Acceleration of cheese ripening

Exploring the genetic information of Lactobacillus helveticus strains hydrolyzing soy protein using genome-wide association analysis

Soy protein is a multimeric globular protein that is less likely to be metabolized and utilized by lactic acid bacteria (LAB) during fermentation compared to milk-derived proteins. Little genetic information is available regarding LAB-mediated hydrolysis of soy protein. In this study, we sequenced the genomes of 46 Lactobacillus helveticus (L. helveticus) strains to analyze genetic-level factors affecting soy protein hydrolytic activity. The analysis revealed that the soy protein hydrolysis capability of these L. helveticus strains showed no correlation with their isolation sources, geographic origins, extracellular protease genes, peptide transporter genes, or peptidase gene distribution. Through genome-wide association analysis (GWAS), we identified two significantly associated missense SNPs (SNP-482062 and SNP-1780770) linked to soy protein hydrolysis activity. These two SNPs changed the local tertiary structure of amino acid permease and ornithine decarboxylase, respectively. Enzymatic assays confirmed that the mutations significantly affected enzyme activity, thereby validating their critical role in soy protein hydrolysis. This study elucidates the genetic basis for differential soy protein hydrolysis capacity among L. helveticus strains, offering practical guidance for selecting highly proteolytic strains to develop soy-based fermented dairy alternatives.

Pyruvate stimulates transamination of leucine into α-ketoisocaproic acid and supports 3-methylbutanal production by Lactococcus lactis

AIM

To investigate the effect of pyruvate and glucose on leucine transamination and 3-methylbutanal production by Lactococcus lactis, including the comparison with cells possessing glutamate dehydrogenase (GDH) activity.

METHODS AND RESULTS

Lactococcus lactis cells were incubated in chemically defined medium (CDM) with the pH controlled at 5.2 to mimic cheese conditions. Pyruvate supplementation stimulated the production of the key flavour compound 3-methylbutanal by 3-4 times after 72 h of incubation. Concurrently, alanine production increased, demonstrating the involvement of pyruvate in transamination reactions. Glucose-metabolizing cells excreted α-ketoisocaproic acid and produced even 3 times more 3-methylbutanal after 24 h than pyruvate-supplemented cells. Conjugal transfer technique was used to transfer the plasmid pGdh442 carrying the gdh gene encoding for GDH to L. lactis. Introducing GDH did not stimulate the excretion of α-ketoisocaproic acid and the production of 3-methylbutanal.

CONCLUSIONS

These results demonstrate that Lactococcus uses pyruvate to transaminate leucine into α-ketoisocaproic acid which supports 3-methylbutanal production. Surprisingly, GDH activity did not stimulate leucine transamination and 3-methylbutanal production.

Preparation of pH-responsive chitosan microspheres containing aminopeptidase and their application in accelerating cheese ripening

Microencapsulated enzymes have been found to effectively accelerate cheese ripening. However, microencapsulated enzyme release is difficult to control, often resulting in enzyme release during cheese processing and causing texture and flavor defects. This study aims to address this issue by developing aminopeptidase-loaded pH-responsive chitosan microspheres (A-CM) for precise enzyme release during cheese ripening. An aminopeptidase with an isoelectric point (pH 5.4) close to the pH value of cheese ripening was loaded on chitosan microspheres through electrostatic interaction. Turbidity titration measurements revealed that pH 6.5 was optimal for binding aminopeptidase and microspheres, affording the highest loading efficiency of 58.16%. Various characterization techniques, including scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier-transform infrared spectroscopy confirmed the successful loading of aminopeptidase molecules on the chitosan microspheres. In vitro release experiments conducted during simulated cheese production demonstrated that aminopeptidase release from A-CM was pH responsive. The microspheres retained the enzyme during the coagulation and cheddaring processes (pH 5.5-6.5) and only released it after entering the cheese-ripening stage (pH 5.0-5.5). By loading aminopeptidase on chitosan microspheres, the loss rate of the enzyme in cheese whey was reduced by approximately 79%. Furthermore, compared with cheese without aminopeptidase and cheese with aminopeptidase added directly, the cheeses made with A-CM exhibited the highest proteolysis level and received superior sensory ratings for taste and smell. The content of key aroma substances, such as 2/3-methylbutanal and ethyl butyrate, in cheese with A-CM was more than 15 times higher than the others. This study provides an approach for accelerating cheese ripening through the use of microencapsulated enzymes.

