Digestion of Raw and Roasted Almonds in Simulated Gastric Environment

13 Pages·2009·0.39 MB·English

FoodBiophysics(2009)4:365–377
DOI10.1007/s11483-009-9135-6
ORIGINAL ARTICLE
Digestion of Raw and Roasted Almonds in Simulated
Gastric Environment
Fanbin Kong&R. Paul Singh
Received:20June2009/Accepted:28September2009/Publishedonline:22October2009
#TheAuthor(s)2009.ThisarticleispublishedwithopenaccessatSpringerlink.com
Abstract Knowledgeofdigestionkineticsofsolidfoodsin duringroastingareimportantforpenetrationofgastricjuice
humanstomach,asaffectedbyfoodprocessingmethods,is that may facilitate an effective digestion.
critical in establishing processing conditions at the manu-
facturing stage to achieve desirable release of nutrients in Keywords Almond.Roasting.Digestion.Disintegration.
the gastrointestinal tract. The objective of this study was to Stomach.Texture.Microstructure
investigate how roasting affected disintegration and solid
release properties of almond in simulated gastric environ-
ment. In vitro trials were performed for raw and roasted Introduction
almonds by using static soaking method and a model
stomach system. The changes in sample weight, dry mass, Food processing has evolved to a step to create and design
and moisture during the trials were determined. Both food structures to affect food bioaccessibility and bioavail-
compression and penetration tests were used to investigate ability and to control the release of nutrients at the desired
the texture of almonds with a focus on the influence of site and rate in the human gastrointestinal (GI) tract. This
absorption of gastric juice. Light microscopy and transmis- requires a good understanding on how food processing
sion electronic microscopy were used to study the change affects structure and texture and its influence on digestion
in microstructure of the raw and roasted almonds after properties. Also, it is important to understand the changes
simulated digestion. The results suggested that the slow that occur in foods in the human GI tract leading to the
disintegration rate and the high amount of swelling of the breakdown of food matrix and release of food nutrients.
almondsinthestomachmaycontributetotheirhighsatiety Currently, available information in the literature is limited
property.Roastingsignificantlyimprovedthedisintegration on the digestion kinetics of foods and its relationship with
rates of almonds and increased loss of solids during material properties such as texture and microstructure. In
simulated digestion, which is well correlated with the this paper, we studied how roasting affected almond
decrease in the rigidity of almond samples after absorbing disintegration and the release of solid matter in a simulated
gastric juice. Microstructure of digested almonds showed gastric environment. The results were related with the
breakage and breach of cell walls due to acid hydrolysis. changes in texture and microstructure of raw and roasted
Intercellular and intracellular channels formed in almonds almonds during digestion.
The consumption of tree nuts has increased by 45% in
: theUnitedStatesoverthelastdecade, andalmond(Prunus
F.Kong R.P.Singh(*) dulcis) consumption has increased the most.1 California is
DepartmentofBiologicalandAgriculturalEngineering,
themajorgrowerofalmondsintheUS,andmorethanhalf
UniversityofCalifornia,
Davis,CA95616,USA ofthestate’sproductionisthe“Nonpareil”variety.Almonds
e-mail:[email protected] contain ∼21% (w/w) protein and ∼50% (w/w) oil content in
which oleic and linoleic acids are the major constituents.
R.P.Singh
Almonds are also a nutrient-dense source of vitamin E,
RiddetInstitute,MasseyUniversity,
PalmerstonNorth,NewZealand manganese, magnesium, copper, phosphorus, fiber, and
366 FoodBiophysics(2009)4:365–377
riboflavin.2Studieshaveshownthatalmondshavebeneficial store. All samples were stored at 3–5°C. Based on a
effectsoncardiovascularhealth,obesity-relateddiseases,and random sampling of ten almonds, the following measure-
certain cancers.2, 3 Roasted almonds are a popular product ments were obtained: weight (1.42±0.04 g), length (2.39±
consumedasasnackfood.Itisalsousedasaningredientin 0.08 cm), width (1.42±0.05 cm), and thickness (0.86±
many bakery and confectionary foods, such as sweets, 0.04 cm). Almonds were roasted in a household toaster
chocolate, and biscuits. Roasting enhances the flavor and oven (Hamilton Beach Brands, Washington, NC, USA) at
significantly alters the color and texture. The conditions of 185°C for 9 min. In vivo studies have shown that, after
roasting generally used by processors are heating to 100– chewing, the size of masticated almond particulates is
200°C and a residence time of 10 to 60 min.4, 5 mostly less than 3 to 4 mm.16 To facilitate convenient
Almonds possess rigid texture that may make it hard to sample loading and achieve a substantial percentage mass
breakdowninthestomachduringdigestion.Ellisandothers loss in the experiment, larger size particulates (6 mm in
reported that a significant proportion of raw almond tissue diameter and length) were used for this study. For
is preserved intact even after chewing, digestion, and large disintegration and solid release trials, rectangular prismatic
bowel fermentation.6 On the other hand, food processing sections (length × width × height=6×6×4 mm, weight
such as boiling significantly changes the food texture, thus 0.15 g) were cut from raw and roasted almonds. Samples
modifying the rate of gastric disintegration.7 To our knowl- with other dimensions were also prepared to investigate
edge, no study has been conducted on the rate of almond how particulate size influences disintegration rates, includ-
disintegration in gastric environment as related to the roast- ing 5×5×4, 4×4×4, and 3×3×3 mm, with a weight of
ing conditions, although in vitro gastric digestion was used 0.10, 0.06, and 0.03 g, respectively.
