CC BY
20
Using Jerusalem artichoke powder in functional food production
Nailya Z. Dubkova , Vitaly V. Kharkov* , Marsel R. Vakhitov
Kazan National Research Technological University"011, Kazan, Russia * e-mail: [email protected] Received March 22, 2019; Accepted in revised form August 31, 2019; Published online December 15, 2020
Abstract:
Introduction. Jerusalem artichoke is a valuable low-maintenance crop whose tubers contain vital nutrients and prebiotics. We propose using Jerusalem artichoke powder as a functional nutrient in the formulation of food products.
Study objects and methods. We studied the influence of vacuum, vibration, and grinding on the kinetics of drying Jerusalem artichoke tubers of a "Skorospelka" variety in the laboratory vacuum vibromixing mill dryer (VVMD).
Results and discussion. The rate of drying in the VVMD was almost 5.5 times as high as that of convective drying. The kinetic curves showed that grinding provided a period of decreasing drying rate until almost complete drying. Vibration drying in the VVMD was twice faster than vacuum drying. The comparison of theoretical and experimental data on moisture and drying time revealed good adequacy. The NMR analysis of changes in the molecular mobility of the samples obtained in the VVMD showed an implicit two-component spectrum, indicative of low moisture. The chemical analysis of the tubers and powders by standard methods confirmed that the proposed gentle technology (fast drying at 30°C) preserved 86% of inulin.
Conclusion. Jerusalem artichoke powder obtained in the VVMD can be used in different branches of the food industry due to its long shelf life, low consolidation, and no caking, with residual moisture of 6.1%.
Keywords: Jerusalem artichoke, tubers, bioactive ingredients, powder, mill dryer, vibration, vacuum drying, NMR, inulin
Funding: Our study was carried out at the Department of Food Production Equipment at Kazan National Research Technological University1*® (KNRTU).
Please cite this article in press as: Dubkova NZ, Kharkov VV, Vakhitov MR. Using Jerusalem artichoke powder in functional food production. Foods and Raw Materials. 2021;9(1):69-78. https://doi.org/10.21603/2308-4057-2021-1-69-78.
E-ISSN 2310-9599 ISSN 2308-4057
Research Article Open Access
(!)
https://doi.org/10.21603/2308-4057-2021-1-69-78 Available online at http://jfrm.ru/en
INTRODUCTION
The demand for functional foods has grown significantly over the past decades. This trend is primarily due to people's desire to consume food of better quality. Functional foods contain physiologically active substances that produce medical and biological effects on our bodies. These health benefits make the development of functional foods a priority in the modern food industry.
Jerusalem artichoke (Helianthus tuberosus L.) is one of the most common ingredients in therapeutic, preventative, and rehabilitation diets. Jerusalem artichoke, also called earth apple (or over 100 other names), is a valuable plant that has several advantages over traditional agricultural crops. For example, it is highly resistant to frost, pests, and diseases. In the non-chernozem zone, its yields can reach 40 t/ha for plants and 65 t/ha for tubers [1, 2]. The commercial production of Jerusalem artichoke in Russia covers an area of only
about 3000 ha, compared to 700000 ha in the USA and 500000 ha in France.
Traditionally, Jerusalem artichoke has been eaten raw or used as animal feed. In recent years, however, scientists have discovered some alternative uses. Low cultivation costs make Jerusalem artichoke a promising plant for biofuel production [3, 4]. Pharmacologists use this crop as a source of bioactive compounds [5, 6]. Other studies focus on its potential for obtaining organic acids such as lactic, butyric, and citric [7-9].
Due to the rich chemical composition, Jerusalem artichoke tubers are a valuable ingredient in functional food production [10]. They contain vital nutrients and prebiotics, especially inulin, a polyfructosan with a low glycemic index [11]. Also, the tubers contain pectin substances, vitamins, as well as macro- and microelements (Table 1).
Jerusalem artichoke tubers do not have a long shelf life, even under optimal conditions. This is due to the decomposition of biologically valuable substances caused by their own enzymes [13, 14].
Copyright © 2020, Dubkova et al. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), allowing third parties to copy and redistribute the material in any medium or format and to remix, transform, and build upon the material for any purpose, even commercially, provided the original work is properly cited and states its license.
