Thesis:

The effect of hazelnut powder on the physical, chemical and sensory properties of probiotic yogurt

Hazelnut is one of the most important nuts worldwide due to its pleasant taste, fat-soluble bioactive compounds, considerable amount of dietary fiber, phenolic and phytochemical compounds, nutritional value including rich types of monounsaturated fats and vitamins, and high mineral content. Nowadays, consumers believe that their health is directly related to the foods they consume; therefore, functional foods are increasingly demanded by health-conscious individuals. Food production methods have also changed significantly to meet consumer expectations. One of the approaches to develop functional foods is to incorporate ingredients containing bioactive peptides, phytochemicals, omega-3 unsaturated fatty acids, dietary fibers, probiotics, and prebiotics during production. Yogurt is a popular dairy product whose production and consumption continue to rise globally. The aim of the present study was to evaluate yogurts enriched with different proportions of hazelnut powder (3%, 6%, and 9%) in terms of physicochemical, microbiological, and sensory properties during refrigerated storage. The addition of hazelnut powder and storage time significantly affected the overall quality characteristics of yogurt. The highest pH value was observed in the 6% treatment on the first day, while the lowest was found in the control and 6% samples with a value of 3.8. Over time, the acidity level increased in almost all treatments. The highest acidity was recorded in the control on day 28, while the lowest was in the 9% treatment on day 1. As storage progressed, the dry matter content increased in almost all treatments, with the highest value in the 9% sample on day 28 and the lowest in the control on day 1. Conversely, consistency decreased over time, with the highest value in the 6% treatment on day 1 and the lowest in the control on day 28. In general, significant differences were found among treatments regarding syneresis and fat content, as well as between different storage times within each treatment. However, enrichment with hazelnut powder improved the water-holding capacity (WHC) of the final product, and this effect increased with higher hazelnut powder levels. Overall, texture parameters and apparent viscosity values were lower. Microbiological analyses showed that during 21 days of storage, there was a significant difference (p<0.05) between control and enriched samples in the counts of Lactobacillus casei and Lactobacillus acidophilus, while no significant difference (p>0.05) was found for mold and yeast. Additionally, the sensory characteristics of enriched yogurts were similar to those of the control, which is promising for consumer acceptance. The addition of hazelnut powder led to firmer, thicker, and less viscous yogurts with improved flow properties. These findings indicate that hazelnut powder enrichment can effectively enhance the functional, structural, and microbiological quality of nut-based yogurt.

Keywords: Hazelnut powder, Synergy, Lactobacillus casei and Lactobacillus acidophilus, Nut yogur.