ARTICLE IN PRESS

FOODMICROBIOLOGY

0740-0020/$ - se

doi:10.1016/j.fm

�CorrespondE-mail addr

Food Microbiology 25 (2008) 13–21

www.elsevier.com/locate/fm

Incorporation of citrus fibers in fermented milkcontaining probiotic bacteria

Esther Sendra�, Patricia Fayos, Yolanda Lario, Juana Fernandez-Lopez,Estrella Sayas-Barbera, Jose Angel Perez-Alvarez

Dpto. Tecnologıa Agroalimentaria, Escuela Politecnica Superior de Orihuela, Universidad Miguel Hernandez, Ctra. Beniel km 3.2,

03312 Orihuela (Alicante), Spain

Received 6 June 2007; received in revised form 4 September 2007; accepted 5 September 2007

Available online 11 September 2007

Abstract

The incorporation of Lactobacillus acidophilus CECT 903, Lactobacillus casei CECT 475 and Bifidobacterium bifidum CECT 870

together with lemon (LF) and orange (OF) fibers obtained from juice by-products were tested in (i) a model system: fiber enriched with de

Man Rogosa Sharp (MRS) broth cultured with each probiotic bacteria and (ii) evaluation of populations of probiotic bacteria in

fermented milks formulated with citrus fibers. Citrus fibers enhanced L. acidophilus CECT 903, and L. casei CECT 475 survival in MRS

during refrigerated storage, whereas erratic results were obtained for B. bifidum CECT 870, OF enhanced its growth and LF had

inhibitory effect. Populations of probiotic bacteria decreased with storage time in MRS broth. The presence of yogurt starter bacteria in

probiotic fermented milks favored the growth and survival of L. acidophilus and B. bifidum. Citrus fiber presence in fermented milks also

enhanced bacterial growth and survival of the tested probiotic bacteria. This study indicates that citrus fiber enriched fermented milk

have good acceptability and are good vehicles for a variety of commercial probiotics but survival of B. bifidum will need to be improved.

r 2007 Elsevier Ltd. All rights reserved.

Keywords: Probiotic; Citrus fiber; Fermented milk

1. Introduction

Production of citrus products in 2004 in FAO countries was63.95 and 12.53 million tonnes of oranges, and lemons andlimes, respectively (FAO, 2006). One-third of the citrus fruitsis processed to obtain several products, mainly juice(Izquierdo and Sendra, 2003). The amount of residue obtainedfrom citrus fruits accounts for 50% of the original amount ofwhole fruit (Cohn and Cohn, 1997). The residue remainingafter juice and essential oil extraction is mainly used to obtainpectins and also as animal feed with little economic value. Theaccumulation of these residues is an environmental problem.These by-products are rich in fiber. The possibility ofsuccessfully including these by-products in the human foodindustry would help in enhancing the economic developmentof citrus producers and processors. Fibers also have beneficial

e front matter r 2007 Elsevier Ltd. All rights reserved.

.2007.09.003

ing author. Tel.: +34966749735; fax: +34966749677.

ess: esther.sendra@umh.es (E. Sendra).

effects for human health. The recommended daily intake offiber is about 38g for men and 25g for women (Trumbo et al.,2002). Fibers may be used to fortify foods. Fermented milkproducts already have a positive healthy image due to thebeneficial action of its viable bacteria and they are goodcandidates to be enriched with citrus fibers. Fiber may interactwith other food components during processing. Theseinteractions may lead to changes in bioavailability ofnutrients, texture or flavor of the product. Fibers may alsointeract with the microbial populations of yogurt, eitherresidual essential oils may inhibit their growth or fibercomponents as oligosaccharides may enhance their growth.To exert beneficial effects in the host, it is essential that

lactic acid bacteria and bifidobacteria be alive and abundantin the product at the time of consumption. No generalagreement has been reached on the concentration ofprobiotics to achieve probiotic effects; usually counts from106 to 108CFU/g are recommended (Lourens-Hatting andViljeon, 2001). In Japan, the Fermented Milks and Lactic

ARTICLE IN PRESSE. Sendra et al. / Food Microbiology 25 (2008) 13–2114

Acid Beverages Association has already established astandard that requires more than 107CFU/mL to be presentin dairy products to claim to contain probiotic microorgan-isms, whereas the Swiss Food Regulation as well as theStandard FIL/IDF requires that such products contain morethan 106CFU/mL.

Donkor et al. (2006) reviewed the factors that may affectthe survival of Lactobacillus and Bifidobacterium spp. inyogurt: strain of probiotic bacteria, inoculation level,incubation temperature, pH, growth promoters and inhibi-tors, presence of hydrogen peroxide and oxygen, concentra-tion of metabolites, lactic and acetic acid, buffering capacityof the media, storage temperature, and availability ofnutrients. The main factors are ultimate pH and accumula-tion of organic acids (Dave and Shah, 1997; Shah, 2000).Ravula and Shah (1998) observed that when probioticbacteria grow together with yogurt cultures the metabolicactivity of Streptococcus thermophilus and Lactobacillus

delbrueckii ssp. bulgaricus during storage (organic acids andamino acids release) may affect probiotics viability.

