Biolech Adv. Vol It, pp. 4,'oq-.479, 1993 0734--'9750,'q3 $24 00
Printed m Great Bntam. ALl Rights Resen ed ¢. Iqq3 Pergamon Press Lid
F E R M E N T A T I O N O F C E L L U L O S I C M A T E R I A L S T O M Y C O P R O T E I N F O O D S
MLIRRAY MOO-YOUNG, YUSUF CHISTI and DAGMAR VLACH
Department qf Chemtcal Engineenng, Univers.'zty t~f Waterloo, Vv'aterloo, Ontario.
Canada N2L 3G1
A b s t r a c t
A new bioprocess is described in which a cellulolytic, food-grade fungus
Neurospora sitophila
converts cellulosic materials to protein-rich products for food and fodder. The optimal conditions for the conversion are identified: 35-37 °C temperature, pH 5.5, 2.35 ms "t agitator tip speed. Scale-up of the production process to 1,300 L is reported. The mycoprotein production data on several types of cellulosic materials (sugarcane bagasse, corn stover, wood cellulose) are presented. The performance ofN. sitophila
is found to compare favourably with that ofChaetomhtm celhdoh,ticum,
another cellulolytic organism previously reported on by us.Key Words
Mycoprotein,
Neurospora s#ophila,
cellulose, single cell protein,Chaetomh~ra cellulo~'ticum.
I n t r o d u c t i o n
Cellulosic residues
(e.g.,
straw, corn stover, sugarcane bagasse) are under-utilized by-products of the agricultural indust~'. Much of these residues originate from plants used traditionally in food and feed production. Because they come from acceptable food sources, the residues could potentially be upgraded to food by improvements in digestibility, nutritive value and palatability.This paper describes a new process for converting various types of cellulosic solid residues to protein-rich products for food and fodder. The process in an extension of a recent invention for converting cereal-grain bran residues into proteinaceous products (Moo-Young et al., 1990). The process is based on the filamentous fungus
Neurospora sitophila
which has a long history of use as food in oriental preparations such asontjorn
(Hesseltine and Wang, 1967; Steinkraus, 1986;Wood and Yong, 1975). Additionally, N.
sitophila
has a processing advantage as being one of the faster growing microfungi. With a maximum specific growth rate of 0.40 h "l it has a doubling time which is shorter than that of some bacteria (Solomons, 1975). By comparison, the469
4-It r'..1 r',1C~,3-'~ OU NG ~ t ,~1
ma'~imum specific growth rates of o t h e r c o m m o n industrial fungi are half (e.g., for
.4~pe@ilh+s
~tt'ger) t~r e x e n les'~ t h a n a third (e.g., f~r
Penicillium cho'sogem~m
t h a n that of N.sitophilu
i Solomons, 1'4;51.
The Process Concept
Conceptually, the
N. siu~phila
m y c o p r o t e m p r o d u c u o n process consists of the following step,,:• Size reduction of the cellulosic residue by mdling or grinding:
• Treatment of the residue with alkah, acid and'or steam to increase the accessiblli~ ~f the cellulose in the particles:
• Fermentation ol the residue with N.
sitt;phila
either in submerged or surface culture:• Solid-liquid ~eparauon and deh.~dration of the product tor direct use as todder:
• Blending, possible nucleic acid reduction, textunzing and flavouring operauons for human food apphcatkm'~.
The size reducuon, sohd-liquid separauon and dehydrahon steps use ~ell knossn chemical engineering operations discussed elsewhere (Chisti and Moo-Young, 1991). The alkah pretreatment step (which, depending on the cellulosic material type. may not be needed'p ts described later in this article. Blending, te\turizing, colouring and fla,.ouring operations enhance the palatabilit~ and the organoleptic properties of the product. These operations are m common use m the rood pr,3ces~ing industry, and haxe been de~,eloped also for the fungal protein food
"Outwn" being marketed m the Llnited Kingdom (Steinkraus, l~Sb). Nucleic acid reducuon i,, al,~o used m Ouorn manufacture [Steinkraus, ]986). The reduction of nucleic acid~ ma~ be reqmred if the product is used for human food. The dicta D le~,el of R N A should not exceed 2 g per da~: breakdo~n ol R N A in human hcMv leads to elevated le',els of uric acid ~hich nta~.
c,tu,~e such metahohc dL,,orders as kidne~ stones. In ammals uric acid is readtl.v e~creted b,, con'~ersion to allantom, and R N A reduction in feeds is not nece'~saD'. The R N A reductton techmques ha~e been revie~ed before (Solomons, 1c)75, Sinske)and 3-annenbaum, ]9?5). Here v.e will fc,~cus only on the fermentaticm aspect'~ ot the N.
