Effect of initial sugar concentration on the production of L (+) lactic acid by simultaneous enzymatic hydrolysis and fermentation of an agro-industrial waste product of pineapple (Ananas comosus) using Lactobacillus casei subspecies rhamnosus

Production of lactic acid by fermentation process has been studied from glucose solutions and other sources because of many important reasons: biotechnological production is cheaper than chemical synthesis; production of biodegradable materials from L (+) lactic acid and, the use of nutrient-rich agro-industrial wastes as raw material, which helps to reduce the environmental impact. The goal of this study was to evaluate the effect of sugar concentration of a pineapple liquid waste as the carbon source on the capacity of Lactobacillus casei subspecies rhamnosus to produce lactic acid by simultaneous enzymatic hydrolysis and fermentation. Three different pineapple waste concentrations were evaluated (60, 80 and 100% v/v) from a pineapple juice with 11.3% (m/v) of sugars (sucrose, fructose and glucose). L. casei was able to consume all sugars present within the levels tested, and converted all into lactic acid, showing efficient yields of 0.91 g lactic acid/g sugars. Final lactic acid concentration increased significantly (p<0.05) with the increase of pineapple waste percentage. Maximum lactic acid concentration (102g/L) was achieved with 100% pineapple waste medium. The highest total productivity (4.0g/h) and maximum productivity (4.48 g/L*h) were obtained with 60% pineapple waste medium and it decreased significantly (p<0.05) when 100% was used. Fermentation time increased with the increment of sugars, but it increased considerably with the medium composed of 100% of pineapple waste in comparison with the other two mediums. Pineapple waste represents a good alternative as a cheap carbon source for bacteria growth and production of L (+) lactic acid

Antibacterial prenylated isoflavonoids and stilbenoids : quantitative structure-activity relationships and mode of action

Prenylated phenolic compounds, i.e. those bearing a C5-isoprenoid (prenyl) substituent, are abundant in plants from the Fabaceae (legume) family and are potential natural antibacterial agents against resistant pathogenic bacteria. To understand the antibacterial properties of these compounds, (quantitative) structure-activity relationships and mode of action of these molecules were investigated against Gram positive and negative bacteria. Compounds belonging to the flavonoid, isoflavonoid and stilbenoid classes were studied. Antibacterial activity was modulated by the (sub)class of phenolic compound, as well as by the configuration, position and number of prenyl groups. Prenylated isoflavones were found to be better antibacterials than prenylated pterocarpans and prenylated stilbenoids. It was also shown that chain prenylation increased the antibacterial activity more than pyran-ring prenylation. Diprenylated compounds were among the most active antibacterials with minimum inhibitory concentrations of less than 10 µg/mL against Listeria monocytogenes. The main molecular characteristics defining antibacterial activity were molecular shape (including flexibility and globularity) and hydrophobicity. Regarding the mode of action of these compounds, it was shown that prenylated phenolic compounds can disrupt the integrity of the membrane by permeabilization very quickly. Interestingly, some good antibacterial prenylated (iso)flavonoids showed good permeabilization capacity whereas others not (including diprenylated molecules), highlighting potential differences in their interactions with the bacterial membrane. Likewise, it was shown that Gram negative intrinsic resistance towards prenylated phenolic compounds is primarily due to the activity of efflux pump systems and that it can be overcome by using an efflux pump inhibitor in combination with antibacterial prenylated compounds. Last, in vitro production of prenylated phenolic compounds was performed with microbial prenyltransferase SrCloQ and novel C- and O-prenylated compounds were produced

Desarrollo de un proceso de fermentación para la producción de ácido láctico, utilizando un sustrato a base de un desecho de piña (Ananas comosus) y el microorganismos Lactobacillus casei subespecie rhamnosus

Tesis (licenciatura en tecnología de alimentos)UCR::Vicerrectoría de Docencia::Ciencias Agroalimentarias::Facultad de Ciencias Agroalimentarias::Escuela de Tecnología de Alimento

