Food Structure
Volume 11 Number 2 Article 9
1992
Microstructural Differences Among Adzuki Bean (Vigna Angularis) Cultivars
Anup Engquist
Barry G. Swanson
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Recommended Citation Engquist, Anup and Swanson, Barry G. (1992) "Microstructural Differences Among Adzuki Bean (Vigna Angularis) Cultivars," Food Structure: Vol. 11 : No. 2 , Article 9. Available at: https://digitalcommons.usu.edu/foodmicrostructure/vol11/iss2/9
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MICROSTRUCTURAL DIFFERENCES AMONG ADZUKI BEAN (Vigna angularis) CULTIVARS
An up Engquist and Barry G. Swanson Department of Food Science and Human Nutrition Washington State University, Pullman, WA 99164-6376
Abstract Introduction
Scanning electron microscopy (SEM) was used to Adzuki beans are one of the oldest cultivated beans study mi crostructural differences among five adzuki bean in the Orient, often used for human food, prepared as a cultivars: Erimo, Express, Hatsune, Takara and VBSC. bean paste used in soups and confections (Tjahjadi and Seed coat surfaces showed different patterns of cracks , Breene, 1984). The starch content of adzuki beans is pits and deposits . Cross-sections of the seed coats re about 50 %, while the protein content ranges between vealed well organized layers of elongated palisade cell s 20%-25% (Tjahjadi and Breene, 1984) . followed by many layers of amorphous parenchyma cells. Typical sub-epidermal layers of organized colum Adzuki beans are a major crop consumed in Japan, nar, hour-glass cells were characteristica11 y absent in the China, and other oriental countries (Sacks, 1977). In five cultivars of adzuki beans. The cross-sections of the Japan most adzuki beans are used in the form of sweet cotyledons revealed intercellular materials between stor ened paste called "An" in many confections, candies, age cells. Storage cell s in Hatsune cultivar were loosely cakes and ice cream (McClary eta/., 1989) . Between packed with many intercellular spaces as compared to 1980 and 1989 about 27% of the adzuki beans consumed the other four cultivars. Cross-sections of storage cells in Japan was provided by imports (McClary et a/., revealed starch granules embedded in protein matrices. 1989). Thus, a very promising future market exi sts in The protein matrix appeared more granular in cultivars Japan for Washington grown adzuki beans. Erimo and VBSC and less granular in cuhivars Express, Hatsun e and Takara. Flours of the five cultivars were Consumer acceptance is an important aspect of examined under SEM to photograph individual starch marketing adzuki beans. Japanese consumer acceptance granul es and protein matrices. Starch granule shape was for adzuk.i beans and substitutes depends upon the characteristic to each cultivar: spherical in Erimo distinct color and shape of the bean and the end use in cultivar, spherical to irregular in Express and Hatsune various foods (McClary eta/., 1989). The size, shape, cultivars, highly irregular to slightly spherical or oval in color and nutritional quality of adzuki beans vary among Takara cultivar, and oval to spherical in VBSC cultivar. different cultivars of adzuki beans (Hsieh, 1991). No grooves or fi ssures were observed in Erimo or Factors such as appearance, functi onal and textural V BSC starch granules. Shallow grooves were observed properties, organoleptic and nutritional qualities, and the on the starch granules of Express and Hatsune cultivars. price of a particular cultivar of ad zuki beans determine A characteristic deep fissure was observed in starch the potential as a marketable crop in the Japanese granules of the Takara cultivar. The characteristic deep market. fissure on starch granules may be used as an identifying feature for Takara cultivar. Microstructural variations can be related to textural, chemical and physical variations among bean cultivars Key words: Adzuki beans, cultivars, seed microstruc (Sefa-Dedeh and Stanley, 1979). Microstructural varia ture, scanning electron microscope, seed coat, storage tions were used to identify different cultivars of soy cell s, starch granules, protein matrix . beans (Wolf et a/., 1981). Scanning elec tron mi cros copy (SEM) is a technique recently employed in various st udies of food microstructure (Swanson et a/., 1985). Initial paper received October 31 , 1991 The objective of this study was to survey microstructural Manuscript received April 28, 1992 variations among five different cultivars of adzuki beans Direct inquiries to B. G. Swanson us ing SEM . Telephone number: 509-335-3793 Fax number: 509-335-4815
