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- Microbial ecology dynamics in portuguese broa sourdoughPublication . Rocha, João M.; Malcata, F. XavierThis research effort aimed at a better understanding of microbial phenomena taking place during time in spontaneous sourdough fermentation for broa, a traditional Portuguese bread. Unlike most microbiological studies of sourdough, viable counts obtained were not limited to Lactobacillus and yeasts, but encompassed also molds, Gram-negative rods, endospore-(non)forming Gram-positive rods and catalase-positive/negative Gram-positive cocci. This less conventional approach unveiled the ubiquitous Bacillus genus throughout spontaneous broa sourdough fermentation. Presumptive yeasts, Lactobacillus and Bacillus were found to low levels after kneading, but became dominant by the end of regular (no aeration) fermentation. They apparently inhibit undesired rods and Staphylococcus, which were found to relatively high numbers after kneading. By 24 h of fermentation, lactic acid cocci accounted for an important fraction of biodiversity, and pH decreased significantly reaching about 4.1. Aeration accelerated the microbial dynamics. In terms of total viable counts, such a long-term fermentation appeared to reach a quasistationary state.
- Antioxidant properties of sterilized yacon (Smallanthus sonchifolius) tuber flourPublication . Sousa, Sérgio; Pinto, Jorge; Rodrigues, César; Gião, Maria; Pereira, Cláudia; Tavaria, Freni; Malcata, F. Xavier; Gomes, Ana; Pacheco, M. T. Bertoldo; Pintado, ManuelaThe objective of this research work was to investigate the antioxidant properties of sterilized yacon tuber flour. The results revealed for the first time the high antioxidant activity of sterilized yacon flour. The best extract obtained by boiling 8.9% (w/v) of yacon flour in deionised water for 10 min exhibited a total antioxidant capacity of 222 ± 2 mg (ascorbic acid equivalent)/100 g DW and a total polyphenol content of 275 ± 3 mg (gallic acid equivalent)/100 g DW associated to the presence of four main phenolic compounds: chlorogenic acid, caffeic acid, coumaric acid and protocatechuic acid, as well as the amino acid tryptophan. The most abundant was chlorogenic acid, followed by caffeic acid. Biological assays revealed that the extract had indeed antioxidant protection, and no pro-oxidant activity. In conclusion, sterilized yacon tuber flour has the potential to be used in the food industry as a food ingredient to produce functional food products.
- Potential use of wool-associated Bacillus species for biodegradation of keratinous materialsPublication . Queiroga, A. Catarina; Pintado, Manuela E.; Malcata, F. XavierFive wool-degrading bacterial strains were selected from a set of 115 isolates from a less conventional source, i.e., the wool of Portuguese Merino sheep, based on their promising keratinolytic abilities. All selected strains belong to the genus Bacillus, probably Bacillus subtilis/licheniformis, according to 16S rRNA sequencing. They were able to grow on and hydrolyse feathers and wool (in both native and milled forms), and human hair and nails to a lesser extent. The maximum keratinase activity was recorded on milled chicken feathers. Biodegradation of such keratin-rich matrices increased the amount of soluble proteins in the fermentation broth and implied the action of extracellular enzymes from those adventitious microorganisms. Therefore, such novel strains have a potential for effective use in solid waste management strategies encompassing keratin-rich materials based on submerged fermentation. Concomitantly, the nutritional value of the broth may be improved for eventual formulation of animal feed.
- Rheological, textural and microstructural features of probiotic whey cheesesPublication . Madureira, A. Raquel; Pintado, Ana I. E.; Gomes, Ana Maria; Pintado, Manuela E.; Malcata, F. XavierWhey cheeses have been manufactured with probiotic bacteria e viz. Bifidobacterium animalis Bo and Lactobacillus casei LAFTIrL26, from combinations of bovine whey and milk, following protein denaturation at 90 ºC; they were subsequently inoculated (at 10%) with those strains, and homogenized afterwards; additives such as salt and sugar were then incorporated; and the resulting solid matrices were stored at 7º C for up to 21 d. Oscillatory measurements and instrumental texture profile analyses were performed, and sensory analyses were carried out by a trained panel. Microstructural features were in addition ascertained by scanning electron microscopy. L. casei exhibited a higher acidifying activity than B. animalis, which produced distinct textures; higher firmness and viscoelasticity were indeed found in matrices inoculated with the former. Incorporation of sugar and L. casei favoured consumer acceptability, relative to plain matrices. Microstructural differences were detected between matrices at different times of storage and formulated with distinct additives.
