International Dairy Journal 13 (2003) 827833

Development of a fermented goats milk containing probiotic bacteria

A.B. Mart!n-Diana, C. Janer, C. Pel!aez, T. Requena*

Department of Dairy Science and Technology, Instituto del Fr!o (CSIC), Ciudad Universitaria, Jose Antonio Novais 10, 28040 Madrid, Spain

Received 19 December 2002; accepted 28 April 2003

Abstract

A set-type fermented milk manufactured from goats milk was developed. Optimal curd tension was achieved by supplementation

of milk with skim milk powder and whey protein concentrate (WPC). Milk was fermented employing a commercial probiotic starter

culture (ABT-2), which contained Streptococcus thermophilus ST-20Y, Lactobacillus acidophilus LA-5, and Bifidobacterium BB-12.

Supplementation of milk with 3%WPC reduced fermentation time by 2 h due to the increase in viable counts of S. thermophilus and

Bifidobacterium by 0.3 and 0.7 log units, respectively. Addition of WPC increased the protein content (1%) as well as potassium and

magnesium content (0.3 and 0.02 g kg1, respectively). Increase of the protein content led to an increase in the apparent viscosity and

gel rmness of the product, and at the same time whey syneresis was reduced. As a consequence, the product received a high score

for appearance, taste, aroma, texture and overall acceptance.

r 2003 Elsevier Ltd. All rights reserved.

Keywords: Whey protein concentrate; Bifidobacterium; Fermented goats milk; Rheological properties

1. Introduction

During recent years, an increasing interest hasdeveloped in foods that contribute to a positive effecton health beyond their nutritional value. Among thesefunctional foods, much attention has been focused onprobiotic products. Probiotic foods contain microor-ganisms or components of microbial cells that have abenecial effect on the health and well-being of theconsumer host (Salminen, Ouwehand, Benno, & Lee,1999). Viability of probiotic bacteria to high counts (atleast 107 cfug1 or mL1 of product) is recognized as animportant requirement during manufacturing and mar-keting of probiotic foods in order to achieve the claimedhealth benets.Goats milk has been described as having a higher

digestibility and lower allergenic properties than cowsmilk. In addition, goats milk has been attributed withcertain therapeutic values in human nutrition (Spuerginet al., 1997; Alferez et al., 2001; Barrionuevo, Alferez,Lopez-Aliaga, Sanz-Sampelayo, & Campos, 2002).However, the manufacture of fermented goats milk

products such as set-style yoghurt faces a problem ofover-acidication due to a low buffering capacity ofgoats milk (Rysstad & Abrahamsen, 1983). Further-more, goats milk has a slightly lower casein contentthan cows milk, with a very low proportion or absenceof as1-casein, and a higher degree of casein micelledispersion (Remeuf & Lenoir, 1986; Vegarud et al.,1999). All these factors inuence the rheological proper-ties of the coagulum in goats milk that is almost semi-liquid. To obtain a satisfactory curd tension in goatsfermented milk, an increase in the content of non-fatsolids is required. Procedures such as concentration ofmilk by membrane processes, addition of stabilizerssuch as gelatine or pectins, and employment ofexopolysaccharide (EPS)-producing lactic acid bacteriaare often used to impart desirable texture characteristicsin low fat fermented milk (Hess, Roberts, & Ziegler,1997; Ozer, Robinson, Grandison, & Bell, 1998; Duboc& Mollet, 2001). Another possibility is the use of wheyprotein concentrate (WPC) that is a cheaper and readilyavailable additive that has been shown to increaseviscosity, reduce syneresis (Mart!n-Diana, G !omez-Guill-!en, Montero, & Fontecha, unpublished results), and toincrease Bifidobacterium growth in milk and fermentedmilks (Janer, Pel!aez, & Requena, unpublished results;Bozanic & Tratnik, 2001).

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*Corresponding author. Tel.: +34-9154-92300; fax: +34-915493627.

E-mail address: trequena@if.csic.es (T. Requena).

