As part of this thesis, we developed and optimized the composition of two creams intended for the care of acne-prone skin and systematically examined the influence of three cosmetic active ingredients (allantoin, bisabolol, and vitamin B3) as well as hydrolysed silk, wheat, and oat proteins on the organoleptic properties, pH, and rheological characteristics of the formulations. The formulations were evaluated immediately after preparation and after one month of storage at room temperature. In preliminary testing, we assessed a broader range of concentrations for the selected cosmetic active ingredients, namely allantoin (0.5%, 1%, 2%), bisabolol (0.1%, 0.3%, 0.5%), and vitamin B3 (3%, 4%, 5%). For the hydrolysed proteins, the concentrations applied were as follows: silk proteins – 10%, wheat proteins – 2.5%, and oat proteins – 2.5%. Based on these results, two basic formulations were selected for further optimization: formulation B (0.5% allantoin, 0.5% bisabolol, 5% vitamin B3) and formulation C (1% allantoin, 0.5% bisabolol, 5% vitamin B3), where the influence of adding both respective types of hydrolyzed protein to each of the formulations was also assessed. All creams exhibited the desired pseudoplastic rheological characteristics and maintained a stable pH within the range of 4.5–5.5, which is suitable for skin application. The added concentrations of hydrolysed proteins influenced viscosity levels and their variation over time, with differences observed between respective protein types. The most pronounced viscosity level reduction was observed in formulations containing silk proteins, whereas creams with hydrolysed oat proteins demonstrated the most stable rheological behaviour. The organoleptic assessment process during storage revealed that the appearance of the creams varied depending on the type of protein added. The most noticeable change was observed in formulations containing silk proteins, where after one month, a browning coloration was developed. On the other hand, formulations with oat proteins maintained their unchanged appearance. In conclusion, hydrolysed oat proteins proved to be the most suitable choice from among formulations containing proteins, particularly those in formulation B with 5 % vitamin B3, where the most optimal combination of physical and chemical stability as well as desirable sensory properties was achieved.
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