Modification of the volatile compound profile of cheese, by a Lactococcus lactis strain expressing a mutant oligopeptide binding protein

Lactococcus lactis strain AMP2I expresses OppA(D471R), a mutant oligopeptide binding OppA protein in which the aspartyl residue at position 471 was replaced by arginine. As a consequence of a different peptide transport in this strain, experimental Hispánico cheese made with Lc. lactis AMP2I had a higher content of total free amino acids than control cheese made with Lc. lactis AMP1I, an isogenic strain expressing wild-type OppA (Picon et al. 2005, 2007). In this work higher levels of diketones, hydroxy-ketones and, to a lesser extent, branched chain aldehydes were recorded for experimental cheese compared with control cheese. These differences levelled off as ripening proceeded. Strong correlations support the hypothesis that the increased levels of these volatile compounds in cheese made with Lc. lactis AMP2I are linked to higher concentrations of free amino acids threonine, valine and leucine.     

Lowering hydrophobic peptides and increasing free amino acids in cheese made with a Lactococcus lactis strain expressing a mutant oligopeptide binding protein

Lactococcus lactis strain AMP2I expresses OppA(D471R), a mutant oligopeptide binding OppA protein in which the aspartyl residue at position 471 was replaced by arginine. This strain was used as starter culture to investigate its ability to lower the levels of hydrophobic peptides in cheese. A 5-fold increased level of chymosin was used to obtain a high initial level of hydrophobic peptides. Cheese made with L. lactis AMP2I contained lower levels of hydrophobic peptides and showed lower ratios of hydrophobic peptides to hydrophilic peptides than control cheese made with L. lactis NCDO712. Both parameters have been correlated with cheese bitterness, which suggests that bitterness in cheese made with the former strain must be lower than in control cheese. Content of total free amino acids was 1.3-fold higher in cheese made with L. lactis AMP2I than in control cheese, an increase that can be attributed to the expression of the mutant oligopeptide binding OppA protein.     

Growth stimulation of a proteinase positive Lactococcus lactis strain by a proteinase negative Lactococcus lactis strain

Lactococcus lactis AMP15/pAMP31(D471R) is a proteinase negative, lactose negative strain with a modified oligopeptide transport system, and potential as a debittering agent due to its efficient utilization of hydrophobic peptides. Five wild L. lactis strains of dairy origin, which produced cheeses of high flavour quality, were cocultured with L. lactis AMP15/pAMP31(D471R) in an attempt to select adequate combinations of strains for use as defined cheese starters with potential debittering ability. Four of these strains, L. lactis B6, K16, M21 and P21, inhibited growth of L. lactis AMP15/pAMP31(D471R) at a level of 10(6) to 10(7) cfu mL(-1) after 24 h of incubation, even though production of bacteriocin-like compounds could only be proven for L. lactis M21. When L. lactis AMP15/pAMP31(D471R) was cocultured with the fifth strain, L. lactis N22, its growth was significantly (P<0.001) inhibited whereas growth of L. lactis N22 was significantly stimulated. The nature of the interaction was studied and it was established that L. lactis N22 is auxotrophic for folate, a compound produced and excreted by L. lactis AMP15/pAMP31(D471R).     

Proteolysis during the ripening of goats’ milk cheese made with plant coagulant or calf rennet

Powdered plant coagulant (PPC) obtained from the cardoon (Cynara cardunculus) was compared with calf rennet (CR) for the manufacture of goats’ milk cheese, by determining difference in the proteolysis throughout ripening. There were no substantial differences between the compositions of cheeses made using the two types of coagulants. However, cheeses manufactured with PPC exhibited higher levels of pH 4.6-SN than cheese made using CR. The extent of breakdown of α_s-casein, as measured by urea-PAGE, was greater in cheese made using PPC than cheese made using CR. The formation of hydrophobic peptides and the ratio of hydrophobic/hydrophilic peptides throughout the ripening were higher in cheeses made with PPC than in cheeses made with CR. Principal component analysis (PCA) of peak heights of RP-HPLC peptide profiles of the ethanol-soluble and ethanol-insoluble fractions distributed the samples according to the coagulant used in their manufacture. Quantitative differences in several peptides were evident between the two types of cheese.     