Table 1 Vitamin and mineral composition of Jerusalem artichoke tubers [12]
Component Content, mg/100 g Percentage of daily intake, %
Vitamins:
^-carotene 0.012 0.2
A 0.001 0.1
B1 (thiamine) 0.2 16.7
B2 (riboflavin) 0.1 4.6
B3, PP (niacin, nicotinic acid) 1.3 8.1
B4 (choline) 30 6.0
B5 (pantothenic acid) 0.4 7.9
B6 0.1 5.9
B9 (folic acid) 13 3.3
C 4 4.4
E 0.19 1.3
Minerals:
Potassium (K) 429 9.1
Sodium (Na) 4 0.3
Calcium (Ca) 14 1.4
Magnesium (Mg) 17 4.3
Phosphorus (P) 78 11.1
Iron (Fe) 3.4 34.0
Zinc (Zn) 0.12 1.1
Copper (Cu) 0.14 15.6
Manganese (Mn) 0.06 2.6
Selenium (Se) 0.7 1.3
Powdering the tubers expands the scope of their uses in the food industry [15-17]. The advantages of food powders include a small volume, low weight, and a high concentration of nutrients. 180-190 g of Jerusalem artichoke powder is nutritionally equivalent to 1 kg of raw tubers. Jerusalem artichoke powder has a rich chemical composition and, therefore, unique properties. It is introduced into food products to improve metabolism and fight diseases such as diabetes, atherosclerosis, and obesity. Such nutrition is also recommended for increased physical and psycho-emotional stress, underperformance, and chronic fatigue syndrome. Finally, it is used to strengthen the immune system, as well as prevent and treat acute and chronic infectious diseases.
The existing technologies for producing powders involve drying the feedstock and its subsequent grinding. Intensifying thermal processes by increasing temperatures has its limitations due to the thermolability of valuable components. High temperatures and long processing times cause significant chemical transformations in the components [18]. These changes lead to losses of bioactive compounds and decrease the quality of finished products. Therefore, we need to find ways to intensify the drying of the feedstock and preserve its useful properties. Among well-known methods are vacuum drying, increasing the particle fineness of the material, as well as non-traditional
methods (freeze drying, microwave drying, infrared drying, etc.) [19-21].
In this paper, we propose combining vacuum drying and vibration grinding in one apparatus to produce Jerusalem artichoke powder [22, 23]. Vacuuming helps increase moisture evaporation at low temperatures to preserve the valuable components of the feedstock. Vibromixing helps equalize temperature and humidity in the apparatus. Using grinding media increases the constant drying rate period to almost complete dehydration of the product.
We aimed to study the kinetics of drying Jerusalem artichoke tubers in a vacuum vibromixing mill dryer (VVMD) and to determine the chemical composition of the resulting powder.
To achieve this aim, we set the following objectives:
- study the influence of vacuum, vibration, and grinding on the kinetics of drying Jerusalem artichoke tubers;
- construct experimental drying curves and drying rate curves for Jerusalem artichoke tubers;
- provide a mathematical description of drying in the VVMD;
- analyze changes in the molecular mobility of the feedstock and the powders obtained under different drying conditions;
- determine the chemical composition of the feedstock and the powder obtained in the VVMD;
- assess the effectiveness of the developed technology compared to other methods of drying Jerusalem artichoke tubers; and
- suggest promising directions for the commercial application of the obtained powder.
STUDY OBJECTS AND METHODS
Samples preparation. The study object was Jerusalem artichoke (Helianthus tuberosus L.) of a large-fruited "Skorospelka" variety harvested in 2018. Its spherical tubers have smooth white skin (Fig. 1).
For drying and chemical analysis, we used tubers without defects with an average weight of 60 g. After harvesting, the tubers were washed, dried, and sealed in polypropylene bags. They were kept at 4 ± 2°C and relative humidity of over 98% for no longer than a week. 10 ± 0.5 g portions of washed and cleaned Jerusalem artichoke tubers were cut into pieces of 10*10x10 mm.
Chemical analysis. The chemical composition of raw Jerusalem artichoke tubers and the resulting powder was analyzed by standard methods: moisture and ash were determined by the gravimetric method; protein was calculated as nitrogen content multiplied by 6.25 using the micro-Kjeldahl method (Pro-Nitro A, J.P. Selecta, Spain) [14]; fat was measured by the Soxhlet method; and inulin was quantified by the Bertrand-Ofner method. The experiments were carried out in triplicate, and the measurements were recorded as a mean ± standard deviation.