~#ophila
mycoprotein process tor upgrading cellulomc~.Fermentation Process Development
Development of the process through shake flask and pdot scale fermentations ~as needed tc~
ans~er st~me fundamental questions: What are the optimum pH and temperature tor protem production and cellulose utihzation? What are the rates and the maximal levels of protein tormatton and cellulose consumption? How does the utihzation orcellulose - a difficult to tmhze
• ,olid substrate - compare with microbial bsomass production on more readil,~ accessible
FERMENTAT1ONI TO MYCOPROTEIN FOODS 471 molasses? i.e., ho~ does the "best ease" protein production performance of the fungus, not limited b) substrate accessibilib, compare with that on less expensh, e cellulosic substrates? Ho~
would some of the common cellulosic residues such as corn stover and bagasse fare in terms of the ability to support protein biosynthesis? Would the fungus perform as well in fermenters as in shake flasks? What is its susceptibility to mechanical and other damage in fermenters? And, hog' does ,\,'euro~pora sitophih~ compare with the capabilities of Chaetomhtm celhtloh.'ticton, one of the better known cellulol~tic organisms? These questions ~ere answered by experimentation which proved the process concept and its ,~calabilit3 as discussed below.
Experimental
Cultures and inocula. The filamentous fungi ,Veurospon~ sitophila (ATCC 36935) and Chaetomittm celhdoh'ticttm (ATCC 32319) were maintained separatel.~ at 4 ~C in submerged cuhures on glucose (It) kgm 3 ) supplemented ~ith )'east extract (Dill'co) f2 kgm 3) and the follo~ ing nutrient salts (per litre): (NH4)2SO 4. 0.47 g; urea, 1/.86 g: KH2PO 4. I),714 g: MgSO4.7H,O, ().2 g: CaCl,.
0.2 g; FeCI 3. 3.2 rag: ZnSO4.TH20. 4.4 mg: HsBO 3. 0.114 rag; (NH4)0Mo,O24.4H20. 0.4S rag:
CuSO4.5H20, 1).7S rag: MnCI~.4H,O. fl. 144 rag. lnocula were grown at 26 ~C on the specified carbon source (5 kgm 3) supplemented ~ith 0.5 kgm -3 molasse~ (Holfman Feeds Ltd.
Heidelberg. OntarioJ and the earher specified sahs.
The fermentation media contained a carbon source ("Solka Floe" wood cellulose, sugarcane bagasse, corn stover, or molasses). The Solka Floc cellulose (a-cellulose) was made from wood pulp (James Ri~er Corporation. Berlin. Ne~ Hampshire). The KS1010 and the BW300 grades used in this ~ork had an a,.erage particle (fibre) length of290 p.m and 22 p.m, re,~pecti~el). The BW300 grade had a degree of crs. stallinit,~ of 62-65 % cDstalline, whereas the KSI016 had a greater proportion of cD'stalline cellulose at 75-7-', %. Apart front the Solka Floc cellulose, all other residues were pretreated v, ith sodium h)droxide (0.15 kgkg residue) at 121 '~C for 30 minutes, .Although the media were supplemented v, ith the full complement of the earlier specified nutrient salts, only ammonium sulfate and phosphates were essential requirement ~ t h certain naturall)-occurrmg cellulosic residues such as straw and corn sto'.er.