Use of high pressure treatment to attenuate starter bacteria for use as adjuncts for Cheddar cheese manufacture

Attenuated starter bacteria cannot produce acid during cheese manufacture, but contain enzymes that contribute to cheese ripening. The aim of this study was to investigate attenuation of starter bacteria using high pressure treatment, for use in combination with a primary starter for Cheddar cheese manufacture, and to determine the effect of such adjunct cultures on secondary proteolysis during ripening. Lactococcus lactis ssp. cremoris HP and L. lactis ssp. cremoris 303 were attenuated by pressure treatment at 200 MPa for 20 min at 20 °C. Cheddar cheese was manufactured using untreated cultures of both these starter strains, either alone or in combination with their high pressure-treated equivalents. High pressure-treated starters did not produce acid during cheese manufacture and starter counts in cheeses manufactured using high pressure-treated starter did not differ from those of the controls. Higher levels of cell lysis were apparent in cheese manufactured using high pressure-treated strains than in the controls after 26 d of ripening. Small differences were observed in the peptide profiles of cheeses, analysed by reversed-phase HPLC; cheeses manufactured using high pressure-treated starters also had slightly higher levels of amino acids than the relevant controls. Overall, addition of high pressure-treated starter bacteria as a secondary starter culture accelerated secondary proteolysis in Cheddar cheese.

Industrial relevance

Attenuated starters provide extra pool of enzymes, which can influence cheese ripening, without affecting the cheese making schedule. This paper presents an alternative method for attenuation of starter bacteria using high pressure treatment and their subsequent use to accelerate secondary proteolysis in Cheddar cheese during ripening.     

Adjunct starter properties affect characteristic features of Swiss-type cheeses

A large number of microorganisms, both starter microorganisms and non-starter lactic acid bacteria originating from the base milk, or from various contamination sources during cheese manufacture, is associated with cheese ripening and the formation of flavour, texture and aroma. Under controlled conditions, Emmental and Bergk?se, a Gruyère-type cheese variety, were produced from pasteurised milk with standard starters and defined strains of facultatively heterofermentative lactobacilli (FHL), and partly with addition of a defined mixture of enterococci. Lactobacillus casei subsp. casei and L. rhamnosus (two strains each) were selected with respect to their potential for the utilisation of citric acid and ribose as sole energy source. The FHL developed up to 10(8) cfu/g within the first weeks of ripening, and viable counts in mature cheeses were 10(7) cfu/g, independent of the cheese variety. Bergk?se made with addition of L. rhamnosus strains showed a more pronounced proteolysis, resulting in reduced firmness and elasticity values of the cheese body, and FHL strains able to utilise citric acid improved the appearance of the cheeses by increasing the number of small eyes to the desired level. In Emmental cheese, the citric acid (+) strains reduced the intensity of propionic acid formation as the FHL apparently competed with the propionibacteria, and enterococci disappeared completely during maturation. Although further work is needed the study shows that, depending on the cheese variety, particular properties of FHL adjunct starters significantly affect important quality attributes of the resulting cheeses.     

Isolation and characterisation of exopolysaccharide-producing Weissella and Lactobacillus and their application as adjunct cultures in Cheddar cheese

This study characterised exopolysaccharide-producing lactic acid bacteria and examined their potential for use in Cheddar cheese manufacture. Two strains were chosen for incorporation as adjunct cultures in Cheddar cheese manufacture: namely, the homopolysaccharide-producers Weissella cibaria MG1 and Lactobacillus reuteri cc2. These strains both produce dextrans with molecular masses ranging from 10⁵ to 10⁷ Da. Both strains were used in the production of miniature Cheddar cheeses that employed a conventional commercial cheese starter culture Lactococcus lactis R604. A cheese was also included that used purified dextran as an ingredient. The W. cibaria strain survived in cheese with levels increasing by 1.5 log cycles over the ripening period. All experimental cheeses (adjunct or exopolysaccharide ingredient) had higher moisture levels compared with the control cheese made using starter alone. Inclusion of the adjunct strains had no detectable negative effects on cheeses in terms of proteolysis.     

