Loading...
6 results
Search Results
Now showing 1 - 6 of 6
- Role of dominant microflora of Picante cheese on proteolysis and lipolysisPublication . Freitas, A. Cristina; Pintado, Ana I. E.; Pintado, Manuela; Malcata, F. XavierFour species of bacteria (Enterococcus faecium and E. faecalis, Lactobacillus plantarum and Lb. paracasei) and three species of yeasts (Debaryomyces hansenii, Yarrowia lipolytica and Cryptococcus laurentii) isolated from Picante cheese were assayed for proteolytic and lipolytic activities. The milk type (caprine or ovine), the ripening time (0–65 d) and the concentration of NaCl (0–14% (w/v)) have been studied in terms of their effects upon in vitro curdled milk. Proteolytic and peptidolytic activities were demonstrated to be high for Y. lipolytica, and at much lower levels for the other strains. Milk type, ripening time and content of NaCl appeared to be statistically significant processing factors in terms of proteolysis. Clear lipolytic activity was detected for Y. lipolytica, but release of free fatty acids to lesser extents was observed for the other strains under study. Ripening time was statistically significant for lipolysis but milk type was not. Lipolytic activities were strongly affected by NaCl content and the extent of fat hydrolysis was affected by the increase of NaCl from 0 to 7% (w/v) more than by change from 7 to 14% (w/v). In view of the experimental results, a mixed-strain starter for Picante cheese including Lb. plantarum, E. faecium (or E. faecalis) and D. hansenii (and/or Y. lipolytica) is of potential interest.
- Fate of nitrogen during metabolism of whey lactose by Rahnella aquatilisPublication . Pintado, Manuela E.; Pintado, Ana I. E.; Malcata, F. XavierThe rate of intake of peptides and free amino acids by Rahnella aquatilis was studied, as well as the evolution of concentrations of exopolysaccharide, biomass, and several metabolites. For this purpose, eight wheybased fermentation media were tested: hydrolyzed bovine whey under 1) aerobic and 2) anaerobic conditions; hydrolyzed bovine whey with 3) 2.0% (wt/vol) NaCl or 4) 0.5% (wt/vol) NaCl; 5) plain bovine whey; 6) bovine whey permeate; 7) hydrolyzed caprine whey; and 8) hydrolyzed ovine whey. The lower peptide fraction (<2000 Da) in plain whey, whey permeate, and hydrolyzed whey fermented aerobically was virtually depleted by 24 h. In all experiments, most consumption of free amino acids occurred at initial stages of fermentation. In caprine whey, ovine whey, and bovine whey fermented anaerobically, free Val was present at high levels until the end of fermentation, and the highest production of acetic acid was also observed. In ovine whey, high levels of peptides and free amino acids were recorded, as well as the highest production of several organic acids (except lactic acid) and the lowest viscosity and polysaccharide concentration. The low concentration of peptides and free amino acids in plain whey and whey permeate did not apparently permit active consumption of lactose, whereas lack of molecular oxygen and presence of salt played a strong role toward inhibition of exopolysaccharide production. The qualitative and quantitative profile of the nitrogen fraction likely might have determined the metabolism of lactose and, consequently, conditioned the production of exopolysaccharide and organic acids even though growth of R. aquatilis was not affected similarly.
- Production of polysaccharide by Rahnella aquatilis with whey feedstockPublication . Pintado, M. E.; Pintado, Ana I. E.; Malcata, F. X.The rates were monitored on biomass increase, polysaccharide production and viscosity development of whey broth and a control synthetic broth during fermentation by Rahnella aquatilis and organic acids, lactose, peptides and free amino acids were measured. Growth curves were similar and characterized by maximum specific growth rates of 0.61 h−1 for whey and 0.63 h−1 for synthetic medium. The yields of polysaccharide were 0.59 g/glactose for the synthetic medium and 0.56 for whey. Small peptides (<4,000 Da) and most free amino acids in both fermentation media were consumed within 24h.
