Amino acid and soluble nitrogen evolution throughout ripening of Serra da Estrela cheese

Four batches of Serra da Estrela cheese originating from as many dairy farms were sampled throughout the ripening period, and assayed for the evolution of free amino acid (FAA) content, total nitrogen content (TN), water-soluble nitrogen content (WSN), trichloroacetic acid-soluble nitrogen content (TCASN) and phosphotungstic acid-soluble nitrogen content (PTASN). The WSN content increased from 1% (on the day of manufacture) up to 43% of TN by 180 d of ripening, thus reflecting the intense proteolytic activity of the enzymes contributed by the plant coagulant utilized. The TCASN was also found to be high in this cheese by the end of ripening (16–20%), which suggests a high extent of FAA release throughout maturation. The major FAA by 180 d of ripening were Glu, Val, Leu and Lys, representing 56–70% of the total in all four dairies sampled. Cheeses produced from refrigerated milk possessed higher amounts of γ-amino-n-butyric acid (Gaba) and lower amounts of Glu when compared with those manufactured with non-refrigerated milk.     

Changes in physicochemical and organoleptic properties of traditional Iranian cheese Lighvan during ripening

Lighvan cheese was studied to determine the physicochemical and biochemical changes over 90 days of ripening in brine. Acidity, pH, dry matter, fat values, lipolysis level, water‐soluble nitrogen (WSN), total nitrogen (TN), ripening index (RI), trichloroacetic acid‐soluble nitrogen (TCA‐SN) and organoleptic assessments were analysed. Dry matter and fat values decreased during ripening. Lipolysis level, RI, TCA‐SN values and salt content increased continuously until the end of the ripening period, but total nitrogen decreased throughout a 90‐day storage period. The ripening stage was the main factor affecting the cheese’s sensory properties.     

海藻酸钠固定化乳酸菌促熟干酪效果的研究

对海藻酸钠固定化乳酸菌促熟干酪的效果进行了研究。结果表明，在干酪粒中添加10^6CFU／g固定化乳酸菌，水溶性氮（WSN）、三氯乙酸氮（TCASN）和磷钨酸氮（PTASN）含量较对照组明显增大；ADV值在添加固定化乳酸菌干酪中成熟初期变化不大，45d后明显增大；感官评定结果表明，干酪粒中添加10^5CFU／g固定化乳酸菌干酪成熟60d时风味和质地较好，可比对照组干酪成熟期缩短30d左右。     

Proteolysis in reduced sodium Feta cheese made by partial substitution of NaCl by KCl

Feta cheeses (five trials) of different sodium content were made, using ewes’ milk, from split lots of curd by varying the salting procedure, i.e. dry salting with NaCl (control) or mixtures of NaCl/KCl (3:1 or 1:1, w/w basis) and filling the cans with brine made with NaCl or the above NaCl/KCl mixtures, respectively, in order to study the influence of the partial substitution of NaCl by KCl on the proteolysis during cheese ripening. The extent and characteristics of proteolysis in the cheeses were monitored during aging by using Kjeldahl determination of soluble nitrogen fractions (water-soluble nitrogen, trichloroacetic acid-soluble nitrogen, phosphotungstic acid-soluble nitrogen), the cadmium–ninhydrin method for the determination of total free amino acids (FAA), urea–polyacrylamide gel electrophoresis of cheese proteins followed by densitometric analysis of the α_s1- and β-casein fractions, reverse-phase HPLC analysis of the water-soluble extracts of cheeses, and ion-exchange HPLC analysis of FAA. The results showed that proteolysis was similar in control and experimental cheeses at all sampling ages, indicating that the partial substitution of NaCl by KCl in the manufacture of Feta cheese had no significant effect on the extent and characteristics of proteolysis during cheese aging.     

Proteolysis in reduced sodium Kefalograviera cheese made by partial replacement of NaCl with KCl

Kefalograviera cheeses (five trials) of different sodium content were made from split lots of curd by varying the salting processes, i.e. brine — and dry — salting, with NaCl (control) or a mixture of NaCl/KCl (3:1 or 1:1, w/w basis). The extent and characteristics of proteolysis in the cheeses were monitored during aging by Kjeldahl determination of soluble nitrogen fractions (water-soluble nitrogen [WSN], trichloroacetic acid [TCA]-SN, phosphotungstic acid [PTA]-SN), the cadmium-ninhydrin method for the determination of total free amino acids (FAA), urea-polyacrylamide gel electrophoresis of cheese proteins, followed by densitometric analysis of the α_s1- and β-casein fractions, reverse-phase high-performance liquid chromatography (HPLC) analysis of the water-soluble extracts of cheeses, and ion-exchange HPLC analysis of FAA. The results showed that proteolysis was similar in control and experimental cheeses at all sampling ages, indicating that the partial substitution of NaCl by KCl in the manufacture of Kefalograviera cheese did not significantly influence the extent and characteristics of proteolysis during cheese aging.     