0958-6946/03/$ - see front matter r 2003 Elsevier Ltd. All rights reserved.

doi:10.1016/S0958-6946(03)00117-1

The aim of this work was to develop a goats milkfermented product (set-type style) of a satisfactoryquality, in terms of sensory characteristics and survivalof bacteria. The starter culture ABT-2 (Streptococcusthermophilus ST-20Y, Lactobacillus acidophilus LA-5,and Bifidobacterium BB-12) was selected as it iscommercially claimed to contain EPS-producing strains,strains with low acidication activity and probioticstrains. Probiotic characteristics described for the strainsinclude transient colonization of gut and alleviation ofallergic inammation (Isolauri, Arvola, Sutas, Moila-nen, & Salminen, 2000; Satokari, Vaughan, Akkermans,Saarela, & De Vos, 2001). Increase of non-fat solidcontent in the goats milk fermented product wasachieved by the addition of WPC.

2. Materials and methods

2.1. Starter cultures and fermented milk manufacture

Two concentrated starter cultures for direct vatinoculation were used (Chr. Hansen, Copenhagen,Denmark): YF-3331, containing Streptococcus thermo-philus and Lactobacillus delbrueckii subsp. bulgaricus,and ABT-2, containing Lactobacillus acidophilus LA-5,Bifidobacterium BB-12, and S. thermophilus ST-20Y.Concentrated starters and pure cultures (L. acidophilusLA-5 and S. thermophilus ST-20Y) were stored at80C.Commercially available cows and goats UHT milk

enriched with 30 g of skim milk powder per litre(Scharlab, Barcelona, Spain) were fermented. Each milkcontained (per litre) 15 g fat, 48 g (cows) or 45 g (goats)carbohydrates and 30.5 g (cows) or 28 g (goats) protein.Goats milk was also fortied with WPC of concentra-tions ranging from 10 to 50 gL1. The WPC was anultraltered cheese whey concentrated to a 35% proteincontent and was kindly supplied by Fermo S.A. (Spain).To assure adequate whey protein denaturation, thesupplemented milk was heated to 80C for 30min beforebeing cooled to inoculation temperature.The lyophilized ABT-2 culture was suspended in 10%

reconstituted skim milk powder, autoclaved at 110Cfor 10min, and used to inoculate the milk samples at aconcentration of 0.2 UL1, as recommended by themanufacturer. Inoculated milk samples were transferredto 100mL, tightly covered glass jars and incubated at44C until a pH of 4.5 was reached. The entireexperimental process was performed twice.

2.2. Microbiological analyses

Viable counts were determined in fermented milksamples (1 g), after the fermentation process and after 21days of storage, by using serial decimal dilutions

prepared in 1/4 strength Ringers solution supplementedwith 5 gL1 cysteine. Appropriate dilutions were pour-plated in duplicate onto selective media. Counts of S.thermophilus were enumerated on M-17 agar containing5 gL1 lactose and incubated aerobically at 37C for48 h. For enumeration of L. acidophilus LA5, appro-priate dilutions were spread out on MRS agar platessupplemented with 0.5 gL1 cysteine, and incubated for34 days at 37C in a 20% CO2 atmosphere (Salvis-Labincubator model Biocenter 2001, Rotkreuz, Switzer-land). Lactobacilli were identied as at, rough colonieswith irregular edges and 23mm in diameter. Identica-tion of L. acidophilus colonies was conrmed bymicroscopic examination of Gram-stained cultures.Neither S. thermophilus ST-20Y nor BifidobacteriumBB-12 grew in these conditions.A medium (Bif-medium) was adapted from bido-

