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Background: Blue is a color not often present in food. Even so, it is especially attractive to children. Today, most blue coloring agents used by the food industry are synthetic. With increasing health issues concern by the scientific community and the general population, there is a trend to look for natural alternatives to most synthetic products. There only exist few natural blue colorants, which are presented in a literature survey, along with the methods currently used for their recovery from natural sources. The best extraction methods and process parameters for the extraction of blue anthocyanins, iridoids and phycocyanin are discussed. Methods: A literature survey was conducted to detect the main sources of blue colorants found in nature. The focus was on the extraction methods used to recover such molecules, with the objective of finding efficient and environmentally safe techniques for application at industrial level, and, thus, allowing the production of natural blue colorants at scale high enough for food industry consumption. Results: The main natural blue colorants found in literature are anthocyanins, phycocyanin, and genipin. While anthocyanins can be recovered from a variety of plants, the source of phycocyanin are algae, and genipin can be obtained specifically from Gardenia jasminoides Ellis and Genipa americana L. Several extraction techniques have been applied to recover blue colorants from such sources, from classical methods using organic solvents, to more sophisticated technologies as ultrasoundassisted extraction, supercritical fluid extraction, pressurized liquid extraction, high-pressure extraction, and enzyme-assisted extraction. Conclusion: There is great potential for anthocyanins, phycocyanin and genipin use as natural food additives with health benefits, besides imparting color. However, the technologies for the colorants recovery and application are not mature enough. Therefore, this area is still developing, and it is necessary to evaluate the economic feasibility of the proposed extraction processes, along with the safety and acceptance of colored food using these additives.

Elaeagnus latifolia is an underutilized plant of the Elaeagnaceae family. The extraction of E. latifolia pulp was carried out from 30 to 120 min by different environmentally friendly extraction methods: agitation, percolation, Soxhlet, and ultrasound-assisted extraction with ethanol, and hydrodistillation. The extracts were analyzed for their total phenolic compounds, carotenoids and ascorbic acid contents, and antioxidant activity. The highest yield of extract, of 63.5 g/100 g of raw material (RM), in dry basis (db), total phenolic compounds, of 3.3 mg gallic acid equivalent (GAE)/g extract, and 2.042 mg GAE/g RM, and carotenoids, of 176.6 mg ��-carotene equivalent/kg RM, were obtained by Soxhlet for 120 min. All the extracts presented similar antioxidant activity. Therefore, E. latifolia can be a source of compounds of interest to the food industry.

In this work, four residual biomasses from the food industry (coconut husk, defatted grape seeds, sugar cane bagasse, and pressed palm fiber) were subjected to subcritical water hydrolysis assisted by CO2 (SubWH + CO2) with the objective of producing fermentable sugars. Hydrolysis kinetics were determined using a semi-batch unit equipped with a 50 mL reactor. The process was conducted at 250 °C for 30 min under 20 MPa. Total reducing sugars recovered using SubWH + CO2 were (wet basis): 13.5% for coconut husk, 10% for defatted grape seeds, 13.2% for sugar cane bagasse, and 11.2% for pressed palm fiber. For coconut husk and defatted grape seeds, adding CO2 increased total reducing sugars by 15 and 56%, respectively. For sugar cane bagasse and pressed palm fiber, adding CO2 to the process did not alter total reducing sugars recovered. In all cases, the byproduct yield increased when adding CO2 to the process.

Two abundant coffee waste residues (powder and defatted cake) were treated using subcritical water (SubCW) for hydrolysis and extraction of reducing sugars (RS), total reducing sugars (TRS), and total phenolic compounds (TPC) under semi-continuous flow conditions. The flow-through process was carried out at 150, 175, 200 and 250 °C, with a water flow of 10 mL/min and reaction pressures of either 22.5 or 30 MPa. For treated coffee powder, the maximum observed sugar recovery was 6.3% for RS (150 °C and 30 MPa) and 9.0% for TRS (150 °C and 30 MPa). The maximum TPC recovery was 26.64 mg GAE (Gallic Acid Equivalent)/g powder coffee, observed at 200 °C and 22.5 MPa. For the defatted coffee cake, the maximum sugar yields were 8.79% and 17.23% for RS and TRS; both observed at a treatment temperature of 175 °C. The highest TPC yield was 55.31 mg TPC GAE/g defatted coffee cake, also at 175 °C. HPLC was used to quantify specific carbohydrates (arabinose, cellobiose, glucose, and xylose), 5-hydroxy-methyl-furfural (5-HMF) and furfural in both coffee waste hydrolyzates, providing evidence of thermal degradation of the coffee carbohydrates. Scanning electron microscopy of the treated samples revealed particles deposited on the surface and other signs of physical degradation of the biomass structure. Fourier Transform Infrared Spectroscopy of the residues revealed that the density of surface bound acid groups increased with increasing treatment temperature. The results presented here provide a basis for the use of subcritical water to obtain reducing sugars and phenolic compounds from coffee residue.

Because of the today’s pursuit for healthy products, the production of vegetable extracts by supercritical fluid extraction (SFE) and ultrasound assisted extraction (UAE) is a field of industrial interest. Nonetheless, the lack of information on scale-up of these technologies to the industrial level and the relatively high investment associated with emergent extraction processes is responsible for the elimination of these technologies at the very early stages of process design, that is, during the selection of the extraction process. In order to avoid this prejudice, a preliminary analysis of the cost of manufacturing (COM) should be conducted with a minimum of experimental information, possibly gathered from the literature. If this tool is available to process design engineers, the various extraction techniques can be analyzed without any high investment bias. Thus, a simple method to estimate the COM of extracts by SFE and UAE is needed. In this chapter, rapid methods to estimate the COM of extracts obtained by these techniques are presented. The information required to perform such analysis is discussed based on scale-up issues. A compilation of the published data on the scale-up and COM of SFE and UAE processes is presented.

This chapter presents a literature review of biomass pretreatments that make use of carbon dioxide. Two supercritical technologies are considered: supercritical carbon dioxide explosion and sub/supercritical water hydrolysis with carbon dioxide. The main advantages presented by both techniques are the short time and improved sugar yield. Nonetheless, they are still under development and need further optimization, along with studies on economics, before they can become feasible at the industrial level.

The original version of this article unfortunately contained a mistake: Juliane Prado was not listed among the authors. The complete authors are given above.