The Giant African Land Snail Achatina fulica (Bowdich, 1720) as a Candidate Species for Bioregenerative Life Support Systems

Abstract

In order to describe the growth of Achatina fulica its logistic function was fitted to the experimental data. It was found that calculated specific growth rate and carrying capacity, as constants of the logistic function, are 1.06 month-1 and 250 g of wet weight correspondingly. Mass ratio shell/whole body in terms of wet weight was 18%-21% irrespective of snail age. Snail meat was characterized by the low content of fat -- 6.0% DM. Essential fatty acids constituted 16.6% of the total sum. Linolenic and linoleic acids dominated in a pool of essential fatty acids. The scores of essential amino acids, except sulfuric amino acids, exceeded 100%. To estimate nutritious properties of snail meat, a computer program was developed. It was observed that the maximum intake of snail meat can reach 497 g/crewmember day. Addition of snail meat to a basic diet enabled increasing food independence of bioregenerative life support system to 97%.

Headnote

The capability of snails to consume and convert inedible plant biomass and kitchen waste was tested. Inedible biomass of wheat and cabbage and also potato peels as a food were worse than lettuce, which is an ordinary feed for snails. In order to describe the growth of Achatina fulica its logistic function was fitted to the experimental data. It was found that calculated specific growth rate and carrying capacity, as constants of the logistic function, are 1.06 month^sup -1^ and 250 g of wet weight correspondingly. Mass ratio shell/whole body in terms of wet weight was 18-21% irrespective of snail age. Snail meat was characterized by the low content of fat - 6.0% DM. Essential fatty acids constituted 16.6% of the total sum. Linolenic and linoleic acids dominated in a pool of essential fatty acids. The scores of essential amino acids, except sulfuric amino acids, exceeded 100%. To estimate nutritious properties of snail meat, a computer program was developed. It was observed that the maximum intake of snail meat can reach 497 g/crewmember day. Addition of snail meat to a basic diet enabled increasing food independence of bioregenerative life support system to 97%.

Keywords: snail, feed, growth, chemical composition, diet, bioregenerative life support system (BLSS).

(ProQuest: ... denotes formulae omitted.)

Introduction

It is known, that two-thirds of protein in a space diet should have an animal origin (Cooper et al., 2011). At least a part of animal food could be produced in Bioregenerative Life Support System (BLSS). In that case, one should reduce the production costs. Small forms of animals such as silkworms (Yu et al., 2008; Yang et al., 2009), yellow worms (Li et al., 2013), and snails were considered as candidate species to solve the problem. A space diet based on the use of rice, soybean, lettuce, strawberry, and land snails Helix pomatia L. was developed (Midorikawa et al., 1993). The calculated amount of snail meat was equal to 110 g/crewmember day according to the Japanese dietary requirements of that time. Snails also took part in waste processing. According to the scheme of the BLSS material balance, the production of plant wastes was calculated as 2583 g/crewmember day and 690 g of this amount was earmarked for the snail feed. Undoubtedly, the search for new animal- candidates for BLSS is an important task. There are some cultivated land snails besides Helix pomatia. One of them is the giant snail Achatina fulica (Bowdich, 1720) (Cobbinah et al., 2008). As compared with Helix pomatia, the giant snail has a greater growth rate. For example, the snails Achatina fulica that are 5 month old had a whole body weight of about 33 g (Upatham et al., 1988), whereas the snails Helix pomatia which were 1 year-old weighed only 23-26 g (Toader-Williams, Bentea, 2010). Hence, the introducing of Achatina fulica into BLSS could help solve a problem related to animal protein.

The aim of this work was to forecast the practicability of Achatina fulica in BLSS. In this connection, the growth, chemical composition and nutritional properties of Achatina fulica were studied. The capability of snails to use plant and kitchen wastes as a food was estimated.

Materials and methods

Conditions of snail growing

The object of the research was the giant African land snails Achatina fulica Bowdich (Fig. 1). Taxonomic Position: Animalia: Mollusca: Gastropoda: Stylommatophora: Achatinidae. Like many snails, they are hermaphrodites. This means that instead of having male and female snails, each snail has both male and female reproductive organs. Young snails produce sperm only, but as they grow larger, they will produce both sperm and eggs. The fertilized eggs hatch, and immature snails grow to adulthood in about six months.