- Controlled whey protein hydrolysis using two alternative proteasesPublication . Pintado, Manuela E.; Pintado, Ana I. E.; Malcata, F. XavierWhole whey was hydrolyzed for 12 h with Protease 2A and Trypsin using two concentrations of enzyme (20 and 40 g/kgprotein). Samples were assayed for total viable counts of adventitious microflora that survived thermization, total acidity, total concentration of free amino acids, peptide profile and overall degree of hydrolysis. The highest total concentration of free amino acids was observed when hydrolysis was effected by Protease 2A, and the major variations in amino acid qualitative composition occurred between 2 and 6 h: Leu exhibited the most significant increase, followed by Lys, Phe and Ile. Hydrolysis with Trypsin led to release of high amounts of Lys. Quantitative depletion of β-lactoglobulin was observed by 2 h under all processing conditions, and hydrolysis of α-lactalbumin was slower when Trypsin was employed. Formation of peptides was more extensive under the action of Trypsin than of Protease 2A, and the major peptides released by the former had molecular weights mainly in the ranges 7500–8000 and 4000–4500 Da, whereas those released by the latter accumulated in the range 7000–7500 Da. The differences between the hydrolytic actions of Trypsin and Protease 2A were significant except with respect to the concentration of Glu, as well as degree of breakdown of immunoglobulin G and β-lactoglobulin. Growth of adventitious bacteria and generation of free amino acids were successfully modeled using postulated mathematical models. The values of vmax for Trypsin were 0.15 and 0.06 g/(l h) for 40 and 20 g/kgprotein, respectively, and for Protease 2A were 0.86 and 0.50 g/(l h) for 40 and 20 g/kgprotein, respectively.
- Organic acids produced by lactobacilli, enterococci and yeasts isolated from Picante cheesePublication . Freitas, A. Cristina; Pintado, Ana I. E.; Pintado, Manuela E.; Malcata, F. XavierFour species of bacteria (Enterococcus faecium and Enterococcus faecalis, Lactobacillus plantarum and Lactobacillus paracasei) and three species of yeasts (Debaryomyces hansenii, Yarrowia lipolytica and Cryptococcus laurentii), previously isolated from Picante cheese, were cultured in ovine and in caprine milk and assayed for sugar and organic acids metabolism for 6 days. The results indicated that both milk types can be coagulated by the four strains of lactic acid bacteria. Lb. paracasei led to a faster and greater reduction in pH. Production of lactic acid correlated to lactose degradation, and was highest for Lb. paracasei followed by E. faecium; citrate metabolism was apparent for E. faecalis and, to a lesser extent, for E. faecium, Lb. plantarum and Lb. paracasei. Relatively high contents of formic acid were found when inoculation was with Enterococcus and with Lb. plantarum.
- Rheological characterization under shear of a fraction of polymer produced via fermentation of whey-related media by Rahnella aquatilisPublication . Pintado, M. E.; Silva, J. A. Lopes da; Pintado, Ana I. E.; Malcata, F. XavierProduction of lactan, a polysaccharide composed of mannose, galactose and galacturonic acid (at the ratio of 5:3:2), starting from a semidefined medium containing lactose via fermentation with Rahnella aquatilis was described previously. In this communication, such polysaccharide was produced from five alternative fermentation media: (1) a synthetic (defined) medium, plain whey (under (2) aerobic and (3) anaerobic conditions), (4) whey permeate and (5) whey with 2% NaCl (w/v). The effect of the concentration of polysaccharide, pH and ionic strength at harvest on the rheological properties of the polysaccharide was studied using lactan-enriched fractions recovered from each medium and analysed in solution under steady shear flow. Lactan solutions showed a shear-thinning behaviour in all cases, and increases in viscosity were observed at increasing concentrations of polysaccharide, as expected. The polysaccharide fraction produced from whey with 2% (w/v) NaCl and plain whey under anaerobic conditions exhibited lower viscosity than that produced from the other media, an observation that is associated with the lower concentration of polysaccharide. Post-harvest addition of salts (KCl or CaCl2) and changes in pH (3–11) affected slightly the viscosity of the polysaccharide solutions. q1998