ID: 2274

• Title:
  Optimization of the extraction of oenological compounds of interest assisted by Pulsed Electric Fields from brewing yeast biomass
  
  Authors:
  

  Berzosa, Alejandro-Universidad de Zaragoza/ Facultad de Veterinaria
  Delso, Carlota-Universidad de Zaragoza/ Facultad de Veterinaria
  Sanz, Jorge-Universidad de Zaragoza/ Facultad de Veterinaria
  Sánchez-Gimeno, Cristina-Universidad de Zaragoza/ Facultad de Veterinaria
  Raso, Javier-Universidad de Zaragoza/ Facultad de Veterinaria

  
  
  Abstract:
  It is estimated that the brewing industry generates an annual spent brewer´s yeast production of around 400 thousand tons. As the disposal of these spent yeast residues represents a problem from an environmental and economic point of view, valorization strategies are being evaluated because this material represents an attractive source of valuable molecules and bioactive compounds. Yeasts are rich sources of different compounds of special interest for winemaking such as glutathione, amino acids, proteins or mannoproteins. Glutathione is a tripeptide with a high antioxidant capacity and is widely used in white winemaking to prevent oxidations. Yeast´s cytoplasm soluble metabolites have been shown that may enhance the alcoholic fermentation rates in a nitrogen-deficient medium. The potential of yeast protein extracts (YPE) for wine clarification has been demonstrated and mannoproteins from yeast cells may contribute to maintaining wine stability modulating wine organoleptic properties.
  
  Pulsed Electric Fields technology that causes the electroporation of the cytoplasmatic membrane allows selective extraction of compounds of interest by a sequential release of cytoplasmic compounds.
  
  The objective of this study was to optimize the extraction conditions after PEF treatment of yeast biomass, to maximize the extraction of different compounds with oenological interest located in the cytoplasm.
  
  A Central composite design (CCD) was used to study the influence of pH (4-8), temperature (20-40 ºC) and incubation time (1-48 hours) on the release of glutathione reduced, amino acids and proteins after treating the yeast biomass by PEF. Brewer´s yeast biomass from a local brewery (La Zaragozana, Zaragoza, Spain) was collected and after washing twice with distilled water, was treated by PEF (15kV/cm, 150 µs, 84 kJ/kg) in media of pH 4, 6 and 8 to electroporated more than 90% of the population. The concentration of reduced glutathione, amino acids and proteins were determined in the supernatant after incubation under the conditions establish by the CCD.
  
  After 1 hour of incubation at pH 8 at any assayed temperature, 2,45 mg/g dry weight of glutathione was released, which represented 84% of the total concentration extracted in the yeast biomass. The protein release increased with increasing pH and incubation time, achieving the highest concentration in the supernatant at 30 ºC and 48 hours. Proteolytic processes occurring during incubation time could explain the decrease in the protein concentration when the extraction was conducted at higher temperatures. This behavior was supported by the fact that despite the low molecular weight of amino acids, the extraction was negligible after 1 hour of incubation by increased with time and temperature. According to these results, it will be able to obtain a glutathione-rich yeast extract after 1 hour of incubation at pH 8 and a second extract rich in amino acids and proteins after extending the incubation for 48 hours.
  
  It can be concluded that PEF treatment facilities the release of cytoplasmic compounds from brewer´s yeast biomass and combined with proper incubation conditions different compounds with potential oenological interest compounds could be obtained.
  
  
  
  Keywords:
  Pulsed Electric Fields, yeast biomass, revalorization, glutathione, amino acids, proteins
  
  Refs:
  
  
  Topic 1:
  9. Biomass processing and biofuel generation
  
  Topic 2:
  10. Food safety and food preservation