Electron Microscopic Investigations of the Cell Structure in Fresh and Processed Vegetables (Carrots and Green Bean Pods)
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Food Structure Volume 3 Number 1 Article 8 1984 Electron Microscopic Investigations of the Cell Structure in Fresh and Processed Vegetables (Carrots and Green Bean Pods) Monika Grote Hans Georg Fromme Follow this and additional works at: https://digitalcommons.usu.edu/foodmicrostructure Part of the Food Science Commons Recommended Citation Grote, Monika and Fromme, Hans Georg (1984) "Electron Microscopic Investigations of the Cell Structure in Fresh and Processed Vegetables (Carrots and Green Bean Pods)," Food Structure: Vol. 3 : No. 1 , Article 8. Available at: https://digitalcommons.usu.edu/foodmicrostructure/vol3/iss1/8 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 MICROSTRUCTURE, Vol. 3 (1984) , pp. 55- 64 0730-5419/84$1 .00+.05 SEM Inc., AMF O'Hare (C hicago), IL 60666 U.S.A. ELECTRQ~ MI CROSCOP I C I~VESTIGATIONS OF 1l1E CELL STRUCTURE I N FRESH AND PROCESSED VEGETAB LES (CARROTS AND GREEN BEAN PODS) t-lonika Gr ote and Hans Georg Fromme I nstitute of Medical Physics, ~ lu enster University Huefferstrasse 68 , D-4400 Muenster, W. Germany The cell structure of fresh, blanched, boiled. dried and Dried carrots and green beans are traditional ingredients of rehydrated tissues from ca rrot roots and green bean pods was bag soups which have become more and more popular on the examined in the scanning and/o r transm ission electron mi cro European ma rket. In comparison with genuine instant prod ucts scope. The secondal)' phloem of carrot roots represen ts a these bag soups are characterized by comparatively long typical plant storage parenchyma characterized by a high starch cooking times which can he inOuenced - within ce rtain limits and lipid content. Gree n bean pods show many characteristics by vary ing process conditions during the production of such of assimilation tissue (e.g. chloroplasts). but they also contain a dried vege tables. The aim of indust rial research now is to considerable amount of starch. Blanching, boiling, de- and find su itable process condit ions in order to produce dried rehydration affec t the tex ture of both vegetables in a simil:u vegetables wh ich need extremely short cooking times and arc way: swe llin g of ce ll wa lls. maceration of tissue during blan similar to well cooked fresh vegetables as regard s taste and ching and boiling COlJpled with a granular denaturatio n of consistency. ln this se nse we tried to evaluat e the relati onship of cytoplasm. Drying leads to :J shrinkage and rwis ting o f th e process conditions to cel l ultr-J.stru cturl.! during the proJuction ce lls and clumping of the cy toplasm. Rch yd r.~t cd tissue is of dried vegetables and the ultrastrucrural alterations which characterized by strong cell wall swelling, ma ce ration, and occur during the rehydration process (i.e. cooking) by compa clumping of cy to plasm. t-.·lorphometric measurements of cell ring them with th e ultrastructural mo rphology of well cooked wall thick nesses after re hyd ration showed that various food fresh products. It is hoped by understanding these in terrelati on technological process parameters may strongly in nuence the ships that process conditions can be optimized to obtain d ried appearance of the rehydrated product. and reh}'d ral ed vege tables of high qualit y. There exbts large li terature on the morphological structure o f both vegetables. carrots and green beans. Most of th em were carricll out with the optical microscope, but in recent times the improved resolution power of the electron mil.:roscope was also utilized. Thus opti ca l microscopic studies in the developmental an3tomy of the root of D:1ucus ca rota we re carried out by !Iav is Initial paper received April 6, 1983 . (14), Esau (9) and Drake and Selstam (7, 8). Reck (18) Final manuscript received November 25, 1983. Direct inquiries to M. Grote. published a detailed paper on the optical microscopical Telephone nu mber : (0251) 835125 . struct urc of the plastids in the root. Scanning electron micrographs of raw and cooked ca rro t tissue arc found in the studies by Davis et al. (3 - 6). Trans miss ion electron microscopical papers on th e roots of Daucus ca rota chietl y deal wi th some cytological problems such :1s the structure of chromopla sts (II), nuclei ( 15) or the in vitro culture of ca rrot cells and tissues (28). (For a more detailed list Ke y words: Carro ts, green bean pods. elect ron microscopy, of lit erature sec the above memioned papers). cell structure, fresh and processed vegetables, morphome try. Most of the morphological studies in green bean pods that have so far been carried out were also done with the o ptical microscope. The first to examine the histological structure of th e legumen we re Kraus ( 16) and Stei