Extraction Of Protein And Nucleic Acid From Waste Beer Yeast Using Pulsed Electric Fields(PEF) And Ultrasound

Beer yeast, a kind of single cell microorganism, which contains abundant proteins, nucleic acids, carbohydrates and minerals, is an important protein and nucleic acid source. With the rapid development of beer industry in China, there are more and more waste beer yeast produced. It is of great significance to have the waste beer yeast recycled. The way to extract intracellular materials is by destroying the yeast cell wall or changing the cell membrane permeability. Some traditional methods like mechanical breakdown, are energy-consuming and low-efficient. Chemical extraction may cause the protein stability lost, and enzymatic autolysis may deprive the biological activity. Pulsed Electric Fields and Ultrasonic Wave could be expected to extract the useful components from beer yeast without destroying biological activities.Pulsed Electric Fields (PEF) was applied to waste beer yeast to improve the permeabilization of membrane so as to extract protein and nucleic acid. The results showed that the liberation of protein and nucleic acid increased with the increasing of the electric fields intensity, treated temperature, ions concen- tration, prolonged treatment time and the time after pulsation. The liberated quantity of protein and nucleic acids achieved 4.04mg/ml and 0.38 mg/ml respectively at 30 kV/ cm electric field intensity , 45℃and 400μs treatment time. The extraction rate of protein and nucleic acid achieved 33.6% and 25.4%,respectively.The application of Ultrasonic Wave for extracting protein and nucleic acid in waste brewer yeast cell was investigated. The waste brewer yeast was processed by probe ultrasound with different parameter and system conditions. The results showed that the liberation of protein and nucleic acid increased with the increasing of ultrasound power, prolonged treatment time, treated temperature and ions concentration. It is also found that the extraction rate achieve best when the pulse-on to pulse-off was 3:4, but the extraction was lowest when pH was around 7.Some sub-effects, such as vibration, emulsification, diffusion, chemistry and thermal effect, were able to improve the extraction rate further after the treatment of PEF. The results showed that the extraction rate of protein and nucleic acid increase 6.4% and 5.9% respectively under the treatment of 100W ultrasound during 10min after PEF; the extraction rate of protein and nucleic acid increase7.6% and 6.9% respectively under the treatment of 300W ultrasound during 6min after PEF.Analysis of beer yeast extract can be acquired by amino acid automated analysis and HPLC. The result showed that most protein exist in macromolecule, only small part exist in amino acid. We can observe electroporation phenomenon visually by SEM.