Food Structure
Volume 12 Number 3 Article 1
1993
Development of the Food Microscopist
D. F. Lewis
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Recommended Citation Lewis, D. F. (1993) "Development of the Food Microscopist," Food Structure: Vol. 12 : No. 3 , Article 1. Available at: https://digitalcommons.usu.edu/foodmicrostructure/vol12/iss3/1
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 Structure, Vol. 12, 1993 (Pages 275-283) 1046-705X/93$5.00+ .00 Scanning Mi croscopy International , Chicago (AM F O' Hare) , IL 60666 USA
DEVELOPMENT OF THE FOOD MICROSCOPIST
D.F. LEWIS
Leatherhead Food Research Association, Randalls Road, Leatherhead, Surrey, KT22 7RY, U.K. Present Address: Food Science and Technology Department, Scottish Agricultural College (SAC), Auchincruive, Ayr KA6 5HW, Scotland, U.K.
Abstract Prologue
This paper describes the processes through which All the world's a stage, the food microscopist develops hi s/her skills. It is based And all tbe men and women merely players: around a framework of Shakespeare's seven ages of They have their exits, and their entrances: man . The first stage is learning about equipment: how And one man in hi s time plays many parts, it works and how not to abuse it. Next, attention turns His acts bein g seven ages ... to how to prepare samples for examination whilst main taining the validity of the observations and avoiding Jacques in "As you like it" damage to the instrument. The "Lover" is the time at by William Shakespeare which an understanding of the basic structures of food There is a considerable amount to be learned as a products is gained and the ~ S o ldi e r " starts to interpret food mi croscopist. It is not simple book learning either, these structures in terms of th e performance of the food but is rather an apprenticeship, and the learning does not stuff. Next, the interpretation must be negotiated with stop . People develop new skills and vi sions as their food technologists in ord er to influence the processes of appreciation expands. A key issue is how to assist food manufacture. The sixth age sees a more managerial mi croscopists to achi eve their full potential. One of the overview of food microscopy. The final challenge is to prime aims of this paper is to describe a view of how avoid the near oblivion of Shakespeare's last scene of food mi croscopists develop. The intenti on is that this all! can act as a guide for mi croscopists and their managers , who, by recognising some of the stages of development, may be able to assist their progression. The view is based on observation of food and other microscopi sts Key Words: Microscopy techn iques, Interpretati on of over a number of years and loosely follows Shake food structure, ice cream, meat, confectionary. spea re's seven ages of man although not all of hi s de scriptions are quite appropriate. It is also necessary to reali se that none of the stages is ever completed; there are always new things to learn about in struments, speci mens and relationships. Hence, th e seven ages represent th e times at which new, additional philosophical approaches are added to the microscopist's armoury.
At First, T he Infant
Most mi croscopists cut their teeth by appreciating in strumentation. There is much to learn . Whether the fi eld is light or electron mi croscopy, the infant micros copists must learn to respect the instrument and di scover Paper received December 2 1, 1992 its limits and limitations. As with a child, much of this Manuscript received July 6, 1993 discovery comes through play and it is wi se to allow Direct inquiries to D.F. Lewis some time for this aspect of learning. "Playing" with Telephone number: (44) 0292 520331 the mi croscope is a vital exploration of its potential al FAX number: (44) 0292 52 111 9 though , of course, the "play" needs to be guided and linked to theoretical considerations. In this respect,
275 D.F. Lewis modem mi croscopes offer some advantages over their Figure 2 illustrates the effect of changing accelerating predecessors, in that , there are generally rather more voltage on the appearan ce of bacteria on polymer-based safety dev ices to prevent damage wh en the operating beads. The effect of using too high an accelerating volt limits are exceeded. As with all benefits, there is a age is to increase the depth from which the signal is de price to pay; computer control is effi cient and o ft en ex rived and hence make it more difficult to see the surface tends the capabilities of the instrument , but it makes the detail , including the bacteria. operator one step removed from the mi croscope and Books help the mi croscopist to appreciate the mi cro some understanding of its working is lost. scope and a short li st of useful books is given in the Also , protecting the user from some of the more bibliography. dire