Development and Evaluation of a Fermented Pistachio-Based Beverage Obtained by Colloidal Mill

The aim of the present study was to develop a fermented pistachio beverage as a plant-based alternative to milk-based drinks. For this purpose, a colloidal mill was used to finely grind and homogenize the pistachios to obtain a homogeneous consistency and prevent sedimentation. In addition, lactic acid bacteria fermentation was used to develop unique flavours and characteristics in the final product and to achieve microbiological stability for up to 30 days of storage a 4 °C. The formulated beverages were evaluated for chemical-physical characteristics (pH, organic acid production, and fructose, sucrose, and glucose content), nutritional profile (proximate composition, amino acid and GABA content), and volatile organic composition by HS-SPME-GC/MS analysis. The pistachio-based beverages were characterized by a good source of protein, fat, fiber, and minerals (mainly K and P). The colloidal mill contributed to creating a homogeneous texture and to making the nutrients readily available to the starter microorganisms, which reached concentrations above 108 ufc/mL in the final products. The beverages were characterized by pronounced acidity and some by the presence of acetoin and 2,3-butanedione, volatile components associated with a yogurt- or kefir-like aroma. This innovative approach provides an alternative to traditional milk-based beverages and highlights the role of LAB in the development of nutritious and attractive plant-based beverages.

Utilization of plant derived lactic acid bacteria for efficient bioconversion of brewers' spent grain into acetoin

Brewers' spent grain (BSG) is a major side-stream from the beer industry, with an annual estimated production of 39 million tons worldwide. Due to its high nutritional value, high abundance and low price, it has been proposed as an ingredient in human food. Here we investigated the ability of different lactic acid bacteria to produce the flavor molecule acetoin in liquid BSG extract, in order to broaden the possibilities of utilization of BSG in human food. All the investigated lactic acid bacteria (LAB) covering the Leuconostoc, Lactobacillus and Lactoccocus species were able to convert the fermentable sugars in liquid BSG into acetoin. Production levels varied significantly between the different LAB species, with Leuconostoc pseudomesenteroides species reaching the highest titers of acetoin with only acetate as the main byproduct, while also being the fastest consumer of the fermentable sugars present in liquid BSG. Surprisingly, the currently best investigated LAB for acetoin production, L. lactis, was unable to consume the maltose fraction of liquid BSG and was therefore deemed unfit for full conversion of the sugars in BSG into acetoin. The production of acetoin in Leu. pseudomesenteroides was pH dependent as previously observed in other LAB, and the conversion of BSG into acetoin was scalable from shake flasks to 1 L bioreactors. While all investigated LAB species produced acetoin under aerobic conditions, Leu. pseudomesenteroides was found to be an efficient and scalable organism for bioconversion of liquid BSG into a safe acetoin rich food additive.

Insight into the Influence of Lactic Acid Bacteria Fermentation on the Variations in Flavor of Chickpea Milk

This study aimed to evaluate the influence of fermentation on the levels of free amino acids (FAAs) and variations of volatile odorants in four groups of chickpea milk. Electronic nose (E-nose) and gas chromatography–mass spectrometry (GC-MS) data were subjected to mutual validation. W2S and W3S sensors of E-nose were sensitive to volatile constituents in the four groups of unfermented and fermented specimens. After fermentation, the levels of FAAs in the four groups of specimens decreased to varying degrees. Additionally, there were remarkable differences in the types and contents of volatile odor substances in all specimens before and after fermentation. The principal component analysis findings based on E-nose identified the changes of volatile odorants in all specimens before and after fermentation. GC-MS identified 35 and 55 volatile flavor substances in unfermented and fermented specimens, respectively. The varieties of volatile odor substances in fermented chickpea milk (FCM) with papain treatment plus yam addition (38) were more than those in FCM (24), indicating that the coupled treatment of enzymolysis and yam addition could enrich the volatile odorants in fermented specimens. After probiotic fermentation, the contents of off-flavor substances decreased to a certain extent, and key aroma substances such as 2,3-pentanedione, 2,3-butanedione, and heptyl formate were detected. These results demonstrated that lactic acid bacterial fermentation on the basis of enzymolysis and yam addition could be utilized as a feasible approach to improve the flavor of plant-based products adopting chickpea as the original ingredient.

