**3. Drying and microalgal quality**

Drying of foods can be defined as a unit operation of water removal aiming to reduce moisture content and water activity and consequently stabilize foods by inhibiting the microbial grow and enzymatic activity and slowing chemical reactions [20]. Dried foods present advantages which are easy to store and transport and have long shelf life.

After separation and concentration, microalgal biomass has a high water content, presenting high perishability once it represents a good substrate to microbial grow and enzymatic activity if commercialized without any stabilization treatment. Stabilization of moist biomass by pasteurization is possible, but the prolongation of the shelf life is limited, refrigerate storage is needed [21], and degradation of functional components may occur if high temperatures are used. Thus, to extend shelf life and allow storage at room temperature, drying of microalgae biomass is generally considered an effective alternative. Many drying technologies can be potentially used to dry microalgae biomass as well as other foods with high viscosity. Different factors should be taken in consideration to choose the best drying method. In most cases the main factors that influence this choice are energy efficiency and installation and operation costs. However, if the dried microalgal biomass is produced to human alimentation, the preservation of nutritional and functional components of the biomass must be also considered [22, 23].

In the literature many drying methods applied to microalgae biomass are discussed. Most of them are related to the stabilization of biomass for nonhuman use such as oil extraction for biofuel industry or feed production. These methods are in general very effective on the point of view of energy efficiency and processing time; among them the following methods can be cited: rotary drying, solar drying, cross-flow and vacuum shelf drying and flash drying. The main challenge in these cases is the processing cost and energy requirement, but not much attention is given to degradation on functional and nutritional components [6, 24].

On the other hand, studies on the assessment of drying methods applied to microalgae to human use are not so common in literature. In **Table 1**, a summary of the different drying methods used to produce dried biomass with potential application in human alimentation is presented in which, together with the engineering of the drying process, the impact on nutritional and/or functional components was assessed.

One of the conditions that affect the choice of method and the drying performance is the initial moisture that the microalgal biomass presents. The algal biomass starts the drying process with initial moisture values between 55 and 88% (wet basis) in different dehydration processes [25–30].

Apart from the color change, the compound degradation, and the drying kinetics, the final moisture content can be one parameter to compare different drying methods and demonstrates how these methods can affect the sample. Based on the initial moisture and the chosen method, the drying can show high or low drying rates, can influence the velocity heat and water mass transfer through the samples, and in some conditions not allow the diffusion between the interior and the surface [26, 28]. In short, apart from the initial moisture that can influence the chosen method, some physical parameters can influence in velocity and water outlet, impacting in final moisture and in quality of the product. Further, some storage conditions, like light, temperature, water activity, oxygen concentration, relative humidity, existence of coating matrix, etc., are important parameters to study compound degradation and product shelf life [31, 32]. Assessing sorption isotherms, stability studies and DSC, the sample behavior during storage, and how the environmental factors influence these parameters is important to evaluate the effect of storage on quality retention of the final products [28, 32–34].

Many different methods were presented in **Table 1**; however, similar drying technologies have the same principle with few modifications of processing parameters or equipment design but are named with different denominations, according to the authors, in papers. **Figure 1** exemplifies this segregation, based on the same principle. The principle depends on the conditions during the drying, physical apparat, and intrinsic processes and interactions that occur with the sample and the drying environment, that is, mass transference process and water outlet [38]. As it can be seen from **Figure 1** in most of the drying methods used for microalgal drying, water is removed by an airflow. Different heat transfer principles can be found, that is, convection, conduction (e.g., cast-tape drying), and radiation. The moisture and the viscosity of the sample are also variable of these processes.

To enrich the discussion about drying methods and applicability to microalgal powder production, the main, traditional, and innovative drying methods are briefly presented in their principle and applications to microalgae.

#### **3.1 Spray drying**

Spray drying is the most common drying method applied to microalgae biomass for human uses [6] and, more general, is one of the most widely diffused drying technologies when dehydration of liquid foodstuff is required.

**75**

**Algae species\***

*Chlorella vulgaris*

[26]

Freeze-drying (FD)

**Dry method**

**Dry specifications/**

**Quality assessment**

**Findings/conclusions**

**variables** Temperature:

• • •

Chlorophyll content

Total carotenoid

Color characterization

• color

• HAD

•

Protein content was not significantly influenced by drying method

Freeze-drying is the most suitable drying method to maintain the nutrient and

bioactive compounds

FD powder shows intense green color, while HAD powder shows dark brown

Carotenoid degradation was of 57.12 ± 3.74% for FD and 91.06 ± 2.37% for

−30°C

Pressure: 3 mbar

Time: 4.5 h

Final moisture

• extracts

Characterization of carotenoid-rich

content:

0.88 ± 0.05% (w.b.)

