Nucleic Acid Degrading Enzymes of Barley Malt. I. Nucleases and Phosphatases

Abstract

Seven enzymes involved in the degradation of nucleic acids and nucleotides were studied in barley and during germination, kilning, and mashing. Among these enzymes were deoxyribonuclease (DNase), two ribonucleases (RNase) (sensitive and insensitive to ethylenediaminetetraacetic acid), phosphodiesterase, 3′- and 5′-nucleotidases, and phosphomonoesterase. The levels of all of the enzymes were low in mature barley and remained low during steeping, but large increases in activity were observed during 10 days of germination. Application of gibberellic acid in the steep had a statistically significant effect on DNase, phosphodiesterase, and phosphomonoesterase. All of the enzymes were quite stable during kilning for 24 hr at 45°C. Phosphodiesterase, 3′-and 5′-nucleotidases, and phosphomonoesterase showed good temperature stability during kilning at 65 and 85° C, whereas DNase and the RNases showed slight losses at these temperatures. The RNases were unstable even at low mash temperatures, and their activities declined very rapidly as the mash temperature rose to 70° C. DNase was more stable than the RNases and had a slower decline in activity as the temperature rose to 70°C. Phosphomonoesterase and the 3′- and 5′-nucleotidases were similar to the nucleases in temperature stability. Only a low level of phosphodiesterase activity was extracted during mashing. Commercial brewers' malts had high levels of these enzymes compared to experimental malts.