bacteria selective media described in the literature (VanLaere, Abee, Schols, Beldman, & Voragen, 2000; Roy,2001) to differentiate Bifidobacterium BB-12 from theother two strains in the starter culture ABT-2. The Bif-medium consisted of M-17 agar supplemented with0.5 g L1 cysteine, 2 gL1 LiCl, 1 gL1 Tween 80 and5 gL1 rafnose or galacto-oligosaccharides (VivinalGOS, kindly provided by Borculo Domo Ingredients,AK Zwolle, The Netherlands). Plates were incubated for3 days at 37C under anaerobic conditions (Gas-pack,Anaerogen; Oxoid, Basingstocke, UK). Colonies oflenticular shape and 23mm diameter were enumeratedas bidobacteria, whereas smaller, pinpoint coloniescorresponding to S. thermophilus. L. acidophilus LA5did not grow on the Bif-medium. To ascertain theefcacy of the Bif-medium for bidobacteria enumera-tion, 20% of the lenticular colonies developed in theplates were subjected to a PCR amplication targetingthe transaldolase gene, which is specic for this genus.Colonies were picked up using a sterile toothpick,suspended in 20 mL milliQ water, boiled at 100C for5min and frozen at 20C. After being thawed, 2 mL ofthe suspension was directly added to the PCR reaction,for which the primers and the conditions described byRequena et al. (2002) were employed. Identication ofseveral colonies was carried out by sequencing theamplied 300 bp fragment.

2.3. Acidifying kinetics

The pH of the samples was monitored during thefermentation and after 21 days of storage at 4C byusing a Metrohm Model 691 pH-meter (Metrohm Ltd.,Herisau, Switzerland).

2.4. Compositional analysis

Total nitrogen content was determined using a LECOFP2000 analyser (LECO Corporation, MI, USA).

ARTICLE IN PRESSA.B. Mart!n-Diana et al. / International Dairy Journal 13 (2003) 827833828

Protein was determined by applying a nitrogen-to-protein conversion factor of 6.38. Non-protein nitrogen(NPN) was determined in the 12% trichloroacetic acid(TCA)-soluble fraction of the samples and analysed inthe LECO analyser after removal of TCA. Mineralcontent (Ca, Na, K, Mg, Mn, Zn, Fe, and Cu) wasdetermined following the method described by De laFuente, Fontecha and Juarez (1996). The chlorideconcentration was determined using the Sigma diag-nostics chloride reagent (Sigma chemical Co., St. Louis,USA) and following the manufacturers instructions.The lactose content was determined using the lactose/d-galactose test for food analysis (Roche, Mannheim,Germany). Total solids were determined by drying thesamples at 10272C to constant weight for gravimetricdetermination. Ash content was determined by ignitionof solid materials at 550C for 24 h in an electric mufefurnace (Guzm!an-Gonz!alez, Morais, Ramos, & Amigo,1999). All the analyses were performed in triplicate.

2.5. Rheological properties

The apparent viscosity (Zapp) of fermented milk wasmeasured during fermentation using a dynamic visco-meter (Brookeld Model-LV; Brookeld EngineeringLaboratory, Stoughton, USA). The spindle used was4 cm in diameter and the speed was kept constant at28 rpm. All the assays were performed in duplicate andresults were mean values in centipoise (cP) units.Gel rmness of the products after fermentation was

analysed by a texturometer (Instron, Model 4501,Instron, Engineering Corp., Canton, USA) through asingle compression test using a cylinder (diameter: 5 cm,distance: 20mm, speed 20mm s1). The analyses wereperformed in duplicate at room temperature. Firmnesswas expressed as the maximum penetration force, in g.The syneresis index (g drained whey kg1 fermented

milk) was calculated according with the methoddescribed by Guzm!an-Gonz!alez et al. (1999).

2.6. Sensory analysis

Sensory evaluation was carried out in fermented milksamples after 24 h of cold storage by ten members of theregular taste panel from our food science laboratory.Appearance, aroma, mouth-feel texture, taste and over-all acceptability of samples were scored on a hedonicscale of 110.

2.7. Statistical studies

The results of the two trials were studied using one-way analysis of variance to determine signicantdifferences (Po0.05) by the addition of WPC tofermented milk samples in bacterial counts, composi-tion, pH, rheological properties and sensory scores by

using the Statgraphics software (version 2.1; StatisticalGraphics Co., Rockville, USA).