Figure 1 Jerusalem artichoke plants and tubers
Experimental mill dryer. A flow diagram of the laboratory vacuum vibromixing mill dryer (VVMD) is shown in Fig. 2. The apparatus has a cylindrical body which oscillates on eight flexible supports with the help of a vibrator and a drive. Discs with debalances are mounted at the ends of the vibrator shaft, which runs along the central axis of the body. A heating jacket is used to heat the dryer. In the upper part of the body, there is a hopper for feeding raw materials. The feedstock is dosed by volume.
Hot water was used as a heat carrier in the jacket of the apparatus. A Wilo Star-RS 15/2-130 circulation pump (WILO SE, Dortmund, Germany) was used to pump hot water from a boiler with a built-in thermostat (Ariston, Italy). The temperature was controlled by an IT-17-C digital thermometer (Exis, Moscow) with a TSP 100 thermocouple installed inside the body. To create a vacuum, we used a STEGLER 2VP-1 singlestage vacuum pump (PRC); the vacuuming degree was monitored by a DV-05-01 vacuum gauge (Steklopribor, Ukraine). A throttle valve was used to regulate the degree of vacuum in the dryer.
The vibration amplitude that depends on composite debalances was measured with a manual VR-1 vibrograph (Vibropribor, Taganrog, Russia). The oscillation frequency was determined by a number of
Figure 2 Laboratory vacuum vibromixing mill dryer: 1 - vacuum pump; 2 - condenser; 3 - condensate collector; 4 - throttle valve; 5 - vacuum gauge; 6 - body; 7 - grinding media; 8 - flexible supports; 9 - debalances; 10 - boiler with thermostat; 11 - electric motor
turnings made by the vibrator shaft and was recorded by a ST-5 stroboscopic tachometer (Analitpribor, Tbilisi, Georgia). Grinding media are balls and rollers sized 10-15 mm. The volumetric ratio of feedstock and grinding media was 1:1 (hereinafter referred to as the "charge").
For comparative analysis, we conducted additional experimental studies using traditional methods of drying Jerusalem artichoke. For convective drying, we used a SNOL 58/350 cabinet for drying under atmospheric pressure (Umega-group, Utena, Lithuania), while vacuum drying (Fig. 3) was carried out in a VTSh-K27-250 vacuum drying cabinet (AKTAN VACUUM, Fryazino, Russia).
Experimental procedure. Our experimental studies of drying Jerusalem artichoke tubers included:
- drying in the VVMD without vibration;
- drying in the VVMD with vibration;
- drying in the VVMD with grinding;
- convective drying under atmospheric pressure; and
- drying in a vacuum cabinet.
In all the experiments, the samples were dried at a constant temperature of the heating wall at 80 ± 1°C. Vacuum drying was carried out at a residual pressure in the drying cabinet within 100 mm of mercury. The samples were periodically weighed on a VIBRA AJH-420CE balance (accuracy class II; Shinko Denshi Co., Ltd, Japan) until a constant weight was achieved.
Based on the experimental data, we calculated the drying parameters as:
P - P
W = ^-^ (1)
where W is moisture content of the material, g moisture/g dry mate rial; Pw is wet weigha, g; andPd is dry weight, g;
AW = W; -W;
(2)
where AW is changed moisture content duningdrying, g moisture/g dry material:
N o
AW At
(3)
where N is the drying rate, h_1 and At is the time interval between measurements, h.
Figure 3 Laboratory vacuum drying unit: 1 - vacuum pump; 2 - vacuum gauge; 3 - throttle valve; 4 - drying cabinet; 5 - material; 6 - shelf; 7 - control panel
Statistical processing of resuIts. The Mathcad software package (Prime 3.0 + Axum S-PLUS Script; PTC, Boston, Massachusettp, USA) was used for the analysis of variance (ANOVA). The significance of difference s m the means was analyzed using the Duncan multiplf range let (DMRk) atP s 0.05.
