effect of underground storage on some chemical, and

AL AWAMIA - No 83 - Décembre 1993

EFFECT OF UNDERGROUND STORAGE ONSOME CHEMICAL, AND RHEOLOGICAL

PROPERTIES OF WHEATBAKHELLA M.. r. KAANANA 4., *t and BABA M .***

é *r*\ d- x.--.il\ J,iiê\*i\ .-1;æ r.i-,-ill ç-y-i d,- J*é ô.I' t3'ir-C-iJ\ ,-1i J! t-:l ôJtjy\

?.r{5,g,0-.,;1-lÀ\ , Laj3*'-,cÈ-r1\ .i*3 .-1;\;u.ljô9,-7 "J. j-ts .rl tASae i.r.-.rr cWV É-Fi.- ili,rJ.Jl "i++ ùJ-Êll

elJôJ i*-.ôTl Ê*iig ,,-3\r*i:l\ i -l\-:r ,.rL i-l;.$l o.tl c:.r-l* ùCa \iÀir . aùl ,2909 çur.r\e L.:l.,6;,-ll 'J t\ C*iJl ; i..:" ar-r+ cr-j4i*|;f.i l l Liltd+ ,'îrL: ,(,'-t-Ult, ,;-rTl .:;6rE* é,t

's f+ rU,:Js.e.r- il-J\ "i" Jl* LJ+ \-:J C^,J .:*o.1,d*: -)l+Jl el ô'L:JLJS .f i:lr rÈo Cf\:^ e:\ cf db..c d.l-i\ L-:9 Ll:+*; p tll al3sl\

.i*+sJs,-r i5_sJ(1Ls +:l*fr3os, i.JLé 6r-ta' Q!U.:9 ir:-À-

t! rr4;'!t oir .:àr.- é\J+J""(.-U! i*+-rt-rrJ\ cl;o-J\ JLj;\ .9.IJJ.J.!l i;:!l l3*l\ a.rl i++rj el> fro.� i,rop ,-i\:jÀdJl .!.J.*: i-r.r , i,i\-

aL-3;-- ûi tJ .+bl\ l-l-J\ a.u cL-c3\ ,;-;*:tt r,..,,'.Jl .:\;tJl ;,or;'Jl 3- !t|jl\ i .r ^ ,: l\ J * "l L\\ çJ I*+- .r* c\r.**ijj\ "iÀ Js

'":<lî -)!l

,j L r<-lf .i\+ -!"n\ Li\rrr.i ôJ. ;j i-o { r ËôL-j tL=*: L;2i "1,\ . Y".t- çi

lr,,, i [;!;L \-*#$ y! d.r-- d Cp .rt ' ,.:ÉjJ\ i:-:-, i l \ ûjLj.\\ô9-+e ' r" F: \-<.ajrt ')LrJ! L"E\.: il-b\il\ ùibl\ ,e.tl cs\jt.(]l oil,LJL-iSJ\ r_l-l\s i€ rr" i*+r-e"-J\ ,1,. tt ùu i-ù{r l+\-" J-\9-.OôJ"â*JL i ^:^,r\\ -,+.1 Ll\

çi olJls ,o,ra\ 5E

i{+ rr- \Jla.*<}_j*iJl.*+ J*:A .uL,{:.-)tJL J+i"tL-l\ :^L:t 6l "J. d9n\ ô<4 r9*-Jl t'l.9

O:Ê\ 4,;J\ ar3,a .'1r Jâtà-l\

.;.l3al\ uFJt ,C-n\ , Lrlg> cl-15

* Professor at the Food Science and Human Nutritlon Section, 'Institut Agronomique etvétérinaire Hassan II". B.P. 6202, Rabat-Instituts, Maroc (Moroccn).*r Associate professor et the Food Sclence and Human Nutrition Section, "InstitutAgronomique et Vétérlnalre Hassan II", BP;6202, Rabat-Instituts, Maroc (Morocco).+r* Research Engineer at the Departemenl of Food Technology, IInstltut Netlonal de laRecherc'lre Agronomique", B.P. 415, Rabrt, Maroc (Marroco).

AL AWAMIA - N" 83 - Décembre 1993

RESUMELe stockage souterrain des grains de blé est pratiqué par beaucoup

d'agriculteurs au Maroc. La qualité du blé peut changer considérablement aucours du stockage. Cette étude a été menée pour suivre ces changements et enévaluer l'importance. Vingt tonnes de blé dur (vuiété Awd Zenati : 2909) ontété stockées pour une durée de seize mois et demi dans des fosses souterraines(<Matmoras>) revêtues de paille ou de plastique. Au cours de celte période,l'évolution de la qualité a été appréciée par des tests chimiques.physico-chimiques, microbiologiques, et rhéologiques .

Des échantillons de blé ont été prélevés de quafre positions différentes, après3, 6, 9, et 16.5 mois de stockage. Les propriétés rhéologiques (test auMixographe) et le degré d'hydrolyse des lipides ont été affectés par la durée destockage. Une augmeutation du temps de développement de la pâte et unaccroissement de I'acidité grasse otrt été enregistés. L'humidité et I'activité deI'eau ont également sensiblement augmenté. Le nombre de colonies demoisissures dans les fosses revêtues de paille a substantiellement augmenté.L'intensité des variations de tous ces paramètres est plus importante dans lesfosses revêtues de paille. Les critères chimiques et rhéologiques ont été mieuxcorrélés entre eux dans les fosses à revêtement en paille. En général, le blé arelativement mieux conservé sa qualité dans les <Matmoras> revêtues deplastique que dans celles revêtues en paille.

