Retrogradation behaviour of milled and brown rice pastes during ageing
M.Mariotti *,N.Sinelli,F.Catenacci,M.A.Pagani,M.Lucisano
Department of Food Science and Microbiology (DiSTAM),University of Milan,Via G.Celoria 2,20133Milan,Italy
a r t i c l e i n f o
Article history:
Received 1January 2008Received in revised form 9July 2008
Accepted 5September 2008Keywords:Rice Gel
Retrogradation Viscoamylograph
Dynamic rheological test FT-NIR spectroscopy
a b s t r a c t
Retrogradation of gelatinised starch is the main phenomenon that influences the texture of cooked rice.The rate of retrogradation is affected by several factors including amylose and amylopectin ratio,protein and fibre.The objective of this study was to analyse the pasting properties and the retrogradation behaviour of six traditional and five aromatic Italian rice varieties.The pasted gels,after cooling,were evaluated by dynamic rheological measurements for up to 7days of storage at 4 C.The samples were also analysed by a NIR spectrometer.The pasting properties and the retrogradation behaviour of milled rice flours strongly depended on the rice varieties.During gel ageing,a noticeable increase of G 0and G 00was observed only for the milled rice varieties Asia,Gange,Fragrance and Vialone Nano,characterised by a high amylose content.No further hardening was found either for the other milled varieties or for all the brown samples.The methods used in this work (dynamic oscillatory rheometry and FT-NIR spectros-copy)turned out to be very useful in the definition of rice starch gels ageing.
Ó2008Elsevier Ltd.All rights reserved.
1.Introduction
During gelatinisation,starch granules swell to several times their initial size as the result of the loss of crystalline order and water absorption;they are partially ruptured,releasing amylose,and form a three-dimensional network with the swollen granules embedded into the matrix.A starch paste can therefore be regar-ded as a composite material consisting of swollen granules dispersed in a continuous biopolymer matrix (Noel et al.,1993).The properties of each phase and the interactions between the components are important elements in determining the rheolog-ical behaviour of pasted gels.These properties depend on several factors,including the type and the concentration of starch,the amylose/amylopectin ratio,the temperature profile applied to the pastes,and the presence and concentration of other soluble and insoluble compounds such as protein,salts,lipids,and fibre (Lii et al.,1995,2004).
The swollen starch granules form a strong packed gel structure with a high shear resistance whose intensity increases on cooling due to starch retrogradation.In fact,if the starch concentration is sufficiently high,the paste can convert into gel upon cooling (Tester
and Morrison,1990).Retrogradation of gelatinised starch involves the reordering of the amylose chains in short-term ageing (Dou-blier and Choplin,1989)and a slower reorganisation of amylopectin after longer periods (Biliaderis and Zawistowski,1990;Lai et al.,2000).
The Brabender Micro-Visco-Amylograph (MVA)and the Rapid Visco Analyser (RVA)are currently used as standard analytical tools to assess the pasting characteristics of starch and flour suspensions in water.Several parameters evaluated from the pasting profiles of milled rice flour have been shown to correlate with the eating quality (Bergman et al.,2004)and with the end-use of rice flour.Relationships have been observed between the amylographic measurements and the amylose and protein content (Sandhya Rani and Bhattacharya,1989)and the instrumental parameters used to measure the textural properties of rice flour pastes.
Dynamic oscillatory rheometry is useful for monitoring struc-ture development during gelling and ageing without breaking the structural elements formed in the sample upon ageing.In a dynamic test,the storage modulus (G 0),loss modulus (G 00),complex modulus (G *)or complex viscosity (h *)are determined using a sinusoidal strain cycle.Many authors have used rheological methods to monitor the changes that occur during the heating of starches and flours (Hagenina and Ding,2005;Hamed et al.,2008;Lii et al.,1995,1996;Rao et al.,1997;Svegmark and Hermansson,1991)and to evaluate the viscoelasticity of starch pastes (Lii et al.,1995;Sandhya Rani and Bhattacharya,1989;Yoo,2006)and gels (Biliaderis and Zawistowski,1990;Chun and Yoo,2004).
Another interesting method for acquiring information about molecular changes during gel ageing is near infrared reflectance
Abbreviations:FT-NIR,Fourier transform near infrared reflectance;G 0,storage modulus;G 00,loss modulus;MSC,multiplicative scatter correction;MVA,Brabender Micro-Visco-Amylograph;NIR,near infrared reflectance;PCA,principal component analysis;Rice varieties:AP,Apollo;AS,Asia;AU,Augusto;BA,Balilla;FR,Fragrance;GA,Gange;GI,Giano;GL,Gladio;RO,Roma;SE,Selenio;VN,Vialone Nano;RVA,Rapid Visco Analyser.
*Corresponding author.Tel.:þ390250319186;fax:þ390250319190.E-mail address:manuela.mariotti@unimi.it (M.
Mariotti).Contents lists available at ScienceDirect
Journal of Cereal Science
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0733-5210/$–see front matter Ó2008Elsevier Ltd.All rights reserved.doi:10.1016/j.jcs.2008.09.005
Journal of Cereal Science 49(2009)171–177
