Incorporation of Cyanobacteria and Microalgae in Yogurt: Formulation Challenges and Nutritional, Rheological, Sensory, and Functional Implications

Abstract

This review presents an approach to the incorporation of cyanobacteria and microalgae in yogurts and explores their impact on the nutritional, rheological, sensory, and antioxidant qualities of these products. First, the yogurt market context and its relationship with nutritional quality are outlined, emphasizing the quest for functional foods that meet consumer demands for healthy and nutritious products. A discussion of the incorporation of cyanobacteria and microalgae, especially Spirulina platensis, in foods, particularly yogurt, is then presented, highlighting the nutritional and functional benefits that this type of biomass can provide to the final product. The fermentation process and the quantity of algae to be incorporated are discussed to understand their fundamental role in the characteristics of the final product. In addition, this article considers some challenges such as sensory and rheological changes in the product resulting from the interaction of milk, algal biomass, and the fermentation process. Addressing these challenges involves delineating how these interactions contribute to changes in the traditionally consumed product, while obtaining a pro- and prebiotic product is crucial for creating an innovative dairy product that diversifies the market for derived dairy products with increased functional properties.

1. Introduction

Growing awareness of the relationship between diet and health has led to significant changes in the food market, driving the search for products that meet consumers’ nutritional needs [1]. In a context where health and well-being have become priorities, the food sector is faced with a demand for alternatives that promote a balance between gastronomic pleasure and nutritional intake. Yogurt, a food that has been around for thousands of years, is emerging as a prominent choice that transcends cultures and geographies, offering versatility and nutritional value [1,2,3].

In today’s food industry, there is a noticeable shift in consumer behavior that reflects a growing awareness of the importance of healthy eating. Individuals are increasingly inclined to choose products that maintain their health and vitality [2]. This movement is the result of several factors, including the spread of nutritional knowledge and the search for information on the benefits of foods and practices that improve health and promote longevity. The demand for functional foods that provide specific health benefits is emerging as a prominent trend [4,5].

The yogurt market, an important element within the food industry, is proving to be a promising and ever-expanding area. As an accessible and convenient product, yogurt is an essential item on supermarket shelves and in daily diets [6]. However, despite the significant growth experienced by the industry, there are still notable gaps between per capita consumption in different regions of the world and international recommendations, which highlights significant room for expansion in this market [7].

At the heart of yogurt’s rise in today’s market is its remarkable nutritional quality. In addition to containing significant amounts of high-quality protein, yogurt serves as an important source of minerals such as calcium and B-complex vitamins, which play a critical role in bone health, neuromuscular function, and metabolism. Furthermore, yogurt has proven to be an adaptable platform for fortification with bioactive components such as fiber and antioxidants, further confirming its ability to be shaped to meet the specific needs of heterogeneous consumer groups [8,9].

Regarding functionality, one of yogurt’s key differentiators is the strategic inclusion of probiotics—live microorganisms that provide health benefits to the gastrointestinal tract and immune system [10]. The growing scientific recognition of the beneficial effects of probiotics has fueled the search for foods that provide these microorganisms, establishing yogurt as an attractive alternative for consumers seeking a healthier lifestyle [11].

However, the growing demand for healthy and functional foods also presents challenges and questions for the yogurt industry. The variation in nutritional quality between brands and formulations is a concern since not all products on the market have the same beneficial profile. The presence of additives, such as added sugars and artificial flavors, contradicts the healthy goals that many consumers are seeking. Addressing these issues requires a collaborative effort between the industry, regulators, and healthcare professionals to establish strict guidelines, inform consumers, and align market expectations [12,13].

Other additives can be added to yogurt, such as plant and microbial sources of high-biological-value proteins, essential fatty acids, vitamins, and antioxidants, giving it a functional character and reaching people who seek to create more sustainable eating habits. This trend has been growing in the scientific community and among the public, who seek meat substitutes and protein supplements of animal origin, driven by the three pillars of ethics, sustainability, and health. In the scientific community, promoting the use of these alternative sources is considered one of the main ways to promote sustainable food systems and prevent chronic non-communicable diseases [14].

Plant or microbial-based foods have many biological properties and can be considered powerful functional foods that improve health. In these sources, proteins are very interesting and exist in different parts of their structure, and some of their active properties are attributed to peptides and active proteins, which can be easily obtained after a fermentation process, as is the case of yogurt from lactic acid bacteria on these sources. In addition, the proteins found have antioxidant properties in the product, adding value. In the food sector, the demand for natural antioxidants is increasing, at the same time as the value of healthy and low-cost foods increases [15,16]. The addition of these protein sources to the human diet to reduce dependence on animal protein has been used to improve nutrition; however, it is important to observe the composition of the chosen source [17,18].

In this sense, biomass from cyanobacteria (prokaryotic) such as Spirulina platensis and microalgae (eukaryotic) like Chlorella vulgaris, mainly used for human nutrition, can be incorporated into foods used in the normal human diet to improve the nutritional quality of traditionally consumed foods at a low cost and with little interference in the nutritional aspects of the food structure currently available on the market. The cyanobacterium Spirulina has been studied for its high content of proteins (50–70% of its weight), essential amino acids, vitamins (especially B12), mineral salts and pigments (carotenoids, phycocyanin, and chlorophyll), polyunsaturated fatty acids, including omega-3 fatty acids, and other active organic compounds [19].

Therefore, this study aims to investigate an innovative approach to yogurt fortification: the incorporation of cyanobacteria and microalgae. Microalgae/cyanobacteria, microscopic photosynthetic organisms, have received increasing attention due to their unique nutritional composition and potential to be used as functional ingredients in foods. Out of several species, the cyanobacterium Arthrospira (Spirulina) platensis and the microalga Chlorella vulgaris stand out for their richness in nutrients and bioactive compounds as well as their well-established large-scale exploitation. This study explores the motivations driving the incorporation of cyanobacteria/microalgae in foods, details their advantages and disadvantages, and investigates the effects of their addition on the formulation and properties of yogurt (physicochemical, rheological, sensory, and antioxidant aspects).

2. The Yogurt Market and the Nutritional Quality of Yogurt

The dairy market, especially the yogurt segment, has experienced exponential growth, driven by a paradigm shift in the lifestyle and preferences of today’s consumers [20]. The relentless pursuit of a healthy and balanced diet has led to a significant evolution in the food sector, with yogurt emerging as one of the protagonists in this context [21].

The nutritional quality of yogurt is a fundamental factor that distinguishes this food in the market [22]. As a product of convenience and gastronomic pleasure, yogurt offers a distinctive nutritional profile, considered a remarkable source of essential nutrients [23]. Substantial amounts of high-quality proteins, vitamins, and minerals such as calcium and potassium enhance the nutritional value of yogurt, giving it a prominent status among dairy products [22] (

Table 1. Comparison of the nutritional composition of the main types of yogurt.

Nutritional Components	Natural Yogurt	Yogurt with Fruit	Fortified Yogurt
Protein (g/100 g)	4.5	3.0	5.2
Carbohydrates (g/100 g)	5.0	15.0	10.5
Fat (g/100 g)	3.0	0.5	3.8
Calcium (mg/100 g)	110	120	150
Vitamin C (mg/100 g)	0.1	15	5

Source: Adapted from Amélia and Rocha [20].

).

