Miniature Cheeses Research Articles

Investigation of Flavor-Forming Starter Lactococcus lactis subsp. lactis LDTM6802 and Lactococcus lactis subsp. cremoris LDTM6803 in Miniature Gouda-Type Cheeses.

Lactic acid bacteria (LAB) play an important role in dairy fermentations, notably as cheese starter cultures. During the cheese production and ripening period, various enzymes from milk, rennet, starter cultures, and non-starter LABs are involved in flavor formation pathways, including glycolysis, proteolysis, and lipolysis. Among these three pathways, starter LABs are particularly related to amino acid degradation, presumably as the origins of major flavor compounds. Therefore, we used several enzymes as major criteria for the selection of starter bacteria with flavor-forming ability. Lactococcus lactis subsp. lactis LDTM6802 and Lactococcus lactis subsp. cremoris LDTM6803, isolated from Korean raw milk and cucumber kimchi, were confirmed by using multiplex PCR and characterized as starter bacteria. The combinations of starter bacteria were validated in a miniature Gouda-type cheese model. The flavor compounds of the tested miniature cheeses were analyzed and profiled by using an electronic nose. Compared to commercial industrial cheese starters, selected starter bacteria showed lower pH, and more variety in their flavor profile. These results demonstrated that LDTM6802 and LDTM6803 as starter bacteria have potent starter properties with a characteristic flavor-forming ability in cheese.

Formation of conjugated linoleic acid by a Lactobacillus plantarum strain isolated from an artisanal cheese: Evaluation in miniature cheeses

Among 129 lactic acid bacteria previously isolated from raw-milk starter-free cheeses manufactured in Galicia (NW Spain), two strains of Lactobacillus plantarum were definitely recognised as producers of conjugated linoleic acid (CLA). Gas chromatography analysis identified cis-9, trans-11 C18:2 as the predominant CLA isomer formed in MRS broth supplemented with linoleic acid. A centrifugation-based model for the manufacture of miniature cheeses was used to evaluate the formation of CLA by Lb. plantarum L200, the highest producer of CLA in MRS broth. The miniature cheeses made with the addition of the L200 strain showed significantly (P < 0.05) higher contents of cis-9, trans-11 CLA than those of the control cheeses (1.09 versus 0.69 percentage of total fatty acids, respectively). These results suggest that Lb. plantarum L200 strain could be used as an adjunct culture to slightly increase the concentrations of CLA in short-ripened cows' milk cheeses.

Miniature cheeses made with blends of chymosin and a vegetable rennet from flowers of Silybum marianum: Enzymatic characterization of the flower-coagulant peptidase

Binary blends of S. marianum–flower extract and chymosin, as coagulant preparations, enabled the manufacture of miniature cheeses with distinctive characteristics compared to those of chymosin-renneted cheeses. The physicochemical parameters, sensory attributes of the cheeses, and in-vitro water-soluble antioxidant activity were analyzed and compared to those properties obtained from control chymosin-renneted cheeses. The preponderant proteolytic constituent in the flower extract was isolated in a two-step-purification protocol. The thus purified aspartic peptidase was maximally active at acidic pHs and exhibited a preference for peptide bonds between hydrophobic residues. Enzymologic characterization revealed differences in the kinetic parameters and specificity compared to other enzymes employed, such as rennet. S. marianum–flower extract, as a source of peptidase with distinctive characteristics, is a suitable substitute for chymosin in miniature-cheese production. The addition of vegetable rennet contributed to the development of an intense aroma and conferred antioxidant activity to the cheeses and wheys.

Fate of Lactococcus lactis starter cultures during late ripening in cheese models

The presence of Lactococcus lactis, commonly employed as starter culture, was, recently, highlighted and investigated during late cheese ripening. Thus, the main goal of the present study was to assess the persistence and viability of this microorganism throughout manufacturing and ripening of model cheeses. Eight commercial starters, constituted of L. lactis subsp. lactis and L. lactis subsp. cremoris, were inoculated in pasteurized milk in order to manufacture miniature cheeses, ripened for six months. Samples were analysed at different steps (milk after inoculum, curd after cutting, curd after pressing and draining, cheese immediately after salting and cheese at 7, 15, 30, 60, 90, 120, 150 and 180 days of ripening) and submitted to both culture-dependent (traditional plating on M17) and -independent analysis (reverse transcription-quantitative PCR).On the basis of direct RNA analysis, L. lactis populations were detected in all miniature cheeses up to the sixth month of ripening, confirming the presence of viable cells during the whole ripening process, including late stages. Noteworthy, L. lactis was detected by RT-qPCR in cheese samples also when traditional plating failed to indicate its presence. This discrepancy could be explain with the fact that lactococci, during ripening process, enter in a stressed physiological state (viable not culturable, VNC), which might cause their inability to grow on synthetic medium despite their viability in cheese matrix. Preliminary results obtained by “resuscitation” assays corroborated this hypothesis and 2.5% glucose enrichment was effective to recover L. lactis cells in VNC state.The capability of L. lactis to persist in late ripening, and the presence of VNC cells which are known to shift their catabolism to peptides and amino acids consumption, suggests a possible technological role of this microorganism in cheese ripening with a possible impact on flavour formation.

