Ultrafiltration Retentate Research Articles

Ameliorative potential of whey protein hydrolysate against paracetamol-induced oxidative stress

The aim of the present study was to validate the antioxidant effect of whey protein hydrolysate (WPH) using a small animal model. Paracetamol is common drug that is safe at therapeutic levels; however, an overdose causes oxidative stress, which may lead to potential hepatic and renal necrosis. The protective effect of WPH against paracetamol-induced hepato-nephrotoxicity in mice was investigated in this study. The WPH was prepared by hydrolyzing ultrafiltered retentate of mozzarella cheese whey with commercial food-grade alcalase; the resulting WPH had substantial in vitro antioxidant activity. Male albino mice were treated with WPH for 4 d [intraperitoneally at 4mg/kg of body weight (BW) per day or orally at 8mg/kg of BW per day] before or after oral administration of paracetamol (300mg/kg of BW) for 2 d. Two control groups were used; the negative control mice were administered water only; the paracetamol group was administered paracetamol at 300mg/kg of BW but received no WPH. Levels of different marker enzymes (glutamate pyruvate transaminase and alkaline phosphatase), creatinine, and blood urea nitrogen were measured in the experimental animal blood sera. The WPH successfully mitigated the increase in the concentration of oxidative biomarkers such as glutathione pyruvate transaminase, alkaline phosphatase, and creatinine, and restored the level of blood urea nitrogen to normal in sera of mice in which oxidative stress was induced with an overdose of paracetamol. Furthermore, the indices of different antioxidant enzymes, such as catalase, superoxide dismutase, and glutathione peroxidase, and lipid peroxidation end-products were determined in liver homogenate. The mice that were given WPH, either intraperitoneally or orally, showed increased activities of antioxidant enzymes and a reduction in thiobarbituric acid reactive substances (TBARS) compared with the paracetamol control group. The protective effect of WPH was less when administered orally than intraperitoneally. We concluded that WPH is the potential protector against paracetamol-induced hepato-nephrotoxicity and can be effectively used in health-promoting foods as a biofunctional ingredient.

Iron speciation in soft-water lakes and soils as determined by EXAFS spectroscopy and geochemical modelling

Complexation of iron by organic matter can potentially compete with toxic metals for binding sites. Iron(III) forms both monomeric and di/trimeric complexes with fulvic and humic acids, but the nature and extent of complexation with natural organic matter samples from soft-water lakes has not been extensively studied. The aim of this study was to determine the coordination of iron in complexes with organic matter in two soft-water lakes and in the surrounding Oe soil horizons. Iron K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy was performed on particles and large colloids (>0.45μm) collected by in-line pre-filtration, and on smaller colloids isolated both on an AGMP-1 anion-exchange column and by concentration using 1000Da ultrafiltration. The results showed that iron(III) was mainly present in monomeric complexes with organic matter, both in the lake water smaller colloids and in the soil samples. Evidence for iron(III) (hydr)oxides was found for the lake particles, in the ultrafiltration retentates, and in some of the soils. Overall, the results suggest that complexation of iron(III) to organic matter prevents hydrolysis into polymeric forms. Strong complexation of iron(III) would lead to competition with other metals for organic-matter binding sites.

Production of antioxidant soy protein hydrolysates by sequential ultrafiltration and nanofiltration

