Effect of Fermentation on the Microbial and Nutrient Composition of Digue: A Fermented Food Obtained with Pumpkin (Cucurbita maxima) and Peanut (Arachis hypogaea)

The aim of this work was to study the evolution of microbiological and selected physicochemical parameters during the production of Digue, food obtained from the addition of the paste of roasted Arachis hypogaea (peanuts) in Yam Digue, fermented juice of Cucurbita maxima (pumpkin). The evolution of the microbial flora, the content of reducing sugars, total polyphenols, phosphorus, potassium and titratable acidity were measured during 30 days. Microbiological analysis at the start of fermentation revealed the presence of 03 groups of pathogenic germs such as staphylococci, enterobacteria and moulds with concentrations of 3.2, 3.8 and 3.24 Log10CFU/ml respectively. We also observed the presence of lactic acid bacteria (LAB) which were are the most represented bacterial flora in the medium with a microbial load of 5.2Log10CFU/ml. During fermentation, enterobacteria, staphylococci and moulds respectively reached maximum values ​​of 3.2, 3.8 and 3.2log10CFU/ml on the 7th day. However, after the 21st day, enterobacteria and mould were eliminated, unlike staphylococci which were completely inhibited only on the 28th day. The highest phosphorus and potassium contents were recorded on the 21st day with values ​​of 0.29% and 2.5% respectively. On the 14th day, the LAB yielded much higher microbial concentration of 8.9Log10CFU/ml which also led to the optimum production of titratable acidity (1.2%) in the medium. During the same period, the sugar content increased by 2.3% and the polyphenols were eliminated at 100%. The data obtained in this work reveal the elimination of microbial growth and increasing the physicochemical qualities at the 21th day with fermentation. Thus, it would be recommended for producers to ferment it for over 21 days as result of appreciable yield in terms of microbial, organoleptic and chemical qualities. Keywords: Cucurbita maxima, Digue, fermentation, nutritional, pathogenic germs DOI: 10.7176/FSQM/103-05 Publication date: December 31st 2020

Formulation of Functional Yogurt by Cofermentation of Milk and Papaya Fruit

This study was carried out to determine the potential of adding Fresh skinned papaya pulp (FSP) into yoghurt for the improvement of the functional properties of yoghurt and the resulting effects of adding PPF on the physicochemical and sensory properties of the product during a 30 days’ storage period at 6°C. Yoghurt samples A (Control), B, C, D and E were respectively produced at 0%, 5%, 10%, 15%, and 20% of milk incorporated with papaya fruit. Incorporation of PPF into the yogurt samples resulted in an increase in pH, proteins and carbohydrates and a reduction in titratable acidity as compared to the control. The microbial analysis showed no presence of coliform bacteria. The sensory evaluation result demonstrated significant differences in all the organoleptic attributes analyzed. Sample C with 10% incorporated papaya had the highest overall acceptability score

Effect of a Previous Acid Adaptation of Zygosaccharomyces bailii on its Growth Kinetic in Acidic Media

The growth response of Zygosaccharomyces bailii acid adapted cells was assessed in acidified media. Yeast cells were first pre-cultured in nutrient broth adjusted with hydrochloric, citric and malic acid to pH 4; 4.5; 5; 5.5; 6 and 6.5. Moreover, they were also grown in two controls consisting of nutrient broth and nutrient broth supplemented with 1% of glucose both adjusted at pH 7. The variation of pH before and after the growth along with yeast concentration was measured. The cells pre-cultured in controls conditions and in the three conditions at pH 5 were then each inoculated in six BHI medium consisting of BHI adjusted with hydrochloric, citric and malic acid at pH 5.5 and 3.5. The growth was monitored by spectrophotometry and the yeast concentration after incubation was obtained by microscopy using a Thoma cell chamber. DMFit 2.1 was used to plot the growth curves and to estimate the growth parameters. All the pre-cultures and cultures were made at 37°C during 24 hours. During the pre-cultures, an important decrease of pH was noted in nutrient broth supplemented with glucose, moving from 7 to 3.81. In all the other pre-cultures, just a little variation was observed ranging from -0.57 to 0.50. Growth was observed in all the conditions, except at pH4. By growing the cells coming from the selected pre-cultures conditions in the different acidic BHI media, it appears that acid adaptation enhance the growth at pH 5.5 no matter the acid contains in the medium and the acid to which the cells were adapted. However, this acid adaptation was not sufficient to initiate growth at pH 3.5 after 24 hours of incubation at 37°C. Growth rate was significantly affected by the pH of the pre-culture medium and the acid present in the culture medium. Pre-culture with glucose supplementation was the only parameter studied affecting the latency

Importanza dell'aspetto microbiologico nella valutazione della shelf-life residua dei prodotti ittici di nuova generazione