Effect of high-pressure treatment on hard cheese proteolysis

The application of high hydrostatic pressure (HHP) treatment has been proposed to reduce the ripening time of cheese via modifications in the enzymatic activities or the substrate reactivity. Investigations on the effect of HHP on cheese proteolysis have been undertaken with either encouraging results or little effect according to the treatment conditions and the type of cheese, but information concerning the effect of HHP on the ripening of hard cooked cheese is still lacking. In this report, we describe the effect of HHP treatment on Reggianito cheese proteolysis. For that purpose, 1-d-old miniature cheeses (5.5-cm diameter and 6-cm height) were treated at 100 or 400MPa and 20°C for 5 or 10min, and control cheeses in the trial were not pressurized. All cheeses were ripened at 12°C during 90d. The HHP did not affect gross composition of the cheeses, but microbial load changed, especially because the starter culture count was significantly lower at the beginning of the ripening of the cheeses treated at 400MPa than in controls and cheeses treated at 100MPa. Cheeses treated at 400MPa for 10min had significantly higher plasmin activity than did the others; the residual coagulant activity was not affected by HHP. Proteolysis assessment showed that most severe treatments (400MPa) also resulted in cheeses with increased breakdown of αS1- and β-CN. In addition, nitrogen content in soluble fractions was significantly higher in cheeses treated at 400MPa, as well as soluble peptides and free AA production. Peptide profiles and individual and total content of free AA in 60-d-old treated cheese were as high as in fully ripened control cheeses (90d). Holding time had an effect only on pH-4.6-soluble nitrogen fraction and plasmin activity; cheese treated for 10min showed higher values than those treated for 5min, at both levels of pressure assayed. We concluded that HHP treatments at 400MPa applied 1d after cheesemaking increased the rate of proteolysis, leading to an acceleration of the ripening process in Reggianito Argentino cheese, whereas 100-MPa treatments did not lead to significant changes.

Comparison of volatile compounds produced by wild Lactococcus lactis in miniature Chihuahua-type cheeses

Strains of Lactococcus lactis used for a long time as starter cultures in the production of cheese have not only acquired special features like fast utilization of lactose, but it is also believed that they have lost certain metabolic capabilities. Certain wild strains of L. lactis isolated from vegetables or raw milk products are able to generate flavors different from those produced by industrial strains. The aim of this work was to assess the production of volatile compounds in miniature Chihuahua-type cheeses manufactured with different strains of L. lactis isolated from vegetables, raw milk products, and industrial cultures. There was variation among volatile profiles in the miniature cheeses manufactured with different strains of L. lactis. However, some compounds were seen in most of the cheeses such as acetic, lactic, butyric, and caproic acids, acetoin, 3-methyl-1-butanol, and 2,3-butanediol. The source of isolation of the strains (plants, raw milk products, and industrial cultures) did not have a clear influence on the production of volatile compounds in miniature cheeses. According to principal component analysis, 19 out of 21 strains of L. lactis produced volatile profiles similar to the three pasteurized Chihuahua cheeses analyzed, but only 2 strains generated profiles similar to the commercial raw milk cheese. However, further research is required to understand the metabolic and genetic differences of these strains.