consequences of hi s/her actions can lead to a less The process of learning about instruments never careful approach to the instrument. It can be frustrating stops; for ex ample, the Leatherhead Food Research As to realise that a trainee mi croscopi st wi ll never learn sociation (LFRA) recentl y bought a confocal microscope some of the fundamental princip les because a computer and this has required a fair amount of "play" time to ex automaticall y makes the necessary correcti ons, but this pl ore its exciting potential. The instrumental learning frustration should be countered by the kn owledge that in phase is common to all strands of mi croscopy and some strumental development will allow today's mi croscopi sts mi croscopists do not progress beyond this stage. The to achieve much more. food microscopist, however, has a fun cti onal role and The process of learning about instrument s is one of can only regard thi s stage as a stepping stone. getting a "feel" for th e mi croscope and so it is difficult to define precisely what wil l be learnt. Some examples, And Then The Whining Schoolboy however, may serve to illustrate the point. For all mi croscopists, one of the key early develop With some reluctance, we have to accept that the ments is to gain a sense of the most appropriate magnifi novelty of the in struments wi ll wear off and having cation. I was told that th e first set of electron mi cro achi eved some mastery of the instrument , th e would-be graphs I took would be at too hi gh a magnification, and mi croscopist now has to grapple with speci men prepara that the second set would be too low! This is an impor ti on. This is especially challenging for food mi croscop tant lesson to learn . The trade-off of increased detail ists since probably no other di scipline has to cope wi th against the benefits of seeing featur..:s in a wiLI..:r contex t such a wide ran ge of sa mpl es and preparati on tech is not always easy to resolve, and does not always ap niques. At the LFRA. for example, preparation may in pear to be appreciated even by some ex peri enced mi volve poli shing glass sa mpl es for X-ray mj croanalysis, croscopi sts. At some stage, th e mi croscopi st also needs cryostat sectioning at -45 °C coupled with cold-shi elded to appreciate the relative values of a range of instru transfer to a cold stage, resin sectioning hi gh-fat or high ments, and knowing, for example, when to use a polar sugar systems, or preparation of samples for specific ised light mi croscope rather than a scanning electron labelling. It is rare indeed for a single technique to give microscope (SEM) is a vital learning step. Some gener all the necessary information and the food microscopist al gu idelines can be given. Magnifications in excess of needs to develop an instinct for how particular samples xl ,OOO wi ll normally di ctate electron mi croscopy in will react to various methods of preparation and for some form , where three-dimensional information is recogni sing the less useful structures resulting from needed then either SEM or confocal light mi croscopy is specimen preparation. indicated, and where the specimen is especially suscepti Many food mi croscopi sts will start with basic hi stol ble to dehydration th en either si mple light mi croscopy or ogy of essentially biolog ical specimens and so sectioning cryo-SEM is likely to be the method of choice. Beyond will be the first technique to be tackled. Here the pupil this basic guidance the microscopist's intuition, based on needs to measure the merits of different approaches. experience is the best gu ide. Cryostat sections are quick and are useful in , say , meat Methods of increasing contrast and maintaining de products, where retention of fat or other soluble struc tail are important to the li ght microscopi st. An appreci tures is important; however, resin or wax secti ons of ation of the use of the condenser diaphragm and under fixed material often show greater detail. The value of standing the importance of front focal plane of the con different stains and stain combinations is al so a vital denser in obtaining contrast ar ~ key features, which point to be learned. As with learning about instruments, should be appreciated at an early stage. Figure l illus a certai n amount of trial and error is needed to develop trates some of these effects. the reference biological methods for food use. In the electron microscope, the choice of accelerat The transmission electron microscopist has a rather ing voltage on the final image is important both in harder time in trying to prepare samples; the high fat, transmission electron microscope (T EM) and SEM. air, sugar, salt and acid levels encountered in some
276 Development of the food microscopist
figure I. Effect of cond enser diaphragm on image contrast and quality. Bar = 10 J.
