The adage “in unity is strength” also applies to fermented foods: the association of lactic acid bacteria (LAB) strains brings benefits to their organoleptic properties and potential health benefits. Such functionalities can depend on positive interactions, as observed between LAB in yogurt. Finding ways to create new functional associations of LAB strains is challenging, especially in the context of the food transition where new resources, notably proteins, are increasingly used. The objective of this PhD work was to understand how to promote positive interactions between LAB, on the basis of their nitrogen metabolism, to conceive new food applications. The interactions were studied in cocultures that associated a proteolytic (prot+) and a non-proteolytic (prot-) strain. These prot+/prot- pairs were first grown in a model medium containing milk and lupin proteins as sole nitrogen nutriments, in which the growth of prot- strain thus depended on the peptides and amino acids released by the prot+ strain. Strong, weak, or no positive interactions were observed between prot+ and prot- strains. Peptidomics results showed that the release of branched-chain amino acids either free or within peptides was important in the positive interactions observed. We then studied the impact of these interactions in alternative yogurts made from milk and lupin, characterized for their physical and sensory properties. Positive interactions between LAB led to diversified functionalities of alternative yogurts, such as flavour compound and organic acid formation, and texture improvement. This work brings new knowledge on the interactions between LAB, which is useful in designing future fermented foods.