Thermal properties and resistant starch content of green banana flour (Musa cavendishii) produced at different drying conditions T.B. Tribess a , J.P. Herna ´ ndez-Uribe b , M.G.C. Me ´ ndez-Montealvo b , E.W. Menezes c , L.A. Bello-Perez b , C.C. Tadini a, * a Department of Chemical Engineering, Escola Polite ´cnica, Sa ˜o Paulo University, P.O. Box 61548, 05424-970 Sa ˜o Paulo, Brazil b Centro de Desarrollo de Productos Bio ´ticos del IPN, P.O. Box 24, 62731 Yautepec, Morelos, Me´xico c Department of Food and Experimental Nutrition, Faculdade de Cieˆncias Farmaceˆuticas, Sa ˜o Paulo University, Bl.14 Av. Prof. Lineu Prestes 580, CEP 05508-900, Sa ˜o Paulo, Brazil article info Article history: Received 23 March 2008 Received in revised form 22 December 2008 Accepted 23 December 2008 Keywords: Green banana flour Gelatinization Resistant starch DSC abstract The objective of this research was to verify the effect of drying conditions on thermal properties and resistant starch content of green banana flour (Musa cavendishii). The green banana flour is a complex- carbohydrates source, mainly of resistant starch, and quantifying its gelatinization is important to understand how it affects food processing and the functional properties of the flour. The green banana flour was obtained by drying unripe peeled bananas (first stage of ripening) in a dryer tunnel at 52  C, 55  C and 58  C and air velocity at 0.6 m s 1 , 1.0 m s 1 and 1.4 m s 1 . The results obtained from differ- ential scanning calorimetry (DSC) curves show a single endothermic transition and a flow of maximum heating at peak temperatures from (67.95  0.31)  C to (68.63  0.28)  C. ANOVA shows that only drying temperature influenced significantly (P < 0.05) the gelatinization peak temperature (Tp). Gelatinization enthalpy (DH) varied from 9.04 J g 1 to 11.63J g 1 and no significant difference was observed for either temperature or air velocity. The resistant starch content of the flour produced varied from (40.9  0.4) g/100 g to (58.5  5.4) g/100 g, on dry basis (d. b.), and was influenced by the combination of drying conditions: flour produced at 55  C/1.4 m s 1 and 55  C/1.0 m s 1 presented higher content of resistant starch. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Banana is mainly produced in tropical and subtropical devel- oping countries. Brazil is the second world producer and the variety Nanica ˜o (Musa cavendischii) is one of the most important crops in Brazil (FAO, 2007; Mota, Lajolo, Ciacco, & Cordenunsi, 2000). About one-fifth of all banana harvested is wasted and rejected banana are normally disposed improperly. Green banana flour is a low-cost ingredient for food industry and an alternative to minimizing banana wastes (Zhang, Whistler, BeMiller, & Hanaker, 2005). According to literature, green banana is very rich in starch and its flour may present (61.3–76.5) g/100 g of starch (d. b.) and also has a fiber content of (6.3–15.5) g/100 g (d. b.) (Juarez-Garcia, Agama-Acevedo, Sa ´yago-Ayerdi, Rodriguez-Ambriz, & Bello-Perez, 2006; Mota et al., 2000), moreover great part of the starch found in green banana flour is the resistant starch type 2 (RS 2 – from (52.7 to 54.2) g/100 g d. b.) (Faisant, Gallant, Bouchet, & Champ, 1995). RS2 are native uncooked granules of some starches, such as those in raw potatoes and green bananas, whose crystallinity makes them scarcely susceptible to hydrolysis (Gonza ´ lez-Soto, Mora-Escobedo, Hernandez-Sanchez, Sanchez-Rivera, & Bello-Perez, 2007). Resistant starch has attracted interest because of its positive effects in the human colon and implications for health (Langkilde, Champ, & Andersson, 2002; Englyst, Kingman, & Cummings, 1992). The disappearance of the starch reserve during ripening appears to be relatively rapid because of several enzymes acting together. Therefore, in order to use green banana, right after harvest, it is necessary to obtain a flour with a high resistant starch content (Zhang et al., 2005). According to Mustaffa, Osman, Yusof, and Mohamed (1998), banana fruit at different maturity stages presents significant difference (P < 0.01) on physico- chemical characteristics and fruit firmness. The soluble solids increase from early stages until the end of maturity, while fruit firmness diminishes during ripening, due to the action of poly- galacturonase and pectin methylesterase enzymes involved in pectin degradation in the cell wall and middle lamella (Mustaffa et al., 1998). Ditchfield (2004) studied the effect of maturation time on physico-chemical characteristics and fruit firmness of * Corresponding author. Tel.: þ55 11 3091 2258; fax: þ55 11 3091 2255. E-mail address: catadini@usp.br (C.C. Tadini). Contents lists available at ScienceDirect LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt 0023-6438/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.lwt.2008.12.017 LWT - Food Science and Technology 42 (2009) 1022–1025