Food Chemistry 73 (2001) 61±66 www.elsevier.com/locate/foodchem

Starch properties of Amaranthus pumilus (seabeach ): a threatened with potential bene®ts for the breeding/amelioration of present Amaranthus cultivars

Massimo F. Marcone * Department of Food Science, Ontario Agricultural College, University of Guelph, Guelph, ON, Canada, N1G 2W1

Received 16 May 2000; received in revised form 14 September 2000; accepted 14 September 2000

Abstract This study reports on the physicochemical properties of starch isolated from the seeds of Amaranthus pumilus (a threatened plant species) and compares it to that of the commonly cultivated/commercially produced Amaranthus hypochondriacus K343 (Plains- man). Seeds of both investigated species were found to possess comparable quantities/levels of total starch. Although no signi®cant di€erences (P50.05) were found between the composition of the two starches with regard to their moisture, ash, protein and fat contents, the starch of A. pumilus was found to contain signi®cantly higher (P50.05) amounts of amylose than that of A. hypo- chondriacus. The higher levels of amylose found in A. pumilus starch were believed to be responsible for the higher di€erential scanning calorimetric To,Tp and Te starch temperatures than those of A. hypochondriacus starch which would indicate higher levels of ordered crystalline structure in the former. Scanning electron microscopy and integrated light scattering techniques both revealed a uniform average starch granule diameter of approximately 1 mm for both investigated species. This study further supports and compliments a previous study which showed that much genetic diversity exists between A. pumilus and A. hypochondriacus, indi- cating that potential breeding possibilities for the improvement of commonly cultivated amaranth lines do exist, if A. pumilus is not ®rst driven to extinction. # 2001Elsevier Science Ltd. All rights reserved.

1. Introduction been aided by the fact that there is a great deal of genetic variation available within the species. Although Much scienti®c information concerning the nutri- several amaranth species, do exist, a few wild species, tional attributes and bene®ts associated with the con- including Amaranthus pumilus (Seabeach Amaranth) are sumption of amaranth grain abound, especially when it quickly being extirpated from their native habitats and is incorporated into thermally processed foods (Leh- this may reduce the overall biodiversity available to mann, 1996; Hozova, Buchtova, Dodok, & Semanovic, plant breeders for the amelioration of present amaranth 1997). Other studies have demonstrated a variety of cultivars. With fewer than 55 remaining populations left important and unique nutraceutical type applications in the wild (or approximately 1000 individuals known), for grain amaranth, including its use as an adjunct to A. pumilus has received federal protection as a threa- lower blood glucose response in non-insulin-dependent tened plant species under the United States Endangered diabetics and in other applications to lower blood serum Species Act (Weakley, Bucher, & Murdock, 1996). If cholesterol levels (Lehmann; Chaturvedi, Sarojini, Nir- not driven to extinction, the seabeach amaranth may malammay, & Satyanarayana, 1997; Dunz & Lupton, potentially serve as a useful plant resource in future 1992). The development of grain amaranth with breeding programs due to its favourable genetic traits, enhanced characteristics for the above purposes, has such as tolerance to high soil salinity and large seed size. In a study by Marcone (1999), A. pumilus was found to possess a larger and more desirable seed size and weight (2±3-fold higher) than Amaranthus hypochondriacus * Corresponding author. Tel.: +1-519-824-4120, ext. 8334 or 2281; fax: +1-519-824-6631. K343 (most commonly cultivated commercial species), E-mail address: [email protected] allowing for greater biomass production in addition to

