Curd Slurries Research Articles

Utilization of a New and Improved Dressing for Implanted Ports

The volatile organic compound (VOC) profile of a Swiss cheese curd slurry system, with and without addition of reduced glutathione (GSH), was investigated on a daily basis for six days of incubation at 30 °C. The VOC profiles of commercial Swiss cheese samples from different stages during manufacture (after press, end of pre-cool, end of warm room and at cut) were also measured. Using the volatiles produced, the time scale of the slurry was matched to that of conventional ripening to determine which day of accelerated ripening corresponded to each stage of commercial ripening. The profiles of most of the VOCs in the slurry system with GSH more closely matched the profiles at the different stages of Swiss cheese ripening than the slurry system without GSH. Moreover, the headspace concentrations of volatiles that are considered to produce off-flavors were significantly decreased in the Swiss cheese slurry system with GSH.

Suppression of propanoic acid, acetic acid and 3-methylbutanoic acid production by other volatiles in a Swiss cheese curd slurry system

The effect of the addition of 5–100 ppm 2,3-butanedione, butanoic acid, methyl mercaptan, ethyl butanoate, diethyl sulfide, 3-methylbutanoic acid, acetaldehyde and ethanol on production of propanoic acid, acetic acid and 3-methylbutanoic acid in a Swiss cheese slurry system was investigated. Enumeration of propionic acid bacteria (PAB) was done to monitor the microbial count in the systems. A Swiss cheese slurry system was used to simulate cheese manufacturing based on accelerated ripening for a 6-day incubation period. The headspace concentrations of propanoic acid, acetic acid and 3-methylbutanoic acid were significantly decreased by the addition of 2,3-butanedione, butanoic acid, and methyl mercaptan, but were generally unaffected by ethyl butanoate, diethyl sulfide, 3-methylbutanoic acid, acetaldehyde and ethanol. Microbial enumeration also showed that there was a significant reduction of PAB in slurry systems with 100 ppm 2,3-butanedione, butanoic acid, and methyl mercaptan.

Volatile organic compounds of a Swiss cheese slurry system with and without added reduced glutathione, compared with commercial Swiss cheese

The volatile organic compound (VOC) profile of a Swiss cheese curd slurry system, with and without addition of reduced glutathione (GSH), was investigated on a daily basis for six days of incubation at 30 °C. The VOC profiles of commercial Swiss cheese samples from different stages during manufacture (after press, end of pre-cool, end of warm room and at cut) were also measured. Using the volatiles produced, the time scale of the slurry was matched to that of conventional ripening to determine which day of accelerated ripening corresponded to each stage of commercial ripening. The profiles of most of the VOCs in the slurry system with GSH more closely matched the profiles at the different stages of Swiss cheese ripening than the slurry system without GSH. Moreover, the headspace concentrations of volatiles that are considered to produce off-flavors were significantly decreased in the Swiss cheese slurry system with GSH.

Proteolysis and Biogenic Amine Formation in Sterilized Edam-Type Curd Slurry Inoculated with Probiotic Strains

Edam-type curd slurry inoculated with 1% Lactococcus lactis subsp. lactis KF147 as control and further added with Propionibacterium shermanii PS-4 + Bifidobacterium bifidum DSM 20082 (1:1), P. shermanii PS-4 + Lactobacillus acidophilus ATCC4356 or P. shermanii PS-4 + B. bifidum DSM 20082 + Lactobacillus acidophilus ATCC4356 (1:1:1), at a rate of 1%, were studied for their effect upon biogenic amine and proteolysis pattern during incubation at 30C for 21 days. Results showed no significant influence of any combination of probiotic microorganisms on total solids, salt and fat of Edam-type curd slurries, but some effect on pH and soluble nitrogen fractions; presence of P. shermanii + B. bifidum + Lactobacillus acidophilus led to the highest concentration (7.9%) of water-soluble nitrogen by the end of incubation. When inoculation included B. bifidum, a significant decrease in total biogenic amines (from 447 to 37 mg/kgDW) was observed by 21 days – with histamine decreasing from 84 to 25 and tyramine from 359 to 6 mg/kgDW. Practical Applications This study was aimed at investigating proteolysis and biogenic amine formation by selected probiotic bacteria added to Edam-type curd slurry. The nitrogen fractions and biogenic amines in control increased significantly throughout incubation at 30C. Inocula of P. shermanii + L. acidophilus + B. bifidum (1:1:1) could effectively reduce biogenic amine contents, especially histamine and tyramine. This observation has potential public health impact because regular curds are often above the maximum legal threshold in regions with warm weather and poor cold storage network. Furthermore, addition of probiotic L. acidophilus and B. bifidum improved the overall flavor profile, owing to extra soluble nitrogen produced.

