Double use of concentrated sweet whey for growth and spray drying [612760]

Double use of concentrated sweet whey for growth and spray drying
of probiotics: Towards maximal viability in pilot scale spray dryer
Song Huanga,b, Serge M /C19ejeanb, Houem Rabahb, Anne Dolivetb, Yves Le Loirb,
Xiao Dong Chena,**,G w /C19ena€el Janb, Romain Jeantetb,a,*, Pierre Schuckb
aSuzhou Key Lab of Green Chemical Engineering, School of Chemical and Environmental Engineering, College of Chemistry, Chemical Engineering and
Material Science, Soochow University, Suzhou Industrial Park 215123, Jiangsu, China
bUMR1253 STLO, Agrocampus Ouest, INRA, F-35042 Rennes, France
article info
Article history:Received 29 July 2016Received in revised form10 October 2016Accepted 14 October 2016Available online 15 October 2016
Keywords:
ProbioticsSpray-drying
Multi-stage drying
Sweet wheyStorageSimulated digestionabstract
Spray-drying is expected to be a cost-ef ficient way to produce probiotic powders. Indeed, a novel
simpli fied process was recently reported, using concentrated sweet whey (30 wt %) as a sole medium for
both growth and spray drying of probiotics. The feasibility of scaling up this process was validated in the
present work with a semi industrial pilot scale spray dryer. A multi-stage mild-conditions drying process,
coupling spray-drying with belt drying and fluid-bed drying, was also applied in this work, in which the
final probiotic survival was improved to approximately 100% ( >109CFU g/C01). The change of probiotic
viability in the powders was monitored during a 6-month storage, which indicated that storage tem-
perature and moisture content of powders play crucial roles in the stability of probiotic powders.
Moreover, spray-drying afforded a strain-dependent enhancement of bacterial tolerance in simulatedintestinal fluid, in comparison with fresh cultures.
©2016 Published by Elsevier Ltd.
1. Introduction
Probiotics are live microorganisms which, when administered in
adequate amounts, confer a bene ficial health effect on the host
(FAO/WHO, 2001 ). Probiotic products are highly demanded
because of the increasing market in the current era, in which pro-
biotic powders are preferred by industries, due to their storage
stability and convenience for both transport and incorporation
within various foods. The speci fic functionality of probiotic strains
is suggested to depend on the adequate ingested dose ( Johansson
et al., 2015; Zhu et al., 2014 ). Hence, high viability of probiotics is
desired when developing probiotic powders. To preserve probiotic
viability during production, long-term storage and digestion thus
become a challenge in both scienti fic and technical perspectives
(Tripathi and Giri, 2014 ).
Freeze drying is the main method currently employed toproduce dried probiotics. However, considering the high produc-
tion cost and low productivity of freeze drying, spray drying is
expected to be an alternative method for production of probiotic
powders at an industrial scale: indeed, the speci fic energy con-
sumption of spray drying is more than 10 times lower than that of
freeze drying ( Schuck et al., 2013 ). However, the harsh spray drying
conditions, in particular high temperature exposure at the last
stage of drying, limit the applicability of spray drying in probiotic
production ( Fu and Chen, 2011; Peighambardoust et al., 2011 ).
Extensive studies thus have been carried out to find the strategy in
order to improve probiotic viability during spray drying. For
example, pretreatment of bacteria with sub-lethal doses of stress
has been reported to be an effective route to induce bacterial
tolerance against spray drying ( Desmond et al., 2001 ). In addition,
using a protective matrix as a drying medium represents another
strategy to protect bacteria from spray drying ( De Castro-Cislaghi
et al., 2012; Perdana et al., 2014 ). Finally, the drying conditions
can also be moderated through technical innovation or process
optimization, decreasing drying temperature by multi-stage drying
process for instance ( Schuck et al., 2013 ). Despite these advances, it
is worth noting that these strategies were mostly applied at
laboratory-scale, while their validation at pilot or industrial scale
spray drying is rarely reported.*Corresponding author. UMR1253 STLO, 65 rue de Saint-Brieuc, F-35042 Rennes,
France.