La qualità complessiva del pesce è profondamente legata a quella microbiologica ed organolettica. La verifica dello stato di freschezza di tali prodotti è sempre stata basata principalmente sull’aspetto organolettico. Infatti, la legislazione, sia comunitaria che nazionale, si basa essenzialmente sul controllo organolettico per definire la fine della vita commerciale del pesce. Si è passati, nel tempo, dallo schema di valutazione Artioli-Ciani, che prevedeva una suddivisione del pescato in 4 categorie in base alle osservazioni sensoriali — vista, olfatto e tatto — al modello uniformato comunitario del Reg. CEE 103/76, che utilizza una valutazione aritmetica delle caratteristiche organolettiche. In seguito, il concetto di valutazione aritmetica è stato superato; tuttavia, l’approccio organolettico per definire la vita commerciale residua del prodotto ittico rimane il filo conduttore di queste leggi. Molti di questi parametri di valutazione organolettica non sono applicabili, se non nel caso di prodotti interi freschi, oppure eviscerati. Da qui, la difficoltà di valutazione della shelf-life residua di pesce filettato, a volte conservato in ghiaccio od in acqua-ghiaccio, (condizione in cui spesso si ha la dissoluzione di composti volatili marcatori dello stato di deterioramento), oppure di semiconserve a base di pesce. Nel DL n. 531/92 vengono forniti parametri microbiologici guida per pesci freschi congelati ed anche per molluschi eduli lamellibranchi e cefalopodi, congelati o surgelati. Questo tentativo, se pur generico (in quanto non tiene in considerazione né la specie microbica degradativa dominante, né la specie e l’origine del pesce in esame), apre una spirale nella rivalutazione da parte del legislatore del ruolo dei microrganismi degradativi nel processo di deterioramento del pesce e della possibilità di utilizzarli come parametri della qualità, soprattutto nel caso di nuovi prodotti semilavorati. Nei laboratori del gruppo di ricerca della professoressa M. E. Guerzoni, presso il campus Scienze degli Alimenti di Cesena dell’Università degli Studi di Bologna, si è cercato di valutare, in questi ultimi anni, se la quantificazione della carica batterica mesofila totale (CMT) possa essere impiegata, così come in altri settori, come parametro per la valutazione del tempo di vita residuo dei semilavorati e semiconserve a base di pesce. Anche lo studio dei fattori che influenzano l’entità e la composizione della carica batterica iniziale, il processo degradativo e la flora microbica colonizzante il prodotto ittico sono stati presi in considerazion

Effect of low thermal pasteurization in combination with carvacrol on color, antioxidant capacity, phenolic and vitamin C contents of fruit juices

Mild thermal treatment in combination with natural antimicrobials has been described as an alternative to conventional pasteurization to ensure fruit juices safety. However, to the best of our knowledge, no study has been undertaken to evaluate what could be its effect on their color and nutritional value. This study therefore aimed at assessing how a low thermal pasteurization in combination with carvacrol could affect these parameters, with orange, pineapple, and watermelon juices as selected fruit juices. The experimental design used had levels ranging from 50 to 90°C, 0 to 60 μl/L, and 0 to 40 min for temperature, concentration of carvacrol supplemented, and treatment length, respectively. The only supplementation of fruit juices with carvacrol did not affect their color. In comparison with high thermal pasteurization (>70°C), a combined treatment at mild temperatures (50-70°C) better preserved their color, antioxidant capacity (AOC), and vitamin C content, and increased their total phenolic content (TPC). Globally, carvacrol supplementation had a positive impact on the TPC of thermally treated juices and increased the AOC of treated watermelon juice, which was the lowest of the three fruit juices. Mild heat treatment in combination with natural antimicrobials like carvacrol is therefore an alternative to limit the negative effects of conventional pasteurization on fruit juices quality. © 2018 Published by Wiley Periodicals, Inc

Antimicrobial Activity of Aroma Compounds against Saccharomyces cerevisiae and Improvement of Microbiological Stability of Soft Drinks as Assessed by Logistic Regression▿