MOTS CLÉS : Blé : Stockage;Qualité.

ABSTRACTUnderground storage of wheat grains is commonly practiced by farmers in

Morocco. Grain quality may be seriously altered over time of storage. Theobjective of this study was to monitor quality changes of wheat stored inunderground pits. Durumwheat (Triticum desf.) cv. Oued Zenati was stored forup to 16.5 months in underground pits (Matmoras) with either straw or plastic asinternal liners, and its quality was monitored using chemical, physico-chemical,microbial. and rheologital tests. Grain was sampled in the pit at four differentpositions in the pit after 3, 6, 9, and 16.5 months of storage. Mixographproperties and the degree of fat hydrolysis were affected by storage duration.The main storage effects included an increase in dough mixing time and anincrease in fat acidity, moisture content, and water activity. the number of moldcolonies increased substancially in pits lined with straw, whereas in plastic-linedpits the mold count did not vary significantly. The magnitude of these changegwas higher in straw-lined pits. Conelation coefficients showed that the chemicaland rheological changes were better related in straw-lined pits compared to thoseobtained fiom pits lined with plastic . Generally, the pits lined with plasticmaintained much of the inital properties of wheat. compared to those lined withstaw.

KEY WORDS : Wheat; Storage; Quality.

AL AWAMTA - No 83 - Décembre 1993

INTRODUCTION

Postharvest losses are quite important in Morocco. The nature andimportance of grain deterioràtion is closely related to the kinds of storagefacllities used. In Morocco, underground storage. still is one of the majormethods used by farmers to store harvested wheat . The storage structqre used iscallcd : < MATMORA >. It is a conc-shaped pit with the diameter increasirtgtiom the top to the bottom. The interior walls are always covered with a thicklining made. of clay and straw. The storagc capacity varies getterally from one tofive metric tons. Despite some handlittg problems, the storage of wheat in suchairtight conditions is supposed to protect the grain from important temperaturetluctuations. and limit insects and mold proliferation via the creation of anenvironment whose oxygeu content decreases with storage duration (Bartali etDebbarh. 1990) . The changes lhat occur in chemical, physico-chemical, andrheological propcrties of wheat during storage depend upon several factors suchas temperatue, humidity and storage duration. The edibility (or) wholesomenessof stored wheat is very sensitive to moisture colltent variation (Fellers & Bean,191'7). ht tact, molds start to grow significantly when moisture content exceeds13 to l4Vo (Sauer, 1988) . When moisture content is above 16 Vo, it leads toextensive deterioratiou of bread-making quality of wheat stored in airtightconditions (Hyde & Burrel, 1982 ; Shearer & Warwick, 1983) . The majorchemical change that occurs durirrg storage of flour or wheat grains in eitheropen-air or airtight conditious is lipid deterioration via enzymatic hydrolysisreactions that generate free fatly acids (Datiary & Pomeraltz, 1965: Daftary etal.. 1970 a I Girish et al.. 1912: Warwick et al., 1979 ; Gallaind, 1983 : Shearer& Warwick. 1983 I Leelavathi et al.. 1984). This hydrolysis is catalyzed by bothseed and microbial lipases (Daftary & Pomeranz, 1965 ; Galliand, 1986) . Matyauthors reported that lipid hydrolysis paralleled wheat quality deterioration.Impaired rheological properties have been observed when wheat or flour storedat high moisture contents and in low or normal oxygen concentration, is invadedby molds . Mixing time, resistance to extension,'and dough stability increased,whereas dough extensibility, tlour water absorption, and loaf volume decreased.indicating that gluten visco-elastic properties are seriously altered (Pomeranz etal.. 1956 ; Pomeranz et al., 1968 ; Daftary et al., 1970b : Leelavathi et al., 1984).

Concerning the gassing power, Pomeranz et al. (1968) reported that it wasnot significantly affected by storage duration . This was also noted by Pixton etal. (1975). who reported that tlrc activity of alpha-amylase reached levels belowthe minimum required for normal fermentatiou. only at'ter eight yean of storage.

The purpose of this study is to look at the quality changes of wheat stored inunderground pits. by analysing some chemical (moisture content, and free fattyacids), physico-chemical (water activity), microbiological (mold count), andrheological (Mixograph : Mixing Time, Peali Height, and Weakening Angle)parameters. Alpha-amylase activity is also assessed using the Hagberg test. Thepits were lined with either straw or plastic so as to look for the benefits of havingone or the other lining material in terms of preserving wheat from adversestorase effects.


