Effect of different drying techniques on flowability characteristics and chemical properties of natural carbohydrate-protein Gum from durian fruit seed.

2.8 MB·English

by  Mirhosseini, Hamed

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RESEARCH ARTICLE Open Access
Effect of different drying techniques on
flowability characteristics and chemical properties
of natural carbohydrate-protein Gum from durian
fruit seed
Hamed Mirhosseini* and Bahareh Tabatabaee Amid*
Abstract
Background: Anatural carbohydrate biopolymerwas extracted from the agricultural biomass waste (durian seed).
Subsequently, thecrude biopolymer was purified by using thesaturated barium hydroxide to minimize the
impurities. Finally,the effect of different drying techniques onthe flow characteristicsand functional properties of
thepurifiedbiopolymer was investigated. The present study elucidated themain functional characteristicssuch as
flow characteristics, water- and oil-holding capacity, solubility, and foaming capacity.
Results: Inmost cases except for oven drying, thebulk density decreased, thus increasing the porosity. This might
be attributed to the increase in the inter-particle voids ofsmaller sized particles with larger contact surface areas
perunit volume. The currentstudy revealed thatoven-dried gum and freeze-dried gum had the highest and
lowest compressibility index, thus indicating the weakest and strongest flowabilityamong all samples. In the
present work,thefreeze-dried gum showed thelowestangle of repose, bulk, tapped and true density.This
indicates the highest porosity degree of freeze dried gum among dried seed gums. It also exhibited thehighest
solubility, and foaming capacity thus providing themost desirablefunctional properties and flow characteristics
among all drying techniques.
Conclusion: The present study revealed that freeze drying among all drying techniques provided the most
desirable functional properties and flow characteristics for durian seed gum.
Keywords: Carbohydrate biopolymer, Durio zibethinus,Agricultural biomass waste, Solubility, Foaming properties,
Water holding capacity, Oil holding capacity, Flow characteristics
Background The physicochemical and functional properties of nat-
Natural carbohydrate biopolymers from plant sources ural plant-based biopolymers are extensively influenced
provide a broad range of functional properties. They are by many factors such as the chemical composition and
appropriate alternatives to the synthetic biopolymers molecular structure of the biopolymer. On the other
due to their biocompatibility, low toxicity, and low price hand, the extraction, purification, drying and/or further
as compared to synthetic biopolymers. Natural carbohy- modification processes can significantly affect the chem-
drate biopolymers are usually originated from nonpollut- ical composition and molecular structure, thereby influ-
ing renewable sources for the sustainable supply with a encingthefunctionalpropertiesof biopolymers.
broad range of functional properties. They are mainly Drying process is a critical food operation because it
used for many applications as drug delivery carrier and may induce undesirable changes in the texture, density
binder, emulsifier, thickener, suspending agents and etc. and porosity, and sorption characteristics and overall
quality of the dehydrated product [1]. Since, the removal
of alarge portion ofmoisturefrom food takes place dur-
*Correspondence:[email protected];[email protected]
ing the drying process, therefore final characteristics of
DepartmentofFoodTechnology,FacultyofFoodScienceandTechnology,
UniversityPutraMalaysia,43400UPM,Serdang,Selangor,Malaysia
©2013 MirhosseiniandAmid;licenseeChemistryCentralLtd.ThisisanOpenAccessarticledistributedunderthetermsof
theCreativeCommonsAttributionLicense(http://creativecommons.org/licenses/by/2.0),whichpermitsunrestricteduse,
distribution,andreproductioninanymedium,providedtheoriginalworkisproperlycited.
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the dried product are extensively influenced by type and techniques (i.e. oven drying, spray drying, freeze drying
condition of the drying process [2].Thesamerawmater- and vacuum drying) were chosen based on the prelimi-
ialmayendupasacompletelydifferentproduct,depend- nary study and previous litrature [3-7,9]. The efficiency
ing onthe typeand conditions of the dryingprocess.The of different drying techniques was determined by asses-
most common used drying techniques for various plant ing flow characteristics, water- and oil-holding capacity
gums included oven drying [3], spray drying [4], freeze (WHC and OHC), solubility and foaming capacity of
drying[5],andvacuumdrying[6].Itshouldbenotedthat differently dried biopolymers.