to evaluate the nutrient bioaccessibility including protein, Simulated gastric juice and saliva were prepared as
lipid, and vitamin E of almonds.8 Research is also required described in a previous paper.7 Simulated gastric juice (pH
to achieve an improved understanding of the role that the 1.8) comprised of pepsin (1 g/L), gastric mucin (1.5 g/L),
texture and microstructure of almonds and their inherent and NaCl (8.775 g/L). Simulated saliva included gastric
changes during digestion play on disintegration kinetics. mucin (1 g/L), α-amylase (2 g/L), NaCl (0.117 g/L), KCl
In vivo approaches such as feeding study, intubation (0.149 g/L), and NaHCO (2.1 g/L). All chemicals were
3
techniques, scintigraphy, ultrasonography, and magnetic purchased from Sigma-Aldrich (USA).
resonance imaging have been used to assess gastric
disintegration and emptying of food and drugs in clinical Static Soaking Test
andresearchsettings.Besides,anumberofinvitroGItract
models, such as the TNO intestinal model, are currently The samples (6×6×4 mm) were first soaked in the
available for nutrition, toxicology, pharmacology, and simulated saliva at 37°C for 15 s to incorporate the effect
safety assessments.9 The advantages of in vitro techniques of oral exposure on food digestion. The samples were
include no ethical constraints, reduced cost, and improved withdrawn from the simulated saliva and blotted to remove
accuracy and reproducibility. In our previous paper, we excess water. The weights were measured as initial weight
have presented an in vitro model stomach system to W (ingrams).Thensamplesweresoakedingastricjuicein
0
investigate disintegration kinetics of solid foods in human a 37°Cwaterbath for different time periods,from 1 to5 h,
stomach.7 This model is useful in studying the disintegra- as most foods empty from stomach to intestine within
tion and release of solid matter from different foods as it 5 h.9
provides adjustable and measurable hydrodynamic and/or Each particulate sample was hooked into the tip of a
mechanical forces. The aim of the current study was to rigid steel wire and suspended in 20 mL gastric juice in a
evaluate the disintegration and solid release characteristics test tube. The sample was suspended in the central part of
of raw and roasted almonds using a static soaking method the tube. After soaking, the weight of the sample Wt (in
and the model stomach system and to investigate the grams) was measured again. The moisture of the sample
relationship between the digestion properties of almonds was determined by using a hot air oven at 105°C until
and their texture and microstructure. constant weight was achieved (typically in 18 h). M (in
0
percent) and Mt (in percent) were denoted as initial
moisture and the moisture after trial time t in dry basis.
Materials and Methods Dry mass of samples was calculated based on the sample
weight and moisture. Weight retention ratio and dry mass
Preparation of Samples retention ratio were calculated as follows:
W
Shelled raw almonds of the Nonpareil variety (Diamond Weight retention ratio; yt ¼ Wt ð1Þ
Foods, Stockton, CA, USA) were purchased in a grocery 0
FoodBiophysics(2009)4:365–377 367
where W0(ingrams)istheinitial weight andWt(in grams) The beads effectively generated mechanical force by
is the sample weight after time t (in minutes). impacting and grinding food samples during trials. The
stable physical and chemical properties of the ABS beads
Dry mass retention ratio; St ¼ DMt ð2Þ and theirhigh mechanical strength toresistfriction provide
DM0 sustainable and repeatable force conditions.
For trial A, samples were first soaked in the simulated
where DM0 is the initial dry mass (in grams) and DMt (in saliva for 15 s (37°C). The sample surfaces were blotted
grams) is the dry mass after time t (in minutes). using a filter paper, and the weight was determined as the
Static soaking of whole almond kernels was also initial weight W (in grams). The samples were then tested
0
conductedtoevaluatethechangeinthedensityandvolume inthemodelstomachsystem.Themodelcontained500mL
ofalmondsduringdigestion.About26g(∼19kernels) raw of simulated gastric juice with a rotation speed set at
and roasted almond samples (whole kernel with skin) were 30 rpm. For each trial, four samples were tested simulta-
soaked in 100 mL simulated gastric juice contained in neously. The force measured using the torque cell was
beakers covered by aluminum foil at 37°C water bath for approximately 0.001 N for each sample. The trials were
16h.Aftersoaking,thesampleswerecarefullydrainedand continued for 1, 2, 3, 4, and 5 h, respectively. Then the
the samples were blotted using filter paper. Changes in the model was stopped and samples were taken out, dried with
sample weight were determined. The kernel volume was afilter paper toremovesurfacemoisture,andmeasured for
obtained by determining the change in the volume of weight Wt (in grams). The moisture and dry mass content
gastric juice with or without almond kernels. were subsequently determined for each sample.