Besides its intrinsic nutritional composition, yogurt is known for its versatility and adaptability, which makes it an option for different age groups and dietary needs [24]. From growing children to seniors seeking to maintain bone health, yogurt offers benefits that transcend age groups and individual preferences [25]. Its presence in the diets of athletes and physical activity enthusiasts is also noteworthy, given its protein content and ability to aid in post-exercise recovery [26].

The nutritional value of yogurt extends beyond its macronutrient composition. Bioactive compounds such as polyphenols, carotenoids, and other antioxidants also add value to yogurt because they can contribute to the prevention of non-communicable chronic diseases, including cardiovascular and degenerative diseases [20]. These bioactive compounds, often present in the raw materials used in yogurt production, are preserved during processing and may, therefore, provide health benefits to consumers [23].

Currently, the yogurt market is in a context of transformation and evolution, reflecting changes in consumer preferences and demands for foods that combine taste, convenience, and nutritional benefits [25]. In addition to its nutritional quality, yogurt has also been influenced by the growing search for products that promote innovation and differentiation in the food industry [20]. However, with ever-changing consumer demands and emerging dietary trends, the yogurt industry faces challenges and opportunities in its quest to offer products that achieve the desired balance between taste enjoyment and health benefits [23].

According to the Food and Agriculture Organization of the United Nations [27], the world’s milk production is about 718 billion liters. Brazil accounts for about USD 35.5 billion, or about 5% of the total. Among the major exporters, the European Union and New Zealand have historically been important producers. Another major country, the United States, which was not a major producer in the past, has risen to the top and is now a leading exporter [27].

In the global market, according to a new Innova Market Insights report, the dairy and non-dairy yogurts market will surpass USD 200 billion this year (INNOVA, 2024). On average, 57% of consumers worldwide regularly buy yogurt, although individual country rates range from 32% in Indonesia to 78% in Spain. Furthermore, 29% of consumers increased their yogurt consumption in 2024, primarily for health reasons, while 60% said their consumption levels remained stable and only 11% said they decreased (INNOVA, 2024). Asia is the largest market, with 43% of yogurt sales by value, and is also seeing the greatest growth. The region is home to the main country in terms of value, with China as the clear leader, with an increase of 4.62% from 2023 to 2024. With the same trend, Kenya saw an increase of 0.47%, followed by Thailand with an increase of 0.44% and finally Mexico with an increase of 0.41% between 2023 and 2024. Finally, Brazil saw an increase of 0.45% in the same period (INNOVA, 2024).

In Brazil, from October 2019 to September 2020, yogurt sales in the country totaled 592 thousand tons or 584.5 thousand tons of yogurt. From October 2020 to September 2021, yogurt sales reached 592 thousand tons, a volume 1.3% higher than the previous 12 months. From September 2021 to September 2022, there was an increase in production of almost 4%, reaching 609.4 thousand tons. In the analysis for 2023, in the first semester alone, 367.4 thousand tons were already produced and sold [28].

Brazil is increasingly becoming a model for the world in terms of food production. Some of these economic activities contribute significantly to the country’s gross domestic product (GDP) growth (e.g., beef, soy, rice, barley, dairy production, etc.) [25].

For example, in the dairy industry, Brazil stands out as one of the world’s largest milk producers and has been noted as one of the fastest-growing segments of Brazilian agribusiness in recent years. The dairy market is categorized by product type, including milk, cheese, butter, milk products, and yogurt. Other dairy products include heavy cream, cream cheese (requeijão), and fresh cheese. In cumulative data through 2023, the price of raw milk is projected to increase by 11.8%, with the average Brazilian net price reaching BRL 2.89 per liter in April, an increase of 9.3% compared to the same period last year [29].

The Brazilian dairy market is striving to carve out a place among the major exporters in the global market, not only to meet local demand but also to seek higher returns in some of the world’s largest markets [20]. In Brazilian legislation, Regulation No. 46, of October 2007, draws up the regulations that refer to fermented milk intended for interstate or international trade, establishing the identity and minimum quality requirements that must be met by fermented milk intended for human consumption. The regulations state that fermented milk must contain an acidity between 0.6 and 1.5%, have a quantity of dairy bacteria of at least 10⁷ CFU/g (CFU—Colony Forming Unit) [30], and agree with the International Regulation based on the Codex Alimentarius Standard for fermented milk (CXS 243-2003), which establishes a minimum protein content of 2.5%, a fat content less than 15%, a minimum of acidity of 0.6%, and a sum of microorganisms constituting the starter culture (lactic acid bacteria—LAB) of 10⁷ CFU/g [31].

3. Incorporating Cyanobacteria and Microalgae into Foods

The diversity and nutritional potential of cyanobacteria and microalgae have attracted the attention of researchers and the food industry, prompting a series of investigations aimed at exploring their applications and benefits [3,26]. These small, unicellular life forms have been recognized for their richness in bioactive compounds, vitamins, minerals, and pigments, justifying their significant impact on food innovation [27,28]. Figure 1 illustrates the primary products in the food sector based on cyanobacteria and microalgae.

According to various studies on food incorporation, the incorporation of cyanobacteria and microalgae in food products varies depending on the type of product, formulation, and specific objectives [11,29,30]. From incorporation in bread and pasta to the fortification of beverages, the versatility of these microorganisms allows for a wide range of applications in the food industry [31,32].

Figure 1. Food products are based on cyanobacteria and microalgae. Source: Adapted from De Oliveira and Bragotto [33]. Microalgae products refer to components extracted from their biomass. Supplements refer to products consumed daily in order to provide a nutraceutical influence. Food products are food and beverages incorporated with microalgal biomass.

Figure 1. Food products are based on cyanobacteria and microalgae. Source: Adapted from De Oliveira and Bragotto [33]. Microalgae products refer to components extracted from their biomass. Supplements refer to products consumed daily in order to provide a nutraceutical influence. Food products are food and beverages incorporated with microalgal biomass.

The relentless pursuit of nutritional and sustainable alternatives has spurred research into the incorporation of cyanobacteria and microalgae in foods, offering a wide range of opportunities to improve the nutritional and functional composition of foods [31,34].

According to Hernandéz et al. (2022), there are several species of cyanobacteria/microalgae that are studied for use in bioterritorial analysis, with some of them belonging to the genera Arthrospira (Spirulina), Chlorella, Nannochloropsis, Haematococcus, and Dunaliella. The physical–chemical and functional composition, proteins, lipids, carbohydrates, minerals, and antioxidants vary greatly depending on the species and growth conditions, such as the composition of the medium, light supply, temperature, and other factors [11].

The abundance of essential fatty acids such as omega-3 and omega-6, as well as the presence of antioxidants, amino acids, and carotenoids, positions these microorganisms as potentially beneficial ingredients for both nutritional [30,35] and functional health [36,37]. In addition, cyanobacteria and microalgae have demonstrated the ability to provide significant sensory improvements in terms of texture, color, flavor, and product stability, further enriching the spectrum of possibilities in the food industry (see

Table 2. Main changes in the conventional properties of yogurt caused by cyanobacteria/microalgae.

Functional Properties	Benefits	References
Generation of gels	Improving texture and consistency	[38,39]
Emulsification	Stabilization of emulsions	[9,36]
Stabilization	Increased product shelf life	[37]
Color improvement	Increased visual appeal	[38,39]
Taste improvement	Sensory enrichment	[9,36]
Stability improvement	Reduced separation and sedimentation	[37]

). These properties have been explored, albeit in a modest manner, allowing the development of foods with exceptional sensory and technological properties (e.g., gels, emulsions, and stable systems) [38,39].