the dryingprocess at hightemperature for long time may
result in the degradation of flavor compounds, color and Results and discussion
nutrients of the dehydrated product, thus reducing the Bulk,tappedandtruedensity
qualityandoverallacceptabilityofthefinalproduct[1,7]. The physical properties such as bulk density, granule
Thebiopolymerfrom durianseed hasa polysaccharide- density, and inter-space porosity, wetting ability, particle
protein structure. D-galactose and glucose were the most size and distribution are critical parameters for control-
abundant monosaccharide in the carbohydrate profile of ling the quality of the powder. The density is a critical
durian seed. The sugar analysis also revealed the pres- parameteraffectingthefunctionalproperties ofthepow-
ence of low content of arbinose and xylose in the che- der. The bulk and tapped densities provide a perspective
mical structure of durian seed gum [8]. As reported in from the packing and arrangement of the particles and
previous studies [8,9], different extraction and further the compaction profile of a material [15]. The drying
processing conditions significantly (p < 0.05) affected process significantly (p < 0.05) influenced the bulk dens-
the chemical composition and molecular structure of ity of theseed gum powder (Figure 1a). Thebulk density
the heteropolysaccharide-protein polymer from durian depends on the attractive inter-particle forces, particle
seed gum. This could be responsible for the consider- size and number of contact positions [16]. As also stated
able changes in emulsifying capacity, rheological and by Singh et al. [17], the bulk density of the powder is
functional properties of the biopolymer from durian primarily dependent on particle size, particle size distri-
seed [10-13]. Previous study [11] revealed that the nat- bution and particle shape. This might be the reason for
ural polymer from durian seed gum had the approprite the significant changes inthebulk density ofdurian seed
interfacial activity (or emulsifying property) in oil in gum. The bulk density of durian seed ranged from
water (O/W) emulsion. This interfacial activity could be 0.173-0.203 g/mL, depending on the drying technique
due to the presence of a low content of the proteineous (Figure 1a). Previous researchers reported different bulk
constituent (< 4%) present in durian seed gum [8]. In densities for various plant gums (Table 1). The freeze
addition, the heteropolysaccharide-protein polymer dryingandspraydryingsignificantly(p<0.05)decreased
from durian fruit seed showed relatively low thickening the bulk density. In the present work, the oven-dried
properties in the aqueous solution [14]. This might be seed gum had the highest bulk density (Figure 1a).
due to itsrelativelylowmolecularweight structure[9]. Amongalldrying techniques,thefreeze-dryingexhibited
It is necessary to have sufficient information on flow- the highest reduction of the bulk density (Figure 1a).
ability characteristics of the biopolymer in the powder The bulk density is reversely associated with porosity
and liquid form. Although, physicochemical and func- ([1- (bulk density/granule density)] × 100) [18]. In fact,
tional properties of durian seed gum have been ex- the substance with lower bulk density has the higher
tensively studied [10-14], but there is no similar study porosity andvice versa.
investigating the foaming properties and flowability In the current study, the freeze-dried gum followed by
characteristics (i.e. compressibility, bulk, tapped and true thespray-driedgumhadthelowestbulkdensity,thuspro-
density) of durian seed gum as a function of drying vidingthehighestporosityamongalldriedgums.Thesig-
conditions. The main goal was to investigate the effect nificant reduction in the bulk density might significantly
of different drying techniques on chemical properties affect the solubility of the freeze-dried and spray dried
and flowability characteristics of durian seed gum. The gums. The bulk density of different dried seed gums was
current study helps the manufacturer for better under- comparable with that of reported for grewia gum (0.140-
standing the functional characteristics of durian seed 0.160g/mL)[19],andreflexagum(0.174±0.06g/mL)[20].
gum as a function of different drying conditions. It also Conversely,itwaslowerthanthebulkdensityreportedfor
provides helpful information regarding the most effi- guar gum (0.474±0.06 g/mL), dioclea gum (0.564±0.05
cient drying technique for the preparation of durian g/mL)[20],afzeliaAfricana(0.610±0.05g/mL),tragacanth
seed gum. To the best of knowledge, the effects of dif- (0.640±0.00g/mL)[21],gumArabic(0.61),andmangifera
ferent drying techniques on the chemical properties and gum (0.74 g/mL) [22] (Table 1). The total volume
flow characteristics of natural biopolymer from durian of inter-particle voids can change with drying and
seed have not been reported on date. Different drying packing processes; therefore, tap density should be
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Figure1Effectofdifferentdryingmethodson(a)thebulkdensity,(b)tappeddensity,and(c)truedensityofdurianseedgum.
