Effects of Infrared and Microwave Radiation on the Bioactive Compounds of Microalga Spirulina platensis after Continuous and Intermittent Drying.

Pharmaceutical, nutritional and food industries have recently become interested in the potential of Spirulina platensis, a kind of cyanobacterium with high levels of proteins, vitamins and bioactive compounds. Because of its high moisture, this microalga needs to be submitted to a preservation technique such as drying to be properly used. The aim of this work is to investigate the use of infrared and microwave radiation in the Spirulina platensis drying process. The experiments were performed in continuous and intermittent modes, evaluating different operating conditions for infrared and microwave drying, as well as their effects on the quality of the final product, expressed by the content of bioactive compounds (i.e., total phenolic, total flavonoid, citric acid and phycocyanin contents). The results proved that the use of electromagnetic radiation in the drying of spirulina is an interesting alternative for processing this material if performed under adequate operating conditions. The experiments carried out continuously at lower temperatures and powers and the combination between different temperatures and powers in the intermittent mode resulted in a final product with satisfactory levels of bioactive compounds and low operation times in comparison with conventional methodologies.

Use of Refractance Window Drying as an Alternative Method for Processing the Microalga Spirulina platensis.

Microalgae such as Spirulina platensis have recently attracted the interest of the pharmaceutical, nutritional and food industries due to their high levels of proteins and bioactive compounds. In this study, we investigated the use of refractance window (RW) drying as an alternative technology for processing the microalga Spirulina biomass aiming at its dehydration. In addition, we also analyzed the effects of operating variables (i.e., time and temperature) on the quality of the final product, expressed by the content of bioactive compounds (i.e., total phenolics, total flavonoids, and phycocyanin). The results showed that RW drying can generate a dehydrated product with a moisture content lower than 10.0%, minimal visual changes, and reduced process time. The content of bioactive compounds after RW drying was found to be satisfactory, with some of them close to those observed in the fresh microalga. The best results for total phenolic (TPC) and total flavonoids (TFC) content were obtained at temperatures of around 70 °C and processing times around 4.5 h. The phycocyanin content was negatively influenced by higher temperatures (higher than 80 °C) and high exposing drying times (higher than 4.5 h) due to its thermosensibility properties. The use of refractance window drying proved to be an interesting methodology for the processing and conservation of Spirulina platensis, as well as an important alternative to the industrial processing of this biomass.

Analysis of the use of a non-conventional rotary drum for dehydration of microalga Spirulina platensis.

The high content of bioactive compounds in the microalga Spirulina platensis has recently attracted attention from food and pharmaceutical industries. However, for its application an effective preservation technique must be developed. In this paper, we investigated the use of a non-conventional rotary dryer (with an inert bed) for drying the microalga Spirulina biomass and the effects of the operational conditions (air temperature, intermittent feeding interval, filling degree of inert particles, and rotation speed) on its bioactive compounds. The results indicated that this non-conventional drying system offers an effective alternative for expanding the use of this biomass in an adequate form. We identified the conditions in which the dried material had maintained satisfactory contents of phenolics (air temperature of 70 °C and intermittent feeding interval of 10 min), flavonoids (intermittent feeding interval of 17.4 min), and phycocyanin compounds (air temperature of 40 °C), which were near to those present in fresh microalga.

Hydrothermal carbonization of acerola (Malphigia emarginata D.C.) wastes and its application as an adsorbent.

Hydrothermal carbonization (HTC) is a promising technique for the improved management and better use of agro-industrial wastes. In this study, the effects of temperature, reaction time, biomass/water ratio, feed-water pH, and agitation speed on the HTC of acerola wastes were investigated. The effects of these independent variables on process yield and on the total oxygenated functional groups of hydrochars were quantified. The best process conditions were obtained using the desirability function and the chemical-morphological properties of the hydrochar produced in these optimal conditions were investigated. The total number of oxygenated functional groups were found to be higher than those described in the literature for similar biomasses. The effects of temperature, solution pH, initial dye concentration, and adsorbent dosage on the adsorption of methylene blue using the obtained hydrochar were also investigated and the conditions necessary for the maximum removal and adsorption capacity were determined. Adsorption isotherms and thermodynamic studies have shown that methylene blue adsorption on the obtained hydrochar is endothermic and spontaneous. Thus, the HTC of acerola wastes may be a sustainable technology for the modification of underutilized wastes and their application as adsorbents of environmental contaminants.

Effects of dehydration methods on quality characteristics of yellow passion fruit co-products.

BACKGROUND: The production and processing of fruits generate a large amount of residues, which are usually disposed of or under-used, representing losses of raw material and energy. The present paper investigates the effect of four dehydration techniques (convective, infrared, microwave and freeze-drying) on yellow passion fruit (Passiflora edulis f. flavicarpa) co-products and the influence of the main variables on moisture removal and bioactive compounds. The compounds analyzed were total phenolics, total flavonoids, ascorbic acid and pectin. RESULTS: The content of phenolics and flavonoids increased after dehydration in all techniques investigated and the process temperatures directly affected the ascorbic acid content. Microwave dehydration showed the best results for most bioactive compounds analyzed, if performed in suitable process conditions. However, the highest levels of pectin content were obtained by freeze-drying and convective dehydration. CONCLUSION: This study reinforces the importance of the adequate use of passion fruit co-products due to the high levels of bioactive compounds in this material. Microwave dehydration presented the best results, which indicates the potential use of this technique for a better exploitation of fruit co-products. Larger quantities of pectin were extracted from samples dehydrated through methodologies with long-time process and low temperatures, such as convective drying and freeze-drying. © 2017 Society of Chemical Industry.