production of fermented goat beverage using a mixed starter culture of lactic acid bacteria and...

486 Eng. Life Sci. 2012, 12, No. 4, 486–493

Lasik Agata

Pikul Jan

Department of Dairy Technology,Faculty of Food Science andNutrition, Poznan University ofLife Sciences, Poznan, Poland

Research Article

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 dm−3. 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 dm−3 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

DOI: 10.1002/elsc.201100126

1 Introduction

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 [1]. 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) [2].

Fermented milk drinks produced with the use of specificstrains of lactic acid bacteria and yeasts are classified as productsof yeast-lactic fermentations. Kefir and kumis are the examples of

Correspondence: Agata Lasik ([email protected]), 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 [3]. 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 [4]. 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 [5].

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 processed milk [6,7].The use of these cultures may lead to an excessive productionof CO2, resulting in the blowing of the packaging container [8].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 [8].

The popularity of alcoholic milk beverages has helped toincrease their consumption and also to promote their reputationas health-promoting products [9]. Drinks produced on the wayof yeast-lactic fermentation are defined as “dairy champagne,”

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Eng. Life Sci. 2012, 12, No. 4, 486–493 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 dm−3

2 As above 0.08 g dm−3 Saccharomyces fragilis 0.2 g dm−3

3 As above 0.08 g dm−3 As above 0.4 g dm−3


5 Sterptococcus thermophilus,Lactobacillus delbruckii subsp.bulgaricus

0.2 g dm−3

6 As above 0.2 g dm−3 Saccharomyces fragilis 0.2 g dm−3



“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 [12]. 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 [16]. 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 [19]. 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-nen nanny-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 4◦C.

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 93◦C for 5 min. Nextmilk was poured to 1 dm3 glass bottles (DURAN R© Protect) andcooled to a temperature of 40◦C. 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 40◦C until pH 4.6 was ob-tained. The product was cooled to 4◦C after the completion ofthe fermentation process.

2.2 Methods

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 wasmeasured using the indirect method, based on the measurementsof changes in impedance in a potassium hydroxide solution [26].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.

Measurements of bacterial metabolic activity were taken usingspecial 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 30◦C. Changes in electrical impedance of the culturemedium were recorded automatically every 10 min throughoutthe culture period [22–24].

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,


488 L. Agata and P. Jan Eng. Life Sci. 2012, 12, No. 4, 486–493

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 inoculum of the tested starter culture, and next placed inthe external test tube, in which 2 cm3 0.2% potassium hydroxidesolution had been placed. Incubation was run for 24 h at 30◦C.Changes in electrical impedance of the culture medium wererecorded automatically every 10 min throughout the cultureperiod [22, 23].

2.2.2 Measurements of pHThe pH was measured every 30 min during fermentation processand 48 h after inoculation using an HI 98230 pH-meter by HannaInstruments [27].

2.2.3 Measurements of colorThe instrumental fermented milk color measurement was basedon the value of the CIE Lab system coordinates established bythe International Commission on Illumination. The measure-ment was carried out with a D65 light source, the continuousspectrum of which in the visible range is the closest to day-light, and with a 10◦ observation angle, using an X-Rite SP-60spectrophotometer (Grandville, USA). The spectrophotometerwas calibrated based on the S6 perfect black and white model(X-Rite). Sample temperature during the experiment was 10–12◦C. The measurements were taken every two hours throughoutthe fermentation process and 48h after inoculation.

2.2.4 Measurement of textureAnalyses of the texture profile were conducted by reverse extru-sion using a TA.XT PLUS texture analyzer by Stable, coupledwith a computer. The attachment used in the analyses consistedof a centralizing mount, three sample containers with the insidediameter of 50 mm, a round piston disc of 40 mm in diameterand a piston connector [27,28]. Texture was measured every 3 hduring the fermentation process and 48 h after inoculation.

2.2.5 Measurement of alcohol contentDetermination of alcohol content was performed by using HPLC[29] 48 h after inoculation. The employment of the HPLC tech-nique required initial protein precipitation from the analyzedsamples. For this purpose 0.010 N sulphuric acid was added.Samples were thoroughly mixed (vortex, 15 s) and placed in aboiling water bath for about 10 min. Next, the samples wereleft at room temperature for approximately 20–30 min to al-low them to cool and then they were centrifuged (3000 g; 10min). The obtained supernatant was filtered using Millex-LCRfilters (Millipore) Low Protein Binding Hydrophilic LRCPTFE0.45 nm [30]. Samples prepared in this way in the amount of20 μL were transferred onto a column (HPX 87H, BioRad) con-nected with a refractive index detector. The mobile phase was0.005 M solution of sulphuric acid. The flow velocity throughthe column amounted to 0.6 cm3/min and the time of analysisat the temperature of 30◦C was 30 min.

