Production of Some Higher Alcohols and Acetate Esters from Rice Bran by Yeasts Metabolisms of Kluyveromyces Marxianus and Debaryomyces Hansenii

Abstract

The aim of this study was to evaluate the biosynthesis of flavor compounds from rice bran by yeast metabolisms. The microbial growth and flavor biosynthesis of Kluyveromyces marxianus and Debaryomyces hansenii in rice bran by microbial fermentation were investigated. Growth of both yeasts was assessed by the calculation of specific growth rates and doubling time. Their aroma biosynthesis was evaluated by gas chromatography-olfactometry (GC-O), gas chromatography-mass spectrometry (GC-MS) and Spectrum™ sensory analysis. The specific growth rate (µmax) and doubling time (td) of K. marxianus were calculated as 0.16/h and 4.21 h respectively, D. hansenii had 0.13/h of µmax and 5.33h of td. K. marxianus and D. hansenii significantly produced higher alcohols and acetate esters from rice bran at high levels. Results showed that K. marxianus can produce 827.27 µg/kg of isoamy alcohol, 169.77 µg/kg of phenyl ethyl alcohol and 216.08 µg/kg phenyl ethyl acetate during 24 h batch fermentation. Isovaleric acid was also synthesed by K. marxianus at high level (4013 µg/kg) in the batch fermentation of 96 hours. The highest concentration of of isoamyl alcohol and phenyl ethyl acetate was determined as 415.64 µg/kg and 135.77 µg/kg, respectively at 24 h fermentation of D.hansenii. Fermented cereals and rose were defined as characteristic flavor descriptors for the fermented rice bran samples. Rose flavor term in fermented rice bran samples were found to associate with phenyl ethyl alcohol, phenyl ethyl acetate, isoamyl acetate and guaiacol. The valorization of rice bran can be achieved with the production of natural flavor compounds by yeast metabolisms.