Mathematical olositii)tlon tuf dtying iu toe vocntm Wboomixmy miiu dpyn;t. Wc cakmkm0 tlie kmeüss of drying with scmultannous grii^d^i^g. Due to a continuous ttnewol of Urx cvapootion su^D^,i, j^ouit monsture wat removed durirg dee caastant diymu talv pottod. Therefcaae, we assumenl Ülatthcpariod vf tuf felling tiitis nopl Ige ahggtcmd. Vacuum drymf in Hco aonpSan3 xUo pdriod wdis ckatly Wetesmind0 Oy tlie preosure in the w orking chamber.
Ths Iseet suhpliecs to phf mateiial from heatim wt)) was uehd to Rem) the mptesirl unO ^^«10.6 moisdure. Bt3e amotne ef hnaa Qcond tauphed from thr sauce totte mmterial wad calaulhPer as:
öcona o Tm )
(4)
where acond is the heat transfer coefficierot zfc^cr conductive heat supply feo m the heattng wnll, kJ/m^Cr f is nhe contact scrfasev m2c anP OwaS, p are thd temperatures of the heating waü and tlie manerial, eespendively, °C.
The peuirJ of herting tte ^air^M ie short Cut te vidrationeixing [24f. Tdurefore, we ccriu)cl rodude the stafe (in tiraJn;(efic hoarici erom dur oalcBaticns. During aar cocf^l;;in^ drying hate ptriod, tree hoot frnm tutie heatingwall was spent code oih wdmc cvef)or¡^(ion^ Tdus, rhe hedU baSanae equ/tiod wat as foStowr:
a(m - a l=gnru
d-1 tJwen a e! ' , da
)5)
wlnere e ps ^Jr^io snecific lisai og vapprizarkm of moisüne, k J/kg
TO. ttmperatsoe ot alie neiaterial to be dried gepends on rhe prersuee in 0Be apparatus, ovhichr )d ksp! uod//ant. Whee a peatide contseu4a the heating I iO ocqpines a gmdlar Srmpnoture. Due pm vüoraüou mlxina, ^he partie/k movss miy from sdre waü ^^tite Üiy clsamuah gividg off its heat tothe nntire charge. Thd u it as guides the teinperadute of the meterinl in tte chamber onsil tue ntxtfOxracn wiHi tnianr lleatmf wcü.
Tpd tedi iudugee uoeffigkxt getwpen hte tearing anO ^(i^ miterit ^Ixc^^^i ai followt:
cond
= ceWerg0" /1^
ct „,
hh
where \ is the thermal conductivity of the charge, W/(mK); pf is the Censmth or the charge, kg/m3; ) is the heat c((achy of the cciazge, .Iggkg-K); and (cont isthe periodofcontactbetweenthechargeandthevibrating heatingsurface,s.
Moisture content and particle size also change duringthedrying process.Achangeinmoisture leads to achange in thermophysical characteristics.Grinding
and drying reduce the volume of the charge in the chan^r. Thim leads to changes in the ratio between grinding media and drying matuM. The dernity and heat capacity of the charge are calculated according to the 3lianged rario.
The thecmal c;onc(i2c;tipc9^}i of thectl//ge ia detami-md I-:
'X
hi r^ai
(S^^ttio
i^-irr r^0 e + 0U8e ^ ^c"s
(ai
whets s is the charge porestiy; )iri )y nr( the therwal con^^^^itl,2s of th<s material and air,rescectively.
Linger the tcbeading lliatd d^d ;poroít-ael
differ: fram ^h^l o^ kluc fixed tied For ^^o lrlcaege,oa is datermintd liroi^ SOe, icjritdîri^on enuction [ot»!^ irsa:
ím(t^fOC
Í nin Pg dt (n
Vg
o r. 0.t92
' n y
n,(
^ 0. ) i|ih
h(s
at
pu id^ te g intfe ^r the R^noids ctS^^^r^i:l:-:e fe^ joiti^^^ gaeticee(; pe rri t[l^ td^n)^)^}' oa ili^ tsdt^iîriigl, ag/:mr; vci1 ist1oeCyna^^v ^f tile maOeiM, Pia tr;
e^^^ C m^nS is the fill^ihg degree: em isthe radies of the dryer body, m; mm is the weight of the material, kg; PeVc01 Ft °s nhe Froede jo is the angelar
steed of rotation of the oidrator shaft, )/s; at is the vibration amplitude| m; og ^ye ^^^ ^jsttniirs of t^e center o^ gravCa ^^ H^e ^^assgo^ end tdeq it ^^e e^llrl'0',erceC etrtidr 0i£tmt^^(^r, 'whiyyin cldaFges tn^emg dayiag ^i^e to conc^antgrind^ieg,^l)ehined frcte:
te„
■ ^ ^xp
- 10x2.99
n(
Se A'
J
De
Ssta)
(9)
where ¿¡t^ istheim1^il£lr particlr diameter,m; nD(lr is the diameter of the dryer, m; and mb is the mass of grinding balls, kg.
