The aim of this work was to evaluate the production of microbial transglutaminase (MTG) by Streptomyces mobaraensis in a reduced nutritional medium based on non-commercial potatoes. Initially, the production was studied comparing 3 culture media based on potato: (i) media based on acid hydrolysed potato, (ii) media based on gelified non-hydrolysed potato and (iii) media based on gelified non-hydrolysed potato supplemented with glucose (20 g/L). All media were supplemented with nutrients and inductors of MTG production (yeast extract, peptone, sodium caseinate, glycerol and mineral salts such as sodium phosphate, potassium phosphate, magnesium sulphate). The best medium was gelified non-hydrolysed potato allowed to obtain up to 2.72 U/mL at 96h. In a second study, it was proposed the substitution of all the nutrients and inductors by exclusively skim milk and glycerol. An experimental design was performed to optimize the composition of milk, potato and glycerol. The economical yield of the process was also evaluated. Fermentations were carried out and samples were taken at 72 h and 96 h. Results showed that the maximum MTG activity was obtained at 72 h. A significant effect of potato and milk on MTG activity was observed, including an effect of interaction between both compounds. Optimal conditions selected were: 600 g/L of skim milk, 40 g/L of potato and 5 g/L of glycerol, yielding a maximum activity of 3.2 U/mL and an economic yield of 8.11 of MTG/(sic) of nutrients. The results showed that the medium milk-potato-glycerol was feasible for the production of transglutaminase, obtaining a high MTG activity in a simple natural medium. (C) 2013 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.