• •

Temperature: 60°C

Time: 4.5 h

Final moisture

content:

3.58 ± 0.19% (w.b.)

*Spirulina* sp. [29]

Heat pump

Temperature: 30,

• • • determination

Total activity antioxidant (DPPH)

Phycocyanin content

Color measure

• • •

TAA loss: 11–87%

The optimal condition for lower color and phycocyanin degradation was air

temperature of 50°C and sample thickness of 5 mm

Phycocyanin content loss: 15–83%

Color difference (

ΔE): 4.22–13.51

40, and 50°C

Sample thickness: 1,

3, and 5 mm

Drying time:

85–560min

Final moisture

content: 10.4 ± 1.2%

(w.b.)

*Spirulina* sp*.* [33]

Convective

Temperature: from

• •

Effect of drying conditions and

temperature on sorption isotherm

Drying kinetic

• •

Spirulina is very hygroscopic in the 25–40°C temperature range

Equilibrium moisture content is not dependent on the storage temperature

40 to 60°C

Air velocity:

1.9–3.8 m/s

drying in thin

layer

drying

Hot-air drying

(HAD)

Determination of antiradical activity

Protein content

*Drying and Quality of Microalgal Powders for Human Alimentation*

*DOI: http://dx.doi.org/10.5772/intechopen.89324*


#### *Drying and Quality of Microalgal Powders for Human Alimentation DOI: http://dx.doi.org/10.5772/intechopen.89324*

*Microalgae - From Physiology to Application*

In the literature many drying methods applied to microalgae biomass are discussed. Most of them are related to the stabilization of biomass for nonhuman use such as oil extraction for biofuel industry or feed production. These methods are in general very effective on the point of view of energy efficiency and processing time; among them the following methods can be cited: rotary drying, solar drying, cross-flow and vacuum shelf drying and flash drying. The main challenge in these cases is the processing cost and energy requirement, but not much attention is given

On the other hand, studies on the assessment of drying methods applied to microalgae to human use are not so common in literature. In **Table 1**, a summary of the different drying methods used to produce dried biomass with potential application in human alimentation is presented in which, together with the engineering of the drying process, the impact on nutritional and/or functional components was assessed. One of the conditions that affect the choice of method and the drying performance is the initial moisture that the microalgal biomass presents. The algal biomass starts the drying process with initial moisture values between 55 and 88%

Apart from the color change, the compound degradation, and the drying kinetics, the final moisture content can be one parameter to compare different drying methods and demonstrates how these methods can affect the sample. Based on the initial moisture and the chosen method, the drying can show high or low drying rates, can influence the velocity heat and water mass transfer through the samples, and in some conditions not allow the diffusion between the interior and the surface [26, 28]. In short, apart from the initial moisture that can influence the chosen method, some physical parameters can influence in velocity and water outlet, impacting in final moisture and in quality of the product. Further, some storage conditions, like light, temperature, water activity, oxygen concentration, relative humidity, existence of coating matrix, etc., are important parameters to study compound degradation and product shelf life [31, 32]. Assessing sorption isotherms, stability studies and DSC, the sample behavior during storage, and how the environmental factors influence these parameters is important to evaluate the effect of storage on quality retention of the final

Many different methods were presented in **Table 1**; however, similar drying technologies have the same principle with few modifications of processing parameters or equipment design but are named with different denominations, according to the authors, in papers. **Figure 1** exemplifies this segregation, based on the same principle. The principle depends on the conditions during the drying, physical apparat, and intrinsic processes and interactions that occur with the sample and the drying environment, that is, mass transference process and water outlet [38]. As it can be seen from **Figure 1** in most of the drying methods used for microalgal drying, water is removed by an airflow. Different heat transfer principles can be found, that is, convection, conduction (e.g., cast-tape drying), and radiation. The moisture

To enrich the discussion about drying methods and applicability to microalgal powder production, the main, traditional, and innovative drying methods are

Spray drying is the most common drying method applied to microalgae biomass for human uses [6] and, more general, is one of the most widely diffused drying

and the viscosity of the sample are also variable of these processes.

briefly presented in their principle and applications to microalgae.

technologies when dehydration of liquid foodstuff is required.

to degradation on functional and nutritional components [6, 24].

(wet basis) in different dehydration processes [25–30].

**74**

**3.1 Spray drying**

products [28, 32–34].