Preliminary observations on proteolysis in Manchego cheese made with a defined-strain starter culture and adjunct starter (Lactobacillus plantarum) or a commercial starter

Different authors have demonstrated the potential of adding lactobacilli as adjunct cultures to pasteurized milk used in cheese manufacture. The aim of this work was to observe the effect of the use of a defined-strain starter culture and the addition of an adjunct culture (Lactobacillus plantarum) to cheesemilk in order to determine their effect on the ripening of Manchego cheese. Manchego cheeses were manufactured using one of the following starter culture systems: a defined starter consisting of Lactococcus lactis ssp. lactis and Leuconostoc mesenteroides ssp. dextranicum; a defined starter, as described above, and Lb. plantarum, which were isolated from a good quality Manchego cheese made from raw milk, or a commercial starter comprised of two strains of Lc. lactis. The cheeses were sampled at 15, 45, 90 and 150 d of ripening. Principal component analysis of peak heights of reversed-phase HPLC chromatograms of 70% (v/v) ethanol-insoluble and -soluble fractions distributed the samples according to the starter used in their manufacture. Quantitative differences in several peptides were evident between the three cheeses. Cheeses made with the defined-strain starters received higher scores for the flavour quality and intensity and for overall impression than the cheeses made with the commercial starter.     

Production of peptides and free amino acids in a sterile extract describes peptidolysis in hard-cooked cheeses

Hard cooked cheeses are mostly manufactured with lactic starters of Lactobacillus helveticus, which constitute a major proteolytic agent in the food. In this work, we assessed the proteolysis produced by enzymes of two strains of L. helveticus in a new cheese model, which consisted of a sterile substrate prepared with hard-cooked cheeses, and identified the time of ripening when main changes in proteolysis are produced. The extract, a representative model of the aqueous phase of the cheeses, was obtained from Reggianito cheeses of different ripening times (3, 90, and 180 days) made with starters composed of the strains tested, either SF138 or SF209. To obtain the substrate, the cheese was extracted with water, then centrifuged and the aqueous phase was sterilized by filtration through membrane (0.45 ??m). The substrates were incubated at 34 °C during 21 days; samples were taken at 0, 3, 7, 14, and 21 days. Sterility was verified by plating samples on skim milk agar and incubating at 37 °C for 48 h. Proteolysis was determined by liquid chromatography of soluble peptides and free amino acids. Great variation in peptide profiles was found as incubation progressed in cheese extracts, which evidenced that proteases and peptidases from the starter were active and able to degrade the proteinaceous material available in the extracts. The extracts derived from cheeses with L. helveticus SF138 showed low production of peptides and a notable increase in free amino acids content during incubation. L. helveticus SF209, on the contrary, caused an increase on soluble peptides, but the free amino acids accumulation was lower than in the first case, which suggested that L. helveticus SF209 had either a low peptydolitic activity or produced an intense amino acids breakdown. This trend was more evident for extracts prepared with 90-day-old cheeses. It was concluded that the strains of L. helveticus assayed showed potentially complementary proteolytic abilities, as SF209 was able to provide a continuous replenishment of peptides during incubation, while SF138 increased their hydrolysis to free amino acids. The extract was an appropriate medium to model hard cooked cheese ripening in short periods of time.     