As the volume of the material decreases, so does cthe active surface of its contact with the heating wall. At the beginning of drying, the filling factor is equal to one. Due to vibration mixing, in 1-2min,the material gets evenly redistributed among the grinding media. raAt this point, the entire hot surface of the body is in contact with the charge. Then, due to grinding and lower moisture, the material decreases in volume, resulting in a smaller contact surface. When moisture is less than 230%, the charge begins to 4circulate intensively. The contact surface is calculated from the charge flight andslidingtimesaccording to thetheoryofinteraction between the material and thevibratingbody[25].
The period of contact between the charge and ohe heating surface; dcont is detenniaed bo ece interaction between the charge and the bodg of the apparatus as the moisture and volume decrease:
7cont =T-T*
(Sf)
where T is the time correspopoling tr ooe aemolutinn of the vibrator shaft, s; en* is the flight of the charge froo its separation froo, to cooe into contact with, thr body
s* = — arccos I--J
m I Am
n
+
t
(I ic
To calculate tie to/al drying time in tire we assumo that the vacim °umf remuves tpe snOre volume of dry air. wn ahls ease, dde pressure in dhe (hyer awrtespondn to tine pressee of s^^u^^dtiicJ. waOer vapor. Tl^e prsssuce in ahe dryorg eltiamben iis eaintvinef fy a Aonfinuously operating vacuum putp. Tfie^efon(, tl^<s ainetics of Priding cs datennmeV °>y ahe raSe oS evtporadion remvndt, vo'ini^cli de8ondt om (lia charealeristici of tlie puan. To desscrid^ ope pmcest ot eva^fetifn at redueed pcessurr,wm prdceed from the fdllowing assumption. Chun.es ic the (mamcd oU dapor in tho chambee cmtnr time ace equal to thw differem. bgtween the rater oe vapor pumping and moisture evaporatioe. Cc nonatunC peacsure, -.i- amoueh uf vapor doItt sua ctonee over Slme. Tte IdntettaS tnkcnee t-calculi^^^e as:
i.h p^Ut m .e
ti2)
wCere utl is the ^tttse; cf ItuCC enaporation, kgim; p isthe vapor mrns-o,kgam3; truer is teepump capaeity, mT. The rate o^:^ Hornd nvqpocatioll iscalcu6a6ed tjs:
d- d-
iev = "^6^— (13) dd
where m6 is da weigit, nle1
The vapaa density is calculated occording to the Ctapem ron equation:
P = PsM/TTm
(14)
where Ps is the pressure of saturated vapor, Pa; M is Vhe molar mass ef water vapog kgekmoi; enl T is the univsrsai gat conIrynti J-dnotKr.
Mre-tiT tss. (TS be aM nut into Etg. til!) leads to:
dg4_ rvedIтltt„l,C^^el/(s^
To
wnere A cud B ore lhe n.efficients frem t^^ Adme equ atom.
With Eg. (5) taTen iuto aaeount, id ^ect and mass transfen is calaunated as:
tcrn
g(V-eaiFC a PMQ^h hp,)
(r6r
do ^es^^dCc^^h^oi
Un^rtioa .he cOTditton!- r = f = amtilvlia;meivl
and d e ^<dyog^ «cC m ^]ttnalufinvl into Eg. (16), we calculate the dryingtiee as:
. p (ainitM NditiV Uo)
ePMOruepm-inm)
The initial datn for calculating the kinetics and drying Sime inn tdet OP dm3 labonvtot•n varaum e^ifeisoi5ii^ing .mil 1 -Winter were as -ellows: - working aarametens: D o f ,6 mi T^ = 80 aC; Ps = rari I0a; eo = 15(6.rn((e(t T n S.5x1f-p e;
mruor = f.003 —tsa a.
