SOME RELATIONSHIPS BETWEEN THE PROTEIN NITROGEN OF BARLEY AND THE PRODUCTION OF AMYLOLYTIC ENZYMES DURING MALTING

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Abstract
Barleys studied (Chariot and Delibes) contained different levels of extractable β-amylase enzymes. The potential levels of β-amylase enzymes of the two varieties studied were similar at 1.4 to 1.7% total nitrogen. Higher values of potential β-amylase enzyme were observed in the Delibes barley of higher total nitrogen of 1.9%. The higher level of β-amylase found in the barleys with the highest total nitrogen was not reflected in the protein banding patterns as revealed by SDS-PAGE protein fractionation. Extraction of barley proteins was largely influenced by the different extractants used. The alcohol soluble proteins, Mr 97 kDa (D-hordeins), were only extracted when mercaptoethanol was included in the extracting solution. Although barleys with the highest nitrogen (1.9%) had the highest apparent potential to develop β-amylase enzymes, the better modified low nitrogen barleys produced higher levels of β-amylase and α-amylase when malted. Dehusking revealed that the high nitrogen barleys contained more steely grains. In contrast, the low nitrogen barleys contained more mealy grains. Steely grains contained more nitrogen than mealy grains and had the greater potential to develop β-amylase. Notwithstanding, the results of this study suggested that the proteins of the lower nitrogen barleys (1.4–1.7%) were capable of producing higher levels of β-amylase and α-amylase than the higher nitrogen barleys (1.9%) over comparable periods of malting. The high apparent β-amylase potential of the barley was linked to high nitrogen levels and associated high levels of steeliness, whilst the corresponding high β-amylase levels of malt were linked to the efficiency of endosperm modification of the malted grain.