Quality attributes and shelf life of goat´s milk kefir

Citation (APA 7)

Ayed, M. (2024). Quality attributes and shelf life of goat’s milk kefir [Master’s thesis, Instituto Politécnico de Bragança]. IPB Repository: http://hdl.handle.net/10198/30718.

Abstract

For centuries, traditional fermented foods have been highly valued for their unique organoleptic properties and relatively long shelf life. They are produced from various sources, particularly milk and meat. Kefir is an example of a beneficial fermented food, known worldwide for its importance in human nutrition. Kefir is a viscous, foamy liquid that resembles thick cream, characterized by its slightly gaseous, sour taste and low alcohol content. It is obtained through the fermentation of goat’s, cow’s, or sheep’s milk using kefir grains. These grains are a symbiotic culture of yeasts and bacteria encased in a matrix of polysaccharides. This study focuses on the processing of plain and flavored kefir made from goat’s milk and their shelf life, as determined by the evolution of their microbiological, textural, and technological quality attributes. The aim of this work is to (1) determine the shelf life of goat’s milk kefir by monitoring the evolution of its physicochemical, textural, and microbiological properties, and (2) assess a bio-preservation method for extending its shelf life. All work was carried out in the Laboratory of Bacteriology of CIMO Research Centre at the Polytechnic Institute of Bragança (IPB). The research involved the production of plain goat’s milk kefir through several steps, including weighing, incubating kefir grains in goat’s milk, and filtering the mixture. The samples were then stored at 4°C. A full characterization of the control kefir was conducted using various physicochemical, textural, and microbiological tests at specific storage intervals to determine the optimum combination of percentage, time, and temperature. Subsequently, plain (Control) and flavored (Treatment) goat’s milk kefir were prepared. The shelf life of kefir was evaluated using statistical modeling at appropriate storage intervals for the different analyses. Sensory analysis was also conducted on control and flavored kefir samples. Finally, the data collected was modelled. This study has demonstrated the unequal influence of several factors—milk type, kefir grains, temperature, incubation time, grains/milk ratio, and kefir aromatization—on the final quality attributes of kefir. Consequently, kefir production must be highly selective in terms of milk and grain types, while also implementing strict controls on incubation parameters throughout the manufacturing process. Adherence to necessary hygiene practices and compliance with national and international food standards are essential. Additionally, consumers should be informed of kefir’s final composition to avoid any risk of intolerance.