J Sci Food Agric 1998, 77, 103È108 Eþect of Acid Treatments and Drying Processes on Physico-chemical and Functional Properties of Cassava Starch Manuel Plata-Oviedo and Celina Camargo* Faculdade de Engenharia de Alimentos, Universidade Estadual de Campinas (UNICAMP), Cx Postal 6121, CEP 13083-970, Campinas-SP, Brazil (Received 24 October 1995 ; revised version received 12 August 1997 ; accepted 11 September 1997) Abstract : The e†ects of acid treatments (HCl or organic acids) and drying processes (oven or sun) on the physico-chemical and functional properties of cassava starch have been studied. The objective was to obtain modiÐed starches with expansion properties similar to those of sun dried fermented cassava starch (polvilho azedo) as produced by an empirical process. Expansion was evaluated using a baking test. Independent of the drying method, organic acid-hydrolysed cassava starch presented the same X-ray di†raction patterns (changes from C to A) and similar intrinsic viscosity values. SEM observations showed no di†erences between granule surfaces of sun dried and oven dried samples. However sun dried organic acid-hydrolysed starches presented lower paste consistency values at 30¡C when compared with oven dried ones. HCl-modiÐed cassava starches were oven or sun dried, giving biscuits with low speciÐc volumes (2É5È 3É1 ml g~1). Similar behaviour was obtained using oven dried organic acid modiÐed cassava starches. When submitted to sun drying, organic acid modiÐed starches showed great improvements in biscuit expansion (5È10 ml g~1). The highest average speciÐc volumes were obtained using lactic acid modiÐed starches. ( 1998 SCI. J Sci Food Agric 77, 103È108 (1998) Key words : cassava starch ; modiÐed starch ; hydrolysis ; lactic acid ; drying process ; functional properties INTRODUCTION During starch fermentation, several organic acids are produced (Cereda 1987). Observations made by scanning electron microscopy showed some holes on the surface of the granules which are characteristic of enzymatic attack (Plata-Oviedo and Camargo 1995). In order to simulate the fermentation e†ects observed in fermented cassava starch, native cassava starch was modiÐed by enzymatic or acid hydrolysis (Cardenas and Buckle 1980 ; Camargo et al 1988) and dried in a conventional oven. These hydrolysed starches showed poor expansion properties. In this work, native cassava starch was treated with HCl or organic acids. The e†ects of oven or sun drying on some functional properties of these acid modiÐed Sour cassava starch (polvilho azedo) is a typical Brazilian product obtained by natural fermentation of cassava starch for a period of approximately 30 days (Cereda 1987). The Ðnal product is sun dried for about 12 h. Sour cassava starch is used in the manufacture of biscuit and “cheese breadÏ in which it is irreplaceable due to its characteristic Ñavour and functional properties, mainly those of expansion. The biscuits have high speciÐc volumes, alveolar structure and crispness, similar to extruded snacks. * To whom correspondence should be addressed. 103 ( 1998 SCI. J Sci Food Agric 0022È5142/98/$17.50. Printed in Great Britain M Plata-Oviedo, C Camargo 104 Fig 1. Biscuits made from sun dried (A) HCl-hydrolysed cassava starch, (B) native cassava starch and (C) sour cassava starch. starches were investigated. MATERIALS AND METHODS Materials Native industrial cassava starch and sour cassava starch (polvilho azedo) were obtained from a local market in Campinas (Brazil). ModiÐcations of native industrial cassava starch Native cassava starch batches (240 g DM basis) were subjected to HCl hydrolysis : 600 ml of 0É1, 0É3, 0É5 and 1É0 M HCl for periods of 0É5, 1É0, 2É0 and 4É0 h at 40¡C. I Organic acid hydrolysis : 600 ml of organic acid solutions (pH 3É6, adjusted with 1É0 M NaOH) containing 0É3 and 2É0% (v/w) of organic acid (starch basis) for periods of 10 and 60 min at 30¡C. The organic acids used were : acetic (A), propionic (P), lactic (L) and