measured to rectify this matter. The tap density is one ranged from 0.199 to 0.258 g/mL, depending on the
of main characteristics of a powder which is the max- drying technique(Figure1b).
imumpackingof apowderachieved undertheinfluence Asreportedbypreviousresearchers,variousplantgums
of well defined, externally applied forces. It indicates showed different flowability characteristics (Table 1). The
the volume of a mass of sample after inducing a closer results exhibited the significant (p < 0.05) effect of freeze
packing of particles by tapping the container. Goldfarb andspraydryingmethodsonthetappeddensityofdurian
and Ramachandruni [23] illustrated that the tapped seedgum (Figure1b).This studyrevealedthatthefreeze-
density should be measured for two crucial reasons. driedseedgumhadtheleasttappeddensity.Ontheother
Firstly, the tapped density value is more reproducible hand, the oven-dried seed gum followed by the control
than the bulk value. Secondly, the flow characteristic of samplecontainedthehighesttappeddensity,thusindicat-
a powder is inferred from the ratio of these two mea- ingtheleastporosityamongalldriedsamples(Figure1b).
sured densities. In the current study, the tapped density The tapped density results showed that the freeze dried
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Table1Physicochemicalpropertiesofdifferentplantgums
Plantgum Bulkdensity Tappeddensity Truedensity Compressibility Angleof
(g/mL) (g/mL) (g/cm3) index(%) repose(°)
Air-driedGrewiaguma 0.160±0.00 0.200±0.01 2.0±0.01 20.20±1.20 30.40±0.50
Freeze-driedGrewia 0.140±0.00 0.170±0.01 1.7±0.01 21.40±0.84 32.60±1.03
guma
Guargumb 0.474±0.06 0.546±0.05 - 13.05±0.7 19.24±0.05
Diocleagumb 0.564±0.05 0.706±0.01 - 20.14±0.2 25.36±0.1
Reflexagumb 0.174±0.06 0.225±0.05 - 22.75±0.5 27.30±0.06
AfzeliaAfricanac 0.610±0.05 0.710±0.00 1.7 14.08 10.61±1.17
Tragacanthc 0.640±0.00 0.740±0.01 - 13.51 21.77±2.74
GumArabicd 0.61 0.86 28.42 -
Mangiferagumd 0.74 0.92 - 19.56 26.75
aNepandConway[19];bBuildersetal.[20];cMartinsetal.[21];dKumarSinghetal.[15].
andspraydriedseedgumsaremoreporousthantheother changesinthetappedandtruedensityofthedehydrated
samples. The true density can be equal to the theoretical products significantly influence their overall quality [24].
density of the material, depending on the molecular ar- In the current study, the true density varied from 1.98 to
rangement of the material. In fact, the true density indi- 2.50 g/cm3 (Figure 1c). This value was comparable with
cateswhetherthematerialisclosetoacrystallinestateor the true density reported for grewia gum (1.7-2.0g/cm3),
theproportionsofabinarymixture.Theresultsindicated and afzelia Africana gum (0.17 g/cm3) [21] (Table 1). As
that the drying process significantly (p < 0.05) affected shown in Figure 1c, the spray drying and freeze drying
the true density of the gum (Figure 1c). The significant led to reduce the true density. This observation was in
Figure2Effectofdifferentdryingmethodson(a)thecompressibilityindex,and(b)angleofreposeofdurianseedgum.
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agreementwiththatofreportedbyNepandConway[19] softness of the shell during drying. The right side image
for grewia gum (Table 1). They also observed that the is a close image showing a shell-type structure. This
truedensityofair–driedgrewiagumwashigherthanthe large magnification shows a large particle with a rough,
true density of the freeze-dried grewia gum (Table 1). In porous surface, which is revealed under the smooth
thisstudy,thefreezedryingcausedthehighestsignificant outer skin. The presence of porous particles is expected
(p < 0.05) reduction in the density of durian seed gum after the sublimation of ice crystals during freeze drying
(Figure1c). process.
