Food Structure Food Structure

Volume 9 Number 4 Article 3

6-9-1990

Microstructure of Peanut Seed: A Review Microstructure of Peanut Seed: A Review

Clyde T. Young North Carolina State University

William E. Schadel North Carolina State University

Follow this and additional works at: https://digitalcommons.usu.edu/foodmicrostructure

Part of the Food Science Commons

Recommended Citation Recommended Citation Young, Clyde T. and Schadel, William E. (1990) "Microstructure of Peanut Seed: A Review," Food Structure: Vol. 9 : No. 4 , Article 3. Available at: https://digitalcommons.usu.edu/foodmicrostructure/vol9/iss4/3

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 digitalcommons@usu.edu.

FOOD STRUCTURE, Vol. 9 (1990), pp. 317-328 1 046-705X/90$3.00 + .00 Scanning Microscopy International, Chicago (AMF O'Hare), IL 60666 USA

MICROSTRUCTURE OF PEANUT SEED: A REVIEW

Clyde T. Young and William E. Schadel

Department of Food Science North Carolina State University

Raleigh, NC 27695-7624

Abstract

Mature peanut seed microstructure of importance to the food industry is examined with regard to: (1) anatomy and cytology of peanut seed; (2) the effects of environment on peanut seed; and (3) the effects of various processing procedures on peanut seed. Current peanut seed microstruc­ture research by the authors is directed toward evaluation of the quality of processed peanuts including using TEM, SEM and LM to evaluate the effects of different times of oven roasting at the same temperature, and a method for evaluat­ing quality of homogenization of broken cell and tissue frag­ments, protein bodies and starch in stabilized peanut butter.

Initial paper received June 9, 1990 Manuscript received October 22, 1990 Direct inquiries to C.T. Young Telephone number: 919 737 2964

Key Words: Arachis hypogaea L., anatomy, cytology, light microscopy, scanning electron microscopy, transmission electron microscopy

317

Introduction

Peanut seed microstructure can be affected by such factors as: (1) peanut seed maturity; (2) environmental condi­tions under which the peanuts are grown; and (3) processing by the food industry. All three of these factors impact the microstructural characteristics that affect the quality of processed peanuts.

In this paper we review the literature of peanut seed microstructure of importance to the food industry. Although there are numerous microstructural investigations of the earlier stages of peanut seed development, here we examine only the mature peanut seed microstructure. References to investigations of earlier stages of development are summarized in the appendix and included in the bibliography.

Anatomy and Cytology of Mature Peanut Seed

According to Woodroof (1983), maturity of peanut is important because quality grades are dependent on factors re­lated to maturity. Seed maturity is highly significant to the food industry because seed size, flavor, texture and color are influenced by it.

\Voodroof and Leahy (1940) describe the mature pea­nut seed (Fig. 1) as having a seed coat which contains five kinds of cells: (1) outer epidermis; (2) spongy parenchyma; (3) vascular bundles; (4) inner epidermis and (5) perisperm. After the peanut seed matures, the seed coat (skin) has no cellular connection with the cotyledons. The seed coat is tougher and has a more heavily cutinized epidermis than the embryo and protects the embryo from mechanical damage.

The embryo or germ of the mature peanut seed con­sists of two cotyledons, a small radicle and a plumule (Fig. 2). Processors are chiefly concerned with the tissue of the peanut seed cotyledons which constitutes about 96% of the seed weight; the radicle and plumule ( 4% of seed weight) are removed in commercial blanching.

Each peanut seed cotyledon consists of epidermal, vascular and parenchyma tissue. The epidermal tissue is made up of a single layer of cells covering the surface of the cotyledon. The epidermal cells of the rounded outer surface are more or less rectangular in outline (Fig. 3). The epidermal cells of the inner surface are irregular in outline and additionally contain numerous guard cells and stomatal

C.T. Young and W.E. Schadel

1 -

Figure 1. Mature peanut with seed coat. Bar = 1.5 mm.

Figure 2. Mature peanut with seed coat removed (left) and with seed separated (right) into one of its two cotyledons. Note the rounded outer surface (left) and the indented inner surface (right) which has the radicle and plumule (arrow) intact. Bar = 3 mm.

