Abstract
The current study aimed to explore the performance of a probiotic Lactobacillus strain as an adjunct culture in yogurt production and to assess Fourier transform infrared spectroscopy as a rapid, noninvasive analytical technique to evaluate the quality and the shelf life of yogurt during storage. In this respect, bovine milk (full-fat) was inoculated with the typical yogurt starter culture without (control case) or with the further addition of Lactobacillus plantarum T571 as an adjunct (probiotic case). The milk was also inoculated with a cocktail mixture of three strains of Listeria monocytogenes in two different initial levels of inoculum, and the fermentation process was followed. Accordingly, yogurt samples were stored at 4 and 12°C, and microbiological, physicochemical, molecular, and sensory analyses were performed during storage. Results showed that the lactic acid bacteria exceeded 7 log CFU/g during storage in all samples, where the probiotic samples displayed higher acidity, lower pH, and reduced counts of Lb. monocytogenes in a shorter period than the control ones at both temperatures. Pulsed-field gel electrophoresis verified the presence of the probiotic strain until the end of storage at both temperatures and in adequate amounts, whereas the survival and the distribution of Listeria strains depended on the case. The sensory evaluation showed that the probiotic samples had desirable organoleptic characteristics, similar to the control. Finally, the spectral data collected from the yogurt samples during storage were correlated with microbiological counts and sensory data. Partial least squares and support vector machine regression and classification models were developed to provide quantitative estimations of yogurt microbiological counts and qualitative estimations of their sensory status, respectively, based on Fourier transform infrared fingerprints. The developed models exhibited satisfactory performance, and the acquired results were promising for the rapid estimation of the microbiological counts and sensory status of yogurt.
Highlights
For almost three decades the popularity of the probiotic concept and the awareness about the health benefits of consuming probiotic products continue to increase, and high demand for fermented dairy products fortified with probiotic microorganisms is still arising (Saad et al, 2013; Casarotti et al, 2014)
The current study aimed to evaluate the performance of Lb. plantarum T571 strain with probiotic potential, as adjunct culture in yogurt production and storage, and its effect on safety regarding the survival of Lb. monocytogenes
No yeasts/molds were detected after enumeration in the current study, and it should be noted that all the noninoculated yogurt samples remained Listeria-free throughout storage at all cases, as no cells were detected after applying the enrichment method
Summary
For almost three decades the popularity of the probiotic concept and the awareness about the health benefits of consuming probiotic products continue to increase, and high demand for fermented dairy products fortified with probiotic microorganisms is still arising (Saad et al, 2013; Casarotti et al, 2014). Tolerans ACADC 4037) in fermentation and storage of traditional Greek settype yogurt, whereas Saxami et al (2016) studied two lactobacilli strains (Lactobacillus pentosus B281 and Lb. plantarum B282, previously isolated from naturally fermented table olives) in mono and mixed cultures, in the production of probiotic yogurt. In both studies, results confirmed that these strains could be promising candidates for inclusion as adjuncts cultures to manufacture yogurt with potential probiotic properties
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