Near-infrared hyperspectral image analysis for monitoring the cheese-ripening process

Ripening is the most crucial process step in cheese manufacturing and constitutes multiple biochemical alterations that describe the final cheese quality and its perceived sensory attributes. The assessment of the cheese-ripening process is challenging and requires the effective analysis of a multitude of biochemical changes occurring during the process. This study monitored the biochemical and sensory attribute changes of paraffin wax-covered long-ripening hard cheeses (n = 79) during ripening by collecting samples at different stages of ripening. Near-infrared hyperspectral (NIR-HS) imaging, together with free amino acid, chemical composition, and sensory attributes, was studied to monitor the biochemical changes during the ripening process. Orthogonal projection-based multivariate calibration methods were used to characterize ripening-related and orthogonal components as well as the distribution map of chemical components. The results approve the NIR-HS imaging as a rapid tool for monitoring cheese maturity during ripening. Moreover, the pixelwise evaluation of images shows the homogeneity of cheese maturation at different stages of ripening. Among the chemical compositions, fat content and moisture are the most important variables correlating to NIR-HS images during the ripening process.

Microencapsulation of a Commercial Food-Grade Protease by Spray Drying in Cross-Linked Chitosan Particles

In this study, the use of spray-drying technology for encapsulating Flavourzyme® (protease–peptidase complex) was evaluated to overcome the limitations (low encapsulation efficiency and no large-scale production) of other encapsulation processes. To the best of our knowledge, spray drying has not been applied previously for the immobilization of this enzyme. Firstly, bovine serum albumin (BSA), as a model protein, was encapsulated by spray drying in chitosan and tripolyphoshate (TPP) cross-linked-chitosan shell matrices. The results showed that the chitosan–TPP microcapsules provided a high encapsulation efficiency and better protein stability compared to the non-crosslinked chitosan microcapsules. The effect of enzyme concentration and drying temperature were tested during the spray drying of Flavourzyme®. In this regard, an activity yield of 88.0% and encapsulation efficiency of 78.6% were obtained with a concentration of 0.1% (v/v) and an inlet temperature of 130 °C. Flavourzyme®-loaded chitosan microcapsules were also characterized in terms of their size and morphology using scanning electron microscopy and laser diffractometry.

Fermentation of plant-based dairy alternatives by lactic acid bacteria

Ethical, environmental and health concerns around dairy products are driving a fast‐growing industry for plant‐based dairy alternatives, but undesirable flavours and textures in available products are limiting their uptake into the mainstream. The molecular processes initiated during fermentation by lactic acid bacteria in dairy products is well understood, such as proteolysis of caseins into peptides and amino acids, and the utilisation of carbohydrates to form lactic acid and exopolysaccharides. These processes are fundamental to developing the flavour and texture of fermented dairy products like cheese and yoghurt, yet how these processes work in plant‐based alternatives is poorly understood. With this knowledge, bespoke fermentative processes could be engineered for specific food qualities in plant‐based foods. This review will provide an overview of recent research that reveals how fermentation occurs in plant‐based milk, with a focus on how differences in plant proteins and carbohydrate structure affect how they undergo the fermentation process. The practical aspects of how this knowledge has been used to develop plant‐based cheeses and yoghurts is also discussed.

Adaptive Laboratory Evolution as a Means To Generate Lactococcus lactis Strains with Improved Thermotolerance and Ability To Autolyze

