Aiello, Alessandra (2022) Functional and biotechnological use of lactobacilli as producers of butyric and pyroglutamic acid in milk and fermented milk. [Tesi di dottorato]

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Abstract

Butyric and pyroglutamic acid (pGlu) are two small compounds with several beneficial effects on human health. In particular, pyroglutamic acid has antimicrobial, antitumoral, mitogenic, anxiolytic and anti-diabetic activity. Butyric acid is, instead, one of the most studied short-chain fatty acids and is known for its anti-inflammatory properties. Recent studies have also shown that butyric acid could be used to manage critical illnesses related to Coronavirus disease 2019. Commercially, butyric acid is produced using a chemical route starting from crude oil as the raw material. As far as pyroglutamic acid is concerned, it is present both in ripened cheeses and in fermented beverages. It is formed during fermentation carried out by thermophilic lactobacilli used as starters. The production of butyric acid from a biological origin, in spite of the significant demand for food and pharmaceutical applications, is still a complex process hard to control. Several efforts have been made to make butyric acid and pGlu production economically feasible, by using abundant/inexpensive raw materials coupled with highly efficient fermentation strategies. Nevertheless, all developed protocols are, especially for butyric acid, essentially based on the use of Clostridium species and this prevents the application in the food industry. Currently, very few searches are focused on non-Clostridial genera. In such light, the aim of this PhD thesis was to explore the ability to produce butyric and pyroglutamic acid by commercial probiotic strains as well as of lactic acid bacteria (LAB) cultures isolated from foodstuffs and belonging to different cultures collections. The goal was the definition of functional and biotechnological use of some bacterial strains interesting for the food industry. Production has been evaluated in synthetic media with lipids- and/or polysaccharides-added, in milk and fermented milk to understand the optimal conditions for metabolites production. As for butyric acid, it was found that Lb.plantarum strains surprisingly produced butyric acid only when there was a lipid and non-oligosaccharide source in the medium. It is known that Lb. plantarum possesses strain-specific intracellular lipases and esterases able to hydrolyse esters containing C4 to C6 fatty acids, such as those occurring in the milk fat. Fiber may not affect the butyrogenic activity of LAB also in yoghurt. As regards pyroglutamic acid, however, yoghurt, kefir and other probiotic fermented milk contained it ranging from 51.65 to 277.37mg/100g d.m. as a function of the thermophilic lactic acid bacteria used as starter cultures. In the yoghurt production process, pyroglutamic acid was constant during the fermentation phase and increased during the storage phase. Moreover, the production of pyroglutamic acid increased when glutamine, used as a precursor, was added to the substrate. The scientific results of the present project led to a deeper understanding of the metabolic versatility of LABs.

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