Proteolysis of Cheese Slurry Made from Pulsed Electric Field-Treated Milk

Raw milk cheeses have unique flavor and texture characteristics not obtainable in cheeses made from pasteurized milk. However, cheeses made from pasteurized milk are widespread, primarily for public health reasons. Pulsed electric field (PEF) treatment as a non-thermal pasteurization method has shown its ability to keep the flavor and natural characteristics of food samples intact, thus providing advantage over conventional heat processing. In this study, PEF treatment was performed in a continuous treatment chamber, consisting of two parallel stainless steel electrodes separated by a 50-mm-thick insulator. A 30-kV pulse generator was used to deliver bi-polar square waveform electric field to milk sample. Pulse width was 2 µs; pulse frequency was 2 Hz, and up to 120 pulses were applied. Cheese curds were made from raw milk, pasteurized milk, and PEF-treated milk, and their proteolysis processes were compared using curd slurry incubated at 30 °C for 5 days. The profiles of water-soluble peptides were measured using an reversed-phase high-performance liquid chromatography (RP-HPLC) system. The concentration of free amino acids was measured by Cd–ninhydrin method. Results indicated that PEF-treated milk has intermediate proteolysis profiles between raw milk and pasteurized milk in terms of peptide and free amino acid concentration. The results showed the potential of making high-quality cheeses by PEF treatment without sacrificing the natural characteristics of the cheeses.

Preliminary screening of Bifidobacteria spp. and Pediococcus acidilactici in a Swiss cheese curd slurry model system: Impact on microbial viability and flavor characteristics

A Swiss cheese curd slurry model system was used as a preliminary screening method to determine the feasibility of the incorporation of probiotic bacteria ( Bifidobacterium breve R0070, Bifidobacterium infantis R0033, Bifidobacterium longum R0175, and Pediococcus acidilactici R1001) into Swiss cheese. The cheese curd was inoculated with probiotic bacteria (8.0 log 10 cfu g −1) and ripened anaerobically for 0, 7, and 10 days at 37 °C. Following ripening, counts of the probiotic bacteria increased to 9–10 log 10 cfu g −1, with no significant difference in the viability of the four probiotic bacteria. Viable populations of Swiss cheese background microflora in the presence of each probiotic culture were comparable with the control. Ripening time, and to a lesser extent probiotic treatment had a significant effect on the content of several volatile flavor compounds. Similarly, ripening time contributed to a significant increase in the content of a majority of the free amino acids. The study demonstrated the feasibility of the incorporation of probiotic bacteria into Swiss cheese to produce a functional food.

Proteolytic activity of some Lactobacillus paracasei strains in a model ovine-milk curd system: Determination of free amino acids by RP-HPLC

Curd slurries were prepared from ovine milk to study the proteolytic properties of various strains of Lactobacillus paracasei. A commercial industrial starter and the strains to be tested in this study, Lb. paracasei strains Pa1, Pa2, Pa3, were inoculated in separate slurries. Free amino acids were analysed on days 0, 2, 5, 7, and 10. As ripening progressed, total free amino acids increased significantly ( P < 0.01); content ranged from 150 mg/100 g dry matter (DM) on day 0 to 600 mg/100 g DM on day 10. Generally speaking, CIT, GLN, LEU, ASN, PRO, and 4-HYPRO were the main free amino acids in all four slurries tested, accounting for 60–82% of the total free amino acids. The slurries made using strains Pa1 and Pa3 were similar to the control slurry, and these three slurries exhibited the highest proteolysis levels. Differences between the strains of the species tested were observed.