The adult snails in an amount of 25 individuals were cultivated in a rectangular container (L×W×H = 140×50×60 cm) and fed ad libitum. At the bottom of the container a soil like substrate (SLS) was placed. It looked similar to natural black soil. Unlike natural soils, SLS did not contain aluminosilicate matrix. SLS included ( % of dry mass): organic matter 64-68, ash 32-36, humic acids 9.19.6, fulvic acids 4.7-5.1, nitrogen 1.63-1.74, phosphor us 0.88-0.95, potassium 1.80-2.18, calcium 1.70-1.78. SLS was produced by processing plant wastes by oyster mushrooms and worms Eisenia foetida (Savigny, 1826) (Manukovsky et al., 1997). The thickness of the SLS layer was equal to 15 cm; bulk density - 785 g/l; moisture - 72 %, moisture capacity - 88 %, pH of water extract - 6.8.

The juvenile snails in an amount of 10 individuals lived separately from adult individuals in the rectangular container (L×W×H = 20×16×10 cm). An air temperature in the breeding containers was equal to 25 °C, and the relative air humidity was 80 %.

Feed testing

SLS Ilanyaenr wexaps eerqimuael ntto s1tu5dcymin; gb uthlke dceonnssiutym-pt7i8o5n of various feeds by one year old snAasi lsa, fweedu, sleadv leaves of lettuce (Lactuca satlievaaveLs .)o,f stthreawPekoifn wheat (Triticum aestivum L.), Lro.)otasndo f frcuaibtsbaogfe (Brassica oleracea L.), and cpheemlsicaol fc ompoptoastoiti (tSoo2l5a n°uCm,antudbtehreorseulamtivLe. )a.irEhaucmh idfeiteTydhwewacsalas8y0 t ae%nstd.edsa separately in three sets of onteh-edfaoyr m(2o4f chhoaulkrs.) trials. In each trial eight snails were used. All ttrsitauldsyinwgerteh e pceornfsourmpetdioni no f tvhaer iotues tfeecdosntbayinoenr c(eL(×LWac×tHuca =s a t3iv7a×3L2.)×,18st rcamw).ofToawvbhilpeoa1tsi t(siTohrnoitwtiocsuomtnheea lcehraecmeiacaLl. )c,oamndp opseiteilosnoof fptohteatsoe (flSeoeogdliasnt.i ucmfutnucbteiorno swum

hree sMetsa sosf oonfe-cdoayn s(u24mheodurfse)etdri awls.aIsn ceaaclchutlraiatel dei by a difference between wmhaesres eMs b -o fwhtohle submitted and residual feed. uTphpe rrbaoteu nodfarfye eodf degradation was calculated by tThhee feoqluloatwioinn g(2 efdo rfmeeudlaw:as calculated by a difference b tween ma

... (1)

weshienr eterFmese docf -DMco.nsumed feed in tAefrtmersstoufdyDiMng; Feces - produced feces in termsanoafl yDsMes. The objec

Studying of snail growth

As a feed, leaves of lettuce (Ldaricetducina saantiovvae Ln .)a,t taproots of carrot (Daucus carboytaKLje.)l,dalehal vmese thoof the Peking cabbage (Brassica sinensis L.), fruits of tomato (Solánum lycopérsicum L.) and fruits of vegetable marrow (Cucurbita pepo L.) were vuskeyd .eTt abl.l,e1299s7h)o. ws the chemical composition of ;thmeosies tfuereed-s .72 %,

of leTttuhcee c(lLaaycatuncda ssantidv awLer.)e, atadpdreodo tstootfhcearfreoetd( taob bimagpero(Bveratshseicad isgiensetniosins. LC.)a,lcfiruimts wofastoamdadteod( Sinol tehteabfloer m aorfr ocwhal(kC.uTcuhrebreit awapse paoshLa.l)lowe rceupu swedit.h rpoeofittnahbetlhsee wfbeareetdesrd. ingt he growth chamber.

wereWadhdoelde tbootdhye mfeaesdstofi2m8psronvaiel sthwe adsi gmeestaisounr. eCda rdeuwriansga sthhael lopwr ocucepsws itho fpottahbelier wagtreor wint hthe fgrroomw oviposition to one year by weighing them at eleaar sot lodnscneaail sw, eweek . To describe a snail's growth, a ilvougmistLic.) ,f urnocotisoonfwas used:

... (2)

owleh ebroedyMmb a-ssw(hcoalrerybinogd ycampacsistya)t; tahned tkim- es pt;e cMifi0c-g wiansitfiaitlt ewdhtoolethbeoddaytamoabstsa iantetdhientithmeem0e; aMsuar-emuepnptesr sbofunthdarsyu bomf wittheodl e body mass (carrying capacity); ianngdf okr m- uslpae: cific growth rate.

The equ(a1ti)on (2) was fitted to the data obtained in the measurements of whole body smnaaisl sg rboywuthsi(nsgeet haeb olevaes) tt-hseq usamrees 2m8eitnhdoidviidnu aElsxcweelr o2f0c0h7e.mical analysis were pedal mass (snail meat), s

eCdhebmy itchael acossnavyesntional

5 ° CAfoftre2r4sthuadnydintgh eonf qsunicakill ygrwoewigthe(ds.eTehaebnoivtreo) Vthoelysnaemtse, 129877in).dTivoi dcuaalclsu lwateerea ucosendtenfot rofc hcerumdiec aplr facnoarlryessepso.nTdihneg osabmjepcltes boyf ac hceomnviecrasli oann acloyesfifsicwieenrteo pedal mass (snail meat), shell, feces and eggs. Ash content of samples was measured by ashing a sample in a muffle furnace at 600 °C. Moisture was measured by the conventional oven-dry method, in which the samples were dried in an oven at 105 ° C for 24 h and then quickly weighed. The nitrogen was determined by Kjeldahl method (Volynets, 1977). To calculate a content of crude protein we multiplied the nitrogen content of corresponding sample by a conversion coefficient of 6.25.

The content of lipids was determined gravimetrically. Extraction of lipids was done by the method of Folch (Folch et al., 1957). Briefly, lipids from samples were extracted thrice with chlorofor m:methanol (2:1, v/v) simultaneously with mechanical homogenization of the tissues with glass beads. Methyl esters of fatty acids were produced after acid methanolysis of lipids (Makhutova et al., 2013). Methanolysis of lipids was carried out in the mixtures of methanol and sulfuric acid (50:1 v/v) at a temperature of 90 °C within two hours on a water bath, using the backflow condenser. Methyl esters of fatty acids were analyzed on a chromatograph with the mass-spectrometer detector 6890N/5975 (Agilent, USA). Conditions of analysis were as follows: gas carrier - helium, speed - 1.2 ml/ min, capillary column HP-FFAP, of length 30 m, of diameter - 0.32 mm, temperature of inlet - 230 °C; star ting temperature - 120 °C, temperature increase up to 190 °C with a speed 3 °C/min, an isothermal mode for 5 min, next temperature increase to 220 °C with 10 °C/ min, finally, the isothermal for 20 min, electronic ionization with 70 EV, and scanning mode from 45 to 580 m/z at 0.5 sec/scan. Identification of fatty acids was carried out on their mass spectra, and a comparison with those of standards. As standards, we used the saturated, branched, and monounsaturated fatty acids with the length of a chain from 10 to 24 carbon atoms, and also linoleic, α-linolenic, γ-linolenic, arachidonic, eicosapentaenoic, and docosahexaenoic acids ("Serva", Germany and "Sigma", USA). Calculation of the relative content of fatty acids was carried out by a method of internal normalization. The location of double bonds in the unsaturated fatty acids was determined on the spectra of dimethyl oxazoline derivatives (DMOX) of fatty acids. DMOX were prepared as follows (Spitzer, 1997): 0.2 ml of 2-Amino-2methyl-1-propanol was added to the saponified lipids. Helium was passed through the mixture. The flask was densely closed and heated to approximately 190 °C within 2 hours. To the reactionary mixture, 2 ml of the distilled water were added and the solution was acidified. DMOX were extracted with a hexane-acetone mixture (96:4 v/v).

Identification of animo acids was performed using A0326V2 analyzer (knauer, Germany). Macro and microelements were determined by the methods described by Kalacheva et al., 2002.