For trial B, 330 g plastic beads were combined with
In Vitro Digestion of Almonds in the Model 170 mL simulated gastric juice to make 500 mL simulated
Stomach System gastriccontent.Thisratioofbeadsweight/juicevolumewas
selected to generate the mechanical force simulating the
Theinvitrodigestiontestforrawandroastedalmondswas highestlevelofstomachforcemeasuredinvivoasreported
conducted in a model stomach system as described in our in literature. All trials were conducted following the same
previous paper.7, 10 The stomach model is comprised of a procedure as trial A. The mechanical force generated by
glass chamber which holds simulated gastric juice at 37°C. beads impacting on the sample was approximately 0.1 N,
Thechamberisplacedonaturntableandrotatedatselected which is comparable to the maximum force present in the
revolutions per minute. Almond samples were fixed in a humanstomach.10Thetrialswerecontinueduntil1,2,3,4,
sample holder and submerged into gastric juice at about and 5 h, respectively. The weight retention, moisture, and
1.5 cm depth. In this study, the sample holder was dry mass retention ratio of samples for each trial were
connected to a reaction torque cell (Omega Engineering, determined accordingly.
TQ201-25Z) and a data acquisition system (Omega Trial B was also conducted to evaluate the effect of
Engineering, OMB-DAQ-54) to measure forces acting on samplesizeondisintegrationratesofrawalmonds.Forthis
the samples during trials. The samples were tested under experiment, samples with different dimensions were tested
two different experimental settings, depending on whether in the stomach model. Same samples were treated for 6 h,
or not plastic beads (GP-22 Natural ABS Plastic Beads, and the weight changes were determined with 1 h time
BASF Corporation, New Jersey) were added into the interval.
simulated gastric juice. These plastic beads, incorporated
into gastric juice to mimic food particulates in human Textural Measurement
stomach,haveasizeof3mmdiameterandspecificgravity
of 1.03. When plastic beads were not combined with the Compression test and penetration test were used to
gastricjuice,whichisreferredtoas“trialA,”sampleswere determine textural properties of raw and roasted almonds,
subjected to hydrodynamic shearing stress caused by the both before and after static soaking in gastric juice.
rotating fluid; when plastic beads were combined with the
gastricjuice,referredtoas“trialB”or“disintegrationtest,” Uniaxial Compression Test
a mechanical force was created resulting from the beads
impacting and grinding the samples that caused food The rectangular prismatic section samples (6×6×4 mm)
disintegration, simulating the forces due to contraction that before and after static soaking for 7.5 h were used for
are present in a human stomach due to peristaltic compression test. A cylindrical flat-end probe (4 cm
movement.7 The approach of using plastic beads to create diameter) was fitted to the Texture Analyzer TA-XT2
mechanical force originated in drug dissolution studies.23 (Texture Technologies, Scarsdale, NY, USA/Stable Micro
This method was adopted in our model stomach system.7 Systems,Godalming,Surrey,UK)equippedwithaloadcell
368 FoodBiophysics(2009)4:365–377
of 50 kg. The probe traveled to 3 mm depth into the 37°C. LM and TEM images were obtained for the soaked
samplesataspeedof1mm/s.Sampleswerecompressedat raw and roasted samples following the method presented
a direction transversal to the sample height. During the test elsewhere.10
run, the resistance of the sample was recorded for every
0.01 s and plotted as a force (in newtons) vs. time (in Statistical Analysis
seconds) graph. The following measurements were carried
outtocharacterizethemechanicalpropertiesoftherawand Weight retention data (yt vs. t) for the disintegration test
roasted almonds before and after soaking 11–13: wereanalyzedandfittedintoempiricalmodels.Thegeneral
linear models procedure (GLM) in the SAS software
(a) Fracture force, F (in newtons): the force at the first
package for Windows V8.01 and the Solver command in
major failure event.
theEXCELsoftwarewereusedtoobtainmodelparameters.
(b) Deformation,δ (in millimeters): the absolute deforma-
Estimates for parameters were obtained by minimizing the
tion where the first break occurred.
mean square error (MSE). MSE is a measure of the
(c) Hardness after fracture, H (in newtons): the maximum
goodness of fit. In addition, the correlation coefficient (r)
force values after fracture point, which were usually
was used as a criterion for evaluating the performance of
the force at 3 mm depth (example curves shown later
the models. A significance test was conducted using
in the “Results and Discussion” section).
analysis of variance in the GLM procedure of the SAS
(d) Compression work, A (in newton millimeter): area
system. Differences between group means were analyzed
under the curve, force vs. distance, in the test for
by Duncan’s multiple-range test. Statistical significance
compression. It is considered as an empirical index of
was set at a probability level of 0.05.
toughness and associated with total energy input
during compression.
(e) Stiffness, S (in newtons per millimeter): the slope of
Results and Discussion
the line joining the origin and the peak force.