**77**

**Algae species\***

*Arthrospira spirulina LEB-18*

Vacuum drying (laboratory scale)

Temperature: 40, 50, and 60°C Pressure: 13.3 kPa

• •

Total phenolic compounds (TPC)

Phycocyanin content

• 60°C drying (71.7%)

• tion to in natura sample

• • • samples

The lipid oxidation increases with the increase in drying temperature

Sample drying at 60°C presented the highest peak of temperature (143.8°C)

Morphologic analysis: rigid shape of irregular and compact particles for both

Vacuum drying at 40°C causes the lowest losses of phycocyanin, phenolic

compounds, the minor lipid oxidation, the good rehydration capacity, and the

TAA values: 34.6 ± 1.1% for CTD sample; TAA increases with the inlet drying

Phycocyanin content, the color difference for samples, and TBA values were

SB drying at 80°C and CT drying obtain minor lipid oxidation and phycocya-

air temperature increase for SBD samples

highest thermal stability

•

and the lowest enthalpy value (189 J/g)

Phycocyanin content: higher losses (80.5%) in OD at 55 °C than the VD at

TPC: VD samples showed increase of values (from 18 to 48% (w/w)) in rela-

•

Lipid oxidation

Final moisture content: 0.10 g/g (w.b.)

• • • • •

> *Spirulina LEB-18* [37]

Spouted bed dryer (SBD)

Temperature: 80, 90, 100, and 110°C

• •

Total antioxidant activity

(TAA)—DPPH

• • nin degradation

SBD drying at 100°C reached greater thermal stability

affected by the temperature in SBD

Centesimal composition

Air velocity:

0.33 ± 0.01 m.s−1

Drying time:

• • •

Temperature: 55°C

Air velocity: 2.5 m.

• •

Tray thickness:

4 mm

Final moisture:

• •

0.10 kg.kg−1 (w.b.)

•

Scanning electron microscopy

FTIR spectroscopy

Thermal analysis

Color analysis

Lipid oxidation (TBA)

Phycocyanin content

Protein solubility

Total phenolic compounds

210 min

Conventional

tray drying

(CTD)

s

−1

Morphologic analysis

DSC analysis

FTIR spectroscopy

Rehydration analysis

Color parameters

[28]

**Dry method**

**Dry specifications/**

**Quality assessment**

**Findings/conclusions**

**variables**

*Drying and Quality of Microalgal Powders for Human Alimentation*

*DOI: http://dx.doi.org/10.5772/intechopen.89324*


*Drying and Quality of Microalgal Powders for Human Alimentation DOI: http://dx.doi.org/10.5772/intechopen.89324*

*Microalgae - From Physiology to Application*

**76**

**Algae species\***

*Spirulina* sp. [35]

Convective

Temperature: 40,

• • •

Total sugar analysis

Protein analysis

Microscope characterization

• •

Protein loss: 10% in FD; 10–15% in SD; 10–25% in ID

Total sugar loss: 30% at 40°C and higher temperatures (mean)

FD showed the highest retention of proteins and sugars

Structure damage is caused by the air-drying temperatures

50, and 60°C

Air velocity:

0.15 m/s

Drying time: 2–3 h

Infrared drying

Temperature: 40,

50, and 60°C

Radiative flux:

2.71 kW/m2

Spray drying

Temperature:

130–150°C

Feed rate: 0.09 l/h

(SD)

Freeze-drying

Temperature: - 20°C

Pressure: 8 Pa

Drying time: 18 h

(FD)

*Spirulina* sp.

Convective

Average

•

Shrinkage coefficient and isotropicity

• •

Final porosity approaching 80%

Weak and anisotropic shrinkage

temperature: 50°C

•

Porosity and apparent density

Relative humidity:

12%

drying

[36]

(ID)

drying (CD)

**Dry method**

**Dry** 

**Quality assessment**

**Findings/conclusions**

**specifications/**

**variables**


**79**

**Algae species\***

*Arthrospira platensis* [39]

Convective drying at atmospheric pressure

**Dry method**

**Dry specifications/**

**Quality assessment**

**Findings/conclusions**

**variables** Layer thickness: 1 and 4 mm Temperature: 45°C

• • •

Cylinder diameters:

2, 3, 4, and 6 mm

Temperature: 45°V

*Haematococcus* 

Spray drying

Not informed

Economic feasibility and the return for

astaxanthin production

*pluvialis* [40]

*Aphanothece* 

Tray drying

Temperature: 40,

• • •

Total lipid determination

Total carbohydrate determination

Total protein determination

• • • •

Lipid fraction: 0.071–0.079 g/g (dry weight)

Fatty acids: chain lengths with 14 and 24 C

The drying conditions were shown to affect the macronutrient composition

(protein, carbohydrate, and lipid contents), but did not influence the

polyunsaturated/saturated ratio of the biomass.