Figures 3 and 4. Scanning electron micrographs (SEM) of the epidermal cells of a peanut cotyledon. Figure 3: Outer rounded surface. Figure 4. Sunken areas (arrows) where guard cells and stomata occur on the inner surface. Bars = 20 ftm.

openings (Fig. 4). The vascular tissue of the peanut seed extends through

each cotyledon of the embryo. Woodroof and Leahy (1940) described the vascular system as composed of two series, one series of six to eight bundles that follow the curvature of the outer surface, with another series of four to six centrally located bundles. This vascular tissue (Fig. 5) comprises only a small part of the total volume of each cotyledon.

The majority of the tissue of the cotyledon is made up

318

of rather large, nearly isodiametric, parenchyma cells (Fig. 6). A cytoplasmic network (Fig. 7) extends throughout each parenchyma cell and surrounds the other subcellular organel­les. The pitted walls of parenchyma cells from the resting seed have conspicuous depressions (Fig. 8). These pitted walls have been previously described (Woodroof and Leahy, 1940; Vaughan, 1970; Yatsu, 1981; Schadel et al., 1983).

The major subcellular organelles of the parenchyma cells are lipid bodies, protein bodies and starch grains. The

Microstructure of Peanuts

8 -Figure 5. SEM of cross-section of the vascular tissue (arrows) comprising a small part of each cotyledon. Bar = 50 J.Lm.

Figure 6. Light micrograph of a cross-section of the parenchyma cells comprising the majority of the tissue of a peanut cotyledon. Note the protein bodies (p), starch grains (s) and cytoplasmic network (c) which delimits the spaces once occupied by lipid bodies (alcohol dehydration during specimen preparation removed the lipids) . Bar = 20 J.Lm.

Figure 7. SEM of a cross-section of the cotyledon network within a parenchyma cell in the mid-region of a peanut cotyledon. The cytoplasmic network (arrows) demarcates the spaces once occupied by lipid bodies. Bar = 2 J.Lm.

Figure 8. Transmission electron micrograph (TEM) of cross-section of a cell-to-cell junction with pit regions (arrows) between parenchyma cells in the mid-region of a peanut cotyledon. Bar = 0. 75 J.Lm.

transmission electron microscope has been used by Jacks et al . (1967) and Yatsu and Jacks (1972) to characterize the lipid bodies as particles about 1-2 micrometers in diameter bounded by a half unit-membrane (Fig. 9) which measures 2-3.5 nanometers in width.

The protein bodies (Fig. 10) of mature peanut seed

319

range from 5-12 micrometers in diameter. Bagley et al. (1963) studied protein bodies during germination of peanut seed and concluded that there is an ordered series of events leading to the degradation of storage protein in cotyledonary cells during germination.

Starch grains (Fig.ll) of mature peanut seed range

C. T. Young and W. E. Schadel

11 -Figure 9. TEM of cross-section of a parenchyma cell in the mid-region of a peanut cotyledon. Note the lipid body membranes (arrows) along the cell wall. Bar = 0. 75 J.Lm.

Figure 10. TEM of a cross-section of a protein body (P) within a parenchyma cell in the mid-region of a peanut cotyledon. Note the checkered matrix created by electron dense and electron transparent areas of the protein body. Bar = 0. 75 J.Lm .

Figure 11. TEM of a cross-section of a starch grain (S) within a parenchyma cell in the mid-region of a peanut cotyledon. Note the hilum (arrow) and the electron dense nature of the starch grain. Bar = 0.5 J.Lm.

Figure 12. SEM of the inner surface of a drought-damaged peanut cotyledon with rough and irregular edges (arrow) due to tissue damage. Bar = 1.0 mm.

from 4-15 micrometers in diameter and are characterized by a central hilum. Bagley et al. (1963), in a germination study, noted that by 15 days the parenchyma cells still con­tained numerous starch grains although all protein bodies had degraded by that time.

320

Effect of Environment on Peanut Seed Microstructure

Poor environmental condition can affect peanut seed microstructure by damaging the structural integrity of the tissue. Drought-induced damage to peanut seed cotyledons has been reported by Young and Schadel ( 1984, 1989).

Microstructure of Peanuts

1mm

............ 4J~~ 16 l

Figure 13. SEM of the rounded outer surface of a drought-damaged peanut cotyledon with tissue damage (arrows) which appear as spotting. Bar = 1.0 mm.

