Thermal stability of the functional ingredients, glucosylated benzophenones and xanthones of honeybush (Cyclopia genistoides), in an aqueous model solution Theresa Beelders a,b , Dalene de Beer a,b , Daneel Ferreira c , Martin Kidd d , Elizabeth Joubert a,b,⇑ a Plant Bioactives Group, Post-Harvest and Wine Technology Division, Agricultural Research Council (ARC) Infruitec-Nietvoorbij, Private Bag X5026, Stellenbosch 7599, South Africa b Department of Food Science, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa c Department of BioMolecular Sciences, Division of Pharmacognosy and the Research Institute of Pharmaceutical Sciences, School of Pharmacy, The University of Mississippi, University, MS 38677, USA d Centre for Statistical Consultation, Department of Statistics and Actuarial Sciences, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa article info Article history: Received 8 February 2017 Received in revised form 7 April 2017 Accepted 14 April 2017 Available online 17 April 2017 Chemical compounds studied in this article: 3-b-D-glucopyranosyliriflophenone (PubChem CID: 53396784) 3-b-D-glucopyranosylmaclurin (PubChem CID: 101876647) isomangiferin (PubChem CID: 5318597) mangiferin (PubChem CID: 5281647). Keywords: Thermal degradation kinetics modelling Mangiferin Isomangiferin 3-b-D-Glucopyranosylmaclurin Structure-stability relationships Degradation pathways abstract Thermal stability of the benzophenones, 3-b-D-glucopyranosyl-4-b-D-glucopyranosyloxyiriflophenone (1), 3-b-D-glucopyranosylmaclurin (2) and 3-b-D-glucopyranosyliriflophenone (3), and the xanthones, mangiferin (4) and isomangiferin (5), was assessed separately in an aqueous model solution (pH 5) to delineate their major degradation products and mechanism(s). Degradation followed first-order /lhword> reaction kinetics and the temperature-dependence of the respective reaction rate constants complied with the Arrhenius equation. The stability of the compounds increased in the order 2 > 4 > 3 > 5 > 1. 4-O-Glucosylation significantly stabilised 1 against degradation compared to 3, enediol B-ring functionality of 2 decreased stability compared to 3 and position of glucosylation affected the stability of the xanthones with 5 being more stable than 4. The xanthone nucleus (C-ring) conferred higher stability to 4 and 5 compared to their benzophenone analogue 2. Cyclisation of 2 to 4 and 5 would underestimate their degradation in mixtures. Other reactions were isomerisation, dimerisation, acetylation and hydrolysis. Ó 2017 Elsevier Ltd. All rights reserved. 1. Introduction Polyhydroxybenzophenones and -xanthones have risen in importance as bioactive phytochemicals, especially in view of their anti-obesity and antidiabetic activities (Beelders et al., 2014; Feng, Yang, & Wang, 2011; Lim et al., 2014; Pan, Yi, Wang, Chen, & He, 2016; Schulze et al., 2016; Wu, Long, & Kennelly, 2014; Zhang, Han et al., 2013; Zhang, Liu et al., 2013). This stimulated interest in the use of plant extracts containing these compounds as functional ingredients by the food industry. Co-occurrence of xanthones and benzophenones in many plants is common, due to a shared biosynthetic pathway. Mango byproducts such as the peels and leaves are well-known sources (Berardini, Carle, & Schieber, 2004; Berardini, Knödler, Schieber, & Carle, 2005; Zhang, Han et al., 2013). Another potential source of these com- pounds is Cyclopia species (Fabaceae). Several of the Cyclopia spe- cies are processed mainly for use as herbal tea, known as honeybush (Joubert, Joubert, Bester, De Beer, & De Lange, 2011). Cyclopia extracts have found application as ingredients in a variety of food and beverage products, including iced tea, food bars and most recently, bread. Considering that many food processing unit operations involve application of high temperatures, the extracts are subjected to elevated temperatures when incorporated into food and beverage products. One such example is ‘‘natural” http://dx.doi.org/10.1016/j.foodchem.2017.04.083 0308-8146/Ó 2017 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Plant Bioactives Group, Post-Harvest and Wine Technology Division, Agricultural Research Council (ARC) Infruitec-Nietvoorbij, Private Bag X5026, Stellenbosch 7599, South Africa. E-mail address: JoubertL@arc.agric.za (E. Joubert). Food Chemistry 233 (2017) 412–421 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem