Influence of salt content, degree of proteolysis and aeration on the production of a polymer via fermentation of whey-related media by Rahnella aquatilis

Utilization of whey as fermentation feedstock has been attempted widely by the dairy industry. Production of lactan, a polysaccharide composed of mannose, galactose and galacturonic acid (at the molar ratio 5:3:2), starting from a semi-defined medium containing lactose via fermentation under aerobic conditions with Rahnella aquatilis was described previously. In this communication, the effect of salt, previous hydrolysis and aeration were studied during the polysaccharide production from whey in alternative fermentation media: hydrolyzed whey (under (i) aerobic and (ii) anaerobic conditions), hydrolyzed whey with 2.0% NaCl (w/v) (iii) and 0.5% NaCl (w/v) (iv),.and plain whey (v). The growth of biomass and the variation in concentration of organic acids, lactose, peptides and free amino acids were monitored. The polysaccharide production and the variation of viscosity of were also followed throughout 48 h of fermentation. Under the different conditions tested, Rahnella aquatillis showed a maximum specific growth rate of 0.61 h-1, 0.60 h-1, 0.61 h-1, 0.64 h-1, and 0.46 h-1 for hydrolyzed whey under aerobiosis and under anaerobiosis, hydrolyzed whey with 2.0% NaCl (w/v) and 0.5% NaCl, and plain whey, respectively; the final yields of the various organic acids were: 0.07, 0.18, 0.07, 0.04 and 0.05 (g/glactose) for acetic acid; 0.06, 0.07, 0.00, 0.04 and 0.02 (g/glactose) for lactic acid; 0.08, 0.09, 0.03, 0.04 and 0.04 (g/glactose) for formic acid; 0.01, 0.04, 0.01, 0.01 and 0.02 (g/glactose) for succinic acid; and 0.11, 0.09, 0.14, 0.19 and 0.00 (g/glactose) for acetoine. Lactose was almost completely depleted during the 48 h of fermentation for hydrolyzed whey; however, lactose was only partly consumed in plain whey (final yield of 0.48 g/glactose).Small peptides (< 2,000 Da) and most free amino acids were consumed by 24 h in hydrolyzed whey fermented under anaerobiosis and plain whey, but these peptides were present until the end of fermentation in the remaining media. R. aquatilis showed similar behavior in free amino acid consumption in hydrolyzed whey with NaCl and hydrolyzed whey fermented under aerobiosis. Plain whey yielded very low concentrations of free amino acids throughout the whole fermentation. The yield of polysaccharide was 0.56, 0.26, 0.39, 0.40 and 0.44 g/glactose for hydrolyzed whey fermented under aerobiosis and under anaerobiosis, hydrolyzed whey with 2.0% NaCl (w/v) and 0.5% NaCl, and plain whey, respectively.info:eu-repo/semantics/publishedVersio

Production of lactan using plain whey, whey permeate and synthetic medium as feedstock

Whey (or whey permeate), a by-product of cheese manufacture, has created a worldwide problem of waste disposal owing to its high biological oxygen demand. Production of lactan has been previously described based on a semidefined medium rich in lactose using Rahnella aquatilis. This research was aimed at obtaining lactan directly from whole whey without additional nutrients, as well as and whey permeate obtained after ultrafiltration, using a similar type of strain, and the fermentation process was compared with that using the synthetic medium previously tested. The growth of biomass growth rate, the polysaccharide production rate and the viscosity of the broth were monitored. Organic acids, lactose, peptides and free amino acids were also determined. The growth curves were similar for the three media, showing a maximum specific growth rate of 0.61 h1, 0.65 h-1 and 0.63 h-1 for whey, whey permeate and synthetic medium, respectively. The major increase in polysaccharide production was observed between 12 h (beginning of stationary phase) and 24 h for whey and the synthetic medium; however, the increase in the case of whey permeate is less pronounced and occurs essentially after 24 h. The yield of polysaccharide was 0.59 g/glactose, 0.56 g/glactose and 0.37 g/glactose for synthetic medium, plain whey and whey permeate, respectively. The larger amount of citrate present in whey was used by Rahnella aquatilis with significant formation of acetic acid in the first 12 h and acetoine thereafter; whey permeate and synthetic media did not lead to acetoine formation. The final yields of the various organic acids for the synthetic medium, whey and whey permeate, respectively, were: 0.08, 0.07 and 0.03 (g/glactose) for acetic acid; 0.02, 0.06 and 0,00 (g/glactose) for lactic acid; 0.08, 0.08 and 0.02 (g/glactose) for formic acid; 0.04, 0.01 and 0.00 (g/glactose) for succinic acid; and 0.00, 0.11 and 0.00 (g/glactose) for acetoine. Lactose was almost completely depleted by 48 h of fermentation in the case of whey and synthetic medium, but only part of lactose was consumed in the whey permeate (final yield of 0.43 g/glactose). Small peptides (< 4,000 Da) and most free amino acids were consumed by 24 h in whey and synthetic medium. The whey permeate possessed low amounts of peptides (virtually consumed by 12 h) and very low concentrations of free amino acids, which increased slightly between 12 and 24 h.info:eu-repo/semantics/publishedVersio