Proteolysis texture and microstructure of low‐fat Tulum cheese affected by exopolysaccharide‐producing cultures during ripening

The objective of the study was to determine the effects of exopolysaccharide (EPS)‐producing or non‐EPS‐producing starters on proteolysis, physical and microstructural characteristics of full‐fat or low‐fat Tulum cheeses during ripening. For this purpose, Tulum cheese was manufactured using full‐ or low‐fat milk with EPS‐producing and non‐EPS‐producing starter cultures. Chemical composition, proteolysis, texture profiles and microstructure of the cheeses were studied during 90 days of ripening. Urea‐PAGE of water‐insoluble and RP‐HPLC peptide profiles of water‐soluble fractions of the cheeses showed that the use of starters resulted in different degradation patterns in all cheeses during ripening. Although β‐casein exhibited similar degradation patterns in all cheeses, small differences are present in α_s1‐casein degradation during ripening. Reducing fat in Tulum cheese changed the RP‐HPLC peptide profile of the cheeses. The use of EPS‐producing cultures improved the textural characteristics and changed the microstructure and proteolysis of low‐fat Tulum cheese.     

Proteolysis during ripening of Manchego cheese made from raw or pasteurized ewes' milk. Seasonal variation

Changes in nitrogen compounds during ripening of 40 batches of Manchego cheese made from raw milk (24 batches) or pasteurized milk (16 batches) at five different dairies throughout the year were investigated. After ripening for six months, degradation of p-kappa- and beta-caseins was more intense in raw milk cheese and degradation of alpha(s2)-casein in pasteurized milk cheese. Milk pasteurization had no significant effect on breakdown of alpha(s1)-casein. Hydrophobic peptide content did not differ between raw and pasteurized milk cheese, whereas hydrophilic peptide content was higher in raw milk cheese. There were no significant differences between seasons for residual caseins, but hydrophobic peptides were at a higher level in cheese made in autumn and winter and hydrophilic peptides in cheese made in winter and spring. Raw milk cheese had a higher content of total free amino acids and of most individual free amino acids than pasteurized milk cheese. The relative percentages of the individual free amino acids were significantly different for raw milk and pasteurized milk cheeses. The relative percentages of Lys and lie increased, while those of Val, Leu and Phe decreased during ripening. There were also seasonal variations within the relative percentages of free amino acids. In raw milk cheeses, Asp and Cys were relatively more abundant in those made in autumn, Glu and Arg in cheeses made in winter, and Lys and Ile in cheeses made in spring and summer. Biogenic amines were detected only in raw milk cheese, with the highest levels of histamine, tryptamine and tyramine in cheeses made in spring, winter and spring, respectively.     

Starter strain related effects on the biochemical and sensory properties of Cheddar cheese

A detailed investigation was undertaken to determine the effects of four single starter strains, Lactococcus lactis subsp. lactis 303, Lc. lactis subsp. cremoris HP, Lc. lactis subsp. cremoris AM2, and Lactobacillus helveticus DPC4571 on the proteolytic, lipolytic and sensory characteristics of Cheddar cheese. Cheeses produced using the highly autolytic starters 4571 and AM2 positively impacted on flavour development, whereas cheeses produced from the poorly autolytic starters 303 and HP developed off-flavours. Starter selection impacted significantly on the proteolytic and sensory characteristics of the resulting Cheddar cheeses. It appeared that the autolytic and/or lipolytic properties of starter strains also influenced lipolysis, however lipolysis appeared to be limited due to a possible lack of availability or access to suitable milk fat substrates over ripening. The impact of lipolysis on the sensory characteristics of Cheddar cheese was unclear, possibly due to minimal differences in the extent of lipolysis between the cheeses at the end of ripening. As anticipated seasonal milk supply influenced both proteolysis and lipolysis in Cheddar cheese. The contribution of non-starter lactic acid bacteria towards proteolysis and lipolysis over the first 8 months of Cheddar cheese ripening was negligible.     