Alternatives to pilot plant experiments in cheese‐ripening studies

Experimental studies on cheese have several objectives, from assessing the influence of the microflora and enzymes indigenous to milk to evaluating starters and adjuncts. Several studies have been undertaken to evaluate the influence of an individual ripening agent in the complex environment of cheese. Cheesemaking experiments, even on a pilot scale, are expensive and time‐consuming, and when controlled bacteriological conditions are needed, pilot plant experiments are difficult to perform. Cheese curd slurries are simple models that can be prepared under sterile conditions in the laboratory and can be used as an intermediate between test tubes and cheese trials, but probably cannot replace the latter. Miniature model cheeses are similar to pilot plant cheeses and can be manufactured under sterile conditions. Several approaches to assess the role of cheese‐ripening agents are reviewed in this paper.

Contribution of Lactococcus lactis subsp lactis IFPL 359 and Lactobacillus casei subsp casei IFPL 731 to the Proteolysis of Caprine Curd Slurries

ABSTRACT: Proteolysis was studied in low‐fat caprine curd slurries pre‐incubated (24 h at 30 °C) with an extra dose of rennet, 10.0 or 22.0 μg g‐1 (LR and HR slurries, respectively), and treated at 70 °C for 15 min prior to incubation with sonicated cells of Lactococcus lactis subsp lactis IFPL 359 alone or combined with Lactobacillus casei subsp casei IFPL 731. The addition of lactobacilli to slurries containing lactococci increased the conversion of water‐soluble nitrogen to nonprotein nitrogen and amine nitrogen. Major differences were found for some free amino acids, such as glutamic acid and proline, and hydrolysis of most hydrophobic peptides produced by lactococci, which are associated with bitterness in cheese.

Proteolysis in Cheese Curd as Affected by Subcellular Fractions from Lactococcus, Lactobacillus and Propionibacterium

ABSTRACTIntracellular fraction (IF) and cell wall‐associated fraction (CWAF) from lactococci, lactobacilli and propionibacteria were added to cheese curd slurries according to a mixture design. Response surface and estimation of Scheffe's polynomial revealed synergistic interaction effects between lactococci and lactobacilli on secondary proteolysis determined by an o‐phthaldialdehyde assay. IFs from propionibacteria had a lower proteolytic activity than those from lactococci and lactobacilli used. Principal component analysis of capillary electropherograms of the trichloroacetic acid‐soluble fraction, discriminated between slurries treated with IFs and CWAFs. It also showed an effect of proteolytic enzymes from the IF of propionibacteria together with IFs from lactococci and/or lactobacilli, on small changes in overall peptide profile.

Role of selected yeasts in cheese ripening:

Yeasts are found within the surface microflora of many cheese types, but not much is known about their direct contribution to cheese ripening. The aim of this study was to investigate, on a laboratory scale, the direct influence of yeasts on cheese ripening by means of aseptic cheese curd slurries. Isolates of all species found in three smear ripened cheese varieties were tested with respect to changes in pH, proteolysis and aroma development. Most yeasts could be assigned to two groups. One group was characterised by the ability to ferment glucose, to utilise lactate and to increase pH values and by the fact that proteolytic activity was not shown. This resulted in alcoholic, acidic, fruity or fermented odours (Clavispora lusitaniae, Pichia jadinii and Williopsis californica). The second group was composed of non-fermenting species which utilised lactate, but the pH was not affected (Galactomyces geotrichum, Trichosporon ovoides and Yarrowia lipolytica). These yeasts were proteolytic yielding a cheesy aroma. Debaryomyces hansenii B comprised characteristics of both groups.