**Corresponding author. Soochow University, 199 Ren'ai Road, Suzhou Industrial
Park, Suzhou 215123, Jiangsu, China.
E-mail addresses: xdchen@mail.suda.edu.cn (X.D. Chen), romain.jeantet@
agrocampus-ouest.fr (R. Jeantet).
Contents lists available at ScienceDirect
Journal of Food Engineering
journal homepage: www.elsevier.com/locate/jfoodeng
http://dx.doi.org/10.1016/j.jfoodeng.2016.10.017
0260-8774/ ©2016 Published by Elsevier Ltd.Journal of Food Engineering 196 (2017) 11 e17

In a recent work, a novel process used for spray drying of pro-
biotics was developed by double-use of concentrated sweet whey
(30 wt%) as a sole medium for both growth and spray drying of
probiotic Lactobacillus casei BL23 and Propionibacterium freu-
denreichii ITG P20 ( Huang et al., 2016a ). It was shown that the hy-
pertonic stress in this concentrated sweet whey led to
overexpression of key stress proteins, accumulation of intracellular
storage molecules, of compatible solutes, enhanced multistress
tolerance acquisition, as well as enhanced survival upon spray
drying ( Huang et al., 2016b ). The high solid content of the feed (i.e.
bacterial culture) furthermore facilitated the spray drying process,
making it possible to lower the drying temperature. In the current
paper, the feasibility of scaling up this process is investigated from
lab scale to semi industrial pilot scale. Besides, a previously re-
ported multi-stage spray drying process is applied to further
improve the probiotic viability after drying ( Schuck et al., 2013 ).
The storage stability of probiotic powders, as well as their protec-
tion towards digestion, are also investigated.
2. Materials and methods
2.1. Strains and pre-culture
Lactobacillus casei BL23 was provided by UMR1219 MICALIS,
(INRA-AgroParisTech, Jouy-En-Josas, France) and Propionibacterium
freudenreichii ITG P20 was maintained and pre-cultured by the
CIRM-BIA Biological Resource Center (Centre International de
Ressources Microbiennes-Bact /C19eries d'Int /C19er^et Alimentaire, INRA,
Rennes, France). L. casei was activated by inoculation (1% inoculum
size) in MRS Broth and static cultivation at 37/C14C for 16 h.
P. freudenreichii was activated (1% inoculum size) in YEL broth and
cultivated statically at 30/C14C for 50 h.
2.2. Fermentation with sweet whey
Sweet whey medium with 30 wt% total solid content was pre-
pared by rehydration of sweet whey powder (Lactalis ingredients,
Mayenne, France) in deionized water.
For preparation of starter culture, the 5 L sweet whey was
autoclaved at 100/C14C for 30 min before inoculation of L. casei or
P. freudenreichii . The inoculation (1 v/v% inoculum size) was made
from the above-mentioned pre-culture of L. casei in MRS broth or of
P. freudenreichii in YEL broth. The inoculated sweet whey culture of
L. casei was incubated statically at 37/C14C for 30 h, and
P. freudenreichii at 30/C14C for 72 h. The obtained culture was used as
starter for further fermentation.
Sweet whey medium for fermentation at the semi industrial
pilot scale was prepared in a steel tank (Goavec, Alençon, France) by
rehydrating 150 kg sweet whey powders in 350 kg water to obtain
30 wt% total solid content. The medium was then pumped through
a scraped surface heat exchanger (HRS Heat Exchangers, France) for
heat treatment. The heating temperature and the residence time of
sweet whey medium within the heat exchanger were 120/C14C and
1 min, respectively. The heated sweet whey medium was then
transferred into a 500 L bio-reactor (Goavec, Alençon, France). The
pipes and the bio-reactor were previously treated by steam. Theabove-mentioned 5 L starter culture was inoculated after the
temperature of sweet whey had been cooled down to the setting
growth temperature (i.e. 37
/C14C for L. casei and 30/C14C
P. freudenreichii ). The sweet whey with L. casei was fermented
statically at 37/C14C for 48 h, and P. freudenreichii at 30/C14C for 96 h.
