Understanding and reducing oxidative flavour deterioration in foods - Oxidation in Foods and Beverages and Antioxidant Applications - page 128

This flavour is due to the formation of carbonyls and methional formed via
photoxidative degradation of sulfur containing amino acids including
methionine. Riboflavin, which is present in substantial amounts in milk, plays
an important role as a photosensitizer in this process.
Dairy products will not only develop off-flavours when exposed to sunlight,
but also exposure to light in the grocery stores will lead to oxidative flavour
degradation if the product is not properly packaged. It is possible to protect dairy
products against such flavour deterioration by excluding all kinds of light
exposure, e.g. by using black or non-transparent packaging material/materials
with light barrier.
Larsen et al. (2009) investigated photooxidation of sour cream packaged in
cups with different light barrier properties. The sour cream was light exposed for
36 h with a standard fluorescent light tube simulating storage conditions in
grocery stores. Three different cups were evaluated: a white cup, a cup with
medium light barrier and a cup with high light barrier. As expected the cup with
the high light barrier resulted in the best protection against photooxidation. A
sensory panel could not distinguish between sour cream stored in the high light
barrier cup and sour cream stored in the dark, whereas the intensities of off-
odours/flavours (sunlight, rancid, acidic) were significantly higher in sour cream
stored in white cups or in cups with medium light barrier. Hence, only the cup
with the high light barrier protected the sour cream sufficiently. Fluorescence
measurements of the sour cream showed that photosensitizers were intact in the
sour cream stored in the high light barrier cup, whereas they were somewhat
degraded in the sour creams stored in the white cup or in the medium light
barrier cup.
In a recent study on sweet cream butter (non-cultured), changes in the sensory
profile and volatiles profile during storage at 4 ëC and ÿ20 ëC were followed
(Lozano et al. 2007). After approximately 6 months at refrigerated temperature
the development of a `stale' flavour was reported by the sensory panel. This
flavour increased in intensity in refrigerated butters between 6 and 12 months of
storage and it could also be detected after 12 months of storage at ÿ20 ëC in
butters packaged in wax paper, but not in butters packaged in foil. Moreover,
during storage positive descriptors for cooked/nutty and milkfat flavour
decreased. During storage the development of volatile lipid oxidation products
(E)-2-nonenal, 2-heptanone, (Z)-4-heptenal and (E,Z)-2,6-nonadienal was
observed. Further, after 12 months of refrigerated storage the concentration of
hexanal also began to increase. Indications of hydrolytic activity in the butters
were also found. Thus, -octalactone and -decalactone increased during
storage. These two compounds were suggested to be formed via hydrolysis of 4-/
5-hydroxy fatty acids or via oxygen attack on fatty acids at positions 4 or 5
followed by hydrolysis.
Recent attempts have been made to improve the nutritional value of butter by
mixing butterfats with lipids with a more healthy profile. Kristensen et al. (2006)
evaluated the oxidative stability and sensory properties of butter blends in which
40% of the fat was replaced by either rapeseed oil, sunflower oil or