Food Structure

Volume 2 Number 1 Article 2

1983

Ultrastructure Studies of Pasta. A Review.

P. Resmini

M.A. Pagani

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Recommended Citation Resmini, P. and Pagani, M.A. (1983) "Ultrastructure Studies of Pasta. A Review.," Food Structure: Vol. 2 : No. 1 , Article 2. Available at: https://digitalcommons.usu.edu/foodmicrostructure/vol2/iss1/2

This Article is brought to you for free and open access by the Western Dairy Center at DigitalCommons@USU. It has been accepted for inclusion in Food Structure by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. FOOD \I ICROSTR UCTURE , Vol. 2 ( 1983), pp. 1-12, 98 0730-5·119/ 83$ I . 00+ . OS SHI l n..: ., AMF O' l l ar~.! (Chicago}.IL 60666 U.S.A.

ULTRASTRUCTURE STUDIES OF PASTA. A REVIEW .

P. Resmini an d M.A. Pagani

ISTITUTO DI INDUSTRIE AGRAR I E. UNIVERSITA' DEGLI STUD! Via Ccloria 2 20 133 Milt~n o, Italy

Abst ract Introduction

Free7c-fracturing ca n be used effective ly to stud y pasta micro­ The world-wide popularity o f pasta and its increasing con­ structure bo th in the dry and cooked state. After a wa ler­ sumption are stimulating t he develo pment o f technologies to glyc(• ro l soaki ng. conventio nal raw wheat pasta shows an obtain new products which so metimes show su rprising cooking uncoagulatcd protein matrix in which the starch granules are qualit ies. considering t he charach:ri stics of the raw materials. uniformly dispersed. St arch granules appear unswo\lcn with a Indeed, phenomena in volved in the processing and cooking of spherulitic structure. Extensive protein denaturation and starch this food are not compl etely understood and . since o ur country swelling may occur during processing when a temperature is an important producer of pasta-m aking equipment. we felt greata than 60° C is attained in dry ing. Extensive structural the need of st udying them. T he objective of o ur investigations transformations t;tk e place in cooking. A fibrillar protein net­ w:1s to try and further understand these phenomena in order to work which envelops gelatinized starch is the typica l structure o ptimize pasta production equipmen t and drying cycles. observed in cooked durum wheat spilghetti. Wh ereas. in soft Basic research on pasta, as we ll foods, requires consideration of the product's water more diffuse starch p<~rticles. distribution, changes in the internal fin e structure of starch Pasta cooking qualit y is determined by a physical competition gr:u1Ul es and interactions in the pro tein matrix. All o f these between protei n coagulatio n into J continuous netwo rk (I) and factors may be studied with high resolut ion electro n microscopy starch swell ing with spherulit e scattering (II) during cooking. (EM) techniques. In 1975 ( 691, we started to usc the systematic If the former (I) prevalls, starch particles are trapped in the contro l of the ultrastruct ure by freeze-frac turing (FF) technique network alveol i promo ting firmness in cooked pasta : Whereas. in the pasta resea rch. T his has been recently recogn ized as a if the latter ( II) prevails, the protein coagulates in discrete pro mising method to st ud y cereal product st ructures [ 341. A masses J.1cking a continuous framework and pasta will show high water content (e.g. cooked pasta, 50-7 0%) m:1y have softness and usually stickiness. High temperature-low mo isture disrupti ve effects in the prepa rat ion of sam ples 1141, an EI\.I (HT-U.·t) drying p:1rtially overcomes this competit ion by technique inducing m inimum damage is requ ired, so we seldom producing a coagulated protein framework in dry pasta without use the better known freeze-etching (FE) technique [ 14. 16, starch swelling. 43). We feel that etching might p romote segregat ion phe· I-IT-LM treatment induces protein-starch interactions and nomena insid e the fine structures of highly hydr:1ted com­ conformational changes in the starch granule fine structure ponents [4 1. during cooking. Li near and branched chain-like fibrils appear In this revi ew, our observations o f the ultrastructure o f pasta in the core of the granules and particle groupings in the outer made with different commercial raw materials (i .e. durum whea t area. The better und erstanding of the role of controlled starch semo lina , soft wheat flour. ric e starch and ri ce nour) are com­ modifica t io n which optimizes pasta processing permits bt::tter pared with published data. emphasizin g implications of the usc of non-conventional raw materials in pasta prepamtion. results to consumer acceptability of the products (l!.g. cooked pasta firmness and stickiness) as we ll as the develo pment of new ingredient and processing technologies. All the raw samples were soaked in a water-giyccrol so lut ion prior to FF. This step yields a detailed view (cross-fracture) o f Initial paper received January 13. 1983. component fea tures otherwise impossible to see in these limited Final ma nuscript received f~ay 13, 1983. moisture systems ( < IS% water). Moreover. for d ry pasta Direct inqu iries toP. Resmin i. soak ing in water-glycerol is necessary in order to produce a Telephone numbe r: 039 2 2365426 . cross rather than a surface-fracture, and not to break the knife. Cooked sa mples are usually not soaked with a cryoprotectant (sec Appendix). To better understand pasta ultrastructure as Key Words: Wh eat Oour. rice Oour, heat starch modifica tio n. shown by FF, it is necessary to consider the ultrastructure o f protein coagulation, pasta, cereal foods, drying conditions, the isolated starch and gluten, before and after heat trea tment. freeze-fract uring, cooking pasta quality. P. Ri.!Sinini and ivi. A. Pagani