Effect of β-lactoglobulin A and B whey protein variants on cheese yield potential of a model milk system

Cheese yield mainly depends on the amount and proportion of milk constituents; however, genetic variants of the proteins present in milk may also have an important effect. The objective of this research was to study the effect of the variants A and B of β-lactoglobulin (LG) on cheese yield using a model system consisting of skim milk powder fortified with different levels of a mixture containing α-lactalbumin and β-LG genetic variants (A, B, or A-B) in a 1:2 ratio. Fortified milk samples were subjected to pasteurization at 65°C for 30min. Miniature cheeses were made by acidifying (pH=5.9) fortified milk and incubating with rennet for 1h at 32°C. The clot formed was cut, centrifuged at 2,600×g for 30min at 20°C and drained for determining cheese yield. Cheese-yielding capacity was expressed as actual yield (grams of cheese curd per 100g of milk) and dry weight yield (grams of dried cheese curd per 100g of milk). Free-zone capillary electrophoresis was used for determining β-LG A or B recovery in the curd during rennet-induced coagulation. The presence of β-LG variant B resulted in a significantly higher actual and dried weight cheese yield than when A or A-B were present at levels ≤0.675% of whey protein (WP) addition. Results of free-zone capillary electrophoresis allowed us to infer that β-LG B associates with the casein micelles during renneting, as shown by an increase in the recovery of this variant in the curd when β-LG B was added up to a maximum at 0.45% (equivalent to 0.675% WP). In general, actual or dried weight cheese yield increased as WP addition was increased from 0.225 to 0.675%. However, when WP addition ranged from 0.675 to 0.90%, a drastic drop in cheese yield was observed. This behavior may be because an increase in the aggregation of casein micelles with a concomitant inclusion of whey protein in the gel occurs at low levels of WP addition, whereas once the association of WP with the casein micelles reach a saturation point at addition levels higher than 0.675%, rearrangements of the gel network result in larger whey expulsion and syneresis. This knowledge is expected to be useful to maximize cheese yield and optimize processing conditions during cheese and cheese analogs manufacturing.

Effects of addition of somatic cells to caprine milk on cheese quality

Milk quality criteria and limits for somatic cell count (SCC) established in many countries make it difficult to maintain SCC of bulk tank goat milk below the threshold, due to non-infection factors linked to goat physiology. The aim of this study was to objectively verify the effects of SCC on fresh caprine milk cheese. Somatic cells were recovered from pooled healthy goat milk, and added to low SCC raw or pasteurised goat milk. Miniature cheeses were made and evaluated after 1 and 7 d. Somatic cells had a major effect on lipolysis, increasing free fatty acids regardless of whether milk was raw or pasteurised. The effect of somatic cells on proteolysis was specific for caseins and the effects were different if cheeses are made from raw or pasteurised milk. It is concluded that somatic cells themselves in caprine milk can directly affect some cheese parameters.

Milk clotting and proteolytic activity of an enzyme preparation from Bromelia hieronymi fruits

A new enzyme preparation (hieronymain), obtained from unripe fruits of Bromelia hieronymi Mez (Bromeliaceae), was assayed for its ability to clot milk and hydrolyze bovine casein and milk whey proteins. Caseinolytic activity at 30 °C and pH 6.5 (milk clotting conditions) was 3.3 Ucas/mL and milk clotting activity was 40 ± 0.2 IMCU/mL. The κ-casein fraction, involved in the clotting formation, began to be degraded after 10 min of reaction, while the degradation of the other casein fractions proceeded slowly enough as to guarantee the production of a firm curd, with no evidence of extensive hydrolysis, a necessary condition for cheese making. In the case of whey proteins, bovine serum albumin and α-lactalbumin were quickly degraded after 30 min, while β-lactoglobulin was considerably degraded only after 60 min at 50 °C. Miniature cheeses were manufactured both with chymosine and hieronymain and analyzed by a taste panel, who found acceptable both cheeses. Hieronymain might be appropriate for cheese making, as well as for the production of milk protein hydrolysates.

A high-throughput cheese manufacturing model for effective cheese starter culture screening

Cheese making is a process in which enzymatic coagulation of milk is followed by protein separation, carbohydrate removal, and an extended bacterial fermentation. The number of variables in this complex process that influence cheese quality is so large that the developments of new manufacturing protocols are cumbersome. To reduce screening costs, several models have been developed to miniaturize the cheese manufacturing process. However, these models are not able to accommodate the throughputs required for systematic screening programs. Here, we describe a protocol that allows the parallel manufacturing of approximately 600 cheeses in individual cheese vats each with individual process specifications. Protocols for the production of miniaturized Gouda- and Cheddar-type cheeses have been developed. Starting with as little as 1.7mL of milk, miniature cheeses of about 170mg can be produced and they closely resemble conventionally produced cheese in terms of acidification profiles, moisture and salt contents, proteolysis, flavor profiles, and microstructure. Flavor profiling of miniature cheeses manufactured with and without mixed-strain adjunct starter cultures allowed the distinguishing of the different cheeses. Moreover, single-strain adjunct starter cultures engineered to overexpress important flavor-related enzymes revealed effects similar to those described in industrial cheese. Benchmarking against industrial cheese produced from the same raw materials established a good correlation between their proteolytic degradation products and their flavor profiles. These miniature cheeses, referred to as microcheeses, open new possibilities to study many aspects of cheese production, which will not only accelerate product development but also allow a more systematic approach to investigate the complex biochemistry and microbiology of cheese making.