171 A. Engquist and B. G. Swanson
Table I - Microstructural Variations Among Adzuki Bean Cultivars
Cultivar Seed coat surface features Storage cells Starch granules
deposits pits cracks shape surface
Erimo irregular shape, few, small no cracks tightly packed, mostly pitted. mostly clustered pits many spherical no grooves. few scattered inter-cellular no fi ssures deposits
Express compressed, not common distinct, • tightly packed, spherical pitted, flower-shaped, convoluted many to with shallow clustered or pattern of intercellular irregular grooves scattered cracks materials
Hatsune irregular shape, deep , long no cracks loosely packed, • spherical pitted, small, scattered, pits few to with shallow some very large intercellular irregular grooves materials
Takara irregular shape. not common no cracks tightly packed, highly pitted • some small many irregular to with deep rod-shaped , intercellular slightly fissure scattered materials spherical
VBSC irregular shape, deep, large no cracks tightly packed, oval to pitted. small. mostly pits many slightly no grooves scattered, some intercellular spherical no fissure very large materials
• 1dent1fymg feature
Materials and Methods the adzuki bean cultivars observed in this study are summarized in Table 1. Five cultivars of adzuki beans (Vigna angularis), Erimo, Express, Hatsune, Takara and VBSC used in this Seed coat surface study were obtained from Washington State University Observations of seed coat surfaces of adzuki Irrigated Agriculture Research Extension Center , cultivars revealed di stinct differences among the five Prosser, W A. cultivars. Seed coat surfaces of adzuki beans were Adzuki beans were surface cleaned with dry characterized by the presence of deposits, pits and Kleenex 13 facial tissue to remove any dirt and other par cracks. On the surface of the Erimo cultivar numerous ticles sticking to the surface. Cleaned beans were freeze deposits and few pits were observed (Figure 1). The fractured by freezing in liquid nitrogen and fracturing surface deposits of Erimo cultivar were large and mostly with a razor blade. Freeze fractured beans were at clustered (Figure 2). The seed coat surface of the tached to standard SEM mounts using double sided adhe Express cultivar was characterized by convoluted pattern sive tape and dried overnight in a desiccator. To pre of cracks (Figure 3). The surface deposits of Express pare adzuki bean flours 100 g of cleaned beans of each cultivars were large, compressed and flower-shaped cultivar were ground to flour for 2 minutes in a Stein (Figure 4) Pits and small scattered surface deposits mill to pass through a sieve of 0.5 nun pore size. A were observed on the seed coat surfaces of Hatsune tiny amount of flour for each bean cultivar was spread (Figure 5) and VBSC (Figure 6) cultivars. At greater on double sided adhesive tape attached to a standard magnification the largest surface deposits were observed SEM mount and dried in a desiccator overnight. Dried on Hatsune (Figure 7) and VBSC (Figure 8) cultivars. specimens were sputter-coated with 300 A gold (Hum Large surface deposits on Hatsune and VBSC cultivars mer Technics). The gold-coated specimens were exam exhibited shapes not observed in the other three cultivars ined and photographed with a Hitachi S570 SEM oper examined. Surface cracks were not observed on sur ating at 20 kV. faces of Hatsune and VBSC cultivars. In Takara culti var, the surface of the seed coat was characterized by Results and Discussion many small scattered irregular and rod shaped deposits The significant microstructural differences among (Figure 9). Rod-shaped deposits were the size of a
172 Microstructural Differences Among Adzuki Bean Cultivars
Figure I. Adzuki bean cv. Erimo. Seed coat surface. SD - surface deposit.
Figure 2. Adzuki bean cv. Erimo. Seed coat surface deposi ts at higher magnification. SD -surface deposit.
Figure 3. Adzuki bean cv. Express. Seed coat surface pattern . C indicates convoluted pattern of cracks.
Figure 4. Adzuki bean cv. Express. Seed coat surface deposits at higher magnification. SD - fl ower shaped , compressed surface deposits.
173 A. Engqui st and B. G. Swanson
Figure 5. Adzuki bean cv. Hatsune. Seed coat surface. P indicate surface pits.
Figure 6. Adzuki bean cv. VBSC. Seed coat surface. P indicates surface pit.
Figure 7. Adzuki bean cv. Hatsune. Seed coat surface deposits (SD) at higher magnification.