in,(ivt
= c8.3x 10-3m2
a
SI-VI
T^x!--. ts-d = 0W imp, m^ = f.6 kg;
- tharmophyli6vr cVfracterTticl oC tee fe^^sjernw
do = 0.6 WOt-iOu to = (0tn fr^nm^, cic = S.OO t"itг)Sl■;gтeo;
end
- themeephysical charaeteristics of the initial charge (feedstock end griaiPing mtdia)^ A. u 24.05 \UUm K); 8l^^^nlela■ h ue kg/m3; a 2.0^ kJ/(kg^R).
Nuclear Magnetic Resonance (NMR) study. We studied changes in the molecular nobility of original Jerusalem artichoke and its powders obtained by different drying methods. For this, we performed the wide-line (lowresolution) NMRona standard RYa-t3f 1 radiospectrometer(Russia)at16.2MHz.
RESULTSANDDISCUSSION
Mathematical description of drying. Visual observations of the drying and grinding of Jerusalem artichoke (Hflianthus tubfaosus L.) in the vacuum vibroeioing mill dryer (VVMD) showed the following results. After ten minutes, the pieces of Jerusalem artichoke turned into a wet puree, which proved that the grinding was ouch faster than drying. The initial particle size wasnot anieportant factor forproducing powder inthisapparatus.
Fig. t shows drying curves and drying rate curves for Jerusalem artichoke tubers based on eoperieentvt and estieateddata.
According to the curves for traditional drying methods, a decreaseinpressurein thedrying chamber to 1ff ee of mercury increased the drying rate by a factor of 1.6—1.1. This was due to the fact that vacuum decreases the boiling point of liquid, making evaporation froo the surface of the material more intensive.
Vacuum drying without vibration revealed the effect ofthe charge voluee(eass ratio) onthe drying rate. In the vacuum cabinet, the feedstock was laid out evenly inonelayer without mutual contact. Therefore, drying in a vacuum oven was 1.3f-1.35 times faster than in the VVMDwithvacuue, but without vibration.
The rate of vibro-vacuue drying was 3.7-3.C times higher compared to the analogous process under atmospheric pressure and 1.t-t.f times higher than under vacuum. Vibromixing intensified the heat and easstransferbetweenthe hotwalland the charge. This wasdue tothe redistribution of heated particles and the equalization of temperature and concentration fields of eoisturein the charge.
T3
M
0.14 ■
0.12
0.10
S
b T3
60
0.08
0.06
g' 0.04 -
Q
0.02
0.00 ■
12 3 4 Moisture content, g water/g diy matter - 1 • ,--2 ▼,-
a
(b)
Figure 4 Curves of drying (a) and drying rate (b). Points - sopsriтsntal data; lines - sstiтatsd data: 1 - conoyctioy drying; t - vacuum drying; 3 - drying in the VVMD without vibration; t - drying in the VVMD with vibration; 5 - drying in the VVMD with grinding
o
3
The highest drying rate was observed when vibration was combined with grinding. The period of constant drying increased due to a continuous renewal of the evaporation surface until complete drying. Thus, our assumption of neglecting the falling rate period when modeling the process in the VVMD was justified. This method increased the drying rate by a factor of 54-5.5 compared to drying under atmospheric pressure.
We compared the estimated and eoperieental data to assess the adequacy of mathematical description.
The average statistical error for the moisture content was ± 8% with a sample correlation coefficient of 0.953, while that for the drying time, ±10% with a sample correlation coefficient of 0.951.
NMR results. Figure 5 shows the qualitative analysis of Jerusalem artichoke powder according to the NMR spectra. The arrows indicate implicit narrow components.