Results of Trial A and Static Soaking Test
Penetration Test
Figure 1 shows the changes of weight retention ratio, dry
Rectangular prismatic section samples (10×10×4 mm) mass retention, and moisture of raw and roasted almonds
were cut from the raw and roasted whole kernel almonds with time during trial A in which the samples were
both before and after soaking for 16 h. A flat-ended needle subjected to hydrodynamic mixing when no mechanical
probe (2 mm diameter) was fitted to the Texture Analyzer force was involved. In the pharmaceutical industry, the
TA-XT2. The probe traveled to 3 mm depth transversal to United States Pharmacopeia (USP) dissolution testing is
the sample height at a speed of 1 mm/s, and the following commonly used for evaluating drug tablets, capsules, and
parameters were calculated for the force–distance curves: nutritionaldietarysupplements,whichalsoinvolvesmixing
(a) Fracture force, F (in newtons): the force at the first samplewith simulatedgastric juicetocause thedissolution
of active ingredients.9 But the advantage of the model
break of the sample.
(b) Deformation,δ(inmillimeters):thedeformationatthe stomach system we usedisthat thehydrodynamicshearing
effect on the tested samples can be controlled by adjusting
fracture point.
(c) Hardness after fracture, H (in newtons): the maximum the rotational speed of the turntable and the hydrodynamic
forcescanbemeasuredwiththetorquecellsimultaneously.
force value after the first break.
(d) Penetrationwork,A(innewtonmillimeter):areaunder When a food material is mixed with gastric juice, two
the force–distance curve. types of mass transfer occur, namely, diffusion of gastric
(e) Stiffness, S (in newtons per millimeter): the slope of juice into the food and leaching of solids (such as proteins,
fibers, oils, vitamins, and minerals) from the food to the
the line joining the origin and the peak force.
gastric fluid. The acid and enzyme in the gastric juice
enhance the leaching of solids due to the hydrolysis and
Microscopy Examination enzymaticreactionsthatreducethecohesiveforcesbonding
the solid material within the food matrix. The liquid
Light microscopy (LM) and transmission electron micros- concentration gradient provides the driving force for the
copy (TEM) were used to investigate changes in the first type of mass transfer, while the concentration
microstructure of raw and roasted almonds after simulated difference of solids causes the driving force for the second
digestion.Rawandroastedalmond(185°C,9min)samples type ofmass transfer.Inourstudy, wequantified these two
(5×5×4 mm) were soaked in gastric juice for 60 min at processes by measuring the sample weight and moisture
FoodBiophysics(2009)4:365–377 369
a 1.6 Toinvestigatehowhydrodynamicmixingofgastricfluids
affectsthesolidreleaseofalmonds,wealsoconductedstatic
1.4 soaking of the raw and roasted almonds. In this case, the
samples were soaked in gastric juice at 37°C. The soaking
1.2 conditionswerethesameasthoseintrialAexceptthatthere
wasnofluidrotationsotherewasnohydrodynamicshearing
o
ati 1 effect. Interestingly, the result indicated that there was no
R
significantdifferencebetweenthestaticsoakingandtrialAof
0.8 thetwosamples(rawandroasted)intermsofweightchange,
Total weight retention, raw almonds moisture increase, and solid (dry mass) loss. This result
0.6 Total weight retention, roasted almonds indicatedthat,forrawandroastedalmonds,whenexposedto
Dry mass retention, raw almonds
a simulated gastric environment similar to what was used
Dry mass retention, roasted almonds
0.4 here, the nutrient release will not be affected by the
0 50 100 150 200 250 300 350 hydrodynamicconditionsofsurroundinggastricfluid.Using
Trial time (min)
b acomputersimulation,Palandothers14 reported maximum
80
retropulsive flow velocities in the stomach antrum of
70 approximately 7.5 mm/s. With 30 rpm rotational speed in
our model, the flow speed impacting the samples is much
60
%) higher (204 mm/s). It is, therefore, reasonable to conclude
b.) ( 50 that, in almond digestion, for leaching of nutrients, the
e (d. 40 internalresistance ismoreimportant than surface resistance.
ur
oist 30 Results of Trial B
M
20
Raw Roasted Whenthemechanicalforcewasincorporatedbycombining
10
plasticbeadsintogastricjuiceinthemodelstomachsystem
0 (trial B), the changes in weight and dry mass retention
0 50 100 150 200 250 300 350
ratios andmoisture for raw and roasted almondsare shown
Trial time (min)
inFigure2.Thechangeinsampleweightanddrymassisa
Fig.1 Retentionoftotalweight,drymass,andchangeinmoisturein combined effect of leaching of solids and surface erosion.
