Polpas de abacaxi, acerola e mistas obtidas por liofilização convencional e liofilização assistida por infravermelho próximo: efeitos na microestrutura e compostos bioativos

Abstract

Pineapple is a fruit produced in tropical and subtropical climates, possessing a pleasant aroma and flavor that, when combined with other tropical fruits, results in a final product with enhanced nutritional and sensory quality. Acerola originates from a fruit-bearing plant that possesses physiologically important phytochemicals, such as anthocyanins and carotenoids, in addition to being nutritionally rich in vitamin C. The production of pineapple and acerola pulps is an alternative for the commercialization of these highly perishable products. One way to facilitate the storage and transport of frozen pulps, as well as to provide a new, highly nutritious product to consumers, is the freeze-drying of these pulps using the conventional method or freeze-drying assisted by infrared radiation. The objective of this thesis was to evaluate the effects of freeze-drying on pineapple, acerola, and mixed pulps. The research was divided into two articles. In the first article, the effects of freeze-drying and powder storage time on the preservation of bioactive compounds and antioxidant activity of mixed pineapple (Ananas comosus) and acerola (Malpighia emarginata) pulps were evaluated. The physicochemical, thermal, rheological, colorimetric characteristics and microstructure of the powders obtained by freeze-drying the mixed pineapple and acerola pulps were assessed. The powders presented attractive coloration, high hygroscopicity (>27 g/100 g), low water activity (≤0.334 ± 0.009), porous microstructure, and low glass transition temperature, ranging from 1.46 to 3.89 °C. Fresh and rehydrated pulps exhibited pseudoplastic rheological behavior. The pineapple/acerola ratio significantly affected all variables, with higher acerola concentrations resulting in a higher content of bioactive compounds after freeze-drying and storage. No synergistic effect was observed between the fruits that would allow for optimizing the preservation of nutritional properties during storage. The second article evaluated the infrared-assisted freeze-drying of acerola, pineapple, and mixed pulps, and investigated the effects of infrared radiation on the physicochemical, rheological, and nutritional characteristics (vitamin C content, phenolic compounds, and antioxidant activity) of the freeze-dried and rehydrated pulps. The application of near-infrared radiation during freeze-drying reduced the process yield, as it accelerated moisture removal. Samples subjected to radiation showed lower water activity (less than 0.340) compared to samples subjected only to freeze-drying (less than 0.441). The rheological profile of the pulps, characteristic of a non-Newtonian pseudoplastic fluid, remained unchanged with the application of infrared radiation. Regarding vitamin C, total phenolics, and antioxidant capacity, all samples freeze-dried with infrared radiation showed results superior to or similar to those of conventionally freeze-dried samples. The microstructure of the freeze-dried pulps treated with infrared radiation was slightly more porous than that of conventionally freeze-dried pulps. In summary, the results of both studies indicated that freeze-drying has good potential for the production of dehydrated fruit pulps, resulting in a powdered product. However, when using infrared radiation, even more satisfactory results are obtained, with good appearance, high nutritional value, and preservation of technological properties.