Effect of Solid Fermentation with Rhizopus oligosporus on the Physicochemical and Functional Properties of a Mixture of Legumes to Produce Tempeh: Application of Mixture Design Methodology

The shortage of protein-rich foods is a major challenge due to the rapid growth of the world’s population. For this reason, efforts are being made to achieve sustainability in the food system to produce nutritious foods with better qualities. The present study aimed to utilize a combination of widely consumed legumes with nutritional properties—such as lentils, chickpeas, and beans—considering their physicochemical and functional characteristics, to produce tempeh as a model. A simple mixture design was employed to develop a legume-based product through the production of fermented flour using Rhizopus oligosporus ATCC 22959. For this purpose, proximate composition, water absorption index (WAI), pH, phenolic content, and antioxidant capacity, via the DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid)) radicals, were determined in the raw legumes. Optimal fermentation conditions were determined through digital image analysis, and fermentations were carried out according to the design. The crude and soluble protein content, phenolic content, and DPPH of the fermented samples were determined, and a statistical optimization was performed by maximizing each variable. Through optimization, it was found that a formulation of 80.81% lentil and 19.19% chickpea presented the best desirability (D = 0.75) according to the criteria mentioned above. These results were also compared with those obtained from the preparation of an original soy tempeh using the microorganism Rhizopus oligosporus; it was found that the protein differences between the original tempeh and the one made from the legume blend were 19 g/100 g dry matter for the original tempeh and 27.5 g/100 g dry matter for the one made with the legume blend, demonstrating that the combination of legumes exerts a favorable interaction within the mixture model on the physicochemical properties of tempeh and could represent significant potential for the production of flours applicable to the development of food products as part of alternative protein sources.