Cutting, by 'pressing and slicing,' of thin floppy slices of materials illustrated by experiments on cheddar cheese and salami

Why it is easier to cut with even the sharpest knife when 'pressing down and sliding' than when merely 'pressing down alone' is explained. A variety of cases of cutting where the blade and workpiece have different relative motions is analysed and it is shown that the greater the 'slice/push ratio' xi given by ( blade speed parallel to the cutting edge/blade speed perpendicular to the cutting edge), the lower the cutting forces. However, friction limits the reductions attainable at the highest.. The analysis is applied to the geometry of a wheel cutting device (delicatessan slicer) and experiments with a cheddar cheese and a salami using such an instrumented device confirm the general predictions. (C) 2004 Kluwer Academic Publishers.

Serpa cheese: technological, biochemical and microbiological characterisation of a PDO ewe's milk cheese coagulated with Cynara cardunculus L

Portugal has a strong tradition of cheesemaking from raw ewe's milk; most of these cheeses are still made on a traditional farmhouse scale. Their production is protected by Protected Designation of Origin (PDO) but the specific biochemical aspects of the majority still need to be characterised. Two different cheesemaking procedures, traditional and semi-industrial, were compared technologically, biochemically and microbiologically. It was observed that, despite the highly significant difference between artisanal and semi-industrial cheeses (P < 0.001), both products were within the limits of national regulations for most parameters except maturation temperature, humidity and the value for the maturation index. Although the present study was not fully representative of the region, the results obtained suggest that the specific regulations for Serpa cheese should be revised and that other parameters, such as moisture and salt-in-moisture content, which are very much dependent on the cheesemaking process, should be included in order to characterise better this traditional cheese.

Evaluation of Serpa cheese proteolysis by nitrogen content and capillary zone electrophoresis

Proteolysis of Serpa cheese produced traditionally (B) and semi-industrially (C) was evaluated for the first time by determination of nitrogen content and capillary zone electrophoresis (CZE). A citrate dispersion of cheese was fractionated to determine the nitrogen in pH 4.4, trichloroacetic and phosphotungstic acid soluble fractions (pH 4.4-SN, TCA-SN and PTA-SN, respectively). The pH 4.4-SN was significantly higher for B ( P < 0.001), while TCA-SN was significantly higher for C ( P < 0.001). PTA-SN was also higher for C but at 60 days ripening no significant difference was found between B and C. Degradation of alpha(s1) - and beta-caseins evaluated by CZE was in good agreement with the maturation index (pH 4.4-SN/TN).

Selenium supplementation of lactating dairy cows: effects on milk production and total selenium content and speciation in blood, milk and cheese

Forty multiparous Holstein cows were used in a 16-week continuous design study to determine the effects of either selenium (Se) source, selenised yeast (SY) (derived from a specific strain of Saccharomyces cerevisiae CNCM 1-3060) or sodium selenite (SS), or Se inclusion rate in the form of SY in the diets of lactating dairy cows on the Se concentration and speciation in blood, milk and cheese. Cows received ad libitum a total mixed ration (TMR) with a 1 : 1 forage: concentrate ratio on a dry matter (DM) basis. There were four diets (T-1 to T-4), which differed only in either source or dose of Se additive. Estimated total dietary Se for T, (no supplement), T-2 (SS), T-3 (SY) and T-4 (SY) was 0.16, 0.30, 0.30 and 0.45 mg/kg DM, respectively. Blood and milk samples were taken at 28-day intervals and at each time point there were positive linear effects of Se in the form of SY on the Se concentration in blood and milk. At day 112 blood and milk Se values for T-1 to T-4 were 177, 208, 248 and 279 +/- 6.6 and 24, 38, 57 and 72 +/- 3.7 ng/g fresh material, respectively, and indicate improved uptake and incorporation of Se from SY. In whole blood, selenocysteine (SeCys) was the main selenised amino acid and the concentration of selenomethionine (SeMet) increased with the increasing inclusion rate of SY In milk, there were no marked treatment effects on the SeCys content, but Se source had a marked effect on the concentration of SeMet. At day 112 replacing SS (T-2) with SY (T-3) increased the SeMet concentration of milk from 36 to 111 ng Se/g and its concentration increased further to 157ng Se/g dried sample as the inclusion rate of SY increased further (T-4) to provide 0.45 mg Se/kg TMR. Neither Se source nor inclusion rate affected the keeping quality of milk. At day 112 milk from T-1, T-2 and T-3 was made into a hard cheese and Se source had a marked effect on total Se and the concentration of total Se comprised as either SeMet or SeCys. Replacing SS (T-2) with SY (T-3) increased total Se, SeMet and SeCys content in cheese from 180 to 340 ng Se/g, 57 to 153 ng Se/g and 52 to 92 ng Se/g dried sample, respectively. The use of SY to produce food products with enhanced Se content as a means of meeting the Se requirements is discussed