- Cytotoxicity and genotoxicity of chitooligosaccharides upon lymphocytesPublication . Fernandes, João C.; Borges, Margarida; Nascimento, Henrique; Bronze-da-Rocha, Elsa; Ramos, Oscar S.; Pintado, Manuela E.; Malcata, F. Xavier; Santos-Silva, AliceTwo COS mixtures and a low molecular weight chitosan (LMWC) were tested for potential cytotoxicity and genotoxicity upon human lymphocytes. Genotoxicity was evaluated in vitro by cytokinesis-blocked micronucleus and alkaline comet assays, while cytotoxicity was assessed by flow cytometry analysis. Our results suggest that COS do not exhibit any genotoxicity upon human lymphocytes, independently of MW or concentration. However, above 0.07 mg/mL COS induced strong cytotoxic effects. According to the concentration used, such cytotoxicity will induce cell death, essentially by necrosis (>0.10 mg/mL) and/or apoptosis (<0.10 mg/mL). The level of necrosis/apoptosis induced by high COS concentrations, suggests a promising use as apoptosis inducers in specific cancer situations.
- Features and performance of edible films, obtained from whey protein isolate formulated with antimicrobial compoundsPublication . Ramos, Óscar L.; Silva, Sara I.; Soares, José C.; Fernandes, João C.; Poças, M. Fátima; Pintado, Manuela E.; Malcata, F. XavierThe goal of this research effort was to assess the efficacy of edible films produced fromwhey protein isolate (WPI) and glycerol, including incorporation of lactic acid (LA) and propionic acid (PRO), chitooligosaccharideswith nominal MW of 3 kDa (COS) and natamycin (NA) as antimicrobial agents. Their features were evaluated in vitro via agar diffusion and viable cell counting, against spoilage microflora often found contaminating cheese surfaces. The effect of incorporating the aforementioned compounds upon thickness, moisture content (MC), solubility (S), density (ρs),water activity (aw) and water vapor permeability (WVP), as well as upon tensile and optical properties of those films were also evaluated. Films formulated with LA, PRO or COS exhibited antimicrobial activity against all microorganisms tested, yet the viable cell count assay was more sensitive and reproducible. COS was the most active against Gram-negative bacteria, whereas LA was the most active against Gram-positive ones. NA was not active against bacteria, but displayed the strongest effect against yeasts. Incorporation of said antimicrobial compounds did not significantly (pN0.05) affect film thickness, yet it significantly (pb0.05) reduced tensile strength (TS). Incorporation of LA and NA in particular did not significantly (pb0.05) affect MC, S, ρs, WVP, elongation at break (EB) and Young's modulus (YM) values; however, a statistically significant increase (pb0.05) of MC, S andWVP, together with a statistically significant decrease (pb0.05) of ρs were attained upon incorporation of PRO or COS. Moreover, PRO produced the highest variation (pb0.05) in EB, TS and YM,whereas COS produced the highest change (pb0.05) in optical properties.
- Incorporation of probiotic bacteria in whey cheese: decreasing the risk of microbial contaminationPublication . Madureira, A. R.; Pintado, M.; Gomes, Ana Maria; Malcata, F. XavierFor dairy products that are consumed fresh, contamination by spoilage microorganisms and pathogens from the environment is a major concern. Contamination has been associated with a number of outbreaks of foodborne illnesses; however, consistent data pertaining to the microbial safety of whey cheeses specifically have not been reported. Hence, the goals of this research effort were (i) to manufacture a probiotic whey cheese with Bifidobacterium animalis and Lactobacillus casei and (ii) to assess the antimicrobial activity of these probiotics against a set of foodborne pathogens (Listeria innocua, Salmonella Enteritidis, and Staphylococcus aureus) and food spoilage microorganisms (Pseudomonas aeruginosa and Escherichia coli). Three ranges of these microbial contaminants were used for inoculation of cheeses: 103 to 104, 104 to 106, and 106 to108 CFU/g. Inoculation in plain culture medium served as a control. The inhibition produced by the probiotics was calculated, and the major effect was found to be bacteriostatic. In specific cases, full inhibition was observed, i.e., by B. animalis against P. aeruginosa and by L. casei against Salmonella Enteritidis and L. innocua. Conversely, the least inhibition was detected for L. casei against P. aeruginosa. Our results suggest that use of these probiotic strains can extend the shelf life of whey cheeses and make them safer by delaying or preventing growth of common contaminant bacteria.