Starch

Wa shed stan.: h e~trad ed from cornmcn:ial whea t fl oor :u.:­ cording to B :mk~ :mel Greenwood 161 :md freeze-fractu red reve:ds a compac t sphcrulitic texture in the ~:~ r anules (fig. Ia) 169. 71\ in agreement wi th what Fretzdorffet a\. report by FF 134] ;me\ many ::~ uthor s observed by FE I L 8, \3, 16. 41. 43. 50. 63]. T hi.! Sflours (i.e .. without con­ sideri ng th e hard wheat varieties) compared to dunnn wheat ~e m o lina. as recentl y confirmed by Scanning Electron Micro­ scopy (S EM) !60\. Assuming that granule size influences its gd:llinization temperature [7. 20. 37]. a statistical evaluat ion of tll c~c differenct·s may be useful for pasta studie<:. bearing in mind that cooking qualiti es are usuall y bcltt.!r in durum wheat than in soft whea t pasta. The granule spherulitt'S arc 5·20 nm in diameter. Mi.ihll!lhaler 163] hypothesized that the range in si7t'S could be due to a specific arrangement of amylose and ;1m ylo· pectin molecules in the spherulites. Several strw;tural changes may take place when starch granules are heated under different time-tt.!lllpcm turc-moisture conditions: 1) progressiw swellin g of granules w hich promote~ a size in crt:a se of the spherulites: 1) shape ch:mgcs: 3) loss of ordered structure [gt:latinization, 21, 37 1: 4) co ll ap~e and 5) solubilization and reorientation of ~ \_,' po l yme r ~ 17. 47] . ~ - F F i~ a suit able method to follow these hydr:llion :md transition st :lles in the granuks. Wh en examint.!d :tftcr frt.!CZe­ tl\ ~ ~ . fra cture. lwat modified rice starch granules :tppear swo ll en with "' -- 1 ~1-m :thigh deg.rct' o f dispersion of the native spht:rulite:- still showing ev id ence o f thei r polygonal t ype shap!.! (F ig. 2a ). Under mo re F ig. 1. Starch granules (s) surrounded b y water (w). a) wheat int cn::.l' h t.!:lling, wheat starch granules absorb more w:ttcr, o;;t;1rch. b) rice starch showing the characteri stic po lygo nal shape oft he granules . gel:it ini7c and lo ~e the distinctive struct ure of the granuh:~ (Fig. 2b ). In high temperature-low moisture treat ed wiH::tt G luten pa ::. ta. the granules may exhibit. a ft er cookhll;\ . linear :mel bra ndll'd ch:lins in the core and subunit grouping.., in outer Glute n extracted from commercial d urum wheat semo lina , a re:t (Fig. 2c). A to t;1l dispersion of the spherulit es b ob::.c rvcd according to La sztit y (48, 491 . ex hibits a loose protein fr amt.!­ in ~olub ili zed rke stan:h ( F ig. 2d). A chain-liJ.. e fib ril pattern b work a ft er FF (Fig. 3a). A ftcr cooking in boilin g tap water. the ::.ecn in re trograbread gluten modifications promoted by hea ting arc a lso found in c nnnb 134] and ~ larch swelling was t•xamined by FE du ring tht• protein matrix of cooked pa,.ta. They play an import ant cake-batte r heat ing 116. 12. 43\. llt'atccl tapioca starch wa~ role in determining the ultrastnJ Cturc :md the cooking qualit ies n .: ported to show a honeycomb-like network by FE 12 1. but we o f pasta. were not able to find si milar structures in whea t o r rice starch. The thinnest fibril s o f gluten (ch :1 ins of :1 ligncd prote in sub­ Since a p:tttcrn of regular hexagonal arr;~ngem t.! nt s ca n be ob­ unit s) have a thickn ess of 10 nm. This figure was:tlso reported tained by FE of a d ilut e (5%) glycerol so lution [4] , one might by Bernardin and Ka sarda !10] for shadow-casted protein :tssume that some scg r eg::~ tion pheno me na are involved. strands in wheat e ndospe rm. Raw gluten ex hibits a fibrillar With SEM. the progressive structural changes in hea ted st:m.: h shape when observed by thin-sect ioning and SEM !1 8 \ . Cum· granules arc easil y obscrwd [II , 15. 36. 39. 401. SEM studies ming and Tung \19\ . u ~ in g SEM , report :1 fibrill~tr protein o f sta rch ultrastructure deal mainly with dwngcs in the su rface ne twork in commercial glute n only whe n it is kneaded with morpho logy of the granules. Miller c t al. 161] pointed out a water and stre tched. ll owcver these patterns probably present fibrillar structure in a gelatiniz.ed starc h exudate. probably some preparational art ifac ts as repo rt ed by Dronzck et aL [32]. fo rm ed by amylose chai ns 142 ] 1-i owevt•r FF is more feusiblc Dronzck c t al. [31 \ reported that durum wheat gluten shows than SEM to ~ tud y modifica tions in starch fin e struct ure due t hicker fibrils than hard red spring whea t gluten. to it s higher resolving power and lower risk of produc ing a rtifacts during sample preparation 114. 2 11 . Nevertheless. Wheat fl our because of the lack of a three-dimensional image and the limit ed field of view in FF micrographs. we think that a Freeze-fractured unsoaked se molina (Fig. 4a) docs not show comparison wit h SEM pictures may help to avoid misi nter­ details of the compone nts. whereas same soaked. but surface­ pre tation in cornplt'x struct ural systems stu.:h as pa ~ ta . fra ctured, sample (F ig. 4b) does no t exhibit the interior struc­ ture o f the starch granules as in soaked cross-fra ctured semolina Pasta Ultrastructure

Fig. 2. Heat-treated starch. a) dough of ri ce starch and water (4:1) heated at 90° C for 15 min , ex truded and then dried at low temperature: ro ugh po lygo nal o utline of the granules is still visible. b) wheat starch cooked in boiling tap wa ter fo r I 5 min . c) whea t starch granules in cooked HT-LM spaghetti (sec the tex t) with fibrils (sf) in the central area and particle agg re­ ga tes (a rrows) in the o ut er part . d ) rice starch overcooked in bo iling tap water. c) retrograded starch in cooked rice pas ta.