We analyzed the shape of the NMR spectra. According to the NMR theory, a complex spectrum
Figure V Wide-lmn NMR n^cta for: initial i-i".!:^ of JyruJaleт s0ithoke tabee! ,1-, gowdne nro<6ucod unTet n-moo^eTi pressure (t), powder produced by vacuum drying (3), and powder produced by vacuum oibroтioinl mill drying (t)
Table 2 NMR parameters for Jerusalem artichoke tubars and powders t^l^aair^ed by differentdrying methods
Sample miR line winUi, 8B Second moment, AH 22
In^^am^e of Jerusalem 2.4 9.2
artichoke tubers
Powder produced under 3.2 13.4
atmospheric pressure
Powder produced by vacuum 3.6 14.6
drying
Powder produced by vacuum 3.8 15.2
vibromixing mill drying
is typical for samples containing proton grouys, whose molecular mobility differs by 103-104. The narrow component refers to the yroton grouys of water contained in the initial Jerusalem artichoke sample. According to the results, the most complex shape of the NMR spectra was for the initial samnla and the powder dried under atmospheric nrаssurа. The samnlas obtained in the vacuum cabinet and in the VVMD featured implicit two-component NMR spectra. Also, the powders obtained under atmospheric pressure contained more moisture than those produced by vacuum drying or in the VVMD.
Taking into account the contribution of the narrow component, we calculated the parameters of the NMR spectra (Table 2). The wide component refers to all other proton groups of the initial Jerusalem artichoke and the dried powders.
Moisture has a plasticizing effect on the system. A decrease in its amount leads to the appearance of local regions with long-range order (analogs of domains). It is these regions that determine the resulting molecular mobility in the system. Changes in the width of the NMR lines are associated with decreased molecular mobility of proton groups in the samples after drying. Structural changes in the Jerusalem artichoke after drying are also evidenced by an increase in the second moments of the NMR absorption line compared to the
Table 3 Chemical composition of Jerusalem artichoke tubers and powders
Comnonаnt Content (per dry weight), %
Raw tubers Powder dried under atmospheric pressure Powder dried in the VVMD
Protein 9.29 ± 0.14 7.19 ± 0.11a 8.72 ± 0.12a-b
Fat 0.51 ± 0.01 n.d. n.d.
Ash 11.87 ± 0.15 11.57 ± 0.14 11.54 ± 0.15
Inulin 27.77 ± 0.27 20.48 ± 0.24 a 23.88 ± 0.25 a-b
a - statistically significant differences (h < 0.05) from the raw sample; b - statistically significant differences (h < 0.05) from the sample obtained under atmospheric nrаssdrа
n.d. - not detected
initial sample;, h lamer spread of local magnetic fields makem u nignificane cowtritiurion to the second moment of the NMR lime, indicating a more rigid structure of the dried samples.
Chemical analysis. The chemical composition of raw Jerusalem artichoke tubers was a basis for a comparative analysis of the powders obtained (Table 3). The moisture content was 80.2% in the initial sample, 12.5% in the sample dried under atmospheric pressure, and only 6.1% in the sample obtained in the vacuum vibromixing mill dryer.
Inulin is the most valuable component of Jerusalem artichoke in functional nutrition. As we can see in Table 3, drying under atmospheric pressure caused a 26% loss of inulin, while drying at 30°C in the VVMD, about 14%. Thus, a gentle mode of drying in the VVMD ensures good preservation of the target component.
Drying efficiency in the VVMD. We compared our results with those reported in the literature. Golubkovich nt al. found that microwave drying of Jerusalem artichoke tubers, which lasted 2.75 h, was 2-3 times more intensive than convective drying, with final moisture under 10% [27]. Another study proposed infrared drying as a method that provides intensive and uniform moisture evaporation with the least loss of polysaccharides, including inulin [28]. To preserve inulin, Rubel nt al. suggested using freeze drying [21]. However, in terms of energy efficiency, microwave drying (2.2-2.5 kWh/kg removed moisture) and infrared drying (1.8-2.0 kWh/kg removed moisture) can only be advisable for products with low moisture. Moreover, in both studies, the tubers were dried at 60°C. Freeze drying is also energy-intensive, requiring 2.2-3.7 kWh/kg of removed moisture. Ermosh nt al. dried Jerusalem artichoke using convactiva-vacuum-imnulsa drying [29]. In their study, the drying lasted 1.5 h (3 times as short as convective drying) at 70°C until the residual moisture reached 7-8%.