Ripening time estimation of Kariesh cheese

Kariesh cheese is a popular cheese in Egypt produced by acid coagulation of milk. It can be consumed fresh or after ripening. Proteolysis in cheese was measured by determining soluble nitrogen (SN), amino acid nitrogen (AAN), total amino acids (TAA) and free amino acids (FAA). SN, AAN and FAA increased during ripening. Free amino acids profile revealed in total 16 amino acids and the same distribution of free amino acids. Cheese ripening was influenced by the type of milk and the method of production. The mildly acid sweet flavour was attributed to the concentration of glutamic acid, aspartic acid, proline and valine. Linear regression analysis was carried out to estimate the ripening time of this cheese. A positive correlation between the accumulation of amino acid and ripening time was established. The highest coefficient of determination near one resulted from glutamic acid (R² = 0.99) followed by lysine (R² = 0.97–0.99), then aspartic acid (0.90–0.98). From the linear regression equation for glutamic acid, lysine, aspartic acid or proline, the ripening time of Kariesh cheese in weeks was determined as follows: Time of ripening [weeks] = mg amino acid 100 g cheese-a/b where b = slope and a = intercept of regression straight line at 0 time.     

Effect of Free or Encapsulated Recombinant Aminopeptidase of Lactobacillus rhamnosus S93 on Acceleration of Cheddar Cheese Ripening

The use of recombinant aminopeptidase (PepN) from Lactobacillus rhamnosus S93 in free or encapsulated form was investigated to shorten the duration of Cheddar cheese ripening. Proteolysis was determined by measuring the soluble nitrogen as phosphotungstic acid (PTA-N) derivatives and free amino acids (FAA) over a 6-month period. The experimental cheeses received higher scores for sensory properties than the control cheese. The amounts of PTA-N and total FAA in the cheese with the encapsulated enzyme after 2 months of ripening were close to those of the control cheese after 6 months, suggesting the acceleration in proteolysis by about 4 months.     

Studies on the ripening of stilton cheese: Proteolysis

The pH of fresh Stilton curd, which 2 h after coagulation was ∼6·7, decreased to ∼4·8 in 4 day-old cheeses but increased gradually thereafter to ∼6 at the end of ripening (70 days). At the end of the normal ripening period, ∼60% of the total N (TN) was water soluble (WSN) and ∼58% of the WSN was soluble in 70% ethanol, while 40% was diffusible on dialysis against water; free amino acid N (phosphotungstic acid-soluble, PTA-N) reached ∼4·8% of TN. The levels of TNBS-reactive amino groups were highly correlated with the values of WSN and 12% TCA-N but showed a greater change in the PTA extract than the value of PTA-N. Dialysable WSN was resolved into five peptide fractions by chromatography on Sephadex G-10; these fractions were very heterogeneous and contained up to eight ninhydrin-positive peptides when examined by TLC. Chromatography on DEAE cellulose revealed a high level of heterogeneity in the 70% ethanol-soluble and -insoluble fractions and this was confirmed by the wide range of N-terminal groups. The free amino acids (FAA, as measured by ion exchange chromatography) represented 6·8% and 9·9% of TN in the 70 day-old experimental cheeses and in commercial samples, respectively. Valine, leucine, lysine and glutamic acid accounted for ∼50% of total FAA throughout the ripening period.     

How milk type,coagulant, salting procedure and ripening time affect the profile of free amino acids in Picante da Beira Baixa cheese

The concentration of total free amino acids (FAA) in Picante cheese increased with ripening time irrespective of the particular protocol used for manufacture (ie ratio of caprine to ovine milks, animal or plant rennet and number of salting steps). The experimental cheeses manufactured with 20% (v/v) caprine milk, coagulated with animal rennet and salted only once exhibited the highest content of total FAA by 120 days of ripening. All four manufacture parameters were statistically significant on the 0.5% level of significance in terms of total concentration of FAA. The dominating free amino acids present in the various experimental cheeses throughout the ripening period were valine, leucine and phenylalanine, each one representing more than 10% (w/w) of the total concentration of FAA. All four manufacture parameters were, in general, statistically significant with respect to the content of every single FAA, with particular emphasis on salting and ripening time. © 1999 Society of Chemical Industry     

Flavour precursor development in Cheddar cheese due to lactococcal starters and the presence and lysis of Lactobacillus helveticus.