Figure 14. SEM of the rounded outer surface of a drought-damaged peanut cotyledon with fissures from which cellular contents have extruded. Note the spherical thickened mass of extruded cellular contents (arrow). Bar = 50.0 J.tm .

Figure 15. Light micrograph of a cross-section of the outer surface of a drought-damaged peanut cotyledon with tissue damage. Note the extruded cellular content (arrow). Bar = 20.0 J.tm.

Figure 16. Electron probe microanalyzer linescan of calcium distribution (below the photograph, intensity being proportional to the amount of calcium) in a developing Florunner peanut inside its pod. The solid white line indicates the scanned area of the pod (pod) which surrounds the testa (T) which likewise surrounds the two developing cotyledons (cots). Note higher calcium concentration in the pod and testa. Bar = 1.0 mm. (Photo supplied by Craig Kvien).

Drought-induced damage includes: (1) tissue damage which appears as a narrow band along the interface of the rounded outer surface and the flattened edge of the inner surface (Fig. 12); and (2) tissue damage which appears macroscopically as spotting on the outer surface (Fig. 13) of the cotyledon. The

321

spotting is a result of cracking and fissuring of parenchyma tissue (Figs. 14 and 15).

Poor environmental conditions can also seriously af­fect peanut seed structural integrity when peanut pods which contain the peanut seeds cannot develop properly. According

C.T. Young and W.E. Schadel

to Smal et al. (1989), developing pods need to absorb ade­quate amounts of calcium from the soil in order to maintain healthy shells. Smal et al. (1989) studied solution calcium concentration and application date effects on pod calcium up­take and distribution (Fig. 16) in two peanut cultivars differ­ing in shell and seed size. It was determined that large pods with thick, dense shells required higher calcium concentration in the soil to achieve the same seed calcium level as small, thin-shelled peanuts. Peanut cotyledon will not develop when when the calcium level is too low.

Peanut pods are also in close contact with many dif­ferent soil organisms which can destroy the structural integri­ty of the pods and seeds (i.e. physical decay). Garren and Jackson (1973) state that three potential pod rot fungi -Sclerotium rolfsii Sacc., Pythium myriotylum Drechs., and Rhizoctonia solani Kuhn - cause extensive pod rot damage in a majority of the peanut growing regions of the world. An­other fungus, Aspergillus flavus Link, produces aflatoxin, which is a potent mycotoxin and carcinogen. Pettit et al. (1976) believe that one solution to the pod rot and mycotoxin problem is to develop disease resistant varieties. Initial microscope studies were directed towards discovering peanut seed coats which could resist fungal invasion (Dieckert et al., 1973; Taber et al., 1973). These studies revealed differences in the compactness of cell layers and type of wax deposition on the seed coats. Other studies have been conducted to identify features of peanut pods which could function as bar­riers to fungal invasion (Pettit et al., 1975; 1976; 1977) The most resistant pods contained compact sclerenchyma (sclereid) bands within the mesocarpic tissues.

Effect of Processing on Peanut Seed Microstructure

Woodroof and Leahy ( 1940) described peanut process­ing as the use and control of moisture, temperature, pressure, mechanical disintegration and solvents to increase the eco­nomic value of the peanuts. The application of such proce­dures involves process-specific conditions, whether peanuts are to be roasted, blanched, made into peanut butter, used in confection, pressed for oil, or treated for the recovery of proteins.

The most extensive light microscope studies on the ef­fects these procedures have on peanut are by Woodroof and Leahy (1940). They studied the effects of numerous proc­esses on peanut seed cells. In that study, they tabulate the changes in cells when peanut were processed by six different methods: (1) grinding or rolling almost to the fineness of peanut butter; (2) cooking at 250°F (121 °C) in presence of high moisture; (3) dry roasting at 300°F (149°C); (4) roast­ing in oil at 280°F (138°C); (5) cold pressing at ordinary temperatures and a pressure of 5000 to 7000 pounds per square inch (psi); and (6) hot pressing at 250°F (121 °C) or higher and a pressure of 5000 to 7000 psi. The results of their study are summarized in Table 1.