277 D.F. Lewis often much more difficult to interpret but provide an es Figure 3. TEM of pork shoulder meat prepared by sential check on the results obtained by sectioning. Fig thin-sectioning (a) and freeze-etching (b). Bar = 1 l'ffi ure 3 shows meat (muscle) structure as revealed by thin Figure 4. Cold-stage light mi croscopy of ice-crystals in sectioning and freeze etching to illustrate this point. commercial ice cream. Bar = 100 J.!m . New instrumental techniques bring wilh them new 5. Cold-stage SEM of commercial ice cream. challenges and opportunities. X-ray microanalysis and Figure Bar = IOO~tm. image processing techniques have implications for speci men preparation. A recent development has been the confocal scanning laser microscope. In this case, it is It is very difficult to teach this aspect of food generally very easy to present the specimen to the mi microscopy; the only real way to learn is to spend time croscope and much of the methodology development is with the prepared specimens in the microscope. Books, based on finding stains to bring out key features. How papers and experienced colleagues can help. Often, ever, the three-dimensional capabilities of this instrument however, the most useful work will be in unexplored also allow some ex perimentation with preparation tech areas and established sources can only be used to pro niques. Freeze substitution has been used in biological vide fixed points of reference to prevent the ardent mi microscopy for some time but has not been applied croscopist from becoming compl etely lost. The manag much to food systems. Studying ice crystals within a er's role in this process is two-fold: firstly, to allow the frozen food is of importance in terms of the eating quali time for exploration of sampl es in sufficient detail, and ty of the product. It is possible to use cryostat section secondly, to make sure that the microscopist is aware of ing coupled with cold-stage light microscopy to see ice th e many traps and pitfalls that can be encountered. crystals (Figure 4) or to use cryo-SEM (Figure 5); how ever, the three-dimensional nature of these approaches Then a Soldier is rather restricted. Freeze substitution offers the pos sibility of retaining the outline of ice crystals within a The battle now is interpretation . Simply feeling at bulk preparation of a product. Groves and Lewis (un home inside the structure is no longer enough; there has published observations) have made a preliminary assess to be a purpose to the exerci se. The purpose of course ment of the application of this technique to ice cream. is to understand how the structure relates to the behav Figure 6 gives an indication of the results. This work is iour of the food system. The strategy is to recognise the not fully developed and undoubtedly there is much to be most important features and to di scover to which aspects learned but it illustrates the possibilities for method of functionality they relate. Changes may be all around development in this area. and at every level of magn ificati on or may be camou flaged within th e finest levels. The campaign is to dis And Then, The Lover cover the key items in th e relationship and then exploit fndeed, this is the stage at whi ch a lo ve of mi cros and develop this intelligence. copy sets in! Now the microscopist can prepare and ex Clearly, a link has to be made between the structure amine sampl es; he (~he) learns to recogni se and appre and other properties of the product. The other charac ciate the key structures and to see th eir many variations teristi cs of the product may be physical (such as viscos and subtleties. ity or hardness), compositional (such as variety of vege At uni versity, one of my flat mates was studying table, protein type or sugar balance), processing per botany and one day he described hi s understanding of formance (such as cooking loss), or sensory (such as plant structure like being able to walk round insid e th e texture or flavour release). tissues. I did not appreciate what he was say ing until I An example of combining sensory results with mi started my doctorate work on meat struct ure, when sud croscopy can be seen in some microscopy work carried denly I had the same experience. Although the work out largely by Kathleen Groves in collaboration with the was mainly TEM of thin sections, and hence very two Sensory team at LFRA led by David Kilcast. Three dimensional, everything was understandable as part of a commercially available fruit pastilles were subjected to three-dimensional world. Recently one of my (younger) sensory analysis and amongst other things showed differ colleagues ex pressed, quite spontaneously and indepen ences in initial bite hardness and toughness on chewing. dently , exactly the same sentiments. Of course, mi cros The textural "star diagram" (Fig. 7) illustrates the senso copy is much more three-dimensional now. This change ry attributes of these three types of pastille. Sample A started with stereo pairs and SEM. It has developed had a fairly hard initial bite but softened fairly quickly with computer reconstructions. The wider use of con on chewing; sample 8 had a hard initial bite and re focal microscopy will extend thi s three-dimensional mained fairly tough through the chewing process; and world and make it more accessible. sample C was fairly soft initially and remained soft
278 Development of th e food mi croscopi st
Figure 7- Texture Star Diagram for Pastilles
Moist 50
Initial Bite
Tough Jelly Figure 6 (above). Confocal light microscopy of freeze substituted ice-cream. Bar = 50 ,urn. --- Pa stille Pastille Figure 7 (at righl). "S tar" diagram showing tex tu ra l A B attributes of pastille sweets.