0308-8146/01/$ - see front matter # 2001Elsevier Science Ltd. All rights reserved. PII: S0308-8146(00)00285-5 62 M.F. Marcone / Food Chemistry 73 (2001) 61±66 lower levels (one-half) of free carbohydrate. In addition 2.2. Starch isolation and puri®cation to having higher edible-oil content than K343, its lower saturated and unsaturated (S/U) ratio make it poten- Starch from both Amaranthus species was isolated tially a better source of nutritional oil. Moreover, the 2 and puri®ed using a modi®ed wet-milling procedure fold-higher quantity of vitamin E found in A. pumilus based on the method of Baker and Rayas-Duarte and the higher levels of squalene also found, may one (1998). day serve as a renewable crop source of this compound and, hopefully, diminish the world's dependence on 2.3. Chemical analyses marine animals. Although several important compositional di€erences Ash, moisture, fat and protein contents of starch were have been observed between the seeds ofA. pumilus and determined according to AACC approved methods 08- A. hypochondriacus (Marcone, 1999), little else is known 01, 44-15A, 30-25 and 46-13 (AACC, 1983). Starch about any di€erences that may exist between their content in amaranth seed was determined according to starch compositions, i.e. the main constituent within the starch-gluco-amylase method 76-11 (AACC, 1995). each seed. Amylose content of starch samples was estimated using Recently, starches with novel properties have attrac- the method of Williams, Kuzina, and Hlynka (1970). ted the interest of several researchers for expanded applications in foods and other non-food formulations. 2.4. Scanning electron microscopy Amaranth starch has received particular attention because of its very small uniform granules with diameters Starch samples were mounted on aluminium stubs of 1±2 mm (Uriyapongson & Rayas-Duarte, 1994; and coated with gold/palladium (60/40) to a thickness Radosavljevic, Jane, & Johnson, 1998; Baker & Rayas- of 25±30 nm, using an Anatech hummer VII Sputter Duarte, 1998) compared to 3±8 mm of rice starch, the Coater (Alexandra, VA). Following coating, samples smallest commercially produced starch. The extremely were visualized and photographed under a Hitachi S- small starch granules of amaranth provide unique func- 570 Scanning Electron Microscope. The size of starch tional properties in food and non-food applications, e.g. granules was estimated by measuring the diameter of food thickeners, paper coatings, laundry starch, dusting >50 randomly selected granules from various photo- powders, cosmetics, fat replacers, thickeners in the micrographs. printing of textiles and biodegradable plastics (Ahamed, Singhal, Kulkarni, Kale, & Pal, 1996; Lehmann, 1992; 2.5. Determination of starch granule size by integrated Breene, 1991). Although it has become exceedingly clear laser light scattering that A. pumilus has many characteristics superior to K343, little information is known about its starch, The diameters of starch granules and their speci®c which constitutes the major component within the seed surface area were determined by integrated light scat- and would dominate the overall characteristics of any tering using a Mastersizer X (Malvern Instruments Inc., manufactured products. It was, therefore, the objective Southboro, MA). The samples were diluted circa. 1:500 of this study to examine the starch properties of the in ®ltered Milli-Q water and measured at ambient tem- threatened A. pumilus species and compare it to that of perature (22C). The presentation factor used was 0303, the more common and commercially cultivated A. representing a relative refractive index between the hypochondriacus, grown under identical and controlled continuous and the dispersed phase (refractive index of environmental conditions. 1.41 and absorption of 0.001). The scattered light was detected at 31angles and analyzed by an inverse fourier transformation by the instrument. 2. Materials and methods 2.6. Thermal properties 2.1. Materials Thermal properties of starch were determined in three Seeds of the threatened plant species Amaranthus independently isolated starch samples (in triplicate) pumilus (seabeach amaranth) were obtained from the using a DuPont Modulated Di€erential Scanning USDA (Ames, Iowa) PI553083 under provision Calorimeter Model 2910 equipped with a TA Instru- 50CFR17.7 (a) of the US Endangered Species Act, ments DSC Cell (New Castle, Delaware, USA) and a whereas A. hypochondriacus K343 (Plainsman) was liquid nitrogen cooling accessory (TA Instruments) and obtained from the Department's germplasm collection. data evaluated using General V4 IC DuPont 2000 ana- Both species were cultivated under identical greenhouse lysis software. Thermograms were obtained employing a environmental conditions and seed was collected at heating rate of 5C/min, from 25±100C. High purity maturity and stored at À20C. (99.9%) indium and gallium were used to calibrate the M.F. Marcone / Food Chemistry 73 (2001) 61±66 63 system. Starch samples (3.0 mg) were weighed into DSC 3. Results and discussion aluminium pans and 10 ml of deionized water added with a microsyringe. After sealing the pans, they were 3.1. Chemical composition of starches allowed to equilibrate for 3 h. An empty pan was used as a reference. Thermal transitions of starch were No signi®cant di€erence (P50.05) was observed de®ned in terms of onset (To), peak ((Tp), and end of between the total seed starch contents of A. pumilus gelatinization (Te) temperatures (C), and enthalpy of and the more common and commercially cultivated A. gelatinization (ÁH, J/g). hypochondriacus K343 (i.e. 60%) which fell within the range reported in the literature for other studied 2.7. Calorimetric determination Amaranthus species (Uriyapongson & Rayas-Duarte, 1994). The proximate composition and amylose con- The colour of starch (L*, a*andb* values) samples tents of both isolated starches are shown in Table 1. The were determined using a Minolta Chroma Meter CR- air-dried starches showed no signi®cant di€erences 2006 (Minolta Camera Co. Ltd. Osaka, Japan).

2.8. Statistical analysis

Statistical analysis was performed using SAS Statis- tical Analysis System package (SAS Institute, 1990). Signi®cant di€erences among treatments were deter- mined by Duncan's multiple range test (P40.05).

Table 1 Comparison of the chemical, physical and thermal properties of the isolated starch and ¯our from the seeds of Amaranthus hypochon- driacus K343 (plainsman) and Amaranthus pumilus (seabeach amar- anth; a threatened plant species)a

Amaranthus hypochondriacus Amaranthus pumilus (plainsman) (seabeach amaranth)

Chemical analysis of starch (%) Total starch (in seed) 61.0a 61.4a Amylose 4.17a 8.20a Moisture 11.1a 10.3b Ash 1.3a 1.0a Protein 0.05a 0.07b Fat 0.87a 1.1a Morphological properties of starch granules Starch granule size 1.1a 1.1a by S.E.M. (mm) Starch granule size by 1.09a 1.07a light scattering (mm) Speci®c surface area 5.5282a 5.5977a (m2/cm3) Starch colour L* 93.20a 93.85a a* 0.85a 0.83a b* 3.07a 2.97a Thermal properties of starch/¯our To(C) (62.0/64.2)a (63.4/66.2)b (Starch/Flour) Tp(C) (70.6/73.2)a (71.6/74.3)b (Starch/Flour) Te(C) (78.9/77.5)a (80.0/82.8)b (Starch/Flour) ÁH (J/g) (13.0/6.6)a (12.2/6.3)a (Starch/Flour)

a To, Tp and Te, onset, peak and end temperatures, respectively. ÁH, Fig. 1. Scanning electron micrographs of starch isolates from (A) enthalpy change. Values within each row are not signi®cantly di€erent Amaranthus pumilus and (B) Amaranthus hypochondriacus magni®ed (P50.05). Values represent the means of three replications. by 2500. Bar represents 3.0 mm. 64 M.F. Marcone / Food Chemistry 73 (2001) 61±66

(P50.05) in moisture, ash, protein, fat or colour and 3.2. Starch granule morphology were comparable to those of other studied Amaranthus species (Uriyapongson & Rayas-Duarte). On the other Examination of the morphological properties of A. hand, A. pumilus starch had signi®cantly higher pumilus starch granules by scanning electron micro-