Drying and Quality of Microalgal Powders for Human Alimentation

*Fábio de Farias Neves, Mariana Demarco and Giustino Tribuzi*

## **Abstract**

The demand for natural foods with high protein content and functional properties is constantly growing in the last years. In this context, microalgae as *Spirulina* (*Arthrospira* spp.), *Chlorella* spp., *Haematococcus pluvialis*, *Dunaliella salina*, and others, assume a key role to diversify the offer of nutritious and functional ingredients and supplements. Microalgae are commercialized, mostly, as dried powders to facilitate their use as food ingredients and to allow easy transportation and long-term stability. Microalgal powder quality and storage stability depend mainly on drying method, packaging, and storage conditions. Most of the studies that approach the subject of microalgal drying evaluate the efficiency of the process and suitability for this raw material. However, studies that assess the effect of traditional and innovative drying methods on quality of microalgal powder for human consumption are rare in literature. In this chapter, the state of the art of drying processing technology for microalgae was reviewed, discussing the effect of dehydration on quality and stability of microalgal powders with potential use in human alimentation.

**Keywords:** microalgae, dry biomass, biomass quality, microalgal powder, functional supplements

### **1. Introduction**

Microalgae are photosynthetic microscopic organisms that convert CO2 and water in biomass and O2. This group of organisms is very diverse and abundant around the globe. They occur most in freshwater and saltwater aquatic ecosystems but also at other environments [1]. The main groups are Cyanophyta, Chlorophyta, Ochrophyta, Dinophyta, Rhodophyta, Euglenophyta, Haptophyta, and Prymnesiophyta [2]. It is estimated that there are around 300,000 of microalgal species around the world [1].

Microalgae have a great ecological importance as they are primary producers contributing to a lot of food chains; they produce around 40–60% of the oxygen available on Earth atmosphere, convert inorganic nutrients in organic matter, and for millions of years have produced the oil that today economy is still dependent [1].

Also, microalgae have been used in different industries for decades. These microscopic organisms are produced in ponds or photobioreactors to be used directly as live feeds for aquaculture hatcheries or to be used in food industry as food supplements or source of nutrients and vitamins, in agriculture as biofertilizer, in pharmaceutical and cosmetic industry as raw material to extract specific molecules, and in other different biotechnology applications [3]. Also, microalgae have been used for environmental purposes as in tertiary wastewater treatment, as system for carbon fixation, and as raw materials to produce biofuels [4].

Despite all economic potential applications of microalgae and the great diversity of species, the microalgal industry is based mainly in few applications and species. The majority of microalgal biomass production is destined for food industry as food supplement. The main species belongs to the genus *Spirulina* also known as *Arthrospira*, *Chlorella*, *Haematococcus*, *Dunaliella*, and few others [5].

*Spirulina* (*Arthrospira*) is a cyanobacteria and the same as the green algae *Chlorella* (chlorophyte); both usually are sold as dry biomass. Meanwhile, the microalgae *Haematococcus pluvialis* and *Dunaliella salina* are usually used as source of the carotenoids astaxanthin and beta-carotene, respectively. However, some companies also sell the entire biomass and, even when extracting the pigments, need to dry the biomass previously [5].

To dry the microalgal biomass is the way microalgae are most commercialized because this method increases the product stability and durability, also allowing easy storage and transportation.

There are different dryers being used in microalgal industry. The main dryer used is the spray dryer [6], and in small spirulina farms, the utilization of ovens with forced ventilation is very common. However, freeze-dryer, drum dryer, natural sun dryer, and other processes to dry the biomass can be also used [6–8].

It is well known that, depending on the drying process method and conditions, there is a potential to lose quality of the microalgal biomass. For example, the microalgal properties change with the dry process, and for the food industry, the nutritional quality can decrease as proteins, lipids, pigments, and other nutrients are lost. In particular, functional components (i.e., phycocyanin from spirulina or astaxanthin from *H. pluvialis*) are very sensible to drying conditions, that is, time, temperature, and oxygen, among others.

