Hort. Sci. (Prague) Vol. 40, 2013, No. 3: 93–101 Grouping of 24 apple cultivars on the basis of starch degradation rate and their fruit pattern L. Szalay1, M. Ordidge2, G. Ficzek1, P. Hadley2, M. Tóth1, N.H. Battey2 1Department of Pomology, Faculty of Horticultural Science, Corvinus University of Budapest, Budapest, Hungary 2School of Biology, University of Reading, Reading, United Kingdom Abstract Szalay L., Ordidge M., Ficzek G., Hadley P., Tóth M., Battey N.H., 2013. Grouping of 24 apple cultivars on the basis of starch degradation rate and their fruit pattern. Hort. Sci. (Prague), 40: 93–101. The ripening processes of 24 apple cultivars were examined in the United Kingdom National Fruit Collection in 2010. Basically the starch content, and additionally ground colour, water-soluble solids content and flesh firmness were studied during ripening. The degradation of the starch content was evaluated using a 0–10 scale. A starch degradation value of 50% was taken to be the optimum harvest date, with harvest beginning at a value of 40% and finishing at 60%. Depending on the cultivar, this represented a harvest window of 9 to 21 days. Later ripening cultivars matured more slowly, leading to a longer harvesting period, with the exception of cv. Feuillemorte. Pronounced differences were observed among the cultivars on the basis of the starch degradation pattern, allowing them to be divided into four groups. Separate charts were elaborated for each group that are recommended for use in practice. Keywords: Malus × domestica; optimum harvest date; harvest window; starch content The storability of apples depends to a great extent ethylene production (Lau 1985). Changes in the fruit on the harvest date. In the course of the ripening starch content can be determined with the iodine process the quality parameters improve, but stor- test, which reveals a different pattern for each cultivar ability deteriorates (Lau 1985; Watkins 2003). The or cultivar group, requiring separate charts for their determination of the harvest date is thus an unavoid- evaluation (Smith et al. 1979). Such charts are avail- able compromise between the quality and storability able in the literature for various cultivars (Reid et al. (Tóth 2003; Streif 2010). The conversion of starch 1982; Lau 1985; Knee et al. 1989) and cultivar groups to sugar is one of the most important processes that (Blanpied, Silsby 1992). Apples contain two types indicate the ripening stage of apples (Jackson 2003; of starch, amylose and amylopectin. Out of these, Watkins 2003). A close correlation was found be- only amylose reacts with iodine (Fan et al. 1995). The tween the rate of starch degradation and the ethyl- different rates of starch degradation in various parts ene production (Tomala, Piestrzeniewicz 1998). of the fruit and the two types of starch components Starch hydrolysis begins at the end of the fruit devel- explain why there is no close correlation between the opment process, around 2–3 weeks before the start of starch degradation values indicated by the iodine test Granted in the framework of the Corvinus Visiting Scholar Programme of the Corvinus University of Budapest and by the Project TÁMOP 4.2.1/B-09/01/KMR/2010-0005. 93 Vol. 40, 2013, No. 3: 93–101 Hort. Sci. (Prague) and the starch content determined analytically separate methods currently available for individual (Fan et al. 1995; Peirs et al. 2002). Despite these cultivars and to allow a reliable determination of uncertainties, the analysis of starch degradation the optimum harvest date and the length of the is the most reliable out of the simple laboratory harvest window. For this purpose a model experi- methods available for determining the optimum ment was set up for studying the starch degrada- harvest date (Watkins 2003; Kállay 2010). The tion patterns and rates, and in addition changes sugar content is a quality parameter rather than in the water soluble content, flesh firmness and an indicator of the maturity (Reid et al. 1982; Lau ground colour during the ripening in a larger set 1985). Flesh firmness is influenced by many factors of apple cultivars. that are independent of the maturity stage, such as nutrient, water and light supplies, or the micro- climate (Harker et al. 1997; Watkins 2003). The MATERIAL AND METHODS aim of the present work was to elaborate a method for establishing the stage of ripening for all culti- Fruit samples were