地衣芽孢杆菌凝乳酶对切达干酪成熟过程中蛋白水解的影响

利用地衣芽孢杆菌凝乳酶制作切达干酪和切达干酪类似物,分析干酪成熟过程中各蛋白水解指标的变化规律,以揭示地衣芽孢杆菌凝乳酶对切达干酪成熟过程中蛋白水解的影响。结果表明,CDF组（添加地衣芽孢杆菌D3.11凝乳酶所制切达干酪）、CD3组（添加地衣芽孢杆菌D3.11凝乳酶但未添加发酵剂制成的干酪类似物）和CCF组（添加商品凝乳酶所制切达干酪）干酪蛋白含量、pH 4.6-可溶性氮、12%三氯乙酸-可溶性氮、5%磷钨酸-可溶性氮、总游离氨基酸含量均随着成熟时间延长呈显著增加趋势,并且成熟期间CDF组干酪均显著高于CCF组干酪（P＜0.05）;十二烷基硫酸钠-聚丙烯酰氨凝胶电泳分析表明,CDF组干酪α-酪蛋白水解程度较大;pH 4.6-可溶性肽段分析表明,随着干酪的成熟,总肽含量呈先增加后下降趋势,但疏水性肽与亲水性肽的比值呈持续下降趋势,在成熟第6个月时,CDF组、CD3组和CCF组干酪疏水性肽与亲水性肽比值分别为2.668、2.822、3.788。主成分分析表明,3 组干酪的蛋白水解程度与成熟度呈正相关,与疏水性肽和亲水性肽的比值呈负相关。以上结果表明,利用地衣芽孢杆菌凝乳酶制作的干酪蛋白水解度更高,但其疏水性肽比例较小,研究结果可为地衣芽孢杆菌凝乳酶在干酪生产中的应用提供理论依据。     

Proteolysis on Reggianito Argentino cheeses manufactured with natural whey cultures and selected strains of Lactobacillus helveticus

Reggianito Argentino cheese is traditionally manufactured with whey starter cultures that provide typical and intense flavor but can cause poor quality standardization. In this study, the influence of natural and selected starters on Reggianito Argentino cheese proteolysis was investigated. Cheeses were manufactured with three strains of Lactobacillus helveticus (SF133, SF138 and SF209) cultured individually in sterile whey and used as single or mixed starters. Control cheeses were made with natural whey starter culture. Cheeses were analyzed to determine gross composition, as well as total thermophilic lactic flora. Proteolysis was assessed by N fractions, electrophoresis and liquid chromatography. Gross composition of the cheeses did not significantly differ, while viable starter cell counts were lower for cheeses made with strain SF209 alone or combined with other strains. Soluble N at pH 4.6 was the same for cheeses made with natural or selected starters, but soluble N in 12% trichloroacetic acid and 2.5% phosphotungstic acid was significantly higher in cheeses made with starters containing strain SF209. Nitrogen fractions results indicated that natural whey starter cultures could be replaced by several starters composed of the selected strains without significant changes to proteolysis patterns. Starter cultures prepared only with SF209 or with the three selected L. helveticus strains produced cheese products with significantly more proteolysis than control cheeses. Chromatographic profiles analyzed by principal components showed that three main peaks on chromatograms, presumptively identified as Tyr, Phe, and Trp, explained most of variability. Principal component scores indicated that cheese samples were grouped by ripening time, which was confirmed by linear discriminant analysis. On the contrary, samples did not cluster by Lactobacillus strain or type of starter.     