Fig. 3. Durum wheat gluten. a) uncooked: b) cooked. Lipid inclusions (1), water (w) , pro tein fibrils (p) and gelatini zed starch material (sm) arc shown. Note that the free pro tein pa rticles (a rrows) in a) are not visible aft er cooking. P. Resmini and M.A. Pagan i

Fig. 4. Durum wheat semolina cross-fractured without soaking Fig. 5. Uncooked spaghetti o f durum wheat (a.b) and soft (a) and, after soaking, surface-fractured (b) or cross-fra ct ured wheat (c). Starch granules (s). protein matrix ( p) with protein (c). Starch granules (s). protein matrix (p). lipid inclusions (1). strands (f). Water coats (arrows) are clearly seen when the membrane residues (m) and water coat (arrows) around the protein material is very close to the gra nules. starch granule. high temperature-low moisture conditio ns. (Fig. 4c). The statement of Chabot [ 141 concerning the ad­ Taking into account the hyd ratio n c ff~c t on the pro tein vantage, in limit ed water sy stems. of a preli minary wa ter matrix and that the water coat could no t be seen by SEM. the ex posure for producing high resolu tio n microg raphs is quite ultrastructure o f freeze-frac tured semo lin a is in agreement with pertinent here. The starch granules . d ue to a surro und ing wa ter the SEM o bservatio ns which showed the starch granules to be coat at least 30 nm wid e, do not adhere to the pro tein mat rix encased in an amorphous protein matri x [ 26. 28. 59] whi ch, due to partial hydratio ns. begi ns to coat over the gnmulcs 145 ]. whi ch looks unifo rml y dispersed in the so aking system. We Pro tein fin e structure does not diffe r systematicall y in semolina can no t state if this wat er layer is due to starch shrinkage 173 1, and soft wheat nour as o bserved by FF, even though character­ pro tein shrinkage 174, 75\ , hydration o f solu ble protein s 18] isti c and different features are noticed by SEM fo r these two o r an osmophilic a n~a. However, we always fi nd it in nour, raw materials (28. 601. ~.. J oreover, SEM micrographs o f Moss do ugh and dry pa sta soak ed in water-gl ycerol as we ll as in cooked et al. [62 ] performed on the soft wheat endosperm show that pa stil witho ut preliminary soaking. Extensive starch·protei n the continuity o f the protein matrix ma y be related to the intera ctio ns <~pp C< lr only in cooked pasta manufactured under grain hardness. Pasta Ultrastructure

Wheat spaghetti dried under co nventional co nditions Fig. 6. Cooked spaghelti of durum wheat (a .b) and soft wheat (c,d ). b) is an SEM mi crogra ph of cookeddurum wheat spaghetti Conven tional p;lsta processing involves the mixing o f sem­ freeze-dried and cross-fra ctured , reported by Angold (3). ol in a o r nour with wa ter ("'30%), kneading, extrusion at 80-90 Starch material {sm) with chain·like fibrils {c ), protein fibrils (p) bar and drying cycle usually below 55°C for at least 20 h. Ruw and protein aggregates (pa). Arrows indicate thinner protein commerciul durum wheat spaghetti shows (after FF) a st ructu re fibrils. similar to a semolina (Fig. Sa). There arc more ex tensive inter­ conventio nal raw pasta ultrastructure. The same conclusions actions inside the protein matrix {protein-protein irHeractions). were reached by opti ca l microscopy !54, 55!. lacking, however a tcx turation in a compact and continuous When viewed with SEM. raw spaghetti exhibit s a d1fierent framework (Fig. Sb). T he relatively low moisture conten t o f feature between the inner and the outer part. The latter presents pasta dough and the insufficient mixing during extrusion do not a smooth continuous enveloping protein film, the rol e of which allow the complete development of a gluten network as takes in detennining cook ing pasta quality is not clear 126. 28]. In place in bread dough [3, 28, 59 ] Furthermore. the relatively the inner part , an amorpho us protein matrix coats the sta rch mild drying conditions (time, temperature. spaghetti moistu re) granules ! 26, 59]. Dunm1 and soft wheat spaghetti ex hibit avoid ex tensive protein coagulation [25, 691 and visible starch similar st n1 cll1res ! 60] granule modifications 117, 23 ] , even though Li ntas and Cooked cormnerci:1l durum wheat spaghetti shows a compact D'Appolonia [51! measured changes in the carbo hydrates fibri ll ar ne twork of coagulated pro teins that envelops the during conventional processing o f spaghetti. No starch-protein gelatinized starch gra nules (Fig. 6a). There ure no significant associations are o bserved. cont rary to what is found in bread differences between the inner and the ou ter part of pasta dough [33. 34 ] where the interactio ns are reportedly intensified cross-sect ion provided that the spaghetti is completely cooked. by yeast ac tion during fermentation. In the FF micrographs o f cooked spaghetti the protein is easily Contrary to what we observed in conventio nally dried pasta. recognized because o f fin er granular structure and lipid inclu­ Banasik ct al. !51 not iced that the ex trusio n processing step sions. We can compare the pattern of Figu re 6a wi th the SEM promotes :1 partial loss of starch granule structure. Their results structure reported by Angold [31 in cross-sectioned cooked arc probably related to d ifferent ex trusion tem peratures. High durum whea t spaghetti (Fig. 6b). keeping in mind the possible tempera tures may easily lead to starch and protein modificatiOns artifacts introduced by both prepa rati on methods. In these two 154 ] . considering the high pressu re and relati vely high moisture micrographs, it is cl ea r that the starch particles are enm eshed of pasta (30%) in ex trusion processing. in the protein network and consequently inside the spaghetti. Even if the ex tent o f the interactions inside t he protei n In soft wheat spaghetti protein usuall y tends to coagulate into matrix of dry pasta is re lated to the quality and quantity of discret e masses (Figs. 6c. 6d). The sta rch spherulite distribution. gluten 15 . 35], common soft wheat and d urum wheat spaghetti due to t he discontinuity of the protein matrix, is more di ffuse show a similar pattern by FF (Fig. 5c). Therefore. it is usually and therefo re. the granules arc easily removed from the network impossible to predict the cooking quality o n the basis of the ( 69, 7 1, 72]. Many autho rs {5 , 26, 35, 541 correlate the qua li ty P. R ~"mini and ~I.A. Pagani

a - .i_OW TfMPfiiATURE TfMPfRATUQf - HIGH MOISTUkt , ~- b (HT l-IM)