Fermentation conditions. Fermentations were conducted either in shake flaskx or in a 75 L (nominal) stirred tank fermenter ( M B R Sulzer, Switzerland). The shake flask runs v, ere performed in 250 m L (nominal) flasks containing lfl0 m L medium including an specified carbon source and the nutrient salts. The flasks ~,ere sterilized at 121 °C for 3fl minutes, co~71ed to ambient, inoculated and held at the specified temperature on a D'rato D' shaker at 250 rpm.
Unless otherwise indicated, the pH at inoculation was 6.0. At desired times, the flasks were
472 M. ~.f (~-~-'~ O L i N G ~t ,tl
rapidly cooled a n d stored at 4 ~C ~f necessar 3. T h e flasks `.~ere analyzed for total d ~ solids.
crude protein a n d cellulo';e.
Crude protein and celhdose. For crude protein a n d cellulose d e t e r m i n a t i o n s , the f e r m e n t a u o n b r o t h was filtered u n d e r s u c u o n t h r o u g h a 25 p,m "Nitex" nylon cloth ( T h o m s o n Co., Scarbrough, O n t a r i o ) , the filter cake was ~`.ashed ~ i t h several broth v o l u m e s of deionized `.`.ater a n d dried o v e r m g h t at 9(~ '~C. T h e d ~ ' b t o m a s s was g r o u n d to l m m particle size a n d u ~ortton ,.,.as analvzed for total m t r o g e n using a mlcroKjeldahl technique (Lang, 1958). T h e crude protein c o n t e n t ol the b i o m a ~ `.`.ere calculated as 6.25 ,, total nitrogen, a n d p e r c e n t I~`..'~s ) protein as g r a m protein per 11)(I g total dr). sohds. The cellulose c o n t e n t ~`.ere d e t e r m i n e d b) the s p e c t r o p h o t o m e t r i c a n t h r o n e - s u l f u r i c acnd m e t h o d (Llpdegrafl, 196t41: p e r c e n t cellulose ~`.a,, calculated on the s a m e bas~s as crude protein.
Shear effects. T h e influence ~3f s h e a r on protein production ~sa~ investigated m the 75 L f e r m e n t e r (,,essel d i a m e t e r = 1).31~ m; working a,;pect ratio = l,t)) w~th a ~ o r k m g ~olume latter inoculatton) of 51) L. T h e t e m p e r a t u r e and pH v, ere controlled at 26, ' C and pH ¢~.1), respecu`.el,,. ]'he dissolved oxygen level ~`.as nc~t allo~`.ed to d r o p b e l o ~ 20 % of air ~aturation, A e r a t t o n rate ',aricd ((1.4 - 11.,',¢, ',~.['n) in re~pon~e to the tlissol~ed o \ 3 g e n le`.el. A O-blade d~.',c turbine `.`.as used Ior agitation I d i a m e t e r ot impeller.'tank d i a m e t e r = 0.57; li3catlon above b o t t o m of tank = q).B impeller d i a m e t e r l at 25ql, 30ql or 350 rpm c o r r e s p o n d i n g respecti`.el.~ t~
tip s p e e d s tlf 2.35, 2.~2 a n d 3.29 n3~l. ,V. situphila was grov, n on Solka Floc ( K S l t l l h i 15 kgnt3'l s u p p l e m e n t e d ~`.sth mola~se~ ((I.5 kgm-~). (NH41_~SO ~ ¢1).28 gL-II: urea (0.52 gL lJ. K H 2 P O 4 I l.(t gL l ) a n d other, pre`. uou~l.v listed, nutrient s a h s at half the c o n c e n t r a t i o n s spec~tied earher.
Results and Discussion
Temperature effects. T h e effect of t e m p e r a t u r e on cellulose milizatton a n d crude protein p r o d u c t i o n i~ sho~`.n m Figure 1. T h e result,; in Figure 1 `.`.ere o b t a i n e d in s h a k e fla.,ks `.`.Lth ,V.