Mini soft cheese as a simple model for biochemical studies on cheese-making and ripening

A new miniature cheese model obtained under controlled microbiological conditions was proposed, characterized and tested for reproducibility. Optimal heat treatment of cheesemilk was defined, as well as maximal ripening time. Miniature cheeses were obtained with batch pasteurized milk (65 °C, 30 min) and ripened at 5 °C. Lactic and nonlactic microbial populations were monitored by plate counts. Proteolysis was assessed by nitrogen fractions, electrophoresis and liquid chromatography, and a sniffing test was applied to evaluate aroma. Coliform bacteria decreased during ripening but moulds and yeasts increased up to 10 4 cfu/g after 60 d, which defined the end of ripening period. Starter population remained constant during all ripening (10 9 cfu/g), while nonstarter lactic acid bacteria increased from ∼10 2 to 10 4 cfu/g. Soluble nitrogen levels at pH 4.6, in trichloracetic acid (0.73 mol/l) and in phosphotungtic acid (0.009 mol/l) were 151, 67, and 10 g/1000 g of the total nitrogen, respectively, after 60 d of ripening, which are usual values for soft cheeses. Proteolytic patterns as measured by electrophoresis were also similar to those of standard cheeses, as well as the aroma of the products. Peptide profiles revealed that the areas of most peaks increased with ripening time. The proposed model showed to be suitable for the production of mini cheese specimens for laboratory testing of cultures and enzymes in similar conditions to their real environment in the food matrix.

A preliminary study on the role of alkaline phosphatase in cheese ripening

A preparation of exogenous alkaline phosphatase (ALP), containing 17,500 mU L−1, was added to pasteurized milk (PM) to study its role in cheese ripening. Three miniature Cheddar-type cheeses were made from PM containing no added ALP (control), PM plus 23 μL ALP (T1), to give ALP concentration similar to that in raw milk, and PM plus 46 μL ALP (T2). Milk, after addition of ALP, was held at 6 °C for 12 h before cheese manufacture and the experiment was replicated three times. The control, T1 and T2 milks contained ALP activity of 415, 2391 and 4705 mU L−1, respectively. The addition of ALP to PM caused significant (P<0.05) changes in moisture content of miniature cheeses but did not cause any changes in protein content. Levels of water-soluble N during ripening of the cheeses were similar for control, T1 and T2 cheeses. The concentration of amino acids was not affected by the level of ALP present in milk. However, reversed-phase HPLC showed differences in the peptide patterns of control, T1 and T2 cheeses, suggesting a role of ALP in cheese ripening. The results suggest that ALP may play a role in cheese ripening, but further studies are needed to confirm this.

Evaluation of the importance of germinative cycles for destruction of bacillus cereus spores in miniature cheeses

Our objective was to determine the effect of high pressure on inactivation of spores of Bacillus cereus ATCC 9139 inoculated into cheese made of raw cow's milk. Inoculated miniature cheeses were manufactured under controlled bacteriological conditions, vacuum packed and kept at 8 °C for 15 days after pressure treatment. Cheeses were submitted to pressures of 300, 400 or 500 MPa at 30 °C, during 15 min. Some of them were treated with a germination cycle of 60 MPa at 30 °C for 210 min. Lethality was calculated comparing surviving sample counts to control ones. Adding the germinative cycle resulted in higher efficiency, and when applied with 500 MPa, lethality reached 2.0 log cfu/mL. We saw that with both cycles initial counts of spores diminish, but all of them were not inactivated. However, considering that in raw milk mesophilic spore counts are 2.6-2.9 log cfu/mL, this treatment may be useful.

