oods
A icle
In luence o Codium omen osum Ex ac in he
P ope ies o Algina e and Chi osan Edible Films
Ana Augus o 1,*ID , Juliana R. Dias 2,3,4, Ma ia J. Campos 1ID , Nuno M. Al es 1, Rui Ped osa 1and
Susana F. J. Sil a 1
1MARE—Ma ine and En i onmen al Sciences Cen e, ESTM, Ins i u o Poli écnico de Lei ia,
2520-641 Peniche, Po ugal; [email p o ec ed] (M.J.C.); [email p o ec ed] (N.M.A.);
[email p o ec ed] (R.P.); [email p o ec ed] (S.F.J.S.)
2Cen e o Rapid and Sus ainable P oduc De elopmen (CDRsp), Ins i u o Poli écnico de Lei ia,
2430-028 Ma inha G ande, Po ugal; [email p o ec ed]
3I3S-Ins i u o de In es igação e Ino ação em Saúde, Uni e sidade do Po o, 4200-135 Po o, Po ugal
4INEB-Ins i u o de Engenha ia Biomédica, Uni e sidade do Po o, 4150-180 Po o, Po ugal
*Co espondence: [email p o ec ed]; Tel.: +351-262-240-200
Recei ed: 26 Janua y 2018; Accep ed: 27 Ma ch 2018; Published: 1 Ap il 2018


Abs ac :
The g owing sea ch o na u al al e na i es o syn he ic ood packaging ma e ials and
addi i es has inc eased, and seaweed ex ac s’ bioac i i y has made hem sui able candida es o
inco po a ion in no el edible ilms. This s udy aims o in es iga e he e ec o Codium omen osum
seaweed ex ac (SE) inco po a ion in algina e and chi osan edible ilms. Algina e- and chi osan-based
ilms wi h and wi hou he inco po a ion o 0.5% SE we e cha ac e ized acco ding o hei physical,
op ical, mechanical, and he mal p ope ies. Seaweed ex ac inco po a ion in chi osan ilms esul ed
in an inc ease o ilm solubili y (50%), elas ici y (18%), and dec ease o punc u e s eng h (27%)
and ene gy a b eak (39%). In algina e ilms, he ex ac inco po a ion signi ican ly dec eased ilm
solubili y (6%), wa e apou pe meabili y (46%), and elas ici y (24%), and had no e ec on he mal
p ope ies. Depending on he ype o applica ion, he addi ion o SE in edible ilms can b ing
ad an ages o ood conse a ion.
Keywo ds: packaging ma e ials; edible ilms; seaweeds; chi osan; algina e; na u al; addi i e
1. In oduc ion
In ecen decades, he use o edible ilms as a bio-based ood packaging has become inc easingly
ele an o esea che s and he ood indus y. Edible ilms can ac as a selec i e ba ie o wa e ,
oxygen, and ca bon dioxide ans e and solu e mo emen s, o ming a hin laye o ma e ial be ween
he ood ma ix and he en i onmen . The inco po a ion o ac i e subs ances wi hin he ilm ma ix
allows addi ional p oduc shel -li e ex ension [
1
,
2
], since ilm unc ionali y can change wi h he na u e
o added componen s [3].
Chi in is he mos abundan na u ally occu ing amino-polysaccha ide, is a by-p oduc
om he c us acean indus ies, and i s deace yla ion p oduces chi osan. Chi osan is an edible
and biodeg adable polysaccha ide wi h a ac i e cha ac e is ics—namely, high an imic obial and
an i ungal ac i i ies
[2,4,5]
. Chi osan ilms a e an en i onmen ally iendly op ion o ood packaging,
and a e known o ha e a high esis ance o b eakage and elas ici y [
6
,
7
], wo impo an cha ac e is ics
o ood packaging ma e ials.
Algina e is a polysaccha ide composed by glucu onic and mannu onic acid uni s ex ac ed om
b own seaweeds (class Phaeophyceae) and widely used in he ood indus y [
3
,
8
,
9
]. Algina e ood
applica ions a e mainly based on he unique colloidal p ope ies ha allow i s gel- o ming abili y
Foods 2018,7, 53; doi:10.3390/ oods7040053 www.mdpi.com/jou nal/ oods
Foods 2018,7, 53 2 o 13
h ough ca ion binding [
9
]. Despi e he abili y o o m s ong ilms, algina e ilms exhibi poo wa e
esis ance due o he ma e ial’s hyd ophilic na u e [10].
Edible seaweeds a e a widesp ead and comme cially aluable esou ce in ood, odde ,
and pha maceu ical indus ies, and as soil condi ione p oduc s [
11
]. They a e also an impo an
sou ce o na u al addi i es, such as an ioxidan s [
12
], an imic obials, and polysaccha ides [
13
].