With the availability of TEM and SEM (transmission and scanning electron microscopes) other investigators were able to study the effects of processing on the ultrastructure of peanut products. Vix et al. (1972) used TEM to examine the ultrastructure of partially defatted peanuts after hydraulic pressing. They noted that lipid body membranes were bro-

322

ken, cell walls were compressedl and protein bodies were coalesced by pressure. This process for making partially de­fatted peanuts consists of: (1) hydraulically pressing deskin­ned (blanched) peanuts to remove oil; (2) expanding the peanuts in boiling water; (3) drying; and (4) roasting (Vix et al., 1967; Pominski et al., 1970a, b). Yatsu (1981) used SEM to study the cell walls of peanut cotyledons in peanut lots which required an unusual amount of pressure to express the oil. He concluded that cell wall material itself could not account for the extra pressure required by difficult-to-press peanuts. Schadel et al. (1983) investigated the cotyledon structure of peanut seed before and after hydraulic pressing and determined that escape of oil from the parenchyma cells (Fig. 17) was facilitated by surface fissures (Fig. 18) of the pressed cotyledons.

Young and Schadel (1990a) investigated the micro­structure of oven-roasted peanuts (160°C, 16 min) using light microscopy (LM) and SEM. After roasting, the cytoplasmic network was disrupted, lipid bodies were burst and protein bodies were distended (Fig. 19 - compare with Fig. 6). Other thermal modifications of roasting including pitting and pock-marking of the epidermis of cotyledons and heat de­struction of some middle lamellae of cell-to-cell junctions. Young and Schadel (1990b) also investigated the microstruc­ture of oven-roasted peanuts (160°C, 16 min) using SEM and TEM. The better resolution of TEM enabled clearer docu­mentation of thermal modifications of roasting on cell walls (Fig. 20).

The effects of oil cooking on peanut seed microstruc­ture were evaluated by Young and Schadel (1990c) using TEM, SEM and LM. Many of the thermal modifications of oil cooking were determined to be similar to oven-roasting. For example, decreased electron stain affinity of starch grains (Fig. 21) was observed in oil-cooked as well as in oven­roasted peanuts.

Our current research (unpublished findings) includes using TEM, SEM and LM to evaluate the effects of different times of oven roasting at the same temperature. By examin­ing peanut microstructure after timed intervals of roasting at 160°C, such as 7, 13 and 16 minutes (Figs. 22, 23 and 24, respectively), we are able to determine the extent of increase in thermal modifications (e.g., presence of cell wall separa­tion; degree of protein body distension; range of cytoplasmic network disrupted) that occurred for each increased roasting time period.

Although we use primarily SEM and TEM to evaluate the effects of oil cooking and oven roasting on peanut seed microstructure, F.O. Flint (Univ. Leeds, personal communi­cation) notes that the light microscope can be a useful tool in examining microstructural features, such as starch grains, after oil cooking or oven roasting. Flint has observed, for example, that the retention of birefringence in starch grains (Fig. 25) of oil-cooked peanuts indicated the absence of ther­mal damage. Young and Schadel's work with the light micro­scope (unpublished findings) also indicated little thermal damage to starch grains after oil cooking at 160°C for 12 min (Fig. 26) or oven roasting at 160°C for 16 min (Fig. 27) since many of the starch grains retained a visible hilum.

Recently we (Young and Schadel, 1990d) have devel­oped a method for evaluating the quality of homogenization

Microstructure of Peanuts

Figure 17. SEM of a cross-section of parenchyma cells of a hydraulically pressed peanut cotyledon. Note the absence of the distinct cytoplasmic network. Bar = 20.0 p.m.

Figure 18. SEM of the rounded outer surface of a hydraulically pressed peanut cotyledon. Note the fissures (arrows) along the epidermal cell caused by hydraulic pressing. Bar = 20.0 p.m.

Figure 19. Light micrograph of a cross-section of the parenchymal cells in a roasted peanut cotyledon. Note the distended protein bodies (P) and starch grains (S). Bar = 20.0 p.m.

Figure 20. TEM of a cross-section of a cell-to-cell junction of parenchymal cells in a roasted peanut cotyledon. Observe that thermal modification has caused the disintegration (arrow) of the middle lamellum. Bar = 0.25 p.m.

of microstructural features of stabilized peanut butter. This method makes it possible to determine the completeness of homogenization of broken cell and tissue fragments, protein bodies and starch grains within the matrix of stabilized oil (Fig. 28).

