Production of fermented goat beverage using a mixed starter culture of lactic acid bacteria and yeasts
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486 Eng. Life Sci. 2012, 12, No. 4, 486493
Department of Dairy Technology,Faculty of Food Science andNutrition, Poznan University ofLife Sciences, Poznan, Poland
Production of fermented goat beverage usinga mixed starter culture of lactic acid bacteriaand yeasts
Cow milk and goat milk can be used to produce fermented milk drinks, which havedifferent properties. To use goat milk as a raw material, the fermentation conditionshave to be carefully adapted to receive an optimal product. The aim of this study wasto find the most appropriate starter culture for producing a health-promoting goatbeverage. The improvement of the quality of fermented goat beverage was done byselection of specific microbial strains and to define a ratio between the compoundsof the starter culture. Goat milk was inoculated with starter cultures each containingtwo specified bacterial strains (Lacococcus lactis and L. lactis subsp. cremoris orSterptococcus thermophilus and Lactobacillus delbruckii subsp. bulgaricus) as well asyeasts (Saccharomyces fragilis) in three concentrations 0.2, 0.4 or 0.6 g dm3. Thebacteria and yeasts growth and their metabolic profile was done by monitoring ofthe impedance. The fermentation process was characterized by pH value, alcoholcontent, color, and texture changes. Sensory evaluation of the final product wasalso performed. It was found that the use of L. lactis, L. lactis subsp. cremoris, andS. fragilis at 0.2 or 0.4 g dm3 gave the most satisfying results and can be successfullyutilized in goat milk fermentation.
Keywords: Fermentation / Goat beverage / Goat milk / Starter culture
Received: September 29, 2011; revised: June 8, 2012; accepted: June 20, 2012
Lactic acid bacteria are the primary group of microorganismsused for years in the production of fermented dairy drinks. Theybelong to the genus Lactococcus, Leuconostoc, Pediococcus, Strep-tococcus, and Lactobacillus and are used singly, multiples, or inmixtures, thus giving the industry the opportunity to manufac-ture different products . Apart from lactic acid bacteria, yeastsand moulds are also used to produce fermented dairy drinksworldwide (Candida spp., Saccharomyces spp., Kluyveromycesspp., Debaromyces spp., and Geotrichum candidum) .
Fermented milk drinks produced with the use of specificstrains of lactic acid bacteria and yeasts are classified as productsof yeast-lactic fermentations. Kefir andkumis are the examples of
Correspondence: Agata Lasik (firstname.lastname@example.org), Departmentof Dairy Technology, Poznan University of Life Sciences, WojskaPolskiego 31, 60-624 Poznan, Poland.
Abbreviations: L*, lightness in the CIE Lab system coordinates estab-lished by the International Commission on Illumination; a*, positionbetween red/magenta and green in the CIE Lab system coordinates es-tablished by the International Commission on Illumination; b*, positionbetween yellow and blue in the CIE Lab system coordinates establishedby the International Commission on Illumination
such products . Specific sensory attributes of these drinks arethe effects of production of lactic acid and other organic acids,carbon dioxide, alcohol, and aromatic compounds formed in thecourse of fermentation . These products are defined as dairyalcoholic drinks, with physical, chemical, and sensory propertiesare dependent on the type of starter culture, the conditions of theprocess, and the type of milk (e.g. cow, goat, sheep, and mare)used in their production .
In the production of kefir, one of the most important as-pects is to appropriately select and prepare the starter culture.At present the traditional method of kefir production is appliedoccasionally, with propagation of kefir grains later used as thestarter culture. Starter culture companies offer semi-direct cul-tures, which are used for the production of the bulk starter, anddirect cultures that are added directly to the processedmilk [6,7].The use of these cultures may lead to an excessive productionof CO2, resulting in the blowing of the packaging container .This problem may be reduced and the product aroma may beimproved because of the selection of an appropriate yeast strain,later used in the formulation of the starter culture .
