Effects of Near-Infrared Assisted Freeze-Drying on the Quality of Pineapple and Acerola Pulp Blends

In this work, pineapple pulp, acerola pulp, or a mixture of these were dried by conventional freeze-drying (FD) or near-infrared freeze-drying (NIRFD). The physicochemical aspects of the dehydrated and rehydrated pulps; the rheological behaviors; the contents of phenolic compounds, vitamin C, and the antioxidant capacities were investigated. The temperature histories of the samples during freezing, FD and NIRFD were obtained and the records of the gradual increase in the samples’ temperatures allowed the identification of the primary and secondary drying phases and drying time. The pulp composed solely of pineapple showed the lowest freezing onset temperature and the mixture composed of 50% pineapple and acerola pulp exhibited the highest cooling rate due to the different soluble solids content. The freeze-dried pulps showed low water activity values (below 0.441) and attractive yellow or reddish-orange coloration. The fresh and rehydrated pulps exhibited non-Newtonian shear thinning (flow indexes, n < 1) and samples containing higher proportions of acerola pulp resulted in higher apparent viscosities. The results showed that the NIRFD maintained and, in some cases, enhanced the nutritional potential of the products, such as the levels of phenolic compounds, antioxidant capacities, and vitamin C content of the freeze-dried pulps. NIRFD produced higher releases of natural antioxidant compounds, probably due to the breakdown of structures. The samples were positively affected by NIRFD yielding porous microstructures that influence rehydration. The study demonstrated the potential of NIRFD for the development of food ingredients with higher nutritional value, stability, and energy efficiency.