Yeast biomass

A. Halas2 and R. Las2tity, Use of Yeast biomass in Food Production, CRC Press, Boca Raton, Fla., 1990. 

Bakers Yeast Production. Bakers yeast is grown aerobicaHy in fed-batch fermentors under conditions of carbohydrate limitation. This maximizes the yield of yeast biomass and minimizes the production of ethanol. Yeasts grown under these conditions have exceUent dough leavening capabHity and perform much better in the bakery than yeast grown under anaerobic conditions. 

Continuous processes may be used for the production of yeast biomass. Raw Hquid feed is added continuously to the fermentor and an equal volume of fermentor Hquid is removed to harvest the yeast ceUs. These may be a single homogeneous fermentation in a stirred fermentor or two fermentors in series. Growth rates are high a typical dilution rate in the production of C. utilis on sulfite waste Hquor is 0.25, ie, one-fourth of the fermentor volume is harvested hourly. 

The most widely available yeast biomass is a by-product of the brewing industry, where the multiplication of yeast during brewing results in a surplus of ceUs. Eor every barrel (117 L) of beer brewed, 0.2—0.3 kg of yeast soHds may be recovered. In the U.S., a substantial fraction is recovered and made available about 40 x 10 kg of brewers yeast aimually. The yeast is recovered from beer by centrifuging and dried on roUer dmms or spray dryers and sold as animal feed or a pet-food supplement. It can be debittered by alkaline extraction to remove the bitter hop residues, and is then sold mainly by the health-food industry. It is available as tablets, powder, or flakes and is often fortified with additional vitamins. Distillers yeast caimot be readily separated from the fermented mash and the mixture is sold as an animal feed supplement. 

Immobilization is the technique of choice in many food industry processes and especially in beverage production. Many immobilization technologies have already been tested and some are applied in the production of beer, wine, vinegar, and other food products using a traditional approach with cultme adhesion (i.e., Acetobacter in vinegar production) or more modem approaches with entrapment of yeast biomass (i.e., sparkling wines, cheeses, and yogurts). 

Brady D., Stoll A.D. Duncan J.R. (1994) Biosorption of heavy metals cations by non-viable yeast biomass. Environ. Technol. 15,429-438. 

Using nonviable cellular biomass for azo dye removal has some advantages, namely the ability to function under extreme conditions of temperature and pH, and without addition of growth nutrients [10]. Also, waste yeast biomass, which is a by-product of industrial fermentations such as beer production, can be used as a relatively cheap source for biosorption of azo dyes. An important setback is the fact that the use of biomass for dye removal leads to an increase in the sludge amount, which requires further removal and treatment. 

El-Sharouny EE, El-Sersy NA (2005) Biosorption of textile dyes by brewer s yeast biomass. Fresenius Environ Bull 14 928-933... 

Yeast artificial chromosome (YAC) cloning experiments, 22 507-508 Yeast biomass... 

Simmons, P., Tobin, J. M. Singleton, I. (1995). Considerations on the use of commercially available yeast biomass for the treatment of metal-containing effluents. Journal of Industrial Microbiology, 14, 240-6. 

Without knowing the detailed metabolic pathways, many fermentative products today are obtained via aerobic fermentation processes. Probably the largest scale, single product aerobic fermentations are those used to produce single cell protein (SCP), or yeast biomass from hydrocarbons [63]. Here, an aerated yeast suspension in water, which contains trace nutrients is used to generate yeast biomass from gas oil, a mixture of straight chain hydrocarbons in the Cn to C20 range (Eq. 16.23). 

Yeast Biomass Production in Brewery s Spent Grains Hemicellulosic Hydrolyzate... 

A possible cheap production approach for SCP and YE is the management of yeast biomass derived or produced within the biorefinery fiamework, namely, Irom the upgrading of the hemicellulosic fraction stream. 

Protein content in the yeast biomass was also determined by the Kjeldahl method using the conversion factor of 6.25. Total carbohydrates in yeast biomass were determined by the anthrone method [21]. RNA content was determined by the Schmidt-Thannhauser method as described in Benthin et al. [22]. Fat content was determined in dried cells by a Soxhlet extraction procedure using petroleum ether (60-80 °C) as solvent [23]. Ash content was determined by igniting the samples at 575 °C for 5 h, both for the feedstock and yeast biomass. All results are reported on the dry basis. 

Yeast biomass was freeze-dried and grounded. Fatty acid extraction and preparation of methyl esters were carried out according to Lepage and Roy [25]. Samples (100 mg) were transmethylated with 5 ml of methanol/acetyl chloride (95 5 v/v). The mixture was sealed in a light-protected Teflon-lined vial under nitrogen atmosphere and heated at 80 °C for 1 h. The vial contents were then cooled, diluted with 1 ml water, and extracted with 2 ml of n-heptane. The heptane layer was dried over Na2S04, evaporated to dryness under nitrogen atmosphere and redissolved in heptane, which contained the methyl esters. 

This bioreactor has a capacity for approximately 20 kg of yeast biomass. This system can potentially relieve product inhibition problems since the ethanol is continuously stripped by the circulating gas. 

Navratil M., Domeny Z., Hronsky V., Stuidic E., Smogrovicova D. and Gemeiner P. Use of biolumi-nometry for determination of active yeast biomass immobilized in ionotropic hydrogels. Analytical Biochemistry 284 (2) (2000) 394-400. 

Before propagation (the production of yeast biomass) but after fermentation and cropping, most (but not all) yeast strains are stored under standard conditions in a brewery or in an accredited culture collection—sometimes both, for security ... 

Bravi, E., Perretti, G., Buzzini, P., Sera, R. D., Fantozzi, P. (2009). Technological steps and yeast biomass as factors affecting the lipid content of beer during the brewing process. Journal of Agricultural and Food Chemistry, 57, 6279—6284. http //dx.doi. org/10.1021/jf9007423. 

For semidiscontinuous processing, often used in fermentations for the production of yeast biomass or secondary metabolites, the basic balance equation is to be modified. Balancing in this case has to distinguish between components that are already present in the reactor at the beginning (number of moles nj q) and components that are fed later on to the reactor (flux of moles n°). The stoichiometric balance in this case of semidiscontinuous reactor operation is... 

Although diammonium phosphate is a potent supplement for stimulation of yeast biomass, it is generally not effective as a nitrogen supplement for LAB, which require more complete supplementation in the form of mixtures of amino acids, vitamins, and yeast extract. 

Favaro L, Basaglia M, CaseUa S. Processing wheat bran into ethanol using mild treatments and highly fermentative yeasts. Biomass Energy 2012 46 605-17. 

One major product of this application of industrial fermentation is baker s yeast biomass. Baker s yeast is required for making bread, bakery products, beer, wine, ethanol, microbial media, vitamins, animal feed, and biochemicals for research. 5feast is produced in lai e aerated fermenters of up to 200,000 liters. Molasses is used as a nutrient source for the... 

The mathematical model of batch beer fermentation used is based on the work of Gee and Ramirez (1988). In mathematical modeling for ethanol production by yeast, biomass growth and ethanol formation are assumed to be limited by three sugars, glucose, maltose and maltotriose. The rates of uptake of the three sugars are given by the equations ... 

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