By-products from a “marginal” plant species, prickly pear, as additional ingredients to fermented milk with potential health and nutritional benefits

The application of processing waste/by-products along with lactic acid bacteria could represent a possible strategy to confer functional aspects to food items. Prickly pear is a plant that grows even in marginal areas, with no input in terms of water, fertilization, etc…Seeds from prickly pear fruits represent by-products that are dried and milled to obtain a commercially available flour, that is rich in fiber, minerals and phenolics. This study aimed to evaluate the impact on yogurt of incorporating prickly pear seed (PPS) flour, together with individual commercial strains of lactobacilli (Lacticaseibacillus casei BGP93, Lacticaseibacillus casei LC4P1, Lacticaseibacillus rhamnosus LRB, Lactiplantibacillus plantarum LPAL), some of which show probiotic traits. Preliminarily, we optimized the protocol by examining various percentages of PPS flour added either before or after fermentation. The best result was achieved adding 5% of PPS flour after fermentation, coinciding with the addition of lactobacilli. The ability of all lactobacilli strains to survive in the yogurt and in the presence of the starter cultures was assessed, during 40 days of refrigerated storage. Adjunct lactobacilli and yogurt starters were quantified using both culture-dependent (plate count on MRS and M17 agar) and culture-independent (real-time qPCR) techniques. The inclusion of PPS flour resulted in elevated levels of fiber (more than 3%) and minerals, especially for magnesium, potassium and phosphorus. Furthermore, the antioxidant capacity, measured in vitro (via DPPH and FRAP assays), showed an increase in the yogurt added with PPS and L. casei BGP93. When the extracts of fermented milk beverages were tested in eukaryotic cell lines, antioxidant and anti-inflammatory activities were detectable. These findings suggest the suitability of integrating PPS flour and adjunct lactobacilli into yogurt formulations to obtain functional yogurt, leading to a greater availability of phenolic compounds. Further research is needed on consumer appreciation and willingness to pay.