279 D.F. Lewis
Pastille A during chewing. At a macroscopi c level the initial hard High Initial Bite ness in sample A could be related to a well -developed Soft, Moist, Breaks Down. crystallised sugar layer at the outside of th e sweet, sam ples Band C showed less ex tensive crystal layers. Light mi croscopy showed differences in the general structure. Sample B had a well -developed protein (gelatin) network with starch inclusions and this produced both the hard initial bite and the toughness on chewin g. Sample C showed a starch-continuous matri x with protein inclu sions and this, coupled with the restricted crystalline layer at the surface, produced a soft initial bite and a soft chewing sweet. The internal structure of sample A showed the protei n as di screte areas and the starch was largely dispersed in a syrupy matrix, which accounted Thick outer shell of sugar crystals for the softness once th e crystalline layer had been bro Continuous syrup phase ken. Figure 8 shows a di ag rammati c representati on of Dispersed protein and starch th ese differences. Using coll oidal gold linked to lectins and electron microscopy, it was possible to show that the discrete areas in sample A were an association of protein with gum arabic. Interestingly, on agei ng, sample A became much tougher on chewing; th is was partly due to the outer crystalline layer growin g but also, as this happen ed, the discrete protein areas fu sed to give a continuous matrix. Of course, not all links between structure and be haviour are as clearly defined as in this illustration and no doubt there are many subtleti es that are not ex plained. However, mi croscopy is often th e key link between a number of apparently disconnected observa tions and the mi croscopi st must be given and take the time to explore th e connection.
Continuous protein phase And Then, The Justice Dispersed starch and syrup The verdict must be publicised, but the microscopist cannot expect food technologists to treat his pronounce Pastille C ments with th e respect afforded to judges. This is per Low Initial Bite haps the most difficult task facing the mj croscopist. The Soft, Jelly-like, Moist training and development so far have given great insight into the structure and behaviour of foods; many complex features are instantly understood. However, show the pi ctures to a non-microscopist and it seems that the most basic understandings are miss ing. People readily accept that everyday objects are recognised by their shape (or morphology) but apply th e same logic to an electron mi crograph and all sorts of doubts arise. Everyone recog ni ses a banana on sight, but tell someone that a feature on Figure 9 is a casein micell e and all sorts of sophis ti cated chemical evidence wi ll be requested . Even when Continuous starch & syrup phase the strict mi croscopical interpretation is accepted as the Dispersed protein and syrup mi croscopi st's domain it is difficult to gain the confi Figure 8. Diagrammatic representation of structures in dence of the technologist in all owing the mi croscopist to pastille sweets. apply his (her) judgement in th e area of explaining the
280 Development of the food mi croscopist
relevance of the structures. This is perhaps the food microscopist's most difficult task and th ere is no uni versal solution. We are now outside the area of scientific laws and into the field of human relationships. Each combinati on of microscopi st and technologist will need to find their own way of working and , from th e mi croscopist's point of view, different approaches should be tried until a sati sfactory relations~ip is established. For some people a clear diagrammatic representa tion of th e structure and highlighting key structural changes with respect to changes in the product will be sufficient. Other people will onl y feel happy with num bers and the mi croscopist wi ll have to find a way of converting his (her) subjective j udgement into a numeri cal fonn. Image analysis systems may help here but the microscopist should retain control and ensure that the numerical output is consisten t with a convent ional inter Figure 9. TEM of toffee pre-mix by freeze-etching. pretation of th e images. Tn some cases, a heated debate, Bar = IJlm. based on mu tual respect, can be a most effective way of progressing. Often the problem lies in a fa ilure to convey the It is a time when the advocacy is for inclusion of three-dimensional aspects of the structure. For exampl~. structural examination as a matter of course, even in when we were working on the fouling of heat exc h a n g~r th ose cases where, at the outset, th ere is no obvious or surfaces, it was quite clear to us that an important fa ctor tangible ex pectation of its value. The argument is based was ai r coming out of solution at the hot surface and on past successes. When microscopy was included in forming a heat-set foam, which cut down heat exchange the studies on ici ng sugar (see "And Then The dramaticall y (Lewis, 1986). However, it was onl y when Justice") there was no plan for its applicati on, simply a stereo pairs were prepared th at