The combined effects of a mild heat treatment (55°C) and the presence of three aroma compounds [citron essential oil, citral, and (E)-2-hexenal] on the spoilage of noncarbonated beverages inoculated with different amounts of a Saccharomyces cerevisiae strain were evaluated. The results, expressed as growth/no growth, were elaborated using a logistic regression in order to assess the probability of beverage spoilage as a function of thermal treatment length, concentration of flavoring agents, and yeast inoculum. The logit models obtained for the three substances were extremely precise. The thermal treatment alone, even if prolonged for 20 min, was not able to prevent yeast growth. However, the presence of increasing concentrations of aroma compounds improved the stability of the products. The inhibiting effect of the compounds was enhanced by a prolonged thermal treatment. In fact, it influenced the vapor pressure of the molecules, which can easily interact within microbial membranes when they are in gaseous form. (E)-2-Hexenal showed a threshold level, related to initial inoculum and thermal treatment length, over which yeast growth was rapidly inhibited. Concentrations over 100 ppm of citral and thermal treatment longer than 16 min allowed a 90% probability of stability for bottles inoculated with 105 CFU/bottle. Citron gave the most interesting responses: beverages with 500 ppm of essential oil needed only 3 min of treatment to prevent yeast growth. In this framework, the logistic regression proved to be an important tool to study alternative hurdle strategies for the stabilization of noncarbonated beverages

Mangifera indica Bark Essential Oil: Chemical Composition and Biological Activities in Comparison with Aqueous and Ethanol Extracts

International audienceEthnobotanic surveys have revealed the use of Mangifera indica L. (Anacardiaceae) bark for the treatment of infectious diarrhea. The essential oil of M. indica bark is described for the first time for its chemical composition, radical scavenging activity (DPPH method) and antimicrobial properties. The total phenols content of its water and ethanol bark extracts as well as their radical scavenging and antimicrobial properties were also evaluated. Four commercial plant extracts were also studied for a comparison purpose. The antimicrobial activities were measured for all samples against three Gram (-): Escherichia coli, Salmonella enteritidis, Shigella and two Gram (+): Staphylococcus aureus and Bacillus cereus bacteria. The M. indica bark essential oil was characterized by the association of two major sesquiterpenes: (E)-β-caryophyllene (60.3%) and α-humulene (36.7%). It presented the lowest ratio of concentration to inhibition zone diameter on all the strains. The aqueous and ethanol extracts of M. indica bark were characterized by high contents of total phenols compounds and high radical scavenging activity compared to the essential oil. Finally, the interesting combination of the antibacterial and antiradical activities of the aqueous M. indica bark extract justifies the traditional use of this plant part in decoction form for the treatment of diarrheal infections

High pressure homogenization vs heat treatment: Safety and functional properties of liquid whole egg

This research investigated the potential of multi-pass homogenization treatment for the inactivation of Salmonella enterica serovar Enteritidis inoculated at different levels in liquid whole egg (LWE) comparing the efficacy of this treatment with a traditional thermal one performed at 65 C. Moreover, the effects of high pressure treatment (HPH) on structural and functional properties such as viscosity, microstructure and foaming abilities of LWE were investigated. The data obtained suggested that the multi-pass high pressure treatment at 100 MPa of S. enterica serovar Enteritidis inoculated in LWE at 7 and 4 log CFU/ml resulted in a first order inactivation kinetic, while the thermal inactivation curves of S. enterica serovar Enteritidis inoculated at 8 and 4 log CFU/ml presented a non-linear behaviour, with a marked tail after 3 min of treatment at 65 C. Additionally, HPH treatment caused an increase in foaming capacity of LWE, with respect to the untreated samples, passing from values of 26% of the control to 50% of pressure treated samples

Acid Stress-Mediated Metabolic Shift in Lactobacillus sanfranciscensis LSCE1 ▿

Lactobacillus sanfranciscensis LSCE1 was selected as a target organism originating from recurrently refreshed sourdough to study the metabolic rerouting associated with the acid stress exposure during sourdough fermentation. In particular, the acid stress induced a metabolic shift toward overproduction of 3-methylbutanoic and 2-methylbutanoic acids accompanied by reduced sugar consumption and primary carbohydrate metabolite production. The fate of labeled leucine, the role of different nutrients and precursors, and the expression of the genes involved in branched-chain amino acid (BCAA) catabolism were evaluated at pH 3.6 and 5.8. The novel application of the program XCMS to the solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) data allowed accurate separation and quantification of 2-methylbutanoic and 3-methylbutanoic acids, generally reported as a cumulative datum. The metabolites coming from BCAA catabolism increased up to seven times under acid stress. The gene expression analysis confirmed that some genes associated with BCAA catabolism were overexpressed under acid conditions. The experiment with labeled leucine showed that 2-methylbutanoic acid originated also from leucine. While the overproduction of 3-methylbutanoic acid under acid stress can be attributed to the need to maintain redox balance, the rationale for the production of 2-methylbutanoic acid from leucine can be found in a newly proposed biosynthesis pathway leading to 2-methylbutanoic acid and 3 mol of ATP per mol of leucine. Leucine catabolism to 3-methylbutanoic and 2-methylbutanoic acids suggests that the switch from sugar to amino acid catabolism supports growth in L. sanfranciscensis in restricted environments such as sourdough characterized by acid stress and recurrent carbon starvation