Viability of Salmonella enterica subsp. enterica during the preparation and cold storage of Egyptian soft cheeses and ice-cream

Changes occurring in the viability of Salmonella enterica subsp. enterica during the preparation and cold storage of Domiati cheese, Kariesh cheese and ice-cream were examined. A significant decrease in numbers was observed after whey drainage during the manufacture of Domiati cheese, but Salmonella remained viable for 13 weeks in cheeses prepared from milks with between 60 and 100 g/L NaCl; the viability declined in Domiati cheese made from highly salted milk during the later stages of storage. The method of coagulation used in the preparation of Kariesh cheese affected the survival time of the pathogen, and it varied from 2 to 3 weeks in cheeses made with a slow-acid coagulation method to 4-5 weeks for an acid-rennet coagulation method. This difference was attributed to the higher salt-in-moisture levels and lower pH values of Kariesh cheese prepared by the slow-acid coagulation method. A slight decrease in the numbers of Salmonella resulted from ageing ice-cream mix for 24 h at 0degreesC, but a greater reduction was evident after one day of frozen storage at -20degreesC. The pathogen survived further frozen storage for four months without any substantial change in numbers.

Assessment of the quality of cottage cheese produced from standard and protein-fortified skim milk

The effects of milk protein fortification on the texture and microstructure of cottage cheese curd were evaluated. Protein powder (92.6% protein) was added to the skim milk at a level of 0.4% (w/w) to produce curds. Control curds with no protein powder addition were also produced. These curds were analysed for differences in yield, total solids, curd size, texture and structure. It was found that the addition of protein powder contributed to a significant yield increase, which can be attributed to increased water retention, with better curd size distribution. Control curds were firmer than the fortified curds and the structure showed less open-pore structure as revealed by electron microscopy. However, the addition of dressing masked the textural differences, and a sensory panel was unable to distinguish between cheeses produced from fortified milk and controls.

Casein and whey exert different effects on plasma amino acid profiles, gastrointestinal hormone secretion and appetite

Protein, generally agreed to be the most satiating macronutrient, may differ in its effects on appetite depending on the protein source and variation in digestion and absorption. We investigated the effects of two milk protein types, casein and whey, on food intake and subjective ratings of hunger and fullness, and on postprandial metabolite and gastrointestinal hormone responses. Two studies were undertaken. The first study showed that energy intake from a buffet meal ad libitum was significantly less 90 min after a 1700 kJ liquid preload containing 48 g whey, compared with an equivalent casein preload (P<0.05). In the second study, the same whey preload led to a 28 % increase in postprandial plasma amino acid concentrations over 3 h compared with casein (incremental area under the curve (iAUC), P<0.05). Plasma cholecystokinin (CCK) was increased by 60 % (iAUC, P<0.005), glucagon-like peptide (GLP)-1 by 65 % (iAUC, P<0.05) and glucose-dependent insulinotropic polypeptide by 36 % (iAUC, P<0.01) following the whey preload compared with the casein. Gastric emptying was influenced by protein type as evidenced by differing plasma paracetamol profiles with the two preloads. Greater subjective satiety followed the whey test meal (P<0.05). These results implicate post-absorptive increases in plasma amino acids together with both CCK and GLP-1 as potential mediators of the increased satiety response to whey and emphasise the importance of considering the impact of protein type on the appetite response to a mixed meal.