Dynamic co-culture metabolic models reveal the fermentation dynamics, metabolic capacities and interplays of cheese starter cultures

In this study, we have investigated the cheese starter culture as a microbial community through a question: can the metabolic behaviour of a co-culture be explained by the characterized individual organism that constituted the co-culture? To address this question, the dairy-origin lactic acid bacteria Lactococcus lactis subsp. cremoris, Lactococcus lactis subsp. lactis, Streptococcus thermophilus and Leuconostoc mesenteroides, commonly used in cheese starter cultures, were grown in pure and four different co-cultures. We used a dynamic metabolic modelling approach based on the integration of the genome-scale metabolic networks of the involved organisms to simulate the co-cultures. The strain-specific kinetic parameters of dynamic models were estimated using the pure culture experiments and they were subsequently applied to co-culture models. Biomass, carbon source, lactic acid and most of the amino acid concentration profiles simulated by the co-culture models fit closely to the experimental results and the co-culture models explained the mechanisms behind the dynamic microbial abundance. We then applied the co-culture models to estimate further information on the co-cultures that could not be obtained by the experimental method used. This includes estimation of the profile of various metabolites in the co-culture medium such as flavour compounds produced and the individual organism level metabolic exchange flux profiles, which revealed the potential metabolic interactions between organisms in the co-cultures.

A genome-scale metabolic network of the aroma bacterium Leuconostoc mesenteroides subsp. cremoris

Leuconostoc mesenteroides subsp. cremoris is an obligate heterolactic fermentative lactic acid bacterium that is mostly used in industrial dairy fermentations. The phosphoketolase pathway (PKP) is a unique feature of the obligate heterolactic fermentation, which leads to the production of lactate, ethanol, and/or acetate, and the final product profile of PKP highly depends on the energetics and redox state of the organism. Another characteristic of the L. mesenteroides subsp. cremoris is the production of aroma compounds in dairy fermentation, such as in cheese production, through the utilization of citrate. Considering its importance in dairy fermentation, a detailed metabolic characterization of the organism is necessary for its more efficient use in the industry. To this aim, a genome-scale metabolic model of dairy-origin L. mesenteroides subsp. cremoris ATCC 19254 (iLM.c559) was reconstructed to explain the energetics and redox state mechanisms of the organism in full detail. The model includes 559 genes governing 1088 reactions between 1129 metabolites, and the reactions cover citrate utilization and citrate-related flavor metabolism. The model was validated by simulating co-metabolism of glucose and citrate and comparing the in silico results to our experimental results. Model simulations further showed that, in co-metabolism of citrate and glucose, no flavor compounds were produced when citrate could stimulate the formation of biomass. Significant amounts of flavor metabolites (e.g., diacetyl and acetoin) were only produced when citrate could not enhance growth, which suggests that flavor formation only occurs under carbon and ATP excess. The effects of aerobic conditions and different carbon sources on product profiles and growth were also investigated using the reconstructed model. The analyses provided further insights for the growth stimulation and flavor formation mechanisms of the organism.

Response of Leuconostoc strains against technological stress factors: Growth performance and volatile profiles

The ability of twelve strains belonging to three Leuconostoc species (Leuconostoc mesenteroides, Leuconostoc lactis and Leuconostoc pseudomesenteroides) to grow under diverse sub-lethal technological stress conditions (cold, acidic, alkaline and osmotic) was evaluated in MRS broth. Two strains, Leuconostoc lactis Ln N6 and Leuconostoc mesenteroides Ln MB7, were selected based on their growth under sub-lethal conditions, and volatile profiles in RSM (reconstituted skim milk) at optimal and under stress conditions were analyzed. Growth rates under sub-lethal conditions were strain- and not species-dependent. Volatilomes obtained from the two strains studied were rather diverse. Particularly, Ln N6 (Ln. lactis) produced more ethanol and acetic acid than Ln MB7 (Ln. mesenteroides) and higher amounts and diversity of the rest of volatile compounds as well, at all times of incubation. For the two strains studied, most of stress conditions applied diminished the amounts of ethanol and acetic acid produced and the diversity and levels of the rest of volatile compounds. These results were consequence of the different capacity of the strains to grow under each stress condition tested.

Sensorically and antimicrobially active metabolite production of Lactobacillus strains on Jerusalem artichoke juice

BACKGROUND

In the tubers of Jerusalem artichoke (Helianthus tuberosus L.) the main carbohydrate is the well-known prebiotic inulin, which is a good growth substrate for gut microorganisms. Jerusalem artichoke tuber is traditionally consumed boiled or pickled rather than in fermented form. Lactic acid bacteria are traditionally used in the production of fermented foods; nevertheless their behavior and metabolite production are considerably influenced by the substrate. The purpose of this study was to investigate the growth and production of the most important sensorically and antimicrobially active metabolites of different Lactobacillus strains on Jerusalem artichoke juice.

RESULTS

All investigated strains grew well (in the range 10(9) cfu mL(-1) ) in the media. The organic acids (lactic acid, 110-337 mmol L(-1) ; acetic acid, 0-180 mmol L(-1) ; and succinic acid, 0-79 mmol L(-1) ), hydrogen peroxide (0.25-1.77 mg L(-1) ), mannitol (0.06-3.24 g L(-1) ), acetoin and diacetyl production of strains varies not only according to the species but also from strain to strain, which will be demonstrated and discussed in the paper.

