Taste active compounds in a goat cheese water-soluble extract. 2. Determination of the relative impact of water-soluble extract components on its taste using omission tests

Sensory-Guided Analysis of Key Taste-Active Compounds in Pufferfish (Takifugu obscurus)

To investigate key taste-active components in Takifugu obscurus, 28 putative taste compounds in cooked muscle of T. obscurus were quantitatively analyzed and the pivotal components were identified by taste reconstitution, omission, and addition tests. Moreover, the role of flavor peptides in the overall taste profile of T. obscurus was evaluated. Sensory evaluation revealed that glutamic acid, serine, proline, arginine, lysine, adenosine 5'-monophosphate, inosine 5'-monophosphate (IMP), succinic acid, sodium, potassium, phosphates, and chlorides were the core taste-active contributors to T. obscurus. Besides glutamic acid, IMP, succinic acid, and potassium, the characteristic T. obscurus-like umami and kokumi profiles were induced by adding flavor peptides, among which Pro-Val-Ala-Arg-Met-Cys-Arg and Tyr-Gly-Gly-Thr-Pro-Pro-Phe-Val were identified as key substances on the basis of the addition test and dose-response analysis. The present data may help to reveal the secret of the delicious taste of T. obscurus and provide the basis for the development of deeper flavor analysis of pufferfish.

Quantitation of Key Tastants and Re-engineering the Taste of Parmesan Cheese

Targeted quantitation of 65 candidate taste compounds and ranking on the basis of dose-over-threshold (DoT) factors, followed by taste re-engineering and omission experiments in aqueous solution as well as in a cheese-like model matrix, led to the identification of a total of 31 key tastants (amino acids, organic acids, fatty acids, biogenic amines, and minerals) with DoT factors ≥1.0 and a total of 15 subthreshold, but kokumi-enhancing, γ-glutamyl peptides in extraordinarily high concentrations of 20468 μmol/kg. Among the γ-glutamyl peptides, γ-Glu-Gly, γ-Glu-Ala, γ-Glu-Thr, γ-Glu-Asp, γ-Glu-Lys, γ-Glu-Glu, γ-Glu-Trp, γ-Glu-Gln, and γ-Glu-His have been identified for the first time in Parmesan cheese. The excellent match of the sensory profile of the taste recombinants and the authentic cheese demonstrated the identified taste compounds to be fully sufficient to create the characteristic taste profile of the Parmesan cheese. This molecular blueprint of a Parmesan's chemosensory signature might be a useful molecular target for visualizing analytically the changes in taste profiles throughout cheese manufacturing and opens new avenues for a more scientifically directed taste improvement of cheese by tailoring manufacturing parameters ("molecular food engineering").

Formation of Kokumi-Enhancing γ-Glutamyl Dipeptides in Parmesan Cheese by Means of γ-Glutamyltransferase Activity and Stable Isotope Double-Labeling Studies

Recently, γ-glutamyl dipeptides (γ-GPs) were found to be responsible for the attractive kokumi flavor of Parmesan cheese (PC). Quantitation of γ-GPs and their parent amino acids in 13-, 24-, and 30-month ripened PC samples by LC-MS/MS and stable isotope dilution analysis (SIDA), in-cheese (13)C-labeling studies, followed by analysis of the γ-glutamyl transferase (GGT) activity revealed γ-GPs to be generated most efficiently after 24 months of ripening by a GGT-catalyzed transfer of the γ-glutamyl moiety of L-glutamine onto various acceptor amino acids released upon casein proteolysis. Following the identification of milk as a potential GGT source in PC, the functionality of the milk's GGT to generate the target γ-GPs was validated by stable isotope double-labeling (SIDL) experiments. Therefore, raw and heat-treated milk samples were incubated with L-glutamine-[U-(13)C] and acceptor amino acids (X) and the hetero- (γ-Glu-[(13)C5]-X) and homotranspeptidation products (γ-Glu-Gln-[(13)C10]) were quantitated by LC-MS/MS-SIDA using γ-Glu-Ala-[(13)C3] as the internal standard. High GGT activity to generate the γ-GPs and preference for L-phenylalanine and L-methionine as acceptor amino acids were found in raw milk and milk samples heat-treated for 10 min up to a maximum of 65 °C. In comparison, GGT activity and SIDL studies performed with inoculated Lactobacillus strains, including Lactobacillus harbinensis and Lactobacillus casei identified in PC by means of 16S rRNA gene sequencing, did not show any significant GGT activity and unequivocally demonstrated unpasteurized cow's milk, rather than microorganisms, as a key factor in γ-glutamyl dipeptide generation in Parmesan cheese.

