Use of Prickly Pears in Cod Fish-Burgers as Functional Ingredients ^†

Since the problem of food waste has become a global concern, this study has the goal to make full use of the zero-waste concept, aiming to find a way to recycle all the parts of a food product, without producing waste. To the end, prickly pears (Opuntia ficus india) were completely used, without discarding the peel as a by-product (the fruit peel is around 50% of the total product). Pulp and peel were each used to produce an active powder to be added as ingredient in fish burgers. Prickly pears are tropical plants, rich in polyphenolic compounds, and able to control microbial proliferation and general detrimental phenomena occurring in food. For the current study, the pulp and the peel were separately dehydrated and reduced to a fine powder in order to be used as a food ingredient in cod fish burgers to improve sensory quality and prevent microbial growth during storage at 4 °C. An in vitro test of the powders was carried out against target microorganisms. After that, three different amounts (i.e., 2.5 g, 7.5 g and 12.5 g) of peel and pulp in proper combination, were added to the fish burger formulation. Results demonstrate that this addition of the entire prickly pear improved the microbial quality of burgers, reducing the growth of fish spoilage microorganisms (i.e., Pseudomonas spp., psychrotolerant and heat-labile aerobic bacteria and psychrotropic bacteria) and that 12.5 g was the best condition of all those used. In addition, the use of the prickly pears enhanced the sensory properties of the burgers, thus demonstrating that this fruit could be advantageously used, without producing any waste, to prolong food shelf life, with beneficial consequences from the environmental, technological and practical points of view.