American Association of Cereal Chem- ists/AOAC collaborative study was conducted to evaluate the accuracy and reliability of an enzyme assay kit procedure for measurement of total starch in a range of cereal grains and products. The flour sample is incubated at 95°C with thermostable α-amylase to catalyze the hydrolysis of starch to maltodextrins, the pH of the slurry is adjusted, and the slurry is treated with a highly purified amyloglucosidase to quantitatively hydrolyze the dextrins to glucose. Glucose is measured with glucose oxidase-peroxidase reagent. Thirty-two collaborators were sent 16 homogeneous test samples as 8 blind duplicates. These samples included chicken feed pellets, white bread, green peas, high- amylose maize starch, white wheat flour, wheat starch, oat bran, and spaghetti. All samples were analyzed by the standard procedure as detailed above; 4 samples (high-amylose maize starch and wheat starch) were also analyzed by a method that requires the samples to be cooked first in dimethyl sulfoxide (DMSO). Relative standard deviations for repeatability (RSDr) ranged from 2.1 to 3.9%, and relative standard deviations for reproducibility (RSDr) ranged from 2.9 to 5.7%. The RSDr value for high amylose maize starch analyzed by the standard (non-DMSO) procedure was 5.7%; the value

Wheat plants exposed to higher than usual temperatures during ripening produced grain with weaker dough properties in glasshouse, field experiments and crop samples. In a review of Prime Hard wheat samples from 1960/61 to 1988/89, those seasons when the dough properties were particularly weak coincided with the years when the number of hours over 35�C during the grain filling period (October to December) was greatest. A five-day period of heat stress in 1988 provided an opportunity to directly investigate the effects of heat stress in the field. A weakening of dough properties was shown, for four varieties, by longer dough development times and faster breakdown in the Farinograph and also by shorter resistance to extension (at 5 cm) in the Extensograph. These (and similar changes for glasshouse grown grain) were accompanied by an increase in the proportion of gliadin (monomeric) proteins. That this increase was associated with the heat stress was shown by demonstrating increased accumulation of 14C amino acids into the gliadin fraction for heat-stressed heads in culture. These results support the hypothesis that episodes of high temperature during grain filling activate the heat shock elements of gliadin genes in wheat causing the mature grain to contain more gliadin and thus to produce weaker doughs.

Grain quality results for variety trials extending over 27 years (3 sites and 5 varieties) were compared with the temperature profiles during the grain filling period (56 days prior to harvest) to determine the effects on quality of high temperatures (>35�C) during this period of growth. Heat stress episodes have been frequent at two (Narrabri, N.S.W., and Turretfield, S.A.) of the three sites studied; spring temperatures were more moderate at the third site, Wongan Hills, W.A. There were highly significant (P< 0.01) correlations of heat stress (as hours above 35�C, during grain filling) with protein content (positive) and with grain yields (negative) at Narrabri for all varieties. In many combinations of site and variety, heat stress correlated negatively with loaf volume, and with dough strength (as Rmax, resistance to stretching with the Extensograph). Heat stress episodes in the Narrabri (N.S.W.) region in 1981 and 1982 gave further opportunity to examine these relationships. Results showed very clearly that high temperatures late in grain filling were associated with weaker dough properties (lower Rmax) in the resulting grain. These trends may form the basis of a predictive system by which to estimate crop quality and to interpret the results of variety trials.

Wheat (Triticum aestivum L.) cultivars Hartog and Rosella were grown at CO2 concentrations of 280 µL L-1 (representing the pre-industrial CO2 concentration), 350 µL L-1 (ambient) and 900 µL L-1 (an extreme projection of atmospheric CO2 concentration). The plants were grown in naturally lit glasshouses in 7 L pots containing soil to which basal nutrients had been added and the pH adjusted to 6.5. Hartog yielded 2.4 g of grain per plant when grown at 280 µL CO2 L-1. This yield was increased by 38% and 75% at CO2 concentrations of 350 µL L-1 and 900 µL L-1 respectively. These changes were due to increases in both grain number and individual grain weight as the level of CO2 was raised. The yield of Rosella was unaffected by altering the CO2 concentration. Increasing the CO2 concentration reduced grain protein concentration of cv. Hartog from 17.4% at 280 µL CO2 L-1 to 16.5% and 16% at CO2 concentrations of 350 µL L-1 and 900 µL L-1 respectively. The grain protein concentration of cv. Rosella was reduced from 10.7% to 10.2% by increasing the CO2 concentration from 280 µL L-1 to 350 µL L-1; however, an additional increase in the CO2 concentration to 900 µL L-1 had no effect on grain protein concentration. In Hartog flour, the highest proportion of polymeric protein in the flour (7.7%) occurred at 280 µL CO2 L-1. This was reduced to 6.3% at 350 µL CO2 L-1 but then increased again to 7.0% at 900 µL CO2 L-1. These changes in concentration of polymeric protein were correlated (r2=0.58) with changes in mixing properties. The mixing time required to produce optimum dough strength was greatest at 900 µL CO2 L-1 (181 s), then 141 s and 151 s at 350 µL CO2 L-1 and 280 µL CO2 L-1 respectively. These changes in mixing time could not be explained by changes in grain protein concentration. The proportion of ‘B’ starch granules (<10 m diameter) increased from 25% of total weight of starch at 280 L CO2 L-1 to 30% at CO2 concentrations 350 and 900 µL L-1. There were generally no effects of CO2 concentration on dough mixing properties or starch granule size distribution for Rosella.

When wheat coleoptiles or plants are subjected to a period of heat stress (e.g, at > 35�C for 1 h or more), there is a reduction in normal protein synthesis, accompanied by de novo synthesis of the classical range of heat-shock proteins (based on radioactive tracer experiments) in virtually all parts of the plant. Study of coleoptile elongation rates indicates that this synthesis is related to a protective effect, whereby a preliminary heat shock provides a degree of protection against a later lethal shock. This thermotolerance is also associated with the appearance in coleoptiles and roots of a small peptide (detected without radioactive labelling) whose amino acid sequence (12 residues) is the same as the N-terminal sequence of the alpha- and beta-gliadin proteins of the endosperm. Heat stress during grain filling leads to important changes in the synthesis of gluten proteins with reduced synthesis of the high molecular weight (HMW) subunits of glutenin, and continuing synthesis of other gluten proteins, particularly various gliadin proteins. This latter group of polypeptides is thus presumed to be acting as heat-shock proteins, and indeed, multiple heat-shock elements are present in the published sequences of representative genes, up-stream of the coding regions. HPLC analysis (with or without radioactive labelling) shows that there is a resulting change from the normal balance of gluten polypeptides immediately after the shock as well as in the mature grain. As a result, there is a lower proportion of large-sized aggregates of glutenin and weaker dough properties. This scenario indicates that it should be possible to identify genotypes that would be tolerant to stressrelated variations in quality by analysis of gluten composition and, at the gene level, by screening for heat-stress elements in the genes encoding HMW-glutenin subunits. In addition, heat stress modifies the particle size distribution of the starch fraction of mature grain, producing an increase in the proportion of large (A-type) starch granules. No change in chemical structure was detectable as a result of heat stress.