However, despite the promise of microalgae, it is important to recognize that the incorporation of microalgae into food is not without significant challenges [40,41]. The search for the most suitable microalgae for each specific application is a delicate and crucial step, as different species have different characteristics that can influence the properties of the final products. Ensuring the stability of bioactive compounds from microalgae during manufacturing and storage processes is also a major challenge, as the preservation of these compounds is essential to deliver the expected nutritional and functional benefits [42,43]. Therefore, understanding the stability of bioactive compounds from microalgae during the processing and storage of yogurt is a complex technical issue that requires careful attention in the product manufacturing process [44,45].

Another critical aspect to consider is the sensory acceptability of products containing microalgae and/or their components by consumers [45,46]. The introduction of innovative ingredients, such as microalgae, may result in distinct sensory characteristics that may be well received by some consumers but may also be met with resistance by others. Therefore, a careful balance between nutritional benefits and taste preferences is essential for the commercial success of foods containing microalgae (

Table 3. Challenges in incorporating microalgae into foods.

Challenges	Importance	References
Selection of suitable microalgae	Influence on final product properties	[40,41]
Development of efficient cultivation processes	Economic feasibility and sustainability	[45,46]
Stability of bioactive compounds	Preservation of nutritional benefits	[45,46]
Sensory acceptability by consumers	Commercial success and taste preferences	[45,46]

).

The use of microalgae represents a link between biotechnology and the food industry, opening new perspectives for the creation of innovative and functional products [38,39]. The synergy between scientific knowledge and technological innovation can open new horizons and place microalgae at the forefront of the future of nutrition [40,47]. In this regard, the continuous improvement of cultivation processes, safety assessments, and consumer acceptance studies plays a crucial role in advancing the research field of microalgae incorporation in food [46,48]. Given these challenges, it is clear that microalgae incorporation in foods requires a multidisciplinary and collaborative approach, involving not only food experts but also researchers from different fields such as biotechnology, process engineering, nutrition, and sensory science. Only through comprehensive research and overcoming these obstacles will it be possible to fully realize the benefits that microalgae can offer both for consumer health and for innovation in the food industry [47].

In Brazil, the legislation that regulates the production of yogurt is normative instruction No. 46/2007 of the Ministry of Agriculture, Livestock and Supply, which is the body associated with the Ministry of Health that regulates processes involved in the manufacture and commercialization of products intended for human consumption and is ANVISA (National Health Surveillance Agency) [48], which does not have specific legislation for the manufacture and commercialization of algae-based foods, as well as the US and European Union.

Despite the nutritional and ecological potential of algae, there are still no specific laws governing the procedures for producing and selling foods derived from these algae. However, in comparative terms, countries that are part of the European Union, with an emphasis on Ireland and France, still stand out. The United States, in addition to having clearer legal structures than Brazil, can be justified by financial issues in research and its purposes [49]; however, some legislation on the use of cyanobacteria and microalgae in food is available and will be cited.

The European Commission Regulation (EC) No. 178/2002 (the General Food Law Regulation), which establishes general guidelines for food production in the European Union, has been the legislation in force in the European Union since 2002, with subsequent updates. In the case of algae intended for food and food in general, the European Food Safety Authority (EFSA) is the entity responsible for providing scientific support to the European Commission on the possible hazards associated with food [50]. It is also important to highlight that algae species are authorized as food or supplements and are most often included as novel foods, i.e., they are classified as foods that are not normally consumed. Therefore, these species must undergo processes that guarantee their safety for consumption, and of the species used in biotechnology, most are not authorized for food purposes.

In the “Novel Food Catalog”, the following species of cyanobacteria and microalgae are mentioned: Spirulina major, Arthrospira (Spirulina) platensis, Limnospira (Arthrospira, Spirulina) maxima, Limnospira (Arthrospira, Spirulina) indica, Limnospira (Arthrospira, Spirulina) indica, Limnospira (Arthrospira, Spirulina) fusiformis, Chlorella vulgaris, Chlorella sorokiniana, Chlorella (Auxenochlorella) pyrenoidosa, Chlorella (Auxenochlorella) protothecoides, Grasiella emersonii, Jaagichlorella luteoviridis, Nannochloropsis oculata, Scenedesmus vacuolatus, Aphanizomenon flos-aque, and Haematococcus lacustris (pluvialis) [51].

Specifically, the General Food Law Regulation of the EU establishes “general principles and requirements concerning food and feed law at Union level by developing an integrated approach to food safety ‘from farm to fork’”. Microalgae/cyanobacteria are subjected to the General Food Law Regulation as far as it concerns already marketable products, such as the dried biomass of Spirulina (A. platensis, and A. maxima) or Chlorella sp. (C. luteoviridis, C. pyrenoidosa, and C. vulgaris), docosahexaenoic acid (DHA) oil from Crypthecodinium cohnii, and β-carotene from Dunaliella salina. Spirulina and Chlorella are commonly used as food supplements in the form of dried biomass (powder or compacted in tablets) [52].

In the United States, food regulation is carried out by the Food and Drug Administration (FDA) and the United States Department of Agriculture (USDA). Algae can be categorized into three distinct categories: food supplement, food additive, and genetically modified food [53]. The legislation in force in the United States (US), with subsequent updates, is the Food Safety Modernization Act (FSMA) No. 204/2011 of the Food and Drug Administration (FDA), which provides general guidelines for food production in the United States (US). For the use of microalgae/cyanobacteria, some have a GRAS (Generally Recognized As Safe) status, recognized by the Food and Drug Administration (FDA), thus ensuring their consumption without harm to health. These microalgae/cyanobacteria are Spirulina, Chlorella sp., Haematococcus sp., Dunaliella sp., and Chlamydomonas reinhardtii [54].

In general, the set of laws in the United States that establishes standards for the food safety of products sold is the Federal Food, Drug and Cosmetic Act (FD&C Act), Title 21/Chapter 9 in the “Code of United States” [55]. Therefore, according to the categories mentioned above, several subchapters of this law apply to algae. Notably, 21 CFR 170, as a food additive, establishes the conditions and procedures to ensure food safety when using substances, such as algae (United States Food and Drug Administration, 2022), in the manufacture of foods intended for human and animal consumption. Additionally, the standard follows the guidelines of section 190 [56], which establishes the stages that precede the sale of the supplement. Finally, bioengineered foods, as defined in 7 CFR 66 [57], are those that have been genetically modified in a laboratory and cannot be obtained in nature or produced through traditional breeding methods.

Regarding the risks associated with these microorganisms in food, the main concerns are mainly in relation to toxins from cyanobacterial species (cyanotoxins) [52,58].

Also, antinutritional factors (AFNs) need to be considered. They are compounds of biological origin contained in foods and feeds that reduce food intake and nutrient utilization and have adverse effects, such as toxicity and reactions, and can cause diseases in humans. The main related problems are allergenicity, the ingestion of nucleic acids (gout and kidney stones problems, which is why the daily recommendation is 30–50 g_alga/kg of body weight), toxicity (for example, some species, mainly cyanobacteria, such as Nostoc sp. and Aphanizomenon flos-aque, can naturally produce cyanotoxins), carcinogenicity (cyanotoxins), pathogenicity (for example, species of Prothoteca sp. and Desmodesmus armatus), and hypervitaminosis. These problems exist in addition to the traditional problems related to cultivation, such as the presence of organic, inorganic, and biological contaminants and the dangers associated with improper handling [52]. It is important to emphasize that Spirulina and Chlorella species are considered safe for application of their biomass directly in food [35,59].