Modeling use of snail meat in BLSS diet

Each food product Pj is presented as a column vector:

...(3)

where mij -^ ma^ss^ of^ nutriecnotmeisp*tiiocnmse1ardr0Dtee0asdbipyglaoycnoacifdnoutprtasodrekoitrendhgoeufrtcotsa ; i1 Pj; ≤- i≤seuq;uence u -the n^um^^^ber numbesrtaonfdaenrsdt*ui ofeIsntmiamod*andti*etdioSoranuecI,mdcnaotmaronkdifuneintoorguifaetctronii tm(rFiaeAtIcenoOdtr;a/raWkec1escHpooo≤Ofrndt,doiin1≤ttag9ol9tutf0oho;) edttsanh;slte j - sequence number joff pthreo dinudci*tv; imdupIanj lt-aakmien itonafokteao ctoaifdl mpnrueotmrdibeuencrtsdj;, agy/;crewmembaecirddianya; reference pattern

ij e(n3t); c1Ao≤rsrei≤ts pouof; nvd sc otolutmhenb"vyneutchttreoierFnsAt-PpOIjFr/(oMW3d)tuHcOto"rmrwmepesrapritesroeiunxssdeRfsod dtotuorc tP;t1h eof "mnuatriexnRt- pproredsuecnto"sTfhtatmhehneIseadFetniMsriunindxttadriciivltcoRiirecomdesouna,pwmaarbrilliipenstacsrgehmihssdfaeiasfrnscoiaoziocfSleotidaNet ec(rnuet+wi1mi)s×ecvma.lbcTeuhrl aedt aefiydr; sbtyctohleufmornamncvuiddelascin:toa*iarl Pre1faFerorifenongdmcifeanatcpdriaelxtpit eeyRnrn( rpsrePsj vme^ecat^ot^.r e(n3t)scot^hrreesnpuotnrditsi ^DP1a^iloyf imn^at^atrkiex ^oR,f oton atlhebcyh"naturh*aterciFteeAnFrtiOo-spot/riWdcosidHnudOoceft pnruetsreiennTtsthtie*hsies icnFuadotliorcdutei lsoia,ntbdeaeeldspicebdhnyeads "pwesmenrdaeitelruni

... (4)

Caloric value of foodsftoa(lsonkltofadcwnathrdli)dnea gir(isdnFpcdA(aFairOvlaAcim/duOWuel/atHWetlerOaHsdm:,Ob1iny,9 the formula: of athc*eidi nindi niavdirdepufeanrledanemcneit npvoa trati

... (5)

where mn2, mn3, mn4 ob-jecptTirvohete esfiuenni,cntdifiocanets,s ,( 8ba-en1sd0i dceadrbtooheysdtirmataete thientbaeknee fit( ocforu)rs eiasnpgdotonhtdeh iesnrngialniyld,imcesagtm/ icetr eawndmeamsbimerildarayo.ne

The model is intended to esDtiimetatoepthime ibzeantieofint of using the snail meat as a ffoDolloioedtwiionpgBtipmLaSirzaSam.tiTeotone rdsio:s tthhea tf,olal obwaisnigc inddieict eas:nd a f soilmloiwlai*nr gopniaenr dawmepietethne rdsen:nativl mfoeoadt maraes so(pItFimMitz),egd/.cAre wbmaseicmdb*ieer*tdiasnydcc:eoopmnesnptdroaesinetdtsv ba-yri a user or adopted from ^any p*ub*lischoeinndsdtrewapioenrntksd.-eTnlthoevw efficay of optimization is estimated accoding to the following indices:

* Intake of total food mass (IMFt) g/ crew member day:

... (6)

IFMi comprises food intale from stories (IFMs) and food intake from BLSS agriculture and snail facility (IFMin)

* Food independence

... (7)

* Daily intake of anai; meat (mp1), g/ crew member day.

* Sum of nutrient imbalances (SNI) - number of nutients in which intakes do not correspond to the daily requirements.

In addition, animo acid scores of ffod protein were estimated according to the FAO>WHO standard (FAO/WHO, 1990). The animo acid score was calculated using the ratio of a content of the individual animo acid in the snai; meat (mg/g of protein) to the content of sames animo acid in a reference pattern (mg/g of protein multiplied by 100. The scorong etterns suggestef by the (FAO.Who, 1990.

These indices, besides SNI, were also used as objective functions of diet optimization

... (8)

... (9)

... (10)

Diet optimization is carried out by using a Solver Add-in for Excel 2007 with the following parameters:

* independent variables - masses of food products (mpj), g/day

* constraints - lower and upper bounds on the independent variables; daily nutrient intakes recommended by NASA (Cooper et al., 2011).

The most important index is the daily edible mass of snail (mp1). The use of different objective functions (8-10) is intended to study their influence on the daily intake of snail meat (mp1) and other indices mentioned earlier.