Selective separation of the major whey proteins using ion exchange membranes

Synthetic microporous membranes with functional groups covalently attached were used to selectively separate beta-lactoglobulin, BSA, and alpha-lactalbumin from rennet whey. The selectivity and membrane performance of strong (quaternary ammonium) and weak (diethylamine) ion-exchange membranes were studied using breakthrough curves, measurement of binding capacity, and protein composition of the elution fraction to determine the binding behavior of each membrane. When the weak and strong anion exchange membranes were saturated with whey, they were both selective primarily for beta-lactoglobulin with less than 1% of the eluate consisting of alpha-lactalbumin or BSA. The binding capacity of a pure alpha-lactoglobulin solution was in excess of 1.5 mg/cm(2) of membrane. This binding capacity was reduced to approximately 1.2 mg/cm(2) when using a rennet whey solution (pH 6.4). This reduction in protein binding capacity can be explained by both the competitive effects of other whey proteins and the effect of ions present in whey. Using binary solution breakthrough curves and rennet whey breakthrough curves, it was shown that alpha-lactalbumin and BSA were displaced from the strong and weak anion exchange membranes by beta-lactoglobulin. Finally, the effect of ionic strength on the binding capacity of individual proteins for each membrane was determined by comparing model protein solutions in milk permeate (pH 6.4) and a 10 mM sodium phosphate buffer (pH 6.4). Binding capacities of beta-lactoglobulin, alpha-lactalbumin, and BSA in milk permeate were reduced by as much as 50%. This reduction in capacity coupled with the low binding capacity of current ion exchange membranes are 2 serious considerations for selectively separating complex and concentrated protein solutions.

Recovery of lactoferrin and lactoperoxidase from sweet whey using colloidal gas aphrons (CGAs) generated from an anionic surfactant, AOT

The recovery of lactoferrin and lactoperoxidase from sweet whey was studied using colloidal gas aphrons (CGAs), which are surfactant-stabilized microbubbles (10-100 mum). CGAs are generated by intense stirring (8000 rpm for 10 min) of the anionic surfactant AOT (sodium bis-2-ethylhexyl sulfosuccinate). A volume of CGAs (10-30 mL) is mixed with a given volume of whey (1 - 10 mL), and the mixture is allowed to separate into two phases: the aphron (top) phase and the liquid (bottom) phase. Each of the phases is analyzed by SDS-PAGE and surfactant colorimetric assay. A statistical experimental design has been developed to assess the effect of different process parameters including pH, ionic strength, the concentration of surfactant in the CGAs generating solution, the volume of CGAs and the volume of whey on separation efficiency. As expected pH, ionic strength and the volume of whey (i.e. the amount of total protein in the starting material) are the main factors influencing the partitioning of the Lf(.)Lp fraction into the aphron phase. Moreover, it has been demonstrated that best separation performance was achieved at pH = 4 and ionic strength = 0.1 mol/L i.e., with conditions favoring electrostatic interactions between target proteins and CGAs (recovery was 90% and the concentration of lactoferrin and lactoperoxidase in the aphron phase was 25 times higher than that in the liquid phase), whereas conditions favoring hydrophobic interactions (pH close to pI and high ionic strength) led to lower performance. However, under these conditions, as confirmed by zeta potential measurements, the adsorption of both target proteins and contaminant proteins is favored. Thus, low selectivity is achieved at all of the studied conditions. These results confirm the initial hypothesis that CGAs act as ion exchangers and that the selectivity of the process can be manipulated by changing main operating parameters such as type of surfactant, pH and ionic strength.