the engineers in volved faith that it would be justified. A role at thi s stage is to accepted the possibility and suggested changes to the promote that fai th with the decision makers. procedure to confirm the hypothesis. In the other cases, Of course, it is not enough simply to include some making models of th e structures may be effecti ve. One mi croscopy in the project, the microscopists must be of my early memories as a young microscopist was to given freedom to contribute fully to the development of see my th en boss, Gerry Jewell , with the then head of the project. Making the resources available for some Confectionery at th e LFRA, Derek Stansell , on th eir playing with the problem is part of the role. Depending bands and knees, bui lding models with small whi te card on the cul ture of the organisation this may be a recog board boxes. They were devising mechanisms for sugar nised feature of the project or may need to be a bootl eg crystal nucleation and the early stages of sugar crystal ac tivi ty. In Peters and Austin 's book "A Passion for growth and this led th em to propose a crystal growth Excell ence" the description "skunk groups" is used to mechanism. ln tum, their thoughts on crystal growth al describe groups of people who operate in unorthodox lowed the demonstration of a novel process for produc ways; in some cases the microscopists are well placed to ing icing sugar, which produced cleaner crystals and was take on this role which is probably vital to th e well less liable to cake. Thi s phase is without doubt the most being of research establishment s. difficult and there are no universally applicable solu There is also a question of equipment and part of ti ons. It is, however, th e most important stage in apply the rol e wi ll be to try to keep the right level of eq uip ing microscopy fi ndings and is one to which microscop ment for the organi sation. Philosophicall y, thi s can be ists and thei r managers need to give considerabl e a difficult balance. The good practical microscopist will thought. always want more, better equipment; managements will generally resist, such is the nature of business life. In The Sixth Age reality, th ere are two criti cal levels. The fi rst wi ll be This age views mi croscopy in a wider field and easi ly appreciated as the point at which it is impossible takes the focus from the short-term interpretation of the to carry out the sort of work expected by th e organi sa pictures and products in order to see the overall rele ti on, for example, it is no use expecting valid observa vance and connections between structure and perfor tions on the association of protein molecul es wi thin a gel mance. structure and onl y providing a simple compound light
28 1 D.F. Lewis mi croscope. There is, however, an upper limit where a as to the mi croscopi sts. So metimes it seems that no laboratory can be too well equipped, thought processes sooner has a techn ologist been "trained" to appreciate are inhibited, and there is a tendency to lose the insight the value of mi croscopy than they are replaced and the that comes from relatively simple equipment. So often process has to start all over again. Somehow it is easier one sees papers and presentations on SEM of problems to accept having to train younger mi croscopi sts than hav that could be better tackled by light mi croscopy . The ing to train technologists but both are essential for the "sin" is often compounded by describing the studies as most effective application of mi croscopy for th e benefit "structural " or "microstructural"; in my view these of the food industry. terms should not be used unless several techniques are applied, each giving di stinctive information. The rol e of Last Scene of All the "sixth age microscopist" is to challenge th eir youn ger coll eagues to ensure that the approaches are That ends this strange, eventful history; being properly considered. Is second childishness, and mere oblivion; Direc t contact with the mi croscope may now be Sans teeth, sans eyes, sans taste, sans everything. quite limited and an element of remote control microsco py is introduced. A key learning element at th is stage Best not to dwell too long here! On a tangibl e note, is how to influence more junior colleagues, whilst all ow many elderly mi croscopists seem to have rather thick ing them to develop and discover thei r own insight s into glasses but hopefull y this is related to monocular th e problems. The role is one of coach and coun sell or. mi croscopes, and the more widespread use of binocular For those, who like to see others develop, th is can be a mi croscopes may preclude thi s defect . Some mi croscop most rewarding age even if the fingers itch to try th e ists do not seem to reach this stage but remain enthusias latest innovations. tic and productive to a great age. An example of this The publication of bibliographies is oft en a feature was Harry Powers, once of Tate and Lyle, who was of this stage in a microscopist's life. I have fond memo wri ting to us about sugar crystallisation when he was ri es of the late George White of Lyons