As shown in Table 1, various plant gums exhibited dif-
Compressibilityindexandangleofrepose ferent compressibility index and angle of repose, thus in-
The effects of different drying techniques on the com- dicating different flow characteristics. The freeze-dried
pressibility index and angle of repose of durian seed durian seed gum showed the least compressibility index,
gum were shown in Figure 2a, b. In the present study, thus providing the most appropriate flowability charac-
the compressibility index of durian seed ranged from teristics among all dried gums. Conversely, the oven-
13.06 to 22.85%, depending on the drying technique dried durian seed gum had the highest compressibility
(Figure 2a). As stated by previous researcher [25], the index, thus indicating the weakest flowability among all
excellent or poor flowability characteristics of the pow- samples (Figure 2a). The flow rate of a material depends
der can be assessed by determining its compressibility upon many factors related to the particle structure and
index (Table 2). If the compressibility index is less than processing conditions. As stated by previous researchers
10%, this shows excellent flow. The low compressibility [25], the compressibility and compatibility of a powder
index(11–15%)indicatesgoodflowabilitycharacteristics; can affect its flow properties in the micro-scale through
while the relatively high compressibility index (16-20%) the adhesion forces between the particles. The angle of
and very high compressibility index (> 31%) indicate fair repose is also one of the critical features indicating the
and very poor flowability characteristics (Table 2) [25]. degreeofflowcharacteristicsofpowdergranules.Thein-
This indicated that the different dried-seed gums crease in angle of repose is associated with decreasing
showed different flow characteristics from fair to good the flowability characteristics (Table 2). It is a measure of
(13.06 to 22.85%). As recommended by Phani Kumar powder resistance to the flow under gravity due to fric-
et al. [22], if the compressibility index varies from 15 to tional forces resulting from the surface properties of the
25%, the modification of particle size distribution is ad- granules [26]. As shown in Figure 2b, the different dried
visable to reach the optimum performance and very durian seed gums showed different levels of angle of re-
goodflow properties. pose ranging from 30.83-42.22°. This range was compar-
Among all samples, the freeze-dried seed gum exhib- able with the compressibility index reported for grewia
ited the lowest compressibility index (13.1%), thus indi- gum (30.40-32.60°). However, this value was higher than
cating good flow characteristics (Figure 2a). Figure 3 theangleofreposereportedfordiocleagum(25.36±0.1°),
displays SEM images of the freeze-dried gum showing reflexa gum (27.30±0.06°) [20], afzelia Africana (10.61 ±
the smooth skin-forming behavior of dried particles. The 1.17°),andtragacanth(21.77±2.74°)[21](Table2).
left side image shows some agglomerations which have As reported by Onunkwo [26], if the angle of repose
been taken place during the drying process. Collisions decreased, the binding level of the granules increased.
are apparent between semi-dried particles (Figure 3). This mightbe due tothe reduction in the cohesiveforces
Collision between particles was expected to take place of the larger granules formed at higher binding level [27].
whilst some of the particles had been still liquid. Some The drying process had a significant (p < 0.05) effect on
of the larger particles show some “deflating”, due to the angle of repose of durian seed gum, thus affecting its
flow characteristics (Figure 2b). The significant effect of
the drying process on the angle of repose was also
Table2Flowpropertiesbasedoncompressibilityindex
reported by Nep and Conway [19]. The oven-dried gum
andangleofrepose[25]
exhibited the highest angle of repose; while the spray-
Compressibilityindex(%) Angleofrepose(°) Flowcharacter
dried gum and freeze-dried gum showed the lowest angle
≤10 25-30 Excellent
ofreposeamongalldriedsamples(Figure2b).Conversely,
11-15 31-35 Good the oven drying resulted in the highest angle of repose
16-20 36-40 Fair (42.22°). Although, the oven drying is a low cost drying
21-25 41-45 Passable technique,butitresultsinpassabletorelativelypoorflow-
ability characteristics for durian seed gum. Nep and
26-31 46-55 Poor
Conway [19] reported that the freeze drying resulted in
32-37 56-65 Verypoor
higher angle of repose (or better flowability) than air dry-
>38 >66 Very,verypoor
ingforgrewiagum.
