Effect of Hydrothermal Treatment on Morphological, Chemical and Physicochemical Properties of Musa (ABB) sp. Kluai Namwa (banana) Flour

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1 P-STARCH-18 Effect of Hydrothermal Treatment on Morphological, Chemical and Physicochemical Properties of Musa (ABB) sp. Kluai Namwa (banana) Flour Panyarat Sophitprapa 1 and Masubon Thongngam 1, * 1 Department of Food Science and Technology, Faculty of Agro-Industry, Kasetsart University, Bangkok 10900, THAILAND. Tel. (662) , Fax. (662) *Corresponding Author. address: fagimbt@ku.ac.th Abstract Banana flour was modified by using hydrothermal treatments in order to improve their swelling power and solubility. Pregelatinization methods (drum drier and spray drier) were chosen and then the properties of modified banana flour were determined. The green banana (ABB cultivar) flour had yielded more than 85 % of modified flours (drum dried and spray dried). The morphological of native and modified flours were observed by LM and SEM. The native banana flour had shown elongated and spheroid shape; while the drumdried banana flour appeared as flake-like shape with no intact granules. However, the spraydried flour still had intact starch granules like native but some swollen starches were observed. When swelling power (SP) of native and modified flours was determined, the SP of spray-dried flour was slightly decreased as compared to that of native. After modification, the cold water soluble properties of drum dried samples were higher; whereas that of spray dried sample was lower than native. However, the water retentions of both drum-dried and spraydried banana flours were increased. Drum-dried banana flours show an instant increase of viscosity but their peak viscosity was lowered compared to native. However, all spray-dried banana flours had pasting temperature higher and lower viscosity profile than native. Keywords: Banana flour, physical modification, hydrothermal treatment, double drum dried, spray dried Introduction Banana (Musa sp.) is easily grown in most part of Thailand. In its green stage, banana contains mainly carbohydrate especially starch; therefore, it is plausible to use as a source of starch and flour. In addition, the green banana also has high amount of resistant starches, which cannot be digested by human enzyme (Gonzalez et al., 2006). However, banana starch has some properties which could limit the use of banana flour in food industry. Therefore the modification of native banana flour is necessary to improve its potential utilization in food products. In food applications, modified flour has been used as an improvement over native flour in various capacities. Different modifications are tailored towards the end use of flour in various products. However, there is considerable interest in physical modifications, as it is considered to be natural and safe as compare to chemical modification (Hodge and Osman, 1976). Hydrothermal treatments, a form of physical modification entailed treatment of starch require a hydration step followed by drying (Loisel et al., 2006). Hydrothermal treatments at various temperatures and amount of water can be used to improve some properties of starches. Pregelatinization is one of the hydrothermal methods used to modify flour by using drum drier, spray drier or extruder (Thomas and Atwell, 1998). 225

2 The purpose of our study was to determine the changes of flour after different modifications. For spray drying modification method, the effect of temperature using prior to drying on flour property was evaluated. Knowledge of these modifications would be tremendously useful to apply banana flour in food. Materials and Methods Raw Material Green banana Kluai Namwa, collected at the 115th day after fertilization, was obtained from Nhongkae (Saraburee, Thailand). Flour preparation method Bananas were peeled and sliced into small pieces (0.5-1 cm. thick), dried by hot air oven at 50 o C for 5 hours. Dried banana slices were then milled and passed through 100 mesh sieve. Banana flour was then modified by using two drying methods: double drum dried and spray dried methods. Drum dried method Banana flour was suspended in distilled water (1:2). Then, the slurry was passed through double drum drier with gap distances 0.35 mm with surface temperature at 127 o C. Then the modified flour was grinded and passed through 100 mesh sieve. Sample was stored at room temperature in a sealed container. Spray dried method Banana flour was suspended in distilled water (1:5) and then preheated the suspension at a certain temperature (65, 75 and 85 o C) for 5 mins. Then the flour suspensions were fed into spray drier with inlet temperature of 180 o C and outlet temperature of 80 o C. Then samples were passed through 100 mesh sieve and stored at room temperature in a sealed container. Morphology of banana flour Morphology of native and modified flours was observed by Light Microscope (Axiolab, ZEISS, Germany) and Scanning Electron Microscope (JEOL, Japan). Swelling power (SP) of banana flour Swelling of banana flour was determined as followed the Waliszewski method (Waliszewski et al., 2003). A flour solution (1% w/w) was heated at 55, 65, 75, 85 and 95 o C for 30 mins. All samples were cooled to room temperature before centrifuging (3,000g) for 15 mins. The supernatant was taken out prior to weigh the sediment and then dried until the constant weight was obtained. Cold water solubility (CWS) Cold water solubility was determined by followed U.S. Pat. No. 5,057,157 (1991). Water retention capacity (WRC) Water retention capacity of samples was determined by using the method of Aloys and Zhou (2005). One gram of sample was thoroughly mixed with 10 ml of distilled water. It was then allowed to stand at room temperature for 30 mins and centrifuged at 3,710 rpm for 25 mins. The amount of water retained by sample was calculated from the different volume of the initial amount of water added to that decanted after centrifugation. Water retention capacity was expressed as gram of water absorbed per gram of sample. Pasting profile analysis Pasting characteristic of native and modified flours was determined by using Rapid Visco Analyzer (Newport Scientific Instruments & Engineering, Australia). Statistical analysis All measurements were analyzed by using ANOVA procedures of the SPSS program (version 15.0). Duncan new s multiple range test was used to compare the difference of mean (p< 0.05). 226