MATERIALS and METHODS

Whest sampling and storage conditions

20 tons of souud durun wheat of the Oued Zenati variety (29W) crop year1987. were stored in sixteen identical underground pits ("mâtmoras") foi i6.5morrths . The pits were lined with sfiaw or plastic material (polyethylene :0.l8mm thick, water permeability : insignificant, and oxygen peimeability : 68cc. / cm 2 /24 hours). A typical scheme of an experimental pil is reported infigurel. After a given storage period, two pits lined with straw and two otherswith plastic are opened and sampled at the 4 positions indicated in fig. I ; Thus,the numbers in table I for instance, are. averages of 16 values : 2 pits x 4positions x 2 replicates . At zero time, 15 determinations were made.

Moisture content

Moisture content was determined by oven drying according to method44-l5a of the American Association of Cereal Chemists (A.A.C.C. Methods,1984)

Water activity (AW)

The water activity was determined using a DT Kaynont hygroscope(Kaymont Instrument Huntington Station, NY) . The DT instrument was firstcalibrated at a temperature of 25 + 0.1o C by exposure to different saturated saltsolutions . After calibration, wheat samples were placed into the meæuringchamber of the instrument which was connected to a circulatins water bath withthe temperature set at 25 + 0.1o C . The Aw of sample*was read whenequilibrium was reached, as noted by no change in the reading over a one hourperiod (Labuza et al., 1985).

Free fatty acids

The content of free fatty acids was determined using the A.A.C.C. method02-02A.

Mold count

The number of molds per gram of wheat are determined using the serialdilution method in 0.9Vo NaCl solution containing 0.01% Tween 80, and thecultivation was made on Potato Dexûose Agar at 25' C for 4 to 5 days. Thenumber of thalli were counted and reportéd on a one grain samplê basis(Mislivec & Bruce. 1977).

Mixograph test

The Swanson-Working Mixograph (30 g version, National Mfg-Co.,Lincoln, Nebraska, U.S.A.) was used . 30 grams of flour were used in every test.The test was conducted as described by Finney and Shogren (1972) .


The flour used for mixographic studies was obtained as follows : Wheatsamples were conditionned to 177o moisture content . Atier at least 24 hours ofrest, wheat was milled in a Brabender Experimental Mill (Quadrumat junior) .

Falling number test

This test evaluates amylasic activity by rapid gelatinisation of flour pafiiclessuspended in water. atd subsequeut measurement of degradation of the starcltpaste by alpha-amylase, under conditions similar to those encountered inpractice (Perten, 1964); the procedure used is the A.A.C.C. method : 56-8lB .

RESULTS AND DISCUSSIONS

Moisture content, water activity, and mold countAu irregular increase in moisture content and water activity occurred over

time of storage, in all pit positions. regardless of the type of lining material used(Table I) . Moisture content and water activity of the samples from straw-linedpits were higher than those recorded in wheat samples from plastic-lined pits(Fig. 2 & 3) . Liner type, storage duration, and sampling position affectedsignificantly moisture content and water activity values (Table II) . After 16.5morrths of storage in plastic-lined pits, moisture content was kept below I4Vo,While in pits lined with straw, moisture exceeded 16 Vo .

Overall moisture and water activity mean values of straw-and plastic-linedpits were significantly different (Table III) . This clearly shows that plastic linercan protect the grain from additional moisture uptake .

High moisture levels promote fungal growth (Shearer & Warwick, 1983 ;Sauer, 1988) . For straw-lined pits. the correlation between moisture content andfungal growth was highly signitïcant (r = 0.72, Table IV) . Such correlation wasnot recorded in pits lined with plastic where fungal growth stayed at a relativelylow level . This is probably because plastic-lining improved the hermeticity ofthe pit ard limited moisture movements in the system which disturbed somehowfungal growth (Fig. 2 & 4) .

Variations of mold count in both types of pits were not similar . They couldhave resulted, because of mirtight conditions, from the fact that oxygen supplywas rlot low enough to help reduce the mold count, especially in sfaw-lined pitswhere a steady increase in the number of mold colonies was noted (Fig. 4) . Thismay be due to recorded high moisture levels, since moisture content and moldcount were significantly correlated in these pits .

Free fatty aci"dsAfler three months of storage, the content of free fatty acids increased

considerably (Table I, Fig. 5) . Fat acidiiy level (76 mg. KOH / 100 g solids) inpits liued with straw was about double of that recorded in plastic-lined pits(43 mg. KOH/100 g solids) . This could be due to the increase in mold countwhich was multiplied by about 400 in the case of strawlined pits, and by almost20 in the case of pits lined with plastic (Table V) .

l 0 AL AWAMIA - N'83 - Décembre 1993

Fig. I : Schema of a typical underground pit with 1,2, 3,and 4 indicating sampling positions.

