2 Comments so far

1. Rawr :]

   Monitoring Chemical Changes in Cheddar Cheese During Aging
   by H igh Performance Liqu id Chromatography
   and Gas Chromatography Techniques
   RAY MARSILI
   Dean Foods Company
   1126 Kilburn Avenue
   Rockford, I L 611Q1
   ABSTRACT
   The concentrations of several chemical
   metabolites in Cheddar cheese were
   monitored by various chromatographic
   techniques during the aging process to
   learn which metabolites were the best
   predictors of the glycolytic, lipolytic, and
   proteolytic age of the cheese. Pyruvic,
   lactic, acetic, and propionic acids were
   measured by ion-exchange high performance
   liquid chromatography; acetone,
   2-butanone, ethanol, 2-pentanone, 2-
   butanol, and n-propanol were monitored
   by headspace gas chromatography; free
   fatty acids were quantitated (without
   derivatization) by gas chromatography;
   and free amino acids were determined as
   their o-phthaldehye derivatives by high
   performance liquid chromatography.
   The best predictors of the glycolytic
   age were propionic acid and acetic acid;
   the best predictors of lipolysis were the
   free fatty acids Cto, C12, C14, and C16;
   and the best predictors of proteolysis
   were the free amino acids leucine,
   methionine, and glutamic acid. The volatile
   metabolites determined by headspace
   gas chromatography were not good indicators
   of aging; however, they did provide
   useful information related to flavor
   problems.
   Cheddar cheese aged at elevated temperatures
   produced propionic acid, acetic
   acid, and free amino acids at significantly
   faster rates than the other chemicals that
   were monitored.
   Received March 6, 1985.
   INTRODUCTION
   The flavor and aroma characteristics of
   Cheddar cheese depend to a great extent on a
   complex balance of organic chemicals produced
   as metabolites during ripening. Although the
   principle reactions-glycolysis, proteolysis, and
   lipolysis-are common to all Cheddar cheese,
   the extent that these reactions occur, in addition
   to chemicals produced from secondary
   reactions, account for individuality. For example,
   hydroxy acids, keto acids, and carboxylic
   acids are produced as the lactose substrate is
   consumed; peptides, proteoses, peptones, and
   free amino acids result from the degradation of
   casein by proteases; free fatty acids are formed
   from the hydrolysis of milk fat by lipases. A
   variety of alcohols, ketones, aldehydes, and
   volatile sulfur compounds are formed during
   aging; the exact mechanisms involved in the
   production of many of these chemicals have
   not been elucidated fully. Chromatographic
   analysis of Cheddar cheese could be a useful
   tool for studying how the various treatments
   used to accelerate ripening affect the production
   of metabolites.
   Chemical profiling of Cheddar cheese is
   challenging because of the wide variety of
   chemicals present and to the complex sample
   matrix. Researchers have used numerous
   chromatographic approaches. For example,
   headspace gas chromatographic (HSGC) studies
   of hard cheese conducted by Manning and
   Moore (4) detected hydrogen sulfide, methanethiol,
   acetaldehyde, acetone, 2-butanol, methanol,
   ethanol, 2-pentanone, 2-butanone, ethyl
   acetate, and n-propanol; in addition, these
   studies revealed that 2-pentanone was a good
   indicator of cheese maturity, and 2-butanone
   was associated with inferior flavored cheese. A
   simple, accurate high performance liquid chromatography
   (HPLC) technique using an ion
   exchange column and ultraviolet (UV) detec-
   1985 J Dairy Sci 68:3155-3161 3155

2. Moira

   As cheese ages the proteins break down, which makes the flavours stronger – some of the chemicals produced from this breakdown are acids and that’s what results in the sharper flavour – eventually the cheese will end up bitter and inedible (but that would take a long time) The calcium also migrates together you get little chalking bits which I presume are calcium carbonate.

   Hope this helps