LWT - Food Science and Technology 79 (2017) 260e266 Contents lists available at ScienceDirect LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt Different thermal drying methods affect the phenolic profiles, their bioaccessibility and antioxidant activity in Rhodomyrtus tomentosa (Ait.) Hassk berries ** Guanghe Zhao a, b, Ruifen Zhang a, b, , Lei Liu a, Yuanyuan Deng a, Zhencheng Wei a, * Yan Zhang a, Yongxuan Ma a, Mingwei Zhang a, a Sericultural & Agri-Food Research Institute, Guangdong Academy of Agricultural Sciences/Key Laboratory of Functional Foods, Ministry of Agriculture/ Guangdong Key Laboratory of Agricultural Products Processing, Guangzhou 510610, China b College of Food Science & Technology, Huazhong Agricultural University, Wuhan 430070, China article info abstract Article history: Extended shelf life and convenient industrial application have led to increasingly wide use of drying Received 22 August 2016 technology in fruits and vegetables processing. However, drying process usually has a negative effect on Received in revised form the active ingredients in fruits and vegetables. In this study, the effects of three thermal drying methods 19 November 2016 (hot air drying (HD), microwave drying (MD) and combined microwave-hot-air-drying (CD)) on phenolic Accepted 14 January 2017 profiles, their bioaccessibility and antioxidant activity in Rhodomyrtus tomentosa berries were estimated. Available online 17 January 2017 The total phenolics, flavonoids and anthocyanins contents of CD-berries were significantly higher than those of HD- and MD-ones. CD-berries had higher contents of individual phenolics and showed stronger Keywords: Rhodomyrtus tomentosa berries antioxidant activity than HD- and MD-ones. Conversely, the bioaccessibility of phenolics in HD-berries Drying methods was remarkably higher than that of MD- and CD-ones, although the latter 2 provided more bio- Phenolics accessible phenolics than the former after in vitro gastrointestinal digestion. Thus, combined microwave- Antioxidant activity hot-air-drying (CD) is a more suitable drying technique for Rhodomyrtus tomentosa berries to maintain Bioaccessibility their phenolics and antioxidant activity. © 2017 Published by Elsevier Ltd. 1. Introduction downy rose-myrtle, is a shrub belonging to Myrtaceae family. It originated from South-East Asia, and mainly distributed in China, Epidemiological studies have shown that consumption of fruits Philippines, Malaysia, Indonesia, and Vietnam (Lai et al., 2015; Liu, and vegetables may offer protection against various chronic dis- Guo, & Sun, 2012). According to a preliminary statistics, the pro- eases, including cardiovascular disease, type 2 diabetes, cancers, duction of Rhodomyrtus tomentosa berries is approximately 100 and may impart other health benefits (Barrett & Lloyd, 2012; Del thousand tons per year in China. It has long been used to treat Rio et al., 2013; Plaza et al., 2011). Increasing evidences have diarrhoea, dysentery, traumatic hemorrhage and also to strengthen shown that these health-promoting properties of fruits and vege- immunity (Agro Forestry Tree Database, 1992; Do, 2011; Geetha, tables are mainly due to their phytochemical constituents, espe- Sridhar, & Murugan, 2010; Institute of Chinese Medicine, 2010). cially phenolics (Crozier, Jaganath, & Clifford, 2009; Noratto, Porter, As a good source of phenolics, till date, more than 19 individual Byrne, & Cisneros-Zevallos, 2009). phenolics, including anthocyanins, phenolic acids, flavonols, ella- Rhodomyrtus tomentosa (Ait.) Hassk, commonly known as gitannins, and stilbenes, have been identified in Rhodomyrtus tomentosa berries (Cui et al., 2013; Lai et al., 2013; Liu et al., 2012; Wu et al., 2015). Furthermore, Rhodomyrtus tomentosa berries * Corresponding author. have been reported strong antioxidant activities and abundant ** Corresponding author. Sericultural & Agri-Food Research Institute, Guangdong supply of nutrients (Cui et al., 2013; Huang, Cai, Corke, & Sun, 2010; Academy of Agricultural Sciences/Key Laboratory of Functional Foods, Ministry of Lai et al., 2015; Wu et al., 2015). In view of the excellent nutritional Agriculture/Guangdong Key Laboratory of Agricultural Products Processing, fl Guangzhou 510610, China. properties and delicious avor, Rhodomyrtus tomentosa berries E-mail addresses: [email protected] (R. Zhang), [email protected] became a popular regional fruit. (M. Zhang). http://dx.doi.org/10.1016/j.lwt.2017.01.039 0023-6438/© 2017 Published by Elsevier Ltd. G. Zhao et al. / LWT - Food Science and Technology 79 (2017) 260e266 261 However, due to short maturity and soft texture, Rhodomyrtus HD: Samples were dried at 70 C in a DHG-9240A electro- tomentosa berries can be easily infected by mold. The timely