Central Labora well into hi s nineties. tories. Towards the end of hi s career, he directed th e If we do reach thi s second childishness, at least producti on of a most comprehensive bibliography of there is the consolation of having passed through six food mi croscopy . Thtst can bt found in a series of arti exciting and challenging ages to get th ere. cles published in the Journal of the Association of Pu bli c Analysts. In earlier years, Kate and Andrew Winton Helpful Sources of lnfonnation for Each Stage had produced a compendium of food structure th at has not been surpassed in over fifty years. John Vaughan in The infant the late 1970's produced th e book Food Mi croscopy th at Bradbury S ( 1984) An Introduction to the Optical showed the way in which emergin g microscopy tech Mi croscope. RMS Mi croscopy Hand books No I. Oxford niques were being appl ied to a wid e range of foods. It University Press. was around this time that the SEM meetings started to Bradbury S, Evennett PJ , Haselmann H, Piller H concentrate on foods and Sam Cohen, Eugeni a Davis, (1989) RMS Dictionary of Light Microscopy. RMS Mi David Holcomb and Milos Kalab were pi oneers in initi croscopy Handbooks No 15 . Oxford University Press. ating the seri es of meetings that has developed to be th e Chescoe D, Goodhow P (1985) The Operation of main international meeting of food mi croscopi sts. Thest: th e Transmission El ectron Mi croscope. RMS meetings, also led to th e formation of thi s journal, Food Mi croscopy Handbooks No 2. Oxford University Press. Structure. In more recent years, David Holco mb has Meek GA ( 1970) Practi cal Electron Mi croscopy for produced a bibliography of papers published in Food Biologists. Wiley·lnterscience. Structure and its predecessors. Morgan AJ (1985) X-ray Mi croanalysis in El ectron This is the age of ex perience, but there is a need to Mi croscopy for Biologists. RMS Mi croscopy Handbooks reali se that good advice is not always heeded; sometimes No 5. Oxford Universi ty Press. people can onl y learn by making their own mi stakes and Shillaber CP ( 1959) Photomi crography in Theory coping with the consequences. This thought may help to ami Practi ce. Chapman & Hall I John Wiley & Sons. avoid the risk of bitterness. There are frustrations too, Thornton PR (1967) Scanning Electron Mi croscopy. especiall y in organisations where there is a reasonably Chapman & Hall. high turnover of personnel. Often the same arguments The schoolboy have to be replayed and sometimes, it is necessary to see Beesley JE (1989) Colloidal Gold - A New Per th e same mi stakes being made over and over again. spec ti ve for Cytochemical Marking. RMS Microscopy This, of course, applies to the technologists just as mu ch Handbooks No 17. Oxford Uni versity Press.
282 Development of th e food microscopist
Conn HJ , Darrow MA , Emmel VM ( 1960) Stai ning The soldier Procedures used by the Biological Stain Co mmission. Bechtel DB (1983) New Frontie rs in Food Mi cro Willia ms & Wilkins, Baltimore. structure. American Assoc iation of Cereal Chemists. Green FJ ( 1990) The Sigma-Aldrich Handbook of Blanshard JVM, Mitchell JR (eds.) (1988) Food Stains, D yes & Indi cators. Sigma-Aldrich Corporation, Structure - Its Creation and Evaluation. Butterworths. Ald rich Chemi cal Co. Holcomb DN, Kalab M (eds.) (198 1) Studies of Gurr E ( 1962) Staining Animal Tissues- Practi cal Food Microstructure. Scanning Electron Microscopy, & Theoreti cal. Leonard Hill (Books) Ltd. Inc, AMF O' Hare, Chicago, IL. Jensen WA (1962) Botanical Histochemistry. W.H. The justice Freeman & Co. Kay DH ( 1965) Techniques for Electron Mi cros Aguilera JM, Stanley DW (1990) Mi crostructural copy. Blackwell Scientific Publications. Principl es of Food Processing and Engineering. Elsevier Lewis DF (ed.) (1978) Manual of Microscopical Applied Science. Methnds. Leatherhead Fond Research Association. Lewis DF (1986) Features of Food Mi croscopy. Munck L (ed.) (1989) Fluorescence Analysis in Food Microstructure 5, 1-8. Fonds. Longmann. The sixth age Pearce AGE (1972) Histochemi stry- Theoretical & Harvey-Jones J ( 1988) Making it Happen. Collins. Applied (Vols. I & 2). Chuhrchill Li vingstone. (ISBN 0-00-2 17663-7). The lover Holcomb DN (1990) Food Mi crostructure - Bl oom W, Fawcett DW ( 1975) A Tex tbook of Cumulati ve Index. Food Structure 9, 153-173. Histology. W.B. Sa unders, Philadelphia. Peters TJ, Austin NK ( 1985) A Passion for Dodge JD ( 1969) An Atlas of Biological Ultra Excell ence. William Collins Sons & Co. Ltd. Glasgow. structure. Edward Arnold Ltd . (London). (ISBN 0-00-637062-4). Esau K (1965) Plant Anatomy. John Wiley & Sons. White GW, Shenton AJ (1974-1980) Food Mi cros Vaughan JG (ed.) (1979) Food Mi croscopy. copy (an annotated bibliography). Various issues of J. Academi c Press. Ass. Public Analysts. Wallis TE (1965) Analytical Microscopy. J & A Last age ol' all Churchill, London. Daily newspaper, gardening books, novels, radi o Win ton AL, Winton KB ( 1932-1939) Structure and and telev ision. Composition of Fonds. Wiley & Sons, New York.
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