Contents lists available at ScienceDirect Food Research International journal homepage: www.elsevier.com/locate/foodres Modeling cereal starch hydrolysis during simultaneous saccharification and lactic acid fermentation; case of a sorghum-based fermented beverage, gowé Christian Mestres a,⁎ , Munanga de J.C. Bettencourt b , Gérard Loiseau c , Brigitte Matignon a , Joël Grabulos a , Nawel Achir c a CIRAD, UMR Qualisud TA B-95/16, 73 rue Jean-François Breton, F-34398 Montpellier Cedex 5, France b Instituto Superior de Tecnologia Agro-Alimentar de Malanje – ISTAM, EN. 230, Cangambo, Malanje, Angola c Montpellier SupAgro, UMR Qualisud, 1101 Avenue Agropolis, F-34398 Montpellier Cedex 5, France ABSTRACT Gowé is an acidic beverage obtained after simultaneous saccharification and fermentation (SSF) of sorghum. A previous paper focused on modeling the growth of lactic acid bacteria during gowé processing. This paper focuses on modeling starch amylolysis to build an aggregated SSF model. The activity of α-amylase was modeled as a function of temperature and pH, and the hydrolysis rates of both native and soluble starch were modeled via a Michaelis-Menten equation taking into account the maltose and glucose inhibition constants. The robustness of the parameter estimators was ensured by step by step identification in sets of experiments conducted with different proportions of native and gelatinized starch by modifying the pre-cooking temperature. The aggregated model was validated on experimental data and showed that both the pre-cooking and fermentation parameters, particularly temperature, are significant levers for controlling not only acid and sugar contents but also the expected viscosity of the final product. This generic approach could be used as a tool to optimize the sanitary and sensory quality of fermentation of other starchy products. 1. Introduction Acid fermentation is one of the oldest ways of enhancing the quality of cereal products. It preserves the products, thereby increasing their shelf life, and their nutritional quality while reducing the anti-nutri- tional compounds they contain. In addition, acid fermentation makes it possible to vary the taste, aroma and texture of cereal products (Blandino, Al-Aseeri, Pandiella, Cantero, & Webb, 2003; Steinkraus, 1983). A wide range of fermented cereal products exists all over the world today, most of which are traditional products that have not re- ceived the necessary scientific scrutiny. These include non-alcoholic but acid and sweet beverages like boza made from millet in Eastern Europe and Turkey, Mahewu from maize in southern Africa (Blandino et al., 2003), and akpan and gowé made from maize and/or sorghum in Benin (Adinsi et al., 2015; Akissoé et al., 2015). An important step in these processes is the hydrolysis of starch during fermentation that provides fermentable sugars for the growth of microflora. Malt is often added to speed up the amylolysis of starch by malt amylases (Dalodé-Vieira, Akissoé, Hounhouigan, Jakobsen, & Mestres, 2015; Gadaga, Mutukumira, Narvhus, & Feresu, 1999). However, the speed of starch hydrolysis depends on the level of gelatinization, which can be low in gowé, for example (Dalodé-Vieira et al., 2015). In addition, malt amylases are rapidly inhibited by acidification (Mestres et al., 2015) due the growth of Lactobacilli. This type of process, which combines enzymatic hydrolysis of starchy substrates and microbial fermentation of the derived glucose in a single step, belongs to the family of simultaneous saccharification and fermentation processes (SSF). SSF can be much cheaper than succes- sive/separate hydrolysis and fermentation (Wingren, Galbe, & Zacchi, 2003) and is applied, for example, in the production of ethanol from lignocellulose (Olofsson, Bertilsson, & Liden, 2008) or from starchy food (Ho, Doshi, Yeoh, & Ngoh, 2015) or food waste (Davis, 2008), or for production of lactic acid from starchy materials (Hetenyi, Nemeth, & Sevella, 2011). The main technical advantage of this process is reduction of the end-product (maltose and glucose) inhibition of the activity of the enzyme due to the simultaneous consumption of the end- product by the fermenting microorganism (Olofsson et al., 2008). Nevertheless, SSF is a complex all-in-one process; optimum pH and temperature conditions are not the same for amylases and micro- organisms. In addition, interactions between amylase end-products (glucose) and the metabolites produced by microorganisms (lactic acid or ethanol, for example) with amylase activity and with microbial http://dx.doi.org/10.1016/j.foodres.2017.06.059 Received 18 April 2017; Received in revised form 20 June 2017; Accepted 25 June 2017 ⁎ Corresponding author. E-mail address: christian.mestres@cirad.fr (C. Mestres). Food Research International xxx (xxxx) xxx–xxx 0963-9969/ © 2017 Elsevier Ltd. All rights reserved. Please cite this article as: Mestres, C., Food Research International (2017), http://dx.doi.org/10.1016/j.foodres.2017.06.059