Edible seaweeds a e ich in bioac i e me aboli es ha a e no p oduced by e es ial plan s [
14
],
and cons i u e a good sou ce o na u al addi i es o edible ilm inco po a ion. Despi e he la ge
numbe o s udies in he li e a u e ega ding edible seaweed ex ac s [
15
], limi ed in o ma ion exis s
conce ning he ex ac o he edible seaweed Codium omen osum (SE) [
16
–
18
]. A ecen s udy showed
ha he imme sion o minimally p ocessed Fuji apple in a solu ion con aining 0.5% C. omen osum
ex ac minimized apple b owning in he e ige a ed p oduc o 20 days and inhibi ed pe oxidase
(POD) and polyphenoloxidase (PPO) ac i i ies [18].
The p esen wo k aims o assess how C. omen osum ex ac inco po a ion in algina e and chi osan
edible ilms in luences he polyme s’ ba ie , op ical, mechanical, and he mal p ope ies. Algina e and
chi osan ilms we e selec ed, as hese a e widely used edible polyme s in he ood indus y. The esul s
o he p esen wo k a e o ele an impo ance o de e mine he po en ial success o he inco po a ion
o C. omen osum seaweed ex ac in edible ilms, add essing public conce ns o educe he use o
adi ional ood packaging, such as plas ic ilms, and ood was e, and longe ood shel -li e.
2. Ma e ials and Me hods
2.1. Chemicals
Alginic acid sodium sal , low iscosi y was pu chased om Al a Aesa GmbH (Ka ls ube,
Ge many) and used as ecei ed. Comme cial chi osan om sh imp shells (
≥
75% deace yla ion deg ee,
Mw 50–190 kDa), 6-hyd oxy-2,5,7,8- e ame hylch oman-2-ca boxylic acid (T olox), and 2,2
0
-azobis
(2-me hylp opionamidine) dihyd ochlo ide (AAPH) we e pu chased om Sigma-Ald ich Co.
(S einheim, Ge many).
2.2. Seaweed Collec ion and Seaweed Ex ac P epa a ion
F esh C. omen osum samples we e collec ed in Peniche, Po ugal in Sep embe 2012. Ex ac ions
we e pe o med using wa e /e hanol as he ex ac ion sol en s [
18
]. The d ied ex ac was s o ed a
−80 ◦C (ul a-low eeze , The mo Fishe Scien i ic, Wal ham, MA, USA) un il u he analyses.
2.3. Ex ac Cha ac e iza ion
SE mois u e con en was de e mined wi h an au oma ic mois u e analyse (model HB 43-S;
Me le Toledo, Giesen, Ge many). Ash con en was quan i ied ollowing he p ocedu es adop ed
by he Associa ion o Analy ical Communi ies (AOAC In e na ional) [
19
]. Ni ogen con en was
de e mined by he Kjeldahl me hod using a con e sion ac o o 6.25 (Kjel ech 2006, Foss Teca o ,
Hille od, Denma k). To al lipid ex ac ion me hod was achie ed as p e iously desc ibed in he
li e a u e [
20
], ollowing a d y ma e basis. Ca bohyd a e con en was es ima ed by di e ence o all
o he componen s. To es ima e o al phenolic con en , he oxygen adical abso bance capaci y assay
(ORAC) o he seaweed ex ac was de e mined [
21
]. The ORAC alue was calcula ed and exp essed as
mic omoles o T olox equi alen s (TEs) pe g am ex ac (
µ
mol o TE g
−1
ex ac ) using he calib a ion
cu e o T olox.
2.4. Film P epa a ion
Algina e ilm- o ming solu ions (FFSs) we e p epa ed by suspending 1% (w/ ) o algina e (A)
in dis illed wa e a 70
◦
C un il comple e dissolu ion. A e cooling o 45
◦
C a oom empe a u e,
glyce ol was added a 1% ( / ) o he o al olume wi h gen le s i ing o 15 min. The same p ocedu e
Foods 2018,7, 53 3 o 13
was used o he p epa a ion o FFS wi h SE, bu he addi ion o 0.5% (w/ ) seaweed ex ac (AE) was
made be o e algina e addi ion.
Chi osan (1% w/ ) was dissol ed in o 1% (w/ ) ci ic acid solu ion (C). The mix u e was s i ed
con inuously a oom empe a u e o 8 hou s o ob ain a homogeneous solu ion. Tween 80 (0.1% / )
was added as plas icize a e homogeniza ion ollowed by il a ion o he emo al o undissol ed
ma e ial. FFS wi h SE inco po a ion was pe o med wi h he same p ocedu e, bu wi h he addi ion o
0.5% (w/ ) seaweed ex ac (CE) be o e chi osan. C and CE we e degassed p io o d ying by keeping
he solu ion in a acuum o en o 3 h o emo e he apped ai bubbles.