4. Incorporation of Cyanobacteria and Microalgae in Yogurt

The relentless quest for foods that not only meet nutritional requirements but also exhibit improved functional and sensory properties has driven the search for new sources of ingredients and innovative technologies in the food industry [33,60]. In this regard, microalgae have attracted considerable interest due to their nutrient-rich composition and potential to impart nutritional and technological benefits to a variety of food products, including yogurt.

The incorporation of algae in yogurt represents a promising strategy to improve the nutritional profile of this widely consumed and valued food product worldwide [47,48]. Numerous studies have explored this innovative approach, seeking to exploit the unique properties of microalgae to fortify yogurt with essential nutrients, bioactive compounds, and distinct functional properties [3,34,37]. Due to their complex chemical composition, cyanobacteria and microalgae can help to improve the sensory and technological properties of yogurt. The ability of microalgae to form gels, emulsify, and stabilize food systems has been used to develop yogurts with smoother, creamier, and more uniform textures, as well as to improve the stability of emulsions in the final product [38,39]. This not only results in a more enjoyable sensory experience for consumers but also provides technological advantages in the production and processing of yogurt.

In addition, cyanobacteria and microalgae can contribute significantly to the nutritional value of yogurt. The abundance of essential nutrients such as high-quality proteins, vitamins, minerals, and antioxidants present in microalgae can be transferred to yogurt, enriching its nutritional composition and potentially conferring health benefits [37,61]. This approach is particularly relevant in a scenario where the pursuit of functional and fortified foods is increasingly prominent among consumers concerned about their health and well-being.

Regarding the fermentative process and the incorporation of algal biomass in the food (i.e., yogurt), since there is a dependence on the activity of lactic acid bacteria for the inherent characteristics of the food, and the microalgae/cyanobacterium is added as a component rather than a biocatalyst, the following steps are typically used: the addition of commercial (processed) algal biomass to pasteurized or to-be-pasteurized milk (80 to 90 °C for 10 to 20 min) before fermentation; fermentation mainly with Lactobacillus bulgaricus and Streptococcus thermophilus (main commercial strains) at temperatures above room temperature (37 to 43 °C) for 4 to 5 h and storage at 4 °C for 28 to 30 days before consumption.

Table 4. Yogurt fermentation conditions for yogurt incorporated with cyanobacteria/microalgae.

Fermentation Process	Temperature (°C)	pHfinal	Storage	Reference
Milk was pasteurized at 85 °C for 30 min. L. bulgaricus and S. thermophiluls cultures were added, 107 cells L−1 of milk. Addition of Chlorella vulgaris and Arthrospira platensis prior to fermentation	42	4.6	30 days at 4 °C.	[12]
Milk was pasteurized at 90 °C for 10 min. L. bulgaricus and S. thermophilus cultures were added, 109 cells L−1 of milk. Arthrospira (Spirulina) platensis was added after fermentation.	42	4.6	30 days at 4 °C.	[62]
Lipid extraction with green solvent from freeze-dried L. galbana biomass added after fermentation. Milk was pasteurized at 80 °C for 15 min. L. bulgaricus and S. thermophiluls cultures added.	43	4.3	28 days at 4 °C.	[63]
Addition of Arthrospira (Spirulina) platensis to milk. Milk was pasteurized at 85 °C for 15 min. Addition of L. bulgaricus and S. thermophiluls cultures, 1:1 ratio for 2–3% w/v inoculum.	42	4.6	28 days at 4 °C.	[37]
Adsorption of the lipid extract of the microalga Pavlova lutheri to milk, 1000 rpm for 5 min. Milk was pasteurized at 93 °C for 15 min. L. bulgaricus and S. thermophilus cultures added.	43	4.3	28 days at 4 °C.	[39]
Buffalo milk (2:1) was pasteurized at 90 °C for 10 min. Arthrospira (Spirulina) platensis was added to the milk and mixed in a blender for 5 min. L. bulgaricus (5%) and S. thermophiluls (1:1) cultures were added, with 10% activated culture as inoculum.	37	4.6	28 days at 5 °C.	[61]
Milk was pasteurized at 90 °C for 5 min. Then, 1.6% Spirulina microalgae was added to the milk. L. bulgaricus and S. thermophilus cultures were added.	45	4.3	For 30 days at 4 °C.	[64]
Addition of Arthrospira (Spirulina) platensis to milk 1.5% w/v. Milk was pasteurized at 82 °C for 15 min. Addition of L. bulgaricus and S. thermophiluls cultures, 1:1 ratio in 2% w/v inoculum.	42	4.6	For 30 days at 4 °C.	[65]
Addition of Arthrospira (Spirulina) platensis to milk. Milk was pasteurized at 90 °C for 10 min. L. bulgaricus and S. thermophiluls cultures added.	42	4.6	30 days at 4 °C.	[66]
Addition of Arthrospira (Spirulina) platensis to milk. Milk was pasteurized at 93 °C for 10 min. L. bulgaricus and S. thermophiluls cultures were added at 3% w/v.	43	4.3	28 days at 4 °C.	[67]
Addition of Arthrospira (Spirulina) platensis to milk. Milk was pasteurized at 80 °C for 10 min. L. bulgaricus and S. thermophilus cultures were added.	43	4.6	28 days at 4 °C.	[68]

provides a summary of the fermentations carried out in the recent literature considering yogurt fermentation with the addition of cyanobacteria/microalga.

In Brazilian legislation, the recommendations of normative instruction No. 46/2007 of the Ministry of Agriculture, Livestock and Food Supply [66] for yogurt state that the yogurt must have acidity between 0.6 and 1.5% of total acidity (g of lactic acid/100 g), hydrogen potential (pH) between 3.5 and 4.6, and a quantity of lactic bacteria of at least 10⁶ CFU/g (CFU—Colony Forming Unit). In this sense, the works of Follen et al. [62] and Nazie et al. [38] showed the yogurt incorporated with Spirulina platensis (0.125–3.5% w/v in dry biomass), which was fermented at 42 °C until pH 4.6, and the parameters required by Brazilian legislation were achieved, even though small differences occurred with the increase in the quantity of cyanobacterial biomass added. In international legislation, it follows the codex standard for fermented milks, stan 243/2010 [69], which states that the yogurt must have an acidity between 0.6% of the total acidity (g of lactic acid/100 g), a quantity of lactic acid bacteria of at least 10⁶ CFU/g (CFU—Colony Forming Unit), a minimum of 2.7% (w/w) of milk protein, and less than 15% (w/w) of milk fat.

To improve the maintenance and viability of probiotic microorganisms present in food, prebiotic substances can be incorporated into the same food matrix [70]. Prebiotics are non-digestible nutrients that benefit the host by selectively stimulating the multiplication or activity of groups of beneficial bacteria in the colon. These elements are commonly found in the large intestine, although they may have some effect on microorganisms in the small intestine [71].

To be classified as prebiotic, the fiber content must not be hydrolyzed by salivary and digestive enzymes, nor be absorbed by the stomach. It must selectively promote the growth and/or activity of beneficial bacteria, such as bifidobacteria and lactobacilli, in addition to being fermented by the intestinal flora [71]. Thus, prebiotics reach the colon without undergoing modifications, being ready to be fermented and, therefore, exerting bifidogenic activity [72]. Human intestinal enzymes are unable to hydrolyze the β (2-1) bonds present in certain foods, resulting in foods reaching the colon intact [73,74].