Lactococcus lactis subsp. lactis (referred to here as L. lactis) is a model lactic acid bacterium and one of the main constituents of the mesophilic cheese starter used for producing soft or semihard cheeses. Most dairy L. lactis strains grow optimally at around 30°C and are not particularly well adapted to the elevated temperatures (37 to 39°C) to which they are often exposed during cheese production. To overcome this challenge, we used adaptive laboratory evolution (ALE) in milk, using a setup where the temperature was gradually increased over time, and isolated two evolved strains (RD01 and RD07) better able to tolerate high growth temperatures. One of these, strain RD07, was isolated after 1.5 years of evolution (400 generations) and efficiently acidified milk at 41°C, which has not been reported for industrial L. lactis strains until now. Moreover, RD07 appeared to autolyze 2 to 3 times faster than its parent strain, which is another highly desired property of dairy lactococci and rarely observed in the L. lactis subspecies used in this study. Model cheese trials indicated that RD07 could potentially accelerate cheese ripening. Transcriptomics analysis revealed the potential underlying causes responsible for the enhanced growth at high temperatures for the mutants. These included downregulation of the pleiotropic transcription factor CodY and overexpression of genes, which most likely lowered the guanidine nucleotide pool. Cheese trials at ARLA Foods using RD01 blended with the commercial Flora Danica starter culture, including a 39.5°C cooking step, revealed better acidification and flavor formation than the pure starter culture. IMPORTANCE In commercial mesophilic starter cultures, L. lactis is generally more thermotolerant than Lactococcus cremoris, whereas L. cremoris is more prone to autolysis, which is the key to flavor and aroma formation. In this study, we found that adaptation to higher thermotolerance can improve autolysis. Using whole-genome sequencing and RNA sequencing, we attempt to determine the underlying reason for the observed behavior. In terms of dairy applications, there are obvious advantages associated with using L. lactis strains with high thermotolerance, as these are less affected by curd cooking, which generally hampers the performance of the mesophilic starter. Cheese ripening, the costliest part of cheese manufacturing, can be reduced using autolytic strains. Thus, the solution presented here could simplify starter cultures, make the cheese manufacturing process more efficient, and enable novel types of harder cheese variants.

Accelerating vinegar aging by combination of ultrasonic and magnetic field assistance

Most fermented foods need a natural aging process to enrich desired flavours. This process is normally the bottleneck for cost-effective production. Therefore, it is desirable to accelerate the process and obtain products with the same flavour profile. Here, we used physical interventions (ultrasonic field, alternating magnetic field, or combination of both) to assist the aging process with naturally brewed vinegar as a case example. Flavour profiles of different physical-assisted aging process were compared with that of the naturally aged vinegar by using gas-chromatography mass-spectrometry (GC-MS) and electronic nose. Principal component analysis (PCA) and Pearson correlation analyses show that ultrasonic and alternating magnetic fields treatment could accelerate the aging process of vinegar. The highest accelerating aging effect was combination of ultrasonic and magnetic field followed by individual ultrasonic or magnetic field and natural process (combination of ultrasonic and magnetic field > ultrasonic or magnetic field individual > natural process). These results suggest that physical field intervention could potentially be used for acceleration of aging of fermented products without affecting flavour quality.

Proteolytic activity of selected commercial Lactobacillus helveticus strains on soy protein isolates

Soy protein isolates were fermented by three commercial Lactobacillus helveticus strains for a maximum of seven days to investigate the resulting proteolysis. The proteolytic activity of the most active strain (LH88) was further analyzed (LC-MS/MS and GC-MS) and it was shown that the β-conglycinin α subunit 1, β-conglycinin α' subunit, glycinin G1, and 2S albumin were specifically degraded. Peptigram analysis and visualization of the crystal structure showed that the hydrolysis sites of β-conglycinin α subunit, α' subunit, and the glycinin G1 were located on the surface of the molecule or at the mobile disordered region, hence being highly accessible for the proteinase of LH88. The proteins were partially further degraded to free amino acids, and subsequently catabolized to volatile compounds. However, most of the proteins remained native, even after seven days of fermentation, thus additional modification of protein structure or adjustment of fermentation conditions are required for effective generation of flavor compounds.

Effects of Proteolytic and Lipolytic Enzyme Supplementations on Lipolysis and Proteolysis Characteristics of White Cheeses