CONCLUSION

Our results showed that lactobacilli can be used for the fermentation of Jerusalem artichoke, which in this form could be used, alone or mixed with other raw food material, as a new synbiotic functional food.

The ‘buttery’ attribute of wine—diacetyl—desirability, spoilage and beyond

The diketone, diacetyl, is a major flavour metabolite produced by lactic acid bacteria (LAB). Of the LAB associated with wine, Oenococcus oeni is encouraged during the malolactic (ML) fermentation, a biodeacidification of wine during which the metabolism of diacetyl occurs. Diacetyl, which imparts a buttery aroma and flavour to many fermented foods and beverages, is a key flavour compound of most fermented dairy products. In wine, diacetyl has important stylistic implications. The biosynthesis of diacetyl is dependent upon citric acid metabolism and diacetyl is an intermediate metabolite which can be further reduced to acetoin and the alcohol, 2,3-butanediol. This review will focus on the sensory perception, metabolism, genetics and analysis of diacetyl during wine production. The extensive knowledge of diacetyl metabolism in dairy LAB is used to enhance the understanding of diacetyl metabolism of wine LAB. Factors which can effect the formation and concentration of diacetyl in wine are discussed. These include malolactic bacterial strain, wine chemical and physical parameters (pH, temperature, citric acid, sulfur dioxide, aeration) and the presence of yeast lees. Finally, the affects of other wine components, such as phenolics, are discussed.

Effect of the metabolism of urea on the acidifying activity of Streptococcus thermophilus

One of the main functions of Streptococcus thermophilus strains used in the dairy industry is the production of lactic acid. In cheese and fermented milk manufacturing processes, the pH evolution kinetics must be reproducible in order to ensure the good quality of the final products. The objective of the present study was to investigate the effect of the metabolism of urea on the acidifying activity of fast- and slow-acidifying strains of S. thermophilus. Milk treatment with a purified urease and utilization of the urease inhibitor flurofamide revealed that urea metabolism by S. thermophilus influences the pH evolution kinetics through 2 distinct means. First, ammonia production from urea tends to increase the pH. This effect is greater when lactic acid concentration is low due to a lower buffering capacity of milk. Second, urea metabolism also modifies growth and lactic acid production by S. thermophilus. Depending on the strains and the growth stage of the cultures, consumption of urea induces either a faster or a slower pH decrease. For the slow-acidifying strain RD678, suppression of urea metabolism by adding flurofamide decreased the time necessary to reach pH 6 by 195 min. This effect was less pronounced for the 2 fast-acidifying strains RD674 and RD677. These results show that urea metabolism may have a considerable influence on the acidifying properties of S. thermophilus strains.

Characterization of lactic acid bacteria strains on the basis of neutral volatile compounds produced in whey

AIMS

Seventy-eight strains of lactic acid bacteria belonging to five genera and showing six different phenotype combinations of Lac (lactose fermentation), Prt (proteolytic activity) and Cit (citrate degradation) characters were investigated for their main flavouring properties with the aim to detect variability among and within the groups.

METHODS AND RESULTS

High resolution gas chromatography-mass spectrometry analysis of neutral volatile compounds produced in whey showed that, considering both neo-formation compounds and substances quantified in the whey cultures at different concentrations in comparison to the extract from sterile whey, the groups of lactococci, enterococci, thermophilic streptococci and mesophilic lactobacilli produced a higher number of volatiles than thermophilic lactobacilli and leuconostocs. Applying principal component analysis (PCA) to the results, enterococci, mesophilic lactobacilli and thermophilic streptococci showed a broad diversity, while lactococci included rather similar strains as well as strains with special flavouring properties. Applying PCA to thermophilic streptococci and enterococci, to lactococci and enterococci, to lactococci and thermophilic streptococci, or to mesophilic and thermophilic lactobacilli, the strains gathered consistently with their systematic position.

CONCLUSION

The study evidenced strains producing some volatile compounds responsible for food flavouring. Flavouring properties were variable among the systematic groups and in some cases different within the same bacterial group.

SIGNIFICANCE AND IMPACT OF THE STUDY

The potential of the findings is discussed with reference to the development of flavouring adjuncts for the dairy industry.

Diacetyl and alpha-acetolactate overproduction by Lactococcus lactis subsp. lactis biovar diacetylactis mutants that are deficient in alpha-acetolactate decarboxylase and have a low lactate dehydrogenase activity

Lactococcus lactis subsp. lactis biovar diacetylactis strains are utilized in several industrial processes for producing the flavoring compound diacetyl or its precursor alpha-acetolactate. Using random mutagenesis with nitrosoguanidine, we selected mutants that were deficient in alpha-acetolactate decarboxylase and had low lactate dehydrogenase activity. The mutants produced large amounts of alpha-acetolactate in anaerobic milk cultures but not in aerobic cultures, except when the medium was supplemented with catalase, yeast extract, or hemoglobin.