Figure 1. Impedance changes in medium caused by bacteriagrowth and their metabolisms. The experiment was run in fivereplicates in three experiments. The error bars show the standarddeviation. The sample number 1–8 is explained in Table 1.

2.2.6 Sensory examinationSensory examination was conducted using the profiling method[31] 48 h after inoculation. The panel comprised a team of 10 ad-equately trained and prepared individuals [32–34]. The sensoryattribute scoring was performed at the Sensory Analysis Work-shop of the Faculty of Food Science and Nutrition, the PoznanUniversity of Life Sciences, meeting respective standard require-ments [35]. An intensity scale of 0–100 mm was used, where 0denotes an undetectable level and 100 corresponds to a highly in-tensive attribute. In case of taste intensity was measured for suchattributes as sweet, sour, bitter, alcoholic, and extrinsic. In aromascoring intensity was measured for such attributes as goat-like,milky, buttery, alcoholic, and extrinsic. Moreover, overall accept-ability was also evaluated, where 0 denotes undesirable and 100most desirable.

2.2.7 Statistical analysisStatistical calculations were performed using a data analysis soft-ware system STATISTICA (version 7.1) by StatSoft, Inc. (2005).The significance of differences was estimated by the Student’st-test at significance level α = 0.05.

3 Results and discussion

3.1 Metabolic activity

The measurement method used for the changes in electricalimpedance had been used previously in the analysis of microbialgrowth in cow milk [36]. The analysis of curves being a graphicimage of changes in electrical impedance in time, expressed inpercent in relation to the initial values, made it possible to isolatetwo groups of media, in which the kinetics of bacterial growthwas very similar (Fig. 1).

The first group included samples of goat milk inoculatedwith Lacococcus lactis and L. lactis subsp. cremoris, while theother group comprised samples, to which Sterptococcus ther-mophilus and Lactobacillus delbruckii subsp. bulgaricus were in-troduced. Similarly, as it was reported by Walker et al. [37], itwas found that the course of impedance changes is determinedby a metabolic pathway of the inoculated microorganisms. The



Figure 2. Impedance changes in medium caused by yeast growthand their metabolisms. The experiment was run in five replicatesin three experiments. The error bars show the standard deviation.The sample number 1–8 is explained in Table 1.

growth, survival, and activity of any one species or strain, inmost cases, determined by the presence of other microorganisms[38].

Changes in impedance caused by yeast growth and activ-ity confirmed the possibility to isolate two groups of startercultures, in which the factor determining the kinetics of yeastmetabolism was not related with their amount, but rather thetype of symbiotic bacteria with which metabolic changes in theculture medium were observed (Fig. 2) which is in agreementwith Giraffa [38].

On the basis of the analysis of data concerning changes inimpedance caused by the metabolic activity of microorgan-isms contained in the starter culture, the highest activities ofbacteria and yeasts were recorded in samples with the high-est proportion of yeasts. This results from a comparison ofdetection times of impedance changes in the culture mediumamounting to 5% (Fig. 3). Monitoring of impedance changesmakes it possible to select the most appropriate starter culturefor the fermentation process run in a specific medium [37], inthis case goat milk. When analyzing all the applied starter cul-tures, it was found that the fastest rate of metabolic changes ingoat milk was observed for the culture containing the highestamount of L. lactis, L. lactis subsp. cremoris, and Saccharomycesfragilis.

Figure 3. Detection time on 5% impedance changes appointedduring fermentation with different starter culture. The experimentwas run in five replicates in three experiments. The error bars showthe standard deviation. The sample number 1–8 is explained inTable 1.

Figure 4. Changes in pH during incubation of sample 1, 2, 3, and4. The experiment was run in three replicates in three experiments.The sample number 1–4 is explained in Table 1.

3.2 Changes in pH value

In all samples of processed milk at the beginning of the incu-bation process pH values were similar, amounting to 6.5 ± 0.1.On-line monitoring of changes in pH values facilitates controlover the fermentation process resulting from the many metabolicchanges of microorganisms contained in the starter culture [39]and at the same time it makes it possible to complete the processwhen pH 4.6 is reached. This eliminates the problem of excessiveacidification of the product, appearing in the production of suchdrinks as kefir made from goat milk [13]. Dynamics of changesin pH value of analyzed samples are presented in the Figs. 4and 5.