The rapid release of intracellular enzymes due to autolysis of lactic acid bacteria in the cheese matrix has been shown to accelerate cheese ripening. The objective of this work was to investigate the evolution of the flavour precursors, individual free amino acids (FAAs), free fatty acids (FFAs) and volatile compounds that contribute to the sensory profiles of cheeses at 2, 6 and 8 months of ripening in Cheddar cheese manufactured using starter systems which varied with respect to their autolytic properties. Starter system A contained a blend of two commercial Lactococcus lactis strains (223 and 227) which had a low level of autolysis. System B was identical to A but also included a highly autolytic strain of Lactobacillus helveticus (DPC4571). System C contained only strain DPC4571. Levels of all individual FAAs were elevated in cheeses B and C relative to A after 2 months of ripening. By 8 months of ripening the main FAA were glutamate, leucine, lysine, serine, proline and valine. Levels of C_6:0, C_8:0, C_12:0 and C_18:0 fatty acids did not vary greatly over ripening, while levels of C_4:0, C_10:0, C_14:0, C_16:0 and C_18:1 were elevated in cheeses B and C. Principal component analysis of the headspace volatiles separated cheese A from cheeses B and C. Cheeses B and C had highest levels of dimethyl disulphide, carbon sulphide, heptanal, dimethyl sulphide, ethyl butanoate, 2-butanone, and 2-methyl butanal and were described as having a ‘caramel’ odour and ‘sweet’, ‘acidic’ and ‘musty’ flavour. Cheese A had highest levels of 2-butanol, 2-pentanone, 2-heptanone, 1-hexanol and heptanal and was described as having a ‘sweaty/ sour’ odour and ‘soapy’, ‘bitter’ and ‘mouldy’ flavour. The results highlight the impact of starter lactococci on flavour precursor development and the positive effect of Lb. helveticus and the lysis of this strain on enhancing levels of substrate and flavour precursors early during ripening resulting in early flavour development.     

Effect of draining temperature on the biochemical characteristics of Feta cheese

Two different draining temperatures, 15 and 21°C were applied to five Feta cheese curds made with different starters, containing mesophilic or thermophilic strains or mixtures of them. After 20 h of draining, the pH of curds made with thermophilic starters ranged from 5.28 to 5.49. The draining temperature significantly affected (P<0.05) the pH and the total solids of the cheeses. The inclusion of whey proteins in the cheese curd due to the insufficient draining of cheeses at 15°C, resulted in higher water-soluble nitrogen (WSN), as % of total nitrogen content. Free amino acid contents were significantly affected (P<0.05) by the draining temperature and by the presence of thermophilic lactobacilli in the starter mixture. Draining temperature also significantly affected (P<0.05) residual α_s- and β-casein and the RP-HPLC profiles of the WSN. The C_2:0 to C_8:0 free fatty acids, hardness (kg) and fracturability (kg), as well as the total organoleptic scores, were significantly (P<0.05) higher in feta drained at 21°C.     

Effect of NaCl on textural changes and protein and lipid degradation during the ripening stage of sufu,a Chinese fermented soybean food

Sufu is made by solid state fungal fermentation (using Actinomucor elegans) of tofu, followed by salting and maturation in dressing mixtures containing salt, alcohol and various other ingredients. NaCl in dressing mixtures strongly affected the changes in textural properties and the hydrolysis of protein and lipid of sufu. Higher salt contents (14% w/w) resulted in increased hardness (+100%) and elasticity (+18%) and reduced adhesiveness (?30%). Hardness and elasticity could be used to judge the extent of sufu ripening. SDS‐PAGE showed the disappearance of all protein subunits at 80 and 110 g kg^?1 salt content; however, some protein subunits were still detectable at 140 g kg^?1 salt content after 60 days of ripening. Higher ratios of free amino nitrogen to total nitrogen (FAN/TN = 0.4–0.45) and free amino acids to crude protein (FAA/CP = 0.24–0.26) were observed in sufu with lower (80 g kg^?1) salt content. FAN/TN and FAA/CP in white sufu (obtained with dressing mixtures containing only salt and alcohol) were higher than those in red sufu (obtained with dressing mixtures containing angkak or kojic red rice) owing to different dressing mixture compositions. Increases in free fatty acids (FFA) were also observed during ripening. FFA levels in sufu with lower salt content increased rapidly during the first 30–40 days and then increased slowly, probably resulting from the formation of fatty acid esters. Lowering the salt content (80 g kg^?1) can shorten the ripening time to 40 days, which is of benefit to manufacturers. However, sufu will spoil, ie undergo souring, during the ripening stage at salt contents of 50 g kg^?1 or lower. Copyright © 2003 Society of Chemical Industry     