3. Results and discussion

Test conditions for fermented goats milk manufac-ture were chosen on the basis of preliminary studiescarried out to nd an acceptable product that couldobtain sensory scores similar to cows set-style fermen-ted milk immediately after manufacture. In theseprevious experiments (results not shown), the maincomplaints for goats fermented milks were related to itsunsatisfactory textural characteristics. Supplementationwith WPC was tried in order to improve the producttexture. A preliminary test was performed to determinethe optimum milk heating temperature to increase wheyprotein denaturation. Heat treatment higher than 80Cfor 30min yielded a product with a manifestly darkcolour that was negatively scored by the test panel(results not shown). With respect to the starter culture,two Chr. Hansen cultures were tested: YF-3331, whichcontains the traditional S. thermophilus and L. bulgar-icus strains, and the ABT-2 culture, characterized by theproduction of EPS and low acidication activity.Fermentation time was signicantly reduced to 4 h bythe regular YF-3331 starter, instead of the 810 h neededfor the ABT-2 starter, but it caused an unpleasantacidity in goats fermented milks. Therefore, only theABT-2 starter culture was employed in further goatsmilk fermentations, and WPC concentration was main-tained as the sole variable. Batch B was without WPCsupplementation and Batches C and D contained 3%and 5% WPC, respectively. Fermented cows milk wasused as a reference (Batch A).

3.1. Fermentation process

Fig. 1 shows changes in pH during the fermentationof milk samples with the ABT-2 starter. The results

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4.0

4.5

5.0

5.5

6.0

6.5

0 5 6 10 12

pH

Time (h)Fig 1. Change in pH during manufacture of fermented milk from

cows milk (o), goats milk (&), and goats milk supplemented with

3% WPC (W) or 5% WPC ().

A.B. Mart!n-Diana et al. / International Dairy Journal 13 (2003) 827833 829

demonstrated a slow acidication prole. The timerequired to reach pH 4.5 for goats milk was 10 h. Thefermentation time was reduced to 8 and 9 h for goatsmilk supplemented with 5% and 3% WPC, respectively.Fermented cows milk was stored at 4C after an 11 hincubation time although the pH was still 4.6. Ingeneral, a faster acidication rate has been reportedfor goats milk as compared to cows milk (Rysstad &Abrahamsen, 1983; Kurmann, 1986). For all fermentedmilk samples, the pH did not signicantly change(Po0.05) during the 3 weeks storage at 4C (resultsnot shown), indicating no acidication during storage.

3.2. Fermented milk composition

Tables 1 and 2 show overall composition of fermentedmilk samples after the fermentation process. The maindifferences between fermented milk samples resultedfrom the addition of WPC, which caused an increase intotal solids, mainly due to the protein content (Table 1).The lactose content of goats milk before fermentationwas enriched by 1.2% with skim milk powder over itsnatural content of 4.5%. Addition of 3% WPC and 5%WPC further increased the lactose content by 1.3% and2.2%, respectively. Lactose was extensively utilizedduring fermentation (Table 1). Protein content wasincreased by an average of 1% by supplementation withWPC, and non-protein nitrogen was also higher insupplemented milk samples.Goats fermented milk showed a higher content of

minerals, mainly Ca, Na and Mg, than cows fermentedmilk (Table 2). These differences could be generally

attributed to differences in milk composition amongspecies (Park, 2000; Flynn & Cashman, 1997; De laFuente, Olano, & Ju!arez, 1997). Addition of WPC togoats milk caused an increase (Po0.05) in K and Mg inthe fermented milk samples, probably due to therelatively high percentage of these minerals that arefound in milk in the soluble phase and fractionatemostly to whey during cheesemaking (De la Fuente et al.,1997; Gastaldi, Lagaude, & Tarodo de la Fuente, 1996).Supplementation of fermented milk samples with WPCcan be advantageous from a nutritional point of view asa source of minerals (Flynn & Cashman, 1997; Massey,2001).