raw and roasted almonds during trial A (n=4). Volume of simulated
Surface erosion indicates the removal of solids from the
gastricjuice=500mL;turntablerotationspeed=30rpm
food surface by an impinging gastric fluid containing
plastic beads that impact and shear the food surface. The
and calculated the loss of dry solids. The weight retention weight retention profiles (disintegration profile) shown in
ratio and the dry mass retention ratio were thus calculated Figure 2 have a delayed-exponential shape, that is, the
respectively to indicate the overall effect of food digestion weightretentionratioincreasedatfirstsothatitwashigher
and the net release of solids. than 1,then decreasedgradually duetosurfaceerosionand
Trial A test showed that, for both raw and roasted leaching of solids. Delayed-exponential profile resulted
almonds,theweightofthesamplescontinuouslyincreased, fromthewaterabsorptionofalmondsduringdigestion,i.e.,
while the dry mass (solids) decreased (Figure 1a). There is thewaterabsorptionratewashigherthantherateofsurface
no significant difference in the dry mass retention ratios of erosion and solid release leading to a net increase in the
raw and roasted almonds, both decreased continually to sample weight.10 It can be also seen that, after the same
approximately 87.5% after 5 h of treatment, corresponding treatment, roasted almonds had more weight loss than raw
to a 12.5% solids loss. The solid loss during soaking is almonds(P<0.05).After5h,theweightretentionratiowas
mainly due to the loss of fat and proteins.8 The increase in 0.93 and 0.77 for the raw and roasted almonds, respective-
sample weight was due to the absorption of gastric fluid ly.Inourpreviouspaper,weproposedalinear–exponential
(Figure 1b). The initial increase in water content was equation to describe data obtained for the weight retention
rapid, leading to a fast increase in sample weight within ratio vs. disintegration time 10:
the first 2 h. At the end of the 5-h trial, raw almonds
absorbed more gastric juice than roasted almonds, 67.7% yt ¼ð1þk(cid:1)b(cid:1)tÞ(cid:2)e(cid:3)b(cid:1)t ð3Þ
and 48.8% in moisture (d.b.), respectively, which
resulted in a higher weight gain in raw almonds than where k is a dimensionless constant and β (1/min) is a
roasted almonds. parameter that measures the concavity of the time–weight
370 FoodBiophysics(2009)4:365–377
a and roasted almonds, respectively. These results indicate
1.6
Total weight retention, raw almonds that roasting improved the disintegration of almonds and
Total weight retention, roasted almonds increased solid release during in vitro digestion.
1.4
Dry mass retention, raw almonds The solid loss of 40–50% for almonds in trial B vs.
Dry mass retention, roasted almonds 12.5%intrialAindicatedthat,foralmonds,themechanical
1.2
forces due to peristaltic contraction of the stomach may be
o critical for the effective release of nutrients. This finding
ati 1
R suggeststhat,when conductinginvitrotestingofbioacces-
sibility of food/drug tablets, the mechanical force should
0.8
not be neglected. The model stomach system used here is
effectiveforstudyingfooddigestionandnutrientreleaseas
0.6
it is capable of providing measureable and controllable
mechanical force to simulate in vivo contraction forces
0.4
present in the stomach.
0 50 100 150 200 250 300 350
Trial time (min)
b Disintegration of Raw Almonds with Different Size
60
in Model Stomach System
50
Asshownintheprecedingsections,largesizesamples(6×
%) 40 6×4 mm) were used to compare the disintegration rates
b.) ( between raw and roasted samples. In reality, after mastica-
e (d. 30 tion, almonds are broken into much smaller pieces of
stur particulates, with only 10% larger than 2 mm.15 In another
Moi 20 Raw Roasted study, Frecka and others 16 reported that ∼3% of the total
weight of masticated almonds have a size >3.35 mm. An
10
experiment was conducted to investigate how the size of
almond particulates affected the disintegration rate. Raw
0
0 50 100 150 200 250 300 350 almond samples with different dimensions were tested in
Trial time (min)
the stomach model subject to a mechanical force of 0.1 N
Fig. 2 Retention of total weight, drymass, and moisture changes in for each sample (trial B). The disintegration profiles and
raw and roasted almonds during trial B (n=4). Volume of simulated fittedmodelcurves(Eq.3)areshowninFigure3.Itcanbe
gastric content=500 mL (gastric juice=170 mL, beads=330 g);
seenthatallthetestedsamplesdisplayeddelayed-sigmoidal
turntablerotationspeed=30rpm
profiles, and the disintegration rate increased with the
reducing sample size. The model parameters are shown in
retentionrelationship.Theadvantageofthisequationisthat Table 2. The half time significantly decreased with the
it provides a good fit of three different disintegration sample size/weight, from 10 h for the 6×6×4-mm sample
profiles, namely, exponential, sigmoidal, and delayed- size (0.15 g) to 5 h for the 3×3×3-mm sample (0.03 g). In
sigmoidal profiles.10 The k and β values can be derived this size range, a linear relationship exists between sample
using regression. The half time (the disintegration time to weight and half time:
a0c.5h.ievTeh5is0%pamraasmseltoesrs),ist1/2u,scuaanllbyecuaslecdulattoedebxypurseisnsgytht=e t1=2 ¼2615:4(cid:1)wþ214:9 R2 ¼0:987 ð4Þ
disintegration rate. Table 1 shows the parameters of Eq. 3. where w is the initial sample weight (in grams) ranging
It shows that the t1/2 for raw and roasted almond were 11 from 0.03 to 0.15 g and t is the half time (in minutes).
1/2
and 7.4 h, respectively. From additional experiments, we
also found that the disintegration rates increased with an
increaseinroasting temperatureandtime (datanotshown). Table1 Modelparametersofsimulatedgastricdisintegrationofraw
and roasted almonds calculated with the linear exponential model
The moisture content of samples had a rapid increase
(Eq.3)
initiallyfollowedbylevelingoff(Figure2b).Rawalmonds
had larger water absorption than roasted almonds (54.8% k β MSE r t
1/2
vs. 50.0%) at the end of the trial. The dry mass retention (×10−31/min) (×10−4) (min)
ratio continuously decreased, with the roasted sample
Raw 1.664 3.789 0.11 1.00 666
exhibiting a slightly higher decrease (Figure 2a). After
Roasted 1.592 4.935 3.80 0.99 445
5 h, the dry mass retention ratio was 0.61 and 0.52 for raw
FoodBiophysics(2009)4:365–377 371
1.4
roasting that resulted in a loss of water absorption ability
in roasted almonds.
