Abstract
In this study, four strains of Lactobacillus casei, as viable cells or cell-free extracts (CFE), were added to elderberry juice in order to evaluate their effect on phenolic and aromatic profile. Two of them were able to grow in juice while the others showed zero-growth. The same strains were lysed and added as extracts in elderberry juice. Multivariate statistical analysis show a separation among samples containing growing cells, non-growing cells, CFE, highlighting the particularities of specific strains. Juices added with CFE presented the highest amount of esters. The strains showing growth phenotype cause an increase of phenyllactic acids. The highest concentration of volatile compounds, particularly of alcohols, terpenes and norisoprenoids (responsible for typical elderberry notes) was observed in samples with strains showing zero-growth. Moreover, a significant increase in anthocyanin content was observed in these samples, suggesting the possible use of Lactobacillus for increasing specific molecules, even for non-multiplying bacterial cell. Considering that this is the first study concerning the use of non-growing cells in fruit juice, the potential of strains is still to be explored and it may have a significant technological application in the development of a microbial collection useful for fruit juice industry.
Highlights
Lactic acid bacteria (LAB) fermentation is an ancient technology of bio-preservation that in the last decade has been extensively applied to vegetable and fruit to increase their consumption
Even if L. plantarum is the LAB species most used to ferment fruits (Rodríguez et al, 2009), a recent study reported that other species, as Lactobacillus casei and Lactobacillus rhamnosus, may be used in fermentation processes (Ricci et al, 2018)
In order to better highlight the differences among juices added with viable cells and cell-free extracts (CFE) we focused on variables that significantly differ among the samples, belonging to the most abundant classes of detected compounds which are alcohols and terpenes for the volatiles and anthocyanins and flavonol glycosides for polyphenols
Summary
Lactic acid bacteria (LAB) fermentation is an ancient technology of bio-preservation that in the last decade has been extensively applied to vegetable and fruit to increase their consumption. Even if L. plantarum is the LAB species most used to ferment fruits (Rodríguez et al, 2009), a recent study reported that other species, as Lactobacillus casei and Lactobacillus rhamnosus, may be used in fermentation processes (Ricci et al, 2018). These closely related species belonging to the Lactobacillus casei group and representing the most widely researched and applied probiotic species of lactobacilli (Hill et al, 2018). Fermentation of elderberry juice with dairy strains was found to be useful to enhance the typical aroma of elderberry (mainly linked to terpenes and alcohols), opening new opportunities in the selection of LAB for fruit fermentation (Ricci et al, 2018)
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