collected in the experimen- vars that could be used by growers to replace the tal orchard of the UK National Fruit Collection Table 1. Grouping of apple cultivars based on the time and rate of starch degradation and their starch degradation pattern, statistical data of starch degradation rate Ripening group Cultivar y = ax + b R2 Starch pattern group 1 Worcester Pearmain y = 0.254x – 1027.3 0.970 C 2 Jonagold y = 0.157x – 6346.3 0.989 B 2 Jonathan y = 0.157x – 6331.0 0.990 B 2 Red Charles Ross y = 0.185x – 7464.2 0.986 C 3 Cox’s Orange Pippin y = 0.148x – 5963.8 0.979 A 3 Fiesta y = 0.132x – 5337.9 0.993 A 3 Florina y = 0.148x – 5963.8 0.979 B 3 Freedom y = 0.148x – 5960.0 0.996 D 3 Fuji y = 0.168x – 6791.5 0.991 D 3 Fyriki y = 0.153x – 6188.0 0.949 D 3 Gala y = 0.154x – 6233.5 0.972 B 3 Golden Delicious y = 0.178x – 7183.7 0.963 C 3 Greensleeves y = 0.148x – 5960.0 0.996 A 3 Lord Derby y = 0.177x – 7155.0 0.970 C 4 Feuillemorte y = 0.208x – 8402.6 0.941 D 5 Braeburn y = 0.127x – 5146.5 0.978 C 5 Edward VII y = 0.141x – 5690.2 0.987 C 5 Elstar y = 0.118x – 4772.7 0.988 C 5 Falstaff y = 0.127x – 5151.0 0.992 C 5 Malling Kent y = 0.144x – 5818.9 0.973 C 5 Starkrimson y = 0.106x – 4297.3 0.985 D 6 Gloster y = 0.111x – 4468.9 0.968 D 6 Granny Smith y = 0.111x – 4477.6 0.989 D 6 Idared y = 0.096x – 3869.6 0.980 B a, b, y – parameters of linear functions between time and starch degradation of cultivars 94 Hort. Sci. (Prague) Vol. 40, 2013, No. 3: 93–101 in Brogdale. The course of ripening was moni- tal photos. The flesh firmness was measured with tored between August 15 and November 30, a Renato Lusa handheld penetrometer (Renato 2010 for 24 apple cultivars (Table 1). In the col- Lusa Co., Ravenna, Italy), using a measurement lection, each cultivar was represented by two head with a surface area of 0.5 cm2 and express- trees. Apple samples, consisting of 5 fruits with ing the results as kp/cm2 (1 kp/cm2 = 0.0981 MPa). average size and colouring from the two trees The ground colour was observed by a chart ofHá - of each cultivar, were picked every 8–10 days moriné (1974). The water-soluble solids content during the ripening period. Depending on how was determined by Atago Pal-1 pocket refractom- rapidly the cultivar ripened, the starch content and eter (Atago Co., Tokyo, Japan). quality parameters of each cultivar were examined on 6–9 occasions. Laboratory analyses were carried out in the Environmental Physiology Laboratory of RESULTS AND DISCUSSION University of Reading, Reading, UK. The stage of starch degradation was determined with the iodine Starch degradation patterns test, using a solution of 40 g KI + 10 g I2/l H2O. Fruits cut along the greatest diameter were dipped Based on the starch degradation patterns, the into this solution for 10–15 min, after which the cultivars could be divided into four groups, in- percentage staining was recorded. This percent- dicated as A, B, C and D in Table 1. The patterns age value was divided by 10 and the resulting are illustrated in Fig. 1. The pattern observed for figure was subtracted from 10 to give a value on Group A revealed that while the starch was gradu- the starch degradation scale (0–10), where 0 rep- ally degraded from the core outwards, the starch resents the max. starch content and 10 the com- content in the vascular bundles was retained for plete degradation of the starch content. Starch a considerable length of time, resulting in distinct degradation patterns were recorded on the digi- round patches in the pattern. Even at a starch deg- A 2 4 6 8 B 2 4 6 8 C 2 4 6 8 Fig. 1. Different types of starch degradation pat- terns for apple cultivars D A–D – starch degradation pattern groups 2–8 – rate of starch deg- 2 4 6 8 radation 95 Vol. 40, 2013, No. 3: 93–101 Hort. Sci. (Prague) Jonathan Greensleeves Starkrimson Fig. 2. Rate of starch y = 0.1567x – 6331 y = 0.1475x – 5960 y = 0.1063x – 4297.3 R2 = 0.9901 R2 = 0.9962 R2 = 0.9854 degradation in apple 10 cultivars (Brogdale, W. Pearmain 9 UK, 2010) y = 0.2542x – 10273 8 R2 = 0.9702 7 6 Granny Smith Worcester Pearmain 5 y = 0.1108x – 4477.6 Jonathan R2 = 0.9889 4 Greensleeves 3 Feuillemorte Feuillemorte 2 y = 0.2078x – 8402.6 Starkrimson Starch degradation index (0–10) 1 R2 = 0.9407 Granny Smith 0 5.9 7.11 7.11 15.8 22.8 29.8 12.9 19.9 26.9 3.10 14.11 14.11 21.11 28.11 10.10 17.10 24.10 31.10 Date radation level of 80–90% (8–9 on the scale), they sugar had already begun.