3.3. Microbiological analyses

Table 3 shows results of bacterial counts after thefermentation process and at the end of storage of thefermented milk samples. The main population wasrepresented by S. thermophilus in all samples, withhigher levels (Po0.05) when WPC was added to milk.This is in agreement with the faster reduction of pHobserved during fermentation (Fig. 1). There were nochanges in the viability of S. thermophilus duringstorage, counts being maintained at 78 108 cfug1 inall fermented milk samples. An increase in L. acidophilusgrowth during fermentation of about one log unit wasalso observed in all fermented milk samples, valuesreaching 23 107 cfug1. However, all counts of L.acidophilus dropped under 106 cfug1 after 21 dayscold storage. Low viability of L. acidophilus LA-5during fermented milk storage has been described by

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Table 1

Content (%, meana 7SD) in total solids, ash, protein, NPN and lactose in the fermented milk samples manufactured from cows milk (A), goatsmilk (B) and goats milk supplemented with 3% WPC (C) and 5% WPC (D)

Fermented milk Total solids Ash Protein NPN Lactose

A 14.270.86a 0.8770.08a 3.7170.01a 0.1870.03a 2.1870.21b

B 14.370.04a 0.8670.01a 3.9570.06a 0.1870.03a 1.1970.30a

C 16.770.81ab 1.2070.21ab 5.0170.41b 0.5870.10b 1.2870.22a

D 17.872.07b 1.3970.25b 5.3170.13b 0.6670.05b 1.2270.31a

aMeans are average from two independent trials. Different letters indicate signicant differences (Po0.05) between batches.

Table 2

Mineral composition (g kg1; meana7SD) of the fermented milk samples manufactured from cows milk (A), goats milk (B) and goats milksupplemented with 3% WPC (C) and 5% WPC (D)

Fermented milk Chlorides Ca Na K Mg Cu Fe Zn

A 2.970.01 1.0170.06a 0.5370.01a 1.5070.04a 0.09670.002a o0.002 o0.002 0.004670.0001B 3.170.05 1.1170.06ab 0.6270.02b 1.5370.21a 0.10670.001b o0.002 o0.002 0.004570.0001C 3.170.05 1.1870.06b 0.6570.04b 1.8470.10b 0.12770.006c o0.002 o0.002 0.004870.0009D 3.070.04 1.1970.07b 0.7070.03c 1.9270.20b 0.13570.007d o0.002 o0.002 0.004670.0006

aMeans are average from two independent trials. Different letters indicate signicant differences (Po0.05) between batches.

A.B. Mart!n-Diana et al. / International Dairy Journal 13 (2003) 827833830

Nighswonger, Brashears, and Gilliland (1996). Additionof WPC did not inuence growth or viability of thisstrain. In contrast, Bifidobacterium growth and viabilitywere greatly enhanced by WPC supplementation (Table3). These results are in agreement with those reported byBozanic and Tratnik (2001) that also reported anincrease in bidobacteria growth after fermentation ofgoats milk supplemented with WPC.The Bif-medium used to enumerate bidobacteria in

this study did not include the antibiotics that are oftenused to inhibit growth of yoghurt bacteria and couldcause under-estimation of bidobacteria counts inselective media (Roy, 2001). The differentiation ofBifidobacterium in the Bif-medium was achieved byreplacing lactose by galacto-oligosaccharides (GOS) andrafnose, considering the ability of these substrates toselectively support Bifidobacterium growth (Gopal,Sullivan, & Smart, 2001). Colonies differentiated betterwhen rafnose was employed (results not shown).Representative colonies were conrmed by PCR usingprimers targeting the transaldolase gene, which arespecic for Bifidobacteria (Requena et al., 2002).Sequencing of several 300 bp fragments revealed 100%identity to B. lactis (results not shown). The capabilityof WPC to increase B. lactis growth in milk has recentlybeen demonstrated (Janer, Pel!aez & Requena, unpub-lished results). When WPC was not added (Batches Aand B), there was no increase in bidobacterial counts,remaining at the initial level of inoculum(3 106 cfug1). Decrease of bidobacterial counts wasseen during storage of all fermented milks, althoughWPC-supplemented fermented milk samples maintainedlevels above 107 cfug1 (Table 3). Due to the poorgrowth of bidobacteria in milk, it is generallyrecommended that their inoculation level in fermentedmilk should be that of the desirable level of the probioticculture in the nal product. However, increasedinoculum does not guarantee viability of bidobacteriaduring fermentation and storage of fermented milk,which has been described as variable depending on thespecies and supplements added (Dave & Shah, 1998;Lamoureux, Roy, & Gauthier, 2002). The present work

