Food Structure Volume 8 Number 1 Article 9 1989 The Effect of Irradiation on Starch Content in Golden Delicious Apples E. Kovacs A. Keresztes Follow this and additional works at: https://digitalcommons.usu.edu/foodmicrostructure Part of the Food Science Commons Recommended Citation Kovacs, E. and Keresztes, A. (1989) "The Effect of Irradiation on Starch Content in Golden Delicious Apples," Food Structure: Vol. 8 : No. 1 , Article 9. Available at: https://digitalcommons.usu.edu/foodmicrostructure/vol8/iss1/9 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. 8 (1989), pp. 67-74 0730-5419/89$3 .00+ .oo Scanning Microscopy International, Chicago (AMF O'Hare), IL 60666 USA THE EFFECT OF IRRADIATION ON STARCH CONTENT IN GOLDEN DELICIOUS APPLES 1 2 E. Kovacs and A. Keresztes 1oepartment of Microbiology, Central Food Research Institute, 1022 Budapest, Herman Ott6 u. 15 . Hungary 2oepartment of Plant Anatomy, EOtvOs Lorand University, 1088 Budapest, MUzeum krt . 4/A Hungary Introduction Starch content in apple (Golden Starch begins . to accumulate in a Delicious) skin and flesh was studied as developing apple fruit 3 to 4 weeks after a function of radiation dose (0, 0.5, 1, bloom . Over the next 2 months it accumu­ 2 and 5 kGy) after 8 weeks shelf life lates to a maximum value and subsequently (l60C, 80-90% RH). declines as the fruit matures. Starch Starch was generally not found in synthesis and decomposition are modified the flesh with the exception of the 5 kGy by different circumstances. Starch is a sample. Starch grains were observed, how­ reserve ~arbohydrate that is eventually ever, in plastids of the epidermis and quantitatively converted to soluble especially in the hypodermis in correla­ sugars, that are stored in the vacuole or tion with the radiation dose. 1 kGy dose metabolized by the cell through respira­ caused a significant effect (P~ 99,98%) tion. on retardation of starch breakdown meas­ Simons and Chu (1982; 1983) investi­ ured by electron microscopic morphometry gated corking, a physiological disorder and chemical analysis. of apples. Cytoplasmic membrane break­ Analysis showed that increasing radi­ down occurred in cortical cells adjacent ation dose increased glucose concentra­ to the vascular bundles at least 45 and' tion in the flesh. In the skin the con­ 60 days prior to fruit maturation . Cell centration of all three sugars, glucose, walls were thick in fruit exhibiting fructose and sucrose, increased with ir­ corking. Starch accumulation occurred radiation up to 2 kGy, but they decreased within l ocalized areas and was attached with higher doses. to the cell walls. Starch grain accumula­ tion on cortical cell walls and prolifera­ tion of starch grains in cells having thick walls was noticed 30 days before maturation (Simons and Chu, 1982; 1983) . Profiles of tissue development and sub­ sequent breakdown indicate that this Initial paper received June 21, 1988 physiological disorder has developed in Manuscript received December 15, 1988 formative and developmental stages of Direct inquiries to E. Kovacs growth, with extensive tissue breakdown. Telephone number: 36-1-152028/157341 Electron microprobe studies provided evidence that both potassium and calcium concentrations were low in all affected tissues, although the potassium level was higher than calcium in most of the sampled areas (Simons and Chu, 1982) . Mahanty and Fineran (1975) investi­ KEY WORDS: apple, shelf-life, irradiation, gated the cellulbr ultrastructure of Identification of irradiation treatment, control and calcium sprayed apples which transmission electron microscopy, ultra­ were cool-stored for 3 months. Cells of structure, chloroplast, amyloplast , starch, the control sample were less well pre­ prolamellar body-like structures, served compared to those of calcium sugar-starch interconversion. sprayed apples. Chromoplasts of the epidermis had prominent plastoglobuliand thylakoids which were scattered or some­ times alveolar rather than compacted. Cells from hypodermis showed increased lysosomal activity. Mitochondria and 67 E. Kovacs and A . Keresztes pl~stids containing starch appeared normal . In the chromoplasts of the calcium sprayed apples, compacted 1a fO(.tJEJJ b£LlCIOUJ thylakoids and plastoglobuli were present . The inner cortical cells had a large central vacuole , and the cytoplasm sur­ rounding this was usually granular and contained numerous plastids with starch . Gamma-irradiation has been reported to increase the sucrose content of potato tubers and s weet pota to roots (Hayashi and Ka wash Jma , 1982a , b ) . Sucrose accumula ­ tion was dep0ndent upon irr adiation dose , and the preferable dos e range was between 1-2 kGy for roots of sweet potato . The sucrose content of irradiated vegetables and fruits increased for a long period after irradiation . It v.