The technology of vacuum vibromixing mill drying that we propose for Jerusalem artichoke tubers has the following advantages over existing drying methods:
- high drying rate: 5.5 times as high as traditional (convective) drying, with 6.1% final moisture;
- preservation of bioactive compounds (including inulin) due to a low temperature (under 30°C);
- energy efficiency (1.2-1.3 kWh/kg removed moisture) due to drying and grinding in one apparatus;
- long shelf life, low consolidation, and no caking due to low residual moisture; and
- no need to buy a additional grinder for the finished product due to drying and grinding in one apparatus.
Prospects for industrial application.
1. Bakery products from grain flour [30, 31]. Adding 2% of Jerusalem artichoke powder to wheat flour during yeast dilution enhances [31]:
- saccharifying and gassing abilities of the dough;
- gluten quality and elasticity;
- hydrophilic properties; and
- nutritional and biological value.
t. Flour co-Sectioner=. Adding 3% of Jerusalem artichoke powder to flour mass in the formulation of sugar and hard-dough biscuits promotes [31]:
- a larger volume of finished products;
- a eore uniform structure when broken;
- lower density and better wetting;
- reducing sugar by 3%; and
- higher nutritional and biological value.
3. Instant porridges (oatmeal, buckwheat, etc.). Adding 1f to tf% of Jerusalem artichoke powder improves the sensory and functional properties of the grains and lowers their glyceeic indeo [17].
t. Fermented milk products. Adding S-S.5% of Jerusalem artichoke powder to a normalized mioture provides [3t]:
- better functional properties;
- higher rate of acid formation and a shorter fermentation time (up to 6 h); and
- an original taste of the finished product.
5. Substitute for raw neat. Adding 1f to 15% of hydrated Jerusalem artichoke powder to the formulation of neat products contributes to [33]:
- better uniformity and plasticity of minced neat;
- lower adhesive capacity of minced neat;
- higher stability of the product due to inulin; and
- higher content of dietary fiber.
CONCLUSIONS
Our study led us to the following conclusions: 1. The eoperieental studies of the kinetics of drying Jerusalem artichoke tubers (Hflianthus tubfaosus L.) by various methods proved the effectiveness of vacuum vibroeioing mill drying. In this case, the drying rate was almost 5.5 times as high as that of convective drying.
t. According to the kinetic curves, grinding provided a period of decreasing drying rate until almost complete drying. Drying was a time-limiting process.
3. Drying in the vacuum vibroeioing mill dryer was approoieately twice as fast as thin-layer vacuum drying.
t. The mathematical description of vacuum vibromioing mill drying showed good agreement with
the eoperimental data. The degree of mismatch was less than C% for the moisture content and 1f% for the process time.
5. The wide-line (low resolution) NMR analysis of Jerusalem artichoke powders obtained by vacuum drying and in the vacuum vibroeioing mill dryer showed implicit two-component spectra. This indicated a low content of proton groups of water, i.e. low moisture. The calculated widths of the NMR lines and the second moments clearly revealed their rigid structure.
6. Comparing the chemical compositions of powders obtained under atmospheric pressure and in the vacuum vibromioing mill dryer with that of the initial Jerusalem artichoke sample was of great importance for the preservation of nutrients and prebiotics. We found that our technology for powdering the tubers at eao. 3f °C preserved C6% of the initial amount of inulin.
7. The comparative analysis of various drying methods with the proposed technology confirmed its effectiveness. It provided a lower power consumption (1.t-1.3 kW h/kg removed moisture) by combining drying and grinding in one apparatus. The low residual moisture (6.1%) ensured a long shelf life, low consolidation, and no caking.
C. Coebimng drying and grinding in one apparatus saves the capital and operating costs of additional grinding eouipeent.
t. Jerusalem artichoke powder can be used in the production of bakery, confectionery, dairy, and meat products. It improves the products' technological indicators, sensory profile, and functional properties.
CONTRIBUTION
The authors were equally involved in writing the manuscript and are equally responsible for any possible plagiarism.
CONFLICT OF INTEREST
The authors declare that there is no conflict of interests related to this article.
ACKNOWLEDGEMENTS
The authors thank Professor of Physics Vladimir Minkm froe Kazan National Research Technological University for his assistance with the NMR study.
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ORCID IDs
Nailya Z. Dubkova https://orcid.org/0000-0001-5207-3701
Vitaly V. Kharkov https://orcid.org/0000-0002-8219-7323
MarselR. Vakhitov https://orcid.org/0000-0002-6191-1022