", ;;AI\ 90 i I\ 90 70 5 ]~ ----" _""" ___ ------_!>!- 70 5 t.l'------_- -_-_:_:0,-~-~-"'-::-_ =_ :------_-_--_-_-_-_-_-_-_-_-_"-Y: 8' ----- __ 503 --- 50 3

30 1 L__ 301

~~·-- -~~~-----'---- 12 ct. y~tim el'v:t 3 6 9 12 dryioJ:,imLOO

d .J:i!Q I-I TfMPfRATU~t ~ f Q!._UM MOISTIJ.!t._ jjl_G!;! TfMPfUJUR.f..=....l_~ MOJ_lllli I , (I·H - MM) P·H t MJ I ""'"'"'

90 90

70 5 ' 70 5 L _ __ _ 0_]

-- 50 3 __' so 3

30 1 30 1

12 drying limt.__bu 12 dr:ying_time_bn

<.~nd quantity of this network to the p h ysic;tl prnpc n ie~ of the Fig. 7. Dr ying cycles performed during the processing of cooked pasta. These properties may al so he affected by th e ex perimental spaghelli. a) conventional conditio ns: b). c). d). slaH:h-protcin ratio at the surf:H:e of the sp:tghell i [78 1 and by high temperature tre:ttmcnts at different spaghetti mo isture. the protein film coating the spaghetti surfarc which (.;a nnat be observed by FF . 79 \ : it s unifonn dist ribution in the granule intersp:tces 162 \ : no On the basis o f our EM observations we havl' cundud ed that random hem denaturated pro teins in dry pasta 135. 54. 55 1 bu t cooking conve nt ionally dried pasta indu ce~ two opposite good coagulability of wheat proteins during cooking 129 \ and ph enomena : complete inlt'raction of coagulating protei ns :ltld the add ition of solubk: pro teins with a low coagu latio n temper­ starch swelling and ge latinization. Since lwat denat uration of at ure [35. 69] The main detrimental fac to r is a low st:t rch glut en [80\ and wh e:ll starch modifica tion !. 1:!3, 27 ] take gelatinization ternpcr:tture which can be rdatcd to the type o f place at approximately the same cooking cond it io ns (moisture starch 127 , 40. 46 \ . th e sizl.! o f gram1 lcs [the large r the size, the and temperature). both contri bute to pa ), ta quality. In the lower the ge lat inizat ion temperatu re 7. 20. 37\. and the interspaccs between the granules, pro tein coag ul<~tion and wat er avai l:tbility 123\ Dr y pasta is a very limited wat t::r system interaction lea ds to the fo rmulation of a con tinuous :md Therefore. when cooking begins a competitio n fo r water is strengthened network which traps the starch while the latter, by established bet ween the starch and pro tein . The less protein swelling and gelatinizing. occludes these intcrspaces. Therefore, surrounding the granules. the faster the rate of st:m;h swell ing it seems reasonable to assume that a physical competition ex ists and gelatinization 123. 38. 56 \ . Furthermore. we can as!'umc between these behaviou rs. The fa ster the starch swe lls and spher­ that this competi t ion is mo re critical in the pe ri pheral p:trt of ulites disperse. the slower the rate of pro tein interaction and the spagh etti wh ere the hydra tio n of the compo nent s takes weaker the protein ne twork inside the sp:tghctt i. If the inter­ place quickly at the beginning of the cooking. act ion of the coagulating proteins is more rapid than the starch On t he basis of the ;~b ovc di sc ussion , we belt cr understand swelli ng and gel:t tiniza t ion :md the protein network is strong the relationships th:1t exist between raw lll<.tll.:rial char:tclcris­ and clast ic enough to prevent breakages IS, 32. 58 \ . the cooked tics and pasta cooking qualit y. T he competition hypo thesis is pasta will be firm. In the opposite case, the pasta wil l be so ft not on ly supported by the experimental data of the prev iously and usuall y sticky . Assum ing that this is true. the factors which cited papers. but is corro bo rated by the findings that past a can improve conventio nal pasta cooking quality are: high prepared from the s;tlne gluten mixed with whe:ll st arches quality and quant it y o f glLII en IS , 24. 26 , 32, 35, 57. 58. 69. ex hibiting slightl y different gela tinization tcmperalltres show Pasta Ultrastructure

~ -:., totol protein

50 <0 30 20 10

t HT HI HT " HM MM LM Fig . 8. Effect of pasta drying conditions on protein solubility in dilute acetic acid solution (0. 1% vfv). a) dried pasta (see Fig. 7): b) same as a), treated at 135°C for 15 min in a dry atmosphere. significantly diffe re nt cooking qualities (201. Relationships . ')';if between the type of starch and spaghetti cooking properties / / . were al so reported by Dexter and ~·lat s uo 127 1. What we have postulated is confirmed by the following ult rastructural studies ' ' on high temperature dried pasta.