FFS we e cas in o dishes (Ø 120 mm) assu ing a su ace densi y o solids in he d y ilms o
70 g m
−2
in all o mula ions and dehyd a ed in a ay d ye (A m ield T ay D ie Type Uop8-A,
Ringwood, UK) un il cons an weigh was eached (ai low a e o 0.70 m s
−1
, 23
◦
C, and ela i e
humidi y (RH) 55%). D y ilms we e p econdi ioned in desicca o s (con aining gel silica) a 20
±
2
◦
C
p io o es ing.
2.5. Film Cha ac e iza ion
2.5.1. FTIR-ATR
The Fou ie ans o m in a ed spec oscopy a enua ed o al e lec ion (FTIR-ATR) echnique was
used o e alua e he unc ional g oups o he ma e ials and o de ec possible changes wi h he seaweed
ex ac inco po a ion. The FTIR analysis was ca ied ou using an Alpha-P FTIR-ATR spec ome e
(B uke Op ik GmbH, E lingen, Ge many) in a ange o 4000–400 cm
−1
, a a 4 cm
−1
esolu ion wi h
64 scans.
2.5.2. Film Thickness and Ligh Abso p ion
All ilms we e isually inspec ed o homogenei y. Films hickness was de e mined using a
manual mic ome e (Me le Toledo L d., Leices e , UK) wi h an accu acy o 0.001 mm, and an a e age
o 15 measu emen s aken a di e en loca ions in ilms was conside ed.
Film ligh ba ie p ope ies we e de e mined using anspa ency alues (T) calcula ed using
he ilm abso p ion, measu ed a 550 nm (A
550
) wi h a UV-160 UV- is spec opho ome e (The mo
Elec on Co po a ion, Wal ham, MA, USA) and ilm hickness (mm) (x) [22]:
T=A550/x (1)
2.5.3. Su ace Colo Measu emen
Film colou was de e mined by a colo ime e Konica Minol a CR-400 (Minol a INC., Tokyo,
Japan). The equipmen was calib a ed using a s anda d whi e e lec i e pla e. CIELab scale was used
wi h colou pa ame e s exp essed in e ms o : L* (ligh ness), a* ( ed/g een), and b* (yellow/blue).
Nine measu emen s o each sample we e aken, placing he ilm sample o e he s anda d whi e pla e
(L* = 95.38;
a* =
−
0.16; b* = 2.48). The Euclidean dis ance be ween wo poin s was de e mined wi h he
colou di e ence equa ion (∆E), and whi eness index (WI) was calcula ed [23].
2.5.4. Mois u e Con en and Film Solubili y
Film mois u e con en was de e mined wi h an au oma ic mois u e analyse . Film solubili y was
de e mined by a g a ime ic p ocedu e [
7
,
24
]. The ini ial ilm d y weigh (W
i
) and inal d y weigh
(W
) we e de e mined a e a d ying p ocess a 105
◦
C o 24 h. Ini ial d ied samples we e imme sed in
30 mL o dis illed wa e and gen ly shaken o 24 h, ollowed by a d ying p ocess o de e mine W
.
Film solubili y (FS%) was calcula ed using he ollowing equa ion:
FS % = (Wi−W )/Wi×100 (2)
Foods 2018,7, 53 4 o 13
2.5.5. Wa e Vapou Pe meabili y (WVP)
Film wa e apou pe meabili y was measu ed g a ime ically [
7
,
25
], wi h sligh adap a ions o
hyd ophilic edible ilms ma ix. Films wi hou de ec s we e sealed o a cup mou h (cell) con aining
100 mL o dis illed wa e (100% RH, 2000 Pa apou p essu e a 23
◦
C) wi h an exposed ilm a ea o
6 cm
2
. Tes cups wi h ilms we e placed in con ac wi h an a mosphe e a 23
◦
C and 75.7% RH (2119.6 Pa
apou p essu e); a e 1 h o a mosphe e adap a ion, he cells we e weighed (
±
0.0001 g) a in e als
o 30 min du ing 4 h. The measu ed WVP (kg Pa−1s−1m−1) o he ilms was de e mined [7,23].
2.5.6. Su ace Film We abili y
The sessile d op me hod was used o es ima e he su ace hyd ophobici y o he ilms. The wa e
con ac angle was de e mined o e alua e he ilm’s su ace we abili y, as well as he in luence o
SE ex ac on i s p ope ies. The s a ic con ac angle (
θ
) was measu ed wi h an op ical ensiome e
(Pa alab Company, model The a, Gondoma , Po ugal) using wa e .