Solver options used in the study: MaxTime: = 300, Iterations: = 1000, Precision: = 0.000001, Tolerance: = 5 %, Convergence: = 0.0001, AssumeLinear: = False, AssumeNonNeg: = True, Estimates: = Tangent, Derivatives: = Forward, Search: = Newton.

To validate the model, we used a space diet intended for a lunar base (Liu et al., 2008). The number of food products in that diet is equal to 21. Data on chemical composition of "lunar base" products were imported from the open access databases (USDA, .SELFNutritionData, Danish Food Composition Databank).

It was suggested that a part of these products could be produced in BLSS: wheat grains, rice grains, pepper, carrot, coriander, tomato, cabbage, salad, radish, oyster mushroom, soy (sprouts out), pumpkin, pumpkin seeds saute, onion, garlic, and peanut oil. The remaining products: sardine, scad, seafood sauce, beef sauce savory, and sugar could be obtained from stories. In our study the number of food products was increased up to 22 because of the addition of snail meat to the basic space diet. The number of monitored nutrients in the study was equal to 40. Therefore, "nutrientproduct" matrix R had the size 41×22.

Results

Data on feeding

The lettuce leaves (0.23 g DM/snail day) were the most used feed (Table 3). This feed also had the greatest extent of degradation - 67 %. Worst of all, the snails consumed the cabbage roots - 0.07 g DM/snail day. However, cabbage roots RFD (60.4 %) was more than the RFD of straw (26.0 %).

Characteristics of snail growth

The upper boundary of whole body mass Ma was calculated as equal to 250 g and growth rate was equal to 1.06 month-1 (Formula 2). At the age of 11 months, a snail was in a stage of active growth. The calculated whole body mass was 174 g (Fig. 2). Mass ratio shell/whole body mass was within 18-21 % (Fig. 2).

Chemical composition of snail meat

Water occupied 80.8 % of total meat mass. Protein dominated in snail meat in terms of dry matter (78 %). The content of fats was found to be 6.0 %, ash - 7 % and carbohydrates - 9 % (calculated by difference) (Fig. 3).

The score of sulfur amino acid was found to be 47 (Fig. 4). Other essential amino acids had a score above 100.

An example of a chromatogram of fatty acids composition in snail meat is given in Fig. 5. There are both saturated and unsaturated fatty acids. The mass of essential fatty acids amounted to 16.6 % of the total sum. Among ω3 fatty acids, 18:3ω3 (linolenic) acid prevailed (3.8 %), whereas 18:2ω6 (linoleic) acid had the highest content among ω6 fatty acids (12.6 %) (Fig. 6). The ω6:ω3 polyunsaturated fatty acid ratio was found to be 4.6. According to the recommendation of NASA, that ratio should be within 8.8-12.7 (Cooper et al., 2011).

The greatest content of nitrogen was found in snail meat - 11350 mg/100 g DM (Table 4).

As a part of a shell, calcium dominated - 38843 mg/100 g DM. It is known, that calcium in a shell is mainly a component of calcium carbonate (Saleuddin, Wilbur, 1969). Therefore, taking into account the content of calcium, it is possible to calculate closely the content of calcium carbonate in a shell. It was found to be 97 % of the total shell mass. The other part of a shell fell on the nitrogen-bearing substances and mineral elements. An unexpected result was the phenomenon of the high iron content in feces - 571 mg/100 g DM and the low content in meat - 7 mg/100 g DM. This testifies as though a snail got rid of excess of iron. A superiority of calcium over nitrogen in eggs could be explained as follows. Calcium is a component of a shell, which almost completely consists of calcium carbonate. Moreover, nitrogen-bearing substances of eggs are distributed in a liquid. It also reduces the content of nitrogen in terms of dry weight.

Efficacy of using snail meat in diet: optimization of basic diet

When minimization of total food intake (IFMt) was used as an objective function, the indices of diet optimization were as follows: IFMt = 3450 g/day, FI = 76 %, SNI = 4 (Table 5).

Use of FImax as an objective function yields the following results: IFMt = 3512 g/day, FI = 94 %, SNI = 4. The increase of FI from 76 % to 94 % occurred due to the decrease of food consumption from stories (IFMs). Accordingly, intake of total food mass (IFMt) increased at the expense of vegetable food produced in BLSS, because vegetables are less caloric as compared with meat and fish products obtained from stories. The imbalances resulted from the excess of iron and low ω6:ω3 polyunsaturated fatty acid ratio as well as from a deficiency of vitamins D and K.