Spirulina, a prebiotic under investigation, is recognized as a rich source of proteins, minerals, B complex vitamins, iron, and antioxidants such as phycocyanin and phenolic compounds. The main antioxidant substance found in Spirulina, phycocyanin, prevents the absorption of cholesterol in the intestine, thus reducing blood fat levels. The prebiotic potential of cyanobacteria/microalgae biomass can alter the composition, metabolic activity, and variety of the human intestinal microbiota [74]. The polysaccharides present in microalgae can exert a prebiotic effect both in vitro and in vivo. This is due to their diverse chemical composition. Cyanobacteria/microalgae, in addition to having a prebiotic effect, also reinforce the beneficial bacteria present in the intestine. With the balance of intestinal flora, vitamin B₆ is produced in greater quantities, contributing directly to increased energy and disposition [73].

Thus, the study of the incorporation of microalgae in yogurt represents a promising area of research and development in the food industry. By improving the nutritional, technological, and sensory properties of yogurt, this innovative approach can contribute to providing healthier, appealing, and differentiated food products that meet the growing consumer demand for functional and fortified foods [37,40,75].

5. Formulation of Yogurt with Cyanobacteria and Microalgae

The formulation of yogurt fortified with microalgae is a crucial aspect in the quest for innovative and nutritious food products. Based on various research conducted and analyzed [75], notable contributions are highlighted by Wang et al. [47], Yamaguchi et al. [64], and Wu et al. [76] for their different strategies to effectively and harmoniously incorporate microalgae into the yogurt matrix. These formulations aim not only to ensure the stability of the bioactive compounds of microalgae during processing but also to improve the sensory and nutritional properties of the final product.

The choice of microalgae species and the determination of the percentage to be added are fundamental considerations in the formulation of fortified yogurt (

Table 5. Percentage of cyanobacteria/microalgae added to yogurt (prior the fermentation process).

Formulations	Reference
0.5%, 1.0%, and 1.5% (w/v). Arthrospira (Spirulina) platensis	[3]
0.25, 0.50, and 1% (w/v). Chlorella vulgaris and Arthrospira platensis	[12]
0.5% and 1% (w/v). Arthrospira (Spirulina) platensis	[16]
0.125% and 0.25% (w/v). Arthrospira platensis	[62]
1% and 2% (w/w). Isochrysis galbana freeze-dried	[63]
1.5%, 2.5%, and 3.5% (w/v). Arthrospira platensis	[37]
0.25% and 0.5% (w/v). Lipid extract Pavlora lutheri	[39]
0.2%, 0.4%, 0.7%, and 1% (w/v). Arthrospira (Spirulina) platensis	[61]
1.6% (w/v). Arthrospira platensis	[64]
1.5% (w/v). Arthrospira (Spirulina) platensis	[65]
0.25%, 0.5%, 0.75%, and 1% (w/v). Arthrospira (Spirulina) platensis	[66]
0.1%, 0.3%, and 0.5% (w/v). Arthrospira (Spirulina) platensis	[67]
0.1%, 0.3%, 0.5% 1%, 5%, and 10% (v/v). Arthrospira platensis	[68]
0.13%, 0.25%, 0.38%, and 0.5% (w/v). Arthrospira platensis	[79]
0.5% and 1% (w/w). Arthrospira (Spirulina) platensis	[80]

). A primary concern is the maximum amount to be incorporated since, as sources of plant proteins (currently the main commercial products), which have a more bitter and astringent taste, their addition in very high concentrations is challenging [72,77,78].

Studies such as those conducted by Chen et al. [81], Nazir et al. [38], and Ahmad et al. [48] have explored the cyanobacterium Spirulina (Arthrospira) platensis and microalgae, such as Pavlova lutheri, Chlorella vulgaris, Isochrysis galbana, and others, to fortify yogurt with their unique nutritional and functional properties. The optimization of the microalgae percentage, as investigated by Ebid, Ali, and Elewa [82] and Abdelhamid, Edris, and Sadek [37], directly affects the balance between the supply of bioactive compounds and the impact on the organoleptic properties of the product, with a recommended maximum of up to 2% w/w (Table 5).

The process of incorporating microalgae into yogurt formulations requires specific methods of mixing and homogenization. Authors such as Mesbah, Matar, and Karam-Allah [3] and Zaid, Hammad, and Sharaf [65] explored different approaches, such as addition before or after fermentation, and mixing techniques to ensure the uniform distribution of microalgae in the yogurt matrix. In addition, the selection of probiotic cultures, as observed in the studies by Matos et al. [42] and Huang et al. [83], plays a crucial role in fermentation and achieving the desired properties.

The incorporation of cyanobacteria and microalgae biomass in milk prior to fermentation is the most commonly used approach. This is because the interaction of the biomass with lactic acid bacteria is of paramount importance. The activity of lactic acid bacteria as probiotics should be enhanced by the addition of microalgae as prebiotics, strengthening the product and avoiding microbial incompatibility during fermentation. This helps to prevent a decrease in the activity of lactic acid bacteria due to inhibitory compounds that may be present in the algal biomass or that may be generated by undesired reactions during fermentation. Another disadvantage of adding microalgae after the fermentation process is the uncertainty about the shelf life and organoleptic characteristics of the product [63].

Finally, it is important to highlight that the formulation of yogurt fortified with cyanobacteria and microalgae is also influenced by the interaction between the compounds of the algal biomass and the milk components. Interaction studies, such as those carried out by Silva and Pandolfi [22] and Ak et al. [84], highlight how the active compounds of microalgae can influence the structure and physicochemical properties of yogurt. This makes the field of microalgae-fortified yogurt formulations a constantly evolving topic where science, technology, and food engineering come together to offer innovative and highly nutritious products to discerning consumers.

6. Physicochemical Characteristics

With regard to the study of physicochemical properties, it is essential to understand the changes that the incorporation of microalgae can bring to fortified yogurts. Several researchers, such as Matos et al. [42], Gölbaşι et al. [45], Mohammadi-Gouraji, Soleimanian-Zad and Ghiaci [85], and Part et al. [86], have focused on studying how the presence of microalgae affects the nutritional and sensory parameters of the final product.

In terms of lipids, the addition of microalgae can lead to significant changes. Studies by Folle et al. [62] and Wu et al. [76] indicate an increase in lipid content, between 5 and 6%, possibly related to the lipid content of the microalgae incorporated.

The interaction between microalgae lipids and milk components can affect emulsion formation and the structure of yogurt. This can lead to changes in texture, consistency, and even the stability of the final product. The presence of additional lipids can also affect mouthfeel and consumer sensory perception [11,62,69,87]. On the other hand, proteins are important constituents that can be affected by the incorporation of microalgae. Some studies, such as those by and Nazir et al. [38] and Ebid, Ali, and Elewa [75], highlight a potential increase in the protein content in fortified yogurt, between 5.2 and 6.3%, indicating that microalgae may contribute to additional protein intake. However, interactions between microalgae and milk proteins can influence the texture and viscosity of the final product, as investigated by Robertson et al. [40] and Lee et al. [41].