Therefore, the purpose of this chapter is to provide a review of the common and innovative dry process technologies available for microalgal biomass, discuss the effect of dehydration on quality and stability of microalgal powders used in human alimentation, and then support the microalgal industry and researchers to choose the most suitable drying method for each different use of dried microalgae.

#### **2. Preprocess in algae drying**

Microalgae have been studied largely because they have an industrial importance with their bioproducts, such as lipids, carotenoids, etc. Also, their lipid content is considered a potential feedstock for biodiesel production [9, 10]. Some adversities found in preprocessing are the presence of rigid cell walls surrounding the algae cells and the biomass moisture that interferes in some extraction solvent performance [11]. It can be solved with chemical, mechanical, and biological means of cell wall disruption and can be used alone or in combined forms [9]. Also, in these cases, the step of dewatering is important, that is, with flocculation and centrifuge [12]. The proportions of microalgal biomass in cultivation are generally relatively low, being around 0.02–0.05% of dry biomass in raceway tanks and between 0.1 and 0.5% of dry biomass in tubular photobioreactors. This aspect, together with the size of microalgae, turns microalgal biomass separation very complex [13]. Ref. [14] presents that separation costs can be around 20 and 30% of the total production cost.

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*Drying and Quality of Microalgal Powders for Human Alimentation*

There are different ways to perform biomass separation. The most common processes are flocculation followed by sedimentation, centrifugation, and filtration. Sedimentation, considered the simplest option, can retain 85% of biomass, with the percentage of dry biomass around 3%, depending on the species used. However, this process requires significant additional space. The most efficient method for separating biomass is centrifugation, but it represents a significant increase in production costs, so it is widely used when the extracted product has high value. Filtration can be performed mainly to separate biomass from filamentous microalgae, but it is a slow process and in large-scale systems requires a large infrastructure [13].

Cell disruption is an alternative to cellular disintegration of many microorganisms, like bacteria, yeasts, and microalgae, and can be classified as mechanical and nonmechanical manner [15, 16]. Among the mechanical methods, there are high-pressure homogenization, ultrasonication, bead milling, autoclaving, lyophilization, and microwaving, being the first and second ones the widely used methods for laboratory-scale microalgal cell disruption. The nonmechanical methods involve

Some mechanisms involved to the cellular disruption are achieved: impingement of the cells on the hard surface of the valve seat and their impact on each other during collision, turbulence, viscous and high-pressure shear, pressure-drop-induced shear passing from the valve to the chamber, and sudden pressure drop caused by

Concerning low-energy input, chemical treatments have advantages, in addition to showing good scalability. However, they should be carefully selected and applied

Physicochemical extraction process can cause thermal and/or chemical stresses inducing structural changes and denaturation/degradations of compounds, like astaxanthin isomers, and affecting significantly the product qualities, such as antioxidative activity, bioavailability, and purity [9]. To guarantee the extraction efficiency of astaxanthin, some operating conditions should be properly considered, like temperature and the use and minimization of less toxic chemicals [19].

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

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

lysing the cell wall with acids, alkalis, enzymes, or osmotic shocks [15, 17].

considering their bio-toxicity and reactivity to some compounds [9].

rapid release of gas bubbles within the cells [10, 15, 18].

**3. Drying and microalgal quality**

the biomass must be also considered [22, 23].

have long shelf life.

*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*

need to dry the biomass previously [5].

temperature, and oxygen, among others.

**2. Preprocess in algae drying**

the total production cost.

easy storage and transportation.

in pharmaceutical and cosmetic industry as raw material to extract specific molecules, and in other different biotechnology applications [3]. Also, microalgae have been used for environmental purposes as in tertiary wastewater treatment, as

*Spirulina* (*Arthrospira*) is a cyanobacteria and the same as the green algae *Chlorella* (chlorophyte); both usually are sold as dry biomass. Meanwhile, the microalgae *Haematococcus pluvialis* and *Dunaliella salina* are usually used as source of the carotenoids astaxanthin and beta-carotene, respectively. However, some companies also sell the entire biomass and, even when extracting the pigments,

To dry the microalgal biomass is the way microalgae are most commercialized because this method increases the product stability and durability, also allowing

There are different dryers being used in microalgal industry. The main dryer used is the spray dryer [6], and in small spirulina farms, the utilization of ovens with forced ventilation is very common. However, freeze-dryer, drum dryer, natural sun dryer, and other processes to dry the biomass can be also used [6–8].