Soy protein hydrolysates, produced by enzymatic hydrolysis of soy protein isolate (SPI) with pepsin and pancreatin, were subjected to sequential ultrafiltration (UF) and nanofiltration (NF). Heat treatment of SPI prior to enzymatic hydrolysis was investigated for its effect on ORAC and FCR antioxidant capacity of the fractions. The ORAC antioxidant capacity was significantly higher than the FCR antioxidant capacity for any given fraction. The UF permeate fractions (MW smaller than 10kDa), containing approximately 50% of the feed total solids, displayed higher ORAC antioxidant capacity compared to the corresponding feed and retentate fractions for soy protein hydrolysate produced from SPI with heating (H-SPH) and without heating (SPH). In contrast, the FCR antioxidant capacity of the UF fractions was affected by SPI heating. The UF permeate fraction had higher FCR antioxidant capacity when compared to the UF retentate for SPH produced from SPI with no heating. The NF permeate fractions produced at pH 8 with a 2.5kDa MWCO thin film composite membrane displayed the highest ORAC antioxidant capacity, 5562μmolTEg−1 TS (SPH) and 5187μmolTEg−1 TS (H-SPH). Due to the significant improvement of the ORAC antioxidant capacity with a loose NF membrane at pH 8, the potential for NF as a viable industrial fractionation process for soy protein hydrolysates with antioxidant capacity was demonstrated.

Determination of insulin-like growth factor-1 and bovine insulin in raw milk and its casein and whey fractions after microfiltration and ultrafiltration

Insulin-like growth-factor 1 (IGF-1) and insulin were analysed from bovine milk during microfiltration (MF) and ultrafiltration (UF) processes using immunochemical methods. IGF-1 was found in the MF retentate and in the UF retentate. A very small fraction of IGF-1 was in the UF permeate. The results indicated that IGF-1 was present in milk as a complex molecule or bound to milk proteins. Insulin showed similar behaviour, but more insulin was found in the MF retentate than in the UF retentate. No insulin was found in the UF permeate. There were no differences in IGF-1 or insulin distribution between pasteurised or non-pasteurised milk. The stability of bovine insulin to heat treatments was also determined. The molecule was stable during pasteurisation at 65 and 72 °C, but lost some of its immunochemical activity at 90 and 135 °C.

Rennet coagulation of sheep milk processed by ultrafiltration at low concentration factors

The ultrafiltration (UF) of sheep milk is carried out in concentration mode in order to evaluate the variation of the rennet clotting properties of the concentrates as a function of the volumetric concentration factors up to a value of 2.0. The UF unit is equipped with 25.5cm2 of membrane surface area. The cellulose acetate laboratory – made membrane has a molecular weight cut-off of 7000Da. The evolution pattern of the rennet clotting properties of the skimmed sheep milk feed and UF retentates was assessed by the Optigraph. A significant increase on curd firmness and rate of curd firming was detected with the increase of the protein concentration, while RCT show a tendency to increase with milk protein content. The variation of curd firmness and rate of curd firming with the protein concentration was linear and correlations were established.

Effect of pasteurization on the distribution of bovine milk transforming growth factor-β2 in casein and whey fractions during micro- and ultrafiltration processes

Whey from bovine milk or colostrum is usually used as a raw material for separation and concentration of small bioactive compounds, such as growth factors. In this work, transforming growth factor-β2 (TGF-β2) was concentrated from farm milk. Casein was separated and concentrated by microfiltration, followed by ultrafiltration of the permeate to concentrate whey proteins. TGF-β2 concentrations were monitored throughout the processes. The distribution of TGF-β2 during microfiltration and ultrafiltration was compared between pasteurized and non-pasteurized milk. For pasteurized milk, 80% of the growth factor was in the casein fraction, in the heat-activated immunoreactive form. For non-pasteurized milk, TGF-β2 was distributed between the casein fraction (55%) and the whey fraction (37%), mostly in the latent form. The highest growth factor concentration was in the ultrafiltration retentate of non-pasteurized milk if expressed per protein content (3.5μgg−1 protein). The total recovery of TGF-β2 was 83% (pasteurized milk) or 93% (non-pasteurized milk).