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Figure3ScanningElectronMicroscopy(SEM)imagesofthefreeze-driedseedgumfromgeneralparticlepopulation(a,c)(X3,000)and
acloserlook(b,d)(X10,000).
Solubility leucine, lysine, aspartic acid, glycine, alanine, glutamic
Solubility is the most reliable criterion to evaluate the acid, valine, proline, serine and threonine present in the
behavior of powder in aqueous solution. This param- chemical structure of durian seed gum. In addition to
eter is attained after the powder undergoes dissolution the chemical composition, drying process had a consi-
steps of sinkability, dispersability and wettability. The derable effect on the molecular structure of durian seed
present study showed that the drying process signifi- gum as reported previously [9]. This might be also re-
cantly (p < 0.05) influenced the solubility of durian seed sponsible for significant (p < 0.05) changes of the solu-
gum (Figure 4a, b). This could be explained by the sig- bility of the durian seed gum as a function of different
nificant (p < 0.05) effect of the drying process on the drying conditions. Durian seed gums exhibited different
chemical composition of durian seed gum as reported solubility levels at the room temperature (43.0-57.5%)
in the previous study [9]. Previous study [9] revealed as compared to the control sample (46%), dependingon
that drying process significantly (p < 0.05) influenced the drying method (Figure 4a). The solubility of different-
the content of galactose, glucose, arabinose and xylose drieddurianseedgumstheroomtemperaturewassimilar
present in the chemical structur of durian seed gum. to that of reported for carob gum (~50%, at 25°C) [28].
This might be responsible for the significant (p < 0.05) NepandConway[19]alsofoundthatthesolubilityofgre-
changes of solubility. On the other hand, drying process wiagumwassignificantly(p<0.05)influencedbythedry-
significantly (p < 0.05) influenced the protein content ing process. They reported different degree of solubility
and amino acid composition of durian seed gum as (0.1-0.3 mg/mL) for grewia gum. This could be explained
reported previously [9]. This might be another reason bythefactthatdifferentdryingtechniquesresultedindif-
for the significant (p < 0.05) changes of solubility as a ferentmolecularweights,thusvaryingthesolubility[19].
function of drying conditions. As reported earlier [9], In the current study, the spray-dried and freeze-dried
drying process significantly affected the content of gums showed remarkably higher solubility than the
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Figure4Effectofdifferentdryingmethodsonthesolubilityofdurianseedgumat(a)theroomtemperature,and(b)elevated
temperature(80°C).
control sample, oven-dried (105°C) and vacuum oven- bonds or weak non-covalent bonds (i.e. such as Van der
dried gums (Figure 4a). Thiscouldbealsoduetothesig- Waals attractions, hydrogen and ionic bonds) that form
nificant size reduction, more particle size uniformity and between one part of the protein chain and another can
complete conversion of particle to more soluble amor- significantly alter the solubility of the protein. The inter-
phous form. Corrigan et al. [29] also reported that high action between water and protein molecules can build up
energyamorphousformcausedbyspraydryingledtoim- new hydrogen bonds with the amide nitrogen and car-
prove the functional properties of powder such as the bonyl oxygen of peptide bonds. These interactions result
enhanced solubility and faster dissolution rate. The high in the further weakness nearby hydrogen bonds, thus
solubility of freeze-dried and spray dried gums could be affectingthesolubilityandfunctionalpropertiesofprotein
due to their low bulk density (or high porosity). The dif- fraction [32]. The resulted indicated that the solubility of
ference couldbealsoexplainedbythesignificanteffectof durian seed gum was relatively high at the elevated
the drying process on the monosaccharide composition temperature (80°C) (Figure 4b). Dakia et al. [28] also re-
present in the backbone and side chains of the gum mo- ported that the solubility of carob gum reached the max-
lecularstructure.AsexplainedbyKuntz[30],thephysico- imum level (~70–85%) at 80°C as compared to the low
chemical properties of gum (such as WHC, viscosity, solubility (~50%) at 25°C. The solubility of durian seed
hydration and solubility) are attributed to its molecular gums at the elevated temperature (80°C) was significantly
structure (i.e. the type and number of monosaccharides, (p < 0.05) different its solubility at the room temperature.