Effect of freeze–dried kefir culture on proteolysis in feta-type and whey-cheeses

The effect of freeze–dried kefir culture on the proteolysis of feta-type and whey-cheese was investigated. All nitrogen fractions increased during ripening. Although no significant differences were observed in total nitrogen (TN), the levels of water-soluble nitrogen (WSN), pH 4.4-soluble nitrogen (SN), 12% trichloroacetic acid-soluble nitrogen (TCA-SN) and phosphotungstic acid-soluble nitrogen (PTA-SN) were significantly higher in cheeses produced by freeze–dried kefir culture during the later stages of ripening. Content of total free amino acids (FAA) was significantly affected by freeze–dried kefir starter culture and it was continuously increased in kefir-cheese while, in rennet-cheese it was increased up to 30 days of ripening and then slightly decreased. On the other hand, FAA content continuously decreased in kefir-whey-cheese whereas it increased in whey-cheese. The cheese samples produced by freeze–dried kefir as starter culture were characterised as high-quality products during the preliminary sensory evaluation and they were accepted by the panel. Overall, the use of freeze–dried kefir suggested acceleration of cheese ripening and resulted in improved sensory characteristics.     

Effects of coagulant type on the physicochemical and organoleptic properties of Kashar cheese

Kashar cheeses were manufactured using different coagulants (calf rennet, chymosin derived by fermentation and proteases from Rhizomucor miehei and Cryphonectria parasitica) and ripened for 90 days. Use of different coagulants did not influence the dry matter, fat, protein, salt, pH, titratable acidity, total free fatty acids and texture profile analyses. The levels of water‐soluble nitrogen, 12% trichloroacetic acid‐soluble nitrogen, and for 5% phosphotungstic acid‐soluble nitrogen, the sensory properties were significantly influenced by the use of different coagulants. β‐casein was more hydrolysed in the cheese manufactured using protease from Cryphonectria parasitica than the other cheeses during 90 d of ripening.     

EFFECT OF HEATING AT DIFFERENT TEMPERATURES TO EXTEND THE SHELF LIFE OF VACUUM-PACKED WHITE CHEESE

The aim of this study was to determine the effects of heating applications on the shelf life of vacuum‐packed white cheese. Shelf life was evaluated for chemical, microbiological and organoleptic properties during the ripening period of 90 days. For this purpose, pickled white cheeses made with commercial starter cultures (Chr. Hansen R707 Lactococcus lactis subsp. lactis, L. lactis subsp. cremoris) were put in polyamide bags for vacuum packaging. During the ripening period, a water bath was used for heating applications at 65, 70 and 72C for 15, 10 and 5 min, respectively. In the ripening period, there were no changes in the values of dry matter in the control group. Dry matter values in control cheese were 40.02–42.09% (average value: 40.87%). Total acidity, protein (%), soluble nitrogen, ripening index (RI), tyrosine content and volatile fatty acid values all showed significant increases between the first and 90th days of the ripening period. However, in the heated cheese groups, dry matter showed no changes, but compared with the control group cheese total acidity, protein (%), soluble nitrogen, RI, tyrosine content and volatile fatty acid values increased but not as much as the control group.     

Ripening of cheese made from full concentrated milk retentate with and without peptidase addition

The aim of this study was to determine ripening of cheese made from full concentrated (FC) milk retentate with and without peptidase addition. No free amino acids (FAAs) were found in FC cheese at the end of ripening. However, added peptidase increased FAA formation. Protein and peptide profile analysis showed that FAA and small peptides increased during ripening and therefore some secondary proteolysis occurred. Added peptidase increased D‐lactic acid formation during ripening of cheeses. This kind of changes in lactose fermentation should be considered during developing the making cheese with different enzyme addition.     

Free amino acid profile during ripening of ewe's milk cheese from the Croatian island Krk

The aim of this study was to determine the content of free amino acids (FAA) and their ratio in ewe's milk cheese from the island Krk during its ripening. FAA content was determined by reversed phase HPLC (RP‐HPLC) of cheese aqueous/ethanol extracts after FAA were transformed into their 6‐aminoquinolyl‐N‐hydroxysuccinimidyl carbamate derivatives. Their concentration increased during ripening, reaching the value of 5% in cheese dry matter. The dominant FAA were glutamic acid>leucine>valine>aspartic acid>phenylalanine>serine>proline, and higher content of nonessential vs essential FAA was revealed. Krk cheese has, in relation to other cheeses, higher values for glutamic acid/leucine, glutamic acid/phenylalanine, glutamic acid/proline and smaller values for leucine/aspartic acid, valine/aspartic acid, phenylalanine/aspartic acid ratios, while other ratios are comparable to those of other hard ovine cheeses.     

