Optimization of a culture medium from cider residues for the production of yeast biomass

FONTANINI, JM; ORIGONE, A; RODRIGUEZ, M.E.; SANGORRIN; MARCELA PAULA

Congreso; XVII Congreso Argentino de Microbiología General; 2022

The fermented beverage industries, particularly cider, generate large tons of waste per year, including bagasse and lees. These wastes represent a potential source of nutrients for the formulation of culture media. The apple bagasse was chemically treated in order to increase the amount of free sugars (SAMIGE 2021). The objective of this work was to optimize the lees autolysis method to increase the availability of Nitrogen and, subsequently, the formulation of an economical culture medium with the two substrates, for the propagation of unconventional yeast strains of Saccharomyces uvarum NPCC 1420 and Saccharomyces eubayanus NPCC 1292.To optimize autolysis, previously lyophilized lees were used and a central design composed of the variables: incubation time (24-48h), lees g l-1 of solution (20-40 g l-1) and pH (3.5-6.5) adjusted with NaOH. The tests were carried out in 200 mL final volume and with constant agitation (150 rpm) at 50°C (water bath equipment). Yeast assimilable nitrogen (YAN) concentration (YAN) was determined as a response variable. The optimal conditions obtained for this design were: pH 6.5 and concentration 20 g l-1 for 36 h, obtaining a value of 97,6 mg N 100 g-1 lees. To increase the yield of YAN, a new CCD Split Plot was performed with the following factors: temperature (40-60 °C), pH (3.5-6.5) and time (24-48 h), with the concentration being YAN as a response variable. The lees concentration was 30 g l-1. The highest nitrogen concentration reached –192mg N 100g-1 lees- was obtained under the conditions pH 5.33 at 60°C for 24h.The study of the growth of the two yeast strains was carried out using a statistical design of mixtures that allowed, in 14 runs, to combine different proportions of the treated residues. The response variables for both strains were dry weight (g l-1) and maximum biomass reached –A- ln(DOf/DOi), being DO the optical density to 640nm. The cultures were adjusted to pH 5 and incubated at 20°C and shaking (150rpm). The NPCC 1420 strain showed the best growth under the following conditions: 20% Bagasse + 80% lees, showing a dry weight of 4.2 g l-1 and an A of 5.1 g l-1 , while for NPCC 1292 strain showed better weight dry values and A -3.2g l-1 and 4.8 g l-1 - when the medium was 35.8% Bagasse + 64.2% Lees.The results obtained suggest the possibility of using these two residues - bagasse and lees - as carbon and nitrogen sources for the formulation of economic culture media for biomass production of yeasts.