Flavour development in aseptic cheese curd slurries prepared with single-strain starter bacteria in the presence and absence of adjuncts

Summary - Eight strains of Lactococcus starter bacteria were tested under microbiologically controlled conditions for their ability to pro duce Cheddar cheese flavour, For this purpose, aseptic Cheddar chee se curds were prepared with each of the organisms, and the resulting curds slurried with sterile salt and water, and stored at 30 C for accelerated f1avour development. Distinct though weak Cheddar cheese flavour was produced by the Lactococcus lactis subsp cremoris strain SK Il, but not by strains ASCC457, ASCC50, ASCC 109, ASCC660, ASCC360, or the L lactis subsp lactis strain ASCC381, or the L lactis subsp lactis biovar diacetylactis strain ASCC250. Different starter strains produced different degrees of bitterness, with strains ASCC457, 109 and 660 producing the most bitter slurries. Strains SKII, ASCC50, ASCC360, and ASCC250 produced only slight bitterness in slurries ripened for 15 days, Free fatty acid concentrations in the slurries differed depending on the starter strain used, implying that different starter strains have different lipase activity. Cheese flavour development was slow in the slurries containing only starter bacteria. In contrast, slurries made with the strain SKII in the presence of the adjuncts Lactobacillus helveticus ASCC395, Brevibacterium linens CSCC750 or Lactobacillus casei subsp casei NCDOl51 underwent rapid f1avour development, giving distinct and strong chee se (but not Cheddar) flavours for each adjunct. These differences in flavour, however, cou Id not be explained in terms of differences in the non-sulphur volatile composition of the slurries determined by static headspace analysis.

Proteolytic activity of lactobacilli in a model goats' milk curd system.

Mesophyllic lactobacilli cultures propagated in MRS broth were inoculated in goats' milk curd slurries and incubated at 30 degrees C for 10 d. The micro-organisms tested were Lactobacillus casei subsp. casei IFPL 731 and IFPL 99, and Lactobacillus plantarum IFPL 3. Whole cells, cell-free extracts and cell lysates were evaluated for acceleration of proteolysis in the curd slurries. Conversion of water-soluble nitrogen to non-protein nitrogen and amino acid nitrogen, reverse phase-HPLC peak areas and ratio of hydrophobic to hydrophilic peptides, were all affected by the type of inoculum used as well as the strain under study. The results suggest that the accelerated-ripening model system developed, containing cell lysates, may be suitable as a good and rapid indicator of the contribution of the strains to proteolysis during cheese ripening.

PROTEIN DEGRADATION IN CHEDDAR CHEESE SLURRIES

SUMMARY— Preferential degradation of caseins was noted in the ripening of Cheddar curd slurries, with the degradation generally being in the order of para‐K, β‐, αs‐caseins. The addition of reduced glutathione to the slurry caused an immediate release of peptides from the protein mass and decreased the initial rate of β‐casein degradation. The peptides appeared to be preferentially utilized during the first 4 days of ripening; thereafter rapid degradation of β‐casein occurred. In quiescent slurries, αs‐casein degradation exceeded that of β‐casein, whereas periodic agitation reversed the degradation rate of the two caseins. The rate and extent of characteristic flavor development appeared to be related directly to β‐casein degradation, but not to changes in concentration of pare‐K or αs‐caseins.

Accelerated Ripening of Swiss Cheese Curd

Studies were conducted on the applicability of the curd slurry process for ripening Swiss cheese curd from pasteurized milk and for selected controlling factors and chemical ripening changes. Swiss curd slurries containing approximately 40% total solids, 18.5% fat, 1.6% salt, and 1.1% added propionic culture developed full, characteristics Swiss cheese flavor after 5 to 6 days storage at 30C. Development of characteristic flavor in slurries was accompanied by increased pH, decreased lactic acid, and formation of active -SH groups. Head-space volatiles produced were quantitatively similar to those of aged Swiss cheese. Rate of development of characteristic flavor in slurries was enhanced by 100ppm reduced glutathione, was related directly to initial pH, amount of propionic culture and inversely related to salt concentration. Flavor of the slurries was affected adversely when methionine or 10ppm copper but not 1ppm copper were added and when curd used for slury was manufactured with only Streptococcus thermophilus.