Siv Skeie

Cooperation between Lactococcus lactis and Nonstarter Lactobacilli in the Formation of Cheese Aroma from Amino Acids

ABSTRACT In Gouda and Cheddar type cheeses the amino acid conversion to aroma compounds, which is a major process for aroma formation, is essentially due to lactic acid bacteria (LAB). In order to evaluate the respective role of starter and nonstarter LAB and their interactions in cheese flavor formation, we compared the catabolism of phenylalanine, leucine, and methionine by single strains and strain mixtures of Lactococcus lactis subsp. cremoris NCDO763 and three mesophilic lactobacilli. Amino acid catabolism was studied in vitro at pH 5.5, by using radiolabeled amino acids as tracers. In the presence of α-ketoglutarate, which is essential for amino acid transamination, the lactobacillus strains degraded less amino acids than L. lactis subsp. cremoris NCDO763, and produced mainly nonaromatic metabolites. L. lactis subsp. cremoris NCDO763 produced mainly the carboxylic acids, which are important compounds for cheese aroma. However, in the reaction mixture containing glutamate, only two lactobacillus strains degraded amino acids significantly. This was due to their glutamate dehydrogenase (GDH) activity, which produced α-ketoglutarate from glutamate. The combination of each of the GDH-positive lactobacilli with L. lactis subsp. cremoris NCDO763 had a beneficial effect on the aroma formation. Lactobacilli initiated the conversion of amino acids by transforming them mainly to keto and hydroxy acids, which subsequently were converted to carboxylic acids by the Lactococcus strain. Therefore, we think that such cooperation between starter L. lactis and GDH-positive lactobacilli can stimulate flavor development in cheese.

Metabolism of amino acids by resting cells of non-starter lactobacilli in relation to flavour development in cheese

Amino acid metabolism by one strain each of Lactobacillus casei and Lactobacillus paracasei subsp. paracasei in resting cell suspensions was studied. The experiment was performed under cheese like conditions in terms of pH, salt concentration, temperature and carbohydrate starvation using a mixture of l-amino acids as substrate. The effect of supplementing the amino acids mixture with α-ketoglutarate was estimated. Asparagine, serine and glutamine were utilised in the suspension with only amino acids. In the suspension with both amino acids and α-ketoglutarate, the degradation of leucine and lysine was observed. Production of metabolites that could be important for cheese flavour such as carbon dioxide, ammonia, organic acids and volatiles was measured. The suspensions with amino acids were characterised by high production of acetoin and ammonia and both increased even more when α-ketoglutarate was added. Carbon dioxide was produced in high amounts in the suspension with both amino acids and α-ketoglutaric acid.

Survival of lactic acid bacteria from fermented milks in an in vitro digestion model exploiting sequential incubation in human gastric and duodenum juice

In the present study, the survival of 9 lactic acid bacteria (5 Lactococcus strains, 3 Lactobacillus strains, and 1 strain of Enterococcus hirae), was investigated in vitro under conditions similar to human digestion using human gastric and duodenal juices. The tolerance of the bacteria was also tested with traditional methods using acidic conditions and bile salts. The strains were subjected to a model digestive system comprising sequential incubation in human gastric and duodenal juices, in a 2-step digestion assay at 37°C, simulating the human upper gastrointestinal tract with human gastric juices at pH 2.5 and human duodenal juices at pH 7. The bacterial strains were tested either as washed cells from culture media or in fermented milk. The initial in vitro testing in acid and bile salts showed that Lactobacillus strains and the E. hirae strain displayed a significantly higher acid tolerance than the lactococci. The lactobacilli and the Enterococcus numbers increased, whereas the lactococci decreased at least 1 log during the bile salt treatment. The Lactobacillus strains showed the highest survival rate in the model digestive system when washed bacterial cultures were used with a minor log reduction, whereas the lactococci numbers were reduced by at least log 4. However, when using fermented milks in the model digestion system it was demonstrated that the Enterococcus strain and 2 strains of Lactococcus lactis ssp. cremoris benefited significantly from the presence of the fermented milk as food matrix, with log numbers >log 7 and 5, respectively, after digestion of the fermented milk. The analyses reported comprise a comprehensive in vitro testing regimen suitable for evaluation of the survival of candidate probiotic bacteria in human digestion as an initial prescreen to clinical trials.

Influence of liposome-encapsulated neutrase and heat-treated lactobacilli on the quality of low-fat Gouda-type cheese

Low-fat Gouda-type cheese (200 g fat/kg dry matter) was made on a pilot plant scale from cheesemilk to which heat-treated lactobacilli and/or Neutrase encapsulated in dehydrated rehydrated vesicles had been added. In cheese containing added Neutrase, there was increased proteolysis after the first day following cheesemaking. The cheese with added heat-treated lactobacilli developed increased amounts of amino N as well as increased amounts of acetaldehyde and other, unidentified, volatile compounds. The addition of heat-treated lactobacilli also influenced the texture of the cheese which was firmer but less cohesive.