Pas ta dried with high temperature (HT) processing

Some producers of pa sta-making equipment have re ce nt ly introdu c~d drying cycles involving controlled high t..:mpe raturc t rc;!tm cnt ( > 60" C - HT processing). T hese tt:chno!ogies. largely u ~e d in Eu rope and introduced to reduce drying times [66. 6 7 ] and rni r..: robial contaminatio n [52, 53, 64,671 . may some times improve pa sta cooking qualities [1 2 ]. In order to Fig. 9. HT·HM spag he tti produced with soft wheat nour. und e r~tand this pheno me na. we have studied the ult rastructurcs a) uncooked. The protein network (pn) looks disrupted :.tro und o f l-IT :-, paghdti produced with common soft wheat under the partially swollen granules (sg). b ) cooked. The starch mate r­ appro priate ex perimental conditions (see Appendix). We report ial (sm ) appears unifo rm ly dispersed while the pro te iu shows he re o nl y the experimental data regard ing common :-,oft whe;ll agg rega tes (pa) and some thin broke n fibril s (arrows). spaglw tti becau:-,e its ultrast ructure dearl y demonstrates the phenomena involw d in t-IT proces!)ing. I-IT-II i\·1 (hig h tem per:tture Table 1: dried past :1 with high mo isture conte nt). l-IT -MM (med ium Cooking test on soft w hea t spaghe tti a) mo isture) and IIT -U\·1 (lo w moisture) indicate the l-IT cxpe ri­ Cooking tim e Cooked weight Cooking loss Spaghetti me ntal drying cond itio ns. wh ile LT ( low temperil turc) indicates min g g quality co n ve nti o n:~! processing. All the drying cycle d iagrams :tre sho wn in Figure 7. A liT proccs!)ing reduces the protein solubilit y as sp:tgh etti LT 10 300 6.36 st icky moisture inc reases (Fig. 8). These results agree with what ha s HT - HM 10 313 6. 59 sticky been re ported by other aut hors (30, 3 1] and confirm the liT- MM II 295 6.28 moderat ely relatio n :-, hip between heat sensitivity of vegetuble proteins and sti cky II 5.73 firm moi~ture conte nt [80] . HT-LM pasta exhibits the best qua li ty liT- LM 290 :tftcr cooking. while I·IT-1·\M is worse than the contro l (LT) [Table 1). 1-IT -1-IM raw pasta exhibits, after soaking, a p:trtial LT 15 280 5.62 firm swelling of the -s t:m;h granules and a discontinuous ndwork o f l-I T- J-I M 15 291 6.4 8 moderately coagulated protein (Fig. 9a). The starch swelling promoted by sti cky liT-l-IM trc:t lment JHeV t: nts the coagulating proteins from IIT -MM 16 280 5.58 firm inter:tcting and fo rming a conti nuous network and due to the HT- LM 16 178 5.58 firm extent o f stre tching. produces b reak:.Jge provided the soft wheat has lo w glute n qua lit y and quant ity. After cooking. the pro te in A : Spaghetti dried unde r e xpe rime nt al conditions (see Fig. 7) netwo rk sho ws further breakdown (F ig. 9b) becau :-;e of the B: Drit:d as A and then treated at 13 5° ( fo r 15 min in dry stresses induced by the pasta volume inc rease. The resul tant conditions. pa sta qualit y is poo r comp:tred to the control ( LT) (Table 11. a) Cooking is carried out o n 100 g d ry spaghetti in 1000 ml of In Figure 9b. some segregat ion between the swollen ~larch tap water. Spaghelli qualit y is ev:lluatcd by a subjective pro­ gr:.tnu lcs and prote in m:ttrix cun be observed. In our opinion. cedure. this must be re bted to the free wutcr content in this area :tnd co nfirms that no starch-protein interact ions have formed . P. R ~smin i and M.A. Pagani

Fig. 10. HT-LM spaghetti prod uced with soft wheat flour. a). b). uncooked. Unswollen st:uch (ug) are su rrounded by a continuous protein network (pn): uncoagulated protein (p) in hydration water (w) are also seen. c) cooked. The starch material is arranged into fibrils (sf) in the co re of the granule and in small regu lar aggregates (sa) in the outer part. The pro­ tein network (pn) shows mainly fibrils (arrows).

Fig . 11. Diagrammatic view of changes which occur in the FF ultrastructure of dry and cooked pasta, regarding protein coagulation, starch swelling and its particle sca ttering. Empty circles represent starch particles and bl:l ck points proteins. Upper Figu res (soaked dry pasta): a (LT). b (HT-LM) , c (HT­ HM ). Lower Figu res (cooked pasta) : d (soft and usuall y stick y), e (firm). Transition from a) to d) implies use of low qualit y raw material; a) to c) hi gh qu:llity raw material: b) is rather indeJ>endent of raw mat erial qualit y. while state c) is related to poor quality. No attempt is made here to sho w conformational changes of the starch fine structure (sec micrographs).

Fig. 12. LT conventio nal spaghetti after heat trea tment ( 135°C) under dry conditions. a) un cooked: b) cooked. Symbols are the same as Figures 9 and 10. Arrows indicate starch-protein interactions. Pasta Ult rastruc tu re