Analysis of acidification curves showed differences in thecourse of the fermentation process run with the applicationof different starter cultures. Depending on the applied starterculture, the process lasted from 4 to 8 h. An increase was ob-served in the rate of fermentation, and thus a reduction ofpH, with an increase in the proportion of yeasts. In case ofsamples inoculated with L. lactis and L. lactis subsp. cremorissignificantly faster changes in milk acidity were observed incomparison to samples inoculated with S. thermophilus and L.delbruckii subsp. bulgaricus, characterized by an analogous pro-portion of yeasts. The greatest dynamics of acidity changes, andthus the fastest rate of reaching pH 4.6, were found for the

Figure 5. Changes in pH during incubation of sample 5, 6, 7, and8. The experiment was run in three replicates in three experiments.The sample number 5–8 is explained in Table 1.



sample in which the fermentation process was run using L. lac-tis, L. lactis subsp. cremoris, and S. fragilis at 0.6 g dm−3. Inturn, the slowest dynamics of changes in acidity were observedin case of samples inoculated with no S. fragilis added or incase of the lowest (0.2 g dm−3) amount of yeasts in the starterculture.

3.3 Evaluation of color components

The color of fermented milk basically represents the reflectionof physicochemical changes in the product. No significant dif-ferences were observed between the lightness in the CIE Labsystem coordinates established by the International Commis-sion on Illumination (L*), position between red/magenta andgreen in the CIE Lab system coordinates established by theInternational Commission on Illumination (a*), and positionbetween yellow and blue in the CIE Lab system coordinates es-tablished by the International Commission on Illumination (b*)components in samples differing in the proportion of yeasts(Table 2). It was stated that lightness of samples (L*) decreasesduring the fermentation process and it was the lowest at theend of the incubation time. A reduction of sample lightness wasobserved with an increase in the amount of yeasts in the starterculture.

Parameter a* for all the tested samples assumed nega-tive values, which indicates a shift toward the green color.It was stated that values of color parameter a* decreasewith an increase in the amount of yeasts in the starter cul-ture and with fermentation time. Parameter b* in all sam-ples assumed positive values, which indicates a shift towardthe yellow color. Similarly, as in case of parameter a*, apositive dependence was recorded between the value of pa-rameter b* and the amount of yeasts in the starter cul-ture.

It was observed that during the fermentation process, pa-rameter a* decreases and parameter b* increases in all sam-ples. This direction of changes is explained by Kneifel etal. [40] as a result of acidification. The color changes alsooccurred with respect to nonenzymatic reaction start withbinding of aldehyde group of lactose with ε-amino group ofmilk proteins. The presence of riboflavin (vitamin B2) makesfermented milk especially sensitive to light-induced oxida-tion.

The incubation temperature also influences the faster increasein parameter b*. The higher is the incubation temperature, thehigher is parameter b* [41].

3.4 Analysis of texture

Analysis of texture covered four attributes, i.e. firmness, con-sistency, cohesiveness, and index of viscosity. The texture pro-file in the analyzed samples is presented in the form of aTable 3.

Analysis of the texture profile showed an increase in curdfirmness during the fermentation process run using differentstarter cultures. It was stated that curd firmness is higher in sam-

ples fermented using S. thermophilus and L. delbruckii subsp.bulgaricus than it is for samples, in which the fermentation pro-cess was run with L. lactis and L. lactis subsp. cremoris. Thehigher value of curd firmness indicated its higher cohesivenessand thicker consistency. Moreover, changes were also found inthe index of viscosity, indicating an increase in product vis-cosity during the fermentation process. It was shown that thehigher the proportion of yeasts in the starter culture, the lowerthe viscosity of the product after the fermentation. Irigoyenet al. [42] studied the effect of an increase in the amount ofthe inoculate on changes in the viscosity of kefir from cow milk,and stated that at the application of kefir grains, viscosity of theproduct increases with an increase in the amount of the inocu-late. However, they recorded a reduction of viscosity in sampleswith a very high grain concentration. Controlling viscosity ofready-to-eat milk drinks is important from the point of viewof sensory attractiveness of the product. Kucukcetin et al. [43]showed that a reduction of viscosity in the fermented milk drinksresults in a deterioration of consumer desirability of the product.Experiments conducted within this study confirmed the resultsobtained by Torre et al. [44] and Mituniewicz–Małek et al. [45]who stated a significant effect of the type of bacterial-yeast starterculture on texture parameters of ready-to-eat fermented goatmilk.

