P-19
Beta-glucan content and endo-betaglucanase activities of individual malted
barley grains. Cell wall modification (beta-glucan breakdown) is regarded as a key step in
extract development during malting and brewing. It has been suggested that the
rate of modification, of the grains of a barley sample, is principally
determined by their contents of cell wall beta-glucan and their potential to
synthesise beta-glucanase. Therefore, malt samples, which contain low
beta-glucan levels and high beta-glucanase activities, are considered suitable for
brewing. However, traditional malt analyses do not detect the homogeneity of
modification of the grains of a sample of malt. The aims of this study were to
(a) assess the distribution of beta-glucan content and endo-betaglucanase
activity in individual grains of barley and malt and (b) compare the degree of
physical modification of single grains of malt with their corresponding levels
of beta-glucan. Barley variety Decanter was malted and samples were collected
after 24, 48, 72 and 96 hours of germination. Samples were analysed for their
total beta-glucan content and beta-glucanase activity, according to the McCleary
Method and the Azo-Barley Glucan Method, respectively. These methods were later
adapted in order to evaluate single grains. The degree of physical modification
and beta-glucan content were analysed in kilned malt; corresponding
beta-glucanase activity was analysed using (unkilned) green malt. The distribution of
beta-glucan content (mg/grain), beta-glucanase activity (U/grain) and degree of
modification in each sample will be presented. Malt samples showed a wide
distribution of the content of beta-glucan and beta-glucanase activity in
individual grains. Total beta-glucan of the whole sample gave no indication of
the differences in beta-glucan content in individual grains and did not
correlate with the variation of physical modification that occurred in
individual grains. This also applied to beta-glucanase activity. A weak
correlation between beta-glucan content of individual malt grains and
endo-betaglucanase activity was observed, indicating that other factors may be
involved in controlling the rate of beta-glucan breakdown and endosperm
modification during malting. These results showed that total beta-glucan content
or total beta-glucanase activity of malt samples are not the best indicators of
overall modification of the endosperm. The results of this study show that
significant variations in levels of beta-glucan and beta-glucanase can occur in
the individual grains of a barley sample during malting. Although beta-glucan
breakdown is important, there are complimentary factors, which control the
overall rate at which the endosperm is modified during malting.
Roberta Marins de Sá is a second year PhD student at the International
Centre For Brewing and Distilling (ICBD), under the supervision of Professor G.
H. Palmer. She is sponsored by Conselho Nacional de Desenvolvimento
Científico e Tecnológico (CNPq), Brazil. She previously received an MSc. in
Food Science from UFSC (Brazil). Her research interests centre on the study of
barley and malt. At present she is engaged in detailed examination of the
physiological relationship between endo-betaglucanase activity, beta-glucan
breakdown and the overall physical modification of the endosperm during
malting.
ROBERTA MARINS DE SÁ and G. H. Palmer. International Centre for Brewing and
Distilling, Heriot Watt-University, Riccarton, Edinburgh, EH14 4AS, Scotland.