211 m Fig. 13. Pa sta from rice starch and rice n our. Bo th uncooked During IIT-Uvl processing starch swelling docs not take pl:~ cc (a) and cooked (b) ''Bee-Hoon" (vermicelli fro m ri ce starch) due to the low spaghetti moisture ( rv 14%) at the high temper­ show fibrillar network o f retrograded starch. Uncooked rice ature step ( Fi!; . 7d) and continuous coagula ted protein fib ril s n o ur pa sta (c) presents unmodified st:rrch granules (s) and envelo pe the granules :ts shown in Figure 10:-~ . The water la ye rs starch particles (sm) in the interspaccs. After cooking (d ) a surrounding the s t:~r c h granules could be due to :t swellin g o f th C' dry pasta during specimen preparation which pro motes the starch strand network is dearly seen. hydrati o n o f uncoagulated prot ein s (Fig. lOb). During cooking starch patterns can be compared wit h the microgra phs o f the mag nitude o f the effect o f starch swe ll in g and gelatinizat io n Becht el et al. (9) an d Po meranz (681 obtained fro m thin­ o n cooking q ualit y will be reduced sin ce a continuous pro tein sectioned bread aft er oven spring, but in our freeze-fractured netwo rk is alread y fo rm ed in the raw pasta (Fig. JOe). This is cooked pasta , protein strands arc interwoven with starch o nly pa rticul arl y true for pasta made from poor qualit y raw mate ri als. in the outer part of the gelatinized granule (Fig. 12b). We can The competitio n pheno mena that takes place during LT an d HT irll erpret the starch features shown in Figures 2c, IDe and 12b spaghetti processing and cooking arc diagrammatically sum· according to the statement s o f Sterling (76 1 who repo rts that m:tri zed in Figure II. If the raw material is of good qualit y swelling and gelatinization begin in the int erio r o f the starch (e.g .. good durum wh eat semolina), no large differences in granul e while the outer regions remain birefringent: during cooking qualities may be expected from l-IT-U..1 or HT-1-\M these physical changes. radial contractio n ~md t:mgential ex­ technology, due to the strength of th e protein network com­ pansion of branched and unbranched component s take place pared to the neg:tt ive effec t of st arch swelling (unreported data). 1771 If the raw mat erial is of poor quality. these d ifferences arc highly significant. An enhancing effect of the HT drying treat­ Pasta from ri ce starch or rice nour ment h:ts been repo rt ed by other authors 130.31 , 53, 8 1] . but they do no t give an y d efinit e explanations for this phenomeno n. High quality pasta can be obtained from starch alo ne by Cooked pasta qualit y can al so be related to the characteristic t ::t king into account the enhancing effect of the heat induced ultrastructure of starch in cooked HT-LM spaghetti (F ig. IDe) starch modifications. An en light ening cx::t mple is the '·B ee­ 172 1 These patterns can be o btained experimentally by trea t· Hoon··. an orient larch va rieties. Protein material in terwoven with show poor c harac t er isti C!~ for p;~:.ta making. the starc h strands is also observed in these kind of pasta. These Spaghetti was prepared by m ixing the nour with 3or;, water modifications. which promote an extensive reticular texture and kneading under vacuum for IS min in :1 Micro C. Braib:mti where most o f the starch material is involved, can ofte n expla in Press, working capacity 100 kg / h with the discon tin uous pro­ cooking qualities of pasta from unconventional raw mah!rials cedure. The extrusion was performed in :1 cy linder with a teflon 127. 651. lined head (hole d iameters 1.8S mrn) :11 40°C. pressure 80 :.ttm. The expe riment<.~l drying cell has an alttomatic system for Conclusions ventilation and resting times. Air now (3m/sec) was p:nallel to the spaghetti. Detailed drying cydc di ag ram ~ arc reported in Pa sta proves to be an interesting limited water-starch-p ro tein Figure 7: T represents the :tir temperature in the drying ce ll: system where ststarches. Cereal (hem .. 54. 1977. gold !l pecimcn holder wi th a drop of pure glycerol and frozen in 783-793 . super-cooled liquid nitrogen. This freezing med ium works a 3. Angold RE. Cereals ami Bakery Products. in : Food Mi cro­ litt k bett e r and is more practical than Freon to preven t the scopy, J.G. Vaughan (ed.). A c ad ~.::mic Press, London, 19 79. Li ecknfrost effect 170] . The sa mple is transferred into :t B:.tl zers 75- 138. ( BAF 30 I) FF unit where a vacuum of :1t least 2 x I o-6 to rr is reached. After defrosting :.tt -95°C for IS min (or more). the 4. Bachmann L. Schmitt·Fumian WW . Spray- freeze-etch ing o f fra cture is carried o ut at -104 to . JQ JOC to producc a cross dissolved macromolecules, emulsio ns and subcellular compon­ 0 fra cture. Shallowing with Pt-C (~ lm thickness "' 20 A) and ents. in: Freeze-Etching tcchniqucs and applicli croscopic structure of replic:t is kept in 70'X- sulfu ric acid fo llowed by 30?r su lfuric durum wheat , semolina dough and spaghetti. Macaroni L 58. acid for at least 48 h. then washed in distilled water, acetone, ( I). 1976, 18-26. and twice in d ist ill ed and double d istilled wat e r. T he replica 6. Banks W, Greenwood CT . Fmctionation of the starch gran· is placed onto a copper grid and observed in :1 Phi lips EM 201 ule, and the fin e structures of it s components, in: Starch and its electron microscope operating ei ther at 40 o r 60 kV . components. Aberdeen Universit y Press, Edinburgh. 197Sa. 5·6.