The Good, the Bad, and the Ugly: Tales of Mold-Ripened Cheese

The history of cheese manufacture is a "natural history" in which animals, microorganisms, and the environment interact to yield human food. Part of the fascination with cheese, both scientifically and culturally, stems from its ability to assume amazingly diverse flavors as a result of seemingly small details in preparation. In this review, we trace the roots of cheesemaking and its development by a variety of human cultures over centuries. Traditional cheesemakers observed empirically that certain environments and processes produced the best cheeses, unwittingly selecting for microorganisms with the best biochemical properties for developing desirable aromas and textures. The focus of this review is on the role of fungi in cheese ripening, with a particular emphasis on the yeast-like fungus Geotrichum candidum. Conditions that encourage the growth of problematic fungi such as Mucor and Scopulariopsis as well as Arachnida (cheese mites), and how such contaminants might be avoided, are discussed. Bethlehem cheese, a pressed, uncooked, semihard, Saint-Nectaire-type cheese manufactured in the United Sates without commercial strains of bacteria or fungi, was used as a model for the study of stable microbial succession during ripening in a natural environment. The appearance of fungi during a 60-day ripening period was documented using light and scanning electron microscopy, and it was shown to be remarkably reproducible and parallel to the course of ripening of authentic Saint-Nectaire cheese in the Auvergne region of France. Geotrichum candidum, Mucor, and Trichothecium roseum predominate the microbiotas of both cheese types. Geotrichum in particular was shown to have high diversity in different traditional cheese ripening environments, suggesting that traditional manufacturing techniques selected for particular fungi. This and other studies suggest that strain diversity arises in relation to the lore and history of the regions from which these types of cheeses arose.

Identification of bitter peptides in aged cheddar cheese

The compounds responsible for the bitter taste of aged "sharp" Cheddar cheese were characterized. Sensory-guided fractionation techniques using gel permeation chromatography and multi-dimension semi-preparative reversed-phase high-performance liquid chromatography revealed the presence of multiple bitter compounds. The compounds with the highest perceived bitterness intensity were identified by tandem mass spectrometry de novo peptide sequencing as GPVRGPFPIIV, YQEPVLGPVRGPFPI, MPFPKYPVEP, MAPKHKEMPFPKYPVEPF, and APHGKEMPFPKYPVEPF; all originated from β-casein. Subsequent quantitative liquid chromatography-tandem mass spectrometry analysis reported that the concentrations of GPVRGPFPIIV, YQEPVLGPVRGPFPI, and MPFPKYPVEP increased during maturation by 28.7-, 3.1-, and 1.8-fold, respectively. When directly compared to young "mild" Cheddar, APHGKEMPFPKYPVEPF was reported only in the sharp Cheddar cheese, whereas the concentration of MAPKHKEMPFPKYPVEPF did not change. Further taste re-engineering sensory experiments confirmed the importance of the identified peptides to the bitterness of sharp Cheddar. The bitter intensity of the aged "sharp" Cheddar model (mild Cheddar with equivalent concentrations of the five bitter peptides in the sharp sample) was rated as not significantly different from the authentic sharp Cheddar cheese. Among the five peptides, GPVRGPFPIIV was reported to be the main contributor to the bitterness intensity of sharp Cheddar. Furthermore, a difference from control sensory test also confirmed the significance of the bitter taste to the overall perception of aged Cheddar flavor. The sharp Cheddar model was reported to be significantly more similar to aged "sharp" Cheddar in comparison to the young "mild" Cheddar cheese sample.

Identification of bitterness-masking compounds from cheese

Bitterness-masking compounds were identified in a natural white mold cheese. The oily fraction of the cheese was extracted and further fractionated by using silica gel column chromatography. The four fractions obtained were characterized by thin-layer chromatography and nuclear magnetic resonance spectroscopy. The fatty acid-containing fraction was found to have the highest bitterness-masking activity against quinine hydrochloride. Bitterness-masking activity was quantitated using a method based on subjective equivalents. At 0.5 mM, the fatty acid mixture, which had a composition similar to that of cheese, suppressed the bitterness of 0.008% quinine hydrochloride to be equivalent to that of 0.0049-0.0060% and 0.5 mM oleic acid to that of 0.0032-0.0038% solution. The binding potential between oleic acid and the bitter compounds was estimated by isothermal titration calorimetry. These results suggest that oleic acid masked bitterness by forming a complex with the bitter compounds.

Kokumi-active glutamyl peptides in cheeses and their biogeneration by Penicillium roquefortii

Recently, a group of gamma-glutamyl dipeptides, but not the alpha-glutamyl dipeptides, were found to induce the attractive kokumi flavor of matured Gouda cheese. In the present investigation, the spatial distribution of alpha- and gamma-glutamyl dipeptides in Gouda cheese wheels and the concentration of these peptides in other cheese types were determined by means of HPLC-MS/MS. Among all cheeses investigated, by far the highest gamma-glutamyl peptide concentration (3590 mumol/kg) was found for Blue Shropshire, a blue-veined cheese. To check whether the gamma-glutamyl transferase (GGT) from Penicillium roquefortii is involved in gamma-glutamyl peptide production in this cheese, the GGT activity was measured and gamma-glutamyl peptides were analyzed in liquid cultures of mold isolated from Blue Shropshire as well as single P. roquefortiii strains incubated with the gamma-glutamyl donor l-glutamine and the candidate substrates l-glutamic acid, l-histidine, l-leucine, and l-methionine. Being well in line with the GGT activity found in Blue Shropshire, P. roquefortii was found for the first time to produce and secrete gamma-glutamyl peptides. Among the amino acids tested, l-methionine was found as a preferred gamma-glutamyl acceptor; for example, gamma-Glu-Met was produced in yields of about 50 mmol/mol and [(2)H(3)]-gamma-Glu-Met was obtained when [(2)H(3)]-l-methionine was used as substrate amino acid.

