Electronic Nose for Monitoring Odor Changes of Lactobacillus Species during Milk Fermentation and Rapid Selection of Probiotic Candidates.

Zoltan Kovacs,Zsanett Bodor,Timea Kaszab,Csilla Mohácsi-Farkas,Tamás Tóth,George Bazar,John-Lewis Zinia Zaukuu

doi:10.3390/foods9111539

Zoltan Kovacs, Zsanett Bodor + Show 5 more

Open Access

https://doi.org/10.3390/foods9111539

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Abstract

Probiotic bacteria have been associated with a unique production of aroma compounds in fermented foods but rapid methods for discriminating between foods containing probiotic, moderately probiotic, or non-probiotic bacteria remain aloof. An electronic nose (e-nose) is a high-sensitivity instrument capable of non-invasive volatile measurements of foods. In our study, we applied the e-nose to differentiate probiotic, moderately probiotic, and non-probiotic Lactobacillus bacteria strains at different fermentation time points (0th, 4th, and 11th) of milk fermentation. The pH of the changing milk medium was monitored with their corresponding increase in microbial cell counts. An e-nose with two gas chromatographic columns was used to develop classification models for the different bacteria groups and time points and to monitor the formation of the aromatic compounds during the fermentation process. Results of the e-nose showed good classification accuracy of the different bacteria groups at the 0th (74.44% for column 1 and 82.78% for column 2), the 4th (89.44% for column 1 and 92.22% for column 2), and the 11th (81.67% for column 1 and 81.67% for column 2) hour of fermentation. The loading vectors of the classification models showed the importance of some specific aroma compounds formed during the fermentation. Results show that aroma monitoring of the fermentation process with the e-nose is a promising and reliable analytical method for the rapid classification of bacteria strains according to their probiotic activity and for the monitoring of aroma changes during the fermentation process.

Highlights

Milk is an important dairy product from mammalian sources such as cows, goats, buffalo, or sheep.Its fermented form has yielded many different foods in the dairy industry such as ice cream, cheese, yogurt, etc
Fifteen different types of Lactobacillus bacteria strains were acquired in a freeze-dried state from reputable sources and separately used to produce fermented milk products based on their probiotic grouping
The general decrease in the pH of all the different bacteria groups can be attributed to the production of lactic acid but the variation in the curves could be due to the different lactic acid-producing activities of the different strains

Summary

Introduction

Milk is an important dairy product from mammalian sources such as cows, goats, buffalo, or sheep. Its fermented form has yielded many different foods in the dairy industry such as ice cream, cheese, yogurt, etc. Fermentation of milk into food products is often associated with starter cultures such as Streptococcus thermophilus and Lactobacillus delbrueckii subsp. Lactobacilli are gram-positive bacteria consisting of both anaerobic and aerobic species. The main product of their fermentation is lactic acid but secondary products are generated as diacetyl, acetoin, and acetone [2]. Lactobacillus strains have significant industrial importance due to their fermentation activity and health benefits

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