sitophila grown on industrial cellulose slur% m e d m m t ll'l kgm -3 Solka Floc grade KS1010)
~ u p p l e m e n t e d v, ith molasse~ t l kgm x ) and the n u t H e m ~alt~,. E'tch d a m point in the figure (Figure 1) c o r r e s p o n d e d to the m a x i m u m cellulose utilization a n d protein productson at the given t e m p e r a t u r e at 3S hour~, since i n o c u l a u o n (1() ~ `.,`., c~a. 0.3 kgm -3 initial p r o t e m ) of the flasks. T h e f e r m e n t a t i o n s p e a k e d ca. 3S h o u r s after initiation. A m a x i m u m cellulose utilizauon of - 86 ~c of orLginal cellulose a n d protein production ol - 35 ¢; of the total dR?,. ~`.eight `.`.ere o b s e ~ ' e d at 37 ~C. The optimal f e r m e n t a t i o n t e m p e r a t u r e range was 35-37 °C- t e m p e r u t u r e s higher t h a n - 3~ ~C c a u s e d s h a r p decline m b t o m a s s production ( M o o - Y o u n g et al., 1992'1.
4 0
ZC,
Z Ld 20 I.-- 0 ['y O_
I C'
FERMENTATION TO MYCOPROTEIN FCKDD5 5 0
PRC, T;IFd-
2 5 3 0 3 5 40 45
T E M P E R A T U R E (°C)
E
o~ 0 2 0
Z
<
b4 I-- 0
- , a:
.z)
N c,'
S 4
2,2, .~
Lxl k-)
473
/
")-' / / / 2"
I I
pH
90 -~
o Z t---
7C,,~
I'M .._J
E.O
LO
.=..2, -J 0 -.,
.-3 1,2' U
• Figure 1. Effect of fermentation t e m p e r a t u r e on N.
sitophila
protein production and cellulose utilization.• Figure 2. Effect o f fermentation pH on crude protein production (,,V.
sitophih~)and
cellulose utilization.
Effect ofptt.
T h e influence o f p H on N.sitophila
fermentations of cellulose (Solka Floe BW300) is shown in Figure 2. T h e s e fermentations were conducted in the 75 L f e r m e n t e r at 37 ° C . The concentration of cellulose and the s u p p l e m e n t s were the same as used in the pe~'ious set of e x p e r i m e n t s on t e m p e r a t u r e effects. The inoculum for these runs was grown on KS1016 grade o f Solka Floc cellulose (10 kgm -3) s u p p l e m e n t e d in the same way as the fermentation medium.All f e r m e n t a t i o n s were inoculated at p H 6.(1, the p H was allowed to fall to one of the set points shown in Figure 2. and was controlled at the set point. The protein production and cellulose utilization r e p o r t e d in Figure 2 ~,ere the maximum values which occurred ~ 38 hours into the fermentation. A pH o p t i m u m of pH - 5,5 was identified. At this p H - 80 % of the cellulose
~hlch was originally p r e s e n t had been used up by 38 hours, and - 2 kgm "3 protein had been produced ~hJch r e p r e s e n t e d - 33 % of dry weight o f the product ( M o o - Y o u n g et al.. 19921.
Typically, in the a m m o n i u m / u r e a containing media as used in this work, the p H in fungal f e r m e n t a t i o n s without pH control, initially declines due to consumption o f NH4 + as the nitrogen source. U p o n exhaustion o f NH4 +, urea supplies the required nitrogen and the p H of the broth rises. This behaviour is observed in
N. sitophila
fermentations (e.g., Oguntimein et al., 19921 as well as those o f o t h e r fungi. T h e ammonium,'urea ratio in the medium can be manipulated for rough p H control particularly in shake flasks: however, superior p H control, e.g., by acid,'alkali addition, in large scale fermentations can e n h a n c e production rate and product }4eld sufficientl}that such control is worthwhile e~en for Io~ value products.
4-4 M. MOO-', OLiNG ,-t al
Agitation.
Mechanical agttation in stirred fermenters i.,, k n o ~ n to danrage mycelial biomass and affect the yield oi: the product (Chisn and M o o - 5 o u n g , 1989, M o o - Y o u n g and Ch~sti, 19gS:Ujcova et al., 1981]). Characterization o{ the influence of the impeller ~peed on N.
~it,'~phila
protein p r o d u c n o n ~ a s r e q m r e d to identify the ~uitable operational condiuons, an},' scale-up hmltation';, and the senblti',it,, of this parncular fermentation to impeller induced shear.
