Abstracts

Global food industry trends are increasingly focused on the development of innovative functional products with added value, such as lactose-free and high-protein foods that offer specific health benefits to consumers. At the same time, growing consumer awareness of the environmental impact of food production, particularly animal-based raw materials, has encouraged manufacturers to explore the replacement of animal proteins with plant-based alternatives. This study investigated the application of pea protein isolate (PPI) to increase the protein content of lactose-free goat kefir by 25 and 35%. Control samples without added PPI included kefir with lactose (K) and lactose-free kefir (K1). The lactose-free samples enriched with PPI, designated as KG1 and KG2, showed an increase in protein content from 2.8 to 3.5% and 3.8%, respectively. The samples were analyzed for titratable acidity (°SH), pH, chemical composition, syneresis, texture and SDS–PAGE electrophoretic protein profile. The flow properties were determined by viscometry technique in the shear rate range 0 - 200 s-1. Sensory quality was evaluated by trained panelists using a five-point scale. The addition of PPI significantly increased the viscosity of KG1 and KG2 samples compared to control samples at all shear rates investigated, suggesting that these samples would remain stable during pumping and transportation, which is especially important as goat milk is characterized by a fragile gel texture. The hysteresis area increased in the following order: K1 < K < KG1 << KG2. Lactose removal reduced the hysteresis area by approximately 25%, indicating weaker structural resistance to shear. In contrast, the addition of pea protein isolates significantly increased the hysteresis area, with a 46% increase at the lower enrichment level (KG1) and a 160% increase at the higher enrichment level (KG2) compared to the lactose-free control, confirming the strong structure- forming effect of PPI. Texture analysis supported the viscometry results, as significantly higher viscosity index and consistency values were observed in the enriched samples. Syneresis levels in K1, KG1, and KG2 were similar. These findings indicate that enrichment of lactose-free goat kefir with pea protein isolate represents a promising strategy for the development of high-protein functional products with solid structural stability, without increasing syneresis, thereby meeting current consumer demands for both nutritional benefits and sustainable protein sources.

Keywords

Goat milk, Kefir, Pea protein, Sustainable protein source, Texture

Acknowledgment

This study was supported by contract number 451-03-137/2025-03/200116 to realize and finance scientific research in 2025, agreed between the Faculty of Agriculture, University of Belgrade and the Ministry of Science, Technological Development and Innovation of the Republic of Serbia.