3 Results and Discussion Morphology of banana flour Light and Scanning electron micrographs of native Kluai Namwa banana flour (NWF) (Fig. 1A and 2A) revealed irregular shape granules among the elongated and spheroid forms. The size of starch granules were µm and the surface of native starch granules appeared smooth. In general, starch granules from various banana types appeared elongated ovals with ridges and irregular shape under microscope (Kayisu et al., 1981 and Zhang et al., 2005). On the other hand, the drum-dried banana flour (DNWF) appeared as flake-like shape with no intact granules observed (Fig. 1B and 2B) because narrow gap distances of drum drier caused high shear force to disrupt starch granules. However, the spray-dried flour (SNWF) still had intact starch granules like native but some swollen starches were observed. In addition, starches became more agglomerated when the preheat temperature increased (Fig. 1(C-E) and 2(C-E)). Figure1. Light micrographs of native (A), drum dried sample (B) and spray dried samples with various preheat temperature 65, 75 and 85oC (C, D, E respectively). The scale bar is 50µm. Figure2. Scanning electron micrographs of native (A) drum dried sample (B) and spray dried samples with various preheat temperature 65, 75 and 85oC (C, D, E respectively). The scale bar is 50µm. %

4 Swelling power (SP) of banana flour Swelling power of samples is presented in figure 3. After modified by spray dried method, the swelling powers were lower than native banana flour at all temperatures. In addition, the SP of SNWF was also affected by the preheat temperatures. The results showed that as the preheat temperature increased, the swelling power decreased. The decrease of swelling powers maybe caused by the transformation of amorphous amylose and the increase of agglomerated granules during preheat treatment. The combination of preheat temperature and drying used in the experiment affected flour swelling property significantly. The method used to measure swelling power in this study was not suited for DNWF. Due to fact that drum dried flour was dispersed in water and instantly raised solution viscosity at room temperature, so the swelling power cannot be determined. NWF SNWF65 SNWF75 SNWF85 Figure3. Swelling power of native (NWF) and spray dried banana flour (SNWF) with different preheat temperatures (65, 75 and 85 o C). Cold water solubility (CWS) and Water retention capacity (WRC) of banana flour Table 1 cold water solubility of native and modified banana flours Sample CWS (%) WRC (g/g) NWF d ± a ± 0.02 DNWF e ± e ± 0.03 SNWF a ± b ± 0.01 SNWF b ± c ± 0.04 SNWF c ± d ± 0.03 Means (n = 3) with different letters within a row were significantly different (p< 0.05) After modification, the cold water solubility of DNWF increased significantly (Table 1) and can be dispersed in water instantly. Due to starch granule disruption, pregelatinized flour can absorb water and increase viscosity immediately even with cold water (Glicksmans, 1969; Colonna et al., 1984 and Singh et al., 2007). However the cold water solubility of spray-dried samples was lower than that of native. When compared the CWS among spraydried samples, the results showed that as the preheat temperature increased, the CWS increased. The disruption of molecular order within starch granules during pregelatinization method might cause the loss of starch granule integrity, resulting in cold soluble property. Water retention capacity of native and modified banana flours is shown in Table 1. Both pregelatinization methods could improve water retention capacity of banana flour. The DNWF showed the highest water retention capacity (6.44 g of water/g of sample). For spray dried method, water retention capacity were increased with increasing temperature of preheat 228