Several authors have studied the interactions amongdifferent fibers and probiotic bacteria. Capela et al. (2006)reported that the prebiotic ‘RaftilosesP95’ when added at1.5% (w/v) to yoghurt improved the viability of thecombined selected probiotic organisms (Lactobacillus acid-

ophilus, Lactobacillus casei, Lactobacillus rhamnosus andBifidobacterium spp.) by 1.42 log during 4 weeks of storage at4 1C. L. casei cells were immobilized on fruit (apple and pear)pieces and the immobilized biocatalysts were used separatelyas adjuncts in probiotic Feta cheese making by Kourkoutaset al. (2006) with satisfactory results. Perez-Conesa et al.(2005) proved the benefits of combining commercialnondigestible oligosaccharides (NDO) (short-chain fructoo-ligosaccharides, inulin, oligofructose, galactosyllactose) withseveral species of Bifidobacterium in powder infant formula.As the pH of the reconstituted formula was always close toneutrality (from 6.74 to 7.06), the number of bacteria wasalways over the recommended level. Martinez-Villaluengaet al. (2005) reported that the raffinose family of oligosac-charides (RFOs) isolated from lupin seeds applied to themanufacture of probiotic fermented milk increased Bifido-

bacterium lactis Bb-12 and L. acidophilus populations at thefinal fermentation time compared with controls, and thattime of fermentation was reduced from 12 to 10h.

The objective of the present study was to investigate theeffect of lemon and orange fiber (obtained from citrus by-products) on growth and survival of the probiotic bacteriaBifidobacterium bifidum CECT 870, L. casei CECT 475 andL. acidophilus CECT 903 in a model system and infermented milk during cold storage.

2. Methods

2.1. Materials

Fiber was obtained from orange (OF) and lemon(LF) juice by-products by a procedure described by

Fernandez-Lopez et al. (2004). To obtain powder with aparticle size of 0.701–0.991mm, a grinder and appropriatesieves were used. The orange fiber product used has: 80.1%crude fiber (determined by Weende method, 962-09 AOAC,1995), 7.34% moisture, 11.3% water holding capacity(WHC), pH 3.92, 30CFU/g aerobic mesophilic bacteriaand 25CFU/g of molds and yeasts. The lemon fiber has:81.3% crude fiber, 3.71% moisture, 12.6% WHC, pH 3.98,165CFU/g aerobic mesophilic bacteria and 90CFU/g ofmolds and yeasts.Pure strains of B. bifidum CECT 870, L. casei CECT 475

and L. acidophilus CECT 903 were obtained from theSpanish Culture Collection (Burjassot, Valencia). Forpropagation sterile 10mL aliquots of the Man RogosaSharpe (MRS) broth were inoculated and incubated at30 1C for L. casei and at 37 1C for L. acidophilus. Forpropagation of bifidobacteria, sterile MRS broth wassupplemented with 0.05% L-cysteine to provide anaerobiccondition and stimulate their growth (Ravula and Shah,1998); inoculated vials were also introduced inside anaero-bic jars for incubation at 37 1C. Incubation time was about72 h. The activated microorganisms after three successivetransfers were used for the trials. Starter commercialyogurt cultures contained S. thermophilus and L. delbrueck-

ii subsp. bulgaricus (Ezals MY900; Rhodia Food, Sasse-nage, France).Skim milk powder used had 34% protein, 52% lactose,

1% fat, 6.8% ash and 5.2% moisture (Central LecheraAsturiana, CAPSA, Granda-Siero, Spain). Deionisedwater was used to reconstitute the milk powder. For allthe tests the same batch of skim-milk powder was used.Culture media and supplements used were: bacteriologi-

cal peptone, MRS broth and MRS agar (Cultimed,Panreac, Castellar del Valles, Barcelona, Spain), M-17and MRS fermentation broth (Scharlau, Barcelona,Spain); D-sorbitol (Acros Organics, Geel, Belgium);L-cysteine, NNLP (nalidixic acid, neomycine sulfate,lithium chloride, paromycine sulfate) and vancomycine(Sigma Chemical Co., St Louis, MO).

2.2. Survival of probiotic bacteria in a model system

Sterile 50mL aliquots of MRS broth (control), MRSbroth with 1% OF and MRS broth with 1% LF wereinoculated with each individual probiotic bacteria. Eachmicroorganism was always incubated at their recom-mended conditions, after 72 h of incubation flasks werecooled and stored at 4 1C. Counts on MRS agar and pHwere determined at days 1, 5, 10, 20 and 40 of cold storage.The whole experiment was run in triplicate, samples wereanalyzed in duplicate.

2.3. Comparison of counts of probiotic bacteria: MRS agar

vs selective enumeration media

Up to this point only work with pure cultures had beencarried out, and so MRS agar had been used for bacterial

ARTICLE IN PRESSE. Sendra et al. / Food Microbiology 25 (2008) 13–21 15

enumeration. From now on mixed cultures (yogurt starterswith individual probiotics) were going to be tested, sowe decided to compare counts of pure cultures ofprobiotic bacteria on MRS agar compared to thoseobtained on selective media. Media to be used andincubation conditions were: MRS-vancomycine at 37 1Cfor 72 h and anaerobiosis for counts of L. casei CECT 475(Tharmaraj and Shah, 2003), MRS-D-sorbitol at 45 1C for72 h and anaerobiosis for L. acidophilus CECT 903(Tharmaraj and Shah, 2003), MRS-NNLP at 37 1C and72 h and anaerobiosis for B. bifidum CECT 870 (Dave andShah, 1996).

2.4. Survival of starter cultures and probiotic bacteria in

fermented milks containing citrus fibers

Procedure to prepare fermented milk: skim milk powderwas reconstituted with water at 12% total solids and 10%sugar was added. Fiber powders were weighed anddistributed into 500mL Pyrexs flasks (3 g to each flask)except for control yogurts. 200mL of milk were pouredinto the flasks and were pasteurized at 80 1C for 30min.Pasteurization was ended by immersion of the flasks in ice-water baths. When 43 1C was reached, the yogurt starterculture was added and the flasks were gently shaken andbrought to incubation at 43 1C till pH 4.7 was obtained, atthat moment gels were cooled down in a cabinet with airconvection at 4 1C.