3.5 The characteristic of the final product

The final products were characterized in 48 h after inocu-lation (Table 4). No significant differences were observed inactive acidity of analyzed fermented milks. The alcohol con-tent increased with higher proportion of yeast in starter cul-ture. The highest alcohol (4.23 μg g−1) content was detectedin goat milk fermented with L. lactis, L. lactis subsp. cre-moris and S. fragilis at 0.6 g dm−3. Wszołek et al. [9] fer-mented caprine milk with commercially available starter cul-ture. In their experiments product contain 3.93 μg g−1 alcohol.L* and a* color parameters decrease and b* increase in sam-ple with higher yeast content. Firmness and index of viscositywas lower in products fermented with 0.4–0.6 g dm−3 S. frag-ilis.

3.6 Sensory examination

Most produced fermented milk drinks are characterized by apleasant taste and flavor (Table 5).

The correlation of the different sensory attributes with ac-ceptability indicated that the panel was positively influenced bythe sweet taste, buttery and sour taste, goat-like aroma, andmilky and buttery odor. The bitter and extrinsic taste as well asextrinsic odor had a negative effect on the evaluation of theproduct. The presence of alcoholic taste and aroma was de-sirable at their slight intensity. The results for certain at-tributes were consistent with the results reported by Irigoyenet al. [42] and Wszołek et al. [9]. It was found that thealcoholic taste and aroma were most intensive in productsmade with the highest proportion of yeasts. Similarly as in



Table 2. Comparison of color components L*, a*, and b* during incubation

Color constituent Incubation time (h) Sample

1 2 3 4 5 6 7 8

L 0 70.11Da 70.04Ea 70.04Da 70.04Ca 70.99Db 70.18Ca 70.18Da 70.18Da

2 69.12Ce 66.46Dc 65.24Cb 64.18Ba 70.97Dg 70.12Cf 68.13Cd 65.57Bb

4 68.78Bf 65.99Cc 64.67Bb 63.75Aa 70.19Cg 68.95Bf 67.88Be 66.01Cd

6 68.65Ad 64.74Ba 64.09Ba − 69.95 Be 68.65Bd 67.45Ac 65.50Ab

8 68.45Ac 64.09Aa 63.56Aa − 69.09Ad 68.01Ac 67.02Ab −a* 0 −2.05Ea −2.05Ea −2.05Ea −2.05Ba −2.05Da −2.05Ea −2.05Ea −2.05Da

2 −2.21Df −2.76Dd −3.13Db −3.52Ba −2.07Dg −2.58De −2.83Dc −2.78Cd

4 −2.32Cf −2.95 Cd −3.47Cb −3.73Aa −2.12Cg −2.67Ce −2.90Cd −3.01Bc

6 −2.52Be −3.01Bc −3.53Ba − −2.56Be −2.79Bd −3.09Bc −3.19Ab

8 −2.78Ae −3.23Ab −3.76Aa − −2.89Ad −2.98Ac −3.27Ab −b* 0 7.89Ab 7.98Ac 7.89Ab 7.98Ac 7.10Aa 7.10Aa 7.10Aa 7.10Aa

2 8.27Bc 8.31Bc 8.86Bd 9.34Be 7.14Aa 7.11Aa 8.13Bb 8.36Bc

4 8.33Bb 8.54Cc 9.03Cd 9.55Ce 7.28 Ba 7.34Ba 8.17Bb 8.44Cc

6 8.40Cc 8.65Dd 9.17De − 7.31Ba 7.43Ca 8.19Bb 8.54Dd

8 8.49Dc 8.79Ed 9.23Ee − 7.45Ca 7.57Da 8.22Cb −A–E, means with different superscripts within same column described one color constituent are significantly different (p<0.05).a–g, means with different superscripts within same line are significantly different (p<0.05).

Table 3. Texture changes profile during and after fermentation

Sample Incubation time (h) Firmness (g) Consistency (g s) Cohesiveness (g) Index of viscosity (g s)

1 3 15.60a 364.04c −7.29b −0.60d

6 16.02b 366.01c −6.92d −0.47f

9 16.10b 379.87d −6.60e −0.46f

2 3 15.60a 364.44c −7.30b −0.63d

6 16.03b 366.14c −6.95d −0.45f

9 16.12b 379.85d −6.64e −0.45f

3 3 15.91b 362.61c −6.87d −0,71b

6 15.48a 363.38c −6.80d −0.68c

8 15.98b 365.19c −6.67e −0.60d

4 3 15.72a 341.86b −7.61a −0.90a

6 15.55a 364.33c −7.25b −0,72b

5 3 15.73a 361.52c −7.10c −0.62d

6 16.50d 365.80c −7.08c −0.60d

9 16.59d 367.02c −6.82d −0.49f

6 3 15.74a 361.57c −7.11c −0.67c

6 16.51d 365.82c −7.10c −0.66c

9 16.55d 367.09c −6.87d −0.50e

7 3 16.69e 376.75d −6.77e −0.76b

6 16.22c 368.08c −6.67e −0.67c

9 16.34c 282.01a −6.66e −0.56e

8 3 16.60e 373.50d −6.82d −0.70b

6 16.48d 375.88d −6.54f −0.52e

a–f, means with different superscripts within same column are significantly different (p<0.05).