Selective separation of beta-lactoglobulin from sweet whey using CGAs generated from the cationic surfactant CTAB

The selective separation of whey proteins was studied using colloidal gas aphrons generated from the cationic surfactant cetyl trimethyl ammonium bromide (CTAB). From the titration curves obtained by zeta potential measurements of individual whey proteins, it was expected to selectively adsorb the major whey proteins, i.e., bovine serum albumin, alpha-lactalbumin, and beta-lactoglobulin to the aphrons and elute the remaining proteins (lactoferrin and lactoperoxidase) in the liquid phase. A number of process parameters including pH, ionic strength, and mass ratio of surfactant to protein (M-CTAB/M-TP) were varied in order to evaluate their effect on protein separation. Under optimum conditions (2 mmol/l CTAB, M-CTAB/M-TP = 0.26-0.35, pH 8, and ionic strength = 0.018 mol/l), 80-90% beta-lactoglobulin was removed from the liquid phase as a precipitate, while about 75% lactoferrin and lactoperoxidase, 80% bovine serum albumin, 95% immunoglobulin, and 65% alpha-lactalbumin were recovered in the liquid fraction. Mechanistic studies using zeta potential measurements and fluorescence spectroscopy proved that electrostatic interactions modulate only partially the selectivity of protein separation, as proteins with similar surface charges do not separate to the same extent between the two phases. The selectivity of recovery of beta-lactoglobulin probably occurs in two steps: the first being the selective interaction of the protein with opposite-charged surfactant molecules by means of electrostatic interactions, which leads to denaturation of the protein and subsequent formation and precipitation of the CTAB-beta-lactoglobulin complex. This is followed by the separation of CTAB-beta-lactoglobulin aggregates from the bulk liquid by flotation in the aphron phase. In this way, CGAs act as carriers which facilitate the removal of protein precipitate. (c) 2005 Wiley Periodicals, Inc.

Functional petit-suisse cheese: measure of the prebiotic effect

Prebiotics and probiotics are increasingly being used to produce potentially synbiotic foods, particularly through dairy products as vehicles. It is well known that both ingredients may offer benefits to improve the host health. This research aimed to evaluate the prebiotic potential of novel petit-suisse cheeses using an in vitro fermentation model. Five petit-suisse cheese formulations combining candidate prebiotics (inulin. oligofructose. hone) and probiotics (Lactobacillus acidophilus, Bifidobacterium lactis) were tested in vitro using, sterile. stirred, batch culture fermentations with human faecal slurry. Measurement of prebiotic effect (MPE) values were generated comparing bacterial changes through determination of maximum growth rates of groups, rate of substrate assimilation and production of lactate and short chain fatty acids. Fastest fermentation and high lactic acid production, promoting increased growth rates of bifidobacteria and lactobacilli. were achieved with addition of prebiotics to a probiotic cheese (made using starter + probiotics). Addition of probiotic strains to control cheese (made using just a starter culture) also resulted in high lactic acid production. Highest MPE values were obtained with addition of prebiotics to a probiotic cheese, followed by addition of prebiotics and/or probiotics to a control cheese. Under the in vitro conditions used, cheese made with the combination of different prebiotics and probiotics resulted in the most promising functional petit-suisse cheese. The study allowed comparison of potentially functional petit-suisse cheeses and screening of preferred synbiotic potential for future market use. (c) 2007 Elsevier Ltd. All rights reserved.

