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					      EFFECT OF NATURAL STARTER CULTURE ACTIVITY ON
       ETHANOL CONTENT IN FERMENTED DAIRY PRODUCT


                            KATJA Zajšek and ANDREJA Goršek
   University of Maribor, Faculty of Chemistry and Chemical Engineering, Smetanova 17,
                                 SI-2000 Maribor, Slovenia
                     katja.zajsek@uni-mb.si, andreja.gorsek@uni-mb.si


                                            Abstract

During the last few years, an interest for fermented milk beverages containing probiotics,
have extremely increased. The reason is the need to find alternatives to conventional therapies
in treatment of various chronic diseases. Probiotics are usually defined as microbial food
supplements with health-promoting influences in human and animals. Most of them fall into
the group of microorganisms known as lactic acid-producing bacteria and are normally
consumed in form of kefir, yogurt and other fermented milks.
Kefir is an acid-alcoholic fermented milk product prepared by inoculating kefir grains,
consisting of bacteria and yeasts, into milk. Beside its health-promoting influences in human
and animals it has an exotic sour and slightly alcoholic flavor and specific aroma. According
to investigations both characteristics are basically due to the mixture of fermentation end
products such as lactic acid, acetaldehyde, ethanol, acetoin, diacetyl and carbon dioxide.
Quality of kefir depends upon amounts of these substances. Therefore, it is extremely
important to direct the fermentation towards the products with the organoleptic properties
desired by the consumers.
The industrial manufacture of kefir using kefir grains as starter culture is difficult due to the
complexity of their microbial composition, which varies widely depending on the origin of
the grains, conditions of storage and handling as well. Only pure starter cultures assure
products with consistent characteristics, although in this case kefir is not unique anymore.
However, in the scientific literature, there are many studies on the microbiological
characteristics of kefir grains and kefir, respectively. Also the changes in organic acids and
volatile flavor substances produced during fermentation were determined. However, the
information on possible influence of different activation time of kefir grains on the kefir
quality has not been reported so far. It is well known that only optimally activated kefir grains
have constant activity and viability. Yeasts, presented in grains, cause the generation of
carbon dioxide and ethanol during kefir manufacture. Ethanol, together with other
fermentation products, create the exotic flavor of kefir and its levels are normally prescribed
by the producers. The aim of our research was to prepare differently active (varying time of
activation) kefir grains and to determine their yeasts content. The fermentations with these
grains were performed afterwards and the ethanol concentration was followed. The
relationship between activation time of kefir grains and ethanol produced in kefir was finally
established. For this purpose a series of experiments were performed at selected process
conditions. A computer-controlled stirred-batch RC1 reactor (Mettler Toledo) was used
providing control and monitoring of important process parameters during fermentations. On-
line concentration profile of ethanol was monitored using in situ FTIR spectrophotometer
(ReactIRTMiC10). We used kefir grains originated from the Caucasian Mountain and were
acquired from an existing local dairy.

Keywords: kefir, kefir grains, ethanol, fermetation, FTIR spectrophotometer

				
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posted:7/24/2011
language:English
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