II

,2ô qt I

l e 0 C n

X x x X x X

/ r r l î J . r r r r \X x r P l r l x x ,

X r X r x x r x r x x+ + + + ++ + + + ++ + + * * \\ + + + + +

Ë ï\ + +

+ + + + ++ + + + +

+ + + + +

l l AL AWAMIA - N' 83 - Décembre 1993

E

. : > \

; >

9 Ox ËÉ >

E }

. Y g

é =È 9 o 'd ^ ^ . := /<=# x :j : ^ o! ! : ? O Ë" * - . != + & -: - -^ ;E 4 } / . 6o Y .- t tE

- F , = ' n9 : > . 1

> a ' 6 : l

G È - d >Q - . e €

Ê . 1 , : *

a

È

C

O . { \ O â \ r Ô \ O O r O lo- --qqv] d1 æ.clr.fli \ o h \ o \ o \ o È < l \ c T

o n n n6 \ o \ o ï$ n \ o t

clæ

Ô eroô lh\o- æ.æ.æ.æ,

dæ æ r . l r C \ O \ O n ôr-r-æ-r- r- æ.F:æ.F:

O Ê æ N O \ Oæ- æ-\æ"\ æ,

r r r o @æh\OO\ l-. E::: : ËgËg

B

q

Uà

3

a r 6 r - , * -o- cr".ic:--i -

d a l Ê c l c l

r , - , T T T O O O h NÊ-O,o:O. o. O,.)æ.æ. --lN a l È a l d c l - d Ê N

o n n o noÈo\ r o .o r ï o o

e q r : : 9 È q h 9 9 9 o o r N r o c - . r c

: x x À À À À À À â o O ô O c ) c ) < ) c ) O O O

rf,5 \ O æ Oc { c t N o cl

sss: Ë HsFe

èo

E . 9C û

( n À

o o oè0 oo è6

1 - n r . ç E - c r r , * f r - e r m ' t E - c t o çi > td € e

È

( r E r :

o o \ o Ô

c)

,

û

u)

a

q)

qt

9 É+ o

: a> r È

.? co

H -o.

d =L ;;i

>1 q). : E

E Eô :: Y O9 r -

e Êô o

= Eo r d

E a. 2 æc a

F . Eê d

;

3

t2 AL AWAMIA - N" 83 - Décembre 1993

E =- a EE r -

Ê FY IË 1o l

o =F 6

5 o1 r =

s !( t Âà l

? l30 1

1 3 AL AWAMIA - N" 83 - Décembre 1993

3 I€ | 5E l -g 6

- = lE 1o l

o =F 6

= o. l t =

s - Eo o -S

o l- aU ' I

t4 AL AWAMIA - N" 83 - Décembre 1993

0 ^'â è\F a

P E =F o,>. !Jy , 9 :3: \ C i Y

} H E. . t ( )3 Eèa. . 9 e . "

E, .!E€ ; È Ë-v 6l l trc 3 > d Â( ) o o x

> . X â

Ë E s PU E"UËE 9 Ë =' .= o.. , Èbo : - * 9 ,

. = * E - y ,

: r - i =: N E ;F q . 9 ( ,

^ . - v . = =

àFE âE. ÊO a ^ c !

; E L à ËÈ t s t s ç 1' : = ' 9 a ^3 : R . = 5A F Y ' L r Ê

; Ë c ? ". F b - ( ) 1.Ê rbèa b F9 i l n 6 :; " ô E v )o 7 Ê d V )Ë T " l H -7 ô'rn a;. . - Z = au q ; : sl lË E eo=

E=PEï= ? ( , > , ' .: ! - - a av ' j - E > =

E ? = E 6 È' - ^ :

. 2 r y ? H ' ; YQ f : = > a -- t * o r J ^ d *I u ' â s n X

r , = i . " " ; = s

x â30Ë Ë

*.

J

tÉ

J

J

q

t Y

J

Èa

,9)r r l

Èa

O

-I r l

èa

;i

.s)

so

t i l

ÈAÊ\

ijFr r l

a, !.)

I r l

s oC ) i

, ( ) . vF

r r 1

l l

v) v) v) v) u) v) u) (hz z z z z z z z

t v a u ) ( h ( h ( h ( â u )i t r Z Z Z Z Z Z Z

côco

æv t r t l

J

I r n c â u ) ( â t h ( h ( âi h z z z z z z zô t ç { ô l a - F - Ê Oq \ o . \ \ $ " - 1 , \O \ O \ . ô Ê - ô . l C -

a.l ôi a.l

t ( * * * * * l ÉJ Ê * . t É * * * 9 É* * * * * * Y J i +t4 tâ q) v) th th z at)

(\ .f, .a9 q ' - : o .a ô Ê ô l o

*I " ( h a r / ) ( h x q )ô c ' Z v ) Z Z . h Z

\ o 0 0 ô l < - o \ o o ' . 1s. o. 9. .? \o. c'l \o. f:c a 0 o r ô ô 1 æ \ O \ OÉ d t t ) C Ô r a ) É t

* * J ç * l É , Gt ç r É * * * * * ** * * J ( * * * *.â v) u) râ a/) (t) (â v)

ô \ . A F * O t O Oq!? rC, cl cq \C. v, ,

\C.C.l C.l T v) oO cO ra)( r r c ô * ô . I Ê $

J É r É * * + . . , ( J Êt É t É * * r É J ( *t É * t É * r È l ê = t êt h a v ) ( h u ) ( h z - ( h

a

!a 3 à î , g H É e g

f()

b çË..Ë> . Ê

Ë p

Ë i :C . !

= 9

. u c Ec ) o9 ô- =oo.=. = :â Ëô Ê9 ' ;Ê q )

Ë r :> Êe r Go ;û =' 4 . =>..:? r

> r T

? -o.

* Ê,, tàÆT0)

F

r5 AL AWAMIA - N' 83 - Décernbre 1993

Tablc III : Mean values comparison using the Fisher's least significantdifference (LSD) method .