Application of exopolysaccharide-producing cultures in reduced-fat Cheddar cheese: composition and proteolysis

Proteolysis during ripening of reduced fat Cheddar cheeses made with different exopolysaccharide (EPS)-producing and nonproducing cultures was studied. A ropy strain of Lactococcus lactis ssp. cremoris (JFR1) and capsule-forming nonropy and moderately ropy strains of Streptococcus thermophilus were used in making reduced-fat Cheddar cheese. Commercial Cheddar starter was used in making full-fat cheese. Results showed that the actual yield of cheese made with JFR1 was higher than that of all other reduced-fat cheeses. Cheese made with JFR1 contained higher moisture, moisture in the nonfat substance, and residual coagulant activity than all other reduced-fat cheeses. Proteolysis, as determined by PAGE and the level of water-soluble nitrogen, was also higher in cheese made with JFR1 than in all other cheeses. The HPLC analysis showed a significant increase in hydrophobic peptides (causing bitterness) during storage of cheese made with JFR1. Cheese made with the capsule-forming nonropy adjunct of S. thermophilus, which contained lower moisture and moisture in the nonfat substance levels and lower chymosin activity than did cheese made with JFR1, accumulated less hydrophobic peptides. In conclusion, some EPS-producing cultures produced reduced-fat Cheddar cheese with moisture in the nonfat substance similar to that in its full-fat counterpart without the need for modifying the standard cheese-making protocol. Such cultures might accumulate hydrophobic (bitter) peptides if they do not contain the system able to hydrolyze them. For making high quality reduced-fat Cheddar cheese, EPS-producing cultures should be used in conjunction with debittering strains.     

Influence of starters on chemical, biochemical, and sensory changes in Turkish White-brined cheese during ripening

Turkish White-brined cheese was manufactured using Lactococcus strains (Lactococcus lactis ssp. lactis NCDO763 plus L. lactis ssp. cremoris SK11 and L. lactis ssp. lactis UC317 plus L. lactis ssp. cremoris HP) or without a starter culture, and ripened for 90 d. It was found that the use of starters significantly influenced the physical, chemical, biochemical, and sensory properties of the cheeses. Chemical composition, pH, and sensory properties of cheeses made with starter were not affected by the different starter bacteria. The levels of soluble nitrogen fractions and urea-PAGE of the pH 4.6-insoluble fractions were found to be significantly different at various stages of ripening. Urea-PAGE patterns of the pH 4.6-insoluble fractions of the cheeses showed that considerable degradation of α_s1-casein occurred and that β-casein was more resistant to hydrolysis. The use of a starter culture significantly influenced the levels of 12% trichloroacetic acid-soluble nitrogen, 5% phosphotungstic acid-soluble nitrogen, free amino acids, total free fatty acids, and the peptide profiles (reverse phase-HPLC) of 70% (vol/vol) ethanol-soluble and insoluble fractions of the pH 4.6-soluble fraction of the cheeses. The levels of peptides in the cheeses increased during the ripening period. Principal component and hierarchical cluster analyses of electrophoretic and chromatographic results indicated that the cheeses were significantly different in terms of their peptide profiles and they were grouped based on the use and type of starter and stage of ripening. Levels of free amino acid in the cheeses differed; Leu, Glu, Phe, Lys, and Val were the most abundant amino acids. Nitrogen fractions, total free amino acids, total free fatty acids, and the levels of peptides resolved by reverse phase-HPLC increased during ripening. No significant differences were found between the sensory properties of cheeses made using a starter, but the cheese made without starter received lower scores than the cheeses made using a starter. It was found that the cheese made with strains NCDO763 plus SK11 had the best quality during ripening. It was concluded that the use of different starter bacteria caused significant differences in the quality of the cheese, and that each starter culture contributed to proteolysis to a different degree.     

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.     