Manufacture of Labneh from Cow's MilkUsing Ultrafiltration Retentate with or WithoutAddition of Permeate Concentrate

Chemical composition, rheological properties and sensory evaluation of fresh labneh made from cow's milk, using ultrafiltration (UF) retentate and traditional process were investigated. Coagulation times showed a synergetic effect of addition of both GDL (1%) and permeate concentrate (1%) on coagulation time of labneh where the two components have been accelerated the acidity development. Consequently, the coagulation time becomes shorter. Addition of 1% permeate concentrate, 1% or 2% GDL already increased total solids significantly. Chemical composition of labneh showed that total solids, total protein, soluble protein, fat, ash, acidity and pH were increased in labneh made from UF retentate comparing with that traditionally prepared. pH was higher in UF labneh although acidity content was markedly higher than that of traditionally prepared one due to the buffering capacity of high content of protein in retentate. Soluble protein content was trebled in UF retentate labneh. Lactose content was lower in UF labneh than control except those treatments where permeate concentrate was added. Texture profile test showed that a correlation between acidity, coagulation time and hardness may be exist. Results also showed that there is no definite correlations between the additions of permeate concentrate or GDL and springiness or adhesiveness of labneh. Addition of 1% permeate concentrate has lowered the cohesiveness values, while addition of 1% GDL had no effect. Values of resilience are consistent with those of cohesiveness. Wide variations were observed among treatments. Addition of 1% permeate concentrate to the UF labneh improved the appearance, consistency and flavor of produced labneh.

High growth rates in Atlantic salmon (Salmo salar L.) fed 7.5% fish meal in the diet. Micro-, ultra- and nano-filtration of stickwater and effects of different fractions and compounds on pellet quality and fish performance.

The intention of this study is to investigate the effect of fish meal soluble protein quality on growth and protein utilisation of Atlantic salmon fed very low fish meal diets. For this purpose stickwater (SW) was separated during herring meal production, fractionated following successive micro- ultra- and nano-filtration steps and reintroduced in the press cake (PC) in order to produce 4 reconstituted fish meals containing different molecular size soluble protein mixes. The SW fractions used for the production of the experimental fish meals were: 1) the micro-filtration (MF) retentate, 2) the ultra-filtration (UF) retentate, 3) the nano-filtration (NF) retentate and 4) the nano-filtration permeate. Four very low fish meal experimental diets were prepared containing 25gkg−1 super prime fish meal and 50gkg−1 diet of one of the 4 experimental fish meals produced. A positive control diet was prepared containing 300gkg−1 diet super prime fish meal. Three more diets were prepared containing 25gkg−1 diet super prime fish meal and 50gkg−1 diet PC. Two of them were supplemented with either crystalline taurine, or crystalline hydroxyproline, up to the levels present in the high fish meal control diet. The experimental diets with the SW fractions contained similar levels of water soluble protein (WSP), which were higher than in the PC diets and lower than in the control. All diets were iso-nitrogenous, iso-lipidic and iso-energetic and were fed to 8 triplicate groups of salmon (80 fish per group of initial body weight 133g), for 69days. High growth rates and low fish in-fish out ratios (FIFO) were achieved in salmon fed all the very low fish meal diets. Feed intake, fish body growth, whole body protein content, protein gain and morphometry were significantly affected by the inclusion of the different SW fractions in the low fish meal diets. The medium size peptides (UF retentate) induced significant increase in feed consumption in salmon and supported higher fish growth compared to the highest (MF retentate) or the lowest molecular weight peptides (NF permeate) where both feed intake and fish growth were reduced. The fish fed the diet containing the NF permeate had significantly lower growth compared to the diets containing the other SW fractions. We did not find any benefits for salmon performance by the supplementation of taurine or hydroxyproline alone to the low WSP PC diets. The present work gives evidence on the multi-dimensional effects of the different marine water soluble components on fish performance. In order to identify novel, high added-value, water soluble marine compounds, advanced large scale separation technologies must be further developed and applied in studies investigating specific functional effects that these compounds may have on fish and other organisms.