Spray drying with TBHQ and α-tocopherol was efficient to preserve algal

carotenoid and minimize degradation of beta-carotene

Between the two antioxidants, α-tocopherol had a small protective effect on

beta-carotene degradation

Protein content: 0.413–0.493 g/g (dry weight)

Carbohydrate fraction: 0.134–0.176 g/g (dry weight)

50, and 60°C

Constant speed:

1.5 m/s

Sample thickness: 5

•

Fatty acid determination

and 7 mm

*Dunaliella salina*

Spray drying

Inlet temperature:

• • •

Carotenoid analysis

Solid determination

Stability studies

130°C

Outlet temperature:

85°C

Sprayed rate:

200 mL.h−1

Prevent

degradation agent:

antioxidants

[32]

with air

circulation

*microscopica* 

*Nugeli* [41]

Volume shrinkage characterization

True density

Photography and SEM view

Cylinders: initial porosity, 20%; final porosity, 65–78%

Layers do not show macroporosity; the product is homogeneous without any pores

Microporosity: present in cylinder and layer forms

Porosity can be linked to the shrinkage phase durations, an improvement of

organoleptic taste of dried spirulina

Cylinders for drying indicate optimum drying conditions

The results have proven the economic feasibility of the production for different

astaxanthin market prices

Evaporative rate: 26.125 kg/h

*Drying and Quality of Microalgal Powders for Human Alimentation*

*DOI: http://dx.doi.org/10.5772/intechopen.89324*


*Drying and Quality of Microalgal Powders for Human Alimentation DOI: http://dx.doi.org/10.5772/intechopen.89324*

*Microalgae - From Physiology to Application*

**78**

**Algae species\***

*Spirulina* 

Perpendicular

Temperature: 50

•

Experimental design for protein

• • • •

Higher solubility results occurred at 60°C

Phycocyanin determination: 12.6% (w.b.)

Oil obtained from spirulina: important source of monounsaturated and

The best drying condition, 55°C and 3.7 mm, showed 37% phycocyanin loss

and 1.5 mgMDAkg−1 TBA value, and the fatty acid composition did not show

significance difference in relation to fresh biomass

Beta-carotene: 140.0 mg/100 g in dried sample at 60°C

Improve the drying rate: 2.5% with the foaming agent

The quality of spirulina dried (color, texture, and beta-carotene content) by foam

mat drying is higher than that of produced by industry

Significant loss of phycocyanin at drying temperatures above 70°C

Significant influence in TPC values at drying temperature of 80°C

Phycocyanin and total phenolic contents were largely dependent on the drying

temperature rather than on humidity

polyunsaturated fatty acids

Protein solubility in acid medium: 42.6–79.1%

Protein content: 74% (d.b.)

solubility response

and 60°C

Air velocity: 1.5 m/s

• •

Phycocyanin content

Centesimal composition

Relative humidity:

7–10%

airflow drying

*platensis LEB-52*

[30]

*Spirulina LEB-18* [38]

Discontinuous tray drying

Temperature: 50, 60, and 70°C

• •

Lipid oxidation (TBA)

Phycocyanin content

Sample thickness:

3, 5, and 7 mm

•

Fatty acid profiles

Hot-air velocity:

2.5 m.s−1

*Spirulina* sp.

Tray drying

Temperature: 50,

• Color

• Texture

•

Beta-carotene

60, and 70°C

Air velocity: 2.2 m.

s

Foaming agent:

glair/albumin

*Spirulina* 

Convective

Benchtop chamber

•

Phycocyanin content

Temperature: 30,

•

Total phenolic content (TPC)

50, 70, and 80°C

Relative humidity:

•

Antioxidant capacity—ABTS

13, 20, 50, and 60%

•

Phycocyanin denaturation kinetics

Air velocity:

2.0 m/s

drying at

atmospheric

pressure

*maxima* [31]

−1

[22]

**Dry method**

**Dry** 

**Quality assessment**

**Findings/conclusions**

**specifications/**

**variables**


 *Different drying methods applied in some microalgal species with an interest in evaluating quality characteristics.*