Be o e measu emen s, samples we e p e-condi ioned a RH 0%. The es s we e made a 23
◦
C
wi hin he i s 10 s (12 F ames Pe Second) a e d opping he sol en (dis illed wa e ) on o ilm
su aces, o a oid a ia ions due o sol en pene a ion on o he specimens.
2.5.7. Mois u e So p ion Iso he ms
Wa e apou so p ion iso he ms we e d awn based on he s a ic me hod [
24
,
26
] by keeping ilm
samples a 23
◦
C in desicca o s wi h sa u a ed sal solu ions (MgCl
2
, KCl, Mg(NO
3
)
2
, NaCl, and KNO
3
)
wi h wa e ac i i y (a
w
) anging om 0.330 o 0.930, un il equilib ium was eached. Mois u e con en
a equilib ium was de e mined by d ying he ilm a 105 ◦C o 48 h.
2.5.8. Mechanical P ope ies
Punc u e es s we e un as epo ed in li e a u e [
27
] using a ex u e analyse Model TA.XT.plus
(S able Mic o Sys ems, Su ey, UK) con olled by he Tex u e Exponen So wa e 32 (S able Mic o
Sys ems, Su ey, UK). A cylind ical punc u e p obe (2 mm diame e ; S ainless P/2) was used o
de e mine he pe cen age o elonga ion a b eak. Nine eplica es o each ilm we e pe o med.
2.5.9. The mal Analysis
The mal p ope ies and s abili y we e de e mined using he Simul aneous The mal Analyse ,
STA 6000 sys em (Pe kinElme , Bos on, MA, USA). Fo his, 3–4 mg samples we e placed in ce amic
pans and es ed unde d y ni ogen pu ge ( low a e o 20 mL min
−1
). Samples we e submi ed o
empe a u e o 30
◦
C o 350
◦
C a a a e o 10
◦
C min
−1
. Mel ing endo he m peaks and peak a eas we e
used o de e mine mel ing empe a u es (Tm) and en halpies o usion (
∆
H
m
), espec i ely. Indium
and sil e samples we e used as calib a ion s anda ds.
2.6. Da a S a is ical Analysis
All measu emen s we e pe o med in iplica e, excep when s a ed o he wise. One-way analysis
o a iance (ANOVA), ollowed by Fishe s Leas Signi ican Di e ence (LSD) es o mul iple
compa isons o g oup means we e applied o de e mine signi ican di e ences be ween ilms (A, AE,
C, and CE). All da a we e checked o no mali y and homoscedas ici y. This p ocedu e was applied o
all measu emen s unde s udy. Whe e applicable, esul s a e p esen ed as mean
±
s anda d de ia ion
(SD). Fo all s a is ical es s, he signi icance le el was se a p
≤
0.05. All calcula ions we e pe o med
wi h IBM SPSS S a is ics 21 (IBM, New Yo k, NY, USA).
Foods 2018,7, 53 5 o 13
3. Resul s and Discussion
3.1. C. omen osum Ex ac Cha ac e iza ion
The p oximal composi ion o C. omen osum ex ac is shown in Table 1. The ela i ely highe ash
p opo ion in seaweed ex ac (SE) (app ox. 74%) can la gely be accoun ed o by he lowe mois u e
con en , which can p obably be a ibu ed o he hyg oscopic na u e o he SE [28].
Table 1.
Mois u e, p o ein, ash, a , and ca bohyd a e con en s (% d y weigh ), and pe oxyl adical
sca enging ac i i y (ORAC) o seaweed ex ac .
Tes Seaweed Ex ac
Mois u e (%) 6.4 ±1.2
P o ein (%) 2.07 ±0.06
Ash (%) 73.97 ±0.33
Fa (%) 1.17 ±0.06
Ca bohyd a e (%) a16.39
ORAC (T olox equi alen , µmol g−1ex ac ) 5.99 ±0.07
Resul s a e he mean ±s anda d de ia ion (SD) (n= 3). aDe e mined by di e ence o all o he componen s.
The pe oxyl sca enging ac i i y o C. omen osum ex ac —as measu ed by he ORAC assay—was
app oxima ely 100 imes lowe han he alues p esen ed in o he s udies [
16
] when me hanol and
dichlo ome hane we e used as ex ac ion sol en s. Howe e , he use o ex ac ion sol en s o ood
applica ions has legal es ic ions, and e hanol is one o he au ho ized sol en s acco ding o he
Eu opean Di ec i e 2009/32/EC [29].
3.2. Thickness, Su ace Colo , and Ligh Abso p ion
The hickness o he o mula ed ilms anged om 0.03 o 0.05 mm (Table 2). Algina e and chi osan
ilms we e anspa en and homogeneous, and he inco po a ion o he SE esul ed in he e ogeneous
egions in bo h ilms. Unde high humidi y condi ions (e.g., labo a o y acili ies), algina e ilms
abso bed mois u e, becoming di icul o handle.