type,numberandlocationofthelinkedglycosidicgroup). Itrangedbetween60to75.2%ascomparedtothecontrol
The current study revealed that purified durian seed sample (63.7%). The high solubility of freeze-dried gum
gumalsoshowedasimilartrendofsolubilityatroomand may be attributedtothe highcontent of hydrophilic frac-
hightemperature(80°C).Thepresenceoftheproteinfrac- tion and soluble materials as well as its low cross-linking
tion along with the monosaccharide structure of gum [33].Thehighsolubilityof thefreeze-driedgum mightbe
most probably affects its water solubility [31]. The struc- alsointerpretedbythefactthatthefreezedryingcouldre-
ture of protein significantly affects it reaction with water sultinthelowbulkdensityandhighporosity.
molecules. It is hypothesized that the drying process sig-
nificantly affects the position of hydrophobic and hydro- Water-andoil-holdingcapacity(WHCandOHC)
philic amino acids in the interior or exterior layer of the The results indicated that the drying process signifi-
protein molecule, thus affecting the solubility of the pro- cantly(p<0.05)influencedthe capacityofwaterabsorp-
tein fraction [32]. The different sets of strong covalent tion (WHC) of durian seed gum. This could be due to
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the significant effect of the drying process on the chem- of water absorption (254.8 g water/100 g fibre) among
ical composition and molecular structure of durian seed all samples. This value was comparable with WHC
gum [9]. Mishra et al. [34] also reported the significant reported for citrus husk DF (360 g water/100 g fibre)
differences between the chemical composition of poly- and pineapple peel dietary fiber (DF) (350 g water/100 g
saccharide gums as a function of the drying process. fibre) [38]. However, it was much lower than WHC
Many hydrocolloids have side units such as sugar units, reported by Adams et al. [39] for some agricultural by-
carboxyl groups, sulfate groups or methyl ether group product from wheat bran (660 g water/100 g fibre),
which influence the functional properties of the hydro- apple wastes (1170 g water/100 g fibre), and orange
colloid. Water molecules are oriented around hydroxyl wastes (1620gwater/100 g fibre).
groups of sugar units and around anionic groups pre- The spray-dried gum also exhibited a significant
senting on some gums. They move around with the gum (p<0.05)higherWHC thanthe control,freeze-driedand
molecules, leading to swelling and increasing the volume vacuum oven-dried gums; while the control sample pro-
[35]. The peripheral polar groups and central hydropho- vided the lowest significant (p < 0.05) WHC among all
bicstemofpolysaccharidemoleculesgivedifferent inter- samples (Figure 5a). It was found that the freeze-drying
actions with water and electrolytes depending on their did not significantly (p > 0.05) influence the capacity of
compositions[36]. water absorption of durian seed gum. It should be noted
In the current study, WHC of different-dried durian thatWHCofgumdoesnotonlydependonthefunctional
seed gums varied from 232.8-254.8 (g water/100 g gum) group of polysaccharide fraction that are hydrophilic
as compared to the control sample (229.6 g water/100 g groups, but also on the protein fraction present in the
gum) (Figure 5a). This value was comparable with WHC gums. They also contain specific functional groups that
reported for fibre-rich fractions (FRFs) (237–320 mL/ are able to bind water molecules [40]. The capacity of
100 g), but lower than the WHC of cellulose (381 mL/ water absorption also depends on the numberand nature
100 g) from the defatted passion fruit seed [37]. Torio of the water-binding sites [37]. Chou and Morr [41] also
et al. [31] reported a relatively low water-holding cap- demonstrated that WHC varies as a function of several
acity (42.55-47.28%) for galactomannan from sugar palm factors such as the hydrophilic–hydrophobic balance of
(Arenga saccharifera Labill.) endosperm. The oven-dried amino acids in the protein molecule, lipid and carbohy-
gum showed the highest significant (p < 0.05) capacity drate fractions associated with the protein. The results
Figure5Effectofdifferentdryingmethodson(a)water-holdingcapacity(WHC)and(b)oil-holdingcapacity(OHC)ofdurianseedgum.