**81**

**Figure 1.**

*denominations used in articles.*

*Drying and Quality of Microalgal Powders for Human Alimentation*

Spray drying uses the atomization of a liquid food to create droplets which are dried as individual particles while moving through a heated gas (hot air) [20]. Drying of single droplet provides a large surface area per unit volume of liquid, which favors rapid drying [43] and also causes a very short exposition of food to a very high temperature causing moderate degradation of product quality (hightemperature exposition for short time). The main steps of the spray drying process are atomization of the liquid, mixing of the droplets with the heated air, and separation of the dried powder in a cyclone [44]. Size of the droplet, air temperature, and liquid flow are the main factors that influence the quality of the dried product. Other factors that should be taken into account for the optimization of quality of spray-dried products are related to the biomass characteristics such as glass transition temperature, surface tension, liquid density, viscosity, and composition. The presence of high content of sugars, for example, impacts negatively the yield of this process. This problem is especially present when fruit pulps are dried; on the other hand for microalgae that present mostly long-chain carbohydrates, it does not

*Drying methods of microalgal biomass. Filled shapes, general method denomination; empty shapes, method* 

Among the advantage of this technology, it can be cited the high versatility, the possibility of pack directly, the powder produced without any milling process, and the easiness of the processing control allowing quality of the product remain constant (uniform) during processing [44]. On the other hand, this technology has a high installation and energy/operation costs, volatile compounds can be lost, and products that present high sensibility to high temperature could lose quality. It can cause rupture of cells, due to the high pressure generated during the atomization process, causing, in some cases, degradation in product quality [6], that is, promoting oxidation. However, spray drying is the only drying technology used in largescale microalgal biomass drying for human consumption [6] mainly due to the equilibrium between high productivity and quality of the dried product. Although this drying method is the most used by the industry, few papers approach the effect of processing parameters, such as air temperature, viscosity of the moist biomass, and size of the biomass droplet on microalgal powder quality loss [32, 35, 40, 42].

*DOI: http://dx.doi.org/10.5772/intechopen.89324*

represent an important issue [43, 44].

#### *Drying and Quality of Microalgal Powders for Human Alimentation DOI: http://dx.doi.org/10.5772/intechopen.89324*

**Figure 1.**

*Microalgae - From Physiology to Application*

**80**

**Algae species\***

*Dunaliella salina*

Fluid-bed

Temperature: 70°C

• •

Stability of total carotenoid during

storage of the beads

Beta-carotene analysis

• •

Total carotenoid losses: 13–20% during fluid-bed drying

Spray dry microencapsulation can reduce degradation of carotenes

*D. salina* cells in alginate followed by fluid-bed drying have the potential in

producing a carotene-rich nutraceutical product with good carotenoid stability

Preservation of 80–92% of beta-carotene and 46–81% of phenolic compounds

in microencapsulated microalgae and dried in spray dryer

characteristics

•

Airflow: 3.5 m.s −1

Time: 10 min

drying with

alginate cells

*Tetraselmis chuii*

Spray drying

Temperature:

• •

Beta-carotene estimation

Carotenoid analysis

110/130/150°C

Pressure: 40 bar

and 2.5 mL/min

•

Antioxidant activity analysis

Microencapsulation

with maltodextrin

*\**

**Table 1.**

*Different drying methods applied in some microalgal species with an interest in evaluating quality characteristics.*

*Species name used in the paper.*

[42]

[34]

**Dry method**

**Dry** 

**Quality assessment**

**Findings/conclusions**

**specifications/**

**variables**

*Drying methods of microalgal biomass. Filled shapes, general method denomination; empty shapes, method denominations used in articles.*

Spray drying uses the atomization of a liquid food to create droplets which are dried as individual particles while moving through a heated gas (hot air) [20]. Drying of single droplet provides a large surface area per unit volume of liquid, which favors rapid drying [43] and also causes a very short exposition of food to a very high temperature causing moderate degradation of product quality (hightemperature exposition for short time). The main steps of the spray drying process are atomization of the liquid, mixing of the droplets with the heated air, and separation of the dried powder in a cyclone [44]. Size of the droplet, air temperature, and liquid flow are the main factors that influence the quality of the dried product. Other factors that should be taken into account for the optimization of quality of spray-dried products are related to the biomass characteristics such as glass transition temperature, surface tension, liquid density, viscosity, and composition. The presence of high content of sugars, for example, impacts negatively the yield of this process. This problem is especially present when fruit pulps are dried; on the other hand for microalgae that present mostly long-chain carbohydrates, it does not represent an important issue [43, 44].

Among the advantage of this technology, it can be cited the high versatility, the possibility of pack directly, the powder produced without any milling process, and the easiness of the processing control allowing quality of the product remain constant (uniform) during processing [44]. On the other hand, this technology has a high installation and energy/operation costs, volatile compounds can be lost, and products that present high sensibility to high temperature could lose quality. It can cause rupture of cells, due to the high pressure generated during the atomization process, causing, in some cases, degradation in product quality [6], that is, promoting oxidation. However, spray drying is the only drying technology used in largescale microalgal biomass drying for human consumption [6] mainly due to the equilibrium between high productivity and quality of the dried product. Although this drying method is the most used by the industry, few papers approach the effect of processing parameters, such as air temperature, viscosity of the moist biomass, and size of the biomass droplet on microalgal powder quality loss [32, 35, 40, 42].