Table 2.
Colou pa ame e s, colou di e ence (
∆
E), whi eness index (WI), and anspa ency (T),
hickness (mm), mois u e (%), wa e solubili y (%), wa e apou pe meabili y (WVP), and con ac
angle (◦) o algina e and chi osan ilms wi h and wi hou seaweed ex ac (SE).
Tes Algina e Algina e + SE Chi osan Chi osan + SE
Thickness (mm) 0.05 ±0.02 0.03 ±0.01 0.05 ±0.01 0.06 ±0.01
L* 92.68 ±0.68 92.87 ±0.15 93.89 ±0.32 93.65 ±0.93
a*−0.44 A±0.02 −0.53 B±0.03 −0.46 A,C ±0.05 −0.66 D±0.11
b* 6.75 A±0.17 9.42 B±0.39 3.96 C±0.21 5.20 D±0.73
∆E#5.09 A±0.42 7.40 B±0.40 2.13 C±0.33 3.36 D±0.85
WI 91.69 A±0.34 88.17 B±0.37 92.70 C±0.35 91.73 A,D ±0.87
T 2.4 A±0.1 13.1 B±0.4 3.1 C±0.3 2.5 D±0.1
Mois u e (%) 24.86 ±0.01 28.29 ±0.01 9.56 ±0.01 10.06 ±0.01
Film solubili y (%) 90.68 A±1.79 86.13 B±1.06 23.83 C±2.96 45.84 D±2.72
WVP (×10−16 kg Pa−1s−1m−1) 0.939 A±0.317 0.514 B±0.26 1.18 A±0.0071 1.22 A±0.0085
Con ac angle (◦) 37.70 A±0.15 8.9 B±0.30 78.58 C±0.27 21.80 D±0.57
Da a shown a e he means (
±
SD) (n= 9 o colou pa ame e s, n= 15 o hickness; n= 3 o he o he es s).
A,B,C,D
show signi ican di e ences in each es (p< 0.05, one-way analysis o a iance (ANOVA), leas signi ican
di e ence (LSD) es ). #colou di e ences be ween he s anda d whi e pla e and ilm samples (see Sec ion 2.5.3).
The op ical p ope ies o ilms a e an impo an indica o o ilm sui abili y as an edible coa ing,
as i in e e es wi h he p oduc appea ance and may lead o consume ejec ion [
23
,
30
]. The esul s o
he ilm colou measu emen s a e shown in Table 2. All ilms we e anspa en wi h a sligh yellowish

Foods 2018,7, 53 6 o 13
colou , in ag eemen wi h he measu ed b* alue. The addi ion o SE esul ed in inc eased b* alues o
bo h ypes o ilm (p< 0.05). P e ious s udies men ioned simila esul s, such as an inc ease in b* alues
in ish gela in ilms wi h he inco po a ion o SE [
31
]. Red/g een (a*), yellow/blue (b*) coo dina es,
and o al colou di e ences signi ican ly inc eased (p< 0.05) wi h he inco po a ion o SE in bo h
algina e and chi osan-based ilms. The a* alue has been used as a physical pa ame e o ep esen
g eenness in colou measu emen s [
32
]. Chlo ophylls— he pigmen s esponsible o he cha ac e is ic
g een colou o plan s and which a e p esen in C. omen osum—a e mos likely esponsible o he
obse ed a ia ion in a* alue. Colou changes in he esul ing ilm may be due o pigmen s emaining
in he SE. As a consequence o L*, a*, and b* changes, he whi eness index alues dec eased wi h he
addi ion o SE (p< 0.05).
The addi ion o SE o algina e ilms inc eased alues (p< 0.05), which indica es a lowe
deg ee o ilm anspa ency, co esponding o highe ligh abso p ion and consequen ly a highe
ilm opaci y
[29,33]
. On he con a y, he addi ion o SE o chi osan ilms dec eased alues (p< 0.05),
inc easing ilm anspa ency appea ance (Table 2).
3.3. FTIR-ATR Analysis
Th ough he in e p e a ion o ilms’ FTIR spec a, i is possible o iden i y speci ic unc ional
g oups and he e o e in es iga e possible in e ac ions be ween he polysaccha ides (algina e o
chi osan) and he inco po a ed SE. FTIR spec a o he di e en o mula ed ilms and he seaweed
ex ac (SE) a e p esen ed in Figu e 1.
Figu e 1.
Fou ie ans o m in a ed spec oscopy a enua ed o al e lec ion (FTIR-ATR) spec um o
he (
a
)C. omen osum seaweed ex ac (blue line) and he di e en es ed ilms: (
b
) 1% algina e ( ed line),
(
c
) 1% algina e wi h 0.5% o C. omen osum seaweed ex ac (g een line), (
d
) 1% chi osan (g ey line),
and (e) 1% chi osan wi h 0.5% o C. omen osum seaweed ex ac (black line).