drying thermal constant-temperature dry box (Shanghai Keelrein instru- of ripe Rhodomyrtus tomentosa berries can effectively prolong their ment Co.Ltd.) for 12 h. storage time and contribute to their usage in food and nutraceutical MD: Samples were dried at 136 W in a MG823LA3-NR domestic production. Traditionally, Rhodomyrtus tomentosa berries are dried microware oven (Midea Group Co. Ltd., China) for 4 h (heat for 300 s in sunlight or shade, which is time consuming, and worse than that then stop for10 s, and again). is mustiness, a common problem due to prolonged drying duration. CD: Samples were dried at 136 W in a household microware Till date, the main industrial methods for fruits and vegetables mentioned above for 2.5 h (heat for 300 s then stop for10 s, and drying include hot air drying, microwave drying and freeze drying. again), then dried at 70 C in a electrothermal constant- Freeze drying is considered as the best drying method for main- temperature dry box as mentioned above for 1 h. taining the maximum amount of phenolic components in fruits but Water contents of the dried samples were approximately 5%. All high equipment cost limits its large scale application. Drying pro- dried Rhodomyrtus tomentosa berries were grinded into powder cesses may have positive or negative effects on phenolic compo- with a FW80 disintegrator (Tianjin Taisite Instrument Co., LTD) (80 nents in fruits and vegetables products compared to their fresh mesh) and stored in refrigerator at À20 C in sealed polypropylene counterparts. In previous research, hot air drying increased bags for further analysis. phenolic contents in tomato at 60e80 Cby13e29% (Chang, Lin, Chang, & Liu, 2006), whereas decreased it in murta berries at 2.3. Extraction of phenolics 40e80 C by more than 70% (Rodríguez et al., 2014). In addition, microwave drying increased phenolic contents in apple slices by The phenolics were extracted by adding 50 mL of 80% acetone 5e31% at 300 W (Tarko, Duda-Chodak, & Tuszunski, 2009), but into 1.0 g of Rhodomyrtus tomentosa berries powder (Liu et al., _ decreased it in goldenberry up to 60% at 160 W (Izli,Yıldız, Ünal, 2015). The mixture was shaken using a SHA-C constant tempera- Isık, & Uylas¸er, 2014). It was observed that drying process can ture oscillation water-bath (Changzhou Aohua apparatus Co.Ltd., have variable effects on fruit's phenolics and mainly depend on the Changzhou, China) at 200 rpm at room temperature for 24 h. The type of drying process and fruit variety. Besides the effects on supernatants were removed after centrifugation at 6800g for phenolics, drying process may alter the microstructure of fruits and 10 min and concentrated at 45 C by using a rotary evaporator (N- subsequently affect the bioaccessibility of their phenolics after 1200B, Eyela, Japan). The concentrated extract was then recon- gastrointestinal digestion (Aydin & Gocmen, 2015; Bondaruk, stituted to a final volume of 10 mL with methanol and stored Markowsk, & Błaszczak, 2007; Caparino et al., 2012). at À20 C until further analysis. Till date, researches on Rhodomyrtus tomentosa berries were focused on the estimation of nutritional, phytochemical profile, and 2.4. Content of total phenolics, flavonoids, and anthocyanins antioxidant activity. Little is known about the effects of drying methods on health-promoting properties of Rhodomyrtus tomen- 2.4.1. Total phenolic content tosa berries. Therefore, this study aims to evaluate the effects of The total phenolic content was analyzed by Folin-Ciocalteu three thermal drying methods (hot air drying (HD), microwave colorimetric method as previously reported by Dewanto, Wu, drying (MD) and combined microwave-hot-air-drying (CD)) on Adom, & Liu, (2002). Total phenolic content was expressed as mg phenolic profiles, their bioaccessibility and antioxidant activity in of gallic acid equivalents (GAE) per g dry weight (DW) of sample. Rhodomyrtus tomentosa berries. The results presented in this study could provide scientific basis for choosing the right drying process 2.4.2. Total flavonoids content of Rhodomyrtus tomentosa berries. The total flavonoids content was determined using the aluminium chloride colorimetric method described by Ti 2. Materials and methods et al.(2014). Total flavonoids content was expressed as mg of rutin equivalents (RE) per g dry weight (DW) of sample. 2.1. Chemical and reagents 2.4.3. Total anthocyanins content 1,1-Diphenyl-2-picrylhydrazyl radical (DPPH$), Folin & Cio- The quantification of total anthocyanins was evaluated by the calteu's phenol reagent, 2,4,6-tripyridyl-s-triazine (TPTZ), 6- pH differential method described by Lee, Durst, and Wrolstad hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox), (2005). The anthocyanin content was expressed as mg