Composition and storage of pear cultivars from Nagykanizsa

The market value of pear is determined primarily by size, weight, appearance, consistency and taste. Although many results on fruit sugars, acids and polyphenols in different cultivars has been published, there are few studies on change of composition of pear during storage (Morvai & MolnárPerl, 1992, Elgar et al., 1997). Data on cultivars grown in our country are mainly available in Hungarian. Our aim was to fill this gap. According to literature data shown in Table 1 the main sugars of pear are fructose, glucose and sucrose. The values are given for 1 kg fresh weight. Hudina and Štampar (2000) determined sugars and acids in 18, European and Asian pear cultivars grown in Slovenia, including all those studied in present paper. Colaric and coworkers (2006, 2007) studied sugars, acids and phenolic compounds in ‘Williams’ and ‘Conference’ pear. They detected chlorogenic acid, syringic acid, epicatechin, catechin, sinapic and vanillic acid with chlorogenic acid being dominating. Main organic acids are malic and citric, with shikimic and fumaric existing as minor compounds. Pear needs suitable post-harvest storage to assure a good transportability and distribution. Elgar et al. (1997) investigated fruit from two winter pear cultivars stored for 20 weeks at –0.5 °C. Titratable acidity of ripened fruit decreased with advanced storage: In case of ‘Bosc’ the acidity changed from 0.187% to 0.116%, while polyphenolic compounds showed a temporary increase in the first two weeks, and a slight decrease during two months, depending on temperature. Morvai and Molnár-Perl (1992) reported the growth of acids (including ascorbic), sugars and sorbitol during storage of Bosc pear, but the duration and circumstances are not known.

'Conference': planted in 1999. Spacing 5×3 m on a Farold 69-87 rootstock, crown shape: free spindle. This cultivar is able to bring a high crop yield, but it is liable to biennial bearing. It is characterised by parthenocarp fruit production, often even the core is vestigial. In 2008 'Conference' brought nice large size fruits at Feketesár.

Methods used
Pear fruits were washed and then the size and weight of 50 fruits was measured according to Hungarian Standard MSZ 967-1:1982. From approximately five kg sample one kg optimally ripened, sound fruit was selected, core removed and disintegrated unpeeled using a Waring (Torrington, USA) blender. The blended fruit sample was used in the different measurements and chemical analyses.

Results and discussion
As it is well known that wheather has a strong influence on fruit properties, a short description is given on the weather conditions of years 2008-2009 at the orchard near Nagykanizsa.
2008.: It was a hot summer with poor precipitate, a +41-+42°C peak temperature in July. High temperature tried trees, there were also sunburst fruits. There was a significant damage by Psylla pyri and sooty mould, grown on honeydew. The continuous irrigation raised the expenses. Crop yield was relevant to the age and condition of trees. Storage was finished in February. Loss on storage was minimal. This was the best year of the interval studied.
2009 started promising, a frost-free blooming and good fruit set. The time of fruit growths was rich in precipitation. Psylla infection was weak. Erwinia amylovora and Venturia caused minimal problem. Afterwards two hailstorms destroyed a significant part of crop. The harvested crop was partly damaged and there was a 7-10% loss in storage.
2010 is found to be an intermittent year. The fluctuating temperature at the end of winter and beginning of March shocked the trees. The greatest problem is the poor bud differentiation of the main cultivar 'Bosc'. The night chills influenced fruit set adversely, further deteriorating the chances of fruit growth. None of the other cultivars produced the expected crop yield. Only 'Packham' approximated the expectations in yield. Because of the extraordinarily rainy weather there was a minimal need for irrigation, but the weather favoured bacterial and fungal infections.
The size and weight values measured in three consecutive years with five cultivars are summarized as Table 2. The average weights per piece are generally lower than those given by Hudina and Štampar (2000). 'Williams' pear ( Figure 1) had the lowest weight per piece in all the three crop years. Table 3 shows the compositional characteristics of cultivars during storage. The changes in glucose, fructose and sucrose at harvest and after two and four months in ULO store can be seen on Figure 2. The water soluble solids (Brix), total sugar, sucrose and water soluble pectin were all decreasing during storage. This is not in agreement with the conclusion of work of Morvai and Molnár-Perl (1992), in Composition and storage of pear cultivars from Nagykanizsa which storage conditions were not described: Decline of water content could lead to a virtual increase of sugars and acids. According to our study, titratable acidity remained practically constant, except that slight decrease was observed in fruits of the cultivar Conference. Polyphenols and free radical scavenging capacity did not show a significant change during four months storage. As comparing the composition of pear cultivars in three consecutive years, (Table 4 and Figure 3), 'Conference' and 'Bosc' contained the highest sucrose level, while 'Williams' pear was found to contain the highest acidity among the cultivars tested. 'Conference' had the highest total sugar content, while 'Abate Fétel' had the lowest sucrose and highest glucose of the cultivars tested. The high sucrose content is interesting, as the AIJN Code of Practice gives an upper limit of 15 g/kg for 100% pear puree. All the sugars measured by our team are much higher (often double) than the values of Hudina and Štampar (2000) found in Slovenian grown fruits.