Separation and Properties of Polysaccharides from Asparagus (<i>Officinalis</i> L) Old Stalks

The polysaccharides of the asparagus old stalks was seperated by ethanol precipitation and ultrafiltration. The molecular weigh distribution and antioxidative capacity of the extracts of the alcohol precipitation(C-1), ultrafiltration retention(C-2), and ultrafiltration penetrates (C-3) were further evaluated. The polysaccharides yields of the C-1, C-2, and C-3 were 1.53, 1.21, and 0.71%, respectively. The weigh average molecular weight of C-1, C-2, and C-3 were 163900, 135880, and 61063 Da, respectively. C-2 showed the strongest antioxidant capacity in all extracts by the scavenging effect on DPPH, superoxide and hydroxyl radicals. Therefore, the ultrafiltration was an alternative to separate the polysaccharides from the asparagus old stalks and kept their antioxidatant capacity.

Nisin Quantification by ELISA Allows the Modeling of Its Apparent Diffusion Coefficient in Model Cheeses

The diffusion of small solutes in cheese is of key importance for most enzymatic reactions involved in the ripening process. However, only a limited amount of data is available on salt diffusion and practically none on peptide diffusion. Nisin, a bacteriocin peptide, migrated in model cheeses made from ultrafiltered (UF) retentate. A profile concentration device and an enzyme-linked immunosorbent assay (ELISA), specifically developed for nisin quantification in cheese, were used to model the apparent diffusion coefficients for nisin according to Fick's law. This average coefficient was 49.5 μm(2)/s in UF cheese (n = 2). When 10% gelatin was added to the retentate, this value decreased to 34.4 μm(2)/s (n = 2). The two cheeses differed in their macrostructure (rheology) and microstructure (confocal microscopy). This study provides the first apparent diffusion coefficients for a peptide in cheese and supports the hypothesis that composition and structure influence the diffusion of small solutes such as peptides.

Standardization of milk using cold ultrafiltration retentates for the manufacture of Swiss cheese: Effect of altering coagulation conditions on yield and cheese quality

Fortification of cheesemilk with membrane retentates is often practiced by cheesemakers to increase yield. However, the higher casein (CN) content can alter coagulation characteristics, which may affect cheese yield and quality. The objective of this study was to evaluate the effect of using ultrafiltration (UF) retentates that were processed at low temperatures on the properties of Swiss cheese. Because of the faster clotting observed with fortified milks, we also investigated the effects of altering the coagulation conditions by reducing the renneting temperature (from 32.2 to 28.3°C) and allowing a longer renneting time before cutting (i.e., giving an extra 5min). Milks with elevated total solids (TS; ∼13.4%) were made by blending whole milk retentates (26.5% TS, 7.7% CN, 11.5% fat) obtained by cold (<7°C) UF with part skim milk (11.4% TS, 2.5% CN, 2.6% fat) to obtain milk with CN:fat ratio of approximately 0.87. Control cheeses were made from part-skim milk (11.5% TS, 2.5% CN, 2.8% fat). Three types of UF fortified cheeses were manufactured by altering the renneting temperature and renneting time: high renneting temperature=32.2°C (UFHT), low renneting temperature=28.3°C (UFLT), and a low renneting temperature (28.3°C) plus longer cutting time (+5min compared to UFLT; UFLTL). Cutting times, as selected by a Wisconsin licensed cheesemaker, were approximately 21, 31, 35, and 32min for UFHT, UFLT, UFLTL, and control milks, respectively. Storage moduli of gels at cutting were lower for the UFHT and UFLT samples compared with UFLTL or control. Yield stress values of gels from the UF-fortified milks were higher than those of control milks, and decreasing the renneting temperature reduced the yield stress values. Increasing the cutting time for the gels made from the UF-fortified milks resulted in an increase in yield stress values. Yield strain values were significantly lower in gels made from control or UFLTL milks compared with gels made from UFHT or UFLT milks. Cheese composition did not differ except for fat content, which was lower in the control compared with the UF-fortified cheeses. No residual lactose or galactose remained in the cheeses after 2 mo of ripening. Fat recoveries were similar in control, UFHT, and UFLTL but lower in UFLT cheeses. Significantly higher N recoveries were obtained in the UF-fortified cheeses compared with control cheese. Because of higher fat and CN contents, cheese yield was significantly higher in UF-fortified cheeses (∼11.0 to 11.2%) compared with control cheese (∼8.5%). A significant reduction was observed in volume of whey produced from cheese made from UF-fortified milk and in these wheys, the protein was a higher proportion of the solids. During ripening, the pH values and 12% trichloroacetic acid-soluble N levels were similar for all cheeses. No differences were observed in the sensory properties of the cheeses. The use of UF retentates improved cheese yield with no significant effect on ripening or sensory quality. The faster coagulation and gel firming can be decreased by altering the renneting conditions.

