**The Impact of Freeze-Drying Conditions on the Physico-Chemical Properties and Bioactive Compounds of a Freeze-Dried Orange Puree**

#### **Marilú A. Silva-Espinoza 1, Charfedinne Ayed 2, Timothy Foster 2, María del Mar Camacho 1 and Nuria Martínez-Navarrete 1,\***


Received: 28 November 2019; Accepted: 24 December 2019; Published: 30 December 2019

**Abstract:** Fruits are essential for a healthy diet, as they contribute to the prevention of cardiovascular diseases and some cancers, which is attributed to their high bioactive compound content contributing to their antioxidant capacity. Nevertheless, fruits have a short shelf life due to their high-water content, and freeze-drying is a well-known technique to preserve their nutritive quality. However, it is an expensive technology, both due to the use of low pressure and long processing time. Therefore, an optimisation of variables such as the freezing rate, working pressure and shelf temperature during freeze-drying may preserve fruit quality while reducing the time and costs. The impact of these variables on colour, porosity, mechanical properties, water content, vitamin C, total phenols, β-carotene, and antioxidant activity of a freeze-dried orange puree was evaluated. The results showed a grea<sup>t</sup> impact of pressure and shelf temperature on luminosity, chroma and water content. Vitamin C and β-carotene were more preserved with higher shelf temperatures (shorter times of processing) and lower pressure, respectively. The optimum freeze-drying conditions preserving the nutrients, and with an interesting structural property, perceived as a crunchy product by consumers, are low pressure (5 Pa) and high shelf temperature (50 ◦C).

**Keywords:** vitamin C; total phenols; total carotenoids; antioxidant activity; colour; mechanical properties; pressure; shelf temperature; freezing rate