1.2 The significant water absorption in raw and roasted
o almonds is accompanied by volume swelling. By measur-
ati
n r 1 ing the volume of whole almonds before and after
o
nti overnight soaking, it was found that the volume increased
e
et by44%and32%forrawandroastedalmonds,respectively.
ght r 0.8 The specific gravity of raw and roasted almonds was
ei
W calculated. It was initially 1.04 and 1.01, respectively, and
0.6 both decreased to approximately 1.00 after overnight
3*3*3 mm (0.03 g) 4*4*4 mm (0.06 g)
soaking. Therefore, the weight retention ratio profiles as
5*5*4 mm (0.10 g) 6*6*4 mm (0.15 g)
showninFigures1a,2a,and3alsoreflecttheapproximate
0.4
0 100 200 300 400 500 value of volume change during digestion. A maximum of
Trial time (min) approximately 10% increase in volume can be seen for the
raw almonds with 6×6×4 mm size (Figures 2a and 3),
Fig.3 Weightretentionofrawalmondsofdifferentsizesfittedwith
Eq. 3 (n=4). Equation parameters fitted to the data in the figure are while for smaller particulates, such as 3 mm cubes, the
showninTable2 swelling can be up to 30% of original volume (Figure 3).
After oral mastication, almonds are broken into even
The reduction of half time with reducing sample size smaller pieces with only 10% larger than 2 mm,15 an even
emphasizes the importance of chewing. In vivo studies higher amount of swelling can be expected. We also
have shown that, during digestion in the stomach, food is observed that the swelling capacity increased with increas-
reduced into 1- to 2-mm-size particulates before the chyme ingtemperatureandtimeofroasting(datanotshown).This
is discharged into the intestine, and this process usually finding may have important implications in developing
completes within 5 h. After 5 h, the indigestible large healthy diets incorporating almonds. A fully chewed
objects are emptied only during phase III activity in the almond diet (or almond powder) may generate a rapid
fasting motilitypattern.17Considering thatthese trials were satiety feeling due to a larger increase in volume but the
conducted under the forces simulating the maximum stomach emptying rate will be also faster, while partially
mechanical force present in a human stomach, the results chewed almonds, with the larger particulate size, may
suggest that a considerable amount of almond particulates generate slower satiety feeling due to lower swelling
(both raw and roasted) may be emptied to intestine with capacity, but the fullness feeling may last for a longer time
relatively large size (>1–2 mm). Furthermore, the slow because of the slower breakdown of the large particulates.
disintegration rate will lead to a slow stomach emptying Nutrition studies have documented that nuts have high
rate and an increased feeling of fullness. Epidemiologic satietypropertieswhilethemechanismremainsunknown;18
studies have documented that a high frequency of almond our results indicated that the significant swelling and the
consumptionmaylowerbodymassindex.18Thiseffecthas slow disintegration rate of the ingested almonds in the
been related with the resistance of nut parenchyma cell stomachmaybeanimportantreason.Althoughnostudyon
walls to microbial and enzyme degradation in the GI tract the swelling of almonds in gastric lumen was found in the
that results in a considerable amount of undigested almond literature, in vivo studies have shown that ingestion of
fractions passingthroughtheGItract withphysicallyintact dietary oat can cause stomach distension and affect satiety
cells.6, 8, 18 due to water absorption and swelling.19 Further research,
especially an in vivo study, is needed to quantitatively
Water Absorption and Volume Swelling of Raw
and Roasted Almonds in Gastric Environment
Table2 Modelparametersofsimulatedgastricdisintegrationofraw
almonds with different dimensions calculated with the linear–
Static soaking tests, trial A, and trial B all indicated that
exponentialmodel(Eq.3)
raw almonds absorbed more gastric juice than roasted
samplesduringdigestion.Thisresultwasfurtherconfirmed k β MSE r t
1/2
by soaking of whole kernel almonds: after 16 h soaking, (×10−31/min) (×10−4) (min)
raw and roasted almonds had 103% and 69% moisture (d.
