Formulation and evaluation of probiotic starter culture: impact on Ethiopian cottage cheese "Ayib" safety, stability, sensory acceptability and antioxidant potential.

Abstract

Background: Ayib is a traditionally processed dairy product in Ethiopia that demonstrates significant variability in shelf life, sensory attributes, and safety, primarily own to the spontaneous fermentation of milk and differing household practices. This study aimed to develop mixed probiotic starter cultures from top seven previously isolated lactic acid bacteria to achieve a synergistic effect on sensory qualities consistent, enhanced safety, extended storage stability, and antioxidant potential.

Methods: Nine mixed starter cultures were formulated using seven lactic acid strains that are known for their superior fermentation and probiotic capabilities. Pasteurized milk was inoculated with 5% of each starter culture and incubated at 37 ± 2 °C for 8 h. Fermented milk was then defatted by shaking at 100 rpm for 1 h. Following fat removal, buttermilk was heated to 50-60 °C for 40-50 min to facilitate curd (Ayib) formation. After cooling, the curd was separated from whey. A 200-g portion of the curd was wrapped in sterile cheesecloth and immersed in pasteurized whey inoculated with 8 log CFU/mL of the formulated starter cultures for 30 min before being re-drained for 1 h.

Results: The physicochemical properties, consumer acceptability, and storage stability of the resulting products were evaluated, revealing total solids ranging from 20.67 to 22.89%, pH values between 3.89 and 4.49, and titratable acidity ranging from 0.63 to 0.93%. Sensory evaluation, conducted using a five-point hedonic scale, showed overall acceptability scores ranging from 3.31 for Ayib treated with (F9) to 4.03 for Ayib treated with (F2). Remarkably, the storage stability of the treated Ayib was enhanced by 2-9 times compared to the control sample. The antioxidant analysis demonstrated that among the isolates, the Lactobacillus curvatus (NZ-44) exhibited the highest individual antioxidant activity of 57.77%. Furthermore, the formulated mixtures, particularly (F6), displayed synergistically enhanced antioxidant activity of 99.27%.

Conclusions: These findings suggest that lactic acid bacteria strains can improve the nutritional value, safety, and storage stability of fermented dairy products, such as Ayib, with potential applications in both the food and pharmaceutical industries.