5 treatment. The increase of water retention capacity of SNWF might indicate that the amorphous region expands and some hydrogen bonds between starch molecules broken. Pasting properties The pasting profile reveals that the modified flour by using drum drier could raise viscosity instantly (at the temperature below 50 o C) but its overall profile was lowered compare to native (Fig. 4). It might be because the high shear force and temperature during drum drying process causing the loss of starch granule integrity and the destruction of granule crystallinity, which resulted in its cold soluble properties by creating high viscosity at low temperature (Lai, 2007). The pasting properties of spray-dried flours (SNWF65, 75 and 85) were significantly affected by the degree of treatment as shown in fig.4. The changes of viscosity of SNWF was a combination effects of preheat temperature and drying, resulting in the increase of pasting temperature and the decrease of peak viscosity. The pasting properties of SNWF are similar to a Type C pasting profile, which is characterized by the lack of pasting peak viscosity and no breakdown, as defined by Schoch and Maywald (1968). The pasting temperature (PT) of SNWF was higher than that of native banana flour; while the peak viscosity (PV), final viscosity (FV) and breakdown (BD) were lower than those of native banana flour. The differences between SNWF and NWF increased as preheat temperature increased. When SNWF was heated at 85 o C prior to spray dried, it gave the highest PT and the lowest PV, FV and BD. These results indicated that the granule rigidity and molecular reassociation might be affected by the spray dried conditions in this study. NWF SNWF65 SNWF75 DNWF SNWF85 Figure4. Pasting profiles of native, drum dried samples and spray dried samples with different preheat temperatures (65, 75 and 85 o C). Conclusion Under hydrothermal methods in this study (drum dried and spray dried methods), characteristics of banana flour were profoundly changed. Drum dried method could rupture starch granules; while spray dried method could only alter granule size. After spray dried modification, the swelling power of flour was reduced. For drum dried method, the cold water solubility was the highest compared to native and spray-dried samples. In addition, the cold water solubility of spray dried flour was increased with increasing preheat temperature. Both drum-dried and spray-dried methods had higher water retention capacity than native. The drum-dried sample had lower pasting temperature; while the spray-dried sample had higher pasting temperature. Both modified banana flours had lower peak viscosity than native. 229

6 Acknowledgement We would like to thank Rice and Carbohydrate Special Research Unit (SRU: Rice and Carbohydrate) and Kasetsart University Research and Development Institute (KURDI) for their financial support. References Aloys, N. and H. M. Zhou Functional and chemical properties of ikivunde and inyange, two traditionally processed Burundian cassava flours. J. Food Biochem. 30, Colonna, P., J. L. Doublier, J. P. Melcion and C. Mercier Extrusion cooking and drumdrying of wheat starch: I. Physical and macromolecular modification. Cereal Chem. 61, Glicksman, M Gum Technology in Food Industry. Academic Press, New York. Gonzalez-Sato, R. A., L. Sanchez-Hernandez, J. Solorza-Feria, M. C. Nunez-Santiago, E. Flores-Huicochea and L. A. Bello-Perez Resistant starch production from nonconventional starch sources by extrusion. Food Sci. Tech. Int. 12, Hodge, S. and M. Osman Carbohydrates. In O. R. Fennema (Ed.), Food chemistry, principles of food science part 1. pp New York:Marcel Dekker. Jane, J. and P. A. Seib Preparation of granular cold water swelling/soluble starches by alcoholic-alkali treatment. U.S. Pat. No. 5,057,157 Kayisu, K., L. F. Hood and P. J. Vansoest Characterization of starch and fiber of banana fruit. J. Food Sci. 46, Lai, H.-M Effects of hydrothermal treatment on the physicochemical properties of pregelatinized rice flour. Food Chem. 72, Looisel, C., Z. Maache-Rezzoug, C. Esneault and J. L. Doublier E ect of hydrothermal treatment on the physical and rheological properties of maize starches. J. Food Eng. 73, Schoch, T. J. and E. C. Maywald Preparation and properties of various legume starches. Cereal Chem. 45, Singh, J., L. Kaur and O. J. McCarthy Factors influencing the physico-chemical, morphological, thermal and rheological properties of some chemically modified starches for food applications-a review. Food Hydrocolloid. 21, Thomas, D. J. and W. A. Atwell Starch modification. pp In D. J. Thomas and W. A. Atwell. (Eds.). Starches Handbook. American Association of Cereal Chemists, Inc., St. Paul, Minnesota. Waliszewskia, K. N., M. A. Aparicioa, L. A. Bellob and J. A. Monroy Changes of banana starch by chemical and physical modification. Carbohydr. Polym. 52, Zhang, P., R. L. Whistler, J. N. BeMiller and B.R. Hamaker Banana starch: production, physicochemical properties, and digestibility a review. Carbohydr. Polym. 59,