|Essential Amino Acids
a There is 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 ripened at room temperature for a given period], but also from protein and the carbohydrate content. 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 lactose content of that found 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 with kefir grain-prepared kefir, the grains are synthesised from lactose [and milk protein] by encapsulated organisms. That portion of lactose synthesized into kefiran, which becomes part of the ever increasing grain matrix, remains unavailable as an energy source, because the kefir grains are separated from the liquid-kefir before the kefir is consumed. Also, any synthesised kefiran found in liquid-kefir, has little to no energy value, for kefiran is not readily digestible by gastric digestion. This is because the variety of linkage types of the kefiran molecule accounts for rather poor accessibility to enzymeic attack, so can not be broken down and used as an energy source. Length of fermentation, and kefir grain-to-milk ratio used for preparing kefir, including the growth rate of kefir grains, may play an important role in determining the contents of, and the value of carbohydrate of kefir grain-prepared kefir. More research to evaluate the carbohydrate of kefir grain-prepared kefir is definitely needed.
b Although Pyruvic and Hippuric acids are produced during fermentation, neither was detected during storage [kefir stored for 21 days at 4°C].
c Orotic acid and citric acid increase slightly during storage [kefir stored for 21 days at 4°C].
d Lactic acid concentration increases during storage, reaching a maximum of 7739 parts per million [ppm] by day 21 [kefir stored at 4°C]. The form of lactic acid found 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. 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. 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 artificial starter-prepared kefir] has the lowest folacin content in the fresh product at day 0 [0.0043mg or 0.43mcg]. However, kefir grain-prepared kefir exhibits the highest rate of folacin production [bio-synthesis] 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 found in kefir grains. Mostly yeasts are responsible for the bio-synthesis of the B group vitamins. Kefir prepared with traditional kefir grains, folacin increased by 116.2% [0.0095mg or 0.95mcg] during storage for 48 hours at 4°C.
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. 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.
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.
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 a particular vitamin]. Milk exposed to direct sunlight will have a reduction in Riboflavin, because of the sensitivity Riboflavin has to Ultra Violet radiation. For this and other reasons, culturing kefir in clear, glass containers should not be exposed to direct sunlight. Figures in Table 1 do not explain the vitamin content of raw milk kefir, for the information was not available at the time of writing. It appears further research is required to establish nutritional composition of kefir made with raw milk.
Characteristics and Evolution of Milk Kefir During Storage
Changes in microbiological, physicochemical, including sensory parameters of kefir were studied during cold storage. Batches of kefir were prepared with 1% and 5% added kefir grains as per the traditional method. Samples for analysis were taken 24 hours after inoculation of fresh milk with kefir grains, followed by 2, 7, 14, 21, and 28 days of the liquid-kefir stored at 4° to 6°C. After fermentation for 24 hours with kefir grains [inoculation], lactobacilli and lactococci were found at levels of 100,000,000 colony forming units per millilitre [cfu/ml]. Yeasts and acetic acid bacteria were present at levels of 100,000 and 1,000,000 cfu/ml, respectively.
Lactic acid producing microflora decreased by approximately 1.5 log units between days 7 and 14, and stabilised at that level. Yeast and acetic acid bacterial counts, lactose, and pH remained constant over the storage period. However, the total fat content and dry matter decreased. The percentage of kefir-grains for fermentation did exert an influence. Sample batches prepared using 1% added kefir-grains had higher lactic acid bacterial counts, lactose, and pH [not as acidic]. The sample batches prepared with 5% added kefir-grains had higher yeast and acetic acid bacterial counts and viscosity a lower pH [more acidic]. The total fat and dry matter contents were similar in both sample batches.
Sensory profile of the kefir samples judged by a panel, revealed maximum acceptability levels in the first 48 hours of storage [sensory acceptability usually varies in different countries]. A sourer kefir may be more accepted in the Balkans, Russia the Middle East and Poland compared to Australia, United Kingdom, Ireland, New Zealand and USA, where a culture-milk yogurt with added sweetener or sweet fruit is preferred over plain, natural yogurt or buttermilk as an example.