The popularity of alcoholic milk beverages has helped toincrease their consumption and also to promote their reputationas health-promoting products . Drinks produced on the wayof yeast-lactic fermentation are defined as dairy champagne,
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Eng. Life Sci. 2012, 12, No. 4, 486493 Production of fermented goat beverage using a mixed starter culture 487
Table 1. The composition of the starter culture
Sample number Bacteria Yeast
Species The inoculate Species The inoculateconcentration concentration
1 Lacococcus lactis, Lactococcus lactissubsp. cremoris
0.08 g dm3
2 As above 0.08 g dm3 Saccharomyces fragilis 0.2 g dm33 As above 0.08 g dm3 As above 0.4 g dm34 As above 0.08 g dm3 As above 0.6 g dm35 Sterptococcus thermophilus,
Lactobacillus delbruckii subsp.bulgaricus
0.2 g dm3
6 As above 0.2 g dm3 Saccharomyces fragilis 0.2 g dm37 As above 0.2 g dm3 As above 0.4 g dm38 As above 0.2 g dm3 As above 0.6 g dm3
the champagne of cultured dairy product, and yoghurt ofthe 21st century [5, 10, 11]. They are characterized by a whiteor yellowish color, a balanced slightly yeast-like aroma, slightlytart and refreshing taste, and thick consistency . Drinks areproduced mainly from cow milk, less frequently from goat orsheep milk [9, 13, 14].
The use of goat milk in the production of fermented milk fa-vors preservation and even enhancement of its nutritive, dietary,as well as therapeutic values [10, 15, 16]. Goat milk is character-ized by a larger diameter of casein micelles and a higher percent-age of short and medium chain fatty acids . It contains freetaurine, a product of sulphur amino acid metabolism [17, 18].Technological processability of goat milk is determined first ofall by its composition and physicochemical properties . Theproperties of this milk differ from those of cow milk and thusin the production process, the processing parameters and con-ditions have to be adapted to the properties of the raw materialto ensure the best possible quality for the final product. Qualityof fermented goat milk may be considerably improved throughthe selection of specific microbial strains [9, 20, 21].
The aim of this study is to verify the applicability of selectedbacterial strains and yeasts to produce fermented goat milk,exhibiting specific attributes and good quality.
2 Materials and methods
Experimental material comprised goat milk, obtained from Saa-nennanny-goats, fed traditional diets, and kept in an experimen-tal flock at the experimental station of the Poznan University ofLife Sciences. Milking was performed mechanically. After milk-ing milk was directly was cooled to a temperature of 4C.
2.1 Production of fermented milk drinks
Goat milk was standardized to 2.5% fat (the initial fat contentwas 5.4%). The percentage contents of the other components inmilk amounted to 3.2% protein, 4.5% lactose, and 11.3% drymatter.
The pasteurization process was run at 93C for 5 min. Nextmilk was poured to 1 dm3 glass bottles (DURAN R Protect) andcooled to a temperature of 40C. Such prepared samples wereinoculated with specifically formulated starter cultures, whichcomposition is presented in Table 1. The bacteria and yeaststrains used in this study belonging to the Culture Collectionof the Department of Dairy Technology, Poznan University ofLife Science. .Incubation was run at 40C until pH 4.6 was ob-tained. The product was cooled to 4C after the completion ofthe fermentation process.
2.2.1 Measurements of metabolic activity of bacteriaand yeasts
Metabolic activity of bacteria and yeasts was determined us-ing the method measuring changes in electrical impedance ofthe culture medium [22, 25]. Measurements were taken using aBacTrac 4100 Automatic Microbial Growth Analyser by Sy-Lab,Austria. Metabolic activity of bacteria was measured using thedirect method, recording changes in impedance directly in theculture medium, i.e. goat milk. Metabolic activity of yeasts wasmeasuredusing the indirectmethod, basedon themeasurementsof changes in impedance in a potassiumhydroxide solution .The parameter used for the purpose of a comparative analysisof microbial activity in the samples was the so-called impedancedetection time, after which a detectable change is observed inimpedance of the medium [22, 23, 25]. For each of the analyzedmicroorganisms, the threshold value of 5% was assumed for achange in impedance.
Measurementsof bacterialmetabolic activitywere takenusingspecial 10 cm3 test tubes, equipped with four electrodes. Eachtest tube was filled with 9 cm3 medium, which was inoculatedwith 1 cm3 inoculum of the tested starter culture and incubatedfor 24 h at 30C. Changes in electrical impedance of the culturemedium were recorded automatically every 10 min throughoutthe culture period .
Metabolic activity of yeasts was measured using special, two-element test tubes, consisting of one, the so-called external testtube, of 10 cm3, equipped with two electrodes, and the other,
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488 L. Agata and P. Jan Eng. Life Sci. 2012, 12, No. 4, 486493
the so-called internal test tube of 5 cm3. A sterile test tube wasfilled with 4.5-cm3 culture medium, which was inoculated with0.5-cm3 inoculumof the tested starter culture, and next placed inthe external test tube, in which 2 cm3 0.2% potassium hyd