Effects of proteolytic (Neutrase, Bacillus subtilis-originate, 0.20 (P1) and 0.40 g 100 L-¹ (P2)) and lipolytic (Piccantase A, Mucor miehei-originated, 0.05 (L1) and 0.10 g 100 L-¹ (L2)) enzyme supplementations to cheese milk on lipolysis and proteolysis characteristics of 90-day ripened cheese samples were investigated in this study. While enzyme supplementation did not have significant effects on titratable acidity, fat and protease-peptone nitrogen ratios of cheese samples, dry matter, salt, protein, water soluble nitrogen, 12% trichloroacetic acid soluble nitrogen ratio (TCA-SN), 5% phosphotungstic acid soluble nitrogen (PTA-SN), casein nitrogen ratios, penetrometer value, total free fatty acids (TFFA) and total free amino acids (TFAA) were significantly influenced by enzyme supplementations. Individual free amino acids (15 of them) were also determined. Free amino acid contents of enzyme-supplemented cheeses were higher than the control cheese and the values increased in all cheese samples with the progress of ripening (p < 0.05). The highest amino acids in all periods of ripening were identified as glutamic acid, lysine, proline and aspartic acid. The major (Ca, P, Na, K, Mg) and minor (Zn, Fe, Cu, Mn) mineral levels of cheeses decreased with the progress of ripening and the effects of enzyme supplementations on these attributes (except for magnesium and manganese) were found to be significant (p < 0.01). As to conclude, enzyme supplementations increased proteolysis and lipolysis and accelerated ripening and thus reduced ripening durations. Especially the enzyme ratios in P1 and L1 cheeses were found to be suitable for reducing the ripening period in White cheese without any adverse effects.

Review article: short chain fatty acids as potential therapeutic agents in human gastrointestinal and inflammatory disorders

BACKGROUND

Butyrate, propionate and acetate are short chain fatty acids (SCFA), important for maintaining a healthy colon and are considered as protective in colorectal carcinogenesis. However, they may also regulate immune responses and the composition of the intestinal microbiota. Consequently, their importance in a variety of chronic inflammatory diseases is emerging.

AIMS

To review the physiology and metabolism of SCFA in humans, cellular and molecular mechanisms by which SCFA may act in health and disease, and approaches for therapeutic delivery of SCFA.

METHODS

A PubMed literature search was conducted for clinical and pre-clinical studies using search terms: 'dietary fibre', short-chain fatty acids', 'acetate', 'propionate', 'butyrate', 'inflammation', 'immune', 'gastrointestinal', 'metabolism'.

RESULTS

A wide range of pre-clinical evidence supports roles for SCFA as modulators of not only colonic function, but also multiple inflammatory and metabolic processes. SCFA are implicated in many autoimmune, allergic and metabolic diseases. However, translating effects of SCFA from animal studies to human disease is limited by physiological and dietary differences and by the challenge of delivering sufficient amounts of SCFA to the target sites that include the colon and the systemic circulation. Development of novel targeted approaches for colonic delivery, combined with postbiotic supplementation, may represent desirable strategies to achieve adequate targeted SCFA delivery.

CONCLUSIONS

There is a large array of potential disease-modulating effects of SCFA. Adequate targeted delivery to the sites of action is the main limitation of such application. The ongoing development and evaluation of novel delivery techniques offer potential for translating promise to therapeutic benefit.

Identification and Functional Validation of Autolysis-Associated Genes in Lactobacillus bulgaricus ATCC BAA-365

Lactic acid bacteria (LAB) are important organisms in food production. Indeed, LAB autolysis is very critical in dairy processing. For example, it influences the development of cheese flavor by releasing intracellular enzymes, and controls cell growth in yogurts and probiotic products. Two component systems (TCS) constitute essential environmental sensors and effectors of signal transduction in most bacteria. In the present work, mutants of one TCS (LBUL_RS00115/LBUL_RS00110) were generated to assess the relationship between TCS and cell autolysis. The mutants displayed decreased autolysis in comparison with wild type; meanwhile, complementation reversed this effect. The interaction between LBUL_RS00115 and LBUL_RS00110 was confirmed by yeast two-hybrid analysis. These observations suggested that the TCS (LBUL_RS00115/LBUL_RS00110) was involved in autolysis in Lactobacillus delbrueckii subsp. bulgaricus.