Essential minerals, such as potassium, calcium, phosphorus, magnesium, zinc, and iron, also increase their percentage in foods enriched with microalgae, as demonstrated, sequentially, by Ebid, Ali, and Elewa [82], with a 4% increase; Mesbah, Matar, and Karam-Allah [3] showed a 3.4% increase; and Nazir et al. [38] showed a 4% increase in minerals in enriched yogurts with microalgae/cyanobacteria. Another relevant aspect is the acidity and pH of yogurt, which can be influenced by the metabolic activities of lactic acid bacteria due to the presence of microalgae during lactic acid fermentation. Authors such as Almeida [34] and Vénica et al. [88] report changes in titratable acidity and pH due to the incorporation of microalgae, which can affect both the sensory properties and the shelf life of the product.

7. Rheological and Sensory Characteristics

Understanding the textural and sensory changes brought about by this incorporation is explored and highlighted by Mesbah, Matar, and Karam-Allah [3], Ak et al. [84], Mohammadi-Gouraji, Soleimanian-Zad, and Ghiaci [85], and Wang et al. [47], who have thoroughly investigated how the rheological and sensory properties of yogurts can be affected by the intrinsic properties of microalgae.

From a rheological perspective, viscosity is a key parameter that can be influenced. Studies suggest that the viscosity of fortified yogurts may increase due to the presence of microalgae, as observed by Mesbah, Matar, and Karam-Allah [3], Barkallah et al. [67], and Agustini et al. [89].

Yogurt fortified with 1% of Spirulina platensis obtained a viscosity of 358.92 ± 44.29 cP, while the control without the addition of cyanobacteria obtained a viscosity of 192.62 ± 13.31 cP [90]. Additionally, Mesbah, Matar, and Karam-Allah [3] observed that yogurts incorporated with 0.5–1.5% Spirulina platensis showed a viscosity between 3410 and 3901 mPa.s (1 mPa.s = 1 cP), while the control without the addition of Spirulina showed 2835 mPa.s. Bchir et al. [66] incorporated fresh and dried Spirulina platensis in yogurt and obtained a viscosity between 748 and 903 mPa.s, proportional to the amount of cyanobacteria added, and there was no difference between fresh and dried biomass (control yogurt presented a value of 703 mPa.s).

On the other hand, Robertson et al. [40] during the evaluation of the technological and sensory properties of yogurt fortified with a lipid extract from the microalga Pavlora lutheri (0.25–0.5%) had similar viscosity values in comparison with the control between 4300 and 4900 mPa.s. However, it is important to highlight that the incorporation was of a low concentration, was of an extract, and was not the complete biomass; therefore, the influence on the viscosity of the yogurt was little accentuated. In addition, the costs of making the extract must be considered, and a sensory analysis showed that the acceptability was not satisfactory when compared to the control.

The complexity of the interactions that occur between microalgae proteins and milk proteins during the formulation of fortified yogurt deserves more in-depth analysis. The increase in yogurt viscosity often observed after the incorporation of microalgae has been linked to the formation of protein complexes between microalgae proteins and milk proteins. Studies by Silva and Pandolfi [16] and Zarrin et al. [39] emphasize that these protein complexes can alter the three-dimensional structure of the milk matrix, resulting in changes in the rheological and textural properties of the final product. The formation of these protein complexes can be influenced by factors such as the charge, size, and hydrophobicity of the proteins involved, and such interactions may vary depending on the microalgae species used.

Viscosity, which is directly related to the perceived texture of yogurt, is a critical sensory attribute that influences consumer product acceptance. Texture plays a fundamental role in the perception of yogurt quality, influencing mouthfeel and the overall consumer experience when tasting the product. Mesbah, Matar, and Karam-Allah [3] state that the incorporation of Spirulina platensis changed the viscosity of the yogurt. Adding 1% (w/w) changed the texture of the yogurt, impacting its sensory acceptability, which was 70%, unlike the yogurt with the addition of 2% with an acceptability of 60%. Nazir et al. [38] obtained a small increase in viscosity with the addition of 2.5% of Spirulina platensis, having an acceptability of 80%, differently an acceptability of 70% when 3.5% of cyanobacteria was added to the yogurt, realizing that the more cyanobacteria are added, the more the viscosity is changed, directly impacting the acceptability of the product.

Therefore, understanding how protein interactions between microalgae and milk affect viscosity and texture is essential for optimizing the formulation of fortified yogurts. Notably, viscosity is not an isolated property but is related to other rheological parameters such as elasticity and viscoelasticity. For example, Pan-Utai et al. [68] investigated the influence of these parameters on yogurt texture and how they may be affected by the presence of microalgae/cyanobacteria, obtaining that with an increase in the amount of Spirulina platensis in the yogurt, there was a change in the texture of the yogurt, where 1, 5, and 10% were added, and the best acceptability of 77% was obtained with the addition of 1% (w/w). Understanding these complex relationships may enable the development of microalgae-fortified yogurts that meet both the sensory, nutritional, and functional requirements of consumers and provide what they perceive as quality yogurt. Therefore, an investigation of the mechanisms behind viscosity and texture changes after the incorporation of microalgae is necessary for the successful production of fortified yogurts and to promote their market acceptance [68].

In addition to viscosity, the consistency and overall texture of yogurt are important rheological parameters that can be modified by the presence of microalgae. The papers of Barros de Medeiros [35], Zhu et al. [61], and Barkallah et al. [67] report that the incorporation of microalgae can result in a firmer and more cohesive texture, possibly due to interactions between the proteins and polysaccharides of microalgae and milk components. However, this texture modification can be challenging as it may affect sensory perception and consumer acceptability. Parameters such as hardness (or firmness) (N), cohesiveness, adhesiveness (N/mm), gumminess (N), and elasticity (mm) are generally used to measure textural parameters.

In the work of Bchir et al. [66] who studied the physical–chemical, nutritional, textural, and sensory properties of yogurt fortified with fresh and dried Spirulina (Arthrospira platensis), incorporating up to 0.5% of cyanobacterium, the authors observed that the parameter hardness of the incorporated yogurt presented a value up to 0.68 N in comparison with the control, which showed a value of 0.64 N. For the parameters of adhesiveness, cohesiveness, and gumminess, there was no significant alteration between the formulations and the control. It is important to highlight that 0.5% of microalgae is still very little to be incorporated, so the perception was not greater. On the other hand, in the work of Barkallah et al. [67], as the yogurts were introduced with 1% of S. platensis, the firmness parameter showed an increase of 0.47 to 0.67 N and cohesiveness between 0.32 and 0.45 when compared with the controls and the higher concentrations of added cyanobacteria. For the elasticity parameter, there was no significant change.

From a sensory perspective, the impact of incorporating cyanobacteria/microalgae into yogurt formulations goes beyond the nutritional aspect and enters a dimension that can play a role in product acceptance by consumers. Studies on this topic highlight that the introduction of microalgae can have a significant impact on the taste, color, and overall acceptance of yogurt, presenting a complex set of challenges and opportunities [39].

Taste emerges as a fundamental consideration in this context. Unique aroma and flavor characteristics of microalgae can be imparted to yogurt, introducing herbaceous, marine, or vegetal notes, as demonstrated by the research of Silva and Pandolfi [16] and Zarrin et al. [39]. While this sensory characteristic can provide product differentiation, it can also pose a challenge to acceptance, particularly in markets with entrenched preferences for traditional flavors. The perception of exotic or unfamiliar flavors can elicit different responses from consumers, which can be a limiting factor in more conservative markets [39].