The probiotic cultures were prepared separately, andthen added into the yogurt, in order to obtain high countsof probiotic bacteria and avoid microbial competition withthe starter cultures. 100mL aliquots of skimmed milk (12%total solids) were pasteurized at 80 1C for 30min andcooled down to 40 1C. Individual probiotic bacteria wereinoculated and incubated at their corresponding optimumgrowing temperature: 30 1C for L. casei, 37 1C forL. acidophilus and for Bifidobacteria enrichment milk wasadded 0.05% L-cysteine and afterwards incubated underanaerobic conditions. The cultured milks were incubateduntil the onset of gelation (approximately 38 h).

Finally, pure cultures of probiotic bacteria (100mLaliquots) were added to the fermented milk flasks (alreadycontaining 200mL of fermented milk) and gently shaken.Flasks containing 300mL of probiotic fermented milk(final fiber dose 1%) were obtained and stored at 4 1C. So,three types of fermented milk (control, OF and LF)inoculated with three individual probiotic cultures (L. casei

CECT 475, L. acidophilus CECT 903, B. bifidum CECT870) were sampled at days 1 and 30 of cold storage. Thewhole experiment was run in triplicate and samples wereanalyzed in duplicate.

Counting of S. thermophilus was done in M17 agar andaerobic incubation at 37 1C for 48 h (Dave and Shah, 1996)and counting of L. delbrueckii ssp. Bulgaricus, in MRS pH5.2 and anaerobic incubation at 45 1C for 72 h (Tharmarajand Shah, 2003).

2.5. pH

pH was determined by means of a pH meter GPL 21Crison (Alella, Spain).

2.6. Sensory evaluation

Sensory analysis was run on 2 and 30 days storedfermented milks, except for those containing B. bifidum,which were not evaluated as the L-cysteine added toenhance its growth provokes a strong sulfur-like odor.Panelists (30) were members of the staff and students of theMiguel Hernandez University, Alicante, Spain. All sensorywork was carried out in the sensory laboratory at theUniversity, which fulfills requirements according to theInternational Standards (ISO, 1988). During evaluation,the panelists were situated in private booths underincandescent light, with an intensity of approximately350 lx. Tap water was provided between samples to cleansethe palate. White plastic cups with 40mL of fermentedmilks at 10 1C were provided. Six samples were evaluated ineach session. The sample presentation order was rando-mized for each panelist. A total of five sessions were run.A seven-point scale (from imperceptible to extremely high)was used to rate the following parameters: citrus aroma,citrus flavor, off-flavors, acidity, creaminess and fibercontent. A seven-point hedonic scale was used to evaluateproduct acceptability.

2.7. Data processing

SPSS 14.0 (Chicago, IL, USA) for Windows was used.General Lineal Model procedures and Tukey test formeans comparison were used for the statistical analysisof data.

3. Results and discussion

3.1. Survival of probiotic bacteria in a model system

containing citrus fibers

All the containers used in the present experiments werePyrexs flasks. Glass containers are always preferred overplastic cups for the storage of fermented milks, as probioticviability is about 30–70% higher when stored in glassbottles than in plastic cups (Shah, 2000). The main reasonfor that is the lower oxygen permeability of glass comparedto plastic cups that helps in maintaining microaerophilicor anaerobic conditions.In general, the viability of all probiotics in MRS broth

decreased during refrigerated storage (Figs. 1–3).B. bifidum CECT 870: pH of citrus fiber enriched MRS

broth was lower than that of control (Table 1). Storagetime did not significantly (P40.05) affect pH. Fiberaddition by itself may contribute to some decrease but anincreased metabolic activity of the Bifidobacteria wouldalso have contributed to the dramatic pH decrease.

ARTICLE IN PRESS

1.00E+00

1.00E+01

1.00E+02

1.00E+03

1.00E+04

1.00E+05

1.00E+06

1.00E+07

1.00E+08

1.00E+09

0 5 10 15 20 25 30 35 40 45

Storage time (days)

CF

U/g

Orange fiber Lemon fiber Control

Fig. 1. Evolution of counts of Bifidobacterium bifidum CECT 870 kept in

MRS (0.05% cysteine) broth enriched with 1% citrus fibers and stored at

4 1C for 40 days.

1.00E+01

1.00E+02

1.00E+03

1.00E+04

1.00E+05

1.00E+06

1.00E+07

1.00E+08

1.00E+09

0 5 10 15 20 25 30 35 40 45

Storage time (days)

CF

U/g

Orange fiber Lemon fiber Control

Fig. 2. Evolution of counts of Lactobacillus acidophilus CECT 903 kept in

MRS broth enriched with 1% citrus fibers and stored at 4 1C for 40 days.

1.00E+05

1.00E+06

1.00E+07

1.00E+08

1.00E+09

1.00E+10

1.00E+11

0 5 10 15 20 25 30 35 40 45

Storage time (days)

CF

U/g

Orange fiber Lemon fiber Control

Fig. 3. Evolution of counts of Lactobacillus casei CECT 475 kept in MRS

broth enriched with 1% citrus fibers and stored at 4 1C for 40 days.