323

Future Research

Suggestions for additional research on the effects of processing on peanut seed microstructure include:

(1) characterization of the surface structure of raw cotyledons as this relates to ease of blanching (skin removal);

C. T. Young and W. E. Schadel

Figure 21. TEM of a cross-section of a starch grain within an oil-cooked peanut cotyledon. Note the electron transparent nature of some regions (arrows) of the starch grain. Bar = 0.5 J.'m.

Figures 22-24. SEM of cross-sections of parenchyma cells in the mid-region of a peanut cotyledon after 7 minutes (Figure 22), 13 minutes (Figure 23) and 16 minutes (Figure 24) of oven roasting at 160°C. Bars = 10.0 J.'m.

(2) determining advantages or disadvantages of diffe­rent cooking methods such as microwave or infrared;

(3) evaluating optimum cooking rates that induce the least physical damage; and

(4) examining surface changes during cooking which may facilitate adhesion of coatings for peanut products.

Appendix - Additional References

For general peanut anatomy and cytology Badami, 1935.

324

Bagley et al., 1963 . Banerji, 1938. Conagin, 1957. Dieckert and Snowden, 1960. Gerassimova-Navashina, 1959. Jacks et al., 1967. Mohammed et al., 1933. Moss et al., 1988. Pattee and Mohapatra, 1986, 1987. Pattee et al., 1983, 1988. Periasamy and Sampoorham, 1984.

Microstructure of Peanuts

Figure 25. Polarized light micrograph of a cross-section of oil-cooked peanut showing distribution of starch which retains birefringence after roasting. Bar = 20 fLm . (Photograph kindly provided by Dr. F. Olga Flint, Univ. Leeds, U.K.).

Figures 26-27. Light micrographs of parenchyma cells in the mid-region of peanut cotyledons after 12 minutes of oil cooking (Figure 26) and 16 minutes of oven roasting (Figure 27) at 160°C. Note the visible hilums of the starch grains (arrows). Bars = 20 l-im (Figure 26) and 10 l-im (Figure 27).

Figure 28. Light micrograph of a cross-section of stabilized peanut butter with complete homogenization of microstructural features. Note that broken cell wall fragments (purple), protein-bodies (red), and starch grains (white) are well-dispersed in a matrix of stabilized oil (grey). Bar = 10 fLI11.

Pettit, 1895. Reed , 1924. Schenk, 1961. Shibuya, 1935. Smith , 1950, 1956a, 1956b.

325

Thomas et al., 1983. Vaughan, 1970. Waldron, 1919. Webb and Hansen, 1989. Winton, 1904.

C.T. Young and W.E. Schadel

Table 1: Changes in cells when peanuts were processed (from Woodroof and Leahy, 1940) .

Cells and Inter-Processing cell cellular Nucleus Aleurone Grains Oil Droplets Starch

walls spaces grains

Grinding About 50% No No change Relatively few were When the cells were Some were or rolling of cells change when cells crushed. Most of them crushed, the oil drop- crushed, almost to ruptured & when were un- rolled about independ- lets ran together to while most fineness emptied of cells injured, ently even when the form larger drops of of them of peanut contents, were otherwise cell wall was severely free oil. If cells were not. butter. many others un- it was crushed. were not crushed , no

were merely injured. crushed. change occurred in crushed, oil droplets. while from 10-25% were uninjured.

Cooking Turgidity Almost Coagulated , Completely separated, Fusing of some droplets Apparently at 250°F destroyed; elimi- granular, scattered throughout to form fewer and larger destroyed (121 °C) cell walls nated. centrally cell and a few become droplets within cells. or in become located but lopsided . Total size A few drops of free oil dissolved . presence slack, but tended to and number unchanged. appeared in each cell. of high only a few break up. Viscosity of oil moisture. were broken. greatly lowered.

Dry Cell walls No Coagulated Drawn away from cell Fused into larger and Remained roasting remained change. into hard walls into hard mass fewer droplets within same in at 300°F unchanged. mass in around nucleus. The the cells. Small amount number and (149°C). center of number and size of of oil escaped into the slightly

cell. grains was little cell as free oil. Cell reduced changed. Proteins were walls and skins became in size. precipitated and very oil -soaked. granular.