Simultaneous Analysis of Glucosinolates and Isothiocyanates by Reversed-Phase Ultra-High-Performance Liquid Chromatography-Electron Spray Ionization-Tandem Mass Spectrometry

A new method to simultaneously analyze various glucosinolates (GSLs) and isothiocyanates (ITCs) by reversed-phase ultra-high-performance liquid chromatography-electron spray ionization-tandem mass spectrometry has been developed and validated for 14 GSLs and 15 ITCs. It involved derivatization of ITCs with N-acetyl-l-cysteine (NAC). The limits of detection were 0.4-1.6 μM for GSLs and 0.9-2.6 μM for NAC-ITCs. The analysis of Sinapis alba, Brassica napus, and Brassica juncea extracts spiked with 14 GSLs and 15 ITCs indicated that the method generally had good intraday (≤10% RSD) and interday precisions (≤16% RSD). Recovery of the method was unaffected by the extracts and within 71-110% for GSLs and 66-122% for NAC-ITCs. The method was able to monitor the enzymatic hydrolysis of standard GSLs to ITCs in mixtures. Furthermore, GSLs and ITCs were simultaneously determined in Brassicaceae plant extracts before and after myrosinase treatment. This method can be applied to further investigate the enzymatic conversion of GSLs to ITCs in complex mixtures.</p

Modulation of Glucosinolate Composition in Brassicaceae Seeds by Germination and Fungal Elicitation

Glucosinolates (GSLs) are of interest for potential antimicrobial activity of their degradation products and exclusive presence in Brassicaceae. Compositional changes of aliphatic, benzenic, and indolic GSLs of Sinapis alba, Brassica napus, and B. juncea seeds by germination and fungal elicitation were studied. Rhizopus oryzae (nonpathogenic), Fusarium graminearum (nonpathogenic), and F. oxysporum (pathogenic) were employed. Thirty-one GSLs were detected by reversed-phase ultrahigh-performance liquid chromatography photodiode array with in-line electrospray ionization mass spectrometry (RP-UHPLC-PDA-ESI-MSn). Aromatic-acylated derivatives of 3-butenyl GSL, p-hydroxybenzyl GSL, and indol-3-ylmethyl GSL were for the first time tentatively annotated and confirmed to be not artifacts. For S. alba, germination, Rhizopus elicitation, and F. graminearum elicitation increased total GSL content, mainly consisting of p-hydroxybenzyl GSL, by 2-3 fold. For B. napus and B. juncea, total GSL content was unaffected by germination or elicitation. In all treatments, aliphatic GSL content was decreased (≥50%) in B. napus and remained unchanged in B. juncea. Indolic GSLs were induced in all species by germination and nonpathogenic elicitation.</p

QSAR-based physicochemical properties of isothiocyanate antimicrobials against gram-negative and gram-positive bacteria

Isothiocyanates (ITCs) derived from Brassicaceae are potential food preservatives. Their antimicrobial ac-tivity is strongly influenced by their subclass and side chain. This is the first quantitative structure-activity relationships (QSAR) study of ITCs as antibacterials. Twenty-six ITCs covering 9 subclasses were tested against Escherichia coli and Bacillus cereus. Minimum inhibitory concentration (MIC) and growth inhibitory response (GIR) were determined and used to develop QSAR models. MIC of the most active ITCs was 6.3–9.4 μg/mL. The QSAR models were validated with leave-one-out cross validation. The proposed models had a good fit (R2adj 0.86–0.93) and high internal predictive power (Q2adj 0.80–0.89). Partial charge, polarity, reactivity, and shape of ITCs were key physicochemical properties underlying antibacterial activity of ITCs. Furthermore, ITC compositions and antibacterial activity of Sinapis alba, Brassica napus, B. juncea, B. oleracea, and Camelina sativa extracts were determined, after myrosinase treatment. B. oleracea ITC-rich extract showed promising activity (MIC 750–1000 μg/mL) against both bacteria. C. sativa ITC-rich extract showed promising activity (MIC 188 μg/mL) against B. cereus. The QSAR models successfully predicted activity of the extracts based on ITC compositions. The models are useful to predict antibacterial activity of new ITCs and ITC-rich mixtures. Brassicaceae ITC-rich extracts are promising natural food preservatives.</p