Var ianccl'actor

Variables

Storage

duratiorr

Position

Lining

11 ,02D l 0 ,60D l

13,48 D4 0,73 D3

13,51 D3 0,75 D2

l'1.25 D2 0,75 D4

16.09 D5 0,76 D5

16 Dl 3.8 Dl 2,8D2

32 D3 5,9 D2 3,0 D3

60 D2 6.? D3 3,1 Dl

98 Ds 8.2 D4 3,2D4

r09 D4 9,8 D5 3,9 D5

2,0 D4 452D5 2,97 Dl

2,1 D5 576 D3 3.36 D3

2,3D2 628D2 3,75D4

2,4D3 663 Dl 4,33 D2

2;7 D\ 6'74D4 4,59 D5

1-1,31 P1 0,70 P2

13.34P2 0,71P4

t3.63P4 0.72Pr

14,41 P3 0,73 P3

( l ) 6,3 P1

6,3 P2

7,0 P4

7 { p ' l

519 P3

599 P4

643 lr2

687 Pl

12,26 Ll 0,6't Lr 44 Ll

15,05 L2 0.76L2 81 L2

'1.9L1 3,0L2 2.0L2 - (2) 2,61Lr

8,6 L2 3,3 L1 2,6L1 - 4,98 L2


è o 9

è0

- (.)o t ^)è, =c ) ' -

J4 S( t r è O^ o ' ô

x t r

L > l

: >> O

9 -

. 2 =^ =. x :

ôl

O\ f-

*l r ) æ O \-q 1n

rô r.) ôl ôlO c a * a ô

tç .tç

O r a ) O O < dv? o" -f" 1.?

JÉ .tÉ *

n c i o ' F - o \ c -q t / . / | r ) ô l - v 1- i - i -J -J -J,{- 9 9 9 9 V

,ç Jç 'Él( J( ,É

C . t C * Q \ O $ r r ) Éo o - 1 c ? \ n 1 o o -

rntar

r n s- i A

r n È -ô 1 a î O

** * . , ÉÉ ô] tr- .a" 1 Q r l V ' )

ç ** * . * * .* - ô l N f too rl 09 v) dlê i o o o o

*? n e + s Eô d d o d o

t r l

* J É l ç * * I* * * J É * ^

O S O \ O t . - c . l Y ;\ \ o . \ o . c . l 9 \ x

^ â ^ v

q

&H

e t E É Ê r i l E É Ê -

Ël ËËsâer€â tl Ëâ,sr.r€a3I eË;EËËËË ËI eË;EFËeË

.âo

k

AIk

Èa

æ.q

AIh

èarô

O

()a).âP

,4.

(t)

**

*

êo

q)

0q)

(Da

q)

a

F .(t) i \

e l l

q ) v9 c

a Ê

F ë-O

FDq :

e =

E.=E çF i =^ a

?C)

t-

I 7 AL AWAMIA - N" 83 - Décembre 1993

2 ,- . UÉ L

e 6Ev lC 1o l

o =F t l ,

a ( Jï t =- oË ( 'o Ào l

- Iq t l

zc!oJ

l ' . ( O t o r f ( r r c \ a O

t 8 AL AWAMIA - No 83 - Décembre 1993

E ta - t t tE

' L

g 6- = lc 1o l

o =F €

= ( ,1 r =

oa g! | Àbo t

- l

o l

t9 AL AWAMIA - N" 83 -Décembre 1993

Fat acidity has attained extremely high levels in straw-lined pits after 16.5months of storage . Such high values (about 160 mg KOH / 1009 solids) havebeen reported in the literature (Girish et a1.. 1972). Sampling position does notaffect significantly fat acidity values (Table II) . The concomitant change of fatacidity and mold count was also reported by Daftary & Pomeranz (1965), andwas explained by the fact that lipid hydrolysis is mainly catalyzed by microbiallipases . Moisture content variation in straw-lined pits is also closely relatedto fat acidity fluctrrations(r= 0.64). Evidently, plastic liner protected the grainfrom being seriously deteriorated by limiting significantly fat hydrolysis . Manyreports have indicated that the content of fat acidity increases with increasingstorage time (Daftary et al., 1970 a; Girish etal.,1972; Fellers &Bean,1977:Warwick etal.,1979: Galliand, 1983 ; Leelavathi et a]. , 1984) . For both typesof pits, tat acidity values reached already over 20 mg KOH after three months ofstorage . The level 20 was considered by some authors to be the maximum valuefound in sound wheat (Fellers & Bean, 1977) .In Moroccan context, we thinkthat this level is quite low.

Mixograph parameters

Mixograph results (Table V) showed that the peah height did not changesignificantly for up to 9 months of storage regardless of the liner type . From 9 to16.5 months, it increased by about 20 to 407o . This quality parameter expressesthe consistency of dough and its resistance to extension, and has been shown tobe sensitive to storage time and pit liner type (Table II) .

These results agree, in essence, with the data reported by Leelavathi et al.(1984) .