It is well known that, depending on the drying process method and conditions,

Therefore, the purpose of this chapter is to provide a review of the common and innovative dry process technologies available for microalgal biomass, discuss the effect of dehydration on quality and stability of microalgal powders used in human alimentation, and then support the microalgal industry and researchers to choose the most suitable drying method for each different use of dried

Microalgae have been studied largely because they have an industrial importance with their bioproducts, such as lipids, carotenoids, etc. Also, their lipid content is considered a potential feedstock for biodiesel production [9, 10]. Some adversities found in preprocessing are the presence of rigid cell walls surrounding the algae cells and the biomass moisture that interferes in some extraction solvent performance [11]. It can be solved with chemical, mechanical, and biological means of cell wall disruption and can be used alone or in combined forms [9]. Also, in these cases, the step of dewatering is important, that is, with flocculation and centrifuge [12]. The proportions of microalgal biomass in cultivation are generally relatively low, being around 0.02–0.05% of dry biomass in raceway tanks and between 0.1 and 0.5% of dry biomass in tubular photobioreactors. This aspect, together with the size of microalgae, turns microalgal biomass separation very complex [13]. Ref. [14] presents that separation costs can be around 20 and 30% of

there is a potential to lose quality of the microalgal biomass. For example, the microalgal properties change with the dry process, and for the food industry, the nutritional quality can decrease as proteins, lipids, pigments, and other nutrients are lost. In particular, functional components (i.e., phycocyanin from spirulina or astaxanthin from *H. pluvialis*) are very sensible to drying conditions, that is, time,

Despite all economic potential applications of microalgae and the great diversity of species, the microalgal industry is based mainly in few applications and species. The majority of microalgal biomass production is destined for food industry as food supplement. The main species belongs to the genus *Spirulina* also known as

system for carbon fixation, and as raw materials to produce biofuels [4].

*Arthrospira*, *Chlorella*, *Haematococcus*, *Dunaliella*, and few others [5].

**72**

microalgae.

There are different ways to perform biomass separation. The most common processes are flocculation followed by sedimentation, centrifugation, and filtration. Sedimentation, considered the simplest option, can retain 85% of biomass, with the percentage of dry biomass around 3%, depending on the species used. However, this process requires significant additional space. The most efficient method for separating biomass is centrifugation, but it represents a significant increase in production costs, so it is widely used when the extracted product has high value. Filtration can be performed mainly to separate biomass from filamentous microalgae, but it is a slow process and in large-scale systems requires a large infrastructure [13].

Cell disruption is an alternative to cellular disintegration of many microorganisms, like bacteria, yeasts, and microalgae, and can be classified as mechanical and nonmechanical manner [15, 16]. Among the mechanical methods, there are high-pressure homogenization, ultrasonication, bead milling, autoclaving, lyophilization, and microwaving, being the first and second ones the widely used methods for laboratory-scale microalgal cell disruption. The nonmechanical methods involve lysing the cell wall with acids, alkalis, enzymes, or osmotic shocks [15, 17].

Some mechanisms involved to the cellular disruption are achieved: impingement of the cells on the hard surface of the valve seat and their impact on each other during collision, turbulence, viscous and high-pressure shear, pressure-drop-induced shear passing from the valve to the chamber, and sudden pressure drop caused by rapid release of gas bubbles within the cells [10, 15, 18].

Concerning low-energy input, chemical treatments have advantages, in addition to showing good scalability. However, they should be carefully selected and applied considering their bio-toxicity and reactivity to some compounds [9].

Physicochemical extraction process can cause thermal and/or chemical stresses inducing structural changes and denaturation/degradations of compounds, like astaxanthin isomers, and affecting significantly the product qualities, such as antioxidative activity, bioavailability, and purity [9]. To guarantee the extraction efficiency of astaxanthin, some operating conditions should be properly considered, like temperature and the use and minimization of less toxic chemicals [19].
