Food Structure Volume 11 Number 2 Article 9 1992 Microstructural Differences Among Adzuki Bean (Vigna Angularis) Cultivars Anup Engquist Barry G. Swanson Follow this and additional works at: https://digitalcommons.usu.edu/foodmicrostructure Part of the Food Science Commons 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 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. II (1992), pp. 171-179 1046-705X/92$3.00+ .00 Scanning Microscopy International , Chicago (AMF O'Hare), IL 60666 USA 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.