Optimization of the fermentation parameters for the growth of Lactobacillus in soymilk with okara flour M.L. Moraes Filho * , M. Busanello, S. Garcia Department of Food Science and Technology, Center of Agricultural Sciences, State University of Londrina, Londrina, Brazil article info Article history: Received 13 February 2016 Received in revised form 9 August 2016 Accepted 9 August 2016 Available online 11 August 2016 Keywords: Byproduct DNA oxidation Isoflavones Lactobacillus acidophilus Lactobacillus plantarum abstract The soybean and its derivatives contain many compounds of biological interest. These compounds comprise a food matrix suitable for the incorporation of probiotic microorganisms. This study aimed to establish the optimal conditions of pH and temperature of soymilk containing 3% (w/v) of okara flour for the growth of Lactobacillus plantarum BG 112 and Lactobacillus acidophilus LA3 using a central composite rotational design (CCRD). The optimized conditions were used for the analysis of total phenolic com- pounds, isoflavone aglycones, antioxidant activity, protection against DNA oxidation, pH, acidity and growth during 72 h of fermentation. The maximal response is in the central point for Lactobacillus plantarum BG 112 and Lactobacillus acidophilus LA3, with correlation coefficients of approximately 0.85 obtained for each microorganism. The 24 and 48 h fermentation times for LPBG 112 and LA3 showed counts above 9.5 log CFU g 1 of sample with averages of 6.23 and 6.15 mmol g 1 of total isoflavone aglycones, respectively. The antioxidant activity measured by DPPH  and ABTS þ  assays resulted in the average values of 0.288 and 1.14 mmol mL 1 of sample (LPBG 112) and 0.260 and 1.08 mmol mL 1 of sample (LA3). All fermented samples showed the ability to protect plasmidial DNA against oxidation. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction The soybean is a grain originating in Asia and has been consumed for thousands of years (Chen et al., 2012). It is a non- animal source of high-quality protein due to its high content and composition of amino acids (Chen et al., 2012; Ficher et al., 2001; Jackson et al., 2002). Consumption of soybeans may occur in their whole natural form and/or in its derivatives, which include soy- milk, tofu, soy sauce, tempeh, etc. (Chen et al., 2012). Among the different products obtained from soybeans, soymilk can be obtained as a drink from soybeans through the following steps: hydration, maceration, milling and filtration (Moraes, Haj- Isa, Almeida, & Moretti, 2006; O'Toole, 1999). Soymilk can be consumed naturally or added to other ingredients, serving as a base for making other products such as soy yogurt and tofu (Cruz et al., 2009; O'Toole, 1999). In addition, soymilk is an alternative for consumers who cannot consume milk because of dietary re- strictions or who are required to follow specific diets (Bao et al., 2012). The okara is the solid byproduct obtained after the filtering step. This product has a high nutritional quality and is a source of phenolic compounds and fibers (Bowles & Demiate, 2006; O'Toole, 1999; Pinto & Castro, 2008). However, its rate of reuse is still low and is intended almost exclusively for animal feed (Pinto & Castro, 2008). The consumption of soy and its derivatives promotes health and confers benefits on its consumers such as a reduced risk of car- diovascular diseases, prevention of osteoporosis and inhibition of the proliferation of cancers (Chen et al., 2012; Liu, 1997; Nautiyal, Govindarajan, Lavania, & Pushpangadan, 2008). These benefits are associated with the presence of compounds such as phytos- terols, saponins and isoflavones (Liu, 1997). There are 12 forms of isoflavones found in soy foods, as follows: the b-glycosidic forms with a glucose molecule attached to the benzene ring (daidzin, genistin and glycitin), the malonyl- and acetyl-conjugated forms (acetyldaidzin, acetylglycitin, acetylgenistin, malonyldaidzin, malonylgenistin and malonylglycitin) and aglycones (daidzein, genistein and glycitein), which are not linked to a glucose molecule (Kuo, Cheng, Wu, Huang, & Lee, 2006; Liu, 1997). The isoflavone forms found in soy products are related to the soybean growing conditions and the process used in the preparation before con- sumption (Liu, 1997). The fermentation by different microorgan- isms is important for the conversion of isoflavones and for product * Corresponding author. Department of Food Science and Technology, Center of Agricultural Sciences, State University of Londrina, Londrina, CEP 86057-970, Brazil. E-mail address: marsilviolimafilho@gmail.com (M.L. Moraes Filho). Contents lists available at ScienceDirect LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt http://dx.doi.org/10.1016/j.lwt.2016.08.009 0023-6438/© 2016 Elsevier Ltd. All rights reserved. LWT - Food Science and Technology 74 (2016) 456e464