Varietal effect of teff (Eragrostis tef) on the dimethyl sulfide (DMS) content and enzyme activities of teff malt

Malt and Grains Session
Mekonnen M Gebremariam, Institute of Brewing and Beverage Technology, Center of life and Food Sciences, TUM, Weihenstephan-Freising, Germany
Co-author(s): Martin Zarnkow and Thomas Becker, Institute of Brewing and Beverage Technology, Center of Life and Food Sciences, TUM, Weihenstephan-Freising, Germany

ABSTRACT: Variations in cereal, growing region, year of cultivation, cultivation practices, and malting conditions have considerable influence on the enzyme activities and DMS level of malt. This research was aimed at studying the influence of using different teff (Eragrostis tef) varieties on the DMS content and enzyme activities of the final malt. Five teff varieties (Kuncho [DZ-Cr-387], Ivory, Brown, Dessie, and Sirgaynia) obtained from Ethiopia and North America were investigated as possible raw materials for the production of gluten free malt. Portions of the samples were used for analysis of thousand corn weight, gelatinization temperature, and germination energy. The remaining portions were steeped for 5 hr on the first day and 4 hr on the second day at 24°C, and germinated for 4 days at 24°C in a temperature controlled chamber with 95% relative humidity. Kilning was for 18 hr at 30°C, 1 hr at 60°C followed by 3 hr at 65°C. Thousand corn weight, germination energy, gelatinization temperature, and malting losses due to rootlets ranged between 0.27 and 0.28 g, 96 and 100%, 69 and 73°C, and 1.95 and 5.49%, respectively. Teff variety Kuncho had the highest malting loss (5.49%), while Brown had the lowest (1.95%). There was a significant increase in amylolytic enzyme activities throughout the germination process, but some of the amylolytic enzyme activities decreased during the kilning process. The moisture contents, DMS levels, and alpha-amylase, beta-amylase, and limit dextrinase activities of the malts ranged from 3.04 to 3.8%, 2.2 to 4.1 mg/kg, 14 to 68 U/g, 10 to 440 U/g, and 375 to 1,072 U/kg, respectively. The enzyme activities were markedly (P < 0.05) influenced by the type of teff cultivar. The alpha-amylase activities of all teff varieties increased in the first few hours of kilning but started to decrease in the later stages. However, the limit dextrinase and beta-amylase activities of all samples decreased throughout the kilning process. At the end of kilning, there was 7–50% higher alpha-amylase activity in the final malts than in the green malts, whereas the more temperature sensitive beta-amylase and limit dextrinase activities were about 8–53% and 5–17%, respectively, less than in the green malts. The highest increase in alpha-amylase activity (50%) during the kilning process was recorded for teff variety Sirgaynia, whereas the lowest increase (7%) was for Ivory. The highest loss in beta-amylase (53%) and limit dextrinase (17%) activities were for teff varieties Dessie and Kuncho, respectively, and the lowest were for Ivory and Brown, respectively. In this study, teff variety Dz-Cr-387 had the highest enzyme activities compared with the other cultivars studied. This variety had the best malting characteristics and brewing potential, with alpha-amylase, beta-amylase, and limit dextrinase activities of 68 U/g, 440 U/g, and 1,072 U/kg, respectively. In general, it can be concluded that the use of different teff varieties yields malts with significantly different malt quality attributes.

Mekonnen Melaku Gebremariam received his B.S. degree in chemistry from Debub University, Ethiopia. He began employment with the Ethiopian Ministry of Education in July 2000 as a chemistry teacher in the South Nations and Nationality People Region. He terminated his contract agreement with the Ministry of Education after four years. He next was employed as a chemist in the Federal Micro and Small Enterprises Development Authority. After 18 months with this company, he terminated the contract agreement and joined Addis Ababa University for further studies. He graduated from Addis Ababa University, Ethiopia, in 2007 with an M.S. degree (with great distinction) in food engineering. Immediately after graduation he was employed as a lecturer and researcher by Hawassa University, Ethiopia. After about two-and-a-half years of work at Hawassa University, he went to Germany for his Ph.D. studies with the support of his employer, Hawassa University. Currently he is pursuing his doctoral studies at the Technical University of Munich, Germany.