Development of a bacterial culture medium from avocado seed waste

Avocado (Persea americana Mill) seeds, a rich source of starch and micronutrients, are a major waste product from the agroindustrial processing of avocados. Here we designed and developed an experimental culture medium (ECM) from hydrolysed avocado seeds, supplemented with M9 salts (10% v/v). Breaking of starch granules of avocado seeds due to hydrolysis treatments was analysed by morphology and morphometry of granules. We evaluated the ECM functionality by measuring the growth of Escherichia coli as affected by (i) the carbon source (reducing sugars concentration), (ii) the nitrogen source, and (iii) mixing and aeration in a stirred tank bioreactor. ECM containing 13.33 and 20 g/L of reducing sugars reached a biomass production of 1.75 and 2.22 gDCW/L, respectively. The biomass yield from ECM was at least 2.5-fold higher than that obtained using Luria-Bertani Broth (LB) medium (0.23 vs 0.09). In addition, the growth rate increased with the agitation velocity (0.44 h^-1 at 200 rpm; 0.36 h^-1 at 150 rpm). Our findings suggest that avocado seeds represent a cost-effective material for producing a sustainable culture medium for bacterial growth of E. coli and other strains of interest in biotechnological processes.