Efficacy of using snail meat in diet: inclusion of snail meat in basic diet

The snail meat was not included in diet if minimization of total food intake (IFMmin) was set as an objective function. The other indices were close to ones obtained under optimization of basic diet. On the contrary, when maximization of food independence (FImax) was assigned to be an objective function, the intake of snail meat reached the value of 118 g/day (Table 5). At that value, intake of total food mass (IFMt) and food independence (FI) increased from 3461 to 3800 g/ day and from 74 % to 97 % correspondingly. The intake of snail meat (mp1) reached the maximal value of 497 g/day when that index was used as an objective function (mp1max). Inclusion of snail meat in diet did not influence the sum (SNI) and nature of imbalances.

Discussion

Definition of the feed base of snails is a necessary condition for their inclusion in the BLSS. Natural food base consists of plant species growing in the locality of snail habitat. For example, the snails Archachatina marginata preferred Clerodendrum paniculatum and Laportea aestuans plants which offered the best potassium, sodium, phosphorus, protein, lipid and cellulose contents (Agongnikpo et al., 2010). The diets for snails Archachatina ventricosa based on four plant species with additives of Ca mineral were also tested (Otchoumou et al., 2004). Two plant species - lettuce and cabbage - from that work have been already entered to the inventory of candidates for BLSS (Advanced Life Support..., 2004). Of course, the new plant species could be included in BLSS, especially to extend a feed base for animals. It was proposed in case of the use of the silkworm, which consumes the leaves of the mulberry tree (Yang et al., 2009). However, it will cause an extra expense, because a sawn area in BLSS should be increased. In view of saving BLSS resources, inedible plant mass and kitchen wastes could be the best feed base for snails. It is stated that the quality of inedible plant parts available and the quantity of necessary feed for the snails are well matched (Midorikawa et al., 1993). In that regard, our results seem to stand in contrast to that statement. Inedible plant mass and potato peels turned out to be worse than the edible part of the lettuce (Table 3).

The selection of bedding plays an important role in snail breeding. It was established that the best bedding of four tested for the snails Archachatina ventricosa was a ground collected under a cassava plantation with addition of sawdust (Kouassi et al., 2007). As compared with the other beddings that substrate had the greatest organic matter content - 10.81 % DM. In our study, SLS was used as a bedding. Organic matter content in the SLS was much higher - 64-68 %.

It was possible to keep worms in SLS after its preparation. In that case, SLS did not have an unpleasant smell, because the worms consumed the snail feces.

Nowadays, there is no approved algorithm to compare snail-candidates to BLSS. One of the approaches to the development of this algorithm is to formalize snail growth. In this study we have used the logistic function to describe the individual growth of the land snail Achatina fulica. A similar description was performed in the case of land snail Helix aspersa (Czarnoleski et al., 2008).

One can see the value of Ca content of feces in Table 4 - 3750 mg/100 g DM. If a snail eats only calcium carbonate, Ca content can be a lot more. On the other hand, the question arises: what is the lower boundary of Ca content? The answer is of practical importance in view of the savings of calcium carbonate as a feed. In a diet of Archachatina ventricosa the optimum calcium content of the feed was found to be 16.01 % (Otchoumou et al., 2004). The lower Ca content is justified because there is a problem of Ca looping in BLSS if snails live in it. To develop Ca looping, the shell and worm casts should be tested as the Ca sources for snails.

The obvious shortcoming of Achatina fulica was the deficiency of essential sulfurcontaining amino acids in the snail meat. We have determined the score of sulfur-containing amino acids to be 40 (Fig. 3). Snail meat of Helix pomatia had a more favorable score - 88 (Midorikawa et al., 1993). However, this value is less than 100. A very high score of 207 was determined for the snail protein of Helix aspersa (Cagiltay et al., 2011). A look at the data raises the question: what factor has an impact on the score? It could be taxonomic position and conditions of snail growing. Undoubtedly, this is an issue of further investigations. In our study, the addition of snail meat did not affect the score, because it was surely established in the basic diet. The meat of Achatina fulica can be characterized as a low-fat one, because protein and fat content was 78 % and 6 %, respectively. A lower protein and fat content in snail meat was determined earlier (Otchoumou et al., 2010).