Spray drying of *D. salina* biomass allowed production of powder with very low degradation of β-carotene and its isomers. On the other hand, during 5 days of storage, it degraded to less than 10% of retention. Damages to the membrane cell caused by the very fast water vaporization facilitate the oxidation and degradation of this functional compound, due to oxygen and light exposition [32]. To avoid this problem, a possible strategy is mixing the microalgal biomass with some encapsulating agent (e.g., maltodextrin, gum arabic, etc.) producing microcapsules by spray drying; in this case the high retention of functional compounds can be maintained during storage [42].

#### **3.2 Drum drying**

Another technology widely diffused in the food industry to produce dried product, from viscous foodstuff, is the drum drying. Drum drying consists in cylindrical metallic heated rollers or drums rotating at a variable speed. The material to be dried comes into contact with the surface of the drum in a thin layer of film, and heat is transferred through the metal. A slide is arranged in the apparatus to remove the dry thin film layer from the drum surface [8]; after that, the dried material is commonly milled to produce a uniform powder. This technology presents low operation costs and can be easily managed by small producers. On the other hand, it presents some limitation such as the processing time/temperature binomial which the sample must be submitted to be dried [8]. Although this method is widely used in microalgae biomass drying, the high temperature of the drum causes degradation of quality of the dried product; for this reason, this method is used to produce raw materials for biofuel industry but presents no particular interest for dried biomass for human alimentation. Alternatives have been developed to overcome the problem of high degradation of nutritional and functional components and allow the use of this technology to produce algal powders for human use. One example that can be cited is the use of an inert bed to increase the surface contact between a hot-air flow inside of the drum and the moist spirulina biomass, increasing the drying rate and the processing yield; this system also allows to overcome problems such as the bed agglomeration [25]; on the other hand, no assessment on biomass quality was done with this method, and further studies should be done to improve quality of products dried by this method.

#### **3.3 Freeze-drying**

Freeze-drying is a well-known drying process that allows production of dried food with high added value and high quality. Freeze-drying consists in two main steps; firstly the product is frozen and is transferred in a vacuum chamber, and water is sublimated [45] providing heat (latent heat of sublimation) by radiation or conduction (hot plates). Freeze-drying is particularly indicated to dry products with high sensibility to high temperature and oxygen exposition and with high added value. On the other hand, it presents high installation and operational cost, especially for industrial-scale equipment and requires long drying time (commonly up to 12 h). This method is highly recommended when the conservation of the nutritional and functional components of the raw material is desired. On the other hand, stability of freeze-dried foods could be compromised by their very high porosity that facilitates the contact with oxygen and air humidity promoting oxidation during storage [46]. In general, freeze-drying of microalgal biomass is considered an ideal method because it causes no degradation of biomass quality [21]. On the other hand, the very low water activity reached in freeze-dried powder could promote, combined with the high porosity, the oxidation of lipids and pigments;

**83**

*Drying and Quality of Microalgal Powders for Human Alimentation*

be used, that is, vacuum, light barrier, and low temperature.

Solar drying is a traditional drying method used for hundreds of years to stabilize the moist algal biomass. In this method the heat for water evaporation is provided by the solar radiation and the moisture removal by the natural airflow. Although it presents the obvious advantage of the low processing cost both in direct solar radiation method or in solar dryers, the efficiency of the method is directly dependent on weather condition and only applicable in few producing locations. Moreover, the long processing time and the exposition to the open environment increase the risk of spoilage or production of off-odors [6]. Strategies and dryers have been developed to overcome these problems optimizing the efficiency of the drying equipment and allowing drying of microalgal biomass

Convective drying of a thin layer of spread biomass or extruded biomass cylinder is a method widely used especially by small-scale producers. Ref. [41] produced an *Aphanothece microscopica* Nägeli powder by spreading, in a convective oven, layers of biomass with thickness of 5 and 7 mm and testing the effect of drying temperature (40–60°C) on protein, carbohydrates, lipid content, and fatty acid profile, finding only small differences among treatments. On the other hand, the same research group found that in the same drying condition, chlorophyll a content and hue angle (related with sample color) were strongly influenced by the process temperature and chlorophyll concentration decreases intensely at temperature up to 40°C of drying [49], demonstrating the importance of the optimization of the drying temperature for producing high-quality dried microalgal powder. The effect of temperature on stability of functional components was also proven with spirulina. Many papers approach this issue [33, 30, among others] showing the importance of temperature and thickness optimization during convective drying (air-drying) to maximize the conservation of phycocyanin. This fact was confirmed by [50] that assessed the effect of drying temperature on spirulina functional components showing that

temperatures above 45°C cause degradation, reducing its health benefits.