mixtures of AÈL, AÈP, PÈL (1 : 1, v/v) and AÈPÈL (1 : 1 : 1). I After hydrolytic treatments, the modiÐed starches were recovered by centrifugation (974 ] g, 3 min) and Ðnally sun (12 h) or oven dried at 45¡C (18 h). Baking test The baking test was performed on native industrial cassava starch, sour cassava starch and acid modiÐed cassava starches, using the basic formulation described by Cereda (1983) : 30 g starch, 7É5 g hydrogenated vegetable fat, 0É9 g salt and water, the water absorption values for the native starch, acid modiÐed starches and sour cassava starch being 21 ml, 24 ml and 30 ml, respectively. The hydrogenated vegetable fat was Ðrst mixed with the salt and 25% of the total water and boiled. This boiling mixture was added to the starch, already moistened with another 25% of the total water, and all the ingredients were mixed into a dough followed by the addition of the remaining water (50%). The total mixing time was 5 min. Portions of 4É0 ^ 0É1 g of the Ðnal dough, having a creamy consistency and smooth appearance were dropped onto metal sheets and cooked for 20 min at 200È210¡C. After cooling at room temperature for 30 min, the biscuits were weighed (g) and the volume (ml) determined by the seed displacement method. Physico-chemical properties and scanning electron microscopy The intrinsic viscosity of starch suspensions, dissolved in 1É0 M KOH, was measured according to Leach (1963), using a viscosimeter (Cannon-Fenske Number 50) maintained at 35¡C in a thermostatic bath. The pasting properties were studied using a Brabender viscoamylograph with a 700 cmg sensitivity cartridge at 75 rpm. The starch dispersions at 6É2% (27É9 g DM basis in 450 ml of water) were heated from 30 to 95¡C at 1É5¡C min~1, kept at this temperature for 15 min, and Ðnally cooled to 30¡C at 1É5¡C min~1. X-ray di†raction patterns were determined using a Shimadzu XD-3A unit with Cu radiation, K line, equal to 0É154 02 nm (LiF as monochromator). The scanning Physico-chemical and functional properties of cassava starch 105 Fig 2. Biscuits made from hydrolysed cassava starches. (A) Acetic acid (2É0% for 60 min) ; (B) lactic acid (2É0% for 10 min) ; (C) aceticÈlactic acid mixture (0É3% for 10 min). Biscuits A, B and C : left (oven dried starch) and right (sun dried starch). velocity was 1¡(2h) min~1 at 30 kV and 20 mA. All samples had moisture contents of 13 ^ 0É2%. The starch samples for scanning electron microscopy observations were dehydrated by lyophilisation. The starches were sprinkled onto a double-sided adhesive tape attached to a circular specimen stub and coated Ðrst with carbon followed by gold, and observed with a JEOL-JSM T300 Microscope at an accelerating potential of 5 kV. RESULTS AND DISCUSSION HCl-modiÐed starches Fig 3. E†ect of lactic acid on biscuit expansion (measured by average speciÐc volumes) performed on sun dried organic acid hydrolysed starches. * mixtures AÈL, PÈL and AÈP (1 : 1, v/v). ** mixture AÈPÈL (1 : 1 : 1, v/v/v). TABLE 1 Intrinsic viscosities (dl g~1) of oven and sun dried organic acid hydrolysed cassava starchesa a b c d Samples Oven dried Sun dried A, 2É0% : 60 minb L, 2É0% : 10 minc AÈL, 0É3% : 10 mind 2É25 2É20 2É44 2É18 2É15 2É21 Intrinsic viscosity of native industrial cassava starch : 2É57. Acetic acid hydrolysed starches (2É0% for 60 min). Lactic acid hydrolysed starches (2É0% for 10 min). AceticÈlactic acid hydrolysed starches (0É3% for 10 min). Oven or sun dried HCl-modiÐed starches gave hard and dense biscuits, with no expanded structure, characterized by low speciÐc volumes (2É5È3É1 ml g~1), similar to those obtained with native cassava starch. Sour cassava starch gave highly expanded biscuits, characterised by high speciÐc volumes (15 ^ 0É3 ml g~1, Fig 1). Organic acid modiÐed starches Baking tests performed on oven dried organic acid modiÐed starches showed biscuits with low speciÐc volumes (3É0È3É3 ml g~1). However, the same acid modiÐed starches, when submitted to sun drying showed great