The FTIR spec a o C. omen osum ex ac (Figu e 1a) showed abso p ion bands a 1100–930 cm
−1
,
which a e no mally p esen in seaweed polysaccha ide s anda ds and can ep esen bo h C-C and C-O
py anoid ing s e ching and C-O-C glycosidic bond s e ching [
28
]. The p esence o p o eins in he SE
could be explained by he abo e-men ioned bonds, ypically p esen in p o ein spec a [
34
]. As seen
in Table 1, SE had 2% p o ein. SE showed a s ong ansmission band a 1630 cm
−1
, ela ed o he
Foods 2018,7, 53 7 o 13
s e ching ib a ion o he (NH) C=O g oup—a g oup also obse ed in ex ac s o Codium capi a um,
a seaweed om he same genus o C. omen osum [
34
]. In hese spec a, i is also possible o obse e a
b oad band a 3357 cm
−1
ha could be ela ed o he p esence o polysaccha ides in SE. The possible
p esence o he sulpha ed polysaccha ide ucoidan in he SE could be associa ed o he sulpha e (SO
4
)
and me hyl (CH
3
) g oup bands signals obse ed a 1414 cm
−1
and 1360 cm
−1
, espec i ely [
35
,
36
].
The use o ucoidan as a nu aceu ical and ood supplemen is unde s udy, and he e o e he p esence
o his polysaccha ide in C. omen osum ex ac can be an ad an age—mos ly due o i s an ioxidan and
an ibac e ial p ope ies [35].
The algina e ilm exhibi ed ou ou s anding bands co esponding o a COO- (asymme ic)
s e ching a 1603 cm
−1
, a COO- (symme ic) s e ching band a 1407 cm
−1
, and a C-O-C s e ching
band a 1025 cm
−1
(Figu e 1b) [
8
,
37
] and he p esence o bands a 817 cm
−1
on he algina e ilms
spec a, which indica es he p esence o mannu onic acid [37].
A b oad band a 3273 cm
−1
ep esen ing hyd oxyl g oups (HO-) was also obse ed. The -CH
ib a ion band occu s a 2928 cm
−1
, which can be o e lapped wi h he COO- ib a ion bands [
8
,
38
].
No signi ican di e ences we e obse ed be ween he FTIR spec a o algina e ilm wi h and wi hou
seaweed ex ac in e ms o wa enumbe abso bance (Figu e 1c). A sligh educ ion o he bands size
in he o me bands was obse ed wi h SE inco po a ion. In bo h spec a, i was possible o iden i y
he ib a ion bands om COO, CH, C-O, OH, and C-O-C g oups.
The FTIR spec um o he chi osan ilm (Figu e 1d) showed a C-H s e ching be ween 2922 cm
−1
and 2920 cm
−1
and bands a 1186 cm
−1
and 1017 cm
−1
, indica ing he p esence o a ee amino g oup
a he C
2
posi ion o glucosamine (a majo g oup p esen in chi osan). The p esence o he i s C-H
s e ching was also obse ed in chi osan ilms wi h seaweed ex ac (Figu e 1e) a he same ange o
wa enumbe ; he second ange o bands we e also p esen , bu wi h a mino in ensi y. The absence
o a b oad band a ound 1610 cm
−1
( ep esen ing ace yla ed amino g oups) in bo h C and CE spec a
is associa ed wi h a high deg ee o deace yla ion, which ag ees wi h sample speci ica ions (
≥
75%
deace yla ion deg ee) [
39
]. A b oad band a 1712 cm
−1
migh be ela ed o ca bonyl ib a ion o he
ca boxylic acid [39].
SE in e ac ions wi h algina e and chi osan ma ices we e mainly e lec ed in he bands’ a eas,
which ep esen he ex en o in e ac ion be ween hem. In all cases, he addi ion o SE led o a a ia ion
in a ea, e lec ing di e en in ensi ies o he chemical bonds es ablished in hese ma e ials. These
di e ences may in luence he ollowing desc ibed ilm p ope ies.
3.4. Mois u e Con en and Film Solubili y
Film hyd ophobici y is ela ed o he amoun o wa e p esen in ilms; he mo e hyd ophilic he
ilm, he highe he mois u e con en [
23
]. Table 2shows he mois u e con en o he s udied edible
ilms. Algina e-based ilms showed he highes alues o mois u e (24–28%), wi h chi osan-based ilms
p esen ing signi ican ly lowe mois u e con en s (9–10%) (en i onmen RH o 75%).