nbrink (25). Like many of the following authors, some o f whom applied modern tec hniques such as polarisation mi croscopy or X-ray diffraction. they put their emphasis on the morphology of mature pericarps, especially on the structure of th e vascular bundles and fibres in 55 Grote, M. and Fromme, 1-l.G. order to investigate the dehiscence mechanism of the pods ( 10, by two different methods: by a sensory test of donenes; and by 13, 17). measuring the shear strengths of the sam ples mechanicolly (For Roth (22) treats the anatomy of the legumen as part of her further details cf. Bielig and Schwaiger ll J). comprehensive work on the anatomy and histology of the fmi ts For transmiss ion electron micoscopy (TEM), fron fresh, of angiospenns. Gassner (1 2), who deals wi th green beans blanched and rehydrated tissues (rehydrat ion by boilirg) cubes within the sco pe of a general optical microscopical in vestigation of approx. I x I mm size (from the secondary phloer.1 of the of vegetable foodstuffs, also gives some histological carrot root and the outer and inner part , respect information. ively of the green bean pod) were cut ~o.ith a sharp razor blade and flxed in 2% phosphat e buff This is even moTe the case with the detailed studies by ered glutaraldehyde (pH 7. 3) for two houn at room Reeve and Brown (2 1), who provide a survey of the develop temperature. After a short washing with the buffer solu:ion, the mental sequence and di fferentiati on of pod tissues and their samples were postfixcd fo r two hours in buffered ! Po Os04 structure and composition at edible ma turity. solution. They were dehydrated in a graded series of ettanol. In Optica l microscopic studies of the morphological cha nges 70% ethanol, block staining with phosphotungstic acil/uranyl occurring in plant tissues during preparation processes, such as acetate was carried out. After embedding the samples in Epon blanching, cooking, and dehydration/rehydration, have been resin, ultrathin sections were cut with a diamond kniff using a published by a number of authors. Reichert ultramicrotome OmU3. Sections were s1ai ned wi th Thus Simpson and Halliday (24) studied the disintegration lead citrate and examined in a Siemens Elmiskop I. of membrane material in vegetables during the cooking The specimens dried by hot air were briefl y imrrersed in procedure. Reeve and Leinbach (20) and Sterling (26) examined ethanol and then embedded in Epon resin, becwse it had the effect of mOisture and high temperature on carrot, potato, proved impossible to obtain sections from specimms directl y and apple tissues. Reeve (19) published a microscopical study embedded in the resin. o n te xtural structural changes in fresh and processed fruits and For scanning electron microscopy (SEM), fixation and vegetables. dehydration were carried out as described above After the The effects of drying and rehydration on cellulose 100% ethanol stage, the samples were critical-po.nt-dried in crystallinity of carrots were investigated by Sterling and Freon 13 using Freon 11 as a transitional fluid . The dried Shimazu (27). (For more detailed literature see the above specimens we re mounted on specimen holders wit.l "Leit-C", mentioned papers). coated with gold by sp uttering and observed in ! STE REO Transmission electron microscopy has so far not been SCAN Mk 1. employed in a systematic fine-structural investigation of For morphometric measurements of cell wall diameters in prepared and processed vegetables. TEM the semi-automatic image analysis system MOP AM /03 Likewise, the applica tion of morphometrical techniques in (Kontron, Germany) was used. In each test 10 - 15 separate combination with transmission electron mi croscopy of measurements were made on at least three parallel samples from vegetables has so far not been reported in literature. three different ex perim en ts, and the mean Vl lues were In the present study we firs t want to present the basic calculated. For obtaining comparable resu lt s, the po ints of morphologica l changes involved in the blanching, cooking, de measurement on cell walls were defin ed as follovs: midway hydration and rehydratio n of ca rrots and green beans without between two intercell ular spaces taking only thos:! ce ll walls correlating them to speciaJ food technological process condi into considcmtion which were not (yet) separated along their tions. The ultrastructural appearance of the fresh, unprocessed mid dle lamell a. cell s and tissues serves as a baseline for structure. Since the morphological appearance of the boiled raw In the second part of the present paper, we want to an a material was considered to be the " ideal" for a rehydrated lyse systemati call y the influence of special process conditions vegetable, the measured cell wall thickness of the boiled raw on the degree of cell wall swelling, which - in our opinion- is tissue was pu t at 100.