## 3 Results and Discussion
### Yield Stress  
The rheological properties of emulsion-type hair conditioners have a significant influence on their functionality. One of the important rheological parameters in emulsions is yield stress, which is the lowest shear-stress value at which a material will behave like a fluid. Generally, it is recognized that the lower the yield stress, the \"lighter\" the consistency of a cosmetic product and the more easily it spreads on the skin and hair [52]. From the point of view of consumers purchasing hair conditioners, the value of the parameter should not be too low, as this would result in the product running off the hair during application, or too high, which would make it difficult to apply the cosmetic on the hair. Yield stress results are also important for the manufacturers of hair conditioners. Determining the optimum yield stress value for different types of cosmetics helps select an appropriate packaging type and method of dispensing the product from the package. The effects of yield stress on the functional characteristics of emulsion-type cosmetic products have been reported in the literature [53]. For example, in their study of cosmetic creams, [PERSON] et al. [48] found that the formulation with the highest yield stress had the best structure and stability of the emulsion system. The results of the yield stress measurements of the hair conditioners under study are shown in Figure 5.  
The yield stress test results (Figure 5) obtained for the evaluated hair conditioners correlate significantly with the results of dynamic viscosity measurements (Figure 5). Again, the type (burdock, black radish) and concentration (0.25; 0.5 and 1.0 wt%) of the plant-derived powders were found to have an impact on the yield stress of the emulsions. There was a clear tendency for an increase in yield stress with rising concentrations of plant-based powders, both derived from burdock and black radish. Incorporating burdock powder (0.25 wt%) into the formulations of hair conditioners caused an increase in yield stress relative to the reference formulation (with no added powder: HC_0) by as much as 43%. For black radish powder, the increase reached 25%. Hair conditioners containing 1.0 wt% of burdock powder (HC_3) and black radish powder (HC_6) were characterized by the highest yield stress of 295 Pa and 280 Pa, respectively. Also, the addition of burdock powder to the hair conditioners led to a slightly higher value of yield stress compared to  
Figure 4: Dynamic viscosity of analyzed hair conditioners.  
the results noted for the formulations containing black radish powder. Lower values of the test parameter obtained for cosmetic emulsions translate into a lighter consistency and potentially better product spreadability on the skin. Similar studies were also conducted by [PERSON] et al. (2020), who investigated facial masks containing _Lonicera caerulea_ Fruit Powder at various concentrations. The authors found that the formulation containing 0.9 wt% of blue honeyuckle powder, which had the lowest yield stress, was characterized by the best spreadability on the skin of all the facial masks tested. Also, in their study, [PERSON] et al. (2020) found a similar correlation between the yield stress results and viscosity results of the studied emulsions to the formulated hair conditioners. The highest yield stress was shown in the most viscous sample, with values declining in proportion to decreases in emulsion viscosity induced--in this case--by a modification in the oil phase.  
Summing up, the results of yield stress tests reveal that the proposed plant-derived powders added to hair conditioners affect the ease of dispensing products from the package and improve spreadability on the hair surface at concentrations as low as 0.25 wt%. Furthermore, incorporating plant-based powders into hair conditioners may potentially contribute to reducing the content of emulsifiers or rheology modifiers in such formulations.