Review Starch digestibility in food matrix: a review Jaspreet Singh * , Anne Dartois and Lovedeep Kaur Riddet Institute, Massey University, Palmerston North, New Zealand (Tel.: D64 6 3505062; e-mail: j.x.singh@massey.ac.nz) In this review, recent reports on in vitro starch hydrolysis kinet- ics are reviewed with regard to the structural characteristics of starches. Factors such as starch granule morphology, amylose to amylopectin ratio, molecular structure, degree of branching in terms of steric hindrance and consequently mass transfer re- sistance and their effects on the digestibility and absorption of digested carbohydrates have been examined. The physical state of the starch ingested has a major impact on the digest- ibility therefore effects of processing techniques (thermal pro- cessing, extrusion cooking, autoclaving etc.) and starch modification have been discussed. The other constituents of the food matrix, such as proteins, lipids and polysaccharides, play a significant role during processing which affects the physico-chemical characteristics of digesta and the final di- gestibility of starch. Some molecules naturally occurring in food sources may confer an inhibitory effect during starch hydrolysis. Introduction Starch is the commonest storage carbohydrate in plants and also the largest source of carbohydrates in human food. Starch consist of two types of molecules: amylose (lin- ear polymer of a-D-glucose units linked by a-1,4 glycosidic linkages) and amylopectin (branched polymer of a-D-glu- cose units linked by a-1,4 and a-1,6 glycosidic linkages). Starch and starchy food products can be classified according to their digestibility, which is generally characterized by the rate and the duration of the glycemic response. Predicting and controlling the glucose absorption due to ingestion of starchy food is of great interest in the context of worldwide health concerns. Most starches contain a portion that digests rapidly (rapidly digesting starch), a portion that digests slowly (slowly digesting starch) and a portion that is resis- tant to digestion (resistant starch) (Englyst, Englyst, Hudson, Cole, & Cummings, 1999). Resistant starch has been defined as the portion of starch that is not hydrolysed by the enzymes in the small intestine and passes to the large intestine. One of the most widely used methods to classify the starches based on kinetics of in vitro digestion was suggested by Englyst, Kingman, and Cummings (1992). The method is based on the in vitro digestion of starch by simulating stomach and in- testinal conditions and measuring glucose release at differ- ent times. Based on the method, different starch fractions are defined as: e Rapidly digestible starch (RDS): amount of glucose release after 20 min. e Slowly digestible starch (SDS): amount of glucose released between 20 and 120 min of in vitro digestion. e Resistant starch (RS): total starch minus amount of glu- cose released within 120 min of in vitro digestion which can be explained by the following equation: RS ¼ TS ðRDS þ SDSÞ ð1Þ where TS is total starch. Accurate determination of bioavailable carbohydrate in a given product enables the manufacturer to communicate the glycemic response per serving of a food, especially in the case of diabetes therapeutic food, management of dia- betes and disorders of carbohydrate metabolism. The con- cept of glycemic index has been introduced to classify foods on the basis of their postprandial blood glucose re- sponse. The glycemic index is defined as the postprandial incremental glycemic area after a test meal, expressed as the percentage of the corresponding area after an equi-car- bohydrate portion of a reference food such as glucose or white bread (Goni, Garcia-Alonso, & Saura-Calixto, 1997; Jenkins et al., 1987). Several workers have indicated a good relationship between the rate of in vitro digestion and the glycemic response to food. Such studies may be used to identify food of potential use in the diet of individ- uals with diabetes. Physico-chemical and structural characteristics of starch vary among different botanical sources (Singh, Kaur, & McCarthy, 2007; Singh, Kaur, & McCarthy, 2009). Several studies have indicated relationships between different * Corresponding author. 0924-2244/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.tifs.2009.12.001 Trends in Food Science & Technology 21 (2010) 168e180