The protein p r o d u c n o n profiles at tanou.,, agitation rates (tip s p e e d s ) are s h o ~ n in Figure 3. For otheD.~,i,.e identical conditions, increa';ing tip speed ol the Rushton dt.,,c turbine impeller loitered the rate ol/ protein production tFigure 31, and the maxm]um protein yield. Thus, a, shou.n in Table l, the ma',:lmum specihc protein productton rate 1~1 d e c r e a s e d fronl a high ot 11.09 h l at 2511 rpm to a Io,*, of 0.05 h -I at 35(I rpm. In relative term.,,, the protein production rate (~UR) at tile htghest rpm v,a~ onl) 55 r;: ol that at the Iov.,est agitatton. Data on peak protein productton and cellulose utdtzation lat 3g hours into tile l e r m e n t a t i o n l are shown in Table 1 in absolute and relative terms. At the hlghe,,t tip speed used ( 3.29 m,. "l ) a dt.,,tinct lag pha',e ~ a s nouced ( Ftgure 3) in protein prcMuct~on c o m p a r e d to tile results at Iot~.er agitation mtensme~,.
Table I. Effect o{ Impeller S p e e d on Protein P r o d u c u o n and Cellulose Utdization Inlpeller S p e e d Tip S p e e d /1 i h 1 ) MR { I ) Crude Protein Cellulose
(rpm) (ms 1 I (~:?) Uttlization (e~,)
250 2.35 O.()q 1.0 31.1 ( 11" 79.8 I 1)*
3t,t 2.S2 ().H7 11.78 2-'..7 (o..~g) 60.0 (O.g6)
35q) 3.29 0.115 0.55 21.2 111.67 ) 55.6 ( 0.7111
2511 rpm.
" Values in parentheses are relatl~.e to the ',alue at
Z •
- - 2
L J p . -
- ' t i,,, ' -
~ ' i / ,' TII: JFCP_-I_-' - 1
- ~
• -92
" ~ --'3
r i 2
T i r , l E ~ Pi ;
F i g u r e 3. E f f e c t of agttation on protein production. Impeller speed (rpm I:L g l 250:
(e~ 3(10: and (o) 350.
Z. ] T ':'= :TE,r.
•
¢ Ell,i £
_,
m7 1 r . 1 ~ , r', I
Figure 4. C o m p a r t s o n o l protein production m shake flasks and the "/5 L tern]enter.
FERMENTATION TO M5 COPRO1T_IN FCY-DDS 475 Clearly, the N.
sitophiht
fermentations were quite sensitive to excessive agitation, and low agitation rates, consistent with adequate mbfing and ox3,gen supply were indicated for the successful production process (Moo-Young et al., 1992). Further experiments (Figure 41 confirmed that an agltauon speed of 251) rpm in the 75 L fermenter was optimal for protein production. At th~s speed the protein production m the fermenter agreed closely with that m shake flasks (Figure 4). The data in Figure 4 were obtained ~ithN. sitophila
grown on Chinese (Peoples Republic of China) bagasse (10 kgm 3) which had been pretreated w~th sodium h>droxide. These fermentations were conducted at 37 °C and pH 5.5.ZC'
,~ IC
Z
Ck
t . I , ' , L ~ ~ : ; z -
.' .%
, ? ~2~,3.:, 5'3E II- i Iij. ~ ,~ rt-,- ] I
~l h -I .'
• O 41
I ' I I
10 15 2~' 2 5
TflYIE th)
Figure 5. Comparison of N.
sitophila
protein production on molasses and bagasse in 75 L fermenter (37 °C. pH 5.5, 250 rpm impeller speed).' - ' " b /' ,7 ,,'
~ ~t / '
.~ I I D
( ~ " , I 4 ~,r-.pr,,I.a
. (.' ~, : c , ~ z ~ , 'o, ._-.co,.
"_- ,- C ~ l l u l , 2 , 1 l I ,,: u r r , : '-' t ~ h -1 3r ] 7 : C
T r M E ~,h)
Figure
6. Protein production: N.sitophila vs. C. celluh~h.,ticum.
Substrate characteristics.