the study by Alvarez-Martin et al. [46] on the applicationof mixed starter cultures in the production of fermentedmilk drinks, no significant level of extrinsic aroma was ob-served for this type of products. The significantly highestdesirability was found for drinks produced with the use ofL. lactis, L. lactis subsp. cremoris and S. fragilis at 0.2 and0.4 g dm−3.

4 Conclusions

The conducted experiments proved the applicability of selectedbacterial and yeast strains in the production of health-promotingfermented goat milk. The time of the fermentation process andproduct quality depend on the microbial strains and ratio be-tween bacteria and yeast in starter culture. The use of L. lactis,



Table 4. The characteristic of final product in 48 h after inoculation

Sample number 1 2 3 4 5 6 7 8

Active acidity (pH) 4.58a 4.60a 4.62a 4.59a 4.59a 4.63a 4.57a 4.61a

Alcohol content (μg g−1) nd 2.30c 3.10d 4.23f 0.10a 1.80b 2.60c 3.80e

Colour L* 68.42c 63.79a 63.26a 63.68a 69.01d 67.59c 66.65b 65.05b

a* − 2.88c − 3.33b − 3.79a − 3.85a − 2.97c − 3.03c − 3.31b − 3.25b

b* 8.51b 8.80b 9.32c 9.58c 7.47a 7.59a 8.23b 8.58b

Texture Firmness (g) 16.12c 16.13c 16.01b 15.57a 16.62e 16.59e 16.33d 16.36d

Consistency (g s) 379.91c 379.95c 365.45b 364.65b 367.33b 367.25b 282.16a 375.95c

Cohesiveness (g) − 6.56c − 6.57c − 6.62c − 7.21a − 6.80b − 6.82b − 6.60c − 6.51c

Index of viscosity (g s) − 0.41d − 0.44d − 0.58b − 0.70a − 0.47c − 0.48c − 0.54b − 0.51bc

a–f, means with different superscripts within same line are significantly different (p<0.05).

Table 5. Sensory attributes and acceptability of fermented milks

Sensory attributes Sample

1 2 3 4 5 6 7 8

Taste Sweet 50a 50a 54b 57c 47a 49a 53b 57c

Sour 54a 55a 56a 57a 53a 52a 56a 57a

Bitter 29a 29a 29a 28a 27a 28a 26a 32b

Buttery 42a 44a 44a 45a 40a 45a 45a 49b

Alcoholic 9a 30c 36d 40e 5a 25b 32c 36d

Extrinsic 3a 4ab 5bc 6cd 4ab 8e 7de 5bc

Flavors Goat -like 38a 39a 45c 49d 40ab 43b 50d 47c

Milky 37a 39a 42b 47c 36a 35a 38a 42b

Buttery 42b 43b 41b 42b 36a 39b 42b 45c

Alcoholic 7c 24b 27c 23e 5c 22b 27cd 29d

Extrinsic 4b 2a 6c 6c 6c 7c 4b 6c

Acceptability 60a 89d 85d 70b 64a 73b 79c 61a

a–e, means with different superscripts within same line are significantlydifferent (p<0.05).

L. lactis subsp. cremoris, and S. fragilis at 0.2 or 0.4 g dm−3 gavethe most satisfying results in shorten fermentation time and information of high-quality goat beverage.

Practical application

Fermented milk drinks produced with the use of spe-cific strains of lactic acid bacteria and yeasts are classi-fied as products of yeast-lactic fermentations. The popu-larity of alcoholic milk beverages has helped to increasetheir consumption and to promote their reputation ashealth-promoting products. Increasing nutritive value ofthat product can also be reached by using goat milk. Theproperties of this milk differ from those of cow milk that isthe optimal medium for commercially available starter cul-tures. The production process and the processing param-eters and conditions have to be adapted to the propertiesof the raw material (goat milk) to ensure the best possiblequality for the final product. Quality of fermented goat milkmay be considerably improved through the selection ofspecific microbial strains. The current work presents dataon the selection of the microorganisms that can be usedas a starter culture for alcoholic goat milk beverages.

The authors have declared no conflict of interest.

5 References

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