6×6×4mmcube(0.15g) 1.78 3.90 0.09 1.00 599
b.), compared with initial moisture of 2.7% and 1.1%,
5×5×4mmcube(0.10g) 2.04 5.04 5.26 0.99 497
respectively. This difference between the moisture of
4×4×4mmcube(0.06g) 2.21 7.29 1.27 1.00 357
soaked raw and roasted almonds may be due to the
3×3×3mmcube(0.03g) 2.32 9.00 8.61 0.99 296
structural damage and cell shrinkage occurring during
372 FoodBiophysics(2009)4:365–377
characterize the swelling phenomenon of almonds in a180
human stomach and its implications in satiety and obesity
control. 150 Raw
Roasted
Textural Changes of Raw and Roasted Almonds 120
During Digestion N)
e ( 90
c
or
In vitro disintegration trials reported in this paper have F
60
shown that roasting can improve the disintegration rate
of almonds and the solid release. It is, therefore,
30
important to understand the underlying mechanisms that
cause the observed changes in the digestion properties
0
from the perspective of food material properties. Food 0 0.5 1 1.5 2 2.5 3 3.5
texture and its change during digestion are crucial for Distance (mm)
b
different rates of food disintegration.7, 10 The texture of 180
raw and roasted almonds before and after soaking in
150 soaked raw almond
simulated gastric juice were studied with the aim to (1)
soaked roasted almond
investigate how almond texture and its change in the
120
gastricenvironmentaffecteditsdigestionperformanceand N)
(2) seek textural properties that can best correlate with its e ( 90
digestion properties. We tried both uniaxial compression orc
F
test with a flat-ended probe and penetration test using a 60
needle probe.
30
Uniaxial Compression Test
0
0 0.5 1 1.5 2 2.5 3 3.5
Figure 4 compares the force–deformation curves for raw
Distance (mm)
and roasted almonds under a compression test. Table 3
Fig. 4 Typical compression curves (force–distance [deformation]
shows the values of textural parameters obtained from the
curve) for raw and roasted almonds before soaking in simulated
curves. Significantly different textural profiles between the
gastricjuice(a)andaftersoakingfor6.5h(b)
almonds, before and after soaking in simulated gastric
juice, can be seen by comparing Figure 4a, b. Firstly, the
overall resistance of almonds to compression (hardness at profile of roasted almonds than the raw samples, indicating
3 mm depth and stiffness) significantly decreased after a more crispy texture for roasted almonds, as a result of
soaking, indicating a softening effect resulting from the reduced moisturecontent,increasedporosity,andstructural
plasticizer effect of water absorption, acid hydrolysis, and alteration during the roasting process.12 The average
enzymatic reaction during digestion. Secondly, before stiffness value for almonds before soaking slightly in-
soaking, the resistance increased continually during com- creased after roasting, although this difference is not
pression, so that the highest force is at the 3 mm depth, significant (Table 3).
while after soaking, the profiles show a large decrease in Absorption of gastric juice caused a significant decrease
the force at the fracture point, so that the highest force is inhardness,stiffness,andtotalenergyinputduetoincrease
alsothefractureforce.Thisindicatesamorestifftextureof in moisture and hydrolysis and enzymatic reactions that
almonds before soaking due to their low moisture, as modifiedthestructure(Table3).Soakingcausedsignificant
indicated by the higher stiffness values in the almonds differencesbetweenthetextureofrawandroastedalmonds.
before soaking. After soaking, raw almonds had a significantly higher
In general, for the almonds before soaking, degree of stiffness(67.23N/mm)thanroastedalmonds(49.68N/mm;
roasting showed a limited influence on the textural Table 3). The hardness and total work input in the raw
propertiesunderstudy,andthereisnosignificantdifference almonds are also slightly higher. This might be related to
among raw and roasted almonds for the hardness, stiffness, thecellularandstructuraldisruptionthattakesplaceduring
andthetotalarea(energyinput;Table3).However,roasted roasting resulting in a loss in elasticity of roasted almonds
samples fractured at lower forces, and the force of the first during water absorption. The lower stiffness values in the
fractureissignificantlylowerfortheroastedalmonds.Also, soaked roasted almonds than the raw almonds are in good
therearemorefracturepoints,i.e.,higherjaggedness,inthe agreement with the increase in their disintegration rate,
FoodBiophysics(2009)4:365–377 373
Table3 Texturalparametersobtainedwithcompressionofa50-mmflat-endprobefor3mmdepthonrawandroastedalmondsamplesbefore
andaftersoakinginsimulatedgastricjuicefor6.5h(samplesize=6×6×4mm;n=10)
F(N) δ(mm) H(N) A(Nmm) S(N/mm)
Beforesoaking
Raw 91.13±17.53a 1.04±0.22b 177.91±14.34a 293.25±14.95a 88.29±7.47a
Roasted 64.39±28.03b 0.64±0.20c 161.25±22.25a 301.80±39.32a 99.27±23.49a
Aftersoakingfor6.5h
Raw 84.44±25.85a 1.24±0.26b 66.09±8.52bc 125.61±16.16b 67.23±13.05b
Roasted 92.05±22.52a 1.85±0.33a 58.57±18.65c 112.49±25.55bc 49.68±8.64c
Ffractureforce,δdeformationatthefracturepoint,Hhardnessat3mmdepth,Acompressionwork,Sstiffness.Differentletterswithinacolumn
indicatesignificantdifferences(p<0.05).