improvement in biscuit expansion (Fig 2). Sun dried lactic acid starches gave the highest average speciÐc volumes (Fig 3). When lactic acid was added to the acetic acid, propionic acid and aceticÈ propionic acid mixture used in the hydrolytic treatments, the sun dried modiÐed starches gave biscuits 106 M Plata-Oviedo, C Camargo Fig 4. Brabender viscograms of native cassava starch (ÈÈÈ) and sun (È È È È) or oven (È Œ È Œ È) dried organic acid hydrolysed starches. (A) Acetic acid hydrolysed starch (2É0% for 60 min) ; (B) lactic acid hydrolysed starch (2É0% for 10 min) ; (C) aceticÈlactic acid hydrolysed starch (0É3% for 10 min). with higher average speciÐc volumes than with the acetic acid, propionic acid and aceticÈpropionic acid mixture sun dried modiÐed starches. These results showed the beneÐcial e†ect of lactic acid on biscuit expansion. Physico-chemical properties and scanning electron microscopy of some organic acid modiÐed starches The intrinsic viscosity of native industrial cassava starch was 2É57 dl g~1. This value is higher than 2É30 and 2É45 dl g~1 reported by Franco et al (1988) and Ciacco and DÏAppolonia (1976), respectively. The organic acid hydrolysed starches showed lower viscosities suggesting some starch degradation (Table 1). The viscograms of native and organic acid hydrolysed starches are shown in Fig 4. Both sun and oven dried hydrolysed starches, when compared with native starch, showed a slight decrease at pasting peak consistency and higher peak consistency temperatures. The initial consistency of organic acid treated starches at 95¡C was higher than the native cassava starch (Table 2). Sun and oven dried hydrolysed cassava starches had lower Ðnal viscosity (at 30¡C) than industrial starch, suggesting a decrease in tendency to retrograde. The difference between sun drying and oven drying starches was small and not signiÐcant. X-ray di†raction patterns of native and sun or oven dried organic acid hydrolysed cassava starches are shown in Fig 5. There were no di†erences between the Physico-chemical and functional properties of cassava starch 107 TABLE 2 Pasting properties of native industrial cassava starch and sun or oven dried organic acid hydrolysed cassava starch Samples Native starch A, 2É0% : 60 minb Oven dried Sun dried L, 2É0% : 10 minc Oven dried Sun dried AÈL, 2É0% : 10 mind Oven dried Sun dried a b c d Initial pasting temp (¡C) Consistency (BUa) Pasting peak temp (¡C) 95¡C 30¡C Peak Initial Final 63É0 71É3 885 330 240 700 62É0 62É0 73É0 74É0 860 830 410 400 280 270 580 495 62É8 62É8 73É5 73É5 795 790 350 370 220 205 425 390 62É8 62É8 73É0 73É5 825 840 395 410 275 275 560 510 BU, Brabender Units. Acetic acid hydrolysed starch (2É0% for 60 min). Lactic acid hydrolysed starch (2É0% for 10 min). AceticÈlactic acid hydrolysed starch (0É3% for 10 min). di†raction patterns of sun and oven dried hydrolysed starches. However, the organic acid treatments changed the original C di†ractogram pattern of native starch to A. Changes from B to A patterns in potato starch (Sair 1964) and from C to A pattern in cassava and arrowroot starches (Lorenz and Kulp 1982) were observed when starches were heated at restricted moisture levels (heatÈmoisture treatments). SEM observations revealed a mild superÐcial corrosion on some granules (less than 1%) of organic acid hydrolysed starches. There were no visual di†erences between sun dried (B1) and oven dried (B2) samples (Fig 6). CONCLUSIONS Fig 5. X-ray di†ractions patterns of native industrial cassava starch and sun or oven dried organic acid hydrolysed cassava starches. (A) Corn starch (A type) ; (B) native cassava starch (C type) ; (C) oven dried acetic acid starch (2É0% for 60 min) ; (D) sun dried acetic acid starch (2É0% for 60 min) ; (E) oven dried lactic acid starch (2É0% for 10 min) ; (F) sun dried lactic acid starch (2É0% for 10 min) ; (G) oven dried acetic-lactic acid starch (0É3% for 10 min) ; (H) sun dried aceticÈlactic acid starch (0É3% for 10 min). Independent