**3.4 Solar drying**

with acceptable quality retention [48].

**3.5 Convective drying and thin layer drying**

thus, vacuum packaging should be considered in freeze-dried powder storage. The effect of drying method on stability of functional components of microalgae was assessed by [7]. Different drying conditions and storage methods were studied assessing their effect on the astaxanthin concentration in *Haematococcus pluvialis*dehydrated powder. As expected, freeze-drying resulted in products with higher (approximately 30%) astaxanthin retention than spray-dried biomass. On the other hand, both powders present similar pattern of degradation during storage under different temperatures (from −20 to 37°C) and packaging (vacuum and air). A higher degradation of functional component was found in samples stored at 20 and 37°C in normal packaging (without vacuum); the highest astaxanthin degradation for freeze-dried powder was >80% at 37°C and > 60% at 20°C, both after 20 weeks of storage. Vacuum packaging efficiency was confirmed avoiding degradation of functional components of microalgae also when storage was performed at room temperature [7, 47]. However, due to the higher initial retention of function components, freeze-drying was considered a good option for high-quality dried biomass production. Stability of dehydrated product during storage plays a key role for the drying method chosen. For freeze-dried products, to maintain the high quality of the product obtained by this expensive method, specifically storage strategies must

*DOI: http://dx.doi.org/10.5772/intechopen.89324*

*Drying and Quality of Microalgal Powders for Human Alimentation DOI: http://dx.doi.org/10.5772/intechopen.89324*

thus, vacuum packaging should be considered in freeze-dried powder storage. The effect of drying method on stability of functional components of microalgae was assessed by [7]. Different drying conditions and storage methods were studied assessing their effect on the astaxanthin concentration in *Haematococcus pluvialis*dehydrated powder. As expected, freeze-drying resulted in products with higher (approximately 30%) astaxanthin retention than spray-dried biomass. On the other hand, both powders present similar pattern of degradation during storage under different temperatures (from −20 to 37°C) and packaging (vacuum and air). A higher degradation of functional component was found in samples stored at 20 and 37°C in normal packaging (without vacuum); the highest astaxanthin degradation for freeze-dried powder was >80% at 37°C and > 60% at 20°C, both after 20 weeks of storage. Vacuum packaging efficiency was confirmed avoiding degradation of functional components of microalgae also when storage was performed at room temperature [7, 47]. However, due to the higher initial retention of function components, freeze-drying was considered a good option for high-quality dried biomass production. Stability of dehydrated product during storage plays a key role for the drying method chosen. For freeze-dried products, to maintain the high quality of the product obtained by this expensive method, specifically storage strategies must be used, that is, vacuum, light barrier, and low temperature.

#### **3.4 Solar drying**

*Microalgae - From Physiology to Application*

maintained during storage [42].

products dried by this method.

**3.3 Freeze-drying**

**3.2 Drum drying**

Spray drying of *D. salina* biomass allowed production of powder with very low degradation of β-carotene and its isomers. On the other hand, during 5 days of storage, it degraded to less than 10% of retention. Damages to the membrane cell caused by the very fast water vaporization facilitate the oxidation and degradation of this functional compound, due to oxygen and light exposition [32]. To avoid this problem, a possible strategy is mixing the microalgal biomass with some encapsulating agent (e.g., maltodextrin, gum arabic, etc.) producing microcapsules by spray drying; in this case the high retention of functional compounds can be

Another technology widely diffused in the food industry to produce dried product, from viscous foodstuff, is the drum drying. Drum drying consists in cylindrical metallic heated rollers or drums rotating at a variable speed. The material to be dried comes into contact with the surface of the drum in a thin layer of film, and heat is transferred through the metal. A slide is arranged in the apparatus to remove the dry thin film layer from the drum surface [8]; after that, the dried material is commonly milled to produce a uniform powder. This technology presents low operation costs and can be easily managed by small producers. On the other hand, it presents some limitation such as the processing time/temperature binomial which the sample must be submitted to be dried [8]. Although this method is widely used in microalgae biomass drying, the high temperature of the drum causes degradation of quality of the dried product; for this reason, this method is used to produce raw materials for biofuel industry but presents no particular interest for dried biomass for human alimentation. Alternatives have been developed to overcome the problem of high degradation of nutritional and functional components and allow the use of this technology to produce algal powders for human use. One example that can be cited is the use of an inert bed to increase the surface contact between a hot-air flow inside of the drum and the moist spirulina biomass, increasing the drying rate and the processing yield; this system also allows to overcome problems such as the bed agglomeration [25]; on the other hand, no assessment on biomass quality was done with this method, and further studies should be done to improve quality of