Figure 8. Adzuki bean cv. VBSC. Seed coat surface deposit (SD) at higher magnification.
174 Microstructural Differences Among Adzuki Bean Cultivars
Figure 9. Adzuki bean cv. Takara. Seed coat surface. SO -surface deposit.
Figure 10. Adzuki bean cv. Takara. Seed coat surface at higher magnification. Arrow bead indicates small rod-shaped surface deposits. SD - irregular surface deposit.
Figure II . Adzuki bean cv . Hatsune. Cross-section of the seed coat. PL - palisade cells, PR - parenchyma cells.
Figure 12. Adzuki bean cv. Express. Cross-section of the bean cotyledon showing arrangement of storage cell s. Arrow head indicates intercellular material s.
175 A. Engquist and B. G. Swanson
Figure 13. Adzuki bean cv. Hatsune. Cross-secti on of bean cotyledon showing loosely packed storage cells. Arrow head indicates intercellular materials.
Figure 14. Adzuki bean cv. Erimo. Starch granules (S) embedded in protein matrix (PM).
Figure 15. Adzuki bean cv. VBSC. Starch granules (S) embedded in protein matrix (PM).
Figure 16. Adzuki bean cv. Erimo. Protein matrix (PM) formed aggregates of loose granular nature in flour sample.
176 Microstructural Differences Among Adzuki Bean Cultivars
Figure 17. Adzuki bean cv. Express. Protein matrix (PM) formed aggregates of loose granular nature in fl our sample.
Figure 18. Adzuki bean cv . Express. Individual starch granule from flour sample. Spherical to irregular shape. S - starch granule, G - groove.
Figure 19. Adzuki bean cv. VBSC. Individual starch granule from flour sample. Oval shape. S -starch granule.
Figure 20. Adzuki bean cv. Takara. Individual starch granule from flour sample. Highly irregular to slightly spherical shape. S - starch granule, F - fissure.
177 A. Engquist and B. G. Swanson bacteria, while the irregularly shaped deposits were Cross-sections or the cotyledons larger (Figure 10). Pits and cracks were not observed Cross-sections of adzuki bean cotyledons revealed on the seed-coat surface of Takara cultivar. storage cells containing starch granules and protein Seed coat surface characteristics are important in matrices. The arrangement of storage cells varied evaluating the differences among legume cultivars. among the five cultivars of adzuki beans. Storage cells Seeds of many plants have species-specific seed coat were compactly packed with few intercellular spaces in patterns (Hughes and Swanson, 1985). Obvious micro Erimo, Express, Takara and VBSC cultivars (Figure structural differences between lentils and other food 12), with many intercellular materials. Contrary to the legumes were observed by examining seed coat surfaces other four cultivars, Hatsune cultivar revealed loosely (Hughes and Swanson, 1986). Size, shape and frequen packed storage cells with large intercellular spaces and cy of papillae on lentil seed coats vary among lentil few intercellular materials (Figure 13). The intercellular cultivars (Trivedi and Gupta, 1988). Numerous pits or materials between the cell walls of the adjacent cells pore-like indentations were observed on intact soybeans may provide mechanical strength and finnness to the by Wolf et al. (1981). Observations of maturing seed plant tissue. coats of common bean (Phaseolus vulgaris L.) seeds re Spherical starch granules were embedded in a gran vealed a characteristic pattern which developed as the ular protein matrix in the five cultivars of adzuki beans. seeds matured (Hughes and Swanson, 1985). Granules of the protein matrix were more distinct in The significance of seed coat surface deposits to Erimo (Figure 14) and VBSC (Figure 15) cultivars, than food processing is unknown, but large quantities of de in Express Hatsune and Takara cultivars. Micrographs posits on the surface can affect the luster and acceptabil of the bean flour indicated that the starch granules re ity of the seed (Swanson et al., 1985). Pits and cracks mained intact upon milling, whereas the protein matrices on the seed coat may be natura11y present or inflicted formed aggregates of a loose granular nature (Figures during harvesting and handling. Pits or cracks may in 16, 17). fluence the moisture retention capacity of the beans dur Bean cotyledons are the storehouses of common re ing storage, which in tum effects the market value of serve starch, which is used for the nourishment of the beans. growing embryo of the germinating seed. Common Cross-sections or seed coats bean (Phaseolus vulgaris L.) cotyledons contain large The cross-sections of seed coats of adzuki bean cul (10-50 ;