Film solubili y de e mines he biodeg adabili y o ilms when used as ood packaging, as well
as hei unc ionali y as a wa e ba ie [
5
]. Highe wa e solubili y indica es lowe wa e esis ance.
A and AE ilms (algina e-based ilms) showed he highes alues o wa e solubili y (86–90%) (Table 2),
indica ing he high hyd ophilic cha ac e o algina e ilms in he p esence o wa e (also epo ed in
li e a u e [
23
]), and lowe ilm in eg i y in high-humidi y en i onmen s [
10
]. The addi ion o SE o
algina e ilms esul ed in a dec ease in wa e solubili y (6%) (p< 0.05) (Table 2), pe haps due o he
p esence o hyd ogen bond and hyd ophobic in e ac ion o p o ein in he ilm ma ix [
31
]. S udies also
showed ha he ex ac o he seaweed Tu bina ia o na a dec eased he solubili y o ish gela in-based
ilms [
31
], p esen ing lowe alues o solubili y when compa ed o algina e-based ilms in he p esen
s udy. As shown in Table 2, chi osan ilm had low wa e solubili y, which was expec ed gi en ha
chi osan is mainly soluble in o ganic solu ions and in acids such as hyd ochlo ic, phospho ic, and ni ic
acid a pH bellow 6.5 [
40
]. The inco po a ion o SE in o chi osan ilms esul ed in a signi ican inc ease
o wa e solubili y (p< 0.05); esea che s also epo ed an imp o emen o he wa e solubili y o
Foods 2018,7, 53 8 o 13
chi osan ilms wi h he inco po a ion o ea ex ac s [
41
]. In his s udy, he in e ac ion be ween chi osan
and SE could induce a dec ease in he c oss-linking deg ee o in e molecula chains in he ma ix, hus
esul ing in he obse ed highe solubili y.
3.5. Wa e Vapo Pe meabili y (WVP)
Films’ WVP a a ela i e humidi y g adien o 100:75 a e shown in Table 2. Measu ed alues
anged om 0.514–1.22
×
10
−16
kg Pa
−1
s
−1
m
−1
. The WVP alues o he analysed algina e ilms
we e lowe han he alues p esen ed in o he s udies [
3
,
42
]. These di e ences migh be caused
by di e en ilm p epa a ion echniques (concen a ion and d ying echnique) and WVP measu ing
condi ions (di e en RH g adien ). The addi ion o SE caused a 45% (p< 0.05) educ ion in he WVP o
algina e ilms, possibly as a esul o changes in he deg ee o c osslinkage ha led o a educ ion in he
polyme ic chain mobili y. This e ec was also epo ed in algina e ilms wi h highe concen a ions
o calcium [
42
]. Simila beha iou o gela in ilms wi h T. o na a ex ac inclusion was obse ed in
p e ious wo ks [
31
], possibly due o he p esence o phenolic compound in he SE ha migh enhance
he c osslinkage o gela in. SE inco po a ion seems o in e e e in he hyd ophilic po ion o ilms,
and consequen ly in he hyd ophilic/hyd ophobic a io, a ec ing wa e apou ans e ha gene ally
occu s in he hyd ophilic zone o he ilms s uc u e [
43
]. The esul s also showed ha he inco po a ion
o SE did no signi ican ly in luence he WVP o chi osan ilms (p> 0.05). Fu he mo e, WVP alues
we e in he ange o WVP ob ained o simila ilms (WVP a e o 1.53 g h
−1
mm
−1
m
−1
kPa
−1
),
e lec ing he low wa e ba ie cha ac e is ics o chi osan ilms [
44
]. The ob ained alues o WVP
we e a om he ones p esen ed by pe oleum-based polyme s commonly used in ood packaging,
which ha e a WVP a e o 9.14
×
10
−13
g m
−1
s
−1
Pa
−1
[
44
], indica ing ha he s udied ilms s ill need
u he imp o emen s i hey a e o be used as an al e na i e o hese ma e ials.
3.6. Su ace Film We abili y
Wa e con ac angle is an indica o o ilm su ace hyd ophilici y; he lowe he con ac angle,
he g ea e he ma e ial su ace hyd ophilici y [
45
]. The con ac angle be ween wa e d ople s and
he su aces o algina e and chi osan ilms we e analysed (Table 2). Chi osan ilms (C) showed a
highe con ac angle (
θ
= 78
◦
) compa ed wi h he emaining ilms. In luences o SE inco po a ion
on con ac angle alues was e i ied, wi h a signi ican dec ease (p< 0.05) o alues in bo h ypes
o ilms. The use o a pola sol en (wa e , ela i e pola i y o 1) and a mode a ely pola sol en
(e hanol, ela i e pola i y o 0.654) [
46
] in he ex ac ion can lead o he ex ac ion o pola compounds.