Sensory and mass spectrometric analysis of the peptidic fraction lower than one thousand daltons in Manchego cheese

A total of 107 different peptides, all derived from alphaS1-, alphaS2-, and beta-casein, were identified in different fractions of artisan or industrial Manchego cheese at 4 and 8 mo of ripening, and their sequences were examined. Most of these peptides are described for the first time in Manchego cheese. Taste characteristics (umami and bitter) were assigned based on their AA sequence and the position of these AA within the sequence. The umami taste was predominant in all fractions analyzed by the panelists, and the peptides EQEEL, QEEL, and EINEL, containing a high number of glutamic residues, were found within the fractions. However, in several fractions described as having umami characteristics, no peptides responsible for this taste were detected. Therefore, compounds other than peptides seem to be involved in the umami properties of water-soluble extracts lower than 1,000 Da of Manchego cheese.

Quantitative studies and taste re-engineering experiments toward the decoding of the nonvolatile sensometabolome of Gouda cheese

The first comprehensive quantitative determination of 49 putative taste-active metabolites and mineral salts in 4- and 44-week-ripened Gouda cheese, respectively, has been performed; the ranking of these compounds in their sensory impact based on dose-over-threshold (DoT) factors, followed by the confirmation of their sensory relevance by taste reconstruction and omission experiments enabled the decoding of the nonvolatile sensometabolome of Gouda cheese. The bitterness of the cheese matured for 44 weeks was found to be induced by CaCl2 and MgCl2, as well as various bitter-tasting free amino acids, whereas bitter peptides were found to influence more the bitterness quality rather than the bitter intensity of the cheese. The DoT factors determined for the individual bitter peptides gave strong evidence that their sensory contribution is mainly due to the decapeptide YPFPGPIHNS and the nonapeptides YPFPGPIPN and YPFPGPIHN, assigned to the casein sequences beta-CN(60-69) and beta-CN(60-68), respectively, as well as the tetrapeptide LPQE released from alphas1-CN(11-14). Lactic acid and hydrogen phosphate were identified to play the key role for the sourness of Gouda cheese, whereas umami taste was found to be due to monosodium L-glutamate and sodium lactate. Moreover, saltiness was induced by sodium chloride and sodium phosphate and was demonstrated to be significantly enhanced by L-arginine.

Sensomics mapping and identification of the key bitter metabolites in Gouda cheese

Application of a sensomics approach on the water-soluble extract of a matured Gouda cheese including gel permeation chromatography, ultrafiltration, solid phase extraction, preparative RP-HPLC, and HILIC combined with analytical sensory tools enabled the comprehensive mapping of bitter-tasting metabolites. LC-MS-TOF and LC-MS/MS, independent synthesis, and sensory analysis revealed the identification of a total of 16 bitter peptides formed by proteolysis of caseins. Eleven previously unreported bitter peptides were aligned to beta-casein, among which 6 peptides were released from the sequence beta-CN(57-69) of the N terminus of beta-casein and 2 peptides originated from the C-terminal sequence beta-CN(198-206). The other peptides were liberated from miscellaneous regions of beta-casein, namely, beta-CN(22-28), beta-CN(74-86), beta-CN(74-77), and beta-CN(135-138), respectively. Six peptides were found to originate from alpha(s1)-casein and were shown to have the sequences alpha(s1)-CN(11-14), alpha(s1)-CN(56-60), alpha(s1)-CN(70/71-74), alpha(s1)-CN(110/111-114), and alpha(s1)-CN(135-136). Sensory evaluation of the purified, synthesized peptides revealed that 12 of these peptides showed pronounced bitter taste with recognition thresholds between 0.05 and 6.0 mmol/L. Among these peptides, the decapeptide YPFPGPIHNS exhibited a caffeine-like bitter taste quality at the lowest threshold concentration of 0.05 mmol/L.

Chromatography in authenticity and traceability tests of vegetable oils and dairy products: a review

The new applications of various chromatographic techniques such as gas-liquid chromatography, high-performance liquid chromatography and electrophoretic methods employed for the analysis in macro- and micro-components in vegetable oils and dairy products are compiled and critically evaluated. The employment of these methods for authenticity tests and traceability is discussed.