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Apples contain substances with health-promoting properties, among them, triterpenes, including oleanolic acid (OA) and ursolic acid (UA), which are thought to have anti-inflammatory activity as well as inhibiting initiation, promotion, and metastasis of cancer. This study evaluated effects of harvest time, rootstock, and storage method on two major triterpenes in apple peel, to enhance the understanding of the relative importance of cultivation and environmental factors influencing triterpene concentration. OA and UA concentrations in the semi-dwarfing ‘MM.106’ rootstock apples were significantly higher than in the dwarfing ‘M.9’ rootstock apples at the majority of harvest times over the 2 years of investigations. In 2012 at harvest time, highest concentrations of OA and UA in ‘MM.106’ rootstock apples were 63.4 and 416.3 mg·cm, respectively, while they were 59.7 and 380.9 mg·cm, respectively, in ‘M.9’ rootstock apples. UA remained fairly stable in most cases during storage, and no difference was found between regular atmosphere storage and controlled atmospheric (CA) storage. OA concentration decreased after harvest time. Furthermore, OA showed different responses to regular atmosphere storage and CA storage, and year-to-year difference was also observed. The two rootstocks showed only slight differences in the effect on total soluble solids (TSS) and fruit color, while the titratable acidity (TA) in apples from trees on ‘M.9’ rootstock had lower levels in most cases at the third harvest time as compared with apples from trees on ‘MM.106’ rootstock. OA concentration was positively correlated with UA concentration both directly at harvest and after storage. OA and UA concentrations were positively correlated with TA and TSS, while they were negatively correlated with red color. Apples play a significant role in the diet in different countries around the world. Epidemiological studies have shown that consumption of apples is linked to reduced risk of cardiovascular disease, some cancers, asthma, and Alzheimer’s disease (Hyson, 2011). Health-promoting properties have been attributed to the presence of a range of secondary metabolites, including triterpenes. OA (3b-hydroxy-olean-12-en-28-oic acid) and its isomer, UA (3b-hydroxy-ursan-12en-28-oic acid, UA), are the two major triterpenes in apple peel (Cefarelli et al., 2006). OA and UA are commonly found in the cuticular waxes of fruit and leaves and they are important components of the wax (Koch and Ensikat, 2008; Qi et al., 2006). Along with antioxidative activity, these compounds have also been reported to have anti-inflammatory activity, and inhibit initiation, promotion, and metastasis of cancer (Shanmugam et al., 2013). UA and its derivatives have also raised much interest for the potential to act as chemopreventive and chemotherapeutic agents against different forms of cancer, and have entered Phase I clinical trials (Shanmugam et al., 2013). Breeding for improved phytochemical and nutrient quality of horticultural products has become an interesting topic in recent years. Phytochemical concentration in melons, peppers, and tomatoes has been increased, including levels of vitamin C, b-carotene, zeaxanthin, and flavonoids (Crosby et al., 2007; Davuluri et al., 2005). Recent results from an investigation of 247 wild and domesticated apple accessions found that main bioactive compounds, including triterpenoids, had been determined, with the purpose of, e.g., assisting in innovative breeding strategies (Farneti et al., 2015). Due to lack of success of many governmental programs for increasing consumption of fruit and vegetables, it has been suggested that increased concentration of bioactive compounds and nutrients by breeding programs could lead to improved health (Patil et al., 2014). However, to elevate health substances within plants, a better understanding of the effects of cultivation and other environment factors is needed. Rootstock is an important feature of apple trees in modern orchards. Due to genetic factors, rootstock controls tree size (Webster, 2001), regulates mineral uptake and leaf mineral composition (Fallahi et al., 2001), and affects hydraulic resistance, water use of scion, and fruit quality (Cohen and Naor, 2002; Cohen et al., 2007; Fallahi et al., 2002). Furthermore, they may have resistance to soil-transmitted diseases (Modgil et al., 2012) and fire blight (Kaja et al., 2015). Many suggestions have been made to explain the separate features in the rootstocks that exert these differences such as the characteristics of the bark, production and movement of different plant hormones, and top-root relationships (Ferree and Warrington, 2003; Rom and Carlson, 1987). Dwarfing rootstock ‘M.9’ and semi-dwarfing rootstock ‘MM.106’ are commonly used in apple orchards in many countries. ‘M.9’ rootstock was introduced as one of the Malling apple rootstock series, a result of a successful trial in England, which evaluated rootstocks of different origin in the early 20th century. ‘M.9’ was a chance seeding found in France. The Malling series was later followed by the Malling–Merton rootstock series, fromwhich ‘MM.106’ originate. This rootstock is a cross between ‘M.1’ (Malling series) and ‘Northern Spy’ (Ferree and Warrington, 2003; Rom and Carlson, 1987). In ‘M.9’, more limited supply of water and minerals was found as compared with ‘MM.106’. Plant hormones levels vary between these two rootstocks. Auxin and cytokinin were lower in ‘M.9’, whereas the level of abscisic acid was found to be higher than in ‘MM.106’ (Tromp et al., 2005). Although compounds with health benefits have been investigated more frequently during recent years, information about the effect of different cultivation factors, such as the rootstock, on triterpene concentration is still lacking. Fruit ripening is a complex process, which includes a series of biochemical, physiological, and structural changes (Leli evre et al., 1997). Apple fruit will experience various metabolic changes during maturation and storage, such as the change of texture (Johnston et al., 2001), anthocyanin and phenolic concentration (Burda et al., 1990; Ju and Bramlage, 1999), antioxidant activity (Ju and Bramlage, 1999), and wax composition (Veraverbeke et al., 2001). The total phenolics concentration in apple peel showed variable responses to storage, including an increase, decrease, or no change (Golding et al., 2001; Kevers et al., 2011; R€ossle et al., 2010). Triterpenes are secondary metabolites and important components in the wax of the cuticle. A study on grapes showed that the young grapes had higher level of triterpenoids, which gradually decreased during ripening, but the neutral triterpenoids showed a slight increase (Pensec et al., 2014). However, changes in the triterpene concentration of apples during the ripening on the tree and after different storage methods have not yet been thoroughly investigated. The aim of this study was to evaluate the effects of harvest time, rootstock, and storage method on two major triterpenes in apple Received for publication 23 Oct. 2015. Accepted for publication 2 Feb. 2016. We thank Karl-Erik Gustavsson for technical assistance of the HPLC analysis and the storage management, and we also thank Jan-Eric Englund for the statistic calculation suggestions. Corresponding author. E-mail: yanrong.lv@slu.se. HORTSCIENCE VOL. 51(4) APRIL 2016 349 peel, OA and UA, to enhance the understanding of the compositional evolution of triterpenes during apple fruit ripening and postharvest storage, which can provide valuable knowledge for prebreeding projects and thereby a sound basis for applied breeding programs. In addition, correlations between different quality parameters were determined. Materials and Methods Fruit material. Twenty-four ‘Aroma’ trees, on two different rootstocks (12 trees on a semi-dwarfing ‘MM.106’ and 12 trees on a dwarfing ‘M.9’), were randomly chosen and divided into three replicate blocks by row, with each block containing four trees in an IP-orchard in Kivik, southeastern Sweden (N 56 6#23##, E 14 40#57##) during 2012 and 2013 seasons. Trees had been planted in 1998 and trained as slender spindle. A similar orchard management program, including fertigation, mechanical weed control, and integrated pest management was applied. Trees were not thinned because they showed an acceptable yield and fruit size as well as very slight differences in their crop load. Fruit were harvested at three times as following: early harvest on 12 Sept. 2012 and 10 Sept. 2013, middle harvest on 17 Sept. 2012 and 2013, and late harvest on 24 Sept. 2012 and 2013 from interior and perimeter of the canopies to show an actual presentation for the total tree yield. The three harvest times were used to reflect different fruit maturity, where the second harvest time was the commercial harvest maturity stage. Fruit harvesting date was estimated according to our experience with this cultivar (Tahir, 2006) using Streif Index {firmness [kg·cm] · [total soluble solid (%) · starch hydrolysis index (degradation stage)]} and previous results (Streif, 1996). Firmness was measured on opposite, peeled sides, at the equator of each fruit, by using a penetrometer (model FT 327; Effigi, Italy, plunger diameter of 11.1 mm and depth of 7.9 mm) and results expressed as kg·cm. Starch index was evaluated by dipping a slide of equator part of apple in an iodine solution [15 g potassium iodide (Grade 99.5%; MERCK, Darmstadt, Germany) and 6 g iodine (Grade: 99%; VWR International AB, Stockholm, Sweden) per liter] for 1 min, and using a grading scale where 1 = full staining and 9 = no stain (Ericsson, 1982). Fruit were harvested in the both seasons when their Streif Index was 0.22–0.24 at the first harvest, 0.16–0.18 at the second harvest, and 0.11– 0.13 at the third harvest. Six medium-sized apples were harvested uniformly (totally 72 apples at each harvest time for three blocks: 6 apples/tree · 4 trees/

Ursolic and Oleanolic Acid in ‘Aroma’ Apple Peel as Affected by Rootstock, Harvest Maturity, and Storage Method