Roasting No No Coagulated Few grains were normal Due to absorption of No in oil apparent change. but almost size, most of them were oil from cooking bath apparent at 280°F change. indistinct swollen 3 to 4 times and consequent swelling, change. (138°C). due to original size due to the original oil droplets

crowding absorption of oil. They lost their identity. in cell. were precipitated and

very granular. Crowding in cells causes some grains to be distorted.

Cold Most of None. Crushed. Mashed and distorted but When the cells were Crushed. pressing cells many of them retained crushed, the oil droplets at ordinary completely their original identity. ran together forming temperature crushed. drops of free oil. If and 5 000- cells were not crushed , 7000 psi no change occurred in pressure. oil droplets.

Hot press- Crushed. None. Crushed . Crushed. Viscosity of oil made Crushed. ing at 250°F very low. All droplets (121 °C) or fused into drops of higher and free oil. 5 000-7000 psi pressure.

326

Microstructure of Peanuts

Woodroof, 1983. Yarbrough, 1949. Yatsu and Jacks, 1972.

For effects of environment on peanut microstructure Dieckert et al., 1973. Garren and Jackson, 1973. Pettitetal., 1975,1976,1977. Smal et al., 1989. Taber et al., 1973. Young and Schadel , 1984, 1989.

For effects of processing on peanut microstructure Mikola et al., 1975. Pominski, et al. 1970a, 1970b. Schadel et al., 1983. Vix et al., 1967, 1972. Woodroof and Leahy, 1940. Yatsu , 1981. Young and Schadel, 1990a, 1990b, 1990c, 1990d.

References

Badami VK (1935). Botany of groundnut. J. Mysore Agric. and Exp. Union .12:59-70.

Bagley BW, Cherry JH, Rollins ML, Altschul AM (1963). A study of protein bodies during germination of peanut (Arachis hypogaea L.) seed. Am. J. Bot. 50:523-532.

Banerji I (1938). A note on the embryology of the groundnut (Arachis hypogaea L.) . J. Bombay Nat. Hist. Soc. 40:539-543.

Conagin CHT ( 1957). Cytology and seed develop­ment in peanut plant. Bragantia 16:15-33 .

Dieckert JW, Dieckert MC, Pettit RE, Benedict CR, Ketring DL (1973). Comparison of Aspergillus flavus tole­rant and susceptible peanut lines. II. Electron microscopy. J. Am. Peanut Res. and Educ. Assoc. 5.:207-208.

Dieckert JW, Snowden JE (1960). Subcellular distri­butions of substances in seeds of Arachis Hypogaea. Fed . Proc. 19:126-127.

Garren KH, Jackson CR (1973). Peanut diseases. In : Peanuts- Culture and uses , Wilson CT (ed .), Stone Printing Co. Roanoke, Virginia , pp 429-494 .

Gerassimova-Navashina EN (1959). Embryological observations on Arachis hypogaea. Bot. Zh . 44:1453-1466.

Jacks TJ, Yatsu LY, Altschul AM (1967). Isolation and characterization of peanut spherosomes. Plant Physiol. 42:585-597.

Mikola J , Yatsu L Y, Jacks TJ, Hebert JJ ( 1975). Disruption of certain aleurone grains by various homogeniza­tion agents. Plant Cell Physiol. 16:933-937.

Mohammed A, Zafar A, Kidor LK (1933). Studies on germination and growth in groundnut (Arachis hypogaea L.) Agric. Live-stock India J:91-115.

Moss JP , Stalker HT, Pattee HE (1988). Embryo res­cue in wide crosses in Arachis. 1. Culture of ovules in peg tips of Arachis hypogaea. Ann. Bot. 61: 1-7.

Pattee HE, Mohapatra SC (1986). Hypanthium and style senescence in relation to ovary development in Arachis hypogaea L. Bot. Gaz. 147:302-311.

Pattee HE, Mohapatra SC (1987) . Anatomical changes during ontogeny of the peanut (Arachis hypogaea L.)

327

fruit: Mature megagametophyte through heart-shaped embryo. Bot. Gaz. 148:156-164.