Protease, peptidase and esterase activities by lactobacilli and yeast isolates from Feta cheese brine

Aims: The study of peptidase, esterase and caseinolytic activity of Lactobacillus paracasei subsp. paracasei, Debaryomyces hansenii and Sacchromyces cerevisiae isolates from Feta cheese brine. Methods and Results: Cell-free extracts from four strains of Lact. paracasei subsp. paracasei, four strains of D. hansenii and three strains of S. cerevisiae, isolated from Feta cheese brine were tested for their proteolytic and esterase enzyme activities. Lactobacillus paracasei subsp. paracasei strains had intracellular aminopeptidase, dipeptidyl aminopeptidase, dipeptidase, endopeptidase and carboxypeptidase activities. Esterases were detected in three of four strains of lactobacilli and their activities were smaller with higher molecular weight fatty acids. The strains of yeasts did not exhibit endopeptidase as well as dipeptidase activities except on Pro-Leu. Their intracellular proteolytic activity was higher than that of lactobacilli. Esterases from yeasts preferentially degraded short chain fatty acids. Lactobacilli degraded preferentially beta-casein. Caseinolytic activity of yeasts was higher than that of lactobacilli. Conclusions: The results suggest that Lact. paracasei subsp. paracasei and yeasts may contribute to the development of flavour in Feta cheese. Significance and impact of the Study: Selected strains could be used as adjunct starters to make high quality Feta cheese.

A study of the effects of adjunct cultures on the aroma compounds of Feta-type cheese

The influence of adjunct brine cultures on the volatile compounds in Feta-type cheeses made from bovine milk was studied. Four batches of brine were produced: one with no added adjuncts, a second containing Lactobacillus paracasei subsp. paracasei, a third containing Lb. paracasei subsp. paracasei plus Debaryomyces hansenii and a fourth with Lb. paracasei subsp. paracasei plus Yarrowia lipolytica. All the cultures were isolated from commercial Feta brines. Aroma compounds were analysed by dynamic headspace analysis, on-line coupled with GC/MS. The most important volatile compounds were quantified in the experimental cheeses; it was concluded that the use of Lb. paracasei subsp. paracasei and D. hansenii as adjuncts in the manufacture of Feta-type cheeses contribute to the formation of a richer pattern of aroma compounds, namely alcohols, aldehydes and esters. The inclusion of Y. lipolytica resulted in the production of undesirable aroma compounds that are not part of the usual volatile profile of high quality Feta cheeses. (C) 2004 Elsevier Ltd. All rights reserved.

Effect of chymosin and salt reduction on the quality of ultrafiltrated white-salted cheese

This study demonstrated that both chymosin and salt-in-moisture (SM) were important factors for proteolysis in the manufacture of ultrafiltrated white-salted cheese, with significant effects on water-soluble nitrogen and nitrogen soluble in trichloroacetic acid. In contrast, the levels of free amino acids were not significantly affected by chymosin and salt treatments. The cheeses made using high levels of chymosin with low SM had lower levels of residual α(s1)- and β-casein at the end of ripening. On texture profile analysis, the hardness and fracturability of the cheeses significantly increased with SM and decreased during ripening. Increases in chymosin significantly contributed to the overall weakening of the structure throughout ripening. Bitter flavour was detected after 12 weeks in the cheese made with the higher chymosin level and lower SM, which could be the result of accumulation of γ-casein fractions. The sensory data indicated that the hedonic responses for low chymosin with low SM cheeses were good and acceptable in flavour, which may be due to the moderate levels of proteolysis products.

Effect of temperature and salt on the maturation of white-salted cheese

White-salted cheeses were prepared from ultrafiltered (UF) cows' milk and salted to give final salt-in-moisture (SM) levels of 2.5, 3.2 and 4.0%. The cheeses were stored at 5degreesC and 10degreesC for up to 15 weeks. The microflora was dominated by lactic acid bacteria (LAB) but some mould growth was evident within 15 weeks at all SM levels and both temperatures. Levels of water-soluble nitrogen (WSN), attributed to chymosin activity, increased significantly with time, the rate being inversely proportional to the SM level and increasing with storage temperature. Similar effects were noted for trichloroacetic acid-soluble nitrogen (TCA-SN) and free amino acid (FAA) levels, both of which would also be affected by bacterial protease activity. The proteolytic activity was reflected by changes in the hardness and fracturability of the cheeses.