Impact of ultrafiltration and nanofiltration of an industrial fish protein hydrolysate on its bioactive properties

Numerous studies have demonstrated that in vitro controlled enzymatic hydrolysis of fish and shellfish proteins leads to bioactive peptides. Ultrafiltration (UF) and/or nanofiltration (NF) can be used to refine hydrolysates and also to fractionate them in order to obtain a peptide population enriched in selected sizes. This study was designed to highlight the impact of controlled UF and NF on the stability of biological activities of an industrial fish protein hydrolysate (FPH) and to understand whether fractionation could improve its content in bioactive peptides. The starting fish protein hydrolysate exhibited a balanced amino acid composition, a reproducible molecular weight (MW) profile, and a low sodium chloride content, allowing the study of its biological activity. Successive fractionation on UF and NF membranes allowed concentration of peptides of selected sizes, without, however, carrying out sharp separations, some MW classes being found in several fractions. Peptides containing Pro, Hyp, Asp and Glu were concentrated in the UF and NF retentates compared to the unfractionated hydrolysate and UF permeate, respectively. Gastrin/cholecystokinin-like peptides were present in the starting FPH, UF and NF fractions, but fractionation did not increase their concentration. In contrast, quantification of calcitonin gene-related peptide (CGRP)-like peptides demonstrated an increase in CGRP-like activities in the UF permeate, relative to the starting FPH. The starting hydrolysate also showed a potent antioxidant and radical scavenging activity, and a moderate angiotensin-converting enzyme (ACE)-1 inhibitory activity, which were not increased by UF and NF fractionation. Fractionation of an FPH using membrane separation, with a molecular weight cut-off adapted to the peptide composition, may provide an effective means to concentrate CGRP-like peptides and peptides enriched in selected amino acids. The peptide size distribution observed after UF and NF fractionation demonstrates that it is misleading to characterize the fractions obtained by membrane filtration according to the MW cut-off of the membrane only, as is currently done in the literature.

Purification of porcine reproductive and respiratory syndrome virus from cell culture using ultrafiltration and heparin affinity chromatography

Porcine reproductive and respiratory syndrome (PRRS) virus is the causative agent of the most significant infectious disease currently affecting the swine industry worldwide. Density gradient ultracentrifugation remains the most commonly used method for porcine reproductive and respiratory syndrome virus (PRRSV) purification. However, this technique has notable drawbacks including long processing time and limited processing volume in each run. To overcome these limitations, a scalable process was developed. PRRSV propagated in MARC-145 was released by three freeze/thaw cycles. After a low speed centrifugation step, the virus particles in the supernatant were concentrated twice by an ultrafiltration step. The ultrafiltration step concentrated the virions effectively with no detectable loss while some cultural/cellular proteins were removed. The virions in the ultrafiltration retentate were then applied to a heparin affinity column on a fast performance liquid chromatography unit. The combined ultrafiltration and heparin affinity chromatography process removed more than 96% of cellular and medium proteins. During a stepwise elution strategy, the viral particles were eluted at two separate peaks recovering 27.5% and 25.4% of viral particles loaded onto the column with a purity of 194 and 3917 particles/μg protein, respectively.

