Trace Thiol Compounds in Aged Cheddar Cheese

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Trace Thiol Compounds in Aged Cheddar Cheese

• J. P. Kleinhenz1, W. J. Harper1 and M. A. Drake2
• 1 The Ohio State University, Columbus, Ohio, USA
  2 North Carolina State University, Raleigh, N.
  C., USA

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WE WILL CONSIDER

• BACKGROUND
• METHOD DEVELOPMENT
• APPLICATION OF METHOD TO AGED CHEESE
• IMPLICATIONS OF POLYFUNCTIONAL THIOLS IN CHEDDAR
  CHEESE FLAVOR

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BACKGROUND
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THIS STUDY WAS BASED ON THE CONCEPT THAT -

• Our knowledge of the chemistry of Cheddar cheese
  flavor remains incomplete
• Sulfur compounds are important to the flavor of
  Cheddar cheese
• There may be sulfur compounds present in aged
  Cheddar cheese, in concentrations above their
  threshold levels, that have not yet been
  discovered

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SULFUR NOTES IN AGED CHEDDAR CHEESE

• Drake and others (2002) have shown recently that
  4 descriptors can be used to differentiate sulfur
  flavors in aged, sharp Cheddar cheese
• Total Sulfur
• Egg-Like
• Match-like
• Catty
• Brothy and Cooked may also include sulfur
  components

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Objectives

• To develop methods for identification and
  quantitation of trace thiols in aged Cheddar
  cheese
• To explore the possible relationship of poly
  functional thiol compounds to the flavor in aged
  Cheddar cheese

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CHEESES EVALUATED
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SENSORY METHODOLOGY

• Descriptive sensory analysis (cheese lexicon) was
  conducted by a trained panel (n12)
• four sulfur related descriptors were utilized in
  respect to sulfur notes total sulfur, egg like,
  match like and catty.

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THIOL METHOD

• 200 G cheese fat diluted with hexane and
  extracted with 25 ethanol
• p-hydroxymercuribenzoic acid in triscarboxymethyl
  phosphine was added to react with thiols
• pH was reduced to pH 6.5 and concentrated on an
  anion exchange column
• thiol compounds eluted with an aqueous cysteine
  solution
• thiols recovered by extraction with 21
  pentanediethyl ether
• solvent solution dried over anhydrous sodium
  sulfate
• Concentrated by evaporation under nitrogen
• Analyzed by GC with a sulfur chemiluninescence
  detector
• 3-methoxythiophenol was used as an internal
  standard

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Sensory Profiles of Cheeses
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Sensory correlations with perception of cheese
age
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Thiol Compounds in aged Cheddar Cheese

• Only two thiol compounds found in fresh curd
• Over 40 thiol compounds found in aged Cheddar
  cheeses, generally 10-15 in any given cheese,
  with concentrations in ppb
• Only three thiol compounds previously reported in
  cheese
• Qualitative and quantitative differences noted
  for thiol compounds among different cheeses

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Examples for Three Selected Cheeses
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Sulfur Notes in 3 Selected Cheeses
 
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Thiols in Selected Cheeses
 
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Identification

• Confirmed as thiols
• Identification extremely difficult because of
  lack of reference compounds and very low
  concentrations in the cheese (ltppm)
• Tentative identification of some compounds based
  on Kovats Indices based primarily on Belgium work
  (J. Agr. Food Chem 495445-5449. 2001)

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Conclusions

• Multiple descriptors are needed to describe the
  sulfur notes in aged Cheddar Cheese
• Total Sulfur and catty appear to relate to the
  age of the cheese
• A method has been developed to measure trace
  thiol compounds in aged Cheddar Cheese
• A number of thiol compounds are present in aged
  Cheddar cheese

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Conclusions

• There are both qualitative and quantitative
  differences in thiol compounds in aged Cheddar
  Cheese
• Definite identification of the thiol compounds
  remains to be determined
• The role of specific multi-functional thiol
  compounds in Cheddar flavor requires further work