•as suggested that an enhanced activity of sucrose synthase and sucrose-phosphate synthase played an important role in the sucrose accumulation in irradiated potatoes (llayashi and Kawashima , 1983 ; Hayas hi and Aoki , 1985 ) . Kovacs and co - workers (1988) inves­ tigated the microstructure of calcium treated and irradiated apples, a short time after treatment and after 3 months ~ubsequent cool storage . All tr~atments (calcium , irradiation , calcium trcatm~nt combined with irradia­ tion ) maintained th~ basic comparlmcn ­ tation of the cells in to cytoplasm, plastids and vacuoles . By con trast , and mainly .in the epidermis , the integ ­ rity of vacuoles had been lost in rhP control by lhe end of storage . Calcium treatment either alone or in combination with irradiation resulted in a som~what better preservation than irradiation alone. Irradiation and combined treatment preserved starch . The difference was ~vident already 4 days after the treat:l'rent , and the effect lasted for at least 3 months . It is known that metabol~c disorders Fig . 1 . Demonstration of starch by ~n apples always cause a decreased starch starch iodine test in apple (Golden breakdown. Early theories on cause of Delicious , stored at 16oc , 80-90\ Rll) bitter pit all were based on starch that a : 5 days after irradiation ; b : 8 weeks remained in the tissue reviewed by Faust after irradiation and Shear ( 1968 ) . The aim of the pr esen t work was to and 5 kGl doses , the dose ra Lc was study the effect of irradiation on t he l kGy . ff ) u sing facilities at the ultrastructure of plastids and the starch­ Instit u t e of Isotopes of Hu ngarian sugar intcrconversion in the apple . An Academy of Sciences . After irradiation , identification method of irradiation samples were stored for 8 weeks ( shelf treatment in apple has also been sought . life at 160C , 80-90% relative humidity ME_erials and Nethods [RH] ) . This tempera lure was chosen to hasten the physiological and biochemical Raw materials and treatments changes . The ripening stages of apple ----;;:ppfes (cv . Golden Delicious) were and the short time effect ( 5 days ) of harvested in an orchard of D~nszentmikl6s irradiation was monitored by the starch Horticultural Station near Budapest , iodine pattern index (Reid ct al . , 1982) Hungary . Harvest time was 100 - 1 10 days {Fig . 1 a . ) . All ultrastructural and following full bloom apples arc harvested chemical investigations were carried out in Hungary in this stage for winter ­ 8 weeks after treatments when the appl e storage . After picking at the green skin was yellow and the starch disap ­ skinned stage fruits were irradiated by peared from the fruit flesh (except a Co - 60 radiation source (0 , 0 . 5 , 1 , 2 5 kGy ) ( Fig . lb ) . 68 The effect of radiation on starch Fig. 2. Ultrastructure of plastids in the epidermis of samples stored for 8 weeks (Golden Delicious appl e ) (a: control; b: lkGy; c : 2kGy ; d: 5 kGy ), s ~ starch grain. Bars = 1 ;urn . Electron microscopy and morhpometry enlarged prints , in 24 - 27 plastids from the outer hypodermis (h - h ) . The \!Olurre Fixation was carried out in 6 % 1 3 of starch grains was expressed as a ~~;~~h~~~t~~~i~~~Y~~ ~:~ ) 0 f~;s2MhK;~a4°C. percentage of plastid volume. After thorough washing in the buffer , petermination of sugar samples were postfixed in 1% (w/v) Os04 for 1.5 h, dehydrated in an acetone 10 g of the skin or flesh sample series and embedded in Spurr ' s resin. was homogenized with 50 ml of 80 % Using flat molds , samples from the skin ethanol for 5 minutes. Each filtrate was were oriented for subsequent transverse evaporated to dryness to remove ethanol , sectioning. then redissolved in 100 ml of water. Sections were cut with a Porter-Blum Each solution was analyzed for soluble ultramicrotome equipped with a diamond sugars by high pressure liquid chroma ­ knife, post - stained with uranyl acetate tography (HPLC) using a LABOR MIM and lead citrate and examined in a (Hungary) apparatus combined with a Tesla BS 500 electron microscope ope.rated Beckman pump (USA) and RI detector _ 5 at 60 kV. (Beckman) , having sensitivity of 2xl0 Starch grains were measured with a square lattice grid superimposed on ~~~x~~~u~) ~a~p;~~~~~i~~NH 250 ~~~~~h 69 E . Kovacs and A. Keresztes acetonitrile-water ( 75 : 25 ) as mobile phase at 1 ml.min-1 flow rate. ~etermination of starch 5 g of skin or flesh of apple was horrogenized with 100 ml of 1 N HCL for 5 minu tes . The homogenate was refluxed on a boiling water bath for 3 hours, made up to 1000 ml , glucose determined by HPLC and expressed as starch . Results a nd Discussio n The skin of stored apples examined after different radiation doses showed several ultrastructural changes. Data concerning the epidermis and hypodermis will be evaluated separately. Plastids in the epidermis of the control sample were roundish with many electron ­ translucent vesicles .