**1. Introduction**

Milk and milk products are a source of vitamins, minerals, lipids, and proteins of high biological value [1]. For decades, fermented dairy products are considered beneficial foods for the health of human beings; this is due to a large part of the microorganisms involved in the fermentation and to the products released during this process [2]. The lactic acid bacteria (LAB), such as *Lactobacillus acidophilus,* are important in fermentation processes, which is why they are widely used in the food industry, due to their ability to acidify the food and preserve it from spores as well as to intervene in the texture, taste, and smell of fermented products [3]. The proteolytic activity of LAB in the milk fermentation process produces bioactive peptides that provide additional benefits in consumer health [2], such as those with antioxidant activity [4]. The composition of milk determines its nutritional quality and its properties in the manufacture of food products; goat milk has high nutritional values only surpassing human breast milk. Among the proteins of cow's milk and goat's milk, there are many differences in their composition [5], which is why fermented beverages based on cow's and goat's milk, inoculated with the probiotic *Lactobacillus acidophilus*, will be made in the present study. Additionally, the

correlation between proteolytic activities, peptide concentrations, and antioxidant activity were determined.