Table 1

pH evolution of a culture of Bifidobacterium bifidum CECT 870 in MRS

broth (0.05% cysteine) enriched with 1% citrus fibers and stored at 4 1C

for 40 days (n ¼ 9)

Storage time

(days)

Orange fiber Lemon fiber Control

Mean Standard

error

Mean Standard

error

Mean Standard

error

1 4.89 70.27 4.63 70.18 5.22 70.03

5 5.01 70.26 5.00 70.22 5.58 70.06

10 4.75 70.18 4.77 70.14 5.40 70.01

20 4.80 70.16 4.89 70.15 5.62 70.05

40 4.77 70.08 4.90 70.11 5.65 70.05

Table 2

pH evolution of a culture of Lactobacillus acidophilus CECT 903 in MRS

broth enriched with 1% citrus fibers and stored at 4 1C for 40 days (n ¼ 9)

Storage time

(days)

Orange fiber Lemon fiber Control

Mean Standard

error

Mean Standard

error

Mean Standard

error

1 3.95 70.03 3.95 70.03 4.95 70.01

5 4.06 70.07 4.05 70.01 5.16 70.05

10 3.99 70.02 4.05 70.01 5.13 70.01

20 4.01 70.04 4.08 70.01 5.11 70.05

40 3.96 70.09 3.99 70.07 5.15 70.12

Table 3

pH evolution of a culture of Lactobacillus casei CECT 475 in MRS broth

enriched with citrus fibers and stored at 4 1C for 40 days (n ¼ 9)

Storage time

(days)

Orange fiber Lemon fiber Control

Mean S.E. Mean S.E. Mean S.E.

1 3.65 70.04 3.68 70.05 3.72 70.05

5 3.84 70.01 3.85 70.02 3.88 70.01

10 3.71 70.02 3.71 70.04 3.78 70.03

20 3.86 70.02 3.88 70.03 3.96 70.04

40 3.87 70.01 3.93 70.01 4.02 70.03

E. Sendra et al. / Food Microbiology 25 (2008) 13–2116

However, pH values were always over 4.5 which is thecritical value for Bifidobacteria survival (Vinderola et al.,2002). Dissolved oxygen and acidity are reported to be thekey factors for Bifidobacteria survival (Dave and Shah,1997).

Commercial shelf life of fermented milks is about 28days, at this time B. bifidum CECT 870 viability was quitelow (Fig. 1): in LF media their populations were reduced1 logCFU/mL whereas in OF media populations increased3 logCFU/mL when compared to control values.

L. acidophilus CECT 903: pH of MRS broth containingL. acidophilus presented the same behavior as that of

Bifidobacteria (Table 2). LF and OF addition significantlyenhanced L. acidophilus viability (Fig. 2), the increasedsurvival rate ranged from 1 to 2 logCFU/mL. Fiber-enriched MRS broth maintained L. acidophiulus countsover 6 logCFU/mL for at least 10 days, whereas at 5 daysof cold storage control media counts were below thistarget.

L. casei CECT 475: pH slightly decreased with fiberaddition (Table 3). Metabolic activity of L. casei wasprobably similar in all MRS broths. Since there was nosignificant difference (P40.05) in pH or decline in pHvalues among batches during storage, it was unlikely thatthese changes would have affected the viability of L. casei

probiotics due to termination pH. Citrus fiber additionsignificantly (Po0.05) increased L. casei survival, which

ARTICLE IN PRESS

Table 4

Counts of probiotic bacteria in milk obtained on MRS agar and selective media (n ¼ 6)

Probiotic microorganism Culture media and conditions Mean S.E.

Lactobacillus casei MRS: at 30 1C, 72 h 2.73E+09 73.90E+08

MRS-vancomycine: at 37 1C, 72 h anaerobiosis 2.97E+09 71.10E+08

Lactobacillus acidophilus MRS: at 37 1C, 72 h anaerobiosis 1.85E+08 73.50E+07

MRS-D-sorbitol: at 45 1C, 72 h anaerobiosis 3.89E+07 75.00E+05

Bifidobacterium bifidum MRS-0.05% L-cysteine: at 37 1C, 72 h 1.09E+07 71.00E+05

MRS-NNLP: at 37 1C, 72 h anaerobiosis 9.25E+06 75.50E+05

E. Sendra et al. / Food Microbiology 25 (2008) 13–21 17

were always over 8 logCFU/mL during 40 days of coldstorage, 1 unit higher than control counts (Fig. 3).

3.2. Counts of probiotic bacteria: MRS agar vs selective

enumeration media

Selective media was going to be used for the nextexperiment. So we decided to evaluate the differences in thecounts of probiotic bacteria in MRS and selective media(Table 4). MRS-vancomycine allowed the recovery ofeven more colonies of L. casei than MRS: 108.79%.MRS-NNLP also showed a good performance, 84.86% ofthe counts of Bifidobacteria detected in MRS. MRS-sorbitol only allowed the recovery of 21.02% of theL. acidophilus counted in MRS. It is well known that thereis no general accepted or fully adequate selective media formost of the probiotic bacteria (Dave and Shah, 1996; Shah,2000; Masco et al., 2005).

3.3. Survival of starter cultures and probiotic bacteria in

fermented milks containing citrus fibers

Based on the available published data, we decided todevelop a liquid probiotic fermented milk as Lin et al.(2006) reported that the viable cell densities of probioticbacteria in liquid products were higher than those in thesolid products. Probiotics were grown as sole starters asShah (2000) recommended a two-step fermentation proce-dure in order to obtain high counts of probiotics and avoidthe inhibitory effect of hydrogen peroxide and acids on theprobiotic bacteria. When probiotic strains were used ontheir own to obtain fermented milk with high counts ofprobiotic bacteria, the acidification was slow (about 38 h)as has been previously reported by Saxelin et al. (1999).

