Malt quality of 4 barley (Hordeum vulgare L.) grain varieties grown under low severity of net blotch at Holetta, west Shewa, Ethiopia
Four malt barley varieties (Beka, HB 120, HB 52 and Holker) and 3 fungicide (propiconazole) spray intervals (7, 14, 21 day) and no spray control were arranged in a RCBD in 4 replications to assess net blotch (Pyrenophora teres) effect on malt quality. The varieties were grown at Holetta agricultural research center in 2005, on 12 m2 plot. Grain flour starch pasting and malt qualities were analyzed. Mash odour and colour were evaluated qualitatively. Significant differences (P < 0.05) in malt qualities were observed among varieties and also due to spray intervals in hot water extract (HWE, mean range = 76.6 to 79.7%). The varieties had a pasting- time and -temperature (Ti) of 4.7 to 5.0 min and 64.7 to 66.3°C, respectively. Peak, hot paste, cold paste, breakdown and setback viscosities were ranged 276.5 to 314.9, 176.3 to 218.3, 294.1 to 333.2, 86.3 to 99.6 and 102.4 to 116.4 BU, respectively. The pasting curves indicate no amylo- or -waxy starches with evidence of no damage by sprout- induced a-amylase activity and spray intervals. The varieties Ti matches mashing temperature (64 to 65°C) used in malt barley brewing. Malts from these grain varieties were prepared under controlled conditions. Malt aroma and flavor was similar with industry malt of sugary sweet taste. Thousand-kernel malting weight loss (TKMWL) was 11 to 13% and is in the range for desirably modified barley grain on malting. The varieties had a malt protein 6.4 to 7.4% and free amino nitrogen (FAN) 124.4 to 140.0 mg/100 g malt (db). The diastatic tendency assessed using malted barley flour as sources of enzymes and refined wheat flour starch as a substrate (1:29) showed a reduction in peak viscosities (mean) of the substrate starch paste from 678.0 to 168.0 BU. The varieties did not show consistent quality requirements in all parameters. Beka and HB 120 were better than HB 52 and Holker in HWE and diastatic tendency. The FAN level was high among HB 120, HB 52 and Holker. The findings indicate that net blotch incidence and severity influenced HWE and filtration time.
Key words: Diastatic tendency, malt extract, FAN, malt barley qualities, net blotch, propiconazole, starch flour pasting