Influence of osmotic stress on the profile and gene expression of surface layer proteins in Lactobacillus acidophilus ATCC 4356

In this work, we studied the role of surface layer (S-layer) proteins in the adaptation of Lactobacillus acidophilus ATCC 4356 to the osmotic stress generated by high salt. The amounts of the predominant and the auxiliary S-layer proteins SlpA and SlpX were strongly influenced by the growth phase and high-salt conditions (0.6 M NaCl). Changes in gene expression were also observed as the mRNAs of the slpA and slpX genes increased related to the growth phase and presence of high salt. A growth stage-dependent modification on the S-layer protein profile in response to NaCl was observed: while in control conditions, the auxiliary SlpX protein represented less than 10 % of the total S-layer protein, in high-salt conditions, it increased to almost 40 % in the stationary phase. The increase in S-layer protein synthesis in the stress condition could be a consequence of or a way to counteract the fragility of the cell wall, since a decrease in the cell wall thickness and envelope components (peptidoglycan layer and lipoteichoic acid content) was observed in L. acidophilus when compared to a non-S-layer-producing species such as Lactobacillus casei. Also, the stationary phase and growth in high-salt medium resulted in increased release of S-layer proteins to the supernatant medium. Overall, these findings suggest that pre-growth in high-salt conditions would result in an advantage for the probiotic nature of L. acidophilus ATCC 4356 as the increased amount and release of the S-layer might be appropriate for its antimicrobial capacity.

Assessment of probiotic, antifungal and cholesterol lowering properties of Pediococcus pentosaceus KCC-23 isolated from Italian ryegrass

BACKGROUND

Lactic acid bacteria (LAB) are important for the processing of various food products. Although genetically modified organisms have contributed to improvements in various food products, there are some limitations. Thus, the discovery of wild strains from natural sources must be considered as the most suitable approach for identifying new LAB. Therefore, we planned to isolate and characterise the LAB from Italian ryegrass forage and evaluate their biological potential.

RESULTS

A total of 28 strains were isolated and screened for their anti-fungal and probiotic properties. A single strain was selected due to its antifungal and probiotic efficiency. The strain was identified as Pediococcus pentosaceus KCC-23. The strain KCC-23 showed effective inhibition against Aspergillus fumigatus, Pencillium chrysogenum, Pencillium roqueforti, Botrytis elliptica and Fusarium oxysporum. Further, it survived low pH, and the presence of bile salts and gastric juice. It exhibited significant aggregation and hydrophobicity properties. The KCC-23 effectively assimilated cholesterol and had the ability to utilise pre-biotics such as raffinose and inulin. Finally, KCC-23 exhibited significant free radical scavenging activity.

CONCLUSION

P. pentosaceus KCC-23 showed effective anti-fungal, probiotic and anti-oxidant properties and would be a promising isolate for exploitation in the formulation of food for ruminants and humans.

Microbial cell-free extracts as sources of enzyme activities to be used for enhancement flavor development of ewe milk cheese

Freeze-dried cell-free extracts (CFE) from Lactobacillus casei LC01, Weissella cibaria 1XF5, Hafnia alvei Moller ATCC 51815, and Debaryomyces hansenii LCF-558 were used as sources of enzyme activities for conditioning the ripening of ewe milk cheese. Compared with control cheese (CC), CFE did not affect the gross composition and the growth of the main microbial groups of the cheeses. As shown through urea-PAGE electrophoresis of the pH 4.6-soluble nitrogen fraction and the analysis of free AA, the secondary proteolysis of the cheeses with CFE added was markedly differed from that of the CC. Compared with CC, several enzyme activities were higher in the water-soluble extracts from cheeses made with CFE. In agreement, the levels of 49 volatile compounds significantly differentiated CC from the cheeses made with CFE. The level of some alcohols, ketones, sulfur compounds, and furans were the lowest in the CC, whereas most aldehydes were the highest. Each CFE seemed to affect a specific class of chemical compounds (e.g., the CFE from H. alvei ATCC 51815 mainly influenced the synthesis of sulfur compounds). Apart from the microbial source used, the cheeses with the addition of CFE showed higher score for acceptability than the control cheese. Cheese ripening was accelerated or conditioned using CFE as sources of tailored enzyme activities.