Developments in microencapsulation science applicable to cheese research and development. A review

Abstract The applications of microcapsules for cheese technology are reviewed. Proteolytic enzymes for use in cheese ripening may be encapsulated in microcapsules to avoid premature proteolysis in cheese milk. Alginate, milk fat, and phospholipid have been used as encapsulating materials. Alginate is not a natural constituent in milk products, and, in addition, the alginate capsules are rather leaky. Milk fat capsules show good encapsulation properties. However, strong detergents, which do not have GRAS status, are needed to keep them stable. Phospholipids form membrane structures, liposomes, in contact with water. These liposomes are stable without added detergents, and the phospholipids are natural constituents of the milk fat membrane. Controlled release of enzymes in the cheese can be achieved by technologically altering the stability of the liposomes with respect to time, temperature and pH. Liposomes may be constructed with different sizes and number of lamellae, according to the preparation method. The various types of liposome (MLV, SUV, REV and DRV) are defined and described. Several enzymes have been encapsulated in liposomes. DRV liposomes have shown the highest efficiency for the encapsulation of enzymes. Various liposome-encapsulated enzymes have been used to accelerate the ripening of Cheddar, Saint Paulin, Domiati and Gouda cheese. Liposome-encapsulated enzymes have a potential for use in accelerated cheese ripening, but the price of the phospholipid must be reduced, and a good and cheap scaled-up preparation method must be developed.

Rapid lactic acid bacteria identification in dairy products by high-resolution melt analysis of DGGE bands

Aim:  To investigate the application of high‐resolution melt (HRM) analysis for rapid species‐level identification of lactic acid bacteria (LAB) communities in dairy products, as well as for bacterial community profiling and monitoring.

Seasonal and regional variation in the composition of whey from Norwegian Cheddar-type and Dutch-type cheeses

The compositional variation in Norwegian whey from two cheese sources (Dutch and Cheddar-type cheeses) was analysed according to the type of cheese, geographical region and season of production. Whey composition found to differ between season and type of cheese in production, with the seasonal variation in the protein composition most clearly expressed in Cheddar-type cheese whey. The lowest protein concentrations were measured during spring season, and the maximum during summer season. The content of fat and urea was also significantly different at various times of the year. The geographical differences in whey composition and its interaction with season were investigated for Dutch-type cheese whey. The northern region of Norway showed a significantly different composition of the whey compared to the other investigated regions. The differences were expressed in higher content of total solids and fat, and different mineral compositions. The composition of Norwegian whey differed from cheese whey sources in other countries, particularly in terms of protein content and pH.

Metabolism of milk fat globule membrane components by nonstarter lactic acid bacteria isolated from cheese

The objective of this study was to investigate how components present in the milk fat globule membrane (MFGM) may be used for growth and survival by cheese-ripening lactobacilli. This was achieved by analyzing metabolites produced during incubation on appropriate media. The lactobacilli investigated were able to utilize components from the MFGM throughout a 24-d incubation period. We observed an apparent connection between the higher proteolytic activity of Lactobacillus paracasei INF448 and its ability to grow in the MFGM media after depletion of readily available sugars. All the studied strains produced large amounts of acetate when grown on an acylated aminosugar, presumably from deacetylation of the monosaccharides. Growth of Lb. plantarum INF15D on D-galactose resulted in a metabolic shift, expressed as different fates of the produced pyruvate, compared with growth on the other monosaccharides. For Lb. plantarum INF15D, the presence of D-galactose also seemed to initiate degradation of some amino acids known to take part in energy production, specifically Arg and Tyr.

Angiotensin I-converting enzyme-inhibitory activity of the Norwegian autochthonous cheeses Gamalost and Norvegia after in vitro human gastrointestinal digestion

The angiotensin I-converting enzyme (ACE) inhibitory activity of Gamalost cheese, its pH 4.6-soluble fraction, and Norvegia cheese was monitored before and after digestion with human gastric and duodenal juices. Both Gamalost and Norvegia cheeses showed an increased ACE-inhibitory activity during gastrointestinal digestion. However, only Norvegia showed pronounced increased activity after duodenal digestion. More peptides were detected in digested Gamalost compared with digested Norvegia. Most of the peptides in Gamalost were derived from β-casein (CN), some originated from α(s1)-CN, and only a very few originated from α(s2)-CN and κ-CN. In general, the number of peptides increased during gastrointestinal digestion, whereas some peptides were further degraded and disappeared; however, surprisingly, a few peptides remained stable. The aromatic amino acids, such as Tyr, Phe, and Trp; the positively charged amino acids (Arg and Lys); and Leu increased after simulated gastrointestinal digestion of Gamalost and Norvegia. After in vitro gastrointestinal digestion, both Gamalost and Norvegia showed high ACE-inhibitory activity, which may contribute in lowering of mild hypertension.

The influence of fat globule membrane material on the microstructure of low-fat Cheddar cheese

Abstract Microstructural characteristics of low-fat Cheddar cheese differing in the content of milk fat globule membrane (MFGM) material achieved by addition of either buttermilk powder (BMP) or skim milk powder (SMP) to the cheese milk were investigated. Scanning electron microscopy and confocal scanning laser microscopy were used to study the cheese structure and the distribution of the starter culture and fat globules. Variations in the microstructure were observed relating to the MFGM content. The structure of the control cheese (made with the addition of SMP) was more irregular with inhomogeneous large voids. In contrast, cheese made with BMP addition had a homogeneous protein network with small voids, showing a smoother, more compact and less coarse structure accompanied by more pronounced fat globules that were uniformly scattered throughout the protein matrix. The starter bacteria were located within the protein networks in clusters that were distributed homogeneously throughout the cheese matrix regardless of treatment.