Influence of starter and adjunct lactobacilli culture on ripening of miniature washed-curd cheeses

Ten strains of Lactobacillus were tested as adjunct cultures in combination with two different Lactocococcus lactis starters in miniature washed-curd cheeses manufactured under controlled bacteriological conditions. Growth of lactobacilli seemed to depend on the strain used, but was not influenced by the starter strain (either L. lactis subsp. lactis lL416 or L. lactis subsp. cremoris AM2). Lactococcal counts in miniature cheeses with AM2 starter and added lactobacilli were higher than in control cheeses without lactobacilli. Consistently good survival (~100% after four weeks) was observed for IL416, regardless of the presence of adjunct culture). In contrast, AM2 starter cell viability decreased slowly over the same time period. Gross composition and protein analyses were performed on the miniature cheeses. Our results indicate that production of soluble nitrogenous compounds was influenced by the lactobacilli adjunct, and depended on the starter strain. We conclude that the use of different combinations of starter and adjunct cultures can result in marked differences in bacterial populations and product properties. Such studies may be used to choose the combination of strains necessary to obtain a product with particular properties.

The influence of starter and adjunct lactobacilli culture on the ripening of washed curd cheeses

Ten strains of lactobacillus from the CNRZ collection were tested as adjunct culture in miniature washed curd cheeses manufactured under controlled bacteriological conditions with two different starters, Lactococcus lactis subsp. lactis IL 416 and Lactococcus lactis subsp. cremoris AM2. Lactobacilli growth seemed to be dependent on the Lactobacillus strain but was not influenced by the starter strain or counts. Lactococci counts were higher in the miniature cheeses with AM2 starter and added lactobacilli than in the control cheeses without lactobacilli. Gross composition and hydrolysis of s1 casein were similar for miniature cheeses with and without lactobacilli. In the miniature cheeses manufactured with IL416 starter, the lactobacilli adjunct slightly increased the soluble nitrogen content, but that was not verified in the AM2 miniature cheeses. Phosphotungstic acid nitrogen content increased in miniature cheeses manufactured with IL416 when Lactobacillus plantarum 1572 and 1310 adjunct cultures were added. That was also verified for several Lactobacillus strains, specially Lactobacillus casei 1227, for miniature cheeses manufactured with AM2 starter. Free fatty acid content increased in miniature cheeses made with lactobacilli adjuncts 1310, 1308 and 1219 with IL416 starter, and with strains 1218, 1244 and 1308 for miniature cheeses with AM2 starter. These results indicate that production of soluble nitrogen compounds as well as free fatty acid content could be influenced by the lactobacilli adjunct, depending on the starter strain.

Lactobacillus reuteri DSM 20016: purification and characterization of a cystathionine gamma-lyase and use as adjunct starter in cheesemaking.

A homo-tetrameric approximately 160-kDa cystathionine gamma-lyase was purified to homogeneity from Lactobacillus reuteri DSM 20016 by four chromatographic steps. The activity was pyridoxal-5'-phosphate dependent and the enzyme catalyzed the alpha,gamma-elimination reaction of L-cystathionine, producing L-cysteine, ammonia and alpha-ketobutyrate. The enzyme was active towards a range of amino acids and amino acid derivatives, including methionine. The pH and temperature optima were found to be 8.0 and 35 degrees C. respectively. Isoelectric pH (pI) was approximately 5.0 as determined by two-dimensional electrophoresis. Sensitivity to chemical inhibitors was typical of lactococcal cystathionine gamma- and beta-lyases, except it was inhibited by sulphydryl reagents. The N-terminal sequence was MKFNTQLIHGGNSED, which had 100% homology with cystathionine beta-lyase of Lb. reuteri 104R (Accession Number (CAC05298). Lb. reuteri DSM 20016. together with 10 other strains of non-starter lactic acid bacteria, was used as adjunct starter in the production of miniature ('anestrato Pugliese-like cheeses. After 40 d ripening, the water-soluble extract of the cheeses with added Lactobacillus fermentum DT41 and Lb. reuteri DSM 20016 contained the highest enzyme activities on cystathionine and methionine substrates. Determinations of methanethiol, dimethyl sulphide, dimethyl disulphide and dimethyl trisulphide in the miniature cheeses confirmed the findings of enzyme activities.

Proteolysis during ripening of miniature washed-curd cheeses manufactured with different strains of starter bacteria and a Lactobacillus plantarum adjunct culture

Abstract Washed-curd miniature cheeses were manufactured under controlled bacteriological conditions with three starters: Lactococcus lactis subsp. lactis IL416, Lactococcus lactis subsp. cremoris HP or Lactococcus lactis subsp. cremoris AM2 (increased lysis rate) and with or without Lactobacillus plantarum 1572 adjunct culture. We examined gross composition and bacterial cell counts, and assessed proteolysis in 28-day-old cheeses by nitrogen analysis, free amino acids determination and RP-HPLC of ethanol soluble peptides and casein fractions. Development and proteolytic activity of lactobacilli adjunct culture depended on the starter strain used in cheesemaking. In the presence of IL416 and AM2 lactobacilli cell counts reached ∼10 7 CFU g −1 the first day of ripening and remained almost constant, while in cheeses made with HP starter strain lactobacilli grew throughout ripening. Soluble nitrogen at pH 4.4 was higher in cheeses made with starter HP. Different values for free amino acids were noted for the three starter strains and between cheeses with and without lactobacilli, while peptide profiles varied from one starter strain to another and showed quantitative differences between cheeses with and without lactobacilli. Casein fraction profile was essentially the same for all cheeses.