References

1. 1. Akin, Z., Ozcan, T. (2017). Functional properties of fermented milk produced with plant proteins. Lwt, 86, 25-30.
2. 2. Arbach, C.T., Alves, I.A., Serafini, M.R., Stephani, R., Perrone, Í.T., de Carvalho da Costa, J. (2021). Recent patent applications in beverages enriched with plant proteins. Npj Science of Food, 5(1), 28.
3. 3. Dalgleish, D.G., van Mourik, L., Corredig, M. (1997). Heat-induced interactions of whey proteins and casein micelles with different concentrations of α-lactalbumin and β-lactoglobulin. Journal of Agricultural and Food Chemistry, 45(12), 4806-4813.
4. 4. Gul, O., Atalar, I., Mortas, M., Dervisoglu, M. (2018). Rheological, textural, colour and sensorial properties of kefir produced with buffalo milk using kefir grains and starter culture: A comparison with cows’ milk kefir. International Journal of Dairy Technology, 71, 73-80. Guyomarc’h, F., Law, A.J.R., Dalgleish, D.G. (2003). Formation of soluble and micelle-bound protein aggregates in heated milk. Journal of Agricultural and Food Chemistry, 51(16), 4652- 4660.
5. 5. Hassoun, A., Bekhit, A.E.D., Jambrak, A.R., Regenstein, J.M., Chemat, F., Morton, J.D., Gudjónsdóttir, M., Carpena, M., Prieto, M.A., Varela, P. (2024). The fourth industrial revolution in the food industry - part II: Emerging food trends. Critical Reviews in Food Science and Nutrition, 64(2), 407-437.
6. 6. Hertzler, S.R., Lieblein-Boff, J.C., Weiler, M., Allgeier, C. (2020). Plant proteins: assessing their nutritional quality and effects on health and physical function. Nutrients, 12(12), 3704.
7. 7. Hovjecki, M., Miloradovic, Z., Mirkovic, N., Radulovic, A., Pudja, P., Miocinovic, J. (2021). Rheological and textural properties of goat’s milk set‐type yoghurt as affected by heat treatment, transglutaminase addition and storage. Journal of the Science of Food and Agriculture, 101(14), 5898-5906.
8. 8. Hovjecki, M., Radovanovic, M., Levic, S.M., Keskic, T., Petricevic, M., Nedovic, V.A., Miocinovic, J. (2025). From waste to worth: almond cake flour as a functional ingredient in goat milk yogurt. European Food Research and Technology, 1-15.
9. 9. Hovjecki, M., Radovanovic, M., Miloradovic, Z., Jurina, I.B., Mirkovic, M., Ignjatovic, I.S., Miocinovic, J. (2023). Fortification of goat milk yogurt with goat whey protein concentrate– Effect on rheological, textural, sensory and microstructural properties. Food Bioscience, 56, 103393.
10. 10. Klost, M., Drusch, S. (2019). Structure formation and rheological properties of pea protein-based gels. Food Hydrocolloids, 94, 622-630.
11. 11. Laemli, U.K. (1970). Cleavage of Structural Proteins during the Assembly of the Head of Bacteriophage T4. Nature, 227(5259), 680-685. doi: 10.1038/227680a0 Li, A., Zheng, J., Han, X., Yang, S., Cheng, S., Zhao, J., Zhou, W., Lu, Y. (2023). Advances in low- lactose/lactose-free dairy products and their production. Foods, 12(13), 2553.
12. 12. Li, H., Tu, M., Wu, Z., Zeng, X., Wu, J., Pan, D., Du, Q. (2025). Comparison of gelation of legume protein and milk protein fermented by mixed starter cultures: Texture, rheological properties and protein structure. Food Chemistry: X, 102576.
13. 13. Medawar, E., Huhn, S., Villringer, A., Veronica Witte, A. (2019). The effects of plant-based diets on the body and the brain: a systematic review. Translational Psychiatry, 9(1), 226.
14. 14. Mession, J.L., Chihi, M.L., Sok, N., Saurel, R. (2015). Effect of globular pea proteins fractionation on their heat-induced aggregation and acid cold-set gelation. Food Hydrocolloids, 46, 233-243.
15. 15. Señorans, F.J., Ibáñez, E., Cifuentes, A. (2003). New trends in food processing. Critical Reviews in Food Science and Nutrition, 43(5), 507-526.
16. 16. Setyawardani, T., Sumarmono, J., Widayaka, K. (2020). Physical and microstructural characteristics of kefir made of milk and colostrum. Buletin Peternakan, 44(1), 43-49.
17. 17. Shand, P. J., Ya, H., Pietrasik, Z., Wanasundara, P. (2007). Physicochemical and textural properties of heat-induced pea protein isolate gels. Food Chemistry, 102(4), 1119-1130.
18. 18. Silva, T.H.B., Baptista, D.P., de Paiva e Silva, K.K., Marfil, P.H.M., Gigante, M.L. (2024). Hybrid high-protein yogurt is made with partial replacement of milk proteins by pea proteins. International Journal of Food Science and Technology, 59(11), 8806-8815.
19. 19. Tan, M., Nawaz, M.A., Buckow, R. (2023). Functional and food application of plant proteins-a review. Food Reviews International, 39(5), 2428-2456. The jamovi project (2024). Jamovi v.2.5 [Computer software]. www.jamovi.org Ünal, Gü., Akalin, A.S. (2013). Influence of fortification with sodium–calcium caseinate and whey protein concentrate on microbiological, textural and sensory properties of set‐type yoghurt. International Journal of Dairy Technology, 66(2), 264-272.
20. 20. Wang, X., Kristo, E., LaPointe, G. (2019). The effect of apple pomace on the texture, rheology and microstructure of set type yogurt. Food Hydrocolloids, 91, 83-91. doi: 10.1016/j.foodhyd.2019.01.004