Pickling brine treatment for possible recycling using high‐pressure homogenization

Pickling is a preservation method of vegetables by brine immersion. Residual pickling solutions cannot be reused owing to high yeast content and the presence of polygalacturonase, which may produce vegetable softening. It has been reported that high‐pressure homogenization can reduce enzyme activity and microbial population in liquid foods. An investigation was aimed at studying the effect of high‐pressure homogenization cycles on polygalacturonase activity and yeast survival of residual pickling solutions, from processing of six vegetables. Each pickling solution was pumped through a homogenizing valve at 69 MPa pressure and was recirculated up to 15 times. Yeast counts and polygalacturonase activity were determined in treated solutions after being subjected to 1, 2, 5, 10, and 15 pressure cycles. Untreated and thermally treated solutions were used for comparison. Up to 4 log reductions in yeast inactivation was observed after five high‐pressure cycles treatments, contrasted with only 2 log reductions in thermal treatment. No clear relationship between enzyme inactivation and the number of high pressure cycles, or a thermal parallel effect, were observed. Copyright © 2007 Society of Chemical Industry     

High-added-value antioxidants obtained from the degradation of wine phenolics by Lactobacillus plantarum

Disposal of the waste from wine production has long been a problem for wineries, mainly because of the presence of phenolic compounds. In this study, we analyzed the antimicrobial activities of 10 wine phenolic compounds against Lactobacillus plantarum strains. Inhibition increased in this order: catechin = gallic acid < epicatechin = salicylic acid < methyl gallate = caffeic acid < ferulic acid = tryptophol < p-coumaric acid. The obtained results indicated that L. plantarum is able to grow in the presence of high concentrations of some wine phenolic compounds. Of the 10 compounds analyzed, only the hydroxycinnamic acids, gallic acid, and methyl gallate were metabolized by the four L. plantarum strains studied. Results also revealed that 4-vinylphenol and 4-vinylguaiacol are originated from p-coumaric and ferulic acids. These phenolic compounds are valuable intermediates in the biotechnological production of new fragrances. In addition, gallic acid and its ester, methyl gallate, are metabolized to produce the powerful antioxidant pyrogallol. Therefore, it might be possible to use L. plantarum strains to obtain high-added-value antioxidants from the degradation of phenolic compounds found in wine wastes.     

Shiga toxin-producing Escherichia coli in healthy young beef steers from Argentina: prevalence and virulence properties

Between July 1999 and December 2000, the prevalence of Shiga toxin-producing Escherichia coli (STEC) was established in 200 Argentine healthy young beef steers (14-16 months old) grown under local production systems with a feed grain period of 3-4 months, and the STEC strains isolated were examined in regard to their phenotypic and genotypic characteristics. Stool samples (n = 70) and rectal swabs (n = 130) were taken at the slaughterhouse level. By polymerase chain reaction (PCR), Shiga toxin (stx) gene sequences were detected in 69% of the samples. Eighty-six STEC strains were isolated from 39% of the animals. Serogroups identified, in order of frequency, were: O8 (16 strains), O113 (14), O103 (5), O91 (4), O171 (3), O174 (3), O25 (2), O112 (2), O145 (2), O2, O11, O104, O121, O128, O143, O146, O157. The most frequent serotype isolated was O8:H19 (12.9%). A total of 17 serotypes, including E. coli O157:H7 found in one animal (0.5%), have been previously associated with hemolytic uremic syndrome (HUS), bloody and non-bloody diarrhea in different countries, including Argentina. The prevalent genotype isolated was stx2 (51 of 86, 59.3%). Subtyping of stx2 variants showed the prevalence of stx2vh-b (25.6%) and stx2vh-a types (24.4%), and revealed the presence of an atypical stx2-v. Only 7.0% of STEC strains carried eae, and 33.7% harbored EHEC-hlyA gene. The full virulent genotype (stx/eae/EHEC-hlyA) was found to be present in 4 of the 86 (4.7%) STEC strains isolated. This research indicates that young steers from the main beef-producing area of Argentina are an important reservoir of STEC strains; however, its importance as agents of human diseases in our country has still to be established.     

Fermentation kinetics and chemical characterisation of vino tostado,a traditional sweet wine from Galicia (NW Spain)

BACKGROUND: Grapes after harvesting are air dried and pressed in order to concentrate sugars, acids and flavour compounds to produce vino tostado (toasted wine), a wine with intense aroma and flavour notes and high residual sugar concentration. In order to get a better knowledge of the difficulties involved, several fermentations were conducted at 12 and 28 °C using 0, 15 and 30 g hL^?1 ammonium sulfate and 0, 25 and 50 g hL^?1 exogenous commercial yeast (Saccharomyces cerevisiae var. bayanus) to study the kinetics of sugar consumption and ethanol, acetic acid and glycerol production. RESULTS: Fermentation kinetic parameters were calculated and metal concentrations and antioxidant activity were analysed. CONCLUSION: The spontaneous fermentation at 12 °C and all fermentations conducted with the commercial yeast gave vino tostado of adequate quality, while the spontaneous fermentation at 28 °C was sluggish. High‐temperature fermentations led to sweeter wines with higher volumetric productivities, although low‐temperature fermentations produced better wines in terms of higher glycerol and lower acetic acid levels. Fructose was the only sugar to be consumed during spontaneous fermentations, while both glucose and fructose were consumed during fermentations of the inoculated musts, with preference for each monosaccharide depending on temperature. Copyright © 2009 Society of Chemical Industry     

Integrating mechanical mixing,headspace, and rheology in a computational model for a fermentation process

Although computational fluid dynamics (CFD) modelling has been applied to study bioprocesses where mechanical mixing and aerations are key, the effect of having a free surface has usually been ignored. This work studies a mixing tank for bioprocess applications to analyze the impact that the assumption of a flat liquid level has upon the modelling results, with and without aeration. The methodology takes an experimental and modelling approach. A dual impeller mixer with a speed of 400 rpm is used for batch systems with both non-Newtonian and Newtonian fluids to characterize the axis torque and surface vortex formation. Several multi-phase CFD models are applied to study the modelling and numerical effects of the headspace on the results. Regarding modelling accuracy, the CFD models are shown to be able to capture the effect of the free surface on the fluid dynamics of the stirred tank for different fluid rheologies. Therefore, the simplification of the liquid level as a flat and fixed surface should not be applied, especially for a process with aeration or when unaerated conditions can lead to a surface vortex. Regarding the numerical accuracy, it is concluded that the mixture model does not predict the interface shape as well as the Eulerian model. However, only the mixture model shows to be numerically stable. Overall, this work provides validated CFD configurations able to predict the effect of a free surface on the mixing mechanisms in stirred reactors.