Asmamaw Tesfaw | Debre Berhan University (original) (raw)

Papers by Asmamaw Tesfaw

Ethanol production from non-food substrate is strongly recommended to avoid competition with food... more Ethanol production from non-food substrate is strongly recommended to avoid competition with food production. Whey, which is rich in nutrients, is one of the non-food substrate for ethanol production by Kluyveromyces spp. The purpose of this study was to optimize ethanol from different crude (non-deproteinized, non-pH adjusted, and non-diluted) whey using K. marxianus ETP87 which was isolated from traditional yoghurt. The sterilized and non-sterilized whey were employed for K. marxianus ETP87 substrate to evaluate the yeast competition potential with lactic acid and other microflora in whey. The effect of pH and temperature on ethanol productivity from whey was also investigated. Peptone, yeast extract, ammonium sulfate ((NH 4) 2 SO 4), and urea were supplemented to whey in order to investigate the requirement of additional nutrient for ethanol optimization. The ethanol obtained from non-sterilized whey was slightly and statistically lower than sterilized whey. The whey storage at 4 °C didn't guarantee the constant lactose presence at longer preservation time. Significantly high amount of ethanol was attained from whey without pH adjustment (3.9) even if it was lower than pH controlled (5.0) whey. The thermophilic yeast, K. marxianus ETP87, yielded high ethanol between 30 and 35 °C, and the yeast was able to produce high ethanol until 45 °C, and significantly lower ethanol was recorded at 50 °C. The ammonium sulfate and peptone enhanced ethanol productivity, whereas yeast extract and urea depressed the yeast ethanol fermentation capability. The K. marxianus ETP87, the yeast isolated from traditional yoghurt, is capable of producing ethanol from non-sterilized and non-deproteinized substrates.

Biochemistry and biophysics , 2021

Yeasts are important microorganisms used for ethanol production; however, they are not equally ef... more Yeasts are important microorganisms used for ethanol production; however, they are not equally efficient in the amount of ethanol production under different environmental conditions. It is, therefore, necessary to screen for elite strains to utilize them for commercial production of these commodities. In this study, yeasts were isolated from different Ethiopian traditional fermented alcoholic beverages (teji, tella, shamiata and areqe tinisis), milk and ergo, teff and maize dough, soil and compost, flowers, and fruits to evaluate their potential use for ethanol fermentation process. Isolates were screened for efficient ethanol production and the selected ones were identified using phenotypic and genetic characters using D1/D2 region of LSU rDNA sequence analysis. The yeast isolates were evaluated based on their growth and fermentation of different carbon sources. Response surface methodology (RSM) was applied to optimize temperature, pH and incubation time using central composite design (CCD) in Design-Expert 7.0.0. A total of 211 yeasts colonies were isolated of which 60% were ethanologenic yeasts (ethanol producers) and 40% were non-ethanol producers. The yeast population detected from various sources was in the range of 10 5 CFU from traditional foods and beverages to that of 10 3 CFU from fruits and soil samples. The data also showed that the number of colony types (diversity) did not correlate with population density. The highly fermentative isolates were taxonomically characterized into four genera, of which 65% of the isolates (ETP37, ETP50; ETP53, ETP89, ETP94) were categorized under Saccharomyces cerevisiae, and the remaining were Pichia fermentans ETP22, Kluyveromyces marxianus ETP87, and Candida humilis ETP122. The S. cerevisiae isolates produced ethanol (7.6-9.0 g/L) similar with K. marxianus ETP87 producing 7.97 g/L; comparable to the ethanol produced from commercial baker's yeast (8.43 g/L) from 20 g/L dextrose; whereas C. humilis ETP122 and P. fermentans ETP22 produced 5.37 g/L and 6.43 g/L ethanol, respectively. S. cerevisiae ETP53, K. marxianus ETP87, P. fermentans ETP22 and C. humilis ETP122 tolerated 10% extraneous ethanol but the percentage of ethanol tolerance considerably decreased upon 15%. S. cerevisiae ETP53 produced ethanol optimally at pH 5.0, 60 h, and 34 o C. pH 4.8, temperature 36 o C, and 65 h of time were optimal growth conditions of ethanol fermentation by K. marxianus ETP87. The ethanol fermentation conditions of P. fermentans ETP22 was similar to S. cerevisiae ETP53 though the ethanol titer of S. cerevisiae ETP53 was higher than P. fermentans ETP22. Therefore, S. cerevisiae ETP53, K. marxianus and P. fermentans ETP22 are good candidates for ethanol production.