2.3. Spray drying
Before spray drying, the sweet whey probiotic culture wasagitated moderately for 20 min. Three processes of spray drying
were performed for each probiotic strain ( Fig. 1 ). For the lab-scale
spray drying ( Fig. 1 a), 1 L sweet whey culture was pumped to a
Mobile Minor ™spray dryer (GEA Niro A/S, Denmark). A two- fluid
spray nozzle with an ori fice diameter of 0.8 mm was used. The
evaporation rate of this dryer was approximately 3 kg h/C01. The inlet
air temperature was at 140 ±1/C14C, and the outlet air temperature
60±3/C14C.
The one-stage semi industrial pilot scale spray drying ( Fig. 1 b)
was performed in the Bionov spray dryer pilot workshop (Niro
Atomizer, GEA, Saint Quentin en Yvelines, France) based in
Rennes (France). A pressure nozzle with an ori fice diameter
of 0.73 mm was used. The evaporation capacity was approxi-
mately 80 kg h/C01. The drying temperatures were set to the same
values as in minor dryer, namely inlet air temperature at
140±5/C14C and outlet air temperature at 60 ±3/C14C. A belt
(GEA, Saint Quentin en Yvelines, France) and a vibro- fluidizer
(GEA, Saint Quentin en Yvelines, France) were used following
the spray drying step ( Fig. 1 b), but respectively for conveying
(turn-off status) and powder cooling purposes in this
configuration.
The multi-stage semi industrial pilot scale spray drying ( Fig. 1 c)
was also performed using the Bionov spray dryer pilot workshop, as
described before ( Schuck et al., 2013 ). Brie fly, the inlet air tem-
perature of spray drying was decreased to 127 ±3/C14C, and the outlet
air temperature 47 ±2/C14C. After spray drying, the partially dried
powder was delivered through the belt dryer at ambient temper-
ature for crystallization purpose. The residence time of powders on
belt was approximately 5 min. Fluid-bed drying was then carried
out in a vibro- fluidizer (VF) with inlet temperature at 80 ±2/C14C and
outlet temperature at 40 ±2/C14C.
2.4. Analysis of physical and chemical properties
For liquid samples, the pH value was measured with a pH-
meter (Ecolab, Issy-l /C18es-Moulineaux, France). Viscosity measure-
ments were performed using an AR 2000 rheometer (TA in-
struments, Guyancourt, France) equipped with coaxial cylindrical
geometry (stator inner radius: 25 mm; rotor outer radius:
23 mm; immersed cylinder height: 30 mm; bottom cap:
4000 mm). Apparent viscosity was determined at 20/C14Cu s i n gt h e
Herschel eBulkley model at a shear rate of 1 s/C01. The water
content of liquid or powder samples was measured according to
the method described by Schuck et al. (2012) :t h es a m p l e
(respectively 5 g for liquid samples and 1 g for powder samples)
was mixed with 25 g pre-dried sand and then dried at 105/C14Cf o r
7 h (liquid samples) or 5 h (powder samples). The water
activity of powders was determined at 25/C14Cu s i n ga na w-meter
(Novasina, a w-center 92T0003) immediately after drying and
cooling.
2.5. Storage of powders
The powders were collected and aliquoted in PA/PE plastic
vacuum bags (La Bovida, France). The bags were then sealed in the
presence of air or under vacuum conditions (Britek, France)respectively. These powders were stored at the controlled tem-
perature of 4
/C14C and 25/C14C and kept away from light.