Lipolysis in probiotic and synbiotic cheese: The influence of probiotic bacteria, prebiotic compounds and ripening time on free fatty acid profiles

The influence of probiotic bacteria (Lactobacillus casei-01, Bifidobacterium lactis B94), prebiotic compounds (FOS and inulin) and ripening time (0-60 days) on the free fatty acid (FFA) profile of cheese, with special emphasis on the conjugated linoleic acid (CLA) content, was investigated. After 60 days of ripening, 10⁹-10¹⁰ cfu g⁻¹ cheese were recorded in both probiotic and synbiotic cheeses, despite harsh conditions of low pH values (4.1-5.1) and low moisture content (<30%, w/w). Increases in total FFA and CLA were observed throughout the ripening period, especially in synbiotic cheeses containing FOS and inulin (50:50) inoculated with B. lactis B94. The addition of FOS alone or combined with inulin did not significantly affect probiotic strain growth and viability during the ripening period; however, the advantage of the addition of prebiotic compounds in probiotic cheese manufacture is that it may allow the production of cheeses with improved performance as far as functional CLA compounds are concerned, as well as an improved nutritional quality reflected in a lower atherogenicity index.     

Compositional and degradative changes during the manufacture of dry‐cured ‘lacón’

The gross and mineral composition, the main physicochemical parameters, the protein extractability and the proteolytic (nitrogen fractions and free amino acids) and lipolytic (acidity index and free fatty acids) changes were studied throughout the manufacturing process of five batches of dry‐cured ‘lacón’, a traditional Spanish meat product made from the fore‐ham of the pig following a similar technological process to that of dry‐cured ham. The main compositional characteristics of this product are the high NaCl content and the low moisture content at the end of the curing process. The pH remained fairly stable (around 6) throughout the whole process and a fall in a_w was observed, reaching very low (0.767 ± 0.052) final average values. It was noted that 76% of the sarcoplasmic and 83% of the myofibrillar proteins became insoluble during the manufacturing process. The values of the different nitrogen fractions increased in a significant manner during manufacture, reaching low final values that indicate that ‘lacón’ undergoes a low level of proteolysis in comparison with other products manufactured by similar technologies. The high NaCl content and the intense dehydration suffered during the manufacturing process appear to be the principal causes of this reduced protein degradation. In accordance with the limited increase in the α‐amino acidic nitrogen during ripening, the total free amino acid content increased slightly but significantly from average values of 4371 mg kg^?1 dry matter in fresh pieces to average values of 13 020 mg kg^?1 dry matter in pieces at the end of the ripening process. The profile of free amino acids in the final product was similar to that observed by other authors in dry‐cured ham. The acidity of the fat increased by a factor of five. The final average values (49.9 g oleic acid kg^?1) were lower than those determined in dry‐cured ham, which indicates that ‘lacón’ undergoes less lipolysis during the ripening process than dry‐cured ham. C18 : 1, C18 : 2 and C16 were the most intensively released fatty acids during curing. The profile of free fatty acids in the end product was in agreement with that observed by other authors in dry‐cured ham. Copyright © 2003 Society of Chemical Industry     

Volatile compounds and proteolysis in traditional Beaten (Bieno sirenje) ewe's milk cheese

Beaten ewe's milk cheese is a traditional autochthonous type of cheese manufactured in Macedonia with a relatively high nutritional value and sensory characteristics. The objective of this study was to characterise the gross composition, proteolysis and volatile profiles of the cheese that is supplied from different retails. The ranges for gross composition were from 31.53% to 42.83% (w/w) for moisture, 41.99% to 50.98% (w/w) for fat‐in‐dry matter, 2.03% to 8.25% (w/w) for salt content and 20.74% to 33.35% (w/w) for protein. Proteolysis results showed various levels of soluble nitrogen ranged from 3.15 to 33.50 for water‐soluble nitrogen (WSN) and from 1.11% to 6.79% for nitrogen soluble in 12% trichloroacetic acid (TCA‐SN). The ranges for total free amino acids were from 1.65 to 8.06 mg Leu/g. Lower proteolysis was observed in the cheese samples due to high salt contents. In total, 65 volatile compounds were identified in Beaten cheese. As a conclusion, the variation of the peptide profile, electrophoresis and volatile contents of Beaten cheeses are due to the lack of standardised manufacture protocols.