demonstrates that WPC supplementation of goats milkbenecially inuences B. lactis growth during fermenta-tion, as well as its viability during fermented milkstorage. Studies will be carried out to characterize theeffect of WPC on the growth and viability of otherbidobacteria species in fermented milks.

3.4. Rheological properties

Fig. 2 shows results of viscosity during manufacturingof fermented milk samples. All samples progressivelyattained characteristic properties of uids duringfermentation. The increase in apparent viscosity

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Table 3

Viability (cfu g1, meana 7SD) of Streptococcus thermophilus ST-20Y, Lactobacillus acidophilus LA-5, and Bifidobacterium BB-12 in the fermented

milk samples manufactured from cows milk (A), goats milk (B) and goats milk supplemented with 3% WPC (C) and 5% WPC (D) after the

fermentation process and 21 days of storage at 4C

Fermented milk Streptococcus thermophilus

(cfu g17SD) 108Lactobacillus acidophilus

(cfu g17SD) 107Bifidobacterium BB-12

(cfu g17SD) 106

1 day 21 days 1 day 21 days 1 day 21 days

A 6.670.7ab 7.171.4a 3.270.7ab o106 4.271.3a 2.271.4aB 5.272.9a 7.271.4a 3.771.0b o106 3.670.4a 2.770.5aC 9.971.7bc 8.771.4a 3.471.0b o106 16.674.8b 13.572.7bD 11.274.0c 8.972.7a 1.970.7a o106 44.0711.7c 19.474.8c

aMeans are average from two independent trials. Different letters indicate signicant differences (Po0.05) between batches.

0

1200

2400

3600

4800

0 5 10 15Time (h)

Visc

osity

(cP)

Fig 2. Changes in the apparent viscosity during manufacture of

fermented milk from cows milk (o), goats milk (&), and goats milk

supplemented with 3% WPC (W) or 5% WPC (}).

Table 4

Rheological properties (meana7SD): viscosity (cP), rmness (g) andsyneresis grade (g kg1) of the fermented milk samples manufactured

from cows milk (A), goats milk (B) and goats milk supplemented

with 3% WPC (C) and 5% WPC (D)

Fermented milk Viscosity Firmness Syneresis

A 23257388ab 11.770.68a 570783bc

B 17867284a 6.1571.48a 635744c

C 30127300b 25.270.98b 508776ab

D 45457487c 34.776.43c 430757a

aMeans are average from two independent trials. Different letters

indicate signicant differences (Po0.05) between batches.

A.B. Mart!n-Diana et al. / International Dairy Journal 13 (2003) 827833 831

corresponded with the increase of solid content (Table 1).Curdling began rst in milk supplemented with 5%WPC, reaching the highest viscosity (Po0.05) at the endof the fermentation process, when the pH reached 4.5.The lowest apparent viscosity was observed duringfermentation of non-supplemented goats milk. Higherwhey protein content, and its denaturation during heattreatment prior to fermentation, highly inuencesviscosity due to an increase of protein binding capacitythat results in a higher gel viscosity during coagulation(Shaker, Jumah, & Abu-Jdayil, 2000). Denaturation ofb-lactoglobulin and its interaction with casein micelleshave been shown to highly inuence gel fermented milkproperties (Needs et al., 2000).An important criterion for quality assessment of set-

style cultured milk products is the texture of the gel.Table 4 shows results of rheological characteristics offermented milk samples after the fermentation process.All parameters signicantly increased (Po0.05) ingoats fermented milk by the addition of WPC. As inviscosity, increase of gel fermented milk rmnessdepends on the total solids as well as on protein contentand type (Oliveira, Sodini, Remeuf, & Corrieu, 2001).Although total solids content for cows milk and non-supplemented goats milk was similar (Table 1), rmnessof goats milk coagulum was about half that of cowsmilk. This demonstrates the high inuence on texturecaused by the differences in casein content and micellestructure between species (Remeuf and Lenoir, 1986;Vegarud et al., 1999).The analysis of the syneresis values of the fermented