The SE inco po a ion in algina e and chi osan inc eased he hyd ophilici y and consequen ly he
ilm we abili y, jus i ying he con ac angle o 8
◦
in AE ilms and 21
◦
in CE ilms. E en hough SE
inco po a ion led o ilms wi h high hyd ophilici y and concomi an inc ease in WVP, he applica ion
o his ype o solu ion in ood ma ixes can be e icien , as high alues o ilm we abili y a e ela ed o
a high su ace coa ing capaci y, enabling easie applica ion on he ood su ace [45].
The con ac angle esul s we e in good ag eemen wi h he ob ained mois u e alues (Table 2);
highe mois u e con en led o lowe con ac angles, indica ing a g ea e abili y o abso b wa e and
hus explaining he high hyd ophilici y.
3.7. Mois u e So p ion Iso he ms
So p ion iso he ms o he ilms a e p esen ed in Figu e 2(0.34 o 0.94 a
w
anges). The ini ial
mois u e con en o each ilm was di e en (Table 2), which means ha he d i ing o ce o he
so p ion p ocess was di e en , esul ing in dis inc cu es. Highe alues o mois u e a equilib ium
in algina e-based ilms we e expec ed, since algina e is a hyd ophilic polyme p one o abso b wa e
apou p esen in he a mosphe e. High ela i e humidi y alues can ha e a nega i e e ec on he
applica ion o algina e based ilms in ood packaging sys ems, as i can lead o ilm solubilisa ion,
causing ailu es in i s s uc u e and comp omising i s ba ie p ope ies [
3
]. Chi osan-based ilms
Foods 2018,7, 53 9 o 13
(C and CE) p esen ed lowe mois u e alues a equilib ium since chi osan had a low wa e solubili y,
p e en ing wa e e en ion in he ilm and esul ing in lowe mois u e alues.
Figu e 2.
Mois u e so p ion iso he ms o algina e wi hou (A) and wi h seaweed ex ac (AE), chi osan
wi hou (C) and wi h ex ac (CE) ilms a 21
±
2
◦
C. Da a shown a e he means (n= 3). a
w
: wa e ac i i y.
The inco po a ion o SE had no e ec on he so p ion iso he m o algina e-based ilm. On he
con a y, in chi osan ilms, SE inco po a ion esul ed in highe equilib ium mois u e o all a
w
es ed in
chi osan based ilms. This obse a ion ag ees wi h he esul s ega ding he e ec o SE in chi osan
ilms, whe e ex ac inco po a ion signi ican ly inc eased he ilm solubili y and dec eased con ac
angle (Table 2).
3.8. Mechanical P ope ies
The mechanical p ope ies o he s udied ilms a e p esen ed in Table 3. Chi osan ilms wi h SE
showed he highes elonga ion a b eak when compa ed o o he ilm o mula ions, indica ing highe
ilm ex ensibili y and mechanical s eng h. Ex ensibili y and mechanical s eng h a e wo impo an
ma e ial cha ac e is ics, ela ed o he capaci y o ilms o ole a e ex e nal s ess and main ain in eg i y
and ba ie p ope ies when applied as ood packaging [
7
]. The addi ion o SE o chi osan ilms
inc eased he elonga ion a b eak (p< 0.05), dec easing he punc u e s eng h (p< 0.05) and ene gy
a b eak (p< 0.05). These esul s we e in con as wi h hose p esen ed in o he s udies, whe e he
elonga ion a b eak signi ican ly dec eased wi h he addi ion o an imic obial compounds [
41
] and
ea ex ac s in o chi osan ilms [
47
]. These changes in mechanical p ope ies could indica e ha ilm
s uc u e so ens, o ming a mo e lexible ilm and consequen ly highe elonga ion alues when
subjec ed o ension and mechanical s ess. SE could ac as a plas icize in ilm o mula ion, inc easing
he molecula mobili y o he polyme s [
48
] and esul ing in he inc ease o elonga ion a b eak and he
dec ease o punc u e s eng h. Mechanical p ope ies o CE ilms we e in ag eemen wi h he esul s o
mois u e and ilm solubili y (Table 2). The inco po a ion o SE in algina e ilms led o a 23% dec ease o
elonga ion a b eak alues (p< 0.05), inc easing punc u e s eng h and ene gy a b eak alues. In his
case, he inco po a ion o SE had he opposi e e ec o when applied on chi osan ilms, esul ing in a
ilm o highe b i leness. An equilib ium be ween he deg ee o polyme c osslinking and seaweed
ex ac addi ion is equi ed o be e ilm wo kabili y cha ac e is ics, which changes ilm p ope ies
such as he solubili y in wa e , a ec ing ilm b i leness (obse ed in Table 2) [48].