Probiotic Potential of Lactobacillus Strains with Antifungal Activity Isolated from Animal Manure

The aim of the study was to isolate and characterize the lactic acid bacteria (LAB) from animal manure. Among the thirty LAB strains, four strains, namely, KCC-25, KCC-26, KCC-27, and KCC-28, showed good cell growth and antifungal activity and were selected for further characterization. Biochemical and physiology properties of strains confirmed that the strains are related to the Lactobacillus sp.; further, the 16S rRNA sequencing confirmed 99.99% sequence similarity towards Lactobacillus plantarum. The strains exhibited susceptibility against commonly used antibiotics with negative hemolytic property. Strains KCC-25, KCC-26, KCC-27, and KCC-28 showed strong antifungal activity against Aspergillus fumigatus, Penicillium chrysogenum, Penicillium roqueforti, Botrytis elliptica, and Fusarium oxysporum, respectively. Fermentation studies noted that the strains were able to produce significant amount of lactic, acetic, and succinic acids. Further, the production of extracellular proteolytic and glycolytic enzymes, survival under low pH, bile salts, and gastric juice together with positive bile salt hydrolase (Bsh) activity, cholesterol lowering, cell surface hydrophobicity, and aggregation properties were the strains advantages. Thus, KCC-25, KCC-26, KCC-27, and KCC-28 could have the survival ability in the harsh condition of the digestive system in the gastrointestinal tract. In conclusion, novel L. plantarum KCC-25, KCC-26, KCC-27, and KCC-28 could be considered as potential antimicrobial probiotic strains.

Phenotypic and genotypic characterization of lactic acid bacteria isolated from raw goat milk and effect of farming practices on the dominant species of lactic acid bacteria

Lactic acid bacteria, in particular Lactococcus lactis, play a decisive role in the cheese making process and more particularly in lactic cheeses which are primarily produced on goat dairy farms. The objective of this study was therefore to identify the main lactic acid bacteria found in raw goats' milk from three different regions in France and evaluate if certain farming practices have an effect on the distribution of species of lactic acid bacteria in the various milk samples. Identification at genus or species level was carried out using phenotypic tests and genotypic methods including repetitive element REP-PCR, species-specific PCR and 16S rRNA gene sequencing. The distribution of the main bacterial species in the milk samples varied depending on farms and their characteristics. Out of the 146 strains identified, L. lactis was the dominant species (60% of strains), followed by Enterococcus (38%) of which Enterococcus faecalis and Enterococcus faecium. Within the species L. lactis, L. lactis subsp lactis was detected more frequently than L. lactis subsp cremoris (74% vs. 26%). The predominance of L. lactis subsp cremoris was linked to geographical area studied. It appears that the animals' environment plays a role in the balance between the dominance of L. lactis and enterococci in raw goats' milk. The separation between the milking parlor and the goat shed (vs no separation) and only straw in the bedding (vs straw and hay) seems to promote L. lactis in the milk (vs enterococci).

Gene knockout and overexpression analysis revealed the role of N-acetylmuramidase in autolysis of Lactobacillus delbrueckii subsp. bulgaricus ljj-6

Autolysis of lactic acid bacteria (LAB) plays a vital role in dairy processing. During cheese making, autolysis of LAB affects cheese flavor development through release of intracellular enzymes and restricts the proliferation of cells in yogurt fermentation and probiotics production. In order to explore the mechanism of autolysis, the gene for the autolytic enzymes of L. bulgaricus, N-acetylmuramidase (mur), was cloned and sequenced (GenBank accession number: KF157911). Mur gene overexpression and gene knockout vectors were constructed based on pMG76e and pUC19 vectors. Recombinant plasmids were transformed into L. bulgaricus ljj-6 by electroporation, then three engineered strains with pMG76e-mur vector and fifteen engineered strains with pUC19-mur::EryBII were screened. The autolysis of the mur knockout strain was significantly lower and autolysis of the mur overexpressed strain was significantly higher compared with that of the wild type strain ljj-6. This result suggested that the mur gene played an important role in autolysis of L. bulgaricus. On the other hand, autolytic activity in a low degree was still observed in the mur knockout strain, which implied that other enzymes but autolysin encoded by mur were also involved in autolysis of L. bulgaricus.