B. bifidum CECT 870: Milk was supplemented with0.05% L-cysteine to favor the growth of B. bifidum asGuler-Akin and Akin (2007) recommended cysteine addi-tion and incubation lower than 43 1C for the manufactureof bio-yogurt. Dave and Shah (1998) reported that theaddition of cysteine adversely affected the viability ofS. thermophilus but in our study such inhibition was notevident (Table 5). Surprisingly, all microbial populationsincreased after 30 days of storage compared to the firstday. Counts were always higher (but not significantly) in

fiber-enriched fermented milks although pH was below 4.5and in control yogurt pH was over 4.7. Vinderola et al.(2002) reported that pH 4.5 or lower negatively affects thecell viability of bifidobacteria in yogurt at 5 1C. Counts infermented milks were much higher than those in MRSbroth after 30 days; it seems that yogurt starter culturesfavored the growth of B. bifidum CECT 870. Dave andShah (1997) stated that S. thermophilus has antagonisticeffect(s) on the growth of Bifidobacteria. Shankar andDavies (1976) reported that B. bifidum grows better in thepresence of L. bulgaricus due to their symbiotic relation.The free amino acids resulting from the proteolytic activityof L. bulgaricus may promote the growth of Bifidobacteria(Singh et al., 1980).Several authors have studied the interactions among

Bifidobacteria and commercial fibers in probiotic fermen-ted milks: Varga et al. (2006) reported that the presenceof inulin at 1–5% (w/v) did not influence significantly(P40.05) the survival rates of either S. thermophilus orL. acidophilus. However, the addition of inulin at 5% (w/v)had a significant beneficial effect (Po0.05) on the viabilityof Bifidobacteria after 28 days of refrigerated storage. Thelargest increase in Bifidobacteria was seen on xylo-oligosaccharides and lactulose, the largest in Lactobacilli was onfructooligosaccharides (Rastall and Maitin, 2002). Martı-nez-Villaluenga et al. (2006) observed that RFOs extractedfrom lupin seeds had beneficial effects on the survival ofB. lactis Bb-12 and L. acidophilus La-5 in fermented milkduring 21 days of storage in refrigerated probioticfermented milk. However, the refrigerated storage de-creased significantly the viable cell counts of probioticbacteria.The inhibitory effect of LF on B. bifidum that was

observed in the experiment in MRS broth was not detectedin fermented milk. Counts of Bifidobacteria were alwaysbelow 6 logCFU/mL. Carr and Ibrahim (2005) evaluatedthe viability of Bifidobacteria among commercial bio-yogurts and reported counts ranging from 0.0 to 6.0 logCFU/mL, 76% of the samples were found to contain viablecultures. Masco et al. (2005) reported that by conventionalcultivation, 70.7% of the commercial bio-yogurts analyzedwere found to contain culturable Bifidobacteria whereasby culture-independent qualitative analysis members ofthe genus Bifidobacterium could be detected in 96.5%

ARTICLE IN PRESS

Table 5

pH and average microbial counts of fermented milk containing Bifidobacterium bifidum CECT 870

Storage

time (days)

Type of

yogurt

S. thermophilus L. delbrueckii subsp.

bulgaricus

B. bifidum CECT 870 pH

Mean Standard

error

Mean Standard

error

Mean Standard

error

Mean Standard

error

1 Orange

fiber

5.38E+07 76.00E+05 8.15E+05 73.50E+04 4.25E+03 76.50E+02 4.37 70.001

Lemon fiber 4.65E+06 71.65E+06 4.05E+05 71.50E+04 2.20E+03 73.00E+02 4.34 70.003

Control 3.10E+06 72.83E+05 6.68E+05 74.40E+04 1.65E+03 71.50E+02 4.72 70.001

30 Orange

fiber

4.40E+08 71.50E+08 9.40E+05 72.00E+04 2.20E+05 75.00E+03 4.26 70.003

Lemon fiber 9.45E+07 72.50E+06 8.80E+05 72.00E+04 2.08E+05 72.00E+03 4.26 70.003

Control 5.22E+07 71.00E+06 7.05E+05 71.15E+05 1.73E+05 77.50E+03 4.71 70.002

Table 6

pH and average microbial counts of fermented milk containing Lactobacillus acidophilus CECT 903

Storage

time (days)

Type of

yogurt

S. thermophilus L. delbrueckii subsp.

bulgaricus

L. acidophilus CECT 903 pH

Mean Standard

error

Mean Standard

error

Mean Standard

error

Mean Standard

error

1 Orange

fiber

6.80E+08 71.40E+08 4.57E+07 76.70E+06 2.55E+07 75.90E+06 4.41 70.001

Lemon fiber 4.70E+08 76.00E+07 5.42E+07 74.39E+07 3.13E+07 73.30E+06 4.33 70.009

Control 8.90E+07 72.00E+06 2.13E+07 75.75E+06 2.07E+07 74.15E+06 4.60 70.003

30 Orange

fiber

2.90E+08 72.00E+07 1.26E+07 76.00E+05 1.20E+07 73.00E+05 4.27 70.003

Lemon fiber 3.40E+08 78.00E+07 1.86E+07 76.00E+05 9.20E+06 75.00E+05 4.31 70.002

Control 1.40E+07 71.90E+06 9.65E+06 75.00E+04 8.85E+06 74.50E+05 4.54 70.003

E. Sendra et al. / Food Microbiology 25 (2008) 13–2118

of the analyzed products. So, there is a possibility that realcounts may be higher. Further studies may be directed toincrease Bifidobacteria viability, may be through increasinginoculum’s dose or microencapsulation. Kailasapathy(2006) observed that microencapsulation increased survivalof L. acidophilus and B. lactis by 2 and 1 log cell numbers,respectively. Kailasapathy and Masondole (2005) reportedthat microencapsulation did not offer protection to theprobiotic bacteria L. acidophilus DD 910 and B. lactis DD920 in feta cheese.

