Exploring low moisture extrudates as A substrate for solid state fermentation to develop a novel chickpea tempeh with enhanced functionalities

Tempeh is a product of fungal fermentation of peas and legumes, predominantly soybeans. It is a great alternative source of protein with supplementary bioactive and functional benefits from its micronutrient and phytochemical constituents. Low-moisture extrusion is a widely used technique for creating expanded products with superior porosity. The high shear and temperatures modify the structures of protein and starch in the matrix, rendering them more bioavailable. This may be beneficial from a fermentation standpoint. The porous matrix may provide ample space, making the modified nutrients more accessible to microbes. The purpose of this study is to validate whether low moisture extrudates are an advantageous substrate for efficient fermentation to produce tempeh that is nutritionally, functionally and sensorially profound. Chickpeas’ balanced starch and protein composition make them an ideal candidate for both extrusion and fermentation. In the first part of the study, chickpea flour was subjected to low moisture extrusion under varied parameters to yield extrudates with desired expansion and porosity. These were appropriately rehydrated before fermenting with Rhizopus oligosporus for 36 hours. From our results, the extrudate prepared at 1 kg/h feed rate with 20% feed moisture at a screw speed of 450RPM in a barrel with a temperature profile of 80˚C, 100˚C, 120˚C, 140˚C, 160˚C and 180˚C had the highest expansion (expansion ratio: 2.77) and protein (23.43%) among the extrudates. Furthermore, it performed exceedingly well under all rehydration and fermentation trials, consistently yielding tempehs with maximum mycelial coverage. In the second part, traditionally fermented chickpea tempeh was used as a benchmark to evaluate the effectiveness of extrusion in improving the fermented product. The extrudate tempeh was physically similar in terms of mycelial coverage, color and intactness. Nutritionally it had 14.8% higher protein, 15.6% higher ash, 30.1% lower fat and 36.2% lower carbohydrates than traditional tempeh. It also comprised a 63% richer content of polyphenols and 38.4% lower trypsin inhibitor. It was 103.5% more efficacious in sequestering ABTS free radicals. In conclusion, our study validates the synergy between low moisture extrusion and solid state fermentation in manufacturing a novel nutritionally profound tempeh. These results necessitate investigation to further confirm the holistic benefits.