a.
There is some room for debate regarding energy value of kefir, which is derived
not only from the fat content [which is slightly changed
and reduced especially during the initial fermentation with kefir grains,
with continual reduction if kefir is ripened at room temperature for a given
period], but also from protein and the carbohydrate of ready-to-drink kefir.
The majority of digestible carbohydrate of kefir is milk-sugar [lactose],
of which at 24 hour fermentation followed by 24 hour storage seems to be
approximately 3.5%, going by the figures available. This is about 50% reduction
of the original lactose content in fresh milk. We need to consider that the
figures given in the table above were assessed from kefir prepared with artificially
prepared commercial starter-cultures [and not prepared with kefir grains].
This needs clarification, for we also
need to consider that kefir prepared with kefir grains, the grains are
synthesised from lactose and milk protein by encapsulated organisms.
Any portion of lactose synthesized into kefiran, which becomes part of the
ever increasing culture, remains unavailable as energy, for the kefir grains
are separated from the liquid-kefir before consumption. Remaining with the
grains is the kefiran synthesized from a portion of lactose of the
original milk. Also, any synthesised kefiran found in liquid-kefir,
may have no energy value, for kefiran is not readily digestible. This is
because the variety of linkage types of the kefiran molecule accounts for
rather poor accessibility of kefiran to enzyme attack. The length of fermentation,
and kefir grain-to-milk ratio for preparing kefir, including the growth rate
of kefir grains, may play an important role in determining the
amount of, and the value of carbohydrate of kefir grain-prepared kefir.
More research in the carbohydrate of kefir grain-prepared
kefir is needed.
b. Although
Pyruvic and Hippuric acids are produced during fermentation, neither
was detected during storage [kefir stored for 21 days at 4°C].[1]
c. Orotic
acid and citric acid increase slightly during storage [kefir stored
for 21 days at 4°C].[1]
d. Lactic acid concentration
increases during storage, reaching a maximum of 7739 parts per million
[ppm] by day 21 [kefir stored at 4°C].[1] The
form of lactic acid in kefir is almost 100% of the isomer L[+] lactic acid.
On the other hand yogurt contains almost equal proportion of both isomers,
D[-] lactic acid and L[+] lactic acid through the fermentation of lactose.
Research in the former USSR
[Russia] concluded that whole milk-kefir is well tolerated and gives adequate
weight gain, providing a high content of indispensable fatty acids in blood
serum of premature infants.[5] It
is therefore logical to conclude that toddlers born at normal gestation
should tolerate kefir quite well. D[-] lactic acid can cause Lactic
acidosis, in which infants
are more susceptible. This is why kefir is quite
suitable for infants.
e.
Initial ethanol alcohol content of fresh kefir can range from about .04
to .5% by volume, and kefir grain-prepared kefir usually contains more ethanol
alcohol than commercial starter-prepared kefir. This is probably due to
yeast content of both kefir types, where it is common to only include 1
yeast strain in commercial kefir production. Although ethanol concentration
increases during storage.[1] Ethanol
may reach a maximum of 2% to 3% alcohol by volume, depending on the
starter, initial lactose content of the fresh milk, including culture and
ripening-conditions and length of fermentation including the amount of kefir-grain
culture used to inoculate milk.
f. Under parallel culture-conditions,
kefir prepared with traditional kefir grains [as apposed to commercial
artificial starter-prepared kefir] has the lowest folacin content in the
fresh product [day 0]. However, kefir grain-prepared kefir exhibits the
highest rate of folacin biosynthesis during storage. This is quite likely
due to the fact that artificial kefir-starters are prepared usually containing
only one yeast strain, as apposed to the vast population of different
yeast strains of kefir grains. Mostly yeasts are responsible
for the bio-synthesis [production] of the B group vitamins. Kefir prepared
with traditional kefir grains, folacin increased by 116.2% during storage
for 48 hours at 4°C.[2]
g. There have been some 40 aromatic compounds
discovered in kefir. Amounts of acetaldehyde and acetoin increased during
fermentation. Acetaldehyde content in kefir samples doubled from day 0 to
day 21, reaching a final concentration of 1.1g/100g. During storage, the
concentration of acetoin decreased from 25 ppm on day 0 to 16 ppm on day
21. However, diacetyl was not detected during fermentation or storage.[1] The
nature of the mother-culture, medium, culture-conditions including storage
play an important roll in the biosynthesis of compounds in kefir.
h. Three
isomers determined by a two-step methylation method followed by gas
chromatography was used to identify conjugated linoleic acids [CLA]
isomers of (c9, t11; t10, c12; t9, t11), butyric, palmitic, palmitoleic,
oleic acids, which have been proven as antimutagenic components [protects
damage to DNA of body cells] of milk fat, were in higher concentrations
in kefir, than that found in fresh milk and yogurt.[3]
i. Research in 1993 in Yugoslavia explains
that the organisms of kefir grains assimilate cholesterol in milk by some
22 to 63% during a 24 hour culture-cycle with kefir grains. Out of 6 batches
of kefir grains obtained from Yugoslavia, Hungary and Caucasus, some batches
were more effective at assimilating cholesterol than others. Further
cholesterol was reduced during storage at 10°C for 48 hours where between
41 to 84% cholesterol had disappeared.[4]
j. Protein digestibility is better with
kefir produced from pasteurised milk than with raw milk. This is due to lack
of oxygen and the denatured amino acid profile in pasteurised
milk, which also has shown to produce kefir with a more favourable consistency.
END
NOTES Raw, unpasteurized milk contains greater quantity of heat-sensitive
vitamins such as some 30% more vitamin B12 than
pasteurised milk. This reflects the content of those vitamins
in kefir, so kefir prepared with raw milk shall contain much
the same greater quantity of those specific heat sensitive vitamins
[while considering *f above regarding bio-synthesis of. Milk exposed
to direct sunlight will have a reduction in Riboflavin content, because
of the sensitivity to Ultra Violet radiation of this particular vitamin.
For this reason among others, culturing kefir in clear, glass containers
should not be exposed to direct sunlight. The table of contents above
does not explain the vitamin content of raw milk kefir, for figures
were not available to the author at the time of writing.