Mixing time has increased slightly in both types of pits (Table V, Fig. 6) .Wheat from pits lined with straw gave flour doughs of high development times.The increase in mixing time, over time of storage, has been reported by severalauthors (Daftary et al.. 1970b ; Pomeranz et al.. 1968) . Mixing time varied withstorage duration, type of liner, and sampling position. As for all the parameterspreviously discussed, storage time is the factor that explained a high percentageof mixing time variations (Table II) .

'Wealiening angle values were significantly affected by storage tme and the

type of lining material . These two factors as well as their interaction explainmost of weakening angle variations (Table II) . Wealiening angle of flourdoughs decreased with storage duration for both types of storage conditions. Thedecrease is more rapid for wheat stored in pits lined with straw than inplastic-lined pits. After 16.5 months of storage, the weakening angle instraw-lined pits reached half the value obtained in pits lined with plastic.

Significant correlations were found between moisture content (or wateractivity) and dough mixing time in both types of pits (Table IV) . Signifiantcomelations were also found between peak height and moisture content but onlyfor pits lined with plastic. Other significant correlations were found between fatacidity and mixing time (r = 0.81 for pits lined with straw, and r = 0.50 forplastic-lined pits), and between fat acidity and wealiening angle (r = -0.82 forsraw-lined pits and r = -0.48 for plastic-lined pits) .

20 AL AWAMIA - N" 83 - Décembre 1993

q)

èo

t r i l

q É

^ -èo.=, E C: 9

c g o

= q l' : t

à gc ) q )

t qa q

ç s P

9. I= v! -

a z

9 E9 c !

o

q

z

t l

' . . . >Z e .tr. ë

d ^. o

ti -,:

* a i

i g

t-- A r* O\ o\O \ \ O V ) e { r ô r )ôl t cô ôl cô c.r

O \ r ô a - ô lÊ c a O a . l- i i - i - ;

O \ * c A O \ôt ra) ç o\rô rô \o rô

c{ \o- c.} oo"ôr c.t ôl ôl

cl. F: O. oo-ô l N c a ô l

oo ra) t oot r n l r ) $

ôl

ta)t

rnc.l

(ri

ca æ o c a r nO i ô . 1 ô .\O tr* \O \O

\ v ? q . qN e i È ô l

c.l ca ôt cô

o . . ? - i v ?|r) lat r.i \t

r/)

rôôl

ô]

Uf

F-

a?)

oo.crl lr)

Èû

È

q

z

J

. -z ?tr- ë

{a-È -

+ E* i ,

i e

t - - $ < - \ o \ o v ) o o < f , F - . o Nq q , Q q - ' i - i - i \ n " \ v lC.l v) .t $ vi r) rô vr rô V') V)

cô r r ô l \ O Næ o 0 0 Êl r ) \ o V ) \ o

q æ. v? oo.ô t * c ' l Ê

0,o- s. 00- qôl c\ ôl (..l

o - q . q s .\o \o t- \c

r- C'f \t t'-- larô.1 oo <- ra)C - t r - @ \ O

c'L ,.i .ù ôlC.l ôt ôl C.r

o - 1 \ qco cô c.l cn

\ o . 1 q qt-- \O t-- |'-

ô.1

I'\

\c'l

cr)

ôt

cô\ôl

coca

|'r coF\

èo

t . Y= a

6 ô ,

Ê N c A . + - ô l ( 1 : 1

2

È ( € =o ! =

cl

èo.=. E eË.8

-q)

;


V16

E>. ( )L 9

. > EX ! ' l ot r v ( J' E ê a s. . , !Y ( ) q )

E P 3, i Ê nÊ É 3

ç c J^ >

- - @ c )È

( . ) ! !

! p d- È L

r ) > i i= . À a < )c J - t - =

Ë l v X t r

È Ê e : =- H t r

g . Ë ; ! Èe i * È 9 ^ ?

. 9 ç c â *F . é e é ;++< - a6 '-1

Ë ;E .F âp : E i . i =È d : o - c

. C ) - g r J

.= "ô .9 Ë . !

h É n 6 . = eù O X r * 5L d ^ r t *

n . Ë : Ï - { 'ë E : : E } 3S H F s E Ë '9 È H g ' . ? p t r3 n ' / )

? b E b € * ;E c E,r i 9 g .9H E H g Ë ; 5: h È ; > T E Eà : ËE Ê À; :. ; a ( ! F O : { - =q F b b ; E Y 2

1 4 ô È a r . i t r

= Ë Ë Ë È Ë rÊ Q t r . 9 q o . = h

- c - 0 ) F . = x xH Ë Ë Ë 8 Ê Et ! F . . =. . , . ^ 1 1 É

^ ^ J É

A L L > Z

O C l T O ' \ \ O $ t - - t r - \ O s -q q $ . v l v ? q q 1 c . l æ .ôl ô.1 N ôl c.l ôt * co ca c'l

O\ \O r.) \O(-r CO O\ O\t - - l r ) $ \ O

q l a qô.1 ô] ô]

v? -L c.l \t.c.r c.) c.) cÔ

q d " \ o " 1v, v) \o ra)

c!ôl

O N $ c -<- t-- \O Or/'/ co c.l \o

-t- a! æ- ,,?cô .ô ô] ô-l

s. .1 cl cit . 1 - $ s

O - q v i v l. d | < F \ o ' f ,

c.)

