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Scientia Horticulturae 129 (2011) 376–381

Contents lists available at ScienceDirect

Scientia Horticulturae

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ate season harvest and storage of Rubus berries—Major antioxidant and sugarevels

iaqat Ali ∗, Birgitta Svensson, Beatrix W. Alsanius, Marie E. Olssonepartment of Horticulture, Swedish University of Agricultural Sciences, P.O. Box 103, SE-23053 Alnarp, Sweden

r t i c l e i n f o

rticle history:eceived 4 August 2010eceived in revised form 22 March 2011ccepted 30 March 2011

eywords:ntioxidantstorageugarsnthocyanins

a b s t r a c t

Late season production of raspberries and blackberries has become more common due to increasedconsumer demand and new production techniques, but information is scarce regarding the effect onnutritional quality, especially during storage. Antioxidant levels in berries can be influenced by pre-harvest climate conditions (light intensity, day length and temperature) and post-harvest storage time.This study analysed the effect of these factors on the content of different antioxidants (vitamin C, ellagicacid, anthocyanins and total phenolics) in raspberries (Rubus idaeus L. cv. Polka) and blackberries (Rubusfructicosus L. cv. Loch Ness) during storage. The analyses were performed using high performance liquidchromatography (HPLC) with photodiode array detection. Ellagic acid content during storage rangedbetween 104 and 114 mg/100 g fresh weight in raspberries and 172 and 182 mg/100 g fresh weight

llagic acidotal phenolics

in blackberries. Anthocyanin content increased during storage from 64 to 77 mg/100 g fresh weight inraspberries, but decreased from 199 to 162 mg/100 g fresh weight in blackberries. Vitamin C content inraspberries ranged during storage between 22 and 28 mg/100 g fresh weight, but in blackberries valueswere lower (10–12 mg/100 g fresh weight). Significant changes in total phenolics and sugars occurredduring different storage periods (0–9 or 10 days). The results suggest that late season raspberries andblackberries maintain high quality in terms of antioxidant content.

. Introduction

During the past decade, efforts have been made in plant breed-ng and cultivation to extend the harvest season of raspberriesnd blackberries (Anttonen and Karjalainen, 2005; Clark and Finn,008; Kassim et al., 2009). Primocane production (fruit develop-ent on first-season canes) has been very important in extending

he fruiting season of raspberries. In addition, greenhouse and highunnel cultivation have expanded the possibilities of late seasonarvesting of raspberries and blackberries. Late season cultivation,hich means harvesting during September and October in Scandi-avian conditions, generally involves lower light intensity, shorteray length and lower temperature, especially during night-time,ompared with production in summer conditions (SMHI, 2007). Aslimate conditions are known to affect various quality parametersf berries, late season production could be expected to influenceuality, although knowledge is scarce in this area.

Fruit quality has been the focus of much research in therea lately and the health-promoting properties of berries havettracted particular interest. A large number of epidemiological

∗ Corresponding author. Tel.: +46 40415368; fax: +46 40462166;obile: +46 765615345.

E-mail addresses: Liaqat.Ali@slu.se, liaqat.ali@ltj.slu.se (L. Ali).

304-4238/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.scienta.2011.03.047

© 2011 Elsevier B.V. All rights reserved.

studies have provided convincing evidence of the health-promoting role of fruit and vegetables in the human diet. Forexample, fresh fruit and vegetables are reported to prevent degen-erative diseases and decrease the risk of cardiovascular diseasesand certain forms of cancer (Joshipura et al., 2001; Maynard et al.,2003). This protection has been attributed to the fact that thesefoods may contain an optimal mix of phytochemicals, such asantioxidants, fibre and other bioactive compounds (Ames et al.,1993).