2.6. In vitro simulated digestion
The effect of spray drying on the probiotic tolerance against
digestion stress was investigated in the in vitro simulated digestion
experiment. The powders obtained from multi-stage drying pro-
cess ( Fig. 1 c; powder 3) were used to compare with the freshS. Huang et al. / Journal of Food Engineering 196 (2017) 11 e17 12

probiotic culture in 30 wt% sweet whey. The powders were rehy-
drated to reconstitute the 30 wt% probiotic suspension. The simu-
lated gastric fluid (SGF) and simulated intestinal fluid (SIF) were
prepared according to Minekus et al. (2014) . In the gastric phase,
the probiotic samples were mixed with SGF (1:1 v/v) containing2000 U/mL porcine pepsin, and incubated at 37
/C14C for 3 h under
agitation. In the intestinal phase, the gastric digesta were mixed
with SIF (1:1 v/v) containing 10 mM porcine bile extract and
porcine pancreatin with 100 U/mL trypsin activity, and incubated at
37/C14C for 3 h under agitation. The pH for the gastric and intestinal
phases were adjusted to 3.0, and 7.0 respectively. The viability of
probiotics during simulated gastric or intestinal digestion were
tested in 1 h interval.
2.7. Enumeration and quanti fication of bacteria
The populations of probiotics in liquid samples were serial
diluted with peptone water (0.1% w/v) and then poured onto agar
plates. MRS agar plates and YEL agar plates were used for L. casei
and P. freudenreichii , respectively. Similarly, the powder samples
were rehydrated by dissolving 3 g of powder in 7 g of peptone water
prior to serial dilution. L. casei was incubated at 37/C14C for 48 h and
P. freudenreichii at 30/C14C for 6 days under anaerobic conditions for
colony counting (Anaerocult®, Merck KgaA, Germany). The survival
(%) of probiotics was calculated as:
Survival¼Nt
N0/C2100
where N tand N 0(CFU/g) refer to the bacteria population after
corresponding treatments, i.e. spray drying or simulated digestion
treatment, and to the initial population before treatments,
respectively.
Besides, total thermophilic and coliform flora populations were
evaluated according to the methods described previously ( Schuck
et al., 2013 ).2.8. Statistical analysis
All the results displayed in this work were obtained from trip-
licate samples. The results are presented as mean value with
standard deviation. The analysis of variance (ANOVA) followed byTukey test was performed using R software with the ‘Rcmdr ’
package (R Development Core Team). Differences between mean
values were considered signi ficant when p <0.05.
3. Results and discussion
3.1. Fermentation of probiotics
The bacterial populations of L. casei and P. freudenreichii after
fermentation in 500 L 30% sweet whey were (1.6 ±0.1)/C210
9and
(5.0±0.6)/C2109CFU mL/C01, respectively. These results are in
agreement with our previous work at laboratory-scale (1 e2 L): it
validates that the two probiotic strains are able to yield high
biomass production at a semi industrial pilot scale when cultivated
in 30 wt% sweet whey without casein peptone supplementation
(Huang et al., 2016a ). Besides, the viscosity of sweet whey signi fi-
cantly decreased after being fermented by both probiotic strains
(Table 1 ), due to the lactose consumption during fermentation,
subsequent transfer of matter to the biomass and last biomass
decantation. More speci fically, the large amount of lactose, which
contributes considerably to the viscosity of sweet whey, was mainly
metabolized into lactic acid and propionic acid by L. casei and
P. freudenreichii , respectively. The control of the viscosity of feed at a
given total solid content is generally desired by industries in order
to facilitate atomization during spray drying ( Cal and Sollohub,
2010 ).
3.2. Spray drying of probiotics in different processes
Spray drying was carried out in three different processes as
illustrated in Fig. 1 . The powders obtained from the semi industrial
Fig. 1. The schematic diagram of three drying process: (A) Lab-scale spray drying (for obtaining Powder 1), (B) Semi industrial pilot scale one-stage spray d rying (for obtaining
Powder 2) and (C) Semi industrial pilot scale multi-stage spray drying (for obtaining Powder 3).S. Huang et al. / Journal of Food Engineering 196 (2017) 11 e17 13

pilot scale process and lab-scale drying were non-signi ficantly
different regarding water content and water activity, except for
the water content of P. freudenreichii powder 3 (Table 1 ). It may be
caused by the variation of drying parameters during process
(Písecký, 2012 ). Nevertheless, the water contents and water activ-
ities were at the whole within a same range, so that the viabilityresults could be compared between different processing shemes.
