## 3 Results
### Water Content, Water Activity (\(a_{w}\)), and Muffin Crumb Color  
The replacement of 50% wheat flour with spelt flour did not significantly affect the moisture content of the muffins (\(p\) = 0.059) (Table 1). The addition of microalgae led to a significant reduction in moisture content across the samples (\(p\) < 0.001). Specifically, the addition of 0.5% microalgae resulted in a decrease in moisture content of about 1 p.p. (percentage point), and 1.5% microalgae reduced the moisture content by about 3 p.p. compared to samples without microalgae (Table 1). Similar results were observed in muffins enriched with brewer's spent grain flours, and grape pomace [17; 24]. Figure 2: Mechanical spectra of raw doughs based on (**a**) wheat flour (CW) and (**b**) a mixture of whole-grain spelt flour (50%) and wheat flour (50%) (SW). Explanations: microalgae addition: a0.5, a1.0, and a1.5%, G\({}^{\prime}\)—preservation modulus, G\({}^{\prime\prime}\)—loss modulus, and tg8—tangent of phase lag angle. The water activity (a\({}_{w}\)) of the muffins was influenced by the type of flour and the interaction between flour type and microalgae addition (Table 1). Muffins made with spelt flour and microalgae exhibited higher water activity compared to samples made with wheat flour and microalgae (\(p<0.001\)). The inclusion of 1 and 1.5% microalgae had the effect of decreasing aw in wheat flour muffins, while it increased aw in samples containing both spelt and wheat flour (Table 1). The interactions between muffin ingredients can affect water binding and, consequently, contribute to variations in water activity. Despite similar water content, the differences in water activity observed may be attributed to the interactions between ingredients and the competition between biopolymers for water. Whole-grain flour, although containing more fiber, has fewer carbohydrates (starch) compared to wheat flour. Color is an important parameter for muffins as it directly impacts the acceptability of the product and is influenced by the type of raw materials used. Table 2 presents various color parameters, including L\({}^{*}\) (brightness), a* (redness), b* (yellowing), C* (saturation), and hab (color tone). Both the use of whole spelt flour (\(p<0.001\)) and the addition of microalgae (\(p<0.001\)) significantly influence the L* value of the muffin (Table 2). Whole-grain spelt flour leads to a darker color of the muffin, as indicated by the lower L* value (Table 2). This dark color is attributed to the high concentration of relatively colorless polyphenic compounds present in whole-grain spelt flour, such as flavan-3-ols, amino-phenolic compounds, benzoic and cinnamic acid derivatives, and proanthocyanidines [25]. In addition, the high fiber content of the spelt flour used may contribute to the darker color of the crumb, which aligns with findings from studies on muffins based on barnyard millet flour [26]. The addition of microalgae also leads to a darker color in the muffins. The green pigment present in microalgae significantly alters the a* and b* parameters, consequently affecting the C* (saturation) and hab (color tone) of the muffin. Color tone represents the dimension of color and describes the specific shade, ranging from red (0\({}^{\circ}\)) to yellow (90\({}^{\circ}\)), green (180\({}^{\circ}\)), blue (270\({}^{\circ}\)), and back to red (360\({}^{\circ}\)). A hab value above 90\({}^{\circ}\) indicates a yellower hue, while higher values suggest less yellow and more green [24]. Muffins made with wheat flour but without microalgae exhibited a yellow color, whereas the use of whole-grain spelt flour resulted in a change in color tone (259\({}^{\circ}\)), indicating a green-blue hue. Samples with added microalgae showed hab angles ranging from 95\({}^{\circ}\) to 109\({}^{\circ}\), indicating a green color for the muffins (Table 2). Previous studies utilizing microalgae (A. platensis) in cakes have reported similar effects [7].