The shell of Achatina fulica in our study accounted for 18-21 % of the live snail weight (Fig. 2). In the previous study the shell/whole body mass ratio was established as 32.61 and 47.20 % for the wild and cultivated snails, respectively (Otchoumou et al., 2010). This discrepancy of published and present data can be attributed to the differences in snail feeding.

The previous work (Midorikawa et al., 1993) and this work have an identical approach: snail meat was added to a diet and the effect of this operation was estimated. Adding snail meat of Helix pomatia in a previous work has eliminated the deficiency of calcium, sodium, vitamin A and vitamin B12 of a basic vegetarian diet. No improvement in the basic diet was obtained if the meat of Achatina fulica was used. The effect from the implication of Helix pomatia could be explained by the poverty of a basic diet. Foods were produced from only four plant species. On the contrary, in this work, the fully- variable basic diet for a lunar base was used. Therefore, the implication of Achatina fulica enabled us to improve only one diet index - the food independence.

The number of imbalances in the basic diet is 4 and the addition of snail meat has no influence on the index (Table 5). Deficiencies of vitamins D and K are most easy to remove by adding vitamin pills to the diet. The ω6:ω3 polyunsaturated fatty acid ratio in the meat of Achatina fulica does not fit into the norm of NASA. However, the contents of polyunsaturated acids in snail meat are small. So, it can hardly be that the inclusion of snail meat in the diet affects the ω6:ω3 polyunsaturated fatty acid ratio. It is not clear how to meet the daily recommended intake concerning iron. The requirement to consume iron within the range of 10-12 mg/crewmember day seems to be very strict. The intake of snail meat (118 g/ crewmember day), calculated in our study, is close to the value of 110 g/crewmember day presented in the previous work (Midorikawa et al., 1993). However, these rates of snail meat seem to be too much for the daily intake. According to the menu of the International Space Station, the intake of the same product is allowed twice to thrice during the 8-day menu cycle (Perchonok, Bourland, 2002). Hence, the rate 118*3/8 = 44.25 g of snail meat/crewmember day is more realistic.

Conclusion

The snails Achatina fulica can produce a food protein by the use of both edible and inedible plant biomass as a feed. In case of inedible plant biomass the process can be considered as the secondary food production. Snails also consume kitchen wastes such as potato peels. The possibility of feeding snails with only inedible plant biomass and kitchen wastes is a subject of further research. Moreover, the problem to return calcium from feces to the matter turnover of BLSS should be solved. The addition of snail meat in a well-balanced basic diet does not eliminate nutrient imbalances; however, it leads to an increase in the food independence of BLSS. The data obtained in the study could be used in the simulation of the BLSS snail facility. Acknowledgments

The work was carried out within the frames of the state task on the subject No 56.1.4 of the Basic Research Program (Section VI) of Russian State Academies for 2013-2020.

References

References

1. Advanced Life Support Baseline Values and Assumptions Document (2004) Anthony J. Hanford, Ph.D., Editor. Lockheed Martin Space Operations Houston, Texas 77058. URL: http://ston.jsc. nasa.gov/collections/trs/_techrep/CR-2004-208941.pdf.

2. Agongnikpo E., Karamoko M., Otchoumou A. (2010) Diet of the giant African land snail Archachatina marginata Swainson, 1821, in Ivory Coast: preferences and estimate of damages. Revue d'Ecologie (Terre et Vie) 65: 319-330.

3. Cagiltay F., Erkan N., Tosun D., Selcuk A. (2011) Amino acid, fatty acid, vitamin and mineral contents of the edible garden snail (Helix aspersa). Journal of FisheriesSciences.com 5: 354-363.

4. Cobbinah J.R., Vink A., Owuka B. (2008) Snail farming. Production, processing and marketing. Agrodok-series No. 47, Wageningen, 78 p.

5. Cooper M., Douglas G., Perchonok M. (2011) Developing the NASA food system for long-duration missions. Journal of Food Science 76(2): R40-R48.

6. Czarnoleski M, Kozlowski J., Dumiot G., Bonnet J.-C., Mallard J., Dupont-Nivet M. (2008) Scaling of metabolism in Helix aspersa snails: changes through ontogeny and response to selection for increased size. The Journal of Experimental Biology 211: 391-399.