of drying method (sun or oven) organic acid hydrolysed starches presented similar physicochemical properties (X-ray di†raction patterns, intrinsic viscosities, Brabender viscograms). Furthermore, SEM observations detected no di†erences between sun dried and oven dried samples. Baking tests demonstrated that sun dried organic acid hydrolysed starches produced expanded biscuits which was not observed when oven drying was used. Unfortunately we could not relate the expansion property of sun dried organic acid hydrolysed starches with the physico-chemical properties studied in this work. Both fermented cassava starch (Dufour et al 1994 ; Plata-Oviedo and Camargo, unpublished) and lactic acid hydrolysed cassava starch (Nunes and Cereda 1994) showed the expansion property when irradiated by UV-lamps. It is well known that UV radiation catalyses photochemical reactions. Herold and Fouassier (1981) using a non-degassed system, grafting methyl methacrylate on potato starch under UV radiation M Plata-Oviedo, C Camargo 108 Fig 6. SEM observations on organic acid hydrolysed starches. (A1) Acetic acid hydrolysed starch (2É0% for 60 min), sun dried (5000]) ; (A2) aceticÈlactic acid hydrolysed starch (0É3% for 10 min), sun dried (7500]) ; (B1) lactic acid hydrolysed starch (2É0% for 10 min), oven dried (5000]) ; (B2) lactic acid hydrolysed starch (2É0% for 10 min), sun dried (5000]). without photo-initiators. We believe that the expansion property of sun dried organic acid hydrolysed cassava starches results from some chemical interactions between the organic acids and the starch, catalysed by the UV segment of solar radiations. The same hypothesis could explain the expansion property of sun dried fermented cassava starch (polvilho azedo). Model experiments are being carried out to conÐrm this hypothesis. REFERENCES Camargo C, Colonna P, Buleon A, Richard-Molard D 1988 Functional properties of sour cassava (Manihot utilissima) starch : polvilho azedo. J Sci Food Agric 45 273È289. Cardenas O S, Buckle T S 1980 Sour cassava starch : a preliminary study. J Food Sci 45 1509È1512, 1528. Cerada M P 1983 PadronizacÓa8 o para ensaios de qualidade da fecula de mandioca fermentada (polvilho azedo). I-FormulacÓa8 o e preparo de biscoitos. Bol SBCT A 17 287È 295. Cereda M P 1987 Tecnologia e qualidade do polvilho azedo. Informe Agropecua rio 13 63È68. Ciacco C F, DÏAppolonia B L 1976 Characterization of starches from various tubers and their use in bread-baking. Cereal Chem 54 1096È1107. Dufour D, Larsonneur S, Alarcon F, Cereda M P, Brabet C 1994 InÑuence of sun drying on sour cassava starch quality, pandebono loaf volume and viscoamylograph studies. In : Abstr International Meeting on Cassava Flour and Starch. Centro Internacional de Agricultura Tropical, Cali, Colombia, p 37. Franco C M L, Ciacco C F, Tavares D Q 1988 Studies on the susceptibility of granular cassava and corn starch to enzymatic attack. Part 2 : Study of the granular structure of starch. Starch/Sta rke 40 29È32. Herold R, Fouassier J P 1981 Photochemical grafting of vinyl monomers onto starch. Starch/Sta rke 33 90È97. Leach H W 1963 Determination of intrinsic viscosity of starches. Cereal Chem 40 593È600. Lorenz K, Kulp K 1982 Cereal and root starch modiÐcation by heat-moisture treatment. I. Physico-chemical properties. Starch/Sta rke 34 50È54. Nunes O L G S, Cereda M P 1994 E†ect of drying processes on the development expansion in cassava starch hydrolyzed by lactic acid. In : Abstr International Meeting on Cassava Flour and Starch. Centro Internacional de Agricultura Tropical, Cali, Colombia, p 110. Plata-Oviedo M, Camargo C R O 1995 DeterminacÓa8 o de propriedades Ðsico-qui micas e funcionais de duas feculas fermentadas de mandioca (polvilho azedo). Cieü nc T ecnol Aliment 15 59È65. Sair L 1964 Heat-moisture treatment of starches. In : Methods in Carbohydrate Chemistry (Vol 4, Starch), eds Whistler R L, Smith R J & Be Miller J N. Academic Press Inc, New York, USA, pp 283È285.