Techniques to grow oyster mushrooms from culture to harvest were evaluated using locally availabl... more Techniques to grow oyster mushrooms from culture to harvest were evaluated using locally available materials. Oyster was successfully grown in Potato Dextrose Agar (PDA). Spawn for Pleurotus ostreatus was prepared from sorghum and wheat without showing significance preference on them. Wheat straw, barley straw, sinar straw, waste paper, and gabi wastes were used as substrates; waste paper and gabi wastes alone or in mixture
with saw dust yielded more oyster than wheat straw, barley straw, sinar straw. Substrates were reused and the
yield was slower when it is compared to original substrates and they were found contaminated during pasteurization. Effects of pore size, temperature, and relative humidity on growth of mushrooms were evaluated. Pin hole size, high temperature (25oC) and high relative humidity were optimal for oyster growth. This temperature is optimal for spawn running both in cultivation and spawn production.

Transglutaminase (TGase) has been used in food industry since it reconstitutes small meat pieces ... more Transglutaminase (TGase) has been used in food industry since it reconstitutes small meat pieces into a steak. In addition, its application in pharmaceutical industry is well investigated and still under further study. However, the application of TGases in textile and leather industry was minimal before a decade. Hence, this paper reviews the potential applications of TGases in textile and leather fabrication. The enzyme recovers the wool and silk damaged during chemical and enzymatic treatment at different stages of wool and silk processing. It enhances the shrink resistance of the wool and it improves the tensile strength of the wool fibers. In addition, TGase allows the grafting of amines or proteins to bring desired properties in wool fibers. Furthermore, smoothed and better color fastness can be obtained from wool treated with TGase. TGase is also used to fill voids with caseins and gelatines in leather industry. TGases play a great role in wool, silk and leather processing.

Bioethanol is one of the most commonly used biofuels in transportation sector to reduce greenhous... more Bioethanol is one of the most commonly used biofuels in transportation sector to reduce greenhouse gases. S. cerevisiae is the
most employed yeast for ethanol production at industrial level though ethanol is produced by an array of other yeasts, bacteria,
and fungi. This paper reviews the current and nonmolecular trends in ethanol production using S. cerevisiae. Ethanol has been
produced from wide range of substrates such as molasses, starch based substrate, sweet sorghum cane extract, lignocellulose,
and other wastes. The inhibitors in lignocellulosic hydrolysates can be reduced by repeated sequential fermentation, treatment
with reducing agents and activated charcoal, overliming, anion exchanger, evaporation, enzymatic treatment with peroxidase and
laccase, in situ detoxification by fermenting microbes, and different extractionmethods. Coculturing S. cerevisiae with other yeasts
or microbes is targeted to optimize ethanol production, shorten fermentation time, and reduce process cost. Immobilization of
yeast cells has been considered as potential alternative for enhancing ethanol productivity, because immobilizing yeasts reduce risk
of contamination, make the separation of cell mass from the bulk liquid easy, retain stability of cell activities, minimize production
costs, enable biocatalyst recycling, reduce fermentation time, and protect the cells from inhibitors.The effects of growth variables
of the yeast and supplementation of external nitrogen sources on ethanol optimization are also reviewed.

The production of transgenic plants by genetic engineering allows a much faster progress. This re... more The production of transgenic plants by genetic engineering allows a much faster progress. This review focuses on stress tolerance on tobacco. Tolerance to salt, drought, water stress, low and high temperature, heavy metals, pathogens and pests were enhanced via overexpression of specific stress related genes from different sources.

The term single cell protein (SCP) refers to the dried microbial cells or total protein extracted... more The term single cell protein (SCP) refers to the dried microbial cells or total protein extracted from pure microbial culture (algae, bacteria, filamentous fungi and yeasts) which serves as food or/and feed supplements. Different substrate and fermentation optimizations are being carried out to maximize SCP production. However, little attention was given to coculturing. SCPs are produced better using coculture than monoculture. This paper reviews the positive roles of coculture in SCP production. First, it results in better saccharification of substrates and efficient carbon source utilization. Second, filling substrate utilization gap is another contribution of coculture. Third, it upgrades biomass and enrich SCP with nutrients than monoculture. Fourth, it reduces fermentation time and production cost by reducing cost of substrate treatment.

Biochemistry and biophysics , 2021