For the two probiotic strains, the remaining viabilities after lab-
scale and one stage semi industrial pilot scale spray drying ( Fig. 1 a
and b) were non signi ficantly different, the survival being at around
60% for L. casei (remaining population ~1.0 /C210
9CFU g/C01) and 100%
forP. freudenreichii (remaining population ~4.5 /C2109CFU g/C01)
(Fig. 2 ). The comparison between two strains indicated that the
robustness of P. freudenreichii upon spray drying was higher than
that of L. casei . It is known that P. freudenreichii can accumulate
intracellular trehalose, glycogen and polyphosphate, which are
involved in improving bacterial tolerance against heat and/or
desiccation stress ( Anastasiou et al., 2006; Leverrier et al., 2004 ).
This thermotolerance acquisition ability is in agreement with the
ability of P. freudenreichii to withstand harsh conditions of Swiss-
type cheese making, including thermal treatment (52/C14C,
30e60 min) and saline stress caused by immersion (48 e72 h) in
saturated brine. These results were fully consistent with the bac-
terial survival previously obtained at lab-scale spray drying, albeit
survival was further increased due to the lower drying temperature
used in this work ( Huang et al., 2016a ). Therefore, the feasibility of
scaling up the process of using concentrated sweet whey to grow
and spray probiotics is validated by this work.
When using the multi-stage semi industrial pilot scale spray
drying ( Fig. 1 c), the probiotic survival was signi ficantly improved to
approximately 100% (p <0.05) for L. casei , and slightly improved for
P. freudenreichii (p<0.2) ( Fig. 2 ). This process was previouslyconducted on two P.acidipropionici stress-tolerant strains ( Schuck
et al., 2013 ). However and given the robustness of the two
strains, the survival of bacteria was shown to be 100% throughout
the whole process. In this work, the multi-stage semi industrial
pilot scale spray drying was performed for the first time on L. casei ,
which represent commonly commercialized and more fragile pro-biotics. The survival of L. casei was increased from 60% to 100%.
Compared to the traditional one-stage drying, the particles con-
taining probiotics suffered less heat stress (around 13
/C14C lower
outlet temperature) at the first stage of spray drying. Hence the
viability of bacteria should be higher at the end of spray drying, in
comparison to the traditional one stage drying ( Zhang et al., 2016 ).
Although the bacteria experienced another heat stress at the sec-
ond stage of fluid-bed drying (80/C14C inlet temperature and 40/C14C
outlet temperature), the bacterial cells were already embedded in
the partially dried powders. Moreover, it has been reported that the
heat resistance of bacteria in a dry state, especially in the a wrange
of 0.3e0.5, was higher than that of the same bacteria in a wet state
(Laroche et al., 2005; Wang et al., 2016; Zhang et al., 2014 ).
Therefore, this process is more suitable for such heat sensitive
bacteria, in comparison with the traditional one-stage semi in-
dustrial pilot scale spray drying.
In addition to the targeted probiotic strains, thermophillic and
coliform flora populations were also evaluated in the powders after
spray drying as indicators of contamination. Thermophilic and
coliform floras represent common microbiological spoilage in dairy
powders and constitute a major concern in controlling the safety of
foods at industrial scale production ( Breeuwer, 2014; Chandan
et al., 2015 ). As shown in Table 2 , low amount of thermophilic
and coliform floras initially contaminated the sweet whey medium,
despite the heat treatment applied and the previous disinfection of
the equipment: the conditions may not have been strict enough toTable 1
The physical properties of feed concentrates and powders.
Sample pH Viscosity (mPa s) Water Content w/w% Water activity
Heat treated media 6.3 ±0.1 33.0 ±0.2 70.7 ±0.1 e
L. casei culture 4.4 ±0.1 22.0 ±0.4 71.0 ±0.0 e
Powder 1 ee 5.3±0.2a0.27±0.02a
Powder 2 ee 5.2±0.2a0.27±0.01a
Powder 3 ee 5.5±0.1a0.28±0.01a
P. freudenreichii culture 5.7 ±0.0 23.0 ±0.1 71.2 ±0.0
Powder 1 ee 5.0±0.2a0.27±0.01a
Powder 2 ee 5.2±0.1a0.27±0.01a
Powder 3 ee 6.0±0.2b0.30±0.01a
The different superscript indicates the signi ficant difference (p <0.05).