indicating that stiffness of soaked almonds may be a From Tables 3 and 4 and Figures 4 and 5, we can
suitable indicator of the disintegration properties. observe that both compression and penetration tests are
able to characterize the significant difference between the
Penetration Test rigidityofrawandroastedalmondsafterabsorbinggastric
juice, as indicated by the stiffness obtained from the
The penetrometry profiles (force vs. depth of penetration)
of raw and roasted almonds before and after soaking are
shown in Figure 5a, b. These profiles show significantly
a
40
different features. In Figure 5a, for the almonds before
soaking, there is a sudden drop in the curves after first 35
fracture, indicating that a break occurred in the sample due
30
to the crisp nature of their texture, while this phenomenon
did not occur for the soaked samples as the crispness 25
decreased after absorbing water. Moreover, these profiles N)
e ( 20
show that, following the first fracture point, the resistance c
or
mayincrease,decrease,orremainunchanged.Accordingto F 15
Bourne,13 force–distance curve obtained from penetration
10 Raw almond
or puncture tests can be categorized into different types
Roasted almond
based on the direction of force change after fracture point 5
(yieldpoint).IntypeA,theforcecontinuestoincreaseafter 0
the yield point; in type B, the force is approximately 0 0.5 1 1.5 2 2.5 3 3.5
constant after the yield point; and in type C, the force Distance (mm)
b
40
decreases after the yield point. In Figure 5a, raw almond
before soaking showed mostly type A and B curves while 35
all of the roasted almond showed type A curve, which is Soaked raw almond
related to a more crisp or brittle texture in the roasted 30 Soaked roasted almond
almonds.Aftersoaking,raw almonds showedtype Bcurve 25
while roasted almonds showed type C curve, indicating a N)
“woody” texture in roasted almonds as a result of water ce ( 20
absorption during soaking.13 For 15
Table 4 shows the mean values of different textural
10
parameters. Before soaking, raw and roasted samples had
noobvioustrendinthechangesoffracture force,hardness, 5
stiffness, and the total work input. However, after soaking,
0
except fracture force, all the parameters showed significant 0 0.5 1 1.5 2 2.5 3 3.5
differences between the raw and roasted almonds, and the Distance (mm)
raw almonds had significantly higher values for all the
Fig. 5 Typical penetration curves (force–distance [deformation]
parameters, which correspond to the slower disintegration
curve) for raw and roasted almonds before soaking in simulated
of the raw almonds during digestion. gastricjuice(a)andaftersoakingfor16h(b)
374 FoodBiophysics(2009)4:365–377
Table4 Texturalparametersobtainedwithpenetrationofa2-mmneedlefor3mmdepthinrawandroastedalmondsamplesbeforeandafter
16hsoakinginsimulatedgastricjuice(samplesize=10×10×4mm;n=10)
F(N) δ(mm) H(N) A(Nmm) S(N/mm)
Beforesoaking
Raw 29.15±3.56ab 0.52±0.06a 29.34±2.80a 77.06±29.12a 56.36±9.21a
Roasted 21.68±3.00b 0.43±0.08a 34.44±3.48ab 96.00±14.84ab 51.45±12.95a
Aftersoakingfor16h
Raw 13.12±1.24c 0.50±0.06c 12.22±0.89c 62.68±5.50c 26.55±5.22b
Roasted 13.32±1.30c 1.02±0.11b 7.55±1.42d 36.26±4.36d 13.23±2.03c
Ffractureforce,δdeformationatthefracturepoint,Hhardnessat3mmdepth,Apenetrationwork,Sstiffness.Differentletterswithinacolumn
indicatesignificantdifferences(p<0.05).
compression and penetration tests. The lower rigidity of space in almonds.4, 5 The moisture decrease and parenchy-
soaked roasted almonds than soaked raw almonds had a ma disruption is the principal cause of the increase in
good correlation with the higher rate of disintegration in brittleness, crispness, and crunchiness in the roasted
the roasted almonds, indicating that rigidity of soaked samples.5
almonds might be a better tool to predict gastric
disintegration rate of almonds. However, penetration test
is more preferable as it can also differentiate hardness and
total energy input during penetration between raw and
roasted almonds after soaking. This may be due to the
different principles involved in compression and penetra-
tion tests: in the compression test, only compression force
is involved, whereas both compressive and shear forces
are involved in the penetration tests.20
Microstructure of Raw and Roasted Almonds
During Digestion
Mechanical and textural properties of a food reflect the
structuralarrangements ofelementsinthemicrostructure.21
The changes in the almond texture are dependent on
alterations in the microstructure that take place during the
roasting and digestion process. Figure 6a, b shows the LM
pictures of raw and roasted almonds after soaking in
simulated gastric juice for 1 h. The shaded area reflects a
diffusion of resin into the tissue, while the white area
indicates no resin diffusion. We observed that the shaded
areaofroastedalmondsissignificantlylarger,i.e.,theresin
penetratedsignificantlydeeperintotheroastedsampletissue
than raw almonds (Figure 6), which may be due to the
looser structure of roasted almonds than raw almonds. In
the edge area, broken cells and the empty cell walls can be
seen where intracellular contents, such as lipid and protein
bodies, were lost (Figures 6 and 7). It can be also seen that
roasting created a significantly different structure. The
shape of the cell changed and cell arrangement was
extensively disrupted, as can be seen by comparing
Figures6a,7aand6b,7b.Ithasbeenreportedthatroasting
causes disruption of the cytoplasmic network, denaturation
Fig. 6 LM images obtained after 1 h of static soaking in simulated
and aggregation of protein bodies, coalescence of oil gastric juice: a raw almond tissue, b roasted almond tissue. Bars
bodies, and increase in the volume of the intercellular indicate100µm