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showed that the drying process significantly (p < 0.05) foam capacity (0.00-4.78%), depending on the drying
influenced the oil-holding capacity (OHC) of durian seed method (Figure 6). Our preliminary study revealed the
gum (Figure 5b). The different-dried durian seed gums presence of the protein fraction (< 4%) in the molecular
exhibited different capacities of oil absorption. This could structure of durian seed gum [9]. It was hypothesized
be interpreted by the significant effect of the drying that the foaming properties of the natural biopolymer
processonthehydrophobicfraction(i.e. lipidandprotein from durian seed could be due to the presence of the
fractions)present in the structure of durian seedgum.As protein fraction along with its carbohydrate structure. In
alsostatedbyHaytaetal.[42],theoilabsorptioncapacity protein/polysaccharide systems, the possible phase sep-
of food material depends on the type and content of aration affects the foam stability. When air is injected
hydrophobic fraction present in the matrix structure. The into a solution containing the protein-polysaccharide
presence of trace fatty acid and hydrophobic amino acid biopolymer, the entrapment in the foam of bubbles
in the structure of durian seed gum may be responsible occurs as a result of the absorption of protein molecules
foritstendencyforoilabsorption.Theexistenceofseveral at the bubble surface. The basic requirements for the
nonpolarsidechainsmaybindthehydrocarbonchainsof proper foaming properties of the protein fraction are its
oil,therebyresultinginhigherOHC[43]. ability to: (a) adsorb rapidly at the air–water interface
As shown in Figure 5b, OHC of different-dried durian during bubbling; (b) undergo rapid conformational
seedgumsvariedwithintherangeof114.9to132.8(goil/ change and rearrangement at the interface, and (c) form
100 g gum) as compared to the control sample (113.2 g a cohesive viscoelastic film via intermolecular interac-
oil/100 g gum). This value was comparable with OHC tions [45]. The rapidly adsorption of the protein at the
reported for orange byproduct fibres (90–130 g/100 g) air–water interface and conformational rearrangement
[44], but lower than that of reported for fibre-rich frac- at the interface are associated with the appropriate
tions (FRFs) (207–372 g/100 g) from the defatted passion foamingability.
fruitseed[37].The current study revealedthat thedrying The freeze-dried gum and oven-dried gum showed the
ledtoincreasethe capacityofoilabsorptionascompared highest and lowest foaming capacity among all samples.
to the control sample. As shown in Figure 5b, the freeze- It was hypothesized that the freeze drying might result
dried gum gave the highest significant (p < 0.05) OHC in the least destructive effect on the protein structure,
among all samples. This might be due to the lower de- thus preserving the functional properties induced by the
structive effect of the freeze drying on the hydrophobic protein fraction present in the molecular structure of
fraction present in durian seed gum than the effects durian seed gum. On the other hand, the poor foaming
induced by other drying techniques. The oven-dried capacity of oven-dried seed gum might be due to the
(105°C) gum had the lowest capacity of oil absorption. thermal denaturation of the protein fraction. In fact, dif-
This could be due to the thermal oxidation (105°C) of ferent drying techniques resulted in different protein
tracelipidfractionpresentinthegumstructure. content, and molecular weight [9]. In the current study,
the freeze-dried and the spray-dried gums showed re-
Foamingcapacity markably higher foaming capacity than the other sam-
The present study showed that the drying process sig- ples (Figure 6). In the current study, the foam caused by
nificantly (p < 0.05) influenced the foaming capacity of stirring the gum solution was not stable for the long
durianseedgum(Figure6).AsshowninFigure6,differ- time. This could be due to the liquid drainage from the
ent dried durian seed gums exhibited different levels of foam. In fact, the air bubbles are spherical, and lamellas
Figure6Effectofdifferentdryingmethodsonthefoamingcapacityofdurianseedgum.
MirhosseiniandAmidChemistryCentralJournal2013,7:1 Page10of14
http://journal.chemistrycentral.com/content/7/1/1
containing large amounts of water are thick, when the fruit was purchased from the local market (Selongor,
foam is initially formed. The lamella becomes thin by Malaysia). Ripened durian fruits were selected based on
the time, and the liquid drainage from the foam starts. the size uniformity and free of visual defects. The fruits
Subsequently, air bubbles pack closer, and assume poly- were then de-husked (cut open the rind), by cutting
hedral shapes. In fact, the liquid drainage from the thin along the suture on the back of the lobules. Durian
lamellaeisthemaindestabilizing forceallowingthebub- seeds were removed, cleaned and rinsed thoroughly with
bles to become closer. Consequently, the large bubbles sterile distilled water. The seed was partially dried by the
are growing at the disbursement of small ones, when the air circulation at the ambient temperature for one over-
film membrane becomes permeable; the disproportion- night. The dried seeds were then packed in plastic bags
ation reaction occurs [46]. It should be noted that dis- and stored in a dry and cool place (10 ± 2°C) until the
proportionation is a typically a redox chemical reaction, extraction process [47]. All the experiments were per-
where a single element is simultaneously oxidized and formedwithdeionizedwater.