7. Danish Food Composition Databank. URL: http://www.foodcomp.dk/v7/fcdb_namesearch.asp

8. FAO/WHO (1990) Protein quality evaluation. Report of joint FAO/WHO expert consultation, Bethesda, MD, 4-8 December 1989. FAO/WHO, Rome, Italy.

9. Folch J., Lees M., Sloane Stanley G.H. (1957) A simple method for the isolation and purification of total lipids from animal tissues. The Journal of biological chemistry 226: 497-509.

10. Kalacheva G.S., Gubanov V.G., Gribovskaya I.V., Gladchenko I.A., Zinenko G.K., Savitsky S.V. (2002) Chemical analysis of Lake Shira water (1997-2000). Aquatic Ecology 36: 123-144.

11. Kouassi K.D., Otchoumou A., Dosso H. (2007) Les escargots comestibles de Cote d'Ivoire: influence de substrats d'élevage sur les parametres de croissance de Archachatina ventricosa (Gould, 1850) en élevage hors sol. Tropicultura 25(1): 16-20.

12. Li L., Zhao Z., Liu H. (2013) Feasibility of feeding yellow mealworm (Tenebrio molitor L.) in bioregenerative life support systems. Acta Astronautica 92: 103-109.

13. Liu H., Yu C.Y., Manukovsky N.S., Kovalev V.S., Gurevich Yu.L., Wang J. (2008) A conceptual configuration of the lunar base bioregenerative life support system including soil-like substrate for growing plants. Advances in Space Research 42: 1080-1088.

14. Mak hutova O.N., Protasov A.A., Gladyshev M.I., Sylaieva A.A., Sushchik N.N., Morozovskaya I.A., Kalachova G.S. (2013) Feeding spectra of bivalve mollusks Unio and Dreissena f rom Kanevskoe Reser voir, U kraine: are they food competitors or not? Zoological Studies 52: 56.

15. Manukovsky N.S., Kovalev V.S., Rygalov V.E., Zolotukhin I.G. (1997) Waste bioregeneration in life support CES: development of soil organic substrate. Advances in Space Research 20: 1827- 1832.

16. Midorikawa Y., Fujii T., Ohira A., Nitta K. (1993) CELSS nutrition system utilizing snails. Acta Astronautica 29: 645-650.

17. Otchoumou A., Dupont-Nivet M., Dosso H. (2004) Les escargots comestibles de Cote d'Ivoire: Effets de quelques plantes, d'aliments concentrés et de la teneur en calcium alimentaire sur la croissance d'Archachatina ventricosa (Gould, 1850) en élevage hors sol en bâtiment. Tropicultura 22 (3): 127-133.

18. Otchoumou A., Dupont-Nivet M., Ocho Anin L., Dosso H. (2010) Body proportions and chemical composition of wild and reared edible snails of Ivory Coast. Italian Journal of Food Science 1(22): 1-6.

19. Perchonok M., Bourland C.B. (2002) NASA food systems: past, present and future. Nutrition 18: 913-920.

20. Saleuddin A.S.M., Wilbur K.M. (1969) Shell regeneration in Helix pomatia. Canadian Journal of Zoology 47: 51-53.

21. SELFNutritionData. URL: http://nutritiondata.self.com/

22. Spitzer V. (1997) Structure analysis of fatty acids by gas chromatography - low resolution electron impact mass spectrometry of their 4,4-dimethyloxazoline derivatives -a review. Progress in Lipid Research 35: 387-408.

23. Toader-Williams A., Bentea M. (2010) Comparative study on the adaptation and growth dynamics of the Helix pomatia and Helix aspersa Muller terrestrial snails under different feeding regimes. Animal Science and Biotechnologies 43(1): 133-142.

24. Upatham E.S., Kruatrachue M., Baidikul V. (1988) Cultivation of the giant snail Achatina fulica. Journal of the Science Society of Thailand 14: 25-40.

25. USDA National Nutrient Database for Standard Reference. URL: http://ndb.nal.usda.gov/

26. Yu X., Liu H., Tong L. (2008) Feeding scenario of the silkworm Bombyx Mori, L. in the BLSS. Acta Astronautica 63: 1086-1092.

27. Yang Yu., Tang L., Tong L., Liu H. (2009) Silkworms culture as a source of protein for humans in space. Advances in Space Research 43: 1236-1242.

28. Volynets V.F. (1977) Analytical chemistry of nitrogen. Moscow: Nauka, 307 p. (in Russian).