milk samples also showed a signicant (Po0.05)decrease of whey drainage in goats milk coagulumalong with the addition of WPC (Table 4). Reduction ofwhey syneresis corresponds to the improvement of wheyprotein water-holding capacity, which increases withdenaturation (Britten & Giroux, 2001). Spontaneouswhey separation increased in cows fermented milkduring storage, a defect that was not observed ingoats fermented milk supplemented with WPC. Thissuggests that WPC could be successfully employed infermented milk manufacture for controlling wheyseparation, and it would avoid the use of non-dairystabilizers.

3.5. Sensory evaluation

Results of the sensory evaluation of fermented milksamples on a scale from 1 (very bad) to 10 (excellent) areshown in Table 5. In general, scores of goats fermentedmilk for all attributes tested increased (Po0.05) by theaddition of WPC. Goats fermented milk was the leastacceptable, tasters objecting to its liquid texture, andnon-typical yoghurt taste. Addition of WPC masked thecharacteristic taste of goats milk. Nevertheless, increaseof WPC up to 5% did not enhance the sensory gradingof fermented milk, and the product was dened by somepanellists as having a non-pleasant salty taste with agranulous texture. Cows fermented milk had a lowgrading for appearance due to wheying-off on thefermented milk surface. The fermented goats milksupplemented with 3% WPC was scored the highest,showing a high overall acceptability, similar to that forcows fermented milk.

4. Conclusion

An acceptable fermented goats milk, when comparedwith a set-style cows milk yoghurt, has been obtainedby supplementation of milk with 3% WPC. The mainadvantages of WPC addition to goats milk are relatedto the reduction of fermentation time, the nutritionalenrichment of the product in protein and minerals, theincrease in bidobacterial growth and viability, and thedevelopment of suitable rheological properties for a set-style fermented milk. Increase in bacterial population byaddition of 3% WPC did not adversely affect thesensory acceptability of the product, which had a highscore for appearance, taste, aroma, texture and over-all acceptance, nor did it cause acidication duringstorage.

Acknowledgements

This research was nanced by Project AGL2000-0727-C03-02. We thank Fermo SA and Borculo DomoIngredients for their kind supply of WPC and Vivinal

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Table 5

Sensory analysis (meana7SD) of the fermented milk samples manufactured from cows milk (A), goats milk (B) and goats milk supplemented with3% WPC (C) and 5% WPC (D)

Fermented milk Appearance Aroma Taste Texture Acceptability

A 7.571.4ab 8.371.1b 8.270.9b 8.070.9b 8.370.8b

B 6.572.2a 6.472.0a 4.371.3a 5.271.2a 4.771.4a

C 8.571.1b 7.970.9b 7.871.3b 8.370.8b 8.171.0b

D 8.371.3b 7.870.9b 7.570.9b 7.970.7b 7.970.9b

Scores vary between 1 (very bad) and 10 (excellent).aMeans are average from two independent trials. Different letters indicate signicant differences (Po0.05) between batches.

A.B. Mart!n-Diana et al. / International Dairy Journal 13 (2003) 827833832

GOS, respectively. C. Janer is the recipient of ascholarship from the Spanish Ministry of Science andTechnology.

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ARTICLE IN PRESSA.B. Mart!n-Diana et al. / International Dairy Journal 13 (2003) 827833 833

Development of a fermented goats milk containing probiotic bacteriaIntroductionMaterials and methodsStarter cultures and fermented milk manufactureMicrobiological analysesAcidifying kineticsCompositional analysisRheological propertiesSensory analysisStatistical studies

Results and discussionFermentation processFermented milk compositionMicrobiological analysesRheological propertiesSensory evaluation

ConclusionAcknowledgementsReferences