Optimization of the solid state fermentation process to obtain tempeh from hardened chickpeas (Cicer arietinum L.)

Solid state fermentation (SSF) represents a technological alternative for a great variety of cereals and legumes, or combination of them, to improve their nutritional quality and to obtain edible products with palatable sensorial characteristics. The objective of this work was to find the best conditions of fermentation temperature and time to obtain tempeh from hardened chickpeas (Cicer arietinum L.) applying SSF. Response surface methodology (RSM) was applied over three response variables (phytic acid, in vitro protein digestibility and available lysine) to find best conditions of fermentation to carry out the process. A central composite experimental design with two factors [X1 = temperature (31-36 degrees C) and X2 = time (48-72 h)] in five levels (2 factorials, 2 axial, I central) was used. Spores from Rhizopus stolonifer were suspended in distilled water (1 x 10(6) spores/mL) and used as starter. According to regression models, minimum and maximum levels of the response variables were 1.24-2.66 mg phytic acid/g of sample DM, 77.6-83.5% in vitro protein digestibility and 2.18-4.63 g available lysine/16 g N. The superposition of contour plots of each one of the response variables allowed researchers to find, graphically, the best conditions for the SSF process: 35.8 degrees C for 42.7 h.