- Influence of L-cysteine, oxygen and relative humidity upon survival throughout storage of probiotic bacteria in whey protein-based microcapsulesPublication . Rodrigues, D.; Sousa, Sérgio; Santos, Nathália Baptista T.; Silva, J.P.; Lobo, J. M. Sousa; Costa, P; Amaral, Gustavo Henrique De Oliveira; Pintado, M.M.E; Gomes, Ana Maria; Malcata, F. Xavier; Freitas, Ana CThe survival rates of Lactobacilus acidophilus Ki, Lactobacillus paracasei L26 and Bifidobacterium animalis BB-12 were studied after whey protein microencapsulation via spray-drying, with or without L-cysteine-HCl, and storage up to 6 months at 5 degrees C and 22 degrees C, with variation in relative air humidity and oxygen levels. Lb. paracasei L26 was the least susceptible to storage conditions: above 10(6) cfu g(-1) were recorded by 180 d at 22 degrees C, irrespective of relative humidity, and the presence/absence of oxygen and L-cysteine. Higher relative humidity, higher temperature and longer storage periods were deleterious to survival of both B. animalis BB-12 and Lb. acidophilus Ki; the effect of L-cysteine-HCl was dependent on the probiotic strain. The effect of overhead oxygen was not significant upon any probiotic strain studied. Whey protein microcapsules containing L-cysteine-HCl protected probiotic cultures from simulated gastrointestinal conditions.
- Modelling respiration of packaged fresh-cut "Rocha" pear as affected by oxygenPublication . Gomes, M. Helena; Beaudry, Randolph M.; Almeida, Domingos P. F.; Malcata, F. XavierRespiration rates were measured in fresh-cut ‘Rocha’ pear (Pyrus communis L.) stored at four temperatures (0, 5, 10 and 15 C) and with oxygen partial pressures ranging from 0 to 18 kPa. Respiratory quotient and ethanol production were used to determine the fermentation threshold. The oxygen concentration effect on the respiration rate was accurately described using Michaelis–Menten kinetics, without noncompetitive inhibition by CO2, and the effect of temperature on the respiration rate was well modelled by exponential functions. The oxygen level at which respiration was half its maximum (apparent Km;O2 ) was similar to or only slightly greater than the fermentation threshold. The narrow range of oxygen between Km;O2 and the fermentation threshold, suggests that modified atmosphere packaging technology has a limited applicability toward extension of the shelf-life of fresh-cut ‘Rocha’ pear.
- Metal uptake by microalgae: underlying mechanisms and practical applicationsPublication . Monteiro, Cristina M.; Castro, Paula M. L.; Malcata, F. XavierMetal contamination of a few aquatic, atmospheric, and soil ecosystems has increased ever since the industrial revolution, owing to discharge of such elements via the effluents of some industrial facilities. Their presence to excessive levels in the environment will eventually lead to serious health problems in higher animals owing to accumulation throughout the food web. Current physicochemical methods available for recovery of metal pollutants (e.g., chemical precipitation, oxidation/reduction, or physical ion exchange) are either expensive or inefficient when they are present at very low concentrations. Consequently, removal of toxic metals by microorganisms has emerged as a potentially more economical alternative. Microalgae (in terms of both living and nonliving biomass) are an example of microorganisms suitable to recover metals and able to attain noteworthy percent removals. Their relatively high metal-binding capacities arise from the intrinsic composition of their cell walls, which contain negatively charged functional groups. Consequently, microalgal cells are particularly efficient in uptake of those contaminants when at low levels. Self-defense mechanisms developed by microalgal cells to survive in metal-containing media and environmental factors that affect their removal (e.g., pH, temperature, and biomass concentration) are reviewed here in a comprehensive way and further discussed in attempts to rationalize this form of remediation vis-a-vis with conventional nonbiological alternatives