The protein production perlormance of N.sitophila
on sugarcane bagasse and molasses was compared as sho~n in Figure 5. A specific growth rate of 0.26 h -t was obtained on bagasse, a less accessible sohd substrate. On the more readily accessible molasses.the specific growth rate (= 0.41 h l ) ~as - 1.6-tbld greater. The growth rate on molasses v, as comparable to the maximum ,,alue of 0.40 h 1 reported for N.
sitophila
growing on glucose at 30 °C (Anderson et al., 1975). These observations confirmed that the protein production process could potentia[I.~ be improved significantly by intpro~,ing the accessibflib of the substrate to the fungus (Moo-Young et al., 1992).Substrate a',ailabili b ~as limited either b~ restricted physical access of the fungal cellulases to the solid particle and,'or by inherent limitations in the rate of hydrolysis of cellulose. The latter could be due to either a limited rate of production of cellulases or due to limitauons in the kmeucs of the hydrolytic reaction itself. The possibility that secretion of N
~#ophila
cellulases and their inherent hydrol)tic capability combined, ~,,ere less than that of other microfungi was dJscnunted in ~iew of the results sho~n in Figure 6, ~,here protein production476 M. M(X3-YOUNG
et al
by
N. sitophila
was compared with that byC. celluloh'ticvm.
The fungi were grown in shake flasks on alkah pretreated corn sto~er (10 kgm -3) supplemented with the nutrient salts. As shown in the figure, N.sitophila
protein production was comparable to that obtained with (2celhdoh'ticum,
e~,en though at 26 °C the cultivation temperature forNeurospora
was less than optimum. The ma.xtmum specific growth rate ofC. celhdoh'ticum
was about 12 % greater than that of N.sitophila.
Both fungi had utilized - 93 c~- of the cellulose by 24 hours into fermentation ( M o o - Y o u n g e t al., 1992). Despite these results, we believe that cellulase secretion by N.sitophila
can be enhanced to further improve its cellulolytic potential. This ~ie~ ts supported by the obse~'ed two-fold increase in cellulase activity per unit biomass upon disruption of N.sitophila
(Baldwin and Moo-Young, 1991) which implies that onl.~ about 5(3 % of the available cellulol}tic acti,,'it)' is normally secreted. More detailed work on the production of cellulases by N.sitophila,
and on the characteristics of those cellulases was reported b.~Oguntimein et al. (1992).
The
product.
TheN. sitophila
raw protein product had a pleasant almond smell. ?dmond or minced-meat flavour occurs also inontjom
produced by fermentation of peanut press cake byA t. sitophila
(Hesseltine and Wang, 1967). The average composition of the fungus was (% v...Iw):45 % crude protein, 40 % carbohydrates. 10 % fats, 5 % minerals, vitamins, etc. The amino acid composition (g per 100 g protein) of the fungal protein is shown in Table 2 where it is compared v, ith that of fodder yeast
(Candida utilis),
soyabean meal and the FAO reference protein.Table 2. ,~nino Acid Composition of Various Proteins
Amino Acid
N. sitophila C. utilis
Soyabean Meal FAO ReferenceThreonine 3.8 5.5 4.0 2.8
ValJne 6.9 6.3 5.0 4.2
Cystine 0.8 0.7 1.4 2.0
Methionine 1.8 1.2 1.4 2.2
lsoleucine 5.0 5.3 5.4 4.2
Leucine 8.0 7.0 7.7 4.8
Tyrosine 2.1 3.3 2.7 2.8
Phenylalanine 4.2 4.3 5.1 2.8
Lysine 5.3 6.7 6.5 4.2
FERMENTATION TO NP(COPRO'FEIN FOODS 477 Process Scale-up
Having identified the optimal fermentation conditions and quantified the fungal susceptibilit) to mechanical damage in fermenters, the fermentation process was further de,,eloped at the 75 L scale and scaled-up to 1,300 L pilot plant (M'oo-Young et al., 1987). The Rushton disc turbine agitators were replaced with axial flow "Prochem" hydrofoil-type impellers (Chisti and Moo- Young, 1991) of equal diameter. A draft tube ~as added to enhance axial flow of the highly viscous, non-Newtonian fermentation broth (Moo-Young and Chisti, 1988) and hence the bulk mixing in the fermenter was improved. Air was sparged in the annulus between the draft tube and the walls of the fermenter. This airlift-stirred tank hybrid bioreactor proved superior to either a basic airlift or a stirred tank. :Mthough the airlift configuration without mechanical agitation could be used (Moo-Young et al., 1987), the bulk mixing of the broth was not as effective as in the hybrid dc~ice. Unhke many ~iscous fermentations which have been successfully performed in airlift bioreactors (Chisti, 1989), N.
