Valorization of the powdered bread waste hydrolysate as growth medium for baker yeast

In this work, the feasibility of baker yeast production using white bread waste is investigated. Grinded and sieved white baguette waste was hydrated and hydrolyzed differently using enzymes preparations to obtain two growth mediums. Medium (I) contained a mixture of alpha amylase and amyloglucosidase; and Medium (II) contained a mixture of alpha amylase, amyloglucosidase and protease enzymes. The clarified media were diluted and supplemented with NH4SO4 (3.5 g/l), and KH2PO4 (2 g/l). A commercial baker yeast strain was reactivated and a preculture was prepared for the mediums inoculation. Fermentation was carried out in Erlenmeyer flasks and incubated in the thermo-shaker (30 °C, 150 rpm). After 48 h of fermentation, important biomass production was recorded in Mediums (I) and (II) (1.04 × 108 CFU/ml and 2.74 × 108 CFU/ml) compared to the control medium (1.63 × 108 CFU/ml). Hence, the productivity ratio of Medium I and Medium II was estimated to be 0.63 and 1.68. Microbial growth, sugars and proteins consumption kinetics were studied. The obtained results indicated that the production of yeast biomass could be an attractive alternative for bread waste valorization ensuring a global biomass yield of 0.77 g/g.