Pattee HE, .Mohapatra SC, Agnello EK (1983). Spe­cimen preparation techniques for scanning electron micros­copy of developing peanut pegs. Peanut Sci. 10:93-97.

Pattee HE, Stalker HT, Moss JP (1988). Embryo res­cue in wide crosses in Arachis. 2. Embryo development in cultured peg tips of Arachis hypogaea. Ann. Bot. 61:103-112.

Periasamy K, Sampoorham C (1984). The morpholo­gy and anatomy of ovule and fruit development in Arachis hypogaea L. Ann. Bot. 53:399-411.

Pettit AS (1895). Arachis hypogaea L. Mem. Torrey Bot. Club 1:275-296.

Pettit RE, Taber RA, Smith OD, Boswell TE (1975). Structural features of peanut pods: Arachis hypogaea culti­vars. J. Am. Peanut Res. and Educ. Assoc. 1:91-99.

Pettit RE, Taber RA, Ives PJ, Thurston EL, Smith OD, Boswell TE (1976). Peanut pods: Structural difference among cultivars as revealed by scanning electron microscopy. Scanning Electron Microsc. 1976;II:505-512.

Pettit RE, Taber RA, Smith OD, Jones BL (1977). Reduction of mycotoxin contamination in peanuts through re­sistant variety development. Ann . Technol. Agric. 27:343-351.

Pominski J, Pearce HM, Spadaro JJ (1970a). Partial­ly defatted peanuts - factors affecting oil removal during pressing . Food Technol. 24(6):92-94.

Pominski J, Pearce HM, Spadaro JJ (1970b) . Factors affecting water solubles of partially defatted peanuts. Food Technol. 24(9):76-79.

Reed EL (1924) . Anatomy, embryology and ecology of Arachis hypogaea. Bot. Gaz. 78:289-310.

Schadel WE, Walter WM, Young CT (1983). Cotyledon structure of resting peanut (Arachis hypogaea L. cv. Florunner) seed before and after hydraulic pressing. J. Food Sci. 48:1405-1407.

Schenk RU (1961). Development of the peanut fruit. Georgia Exp. Sta. Tech. Bull. , N.S. 22:1-53.

Shibuya T (1935). Morphological and physiological studies on the fructification of peanut (Arachis hypogaea L.) Mem. Fac. Sci. Agric. Taihoku Imp. Univ . 17:1-120.

Smal H, Kvien CS , Summer ME, Csinos AS (1989). Solution calcium concentration and application date effects on pod calcium uptake and distribution in Florunner and Tifton-8 peanut. J. Plant Nutr. .12:37-52.

Smith BW (1950). Arachis hypogaea. Aerial flower and subterranean fruit. Am. J. Bot. 37:802-815.

Smith BW (1956a). Arachis hypogaea. Normal Mega­sporogenesis and syngamy with occasional single fertilization . Am. J. Bot. 1J:81-89.

Smith BW (1956b). Arachis hypogaea. Embryogeny and the effects of peg elongation upon embryo and endo­sperm growth. Am. J. Bot. 43:233-240.

Taber RA, Pettit RE, Benedict CR, Dieckert JW, Ketring DL (1973). Comparison of Aspergillus flavus tole­rant and susceptible peanut lines. I. Light microscopic inves­tigation. J. Am. Peanut Res. and Educ. Assoc. 5.:206-207.

Thomas RJ. Pettit RE, Taber RA, Jones BD (1983). Peanut peg strength: Force required for pod detachment in

C.T. Young and W.E. Schadel

relation to peg structure. Peanut Sci. 10:97-101. Vaughan JG (1970). Groundnut or peanut (Arachis

hypogaea L.). In: The Structure and Utilization of Oil Seed, Vaughan JG (ed.), Richard Clay (The Chaucer Press) Ltd., U.K. pp. 129-133.

Vix HLE, Porn in ski J, Pearce HM, Spadaro JJ (1967). Development and potential of partially defatted peanuts. Peanut J. and Nut World ~(3):10-11.

Vix HLE, Gardner HK, Lambou MG, Rollins ML (1972). Ultrastructure related to cottonseed and peanut processing and product. In: Symposium: Seed Protein, Inglett GE (ed.), AVI Pub. Co., Westport, Connecticut, pp. 223-227.

