase activity in cereals. The validity of using these kits for the determination of α- and ß-amylase activity in potato tuber tissue is discussed.

Correlation of gibberellin-induced growth, polyamine levels and amine oxidases in epicotyl, root and leaf blade of barley seedlings

The potential role of diamine oxidase (DAO) and polyamine oxidase (PAO) in relation to polyamines was investigated in epicotyls, roots and leaf blades at 3 and 6 days after gibberellic acid (GA) application in barley (Hordeum vulgare L.) seedlings of cvs. Maythorpe (non-mutant parent) and Golden Promise (semi-dwarf mutant). There was a significant increase in epicotyl and leaf-blade elongation rates in GA-treated seedlings of cv. Maythorpe as compared to cv. Golden Promise. DAO and PAO were detectable in all segments of the leaf blade, but the highest activities were present in basal segments. These enzymes, which are thought to have a role in the elimination of cellular polyamines, increased in activity following GA application compared to controls. Application of 10−6 M GA to the first leaf, significantly increased endogenous bound putrescine (Put) levels in both the epicotyl and leaf blade of cv. Maythorpe. In contrast, there was only a slight increase in cv. Golden Promise. Levels of soluble Put increased in roots and leaf blades of both cultivars following GA treatment but the effect was greatest in leaves of cv. Maythorpe. It is suggested that polyamines may play a role in GA-induced epicotyl and leaf-blade elongation in barley.

The location of (1-3)-β-glucan in the nucellar projection and in the vascular tissue of the crease in developing barley grain using a (1-3)-β-glucan-specific monoclonal antibody

Abstract. Immunocytochemical localization of the (1-3)-β-glucan, callose, in developing barley (Hordeum vulgare L.) grain was investigated using a specific monoclonal antibody and observed by means of confocal laser-scanning microscopy. The nucellar projection (NP) and vascular tissue (VT) of the crease cells were specifically labelled by this antibody at all stages of grain development. Maximum intensity of label was found in the NP at 12–15xa0days post anthesis; thereafter, label was localized in the VT of the crease. The location of (1-3)-β-glucan in the NP and VT of the crease was also monitored by means of aniline blue-induced fluorescence of callose. The results obtained using both methods were found to be similar. The possible significance of the presence of callose in these tissues is discussed in relation to the uptake of assimilates into the developing grain.