Freeze-drying is a well-known drying process that allows production of dried food with high added value and high quality. Freeze-drying consists in two main steps; firstly the product is frozen and is transferred in a vacuum chamber, and water is sublimated [45] providing heat (latent heat of sublimation) by radiation or conduction (hot plates). Freeze-drying is particularly indicated to dry products with high sensibility to high temperature and oxygen exposition and with high added value. On the other hand, it presents high installation and operational cost, especially for industrial-scale equipment and requires long drying time (commonly up to 12 h). This method is highly recommended when the conservation of the nutritional and functional components of the raw material is desired. On the other hand, stability of freeze-dried foods could be compromised by their very high porosity that facilitates the contact with oxygen and air humidity promoting oxidation during storage [46]. In general, freeze-drying of microalgal biomass is considered an ideal method because it causes no degradation of biomass quality [21]. On the other hand, the very low water activity reached in freeze-dried powder could promote, combined with the high porosity, the oxidation of lipids and pigments;

**82**

Solar drying is a traditional drying method used for hundreds of years to stabilize the moist algal biomass. In this method the heat for water evaporation is provided by the solar radiation and the moisture removal by the natural airflow. Although it presents the obvious advantage of the low processing cost both in direct solar radiation method or in solar dryers, the efficiency of the method is directly dependent on weather condition and only applicable in few producing locations. Moreover, the long processing time and the exposition to the open environment increase the risk of spoilage or production of off-odors [6]. Strategies and dryers have been developed to overcome these problems optimizing the efficiency of the drying equipment and allowing drying of microalgal biomass with acceptable quality retention [48].

#### **3.5 Convective drying and thin layer drying**

Convective drying of a thin layer of spread biomass or extruded biomass cylinder is a method widely used especially by small-scale producers. Ref. [41] produced an *Aphanothece microscopica* Nägeli powder by spreading, in a convective oven, layers of biomass with thickness of 5 and 7 mm and testing the effect of drying temperature (40–60°C) on protein, carbohydrates, lipid content, and fatty acid profile, finding only small differences among treatments. On the other hand, the same research group found that in the same drying condition, chlorophyll a content and hue angle (related with sample color) were strongly influenced by the process temperature and chlorophyll concentration decreases intensely at temperature up to 40°C of drying [49], demonstrating the importance of the optimization of the drying temperature for producing high-quality dried microalgal powder. The effect of temperature on stability of functional components was also proven with spirulina. Many papers approach this issue [33, 30, among others] showing the importance of temperature and thickness optimization during convective drying (air-drying) to maximize the conservation of phycocyanin. This fact was confirmed by [50] that assessed the effect of drying temperature on spirulina functional components showing that temperatures above 45°C cause degradation, reducing its health benefits.

Other technology that can be used to dehydrate viscous foodstuff is the refractance window drying [51] or the cast-tape drying [52–55]. In both methods the liquid food is spread on surface, and the heat transfer occurs by radiation or by conduction. These methods allow producing high-quality fruit pulp powder with very low processing time. On the other hand, the temperature used in these processes could be above the limit for functional component preservation in microalgal biomass; thus, a vacuum chamber can be coupled to the cast-tape drier, and lower processing temperature can be used [56]. The vacuum drying removes the sample moisture thru low atmospheric pressure, showing many advantages comparing the conventional drying methods, that is, oxidation reducing. The low pressure in the drying chamber substitutes the hot-air flow, avoiding significantly compound degradations that lead to low product quality [57, 58]. This technology has been studied recently to spirulina biomass with interesting results in terms of quality and processing time [59, 60]. The cast-tape drying method used in preliminary studies for spirulina biomass drying has proved to be a very effective method in terms of drying time and efficiency. Using the same principle (thin layer of sample on a heated surface), vacuum cast-tape drying allows drying at lower temperatures, thus avoiding the degradation of important compounds such as phycocyanin. Preliminary studies conducted by our group showed phycocyanin preservation values greater than 60% in the method using vacuum and milder temperatures. The authors showed and reported that this technology is a promising method, which can achieve excellent moisture and water activity values, better performance, and low energy costs compared to conventional and/or expensive drying processes.