178 Microstructural Differences Among Adzuki Bean Cultivars
The surfaces of the starch granules appeared smooth References at low magnification, but at bjgher magnification, the su rfaces were pitted with no noticeable cracks. Pitted Chilukuri A, Swanson BG . (1991). Microstructure surfaces on starch granules was also observed in faba of adzuki beans (Vigna angularis cv Express). Food beans by McEwen era/. ( 1974) and in Express cultivar Struct. 3: 131-135. by Chilukuri and Swanson (1991). Tjahjadi and Breene Comer EJH. (1951). The leguminous seed. (1984), observed deep fissures on starch granules of Phytomorph. 1: 117-150. Takara cultivar of adzuki beans and suggested that the Hsieh H. (1991). Azuki maturation and composi shape and surface characteristics of the starch granules tion, cooking times, and lipoxygenase activity. M.S. can be used to identify different cultivars of adzuki thesis. Department of Food Science and Human Nutri beans. tion, Washington State University, Pullman, WA 99164.{;376. Conclusions Hughes JS , Swanson BG. (1985). Microstructural changes in maturing seeds of the conunon bean The five cultivars of adzuki beans examined in this (Phaseolus vulgaris L.). Food Microstruct. 5: 241-246 study showed different patterns of cracks, pits and de Hughes JS, Swanson BG. (1986) Microstructure of posits on the seed coat surfaces. A convoluted pattern lentil seeds. Food Microstruc. 5: 241-246. of cracks on the seed coat surface was unique to Express McClary DL, Raney TL, Lumpkin TA. (1989). cultivar. Examination of cross-sections of the seed coat Japanese food marketing channels. A case study of indicated the absence of typical sub-epidermal layer of Azuki beans and Azuki bean products. IMPACT infor columnar, hour-glass cell layer. Cross-section of the mation series # 29. IMPACT Center, College of Agri cotyledons in Hatsune cultivar revealed loosely packed culture and Home Economics, Washington State Univer storage cells with few intercellular materials and many sity, Pullman, WA 99164.{;214. intercellular spaces, which are in contrast to the McEwen TJ, Dronzek BL, Bushuk W. (1974). A cotyledon features observed in the other four cultivars. scanning electron microscopy study of faba bean seed. Observation of flours under SEM indicated that protein Cereal Chern. 51: 750-757. matrix formed aggregates of loose granular nature, dur Sacks FM (1977). A literature review of Phaseolus ing milling, while starch granules remained intact. The angularis. The adsuki bean. Econ. Bot. 3I: 9-15. shape of the starch granules was characteristic to each Sefa-Dedeh S, Stanley OW. (1979). Textural impli- cultivar. Irregularly shaped starch granules with a deep cations of the microstructure of legumes. Food fi ssure on each granule, were unique to Takara cultivar. Technol. 33(10):77-83. Microstructural differences among adzuk.i beans are Swanson BG, Hughes JS, Rasmussen HP (1985). of significant economic importance because they effect Seed microstruc: Review of water imbibition in legumes. grading, handling, storing and marketing conditions. Food Microstruct. 4: 115-124. Microstructural differences may also account for differ Tjahjadi T, Breene WM. (1984). Isolation and char ences in functional, textural and physical properties. acterization of adzuki bean (Vigna angularis CV. Seed coat surface characteristics such as deposits, pits Takara) starch. J. Food Sci. 49: 558-562. and cracks, different cell layers and thickness of the Trivedi BS, Gupta M. (1988). SEM studies on seed seed coat, and starch granules account for important coat of some varieties of Lens culinaris Medikus (lentil). microstructural variations among adzuki bean cu1tivars. Phytomorph. 38: 179-186. Thus a knowledge of microstructural variations among WolfWJ, Baker FL, Bernard RL (1981). Soy bean adzuki beans will enable us to determine conditions for seed coat structural features: Pits, deposits and cracks. optimum storage. and marketing conditions. Scanning Electron Microsc. 198I;lll: 531 -544.
Acknowledgements Editor's Note: All of the reviewer's concerns were ap propriately addressed by text changes, hence there is no The authors acknowledge the use of the facilities of Discussion with Reviewers. Electron Microscopy Center, Washington State Univer sity, Pullman, Washington, and partial financial support from USAJD Title XII Bean/Cowpea CRSP.
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