sitophila
broths containing cellulosics particulates are more ', iscous and pseudoplastic. For example,C. cellulog.'licum
broths are rheologicall.v easier to handle than those of N.sitophila
(Moo-Young et al.. 1987). The bioreactor scale-up considerations such as gas-liquid mass transfer and gas holdup effects in those broths have been reported on previously (Chisti and Moo-Young, 1988: Moo-Young et al., 1987). O t h e r general aspects of fermentation plant design which apply in different degrees to food and feed plants ha~,e been detailed elsewhere (Chisti, 1992: Chisti, 1992a: Chistl and Moo-Young, 1991 ).Process Economics
The economics of fungal protein manufacture were discussed in detail by Moo-Young et al.
( 1979: 1986) for a production processes based on
C. celhdo~.'ticum.
Those economic analyses are equally valid for theN. sitophila
based process because of the similarities between the t~o production schemes: same cellulosic substrates, media supplements, and pretreatment operations: identical downstream processing of the product and similar growth and protein production characteristics of the two fungi.For conversion of Kraft paper pulpmill clarifier sludge (95 % cellulose) to mycoprotein, Moo-Young et al. (1986) determined that a minimum processing capacity of 6.5 tonne per day of sludge was required to break-even. A 96 % conversion of the cellulose to a product containing 38 % protein was assumed with so)meal-based protein being the reference selling price. The major contributors to production cost were the utilities (at 37.2 % of total cost), the nutrients (at 36.4 c~ of total cost) and the equipment depreciation /at 18.1 c~, of total cost).
47,., M.b.lL~3-', OUNG ,'t al.
In speciality, toods industr~ the production cost cons~derauons are of lesser map,)rtance thau in l e e d s m a n u f a c t u r e . For e x a m p l e , the Q u o r n m s c o p r o t e m is commerc~all.,, p r o d u c e d using hydrolysed starch - a m,~re expen,,ixe .,,ub,~trute than celluloaic re~.~due - toe fungal culti',au~m t Steinkraus, 198bl. H e n c e , the ,'\., fft,',l#tda protein proce,,,; is e x p e c t e d ~o be ec~momicall,. ,. iable in spemalit} foods m a r k e t , , e.g.. Mr vegetariun,~,
C o n c l u s i o n
T h e f o o d - g r a d e f u n g u s ,\'euro~pr,ra fft~phila ~ a ~ cultured on ~ariou.,, solid celluMslc sub.,,trate,, (v~ood cellulose, :,ugarcane bagasse, c~rn sto~erl f~,r m y c o p r o t e i n production. The optml,.I conditions for cellulose utihzati~m a n d protein prc, duction .,tere found t,~ he 35-37 : C t e m p e r a t u r e , p H 5.5 a n d agitator tip s p e e d n,,t exceeding 2.35 nl.,, -I m a -',5 k , t i r r e d tank l e r m e n t e r . Lip to c,. 9~1 c~. u t d i z a u o n cff cellulo,,e could be achle,.ed. T h e cellulol,.uc perforntance of ,V. silophila c~mlpared latourabl~ ~[th that ot (lu,'temffum c~,lhtloh'ticum ~hich is well knov. n for m, ability, to d e g r a d e cellulo,,.e. The nlycoprotein p r o d u c t i o n process ~.a,, pro'.en to 1,311tl L tqlot ,,tale. The pr,~ce',~, is an etfecte, e Illeth~d for Fro,tern-enrichment ol cellulo~,~c ,,ub~,tance,, lot lo~d a n d fi,dder u,.e.
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