Isolation and identification of the microbiota of Danish farmhouse and industrially produced surface-ripened cheeses

For studying the microbiota of four Danish surface-ripened cheeses produced at three farmhouses and one industrial dairy, both a culture-dependent and culture-independent approach were used. After dereplication of the initial set of 433 isolates by (GTG)5-PCR fingerprinting, 217 bacterial and 25 yeast isolates were identified by sequencing of the 16S rRNA gene or the D1/D2 domain of the 26S rRNA gene, respectively. At the end of ripening, the cheese core microbiota of the farmhouse cheeses consisted of the mesophilic lactic acid bacteria (LAB) starter cultures Lactococcus lactis subsp. lactis and Leuconostoc mesenteorides as well as non-starter LAB including different Lactobacillus spp. The cheese from the industrial dairy was almost exclusively dominated by Lb. paracasei. The surface bacterial microbiota of all four cheeses were dominated by Corynebacterium spp. and/or Brachybacterium spp. Brevibacterium spp. was found to be subdominant compared to other bacteria on the farmhouse cheeses, and no Brevibacterium spp. was found on the cheese from the industrial dairy, even though B. linens was used as surface-ripening culture. Moreover, Gram-negative bacteria identified as Alcalignes faecalis and Proteus vulgaris were found on one of the farmhouse cheeses. The surface yeast microbiota consisted primarily of one dominating species for each cheese. For the farmhouse cheeses, the dominant yeast species were Yarrowia lipolytica, Geotrichum spp. and Debaryomyces hansenii, respectively, and for the cheese from the industrial dairy, D. hansenii was the dominant yeast species. Additionally, denaturing gradient gel electrophoresis (DGGE) analysis revealed that Streptococcus thermophilus was present in the farmhouse raw milk cheese analysed in this study. Furthermore, DGGE bands corresponding to Vagococcus carniphilus, Psychrobacter spp. and Lb. curvatus on the cheese surfaces indicated that these bacterial species may play a role in cheese ripening.

Mammals, Milk, Molecules, and Micelles

After a brief description of my family background and school days, my professional career as a dairy scientist is described under three headings: research, teaching, and writing. My research activities fall into four areas: biochemistry of cheese, fractionation and characterization of milk proteins, heat stability of milk, and dairy enzymology. Finally, I offer some advice to young scientists.

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 1.7 mL of milk, miniature cheeses of about 170 mg 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.

Recovery and differentiation of long ripened cheese microflora through a new cheese-based cultural medium

A partial picture of the typical microflora of PDO Parmigiano Reggiano cheese was achieved by studying the cultivability of lactic acid bacteria associated with its manufacturing and ripening. A comprehensive sampling design allowed for the analysis of the cheese microflora during its production over 20 months of ripening. An innovative cheese agar medium (CAM) was prepared after testing 18 formulations all based on grated Parmigiano Reggiano ripened cheese. During cheese manufacturing and ripening, different samples were sampled and their microflora was recovered using CAM in comparison with other traditional media. Colonies which formed units from the different agar media tested were picked and isolated; the phylogenetic positions of 154 isolated strains were studied at level of species by 16S-rRNA gene sequencing. CAM seems to be able to recover the minority population coming from milk and whey starter, hardly estimable, during the first hours of production, on traditional media.

Purification and kinetics of two novel thermophilic extracellular proteases from Lactobacillus helveticus, from kefir with possible biotechnological interest

Two thermophilic extracellular proteases, designated Lmm-protease-Lh ( approximately 29 kDa) and Hmm-protease-Lh ( approximately 62 kDa), were purified from the Lactobacillus helveticus from kefir, and found active in media containing dithiothreitol; the activity of Lmm-protease-Lh was increased significantly in media containing also EDTAK(2). Both novel proteases maintained full activity at 60 degrees C after 1-h incubation at 10 degrees C as well as at 80 degrees C, showing optimum k(cat)/K(m) values at pH 7.00 and 60 degrees C. Only irreversible inhibitors specific for cysteine proteinases strongly inhibited the activity of both novel enzymes, while they remained unaffected by irreversible inhibitors specific for serine proteinases. Both enzymes hydrolyzed the substrate Suc-FR-pNA via Michaelis-Menten kinetics; conversely, the substrate Cbz-FR-pNA was hydrolyzed by Lmm-protease-Lh via Michaelis-Menten kinetics and by Hmm-protease-Lh via substrate inhibition kinetics. Valuable rate constants and activation energies were estimated from the temperature-(k(cat)/K(m)) profiles of both enzymes, and useful results were obtained from the effect of different metallic ions on their Michaelis-Menten parameters.