ô1 vs

saô

ca.i'

r/)ærar

v v 1 æ ! a c a o ' c ) r n < -|: vl cv) o o\ o c,] ca tr- a.)'û .if rô lfi S V, t-- \O \O \O

s 6 8 F eô I - - $ ! î r r

\ t f - F - v )(.l a- \O \Of* C- C.l

s - v l c l \o

\o. 09 v? o"ca cq cô ca

ooil.).i.

\o. o. 1 o"N Ô'I

r- c.l

O\ N I-- fr O\ct cô c'.1 ôi N

rr)c-)

q o - - a r ô \ o É v 1 v ) r ô0 O O \ $ O O c e , ç o OÊ *

Ê (.1 cô .t

C *

3 - c . r k o I

rn

AL AWAMIA - N" 83 - Décembre 1993

The negative correlations between the amount of free fatty acids andmixograph wealiening angle were unexpected since the deterioration of doughquality by fatty acids should normally enhance the weakening angle, since lipidhydrolysis would contribute in having doughs of poor rheological properties.Probably the extension of mixing times resulted in fairly flat curves whoseweakening angles were low. In fact a negative and highly significant correlationyas found between mixing time and weakening angle (r = -0.92) in straw-linedpits . The positive correlation between fat acidity and mixing time would meanthat probably lipid hydrolysis by itself and the presence of fatty acids in thesystem prevented dough from being optimally developped in reasonable times .Figures 7a, 7b, and 7c show an extreme situation where dough rheology hasbeen practically and totally impaired. The very sffong oscillations at thebeginning of the curve may indicate that proteins have been depolymerized assuggested by Hoseney et al. (1966). Isolation of gluten by hand-washing fromflours, obtained after milling highly damaged wheat has been very difÏicult,probably because proteius have lost their basic rheological properties . Glutenyield was low, and protein fractionation of the highly damaged flour showed thatwater soluble proteins increased considerably whereas acid soluble proteins

decreased to a low level (data not shown) These results agree with thosereported by Daftary et al. (1970b) . It is more likely that these rheologicalchanges resulted from extensive hydrolysis ofboth proteins and lipids .

Falling number

Falling number data were repofted in Table V . Variance analysis shows thatthis qualily parameter is not sensitive to the liner type but quite sensitive tosampling position, storage duration, and their interaction (Table II) . Despite thechanges recorded in amylase activity, all wheat samples stayed- hypodiastasicduring the first 9 months of storage . From 9 to 16.5 months, falling numberdecreàsed significantly, especially for wheat grain samples from the middle(sides) and the bottom of the pits (positions 3 and 4) . Variations in amylaseactivity were negatively and significantly correlated with moisture uptalie inboth types of pits (table IV) .

These results indicate that alpha-amylase activity stfl"ts to changesignificantly after about one year of storage . This period is much shorter thanthe one indicated by Pixton et al. (1975) .

GENERAL CONCLUSIONS

Significant quality changes have taken place in wheat grain stored inunderground pits lined with both plastic and straw . For sraw-lined pits, a oneyear siorage period appeared to be the limit not to be exceeded if serious qualityôhanges are tb be avotiited . However, for pits lined with plastic, the deteriorationhas been limiæd even after a one year storage period .

Plastic-lining was much better than straw-lining in terms of preserving muchof the initial prôperties of wheat . It requires a very low investment and allowsthe farmer to avoid important quality losses .

23 AL AWAMIA - No 83 - Décembre 1993

E '- | l 'C L

9 6c9 l

c +o l

o =t- .tt

t oT ' =

aË 1 9o o .o l6 l

32q)

èo

x

(u

q)

C)èo

q2

.o)

\oèo

Fj

( o t c \ t ( ) c o ( o ç C \ . oF F

,,À AL AWAMIA - N" 83 - Décembre 1993

a

o!

.xË , Â -Ë Ë.e5 t Èo É ( uq ) - , . =È . = Jà 2 ,l - - = L

9 È ;È .= .=E 2 Êi E E. E Ë E: ra rrrryo \t\i€ E F F <

ë Ë ëts .EEË Ë ë 5g Ë 6 - -Ë } E Ë

; iËËk cûÊ cJ

AL AWAMLA - No 83 - Décembre 1993

ACKNOWLEDGMENTS

Financial assistance from AID Washington (AID Science Advisor Grant,Underground Grain Storage Project, Grant N DPE 5542-G-SS-7030-00, ProjectNumber 7336) is gratefully acknowledged This study was part of amultidisciplimary investigations on undergrouud storage conducted at I.A.V. HII,Rabat, Morocco.

We thank Mr. Allal Hammouda and Ahmed Goumari (Department ofApplied Statistics, I.A.V. Hassan II) for their advices .

We also thank Dr. T.P. Labuza (University of Minnesota. St. Paul, MN.U.S.A.) for his helpful comments.

We also thank Dr. Abdelghafour Tantaoui-El Amki (MicrobiologyDepartment, I.A.V. Hassan ii) for providing us mold count values.

27 AL AWAMTA - N'83 - Décembre 1993

REFERENCES BIBLIOGRAPHIQUES

A.A.C.C. METHODS . 1984 .Eight Edition (Reprinted) ; Published by TheAmerican Association of Cereal Chemists, Inc. St. PaulMlnnesota' U.S'4.