Berries contain a number of different antioxidants, such asascorbic acid, phenolics, ellagic acid, ellagitannins and flavonoidsincluding anthocyanins (Rommel and Wrolstad, 1993b; Cliffordand Scalbert, 2000). Berries have a high antioxidant effectagainst reactive oxygen species (ROS) produced in the humanbody (Kahkonen et al., 2001; Mullen et al., 2002b). SuchROS can lead to pathological conditions such as ischaemia-reperfusion damage, inflammatory and degenerative diseases,cancer, DNA damage and ageing (Joshipura et al., 2001;Catalá1, 2006). Raspberries are among the berries that havebeen identified as providing a rich source of the ellagitan-nins sanguiin H-10, lambertianin C and sanguiin H-6, as well

as ellagic acid, flavonoid glycosides and anthocyanins (Mullenet al., 2003). The major raspberry anthocyanins are cyanidin-3-glucoside and cyanidin-3-sophoroside, with smaller quantities ofother anthocyanins, including cyanidin-3-(2G-glucosylrutinoside),

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yanidin-3-rutinoside, pelargonidin-3-sophoroside, pelargonidin--(2G-glucosylrutinoside) and pelargonidin-3-glucoside (Spanosnd Wrolstad, 1987; Mullen et al., 2002a). Blackberries are also aood source of natural antioxidants such as anthocyanins, ellagiccid, ellagitannins and phenolic acids (Wang et al., 1996; Wang andin, 2000).

Fresh berries are highly perishable and their quality and shelf-ife can be greatly affected by different pre- and post-harvestactors. A number of studies have reported the effect of pre-harvestactors, including climate conditions and cultural practices, on dif-erent phenolic compounds and antioxidant values at harvest, andlso on shelf-life during storage (Perkins-Veazie and Kalt, 2002;nttonen and Karjalainen, 2005; Anttonen and Karjalainen, 2009).ight and average temperature during fruit growth have a strongffect on the chemical composition and antioxidant values of berryruits (Lee and Kader, 2000; Wang and Zheng, 2001; Anttonennd Karjalainen, 2005). The amount and extent of low and highemperatures during the growth and maturation period of raspber-ies and blackberries have a definite influence on the antioxidants,ncluding anthocyanins, vitamin C and total phenolics (Rommel and

rolstad, 1993a; Perkins-Veazie and Kalt, 2002). Berries grownith lower light intensities and shorter day length have lower lev-

ls of sugars and antioxidants (Wang and Zheng, 2001). Fruitingrder has also been shown to have a significant effect on phenolicontent in strawberry, and the phenolic content generally increasesrom primary to tertiary fruits. Tertiary fruits have been reportedo contain 10, 25 and 11% higher amounts of total phenolics, ellagiccid and antioxidant capacity, respectively, than primary fruitsAnttonen and Karjalainen, 2009). The effects of storage on the con-ents of anthocyanins, ellagic acid and vitamin C in raspberries haveeen investigated (Mullen et al., 2002b). A number of authors haveoted that storage at low temperatures (2 ◦C) positively affects theuality and shelf-life of fruit, including blueberries and blackber-ies (Perkins-Veazie and Collins, 2002), raspberries (Reynoso ande Michelis, 1994) and strawberries (Pelayo et al., 2003). For grow-rs and distribution chains, increasing the shelf-life of berries andxtending their growing season would be profitable. However, theoncentrations of antioxidant compounds in these berries at lateeason harvest and during subsequent storage are unknown. Theim of this study was therefore to determine how the quality ofhe berries in terms of antioxidant values and sugar content wasffected by late season production, and whether storage of theerries produced late in the season affected the levels of theseompounds.

. Materials and methods

.1. Plant material

Raspberries (Rubus idaeus L. cv. Polka) were obtained from a highlastic tunnel culture located near Sjöbo, Sweden (55◦38.074′N,3◦42.393′E). Blackberries (Rubus fruticosus L. cv. Loch Ness)ere collected from an unheated glasshouse culture located near

inköping, Sweden (58◦19.153′N, 15◦49.301′E). Sampling was car-ied out late in the season, during September and October 2007.he samples were stored in plastic containers at 2 ◦C and 75% rela-ive humidity. Raspberries were analysed on day 0, 1, 4, 6 and 9 oftorage, while blackberries were analysed on day 0, 3, 7 and 10.