reduced. Finally, the film membrane at the air–foam
interfaceruptures,leading tocollapse the foam[46]. Chemicalextractionprocess
Chemical extraction was performed according to the
Conclusions method described by Singh et al. [17] with the minor
The main objective of the current study was to investi- modification. Durian seed were washed and chopped
gate theeffect ofdifferentdrying techniquesonflowabil- into small pieces. Then, it was air dried by using the air
ity characteristics and functional properties of the circulation before milling into flour. The cold extraction
natural carbohydrate polymer from durian fruit seed. was used to extract the oil from durian seed flour in
The present work revealed that the freeze drying pro- order to avoid the thermal degradation. The defatting
vided the most suitable flowability characteristics for process was carried out successively using hexane and
durian seed gum. The freeze dried gum showed the isopropanol (60:40) at the room temperature (25 ± 1°C).
highest porosity, solubility and foaming capacity among Preliminary trials showed that the solvent mixture con-
differently dried seed gums. This might be due to the taining hexane and isopropanol (60:40) was the most ef-
least thermal degradation, which probably resulted in ficient solvent for defatting process among all studied
less compact structure than other samples. On the other solvents (i.e. petroleum ether, hexane, isopropanol and
hand, the spray drying also also produced durian seed ethanol). The solvent residue was removed by centrifu-
gum with the appropriate flow characteristics and func- gation at ~3000 rpm for 15 min using the Beckman
tional properties as compared to freeze drying. Since, Coulter Centrifuge (JA-14, Beckman Coulter GmbH,
freezedryer isanexpensivemethodtoapplyinthe com- Krefeld, Germany). Then, defatted-durian seed flour
mercial scale; spray dryer may be a proper alternative (1 kg) was exhaustively decolored using ethanol at the
technique for producing durian seed gum. Although, the decoloringtime 120min. The decolorized seedflour was
oven drying is a low cost drying technique as compared vacuum filtered and then soaked in 1% aqueous acetic
to spray drying and freeze drying, but the current study acid for 1.5 h at the ambient temperature. Then, the
reveals that it provides a low quality durian seed gum slurry was filtered by using Nylon cloth filter and the fil-
withundesirable functionalproperties (i.e.poorflowabil- trate was precipitated with 95% ethanol. The precipi-
ity characteristics, low foaming capacity, and relatively tated slurry was washed three times using absolute
low solubility and oil holding capacity). It was hypothe- ethanol (99.9%) to achieve very light brown amorphous
sized that the oven drying at the elevated temperature crude gum [48]. The crude gum was collected and oven
(105°C) might have caused the collapse in the gum driedat 40°C.
structure. The thermal degradation possibly induced by
high drying temperature might result in more compact Purificationprocess
and rigid powder with the low porosity. The present The crude seed gum was purified through barium com-
work suggests a further study to produce durian seed plexing according to the method described by previous
gum with mono-dispersed particles and explore its dis- researchers [10,49]. In this method, the gum solution
solution mechanism. (2.5% w/v) was prepared by dissolving 2.5 g of the crude
durian seed gum in 100 mL of water and stirring for
Experimental 12 h at 60°C. Then, the gum solution was precipitated
Chemicalsandmaterials with saturated barium hydroxide solution. The precipi-
Isopropanol, ethanol (95% and 99.9%), acetone, hy- tate was separated by the Beckman centrifuge at
drochloric acid, saturated barium hydroxide, sodium 3500 rpm for 15 min. Then, the precipitate was stirred
hydroxide, acetic acid were purchased from Fisher with 1 M acetic acid for 8 h and again centrifuged. The
Scientific (Pittsburgh, PA, USA). Durian (D. zibethinus) supernatant was precipitated with 90% ethanol. The