The interplay between antimicrobial activity and reactivity of isothiocyanates

This study aimed to determine antimicrobial activity (minimum inhibitory concentration, MIC; minimum bactericidal/fungicidal concentration, MBC/MFC) of novel ITCs against food spoilage and pathogenic Gram– bacteria, Gram+ bacteria, and fungi. The activity of the long-chain (C9) 9-(methylthio)nonyl ITC (9-MTITC), 9-(methylsulfinyl)nonyl ITC (9-MSITC), and 9-(methylsulfonyl)nonyl ITC (9-MSoITC) was determined for the first time. Due to the electrophilicity of ITCs, the activity of ITCs was evaluated in nucleophile-rich and nucleophile-poor growth media. ITCs reacted via conjugation with components in a nucleophile-rich growth medium at a rate of 39–141 μmol L−1 h−1, depending on their side chain configuration and temperature. The reaction rates were lowered by a factor of 2–21 when using nucleophile-poor growth media. Consequently, the activity of ITCs was generally improved, with MSITC and MSoITC being the most positively affected (activity increased by a factor of > 4). 9-MSITC and 9-MSoITC had good activity (MIC ≤ 25 μg/mL) against Gram+ bacteria and fungi. The short-chained (C3) analogues had good activity against Gram+ bacteria and Gram– bacteria. The highest bactericidal/fungicidal activity was obtained for 9-MSITC and 9-MSoITC (MBC/MFC 17.5–25 μg/mL). Overall, MSITC and MSoITC might be potential new natural food preservatives, but their reactivity with food matrix components should be considered.</p

Impact of food-relevant conditions and food matrix on the efficacy of prenylated isoflavonoids glabridin and 6,8-diprenylgenistein as potential natural preservatives against Listeria monocytogenes

Prenylated isoflavonoids can be extracted from plants of the Leguminosae/Fabaceae family and have shown remarkable antimicrobial activity against Gram-positive food-borne pathogens, such as Listeria monocytogenes. Promising candidates from this class of compounds are glabridin and 6,8-diprenylgenistein. This research aimed to investigate the potential of glabridin and 6,8-diprenylgenistein as food preservatives against L. monocytogenes. Their antimicrobial activity was tested in vitro at various conditions relevant for food application, such as different temperatures (from 10 °C to 37 °C), pH (5 and 7.2), and in the presence or absence of oxygen. The minimum inhibitory concentrations of glabridin and 6,8-diprenylgenistein in vitro were between 0.8 and 12.5 μg/mL in all tested conditions. Growth inhibitory activities were similar at 10 °C compared to higher temperatures, although bactericidal activities decreased when the temperature decreased. Notably, lower pH (pH 5) increased the growth inhibitory and bactericidal activity of the compounds, especially for 6,8-diprenylgenistein. Furthermore, similar antimicrobial efficacies were shown anaerobically compared to aerobically at the tested conditions. Glabridin showed a more stable inhibitory and bactericidal activity when the temperature decreased compared to 6,8-diprenylgenistein. Therefore, we further determined the antimicrobial efficacy of glabridin against L. monocytogenes growth on fresh-cut cantaloupe at 10 °C. In these conditions, concentrations of glabridin of 50, 100 and 250 μg/g significantly reduced the growth of L. monocytogenes compared to the control, resulting on average in >1 Log CFU/g difference after 4 days compared to the control. Our results further underscored the importance of considering the food matrix when assessing the activity of novel antimicrobials. Overall, this study highlights the potential of prenylated isoflavonoids as naturally derived food preservatives