**Elena Diez-Sánchez 1, Antonio Martínez 2, Dolores Rodrigo 2, Amparo Quiles <sup>1</sup> and Isabel Hernando 1,\***


Received: 25 February 2020; Accepted: 6 March 2020; Published: 1 April 2020

**Abstract:** High hydrostatic pressure is a non-thermal treatment of great interest because of its importance for producing food with additional or enhanced benefits above their nutritional value. In the present study, the effect of high hydrostatic pressure processing parameters (200–500 MPa; 1–10 min) is investigated through response surface methodology (RSM) to optimize the treatment conditions, maximizing the phenol content and antioxidant capacity while minimizing microbiological survival, in milkshakes prepared with chokeberry pomace (2.5–10%). The measurement of fluorescence intensity of the samples was used as an indicator of total phenolic content and antioxidant capacity. The results showed that the intensity of the treatments had different effects on the milkshakes. The RSM described that the greatest retention of phenolic compounds and antioxidant capacity with minimum microbiological survival were found at 500 MPa for 10 min and 10% (*w*/*v*) chokeberry pomace. Therefore, this study offers the opportunity to develop microbiologically safe novel dairy products of high nutritional quality.

**Keywords:** antioxidant capacity; microbial inactivation; image analysis; high pressure processing; total phenolic content