L. acidophilus CECT 903: Counts of L. acidophilus wereover 6 logCFU/mL in all evaluated samples (Table 6) andpH values were higher for control fermented milks.Donkor et al. (2006) reported that Lactobacilli strainsshowed a good cellular stability maintaining constantconcentration throughout storage period regardless oftermination pH. Counts of all three evaluated populationswere slightly lower in control than in fiber-enrichedfermented milks (although not significantly). The combina-tion of L. acidophilus with yogurt starter cultures clearlyenhanced its growth as counts in fermented milk weremuch higher than in MRS broth at 30 days. Whenprobiotics are mixed with yogurt cultures, higher levels of

essential growth factors in the form of peptides and aminoacids in the yogurts may have promoted the growth ofL. acidophilus and sustained the growth of B. lactis andLactobacillus paracasei (Donkor et al., 2006).The interaction of L. acidophilus with several fibers and

fiber extracts has also been studied by several authors:Desai et al. (2004) tested several prebiotic substancesand observed best viability of Lactobacilli with inulinand raftilose whereas lactulose was the least effectivein maintaining viability. Hi-maize was also tested. Thecontrol samples containing no prebiotics had averagesurvival rate of 33% at 28 days of cold storage. Additionof prebiotics improved the growth rates and decreasedfermentation time, there was also slight improvement insurvival rate with prebiotics. Survival of Lactobacilli wasstrain specific. Ozer et al. (2005) successfully used lactuloseand inulin as growth promoters for B. bifidum andL. acidophilus to keep probiotic counts over 107 during coldstorage. Lactulose did not promote the viability of Lactoba-

cillus spp. Gokavi et al. (2005) in an oat-based symbioticbeverage containing 0.9% dietary fiber observed thatL. plantarum and L. casei survived for 10 weeks whereasL. acidophilus survived for about 4 weeks over 107CFU/g.

ARTICLE IN PRESSE. Sendra et al. / Food Microbiology 25 (2008) 13–21 19

L. casei CECT 475: Counts of all microbial populationswere over 6 logCFU/mL in L. casei containing probioticfermented milks except for L. delbrueckii subsp. bulgaricus

in LF and control samples after 1 day of storage (Table 7)and all populations increased after 30 days of cold storage,probably due to synergisms among microbial populations.No significant differences were detected among pH due tostorage time or fiber presence. L. casei CECT 475 was thebest-performing probiotic bacteria judging from its highestcounts in all the experiments.

3.4. Sensory analysis

Sensory evaluation results of probiotic milks containingL. casei and L. acidophilus are presented in Table 8. Therewere significant differences (Po0.05) in citrus aroma andflavor as well as fiber content perception between controland fiber added yogurts, whereas no differences were dueto the probiotic bacteria used. There was a tendency (notsignificant P40.05) to increase citrus aroma and flavor

Table 7

pH and average microbial counts of fermented milk containing Lactobacillus

Storage

time (days)

Type of

yogurt

S. thermophilus L. delbrueckii su

bulgaricus

Mean Standard

error

Mean S

e

1 Orange

fiber

6.00E+07 71.00E+06 1.30E+06 7

Lemon fiber 4.65E+07 71.65E+06 9.65E+05 7Control 3.82E+07 73.80E+06 5.00E+05 7

30 Orange

fiber

1.10E+09 71.50E+08 1.08E+08 7

Lemon fiber 9.80E+08 74.00E+07 9.65E+07 7Control 1.17E+08 74.50E+06 4.85E+06 7

Table 8

Scores obtained by sensory evaluation of probiotic-fermented milks with lemo

Type Citrus aroma Citrus flavour C

2 days 30 days 2 days 30 days 2

L. casei control 0.23a

(0.16)�0.36a

(0.28)

1.17a

(0.97)

1.21a

(0.76)

2

(

L. casei lemon 2.76b

(0.65)

3.43b

(0.63)

3.56b

(0.84)

3.83b

(0.71)

1

(

L. casei orange 3.55b

(0.95)

3.96b

(0.87)

3.99b

(0.85)

4.12b

(0.93)

2

(

L. acidophilus control 0.27a

(0.16)

0.32a

(0.23)

0.97a

(0.57)

1.03a

(0.79)

2

(

L. acidophilus lemon 2.76b

(0.90)

3.63b

(0.78)

3.47b

(0.63)

3.75b

(0.98)

1

(

L. acidophilus orange 3.65b

(0.98)

4.12b

(0.89)

3.67b

(0.87)

3.96b

(0.93)

2

(

Mean values for each parameter (combining 2 and 30 days) with different sup�Values in parentheses denote standard deviation.

perception after 30 days of storage, probably due to thediffusion of compounds from the fiber. The perception ofcitrus flavor tended to be higher than that of citrus aroma.Acidity and off flavors did not show significant differencesdue to any of the studied variables and presented averagevalues of 3.53 (S.D. ¼ 1.21) and 1.58 (S.D. ¼ 0.72),respectively, the results are not presented in the table.Creaminess perception was highest in control probioticmilks (Po0.05), storage time also enhanced the perceptionof creaminess whereas no effect could be attributed toprobiotic bacteria. Fiber particles may be responsible forthe reduced creaminess of fiber-fermented milks. Thefermentation process which includes pH decrease andformation of exopolysaccharides may be responsible forthe increased creaminess of fermented milks stored for 30days. Garcıa-Perez et al. (2006) reported by instrumentaland sensory analysis, increased viscosity with storage timein orange fiber-enriched yogurts. Fiber content and overallacceptability are quite balanced as fiber and sugar contentsas well as yogurt cultures had been previously established

casei CECT 475

bsp. L. casei CECT 475 pH

tandard

rror

Mean Standard

error

Mean Standard

error

1.00E+05 1.11E+08 71.00E+06 3.99 70.001

1.50E+04 9.90E+07 72.50E+05 4.01 70.003

1.00E+05 9.92E+07 71.50E+05 4.16 70.001

2.00E+06 3.04E+08 76.80E+07 3.92 70.003

1.50E+06 1.93E+08 75.50E+06 3.97 70.003

3.50E+05 1.42E+08 73.50E+06 4.00 70.003

n and orange fibers at days 2 and 30 after manufacture (1–7 points)

reaminess Fiber content Overall acceptability

days 30 days 2 days 30 days 2 days 30 days

.82b

0.44)