10 P:hta Ultrast ructun:

7. B:l nks W. Greenwood CT. Fractio nat ion o f th ~ starch gran­ 29. Dex ter JE. Matsuo RR Changes in spag hl.'t ti proh:in solu­ ule. and tlw fi ne structure!\ o f its component s. in : Starch and it s bilit y d uri ng cooking. Cereal Chern .. 56. 1979.394-398. components. Abe rd een Universit y Press. Edinburgh. 1975b. 30. Dexter JE. Matsuo RR, Morga n BC. High tcmpcrdoughs treat ed with oxidizing and mo rphologi cal changes which occur on heating lenticular wh eat reducing agents. Scanning Electron Microsc. 198 1; Ill : 583-592. s t ~ r c h in water. Starke. 32. 19 80. 186-189. 34. Fretzclorff B, Bechtel DB. Pomeranz Y. Freeze-fracture 12 . Braibanti & C. S.p.A. New develo pm ent in pasta dry ing ultrastructure of wheat flour ingredient s. dough and brtad. techno logy. Maca roni L 6 1 ( 12). 1980. 48-50. Ce r e:-~ 1 Chern .. 59. \982. 113-1 20 . 13 . Chabo t JF. Allen JE, Lamartine FH. Freeze-etch ultra­ 35. Frey A, Holliger A. II compo rtamento in cottur;t ddla pasta structu re of wax y maize and acid hydrolyzed w:txy maize vista al microscopic. Tee. Molito ria. 23. 1972. 4 8 1-4 85. starch granules. J. Food Sci.. 43 . 1978.727-734. 36 . Ghiasi K. Hose ney RC. V:miano-Marsto n E. Gelatiniza tio n 14. Chabot JF. Preparatio n o f food sc ience sa mples fo r SEM. of wheat starch. I. Excess-water sy~ t c m s. Cereal Chem .. 59. Scanning Electron Microsc. 1979: Ill : 279-286 ; 298. 1982. 8 1-85. 15. Christianson DD . Baker FL, Loffredo AR, Bagley EB . 37. Ghiasi K. Hosc ney RC. Varri a n o-M <~ r s t on E. Gelatiniza tio n Co rrelatio n o f mi croscopi c structure of corn starch gr;uwlcs o f wh c;tt starch. Ill. Comparison by differential ~ca nning with rh eological pro pt: rties of cooked pastes. Food Mil..: rostruc­ calo rimetry and light mi croscopy. Cereal Clr cm ., 59. 1982. ture. 1. No. 1. 1982. 13 -24 . 258-26 2. 16. Cloke JD. Gordo n J .. Davis EA. Freeze-etch of emulsifi ed 38. Grzybowski RA. Donnelly BY. St:.~r c h gebtiniz;rtio n in cake ba tt ers during bnking. Food t-.·licrostructure. I . No . 2. coo ked spagh etti. J . Food Sci .. 42. 19 77, 1304-1305. 131 5. 1982. I 77- 187. 39 . Han se n LP . Jones FT. A microscopic view of thermal 17. Colliso n R. Chilto n WG. Starch gelation as a fun <.· tion o f processed wh eat nour. J . Food. Sci .. 42. 1977, 1236-1 24 2. wat er content . J . Food Techno!.. 9, 19 74. 309-315 . 40. Hill RD. Dronzck BL. Scanning electro n microscopy studies 18. Crozet N. Codo n B. Peti t L. Guilbot A. Submicroscopic o f wh cllt, potato. and corn st ardr d uring ge latinizati o n. St arch. structure o f wh ~ at flo ur and gluten lipopro tein pro tein s. Ct.: rcal 25 . 1973, 367-372. Chem .. 5 1. 1974 ,288-299. 4 1. l lo lzl J . Uber den Feinbau von Karto ffel und we irenstark e. 19 . Cumming DB. Tung MA. The ultrastruc\ure of commercial Starch. 25 . 1973 , 292-297. wh ~a t gluten. J . lnst. Can. S.: i. Techno!. Alim ent.. 8. 19 75. 67-73. 4 2. Hoover R. 1-J adziyev D.Characteriza tionof po t:r to stan.: h and 20 . Dal bo n G . Pagam MA . Rcsmim P. Caratte ri slichc dell'armdo it s mo noglycerid c complexes. Sta rk e. 33 (9). 198 1. 290-300. di grana duro c tcnut a in cottura della pasta. Alcune consid cr­ 43. llsich SJ. Davis EA. Go rd o n J . Cryo fi xation freeze-etch of azio ni prcliminari. Tee. Mo lit o ria , 32. 198 1. 599-60 3. cak e-ba tters. Cereal Food World , 26. 198 1, 56 2-564. 2 1. Davis EA . Gordo n J . Applications of lo w tempcr:llurc 44. Jones RW . Tay lor NW. Senti FR. Electro pho resis and micros<.:opy o f food system. J . Mi crosc .. 112. 1978, 20 5-2 14 . fra ctio natio n o f wheat gluten. Arch . Biochcrn . Bio ph ys .. 84. 22. Davis EA. Gordo n J . Food mi crostructure: an integrative 1959, 363-376. appro:..~ c h. Food Mi crostnrcture. I . No. I, 198 2, 1-1 2. 4 5. Khoo U, Christianson DD. Inglett GE. Scanning and trans· 23. Derby Rl. Miller BS . Mill er BF. Trimbo l-IB . Vi sual obser­ mi ss ion microscopy of dough ~md bread. Bakers Dig .. 49 (4). v<~tion of wh eat-starch gelatinization in limited wat er systems. 19 75. 24-26. Cereal Chcm .. 52. 19 75,70 2-7 13 46. Kni ght J\V . Starch-Introduction. properti es. world produc­ 24. Dexter JE. Mat suo RR. lnnuence o f protein ~.;o ntcnt on tio n. in : The starch industry, Pergamon Press. Oxford. 1969. some clurum wheat qualit y p:r r :-~meter s . Can. J. Plant Sci .. 57. 1- 13. 19 77 , 7 17-727. 4 7. Kulp K. Lo renz K. Heat moisture treatment of starches. I. 25. Dexter JE. M:rt suo RR. Changes in se molina pro teins during Ph ysico-chemical properties. Cereal (hem .. 58. 198 1. 46-4 8. spaghetti processing. Cereal Chem., 54. 1977. 882-894. 48. Lasz lit y R. Investigatio n o f the stress rela x:rtio n o f do ughs 26. Dexter J E. Dro r11:ek BL . Matsuo RR . Scanning electro n by l ab oro g r :.~ph.l l. El elmiszervizsg . Kozl.. 6. 1960 . 1970-198 1. mi croscopy o f cooked spaghett i. Cereal Chem .. 55. 1978. 23-30 . 49. La sz tit y R. Investigation o f the rh eological p roperties o f 27. Dex ter J E. Mat suo RR . Effect of starch on pasta do ugh gluten. I. Vi scoelastic properties o f gluten. Acta Clrinrica Ac. rheology and spaghetti cooking qualit y. Cereal Chcm .. 56. Sci. Hung .. 53. 1967. 169-1 78. 1979. 190-1 95. 50. Leo nard R. Sterling C. F reeze-etched surfaces in potato 28 . Dex ter JE. Mat suo RR . Dronze k BL. A scanning electro n starch. J . Ultrastructure Res .. 39. \ 972. 8 5-95. microscopy stud y o f J;tpanese noodles. Cereal Chem .. 56. 1979. 5 1. Lint:ts C. D'Appolonia BL. Effect of spaghetti processing o n 202-208. se molina carbohydrates. Cereal Chern. , 50. 19 73.563-570.