Fractionation of process water in thermomechanical pulp mills

In this work process water from a thermomechanical pulp mill was divided into five fractions by filtration and membrane filtration. Suspended matter was mainly isolated in the retentate from the drum filter, extractives in the microfiltration retentate, hemicelluloses in the ultrafiltration retentate and lignin in the nanofiltration retentate. The final water fraction was of fresh water quality. For each tonne of pulp produced, about 10 kg of suspended matter, more than 0.3 kg of extractives, 11 kg of hemicelluloses and 8 kg of aromatic compounds (lignin) could be recovered from the drum filtration retentate, the microfiltration retentate, the ultrafiltration retentate and the nanofiltration retentate, respectively. About 40% of the treated process water could be recovered as fresh water.

Substituting Citrate for Lactate in Peritoneal Dialysis Fluid Improves Ultrafiltration in Rats

Exposure to peritoneal dialysis (PD) fluid induces an inflammatory response in the peritoneal cavity. Blockers of complement and coagulation have improved ultrafiltration in animal models of PD. Citrate is a clinically established anticoagulant that also blocks complement activation. The aim of the present study was to evaluate the effects on ultrafiltration of a gradual substitution of citrate for lactate in an experimental model of PD. Fractions (0, 5, 10, and 15 mmol/L) of the 40 mmol/L lactate buffer of filter-sterilized 2.5% glucose PD fluid were replaced by citrate. The modified fluids were compared in a rat model of single PD fluid exposure through an indwelling catheter. The initial kinetics of citrate and ionized calcium were evaluated in separate, single, short time dwell experiments. Replacing 10 and 15 mmol/L of the lactate buffer by sodium citrate significantly increased osmotic ultrafiltration (by 24.7%+/-7.7% at 10 mmol/L), net ultrafiltration, and glucose retention at 4 hours of dwell time in the rat model. Osmotic ultrafiltration was significantly correlated to citrate concentration and glucose concentration. Citrate was rapidly eliminated from the peritoneal cavity, concentrations falling to less than half in 1 hour and concentrations of calcium ions concomitantly normalized. Substituting citrate for lactate induced a dose-dependent increase in ultrafiltration. Mechanisms probably involve the relation between diffusion and ultrafiltration, leading to increased glucose retention. The increase in ultrafiltration was quantitatively important at a citrate concentration (10 mmol/L) that is compatible with clinical applications of citrate.

Characterization of Echinacea fractions obtained by an ultrafiltration process

Echinacea extracts are widely used in Romania accordingly or in combination with other plant extracts, usually as ethanolic extracts. The main objective of the present study was to obtain an Echinacea purpurea extract with a high content of polymeric compounds using an ultrafiltration process. The second target was to characterize the fractions obtained by this process. E. purpurea roots were extracted with 30 percent ethanol (1: 10 w/v), and polymers of 10 kDa or more were collected as ultrafiltration retentates. The ultrafiltration process was performed using two types of membranes with a cut off 5000 Da and 1000 Da. Permeates were collected in two stages in order to follow the process of polyphenol concentrations. We obtained a concentration report 1.5:1 (v/v). The content of bioactive compounds (another than polysaccharides) and free radical scavenging activity of retentates and permeates was determined and compared with those of initial extracts. The total phenolic content was determined using the Folin-Ciocalteu method [1] and the free radical scavenging activity was evaluated using DPPH and ABTS scavenging methods and the results were expressed as Trolox equivalent antioxidant capacity (TEAC) [2]. Chemical constituents of all the samples were analysed by an RP HPLC–DAD method. The results show that even low molecular mass compounds like polyphenols pass through membranes, the content of polyphenols in retentate (2.8±0.02mg/ml) was higher than all the permeates (1.7±0.023mg/ml). The data were sustained by TEAC values obtained for retentates (11.89mM/L TEAC by DPPH method and 26.77mM/L TEAC by ABTS method) and permeates (8.83 mM/L TEAC by DPPH method and 9.36 mM/L TEAC by ABTS method). Small differences were observed between the two permeates collected. The same results were obtained by HPLC determinations.