3.32b

(0.39)

0.80a

(0.62)

0.69a

(0.34)

5.22a,b

(0.19)

5.48b

(0.18)

.98a

0.52)

2.47b

(0.51)

3.91b

(0.73)

3.78b

(0.93)

5.03a

(0.21)

5.36b

(0.27)

.10a

0.54)

2.67b

(0.49)

3.55b

(0.82)

3.42b

(0.87)

5.43b

(0.24)

6.01c

(0.18)

.72b

0.44)

3.19b

(0.53)

0.76a

(0.39)

0.71a

(0.31)

5.13a,b

(0.18)

5.59b

(0.28)

.78a

0.55)

2.39a,b

(0.61)

3.71b

(0.89)

3.56b

(0.91)

4.78a

(0.23)

5.23a,b

(0.24)

.03a

0.64)

2.94b

(0.37)

3.63b

(0.96)

3.47b

(1.02)

4.96a

(0.28)

5.79b,c

(0.23)

erscript letters (a, b, c) are significantly different (Po0.05).

ARTICLE IN PRESSE. Sendra et al. / Food Microbiology 25 (2008) 13–2120

based on sensory studies (Garcıa-Perez et al., 2005, 2006).All types of fermented milks received average scores of atleast 4.78 on a seven-point scale. Orange enrichedfermented milks got the best results for overall accept-ability followed by control and lemon milks. It has to bepointed out that acceptability increased with storage timeand that is probably due to the increased perception ofcreaminess.

4. Conclusions

Citrus fibers enhanced L. acidophilus CECT 903 andL. casei CECT 475 survival in MRS broth duringrefrigerated storage, but uneven results were obtained forB. bifidum CECT 870. OF enhanced its growth and LF hadinhibitory effect. Populations of probiotic bacteria de-creased with storage time in MRS broth. The combinationof yogurt starter cultures and the tested probiotic bacteriaresulted in a symbiotic interaction that favored the growthand survival of all probiotic bacteria in fermented milks.Citrus fiber presence in fermented milks also enhancedbacterial growth and survival of the tested probioticbacteria. This study indicates that citrus fiber-enrichedfermented milks are good vehicles for a variety ofcommercial probiotics, as proved by bacterial counts andsensory scores, but survival of B. bifidum will need to beimproved and the use of L-cysteine suppressed or reducedto avoid off-flavors.

Acknowledgment

The financial support by Bancaja-UMH through theProject ‘‘seguridad alimentaria y propiedades funcionalesde leches fermentadas formuladas con subproductoscıtricos y bacterias probioticas: interacciones fibra decıtricos-bacterias probioticas’’ is gratefully acknowledged.

References

AOAC, 1995. Official Methods of Analysis, 15th ed. Association of

Official Analytical Chemist, Washington, DC.

Capela, P., Hay, T.K.C., Shah, N.P., 2006. Effect of cryoprotectants,

prebiotics and microencapsulation on survival of probiotic organisms

in yoghurt and freeze-dried yoghurt. Food Res. Int. 39 (2), 203–211.

Carr, J.P., Ibrahim, S.A., 2005. Viability of bifidobacteria in commercial

yogurt products in North Carolina. (2005). Milchwissenschaft 60 (4),

414–416.

Cohn, R., Cohn, A.L., 1997. Subproductos del procesado de las frutas. In:

Arthey, D., Ashurst, P.R. (Eds.), Procesado de frutas. Acribia,

Zaragoza, pp. 213–228.

Dave, R.I., Shah, N.P., 1996. Evaluation of media for selective

enumeration of Streptococcus thermophilus, Lactobacillus delbrueckii

spp. bulgaricus, Lactobacillus acidophilus and Bifidobacterium spp.

J. Dairy Sci. 79, 1529–1537.

Dave, R.I., Shah, N.P., 1997. Viability of yogurt and probiotic bacteria

in yoghurts made from commercial starter culture. Int. Dairy J. 7,

31–41.

Dave, R.I., Shah, N.P., 1998. Ingredient supplementation effects

on viability of probiotic bacteria in yogurt. J. Dairy Sci. 81, 2804–2816.

Desai, A.R., Powell, I.B., Shah, N.P., 2004. Survival and activity of

probiotic Lactobacilli in skim milk containing prebiotics. J. Food Sci.

69 (3), 57–60.

Donkor, O.N., Henriksson, A., Vasiljevic, T., Shah, N.P., 2006. Effect of

acidification on the activity of probiotics in yoghurt during cold

storage. Int. Dairy J. 16 (10), 1181–1189.

FAO, 2006 /www.fao.orgS.

Fernandez-Lopez, J., Fernandez-Gines, J.M., Aleson-Carbonell, L.,

Sendra, E., Sayas-Barbera, E., Perez-Alvarez, J.A., 2004. Application

of functional citrus by-products to meat products. Trends Food Sci.

Technol. 15, 176–185.

Garcıa-Perez, F.J., Lario, Y., Fernandez-Lopez, J., Sayas, E., Perez-

Alvarez, J.A., Sendra, E., 2005. Effect of orange fiber addition on

yogurt color during fermentation and cold storage. Color Res. Appl.

30 (6), 457–463.

Garcıa-Perez, F.J., Sendra, E., Lario, Y., Fernandez-Lopez, J., Sayas, E.,

Perez-Alvarez, J.A., 2006. Rheology of orange fiber enriched yogurt.

Milchwissenschaft 61 (1), 55–59.