BARTALI. H. and DEBBARH, A. 1990 . Evaluation et amélioration de latechnique traditionnelle de stockage au Maroc P. 387-406. SéminaireInternational sur les Structures de Stockage des Céréales, des Légumineuses etde leurs dérivés. Actes du séminaire, 28-30 novembre 1990, I.A.V. HII, Rabat,Maroc.

DAFTARY, R.D., and POMERANZ, Y .1965 . Changes in lipid composition inwheat during storage deterioration . J. Agric . Food chem. 13 :442-446

DAFTARY. R.D., POMERANZ, Y. . and SAUER, D'B. 1970a . Changes inwheat flour damaged by mold during storage . Effect on lipid' Lipoprotein, andprotein. J. Agric. Food Chem. l8 : 613-616 .

DAFTARY. R.D.. POMRANZ, Y.. HOSNEY, R.C.. SHOGREN' M.D., andFINNEY, K.F; 1970b. Changes in Wheat flour damaged by mold during storage.Effects in bread-maliing . J. Agric. Food Chem. l8 : 617-619 .

FELLERS, D.A. zurd BEAN, M.M. 1977 . Storage stability of wheat-basedfoods: A Review . J. Food Sci.42 : 1143-1147 .

FINNEY, K.F. and shogren. M.D. 1972 A Ten-gram mixograph fordetermining and predicting functional properties of wheat tlours

Bakers Digest. 46 (2) :32-35,3842,77

GALLIARD. T. 1983 . Enzymic degradation of cereal lipids. P I I l-148 . In P.J.Barnes (ed). Lipids in cereal technology. Academic Press, London.

GALLIARD, T. 1986 Hydrolytic and oxidative degradation of lipids duringstorage of wholemeal flour . Eft'ects of bran and germ components .

J. Cereal Sci.4 : 119-192 .

GIRISH. G.K.. GOYAL. R.K., TOMER, R.P.S., SRIVASTAVA, P.K., ANdKRISHNAMURTHY, K. 1912. Studies on preservation of food grains in ruralstorage structures . Bull. Grain Technol. 10(l) : I l-21 .

HOSENEY, R.C., FINNEY, K.F., and POMERANZ, Y. 1966 " Changes inurea-dispersibility of proteins during wheat maturation .J. Sci. Food Agric. 17 :273-216.

HYDE. M.8., and BURREL , N.J. 1982 . Controlled atmosphere storage :443-478. Clyde Christensen (ed) . Storage of cereal grains and theirproducts.3 rd ed., A.A.C.C. Inc., St. Paul, Minnesota U.S.A.

LABIJZA, T.P., KAANANE, A., and CHEN, J.Y. 1985 . Effect of temperature

AL AWAMLA - N' 83 - Décembre 1993

on the Tglstu-re^ sorption isotherms and water activity shift of two dehydratedfoods . J . Food Sc i .50 :385-391 .

TIFELAVATHI, K., RAO, P.H., and INDRANI, D. 1984 . physicochemicalchanges in whole wheat flour (atta and resultant atta during storage).

J . Food Sci. Technol .21 : 68-7 | .

MISLIVEC. P.B. and BRUCE, v.R. 1977 . Direct plating versus dilution platingln grylilat1ve]y determining the mold flora of driedbeans and soybeans .J. A.O.A.C. 60 :741-743 .

PERTEN, H. 1964 . Application of the falling number method for evaluatingalpha-amylase activity. Cereal Chem.4l : 127-140

PIXTON. S.W.. WARBURTON. S.. and HILL, S.T. 1975 . Lons-rerm sroraseof wheat . III . some change in the qgality of wheat observed duriTrg l6 years ôfstorage. J . Stored Prod. Res. ll : 177-185.

POMERANZ, Y. 1982 . Biochemical. functional, and nutririve chanses durinsstorage . p:: 145-217 . Çly_de christensen (ed). storage of cereal graini and theiiproducts. 3rd. ed., A.A.C.C.,Inc., St. Paul, Minnesota, U.S.A.

POMERANZ. Y. , HALTON, P., and PEERS, F.G. 1956. The effects on flourdough and bread quality of molds grown in wheat and those added to flour inthe form of specific cultures . Cereal Chem. 33 : 157-169 .

POMERANZ, Y., DAFTARY, R.D., SHOGREN, M.D., HOSENEY, R.C., ANdFINNEY, K.F. 1968 . Changes in biochemical and breadmaking properties ofstorage-damaged flour . J. Agric. Food Chem. 16:92-96

SAUER, D.B; 1988 . Mold invasion in relation to grain damage . Cereal FoodsWorld. 33 :489-490

SHEARER. G., and WARV/ICK, M.J., 1983 . The Effect of storage on lipidsand bread-making properties of wheat flour. P.253-268 . In p.J. Bames (èd).Lipids in cereal technology . Academic Press, London .

WARWICK. M.J.. FARRINGTON, W.H.H., and SHEARER. c. 1979. Chansesin total fatty acids and individual lipid classes on prolonged storage of whéatf lour . J . Sc . Food Agr ic .30 : 1131-1138.

effect of underground storage on some chemical, and

Documents