Rheological properties of reduced fat mozzarella cheese made by direct acidification using low concentration factor ultrafiltration retentates

Rheological properties of reduced fat mozzarella cheese made by direct acidification using low concentration factor ultrafiltration retentates

Altering Renneting pH Changes Microstructure, Cell Distribution, and Lysis of Lactococcus lactis AM2 in Cheese Made from Ultrafiltered Milk

The objective of this study was to investigate the lysis of a highly autolytic strain of Lactococcus lactis ssp. cremoris AM2 in a model cheese made from concentrated ultrafiltered milk. From the same initial ultrafiltered retentate inoculated with L. lactis AM2, 5 cheeses were made by the addition of rennet at different pH values (6.6, 6.2, 5.8, 5.4, and 5.2). Lysis was monitored by measurement of the release of lactate dehydrogenase, an intracellular marker enzyme, and by immunodetection of intracellular proteins with species-specific antibodies. Confocal scanning laser microscopy (CSLM) was used to investigate the cheese microstructure by staining for protein and fat. Dual staining with a bacterial viability kit with CSLM was performed to reveal the integrity and localization of the bacterial cells. Levels of soluble calcium significantly increased when the pH at which the rennet was added decreased. In cheese renneted at pH 6.6, CSLM revealed an open porous structure containing a dense protein network with fat globules of different sizes distributed in the aqueous phase. In cheese renneted at pH 5.2, the protein network was homogeneous, with a less dense protein network, and an even distribution of fat globules. On d 1, bacterial cells were organized into colonies in cheese renneted at pH 6.6, whereas in cheeses renneted at pH 5.2, bacteria were evenly dispersed as single cells throughout the protein network. Lysis was detected on d 1 in cheeses renneted at high pH values and continued to increase throughout ripening, whereas induction of lysis was delayed in cheeses renneted at lower pH values until the end of ripening. This study demonstrates that alterations in the microstructure of the cheese and the distribution of cells play a role in lysis induction of L. lactis AM2.

Use of low concentration factor ultrafiltration retentates in reduced fat “Minas Frescal” cheese manufacture: Effect on composition, proteolysis, viscoelastic properties and sensory acceptance

Abstract Composition, proteolysis, viscoelastic properties and sensory acceptance of reduced fat “Minas Frescal” cheese made from low concentration factor (CF) retentates were studied. Three different CFs (1.2, 1.5 and 1.8) were tested. The cheeses were monitored for proteolysis and rheological characteristics during 16 days of storage at 7 °C. The moisture content of the cheeses decreased with increasing CF. Proteolysis was not significantly influenced by CF, but increased with time for all cheeses. The viscoelastic properties were significantly affected by CF, but not by storage time. As CF increased, fracture stress, elasticity, maximum stress, creep Newtonian viscosity and stress-relaxation parameters (elastic moduli E0, E1, E2, and viscosities η 1 , η 2 ) increased, while creep compliances (J0, J1, J2) decreased. Increasing CF to 1.8 significantly reduced the grading scores for appearance, texture and overall impression; in contrast, increasing the CF from 1.2 to 1.5 did not significantly influence the grading scores for these parameters.

Modification of casein micelle structure caused by ultrafiltration and heat treatment: A spectrofluorimetric and kinetic approach

The effect of heat treatment on the structure of the milk protein system has been investigated in unconcentrated bovine skimmilk and its twofold and threefold ultrafiltered retentates. A variation in hydrophobic binding sites of proteins which gives information on hydrophobicity was observed. The energy of activation ( E a) values of the samples were compared with each other in the initial phase. The protein surface hydrophobicity of the samples was plotted versus time for four different temperatures. The E a values which calculated for each temperature were compared with each other in unconcentrated skimmilk and the retentates. This kinetic approach suggests that the heat-induced structural modification of milk proteins is related to the concentration factor of the ultrafiltration treatment.