Gokavi, S., Zhang, L., Huang, M.-K., Zhao, X., Guo, M., 2005. Oat-

based symbiotic beverage fermented by Lactobacillus plantarum,

Lactobacillus paracasei ssp. casei, and Lactobacillus acidophilus.

J. Food Sci. 70 (4), 216–223.

Guler-Akin, M.B., Akin, M.S., 2007. Effects of cysteine and different

incubation temperatures on the microflora, chemical composition and

sensory characteristics of bio-yogurt made from goat’s milk. Food

Chem. 100 (2), 788–793.

ISO, 1988. International Standard 8589. Sensory analysis general guidance

for the design of test rooms. Ref. No. ISO 8589:1988 (E). International

Organization for Standardization, Geneva.

Izquierdo, L., Sendra, J.M., 2003. Citrus fruits: composition and

characterization. In: Caballero, B., Trugo, L., Finglas, P. (Eds.),

Encyclopedia of Food Sciences and Nutrition. Academic Press,

Elsevier Science Ltd., Oxford.

Kailasapathy, K., 2006. Survival of free and encapsulated probiotic

bacteria and their effect on the sensory properties of yoghurt. Food

Sci. Technol. 39 (10), 1221–1227.

Kailasapathy, K., Masondole, L., 2005. Survival of free and micro-

encapsulated Lactobacillus acidophilus and Bifidobacterium lactis and

their effect on texture of feta cheese. Aust. J. Dairy Technol. 60 (3),

252–258.

Kourkoutas, Y., Bosnea, L., Taboukos, S., Baras, C., Lambrou, D.,

Kanellaki, M., 2006. Probiotic cheese production using Lactobacillus

casei cells immobilized on fruit pieces. J. Dairy Sci. 89 (5), 1439–1451.

Lin, W.-H., Hwang, C.-F., Chen, L.-W., Tsen, H.-Y., 2006. Viable counts,

characteristic evaluation for commercial lactic acid bacteria products.

Food Microbiol. 23 (1), 74–81.

Lourens-Hatting, A., Viljeon, B.C., 2001. Yogurt as probiotic carrier

food. Int. Dairy J. 11, 1–17.

Martinez-Villaluenga, C., Frias, J., Vidal-Valverde, C., Gomez, R.,

2005. Raffinose family of oligosaccharides from lupin seeds as

prebiotics: application in dairy products. J. Food Prot. 68 (6),

1246–1252.

Martınez-Villaluenga, C., Frias, J., Gomez, R., Vidal-Valverde, C., 2006.

Influence of addition of raffinose family oligosaccharides on probiotic

survival in fermented milk during refrigerated storage. Int. Dairy J. 16

(7), 768–774.

Masco, L., Huys, G., De Brandt, E., Temmerman, R., Swings, J., 2005.

Culture-dependent and culture-independent qualitative analysis of

probiotic products claimed to contain bifidobacteria. Int. J. Food

Microbiol. 102 (2), 221–230.

Ozer, D., Akin, S., Ozer, B., 2005. Effect of inulin and lactulose on

survival of Lactobacillus acidophilus LA-5 and Bifidobacterium bifidum

BB-02 in acidophilus–bifidus yogurt. Food Sci. Technol. Int. 11 (1),

19–24.

Perez-Conesa, D., Lopez, G., Ros, G., 2005. Fermentation capabilities of

bifidobacteria using nondigestible oligosaccharides, and their viability

as probiotics in commercial powder infant formula. J. Food Sci. 70 (6),

279–285.

ARTICLE IN PRESSE. Sendra et al. / Food Microbiology 25 (2008) 13–21 21

Rastall, R., Maitin, V., 2002. Prebiotics and synbiotics: towards the next

generation. Curr. Opin. Biotechnol. 13, 490–496.

Ravula, R.R., Shah, N.P., 1998. Viability of probiotic bacteria in

fermented frozen dairy desserts. Food Aust. 50, 136–139.

Saxelin, M., Grenov, B., Svensson, U., Fonden, R., Reniero, R., Mattila-

Sandholm, T., 1999. The technology of probiotics. Trends Food Sci.

Technol. 10, 387–392.

Shah, N.P., 2000. Probiotic bacteria: selective enumeration and survival in

dairy foods. J. Dairy Sci. 83, 894–907.

Shankar, P., Davies, F., 1976. Associative bacterial growth in yogurt

starters: initial observations on stimulatory factors. J. Soc. Dairy

Technol. 30, 31–32.

Singh, J., Khanna, A., Chandar, H., 1980. Effect of incubation

temperature and heat treatments of milk from milk of cow and

buffalo on acid and flavour production by St. termophilus and L.

bulgaricus. J. Food Prot. 43, 399–400.

Tharmaraj, N., Shah, N.P., 2003. Selective enumeration of Lactobacillus

delbrueckii ssp. bulgaricus, Streptococcus thermophilus, Lactobacillus

acidophilus, Bifidobacteria, Lactobacillus casei, Lactobacillus rhamno-

sus, and Propionibacteria. J. Dairy Sci. 86, 2288–2296.

Trumbo, P., Schlicker, S., Yates, A., Poos, M., 2002. Dietary

reference intakes for energy, carbohydrate, fiber, fat, fatty acids,

cholesterol, protein, and amino acids. J. Am. Diet. Assoc. 102 (11),

1621–1630.

Varga, L., Szigeti, J., Gyenis, B., 2006. Influence of chicory inulin

on the survival of microbiota of a probiotic fermented milk during

refrigerated storage. (2006). Ann. Microbiol. 56 (2), 139–141.

Vinderola, C.G., Mocchiutti, P., Reinheimer, J.A., 2002. Interactions

among lactic acid starter and probiotic bacteria used for fermented

dairy products. J. Dairy Sci. 85, 721–729.