Fig. 2. The bacterial population (refers to column, left Y-axis) and survival (refers to curve, right Y-axis) of (A) L.casei BL23 and (B) P. freudenreichii ITG20 after spray drying.S. Huang et al. / Journal of Food Engineering 196 (2017) 11 e17 14

achieve a fully aseptic medium. However, the bacterial population
of thermophilic and coliform floras kept constant without break out
during probiotic fermentation probably due to the competitive
inhibition ( Verschuere et al., 2000; Wilderdyke et al., 2004 ). After
spray drying, the coliform flora was undetectable in the powders
but the thermophilic flora still remained. This indicates that the
coliform flora is sensitive to spray drying stress, while the ther-
mophilic flora is more resistant during spray drying probably due to
its higher heat resistance. It suggests that the spray drying may be a
means to lower foods contamination by coliform flora. However,
more attention should be paid on controlling the thermophilic flora
during spray drying.3.3. Storage of probiotic powders from different drying processes
Probiotics stability upon storage was compared among the
powders obtained from different drying processes ( Figs. 3 and 4 ).
ForL. casei at 4/C14C, the viability kept constant during the first 2
months. A one log CFU g/C01reduction of viability was reached after 6
months of storage. In contrast, the L. casei viability reduced grad-
ually after 7 days at 25/C14C. Within one month, the viability loss was
around 2 logs CFU g/C01whatever the drying process and scale
considered. After 6 months storage, the L. casei viability remained
at approximately 4 logs CFU g/C01. Moreover, the conditioning envi-
ronment (vacuum or atmosphere) had no signi ficant effect on the
stability of L. casei powders at both 4/C14C and 25/C14C(Fig. 3 ).
Similarly, the viability of P. freudenreichii in powders also kept
constant at 4/C14C for first 2 months and reduced by around 1 log
CFU g/C01after 6 months storage whatever the drying process
considered. However, at this time, the powders from pilot scale
one-stage drying process (P2) displayed slightly better stability
when conditioned under vacuum. At 25/C14C, a larger viability loss
was also observed in all powders, reaching around 5 logs CFU g/C01
after 6 months storage under these conditions. This result high-
lights the predominant in fluence of the storage temperature on the
stability of probiotic powders. Moreover, the P2 powder of
P. freudenreichii stored under vacuum at 25/C14C showed a better
stability in the first 2 months, compared to the P2 powder stored
under atmosphere: indeed, the corresponding viability losses atTable 2
The enumeration of contaminating flora (thermophillic and coliform floras).
Sample Thermophillic flora
(log CFU g/C01)Coliform flora
(log CFU g/C01)
Heat treated media 2.6 ±0.1 2.8 ±0.0
L. casei culture 2.4 ±0.0 2.8 ±0.1
Powder 1 2.6 ±0.0 ND
Powder 2 2.4 ±0.1 ND
Powder 3 2.2 ±0.2 ND
P. freudenreichii
culture1.9±0.6 2.0 ±0.2
Powder 1 1.4 ±0.6 ND
Powder 2 1.4 ±0.6 ND
Powder 3 0.9 ±0.2 ND
ND means undetectable in plate agar counting method.
Fig. 4. The storage stability of P. freudenreichii ITG20 powders at (A) 4/C14C and (B) 25/C14C.Fig. 3. The storage stability of L.casei BL23 powders from different drying processes (expressed as reduction of survival) during 6 month storage at (A) 4/C14C and (B) 25/C14C.S. Huang et al. / Journal of Food Engineering 196 (2017) 11 e17 15

this time were lower than 1 log CFU g/C01and approximately
2 logs CFU g/C01, respectively. By comparison, the viability of
P. freudenreichii in powders was more stable than that of L. casei in
powders. Such a difference may be attributed to the better ability of
P. freudenreichii to accumulate energy and carbon storage com-
pounds such as polyphosphate, trehalose, glycogen, glycine betaine
(Huang et al., 2016b ), as well as its absence of lysis during stationary
phase or in the dormant phase, which allows long-term survival
even under carbon starvation ( Aburjaile et al., 2016; Falentin et al.,
2010 ).