The addition of cyanobacterial/microalgal biomass to yogurt can affect the overall acceptability of the final product, mainly related to the flavor and color [40,67]. In the work of Robertson et al. [40] who evaluated the technological and sensory properties of yogurt fortified with a lipid extract of the microalgae Pavlora lutheri (0.25–0.5% w/v), the authors obtained an acceptance rate of 66.1 and 68.2% for incorporation with 0.25% and 0.5%, respectively, and the control obtained a value of 91%, indicating a significant reduction in this property due to incorporation. The attribute with the lowest acceptance was the flavor, having 40.33% and 50.1% for yogurts incorporated with 0.25 and 0.5%, respectively. Similarly, Bchir et al. [66] incorporated fresh and dry Spirulina platensis at concentrations of 0.1, 0.3, and 0.5% (w/v) in yogurt, obtaining a very greenish color and sedimentation of cyanobacteria in the yogurt, which are factors that made for the low score obtained; in terms of flavor, values of 4.88 for the incorporation of 0.5% and 5.08 for the incorporation of 0.1% were obtained, on a rating scale that varies from 1 (extremely disliked) to 7 (extremely liked).

The color of yogurt, often associated with freshness and quality, can be influenced by the incorporation of cyanobacteria and microalgae. The color of fortified yogurt can also be affected by the presence of microalgae. Studies by Zarrin et al. [39] and Lee et al. [41] show that the natural pigments in cyanobacteria and microalgae (e.g., chlorophyll, carotenoids, and phycobilins) can give the yogurt a green or yellow hue, depending on the species used, generally measured in the CIELAB system through the parameters L* (luminosity/(+) white and (−) dark perception), a* ((+) red/(−) green perception), and b* ((+) yellow/(−) blue perception). This can be a determining factor in consumer sensory acceptance. According to Zarrin et al. [39] and Lafarga at al. [36], the addition of 1% of Spirulina platensis to yogurt caused a change in color to yellowish-green tones, with an increase of 23% and 20% of chlorophyll-a in the final product, respectively. Yogurt color is very sensible to cyanobacteria/microalgae incorporation as shown in Figure 2.

Additionally, Barkallah et al. [67], Mesbah, Matar, and Karam-Allah [3], Bchir et al. [66] and Alizadeh et al. [72] noticed a decrease in the three parameters (L, a, and b) in relation to the control for yogurts incorporated with Spirulina platensis, changing its characteristic from yellowish-white to a darker and greenish tone, which was already expected due to the color cyanobacteria with the striking presence of its pigments, especially chlorophyll a, but there are other characteristic pigments depending on the cyanobacteria/microalgae that can be enhanced depending on the cultivation conditions (such as phycobilins, which are more bluish, and carotenoids, which are more yellowish).

The authors Mesbah, Matar, and Karam-Allah [3] observed that yogurts incorporated with 0.5–1.5% Spirulina platensis have a change in their color from green to yellow tones going to blue-green, decreasing their acceptability, thus obtaining an acceptability of 70% with a concentration of 0.5% and decreasing to 60% with a concentration of 1.5% of Spirulina. Similarly, Ebid, Ali and Elewa [82] observed that yogurts incorporated with 0.2, 0.4, 0.7, and 1.0% of Spirulina platensis changed their color proportionally to the amount of Spirulina biomass added, leaving whitish-green tones going to blue-green and thus obtaining an acceptability of 80% with a concentration of 0.2% and decreasing to 70% with a concentration of 0.7% of Spirulina.

In support of that claim, Almeida [34] and Atik et al. [91] observed variations in the coloration of fortified yogurts, ranging from green to yellow hues, depending on the microalgae species used, where they achieved a 15–20% increase in the color of the final product. These color variations can add aesthetic value to the product, positioning it as a distinct and innovative alternative in the market. However, color variations can also lead to misconceptions about the quality of the yogurt, causing consumers to question the authenticity or freshness of the product [82].

In this context, achieving a balance between the introduction of characteristic microalgae flavors and consumer sensory acceptance is a complex task. Not only individual preferences for less familiar flavors must be considered but also the harmonious integration of these unique sensory characteristics into the overall profile of the yogurt [81].

Formulation strategies that allow the adjustment of the intensity of the microalgae/cyanobacteria flavors and the resulting coloration can be crucial to meeting both the nutritional requirements and the sensory appeal of the final product. Analysis of the rheological and sensory properties of microalgae-fortified yogurt reveals a complex landscape of changes that can affect perceived texture, consistency, and sensory acceptability. The interaction between the intrinsic properties of the algal biomass and the milk components plays a fundamental role in determining the final product characteristics. This in-depth understanding is essential to guide the development of fortified yogurts that meet consumer expectations in terms of taste, texture, and overall acceptability but remains a subject of ongoing research [85].

8. Antioxidant Characteristics

The antioxidant properties of yogurts fortified with cyanobacteria and microalgae reveal a promising facet in the field of human health. The presence of antioxidant compounds from this type of biomass can provide significant benefits, as antioxidants play an essential role in protecting against oxidative stress and its adverse effects. Studies by Nazir et al. [38], Abdelhamid, Edris, and Sadek [37], and Mohammadi-Gouraji, Soleimanian-Zad, and Ghiaci [85] were devoted to exploring how the incorporation of cyanobacteria and microalgae can improve the antioxidant capacity of yogurts.

Microalgae are emerging as natural reservoirs of potent antioxidants such as carotenoids and other accessory pigments, as well as phenolic compounds, which offer potential health benefits when incorporated in yogurts. This bioactive property has stimulated a growing interest in exploring its antioxidant properties to improve the nutritional and functional profile of dairy products. In line with this perspective, scientific studies indicate that the addition of antioxidant compounds derived from cyanobacteria and microalgae can have a positive impact on the nutritional quality and health properties of yogurts [78].

Carotenoids, such as β-carotene, are prominent among the antioxidants found in microalgae and have been reported in studies as components present in some species [41,79]. β-Carotene, a precursor of vitamin A, plays a fundamental role in eye and immune health in addition to possessing antioxidant properties that contribute to the neutralization of free radicals in the body [34]. Incorporating these carotenoids into yogurts provides an opportunity to increase the vitamin A content and antioxidant activity of the final product, thereby adding value to its nutritional composition.

Yogurt incorporated with 1.5% Spirulina platensis showed a content of 4.35 mg/100 g of β-carotene, significantly higher than the control (without the addition of cyanobacteria), which obtained a value of 0.23 mg/100 g [38]. Similarly, Mesbah, Matar, and Karam-Allah [3], evaluating yogurt fortified with Spirulina platensis (1.5% w/w), observed a concentration of 7.43 mg/100 g of β-carotene compared to the control, which had 0.82 mg/100 g. Confirming the increase in this antioxidant, Robertson et al. [40], incorporating lipid extract from the microalga Pavlora lutheri (0.5% w/w), obtained 8.30 mg/100 g of β-carotene compared to the control, which presented 2.30 mg/100 g.

In addition, phenolic compounds identified in microalgae have attracted attention for their bioactive properties, including antioxidant, anti-inflammatory, and potential cardioprotective activities [77]. Flavonoids, a group of phenolic compounds, have been extensively studied for their health benefits, such as the ability to reduce oxidative stress and inflammation in the body [82]. The presence of these compounds in microalgae offers the prospect of fortifying yogurts with substances that go beyond basic nutritional value and contribute to health promotion and disease prevention.