Controlled whey protein hydrolysis using two alternative proteases

Whole 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

Dominant microflora of picante cheese: Independent role upon proteolysis and lipolysis in model systems

Four species of bacteria (two species of enterococci, Enterococcus faecium and Enterococcus faecalis, and two species of lactobacilli, Lactobacillus plantarum and Lactobacillus paracasei) and three species of yeasts (Debaryomyces hansenii, Yarrowia lipolytica and Cryptococcus laurentii), previously isolated from Picante cheese were assayed for biochemical performance in proteolysis and lipolysis. In addition to the difference of the microbiological strains, the milk type (caprine or ovine), the ripening time (0 to 65 days) and the concentration of NaCl (0 to 14%(w/v)) have been deliberatly fixed in vitro curdled milk (previously prepared from heat-sterilized milk, coagulated with animal rennet and inoculated with each strain) and subject to 12 ºC. High proteolytic activity was demonstrated by Y. lipolytica and by all the other strains to a lesser extent; Y. lipolytica produced ca. 85% of WSN by 65 days of ripening whereas E. faecium, D. hansenii and C. laurentii produced levels of WSN ranging in 40-50%, and E. faecalis, L. plantarum and L. paracasei in 30- 40%. In terms of peptidolytic activity, measured by NPN contents and by release of free amino acids, once again Y. lipolytica presented the highest activity, followed by L. plantarum, L. paracasei, E. faecium and E. faecalis. Milk type, ripening time, and content of NaCl revealed to be statistically significant processing factors in terms of proteolysis; caprine milk, 65 days of ripening and lower contents of NaCl led to the highest values. The lipolytic activity, assessed by the release of butyric acid from tributyrin, was strong for Y. lipolytica and C. laurentii, whereas release of free fatty acids was observed at different rates for all strains under study. Ripening time proved to be a statistically significant factor for lipolysis, whereas milk type was not; lipolytic activities, measured as fat acidity index, were strongly affected by NaCl content and, as happened with release of free amino acids, the extent of fat hydrolysis was much more affected by the increase of NaCl from 0 to 7% than by its increase from 7% to 14%. Although it is not possible to directly compare results obtained in vitro using pure, single cultures with those obtained in loco using actual cheese, our results suggest that a mixed-strain starter for Picante cheese including L. plantarum, E. faecium (or E. faecalis) and D. hansenii (and/or Y. lipolytica) would be of potential interest.info:eu-repo/semantics/publishedVersio

Dominant microflora of Picante cheese: effects on proteolysis and lipolysis

Four species of bacteria (Enterococcus faecium and E. faecalis, Lactobacillus plantarum and L. paracasein and three species of yeasts (Debaryomyces hansenii, Yarrowia lipolytica and Cryptococcus laurentiU previously isolated from Picante cheese, were assayed for proteolysis and lipolysis. Milk type (caprine or ovine), ripening time (0 to 65 d) and concentration of NaCl (0 to 14 %(w/v)) have been assessed in terms of their effects upon in vitro curdled milk. Good evidence of proteolytic and peptidolytic activities was provided 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 also observed for the other strains under study. Ripening time was statistically significant with regard to lipolysis but milk type was not. Lipolytic activities were strongly affected by presence of NaCl. According to experimental results, it is suggested that a mixed-strain starter for Picante cheese including L. plantarum, E. faecium (or E. faecalis,) and D. hansenii (and/or Y. lipolyticaj is of potential interest.info:eu-repo/semantics/publishedVersio

Rheological, textural and microstructural features of probiotic whey cheeses

Whey 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.info:eu-repo/semantics/acceptedVersionhttps://creativecommons.org/licenses/by-nc-nd/4.0

Organic acids produced by lactobacilli, enterococci and yeasts isolated from Picante cheese

Four 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

Role of dominant microflora of Picante cheese on proteolysis and lipolysis

Four 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