Last, we observed a signi ficant better stability of P. freudenreichii
in P2 powders compared to P3 powders at 6 months storage under
4/C14C and at 2 months storage under 25/C14C. This could be explained
by the detrimental effect of higher water content in P3 powders
(Table 1 )(Teixeira et al., 1995; Vesterlund et al., 2012 ). Besides,
storage under vacuum improved the stability of P. freudenreichii
powders at both 4 and 25/C14C, but not that of L. casei powders. The
reason may be the facultative anaerobic phenotype of L. casei ,
leading to oxidative stress tolerance. However, storage under vac-
uum didn't make it possible to enhance the P. freudenreichii viability
in the P3 powder. It may indicate that the in fluence of moisture is
more detrimental than the oxidation on the stability of probiotic
powders in long-term storage.
3.4. Simulated digestion of probiotic powders
The simulated digestion of probiotic powders from pilot scale
multi-stage drying process (P3 powders) was investigated in
comparison with the fresh 30 wt% sweet whey culture ( Fig. 5 ). The
results showed that both strains were resistant to the simulated
gastric fluid (SGF) within 3 h regardless of the rehydrated or fresh
culture type. It may be explained by the large amount of whey
proteins in concentrated sweet whey, which can protect bacteria
from digestion stress through its buffer effect ( Chen et al., 2006;
Doherty et al., 2011; Tavares et al., 2014 ). Besides, it has also been
previously reported that the osmolality of concentrated sweet
whey could trigger the multi-stress tolerance of bacteria during
growth, leading to the higher survival of bacteria under acid andbile salt stresses ( Huang et al., 2016b ).
However, the viability of two probiotics both decreased gradu-
ally in the simulated intestinal fluid (SIF) within 3 h. It may be
caused by the effects of bile salt and trypsin, since there is barely
lipid in the sweet whey to buffer the bile salt and the whey proteins
would be largely digested. Interestingly, P. freudenreichii powders
showed a stronger tolerance, compared to the fresh culture, during
simulated intestinal digestion ( Fig. 5 D). This enhanced tolerance
however did not emerge on the L. casei strain ( Fig. 5 B). It indicates
that the heat, osmotic or oxidative stress underwent during spray
drying or the desiccate environment in the spray-dried powders
may further trigger the stress tolerance of bacteria and this cellular
stress response may be strain-dependent. This hypothesis however
remains further research.
4. Conclusion
In this work, the double use of concentrated sweet whey for
growth and spray drying of two probiotic bacteria was validated at
the semi industrial pilot scale (500 L fermentation and spray dry-
ing). Indeed, a high viability of probiotics was obtained after spray
drying. The multi-stage drying process was shown to be effective in
further improving the probiotic survival rate, compared to con-
ventional one-stage spray drying. The storage temperature and
powder moisture content were found to be the key factors in flu-
encing the stability of probiotic powders. In addition, spray drying
was found to improve the tolerance of P. freudenreichii against
simulated intestinal fluid. Based on the process proposed in this
work, a new technological route could be developed to produce
probiotic powders in a more sustainable, low cost and productive
way, using spray drying.
Acknowledgements
The authors sincerely thank the joint PhD project between
Agrocampus Ouest and Soochow University. They thank Marie-
No€elle Madec, Garnier-Lambrouin Fabienne, Paulette Amet, Jessica
Musset and Gw /C19enol /C19e Le Maout for their excellent technical support.Fig. 5. The survival of probiotic in 30 wt% fresh culture and powders from Multi-stage drying process (P3), (A) L.casei BL23 in simulated gastric fluid, (B) L.casei BL23 in simulated
intestinal fluid, and (C) P. freudenreichii ITG20 in simulated gastric fluid, (D) P. freudenreichii ITG20 in simulated intestinal fluid.S. Huang et al. / Journal of Food Engineering 196 (2017) 11 e17 16

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