Protocol for the manufacture of miniature washed-curd cheeses under controlled microbiological conditions

Abstract A protocol for the preparation of miniature washed-curd cheeses under controlled bacteriological conditions was designed and tested for reproducibility. The process was adapted from “Saint-Paulin” technology, and involves inoculation and renneting in autoclaved bottles, and cutting, stirring, curd washing and removal of whey by centrifugation. Pressing was simulated by low-speed centrifugation. All operations were performed using sterile techniques and autoclaved equipment. Forty miniature cheeses (approximately 40 g) were produced over 10 working days, and ripened for 28 days. Gross composition (dry matter, salt-in-moisture and pH) of the one-day-old cheeses did not differ significantly between cheesemaking days, and average values were 45.16 , 2.46 and 5.15%, respectively. Adventitious Lactobacillus population remained less than 200 CFU g −1 all during ripening, and phages were absent. Nitrogen soluble at pH 4.4 and in phosphotungstic acid attained 21 and 3% of total nitrogen, respectively, in 28-day-old cheeses. The proposed model was shown to be suitable for the preparation of miniature cheese specimens for use in microbiological studies of cheese manufacture and ripening.

Comparative study by multivariate statistical analysis of proteolysis in a sodium caseinate solution under cheese-like conditions caused by strains of Lactococcus

Abstract Sonicated cells of Lactcoccus lactis subsp. cremoris 223, 227, SK11, AM1, Wg2 or L. lactis subsp. lactis UC317 were added to a sodium caseinate solution under conditions found in Cheddar or Gouda cheese during ripening (pH 5.25 and 5.0% (w/v) NaCl). Proteolysis was assessed by urea-polyacrylamide gel electrophoresis of the pH 4.6- and ethanol (70%)-insoluble fractions and reverse-phase-high-performance liquid chromatography of the ethanol (70%)-soluble fraction, and the resulting peptide profiles were analysed by principal component analysis and hierarchical cluster analysis. Statistical analysis of peptide profiles of the ethanol (70%)-soluble fraction from 2, 9, 17 or 23 d-old samples grouped the strains into three clusters which were similar to those found earlier for the same strains in an experiment with miniature Cheddar-type model cheeses by Shakeel-Ur-Rehman, Pripp, McSweeney and Fox (1999, Lait , 79 , 361–383).

Assessing the proteolytic and cheese ripening properties of single strains of Lactococcus in miniature cheeses

The performance of Il single strains of Laetoeoeeus (Le. laetis ssp. eremoris 223, 227, 250, 255, 267, 303, AM 1 and SK Il and Le. laetis ssp. laetis UC317 (non-bitter strains), and Le. lae- tis ssp. cremoris Wg2 and HP (bitter strains)) was studied in miniature Cheddar-type model cheeses. Different inocula were used to give equivalent rates of acidification during manufacture and the cheeses made differed in flavour development and proteolysis during ripening. Urea-polyacrylamide gel electrophoretograms (PAGE) of the water-insoluble fraction (WISF) of ail cheeses were similar after 2 and 4 months of ripening, while the level of water-soluble nitrogen (WSN; as % of total N) showed only small differences between cheeses made with different starter strains. The cheese made with Le. laetis ssp. eremoris Wg2 differed considerably from the other cheeses as indicated by urea- PAGE of the water-soluble fraction (WSF), reverse-phase high performance Iiquid chromatogra- phy (RP-HPLC) of the 70 % ethanol-soluble and -insoluble fractions of the WSF, concentration of amino acids and flavour characteristics; it had the highest pH (5.7) and the highest concentration of most of amino acids except Asp, Ile and Arg after 4 months of ripening. The cheese made with Le. laetis ssp. cremoris SKII received the highest score for flavour and that made with Wg2 received the lowest score. The results ofthis study indicate that the strain(s) of Laetocoeeus used as starter plays an important role in the biochemistry of cheese ripening and produces a characteristic profile of peptides and amino acids. © InralElsevier, Paris.