The aim of this work was to optimize the drying operation of Spirulina sp. using the heat pump to dehumidify the air. An experimental design using the drying air temperature (30, 40 and 50C) and the initial sample thickness (1, 3 and 5 mm) was performed. The responses were the physicochemical properties and the color parameters of the dried microalgae. The air temperature presented the highest effect on the phycocyanin content, while the sample thickness showed the highest influence on the other responses. The optimal operating conditions for the heat pump drying of Spirulina sp. were at air drying temperature of 50C and sample thickness of 5 mm. The phycocyanin content, total antioxidant activity and color difference were found to be 19.60 mg/g, 52.6% and 5.71, respectively. Thermograms (differential scanning calorimetry) showed that under these conditions, the product showed the highest thermal stability. PRACTICAL APPLICATIONSThe culture of Spirulina sp. is attractive for various commercial purposes, such as nutritional supplement for humans and animals and supply of active metabolites in the pharmaceutical and cosmetic industry. The conventional tray drying is a traditional method that is used in the microalgae drying. However, the heat pump drying enables operation in lower temperatures than the traditionally used in convective hot air drying. This operation occurs in moderate conditions of temperature and humidity due to air dehumidification, leading to retention of bioactive compounds in products that are heat sensitive. Therefore, the use of heat pump dryer for the production of dried Spirulina should be promising to preserve its phytochemicals and physical characteristics. The benefits of heat pump drying have been shown in different studies in the literature, but there are no reports about its use in Spirulina drying and its influence on the physicochemical and functional characteristics.
a b s t r a c tThe pretreatment operations (drying, cell disruption and oil extraction) of microalgae biomass to the lipids extraction are important steps to the product quality and production cost. In this study, the lipids from Spirulina were obtained by different methods of biomass drying (tray and spouted bed), cell disruption (microwave, autoclaving and milling) and solvent extraction (hot and cold). The average content of lipids extracted by the cold method, using polar solvents, was of 5.8 ± 0.6 g 100 g À1 . The spouted bed drying with cell disruption by milling achieved the best performance with the hot extraction method. Under these conditions, the TBA value was of 0.57 ± 0.09 mg MDA kg À1 . FT-IR spectra and thermal analysis indicated that the hot extraction resulted in a more purified lipid extract than the cold extraction. The Brimberg model showed the best fit to the lipid extraction kinetics and the activation energy in the best conditions was of 6.11 ± 1.41 kJ mol À1 .
The disposal of fruit and vegetable by-products has drawn the attention of several sectors worldwide, not only due to the concern over environmental impacts but also due to high ratios of nutrients and bioactive compounds that are found in these nonedible parts. These by-products still have great technological potential, because they can be processed and transformed in cosmetics, pharmaceuticals, food, and other products and biomaterial with high added value. The most common form of incorporating them into food is flour. Drying operations enable waste to keep higher concentration of nutrients, less susceptibility to be attacked by microorganisms (due to low humidity), lower storage volumes, and longer shelf-life. The process of transforming residue into flours can be carried out by different equipment whose goal is to remove moisture. Afterwards, dry products pass through mills to reduce particle size. Then, standardization of granule size is recommended. In the conversion steps, processing conditions are particularly important because they should not cause any loss of nutrients, bioactive compounds, and antioxidant activity to the final product.In view of the need to control production steps, this review aimed at compiling information on the theme found in the literature and at highlighting existing gaps to show the scientific community the importance of studying the factors that affect the quality of dehydrated final products. Practical applicationsThe disposal of fruit by-products attracts the attention of several segments, not only due to the concern with environmental impacts worldwide but also due to the high levels of nutrients and bioactive compounds that are still present in these inedible parts that are not properly used. This review provides nutritional and technological information on fruit residues and their potential for application in food. The most common way of inserting these products in food matrices is through flour, but this process is not just about removing moisture from the product, several factors need to be studied and controlled aiming at the minimum of nutritional and technological losses, reduction of antinutritional factors that may be present in the residues, reduced development of microorganisms, and enzymatic activity, and for these reasons, this review was constructed, to bring the main scientific findings in the literature that reports studies on these subjects to the scientific community. Papaya seed Carica papaya L. Oven drying at 45°C Devi and Khanam (2019) Havai and Calimosa Tray drying at 45°C for 4 days Santos et al. (2014) C. papaya L. Spouted-bed drying 40°C-100°C with 9.24, 9.75, 10.50, and 11.76 m/s of flow air, for 0.5, 1.21, 2.25, 3.29, and 4.0 hr Chielle et al. (2016) C. papaya L. Convective air-drying at 40°C-100°C, air velocity (1-3 m/s) Chielle et al. (2016) Papaya peel Havai and Calimosa Tray drying at 45°C for 4 days Santos et al. (2014) C. papaya Oven drying at 60°C for 48 hr Morais et al. (2017) Freeze drying for 24 hr C. papaya L. Formosa Oven drying at 70°C...
The aim of this study was to evaluate the effects of different temperatures in vacuum drying of Arthrospira Spirulina sp. on the physical properties and on the bioactive compounds, and to compare with the traditional oven dryer. The samples were evaluated according to phycocyanin content, phenolic compounds, lipid oxidation, color parameters and rehydration. The phenolic methanol extracts were analyzed by FTIR, and thermal analysis (DSC), scanning electronic microscopy and X-ray diffraction of the samples were also performed. The results showed that the characteristics of the dried products were influenced by the different temperatures of the drying methods. Vacuum drying at 40C was the more suitable to dry Arthrospira Spirulina sp. in relation to the characteristics products due to the minor losses of phycocyanin content, the great source of phenolic compounds, the minor lipid oxidation, the good rehydration capacity and the highest thermal stability. PRATICAL APPLICATIONSArthrospira Spirulina sp. is a microalgae which is a promising source of compounds with biological activity that could be used as functional ingredients, due to presence of pigments, phenolic compounds and fatty acids. However, this algae is very perishable and it should be dried after cultivation in order to prevent fungal deterioration. Phycocyanin content, phenolic compounds and lipid oxidation of the Arthrospira Spirulina sp. are affected by temperature and time drying processing. Thus, the vacuum drying process is a technique which leads to a product with best quality due to the low air temperatures and less oxygen content present in environment of dryer under subatmospheric pressure. Therefore, selection of the most appropriate technique and the drying conditions are very important to avoid major losses of bioactive compounds during the drying process of Arthrospira Spirulina sp.
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