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

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 great 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).

The Freeze-Drying of Foods—The Characteristic of the Process Course and the Effect of Its Parameters on the Physical Properties of Food Materials

“…Similar phenomena were observed for freeze-dried apples when the heating shelf temperature exceeded 55 °C [ 85 ]. Silva-Espinoza et al [ 14 ], during the freeze-drying of orange puree, did not observe changes in lightness L* with an increasing process temperature from 30 to 50 °C, but the chroma C* was enhanced at the higher shelf temperatures of 40 and 50 °C and the hue angle decreased for temperatures below 50 °C.…”

“…The effect of shelf temperature on the texture of freeze-dried products can be found in a few research studies. Silva-Espinoza et al [ 14 ] noted that the compressed cylinders of freeze-dried orange puree obtained at a higher shelf temperature behaved the same as a material with higher rigidity. Additionally, the values of the slope of the fracture curve were related to the sample resistance and the deformation increase with raising shelf temperature.…”

“…The application of adequate working parameters of lyophilization, including the working pressure, may significantly affect the course of the process but also the quality of the obtained products [ 12 , 14 , 101 , 120 ]). The orange puree was freeze-dried at different pressures inside the chamber (5 and100 Pa).…”

“…The effect of freeze-drying conditions on the nutritional properties, antioxidant activities [ 11 , 12 , 13 , 14 ], and glass transition characteristics [ 12 , 15 , 16 ] of different food materials can be found in the literature. It is widely believed that freeze-drying is the best method of drying.…”

Effect of Freeze-Drying on Quality and Grinding Process of Food Produce: A Review

“…The freezing rate is, however, a critical parameter contributing to the distribution and morphological variation observed in the microstructure of freeze-dried food materials. Silva-Espinoza et al [99] reported the influence of the freeze-drying rate on orange puree with added gum arabic and bamboo fiber. In the research, it was established that a slow rate of freezing resulted in the formation of bigger ice crystals and an expansion of the cells in the structure, resulting in larger pore formation.…”