Behavior of Escherichia coli O157:H7 during the manufacture and ripening of feta and telemes cheeses

Pasteurized whole ewe's and cow's milk was used in the manufacture of Feta end Telemes cheeses, respectively, according to standard procedures. In both cases, the milk had been inoculated with Escherichia coli O157:H7 at a concentration of ca. 5.1 log CFU/ml and with thermophilic or mesophilic starter cultures at a concentration of ca. 5.3 to 5.6 log CFU/ml. In the first 10 h of cheesemaking, the pathogen increased by 1.18 and 0.82 log CFU/g in Feta cheese and by 1.56 and 1.35 log CFU/ g in Telemes cheese for the trials with thermophilic and mesophilic starters, respectively. After 24 h of fermentation, a decrease in E. coli O157:H7 was observed for all trials. At that time, the pH was reduced to 4.81 to 5.10 for all trials. Fresh cheeses were salted and held at 16 degrees C for ripening until the pH was reduced to 4.60. Cheeses were then moved into storage at 4 degrees C to complete ripening. During ripening, the E. coli O157:H7 population decreased significantly (P < or = 0.001) and finally was not detectable in Feta cheese after 44 and 36 days and in Telemes cheese after 40 and 30 days for the trials with thermophilic and mesophilic starters, respectively. The estimated times required for one decimal reduction of the population of E. coli O157:H7 after the first day of processing were 9.71 and 9.26 days for Feta cheese and 9.09 and 7.69 days for Telemes cheese for the trials with thermophilic and mesophilic starters, respectively.     

The effects of freezing and frozen storage of ewe's milk cheese on the viability and proteolytic activity of lactococci used as a starter

A study has been conducted on the effect of two freezing conditions (slow and fast) and frozen storage of ewe's milk cheese (?20 °C for 4 months) on the viability and the proteolytic (cascinolytic and aminopeptidase) activity ofLactococcus lactis subsp.lactis andL. lactis subsp.cremoris used as starters in the manufacture of cheese. The study was carried out on the lactococci subjected to freezing and frozen storage, either in the cheeses or in curds simulating a model system. As well as other parameters used to quantity microbial activity, the total viable counts during the subsequent cheese ripening have been analysed in the frozen cheeses. Frozen storage of the investigated lactococci, either in the cheese or in model systems, gave rise to significant decreases in the caseinolytic and aminopeptidase activities greater than did freezing alone. No clear differences were found in enzymatic activity values when using slow or fast freezing conditions. Storage of the cheeses under frozen conditions also affected microbial viability and consequently caused a greater decrease of the viable flora during subsequent ripening of the frozen stored cheeses.     

Study of the chemical composition,proteolysis, volatile compounds,and textural properties of industrial and traditional Beaten (Bieno sirenje) ewe milk cheese

The objective of this study was to determine the gross composition, proteolysis, and volatile and texture profiles during ripening of industrial (IND) and traditional (TRD) Beaten (Bieno sirenje) cheeses made by using ewe milk. In the course of the analyses, statistical differences were determined in some physicochemical parameters, nitrogen fractions, and total free amino acid levels between TRD and IND types of cheese. Higher levels of proteolysis were observed in IND cheeses than in TRD cheeses during ripening. Levels of residual β- and α_s-caseins were 72.2 and 48.7%, respectively, in 180-d-old TRD cheeses. However, the residual levels were 52.8% for β-casein and 18% for α_s-casein in IND cheeses. Similar differences were noted for the reversed-phase HPLC peptide profiles of 2 types of cheeses. Also, higher concentrations of peptides were eluted in IND cheeses than in TRD cheeses during ripening. A total of 73 volatile compounds, including alcohols (16), esters (17), acids (14), terpenes (7), ketones (5), aldehydes (4), and miscellaneous (10) were identified. The IND cheeses contained higher levels of carboxylic acids, esters, alcohols, and terpenes than the TRD cheeses; however, the same levels of methyl ketones were determined in the 2 types of cheeses at the end of ripening. These may be due to some differences (e.g., pasteurization and scalding temperature, among other factors) in the manufacture of the 2 types of Beaten cheeses. The textural profile of Beaten cheeses showed that TRD production method resulted in firmer, less fracturable, and stiffer cheeses than the IND production method. In conclusion, the results suggest that the use of industrial production method (pasteurization of cheese milk and curd scalding at 70°C) in the manufacture of Beaten ewe milk cheese enriched the volatile profile of the cheese.