The increase in this antioxidant was verified by Nazir et al. [38] who, when incorporating 1.5% of Spirulina platensis in yogurt, added 11.37 mg/100 g of phenolic compounds, higher than the content obtained in the control formulation of 5.07 mg/100 g. Similarly, Mesbah, Matar, and Karam-Allah [3], after incorporating 0.5% of Spirulina platensis in yogurt, observed a value of 16.80 mg/100 g of phenolic compounds, while the control had 7.12 mg/100 g. Finally, Ebid, Ali, and Elewa [82], with an incorporation of only 0.4% of Spirulina platensis, observed 17.00 mg/100 g of phenolic compounds, while the control had 4.59 mg/100 g.

It should be noted that the effective incorporation of microalgae antioxidants into yogurts requires careful consideration of the stability of these compounds during manufacturing and storage processes. Processing conditions, such as temperature and pH, can affect the retention of antioxidants and, consequently, the antioxidant capacity of the final product [26]. Therefore, to effectively utilize the antioxidant benefits of cyanobacteria and microalgae, it is necessary to develop formulation strategies that ensure the preservation of these compounds throughout the production cycle and shelf life of the yogurt [81].

The combination of carotenoids and phenolic compounds in microalgae can create synergies that enhance the antioxidant potential of fortified yogurt. This synergistic effect can be attributed to the interaction between different antioxidant compounds that can complement and enhance their ability to neutralize free radicals [61].

When exploring the dimension of antioxidant properties in the incorporation of cyanobacteria and microalgae in yogurts, it becomes important to address the variability of this process, which can result in a wide range of levels and types of antioxidants in the final product. The concentration and diversity of antioxidants present can be influenced by a complex interaction of variables such as the specific species of microalgae/cyanobacteria used in the formulation, as well as the rate and method of addition to the yogurt. Phycocyanin has an important antioxidant function in inhibiting hepatic lipid peroxidation, playing a great role in protecting mainly the liver [91].

The authors Ebid, Ali, and Elewa [82] found that the incorporation of 0.7% Spirulina platensis in yogurt added 4.73 mg/100 g of phycocyanin compared to the control, which had only 0.10 mg/100 g. Additionally, Barkallah et al. [67] observed that just 0.25% of Spirulina platensis in yogurt added 0.297 mg/g of phycocyanin compared to the control, which did not have this antioxidant detected. Similarly, Pan-Utai et al. [68] incorporated 0.5% Spirulina platensis in yogurt and measured a value of 0.345 mg/g of phycocyanin, unlike the control, which did not present this antioxidant in its original formulation.

The selected algal species play an important role in determining the antioxidant profile of fortified yogurt. Studies such as those by Nazir et al. [38] and Abdelhamid, Edris, and Sadek [42] have shown that different microalgae have unique compositions of antioxidant compounds, such as carotenoids, chlorophyll, and other secondary metabolites, which can impart different antioxidant potentials to the final product. For example, the presence of carotenoids is often associated with antioxidant activity due to their ability to neutralize free radicals and protect cells from oxidative stress. In addition, the presence of chlorophyll is often associated with antioxidant activity due to its ability to neutralize free radicals, improving the activity of human lymphocytes in persisting water-induced oxidative damage. Barkallah et al. [67] verified that the incorporation of 0.25% Spirulina platensis in yogurt added 27.06 mg/g of chlorophyll a compared to the control, which did not have the pigment detected. Similarly, Mesbah, Matar, and Karam-Allah [3], incorporating 1.0% Spirulina platensis, measured 11.32 mg/g of chlorophyll a, while in the control formulation, there was no detection of the pigment.

Studies by Wang et al. [86] and Wu et al. [76] show that different concentrations of microalgae can lead to significant variations in the antioxidant activity of yogurts. The ratio of microalgae/cyanobacteria added can directly influence the quantity of antioxidants available in the product, contributing to the enhancement of or reduction in antioxidant properties. In addition, the method of addition, whether before, during, or after fermentation, can affect the bioavailability and interaction of these compounds with the yogurt matrix, thus influencing the antioxidant potential.

Importantly, synergistic interactions between different antioxidants present in microalgae may contribute to a more pronounced overall antioxidant effect in fortified yogurts. Studies by Zarrin et al. [39] and Robertson et al. [40] show that the combination of several antioxidants, such as carotenoids, chlorophyll, and other phenolic compounds present in cyanobacteria and microalgae, can result in a more comprehensive antioxidant response beyond the individual effects of these compounds, increasing the antioxidant capacity between 100 and 200% in the fortified yogurt [40,47,48,69]. These antioxidant synergies can be enhanced or attenuated by the composition of the yogurt matrix and its processing, paving the way for formulation strategies that maximize the antioxidant benefits of microalgae [39].

Therefore, a holistic approach that considers the complex interactions among algal species, concentrations, addition methods, and antioxidant synergies is essential to optimize the incorporation of cyanobacteria and microalgae into yogurts to maximize their benefits for human health [92].

9. Final Considerations and Future Prospects

In the quest for functional and nutritious foods, the incorporation of cyanobacteria and microalgae in yogurt is a promising approach to improve the nutritional and functional value of this widely consumed product. This analysis underscores the relevance of this field of study, considering its nuances regarding the physicochemical, rheological, sensory, and antioxidant characteristics of fortified yogurts. The integration of microalgae as a source of additional nutrients and bioactive compounds proves to be a viable strategy to improve the nutritional profile of yogurts, expand their functionalities to meet the demands of health-conscious consumers, and drive the sector with innovative food products.

Research into the incorporation of cyanobacteria and microalgae offers significant advantages, such as the provision of antioxidants, phenolic compounds, and high-quality proteins. However, there are also drawbacks, such as the influence on color, taste, and texture. The complex interactions between microalgae and the food matrix make it crucial to carefully consider the species used, concentrations, and addition methods to maximize benefits without compromising consumer sensory acceptance. The specific study of the incorporation of cyanobacteria and microalgae in yogurts shows that, in addition to the nutritional value, the rheological and sensory properties of these products are influenced. The interaction between microalgae and milk proteins can lead to changes in the viscosity and texture of the yogurt, affecting the sensory experience. These aspects must be carefully considered in the formulation, as the perceived texture by the consumer plays a crucial role in acceptance.

In terms of antioxidant properties, it is clear that incorporation can offer the potential to fortify yogurts with bioactive compounds capable of combating oxidative stress and promoting human health. However, the magnitude of these benefits is closely related to the choice of microalgae species, concentration, and incorporation methods. Antioxidant synergies between different compounds present in microalgae can be explored to enhance beneficial effects, provided that the complex interactions between matrix components and processing are considered.

One research topic in the literature is to incorporate not the whole microalgal biomass in the yogurt but extracted substances from it, for example, lipid content (fatty acids), pigments (as antioxidants), and peptides (obtained from protein content) among others, because this could help in decreasing the sensory changes that are negatively associated with microalgae presence in a color-sensitive food such as yogurt (generally white). This was not discussed in this review article because there are costs involved in the extraction processes and by-products generated after them that can increase the yogurt price by a lot and was not considered at this moment.

In conclusion, this review provides a comprehensive overview of the topic. The detailed analysis of selected studies allows for a judicious consideration of technical and sensory aspects. Considering the continuously growing demand for healthy and functional foods, the prospects for this field of research are promising. Advances in microalgae/cyanobacteria selection, product formulation, and processing methods have the potential to further expand the range of fortified yogurts and provide consumers with nutritionally rich and sensorially acceptable alternatives. This, in turn, promotes the intersection of food innovation and health promotion.