Waldron RA (1919). The peanut (Arachis hypogaea) -its history, histology, physiology, and utility. Contrib. Bot. Lab. Univ. Pennsylvania ~:301-338.

Webb AJ, Hansen AP (1989). Histological changes of the peanut (Arachis hypogaea) gynophore and fruit surface during development and their potential significance for nutrient uptake. Ann. Bot. 64:351-359.

Winton AL (1904). The anatomy of the peanut with special reference to its microscopic identification in food products. Conn. Agric. Exp. Sta. Report for the Year 1904:191-198.

Woodroof JG (1983). Peanuts: Production, Proc­essing, Products. A VI Pub. Co., Westport, Connecticut, pp. 99-101.

Woodroof JG, Leahy JF (1940). Microscopical studies of peanuts with reference to processing. Georgia Exp. Sta. Bull. No. 205:1-39.

Yarbrough JA (1949). Arachis hypogaea. The seed­ling, its cotyledons, hypocotyl and roots. Am. J. Bot. 36:758-772.

Yatsu L Y (1981). Cell wall architecture of peanut (Arachis hypogaea L.) cotyledon parenchyma cells and resis­tance to crushing. J. Am. Oil Chern. Soc. 58: 148A-150A.

Yatsu LY, Jacks TJ (1972). Spherosome membranes. Plant Physiol. 49:937-943.

Young CT, Schadel WE (1984). Effect of environ­ment on the physical structure of peanut (Arachis hypogaea L.). Food Microstruct. :1:185-190.

Young CT, Schadel WE (1989). A method for light and scanning electron microscopy of drought-induced damage of resting peanut seed tissue. Food Microstruct. ~:253-256.

Young CT, Schadel WE (1990a). Light and scanning electron microscopy of the peanut (Arachis hypogaea L. cv. Florunner) cotyledon after roasting. Food Struct. 2:69-73.

Young CT, Schadel WE (1990b). Transmission and scanning electron microscopy of peanut (Arachis hypogaea L. cv. Florigiant) cotyledon after roasting. Food Struct. 2:109-112.

Young CT, Schadel WE ( 1990c). The microstructure of peanut (Arachis hypogaea L. cv. Florigiant) cotyledons after oil cooking. J. Food Sci. accepted for publication.

Young CT, Schadel WE (1990d). A method for the examination of the microstructure of stabilized peanut butter. Food Struct. 2:105-108.

328

Discussion with Reviewers

Y.C. Hung: How much thermal modification is needed for peanuts during roasting in order to provide good eating quality? Authors: Thermal modification of peanuts during roasting creates chemical as well as physical changes. When peanuts are roasted, amino acids combine with sugars to form flavor components of roasted peanuts. The production of these fla­vors combined with textural changes resulting from thermal modification of microstructure is optimal after roasting peanuts for 16 minutes at 160°C.

R.A. Taber: Can you, at this point in your research pro­gram, relate changes in cv. Florunner seed to changes in Spanish peanut cultivars after roasting? Authors: Changes in peanut microstructure after roasting ap­pear to be related to size and shape of cotyledons. As size and shape of cotyledons vary among cultivars, we believe rates of thermal modification also will vary. Roasting studies of cultivars that are smaller than cv. Florunner (e.g., Spanish peanuts) are best for testing this hypothesis.

R.A. Taber: Do the temperatures reached during roasting impact on the cuticular waxes such that they enter the seed coat? Authors: Structural observations reveal that the .epidermis which contains the cuticular waxes becomes pitted and pock­marked during roasting. We have not yet done histochemical tests for waxes in the seed coats to determine if the waxes enter the seed coat after roasting.

R.A. Taber: Could SEM X-ray microanalysis provide some helpful additional information concerning differences in element distribution in treated and untreated seeds? Authors: Qualitative and quantitative elemental analysis using SEM should provide additional helpful information concerning the differences in treated and untreated seeds. However these methods have yet to be extensively applied in the studies of peanuts.

R.A. Taber: It would be helpful to have more detailed comparisons between effects on structures of roasted versus oil cooked peanuts. Authors: We have recently completed an investigation com­paring the effects on structures of roasted and oil cooked peanut seeds and are currently working on the manuscript for publication.