II P. Rcsmini and M.A. Pagani

52. Manser J. lnOucnze dell'essiccamcnto su i contcnuto batter­ 73. Seckinger Ill. Wolf MJ . Lipid d istribution in the protein icc di paste alimentari. Di agramma Buhler .. 64. 1977. 9- 14. matrix of wheat endosperm as observed by electron microscopy. 53. Manse r J . High temperature drying. of pasta products. Cereal Chem .. 44. 1967. 669·674. Macaro ni J .. 60 (9). 1979. 30-32. 74. Simmonds DH. The ultrastructure of the mature wheat 54. t<. lanser J. Pa ramet ri ottimati per Ia produzione dclll• paste endosperm . Cereal Chem .. 49. 1972. 211-222. alimcn tari. I. Mo\ini cl" ltalia . 32 (6), 1981.25 1-156. 75. Simmonds DH. Wheat-grain morphology and its relationship 55. Manser J . Parametri ottimali per Ia produzione cldle paste to dough structure. Cereal Chem .. 49. 1972.324-335. ~llirnentari. II. Molini d" ltalia, 32 (7). 1981,305-323. 76. Sterling C. Fibrill3r structure of starch. Evidence for crossed 56. MarshallS. Wasik R. Gelatinization of starch during cooking fibrils from in cipient gelatinization. Starke. 26, 1974. 105-110. spaghetti. Cereal Chcm .. 5 1. 19 74, 146- 147. 77. Sterling C. Textural qualiti es and molecular structure of 57. Mat suo RR , lnvinc GN. Effect of gluten on the cooking starch products. J. Texture Stud., 9. 1978. 225-255. quality of spaghctl i. Cereal Chem .. 4 7, 1970. I 73-180. 78. Voisey PW, Wasik RJ . Loughhccd TC. Measuring the tex­ 58. Matsuo RR. Bradley JW , Irvine GN. Effect of protein con­ ture of cooked spaghetti. 2. Exploratory work on instrumental tent on the cooking quality of spaghetti. Ccre31 Chem .. 49. assessment of stickiness and it s relationship to microstructure. 19 72.707-7 11. J. lnst. Can. Sci. Techno!. Aliment., I I. 1978. 180- 188. 59. Matsuo RR. Dexter JE, Dronzek BL. Sca nning electron 79. Wasik RJ . Bu shuk W. Relation between molecular weight microscopy study of spaghetti processing. Cereal Chem .. 55. distribution of endosperm proteins and spagheHi - making 1978. 744-753. quality of wheats. Cereal Chem .. 52. 19 75, 322-318. 60. Med vedev GM. Burov LA. Semko VT. Jn Ouenza del tipo 80. Wu YV. Inglett CE. Denaturation o f plant proteins re lated di frumen to sulla qualita delle paste alimentari. Tee. Molitoria. to functionalit y and food application. A review. J. Food Sci .. 32. 198 1.677-684. 39. 1974.218-225. 61. Miller BS. Derby Rl. Trimbo HB . A pictorial explanation 8 1. Wyland AR. D'Appolonia 13L. lnOuence on drying temper­ for in crease in viscosity of heated wheat sta rch-wa ter SUS Jh:: nsion. :nure and farin::~ blending on spaghetti qualit y. Cereal Cbem., Ce real (hem., 50. 1973,271-280. 59. 1982. 199-201. 62. Moss R. Stenvert NL. Kingswood K. Pointing G. The re­ lationship between wheat microstructure and Oour milling. Discussion wi th Rev iewers Scanning Electron Microsc. 1980: Il l: 6 13-620. R. Moss: Could the authors provide some information of the 63. Miihl ethalcr K. Die Ultrastruktur dcr stark ckorncr. Starch. humidity profil es used in the drying processes referred to in 17. 1965.245-249 . Figure 7? Presu mably control of humidit y is as important in 64. Oltogalli G. Galli A. Dalbo n G. Lcnner A. Ri cerche su lla liT drying as it is in LT drying? microbiologia delle paste alimentari secche. Tee. Mol itoria, 30. Autho rs: The humidity pro files in the drying ce ll can be 19 79. 813-819. immediately calculated on the basis of the va lu es of 6 T and T 65. Pagani MA , Rl!sm in i P. Dalbon G. Fo rmulazionl! e produz­ reported in the drying dia)!rarns. These profiles are important ionc di paste alimcntari a partirc da matcric prime non con­ both in LT and liT drying: however. for \IT processings the vcnzionali. T ee. Molitoria. 32. \981, 1-24. moisture content of spaghetti at which the l iT treatment is performed is critical. 66. l)avan G. L'impiego dell'alta tcmperatum nc\ pror.:esso di cssiccam cnto dell e paste alimen tari. Tee. Molitoria. 30 . \979. E.A. Davis: Why do you not consider "defrosting" at -95° C 362-370. etch ing? When we etch. we do this :11 -105°C for 2 min. There­ 67. Pavan G. High temperature drying improves past:l quality. fore etching o r sublimation should be taking place during the Food Engim·ering Intern at io nal. Feb. 1980, 37-40. I 5 min of "defrosting"? 68. Pomeranz Y. Interaction bet ween lipids and gluten protein s. Au llwrs: Since the tlefrosting step is performed before fractur­ Ann. Techno!. Agric., 29. 1980.385-397. ing. it cannot inOuence the ul!rastructurcs of the repl ica, as in freeze-etching. Fo r this reason it is better to indica te this step 69. Resmini P. Volonterio G. Saracchi S. Pi ergiov:tn ni L. as ·'defrost ing" than as "etching". even if a w::~ter sublimation Cara ttc ri ch imici c nutrizion:.tli eli paste alimcntari integrate con takes place. proteim• non convenzionali. Riv. Soc. !t al. Sci. Alim .. 4. 1975. 32 1-330.(FSTA.9. 19 77. IM 128/129). E.A. Davis: The gluten material shown in Fi gure 3 may have 70 . Rcsmini P. ll vuoto in a\cunc tecniche preparative per Ia some freeze damage. Wh at preparation techniques did refs. 48 microscopia e\ectronica. in: II vuoto nella scicnza e nella tec­ and 49 usc to prepare their samples prior to fracture? nologia d<.·gli alimenti. C.R. Lerici (cd.). Cooperativa Librari3 Autho rs: Lasztit y's works (refs. 48 and 49) do not refer to Universitaria Edit rice. Bologna. 1975. 109-\40. the freezing technique used prior to fracturing but to the 7 1. Rcsmi ni P. De Bernardi G. Mazzolini C. lnOuenza delle method of gluten ex traction from semolina. Since the ultra­ cond izioni di essiccazione su alcune carattcristiche della pasta structures shown in Figure 3 have been obtained according to aliment are. Bol l. (him. Lab. Prov., 27. 1976, 283-293, (FSTA. our FF technique, we think that freeze damage in the sample is 9. 1977. 5M67 1). unlikely. 72. Rcsmi ni P. Study of pasta structure by electro n m icroscopy. Mlynsko-Pckarensky Prumysl, 25 (7), 1979, 195- 197. (FSTA. 12. 1980. 2M230). For additional discussion see page 98 .

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