.2. Chemicals

Meta-phosphoric acid were purchased from Sigma–Aldrich Inc.Germany). Dithiothreitol (DTT), potassium di-hydrogen phos-hate (KH2PO4) and ascorbic acid were obtained from VWR

nternational (Belgium). Acetone (Lichrosolv), acetonitrile (Lichro-

rae 129 (2011) 376–381 377

solv), hydrochloric acid (HCl) and methanol (Lichrosolv) wereobtained from Merck (Germany). Ethanol was obtained fromSolveco (Sweden).

2.3. Analysis of vitamin C

The samples was homogenised with a Waring Blender 8011G,Dynamics Corporation (USA). A 5 g portion of the homogenatewas extracted with 25 ml 1.5% meta-phosphoric acid and storedat −80 ◦C until analysis, and then thawed and centrifuged at12,500 × g for 12 min. The amount of vitamin C was determinedafter a reduction treatment by dithiothreitol (DTT) (Esteve et al.,1997). Samples were run on a 6000 HPLC system (Merck-Hitachi,Germany) with a UV detector at 248 nm (binary gradient; solventA 20 mM K2HPO4: methanol (96:4 with pH adjusted to 2.3 usingconcentrated H3PO4), solvent B 100% methanol). The flow rate was1 ml min−1, the injection volume 10 �l, a Phenomenex synergi col-umn (polar RP 250 × 4.6 mm, particle diameter 4 �m) was used, andquantification was carried out by comparison with ascorbic acid asexternal standard. A mobile phase gradient was used: 0–4 min: 0%eluent B, 4–7.5 min: 0–80% B, 7.5–8 min: 80–0% B, and 8–18 min:0% B.

2.4. Analysis of ellagic acid and anthocyanins

Ellagic acid was extracted as in Siriwoharn et al. (2005),with some modifications. A 1 g portion of lyophilised samplewas extracted in 20 ml 70% acetone at 2 ◦C for 20 h on a rotaryorbital shaker (Forma Scientific Inc., USA), and then centrifugedat 12,500 × g for 12 min. Aliquots of 1 ml of the supernatant wereadded to 1 ml 4 M HCl, hydrolysed for 4 h at 93 ◦C, and then dilutedwith 0.1% HCl, so that the concentration of acetone was 8% beforethe samples were applied to a STRATA Phenomenex C-18 cartridgeequilibrated with 0.1% HCl. The ellagic acid was eluted with 2.5 ml99.7% methanol.

Anthocyanins were extracted by agitating 1 g of lyophilisedsample in 20 ml 50% ethanol (v/v) and 1% HCl at 2 ◦C for 20 hon a rotary shaker, and then centrifuged at 12,500 × g for 12 min.Aliquots of 1 ml of the supernatant were analysed directly by HPLC,and the results are expressed as mg cyanidin-3-glucoside equiva-lents/100 g fresh weight.

The extracted samples of ellagic acid and anthocyanins wereinjected onto a 7000 HPLC system (Merck-Hitachi, Germany) usinga modified method of Siriwoharn et al. (2005). The mobile phasesconsisted of A: 20 mM KH2PO4 (with pH adjusted to 2.3 using conc.H3PO4) and methanol 97:3; and B: 99.7% acetonitrile. The flow ratewas 1 ml min−1, the injection volume 10 �l and with a Phenomenexsynergi column (fusion RP 250 × 4.6 mm, 4 �m). Binary gradientswere used: 0–7 min 0% eluent B, 7–59 min 0–22% B, 59–65 min22–55% B, 65–69 min 55–0% B. Ellagic acid was identified andquantified at 254 nm using a diode array detector, by an exter-nal standard ellagic acid (Sigma–Aldrich, USA), and by retentiontime and light spectrum. Anthocyanins were identified with a diodearray detector at 520 nm and by comparing with the literature data(Mullen et al., 2002a; González et al., 2003) and quantified by com-parison with cyanidin-3-glycoside (Polyphenols Laboratories AS,Norway).

2.5. Analysis of total phenolics and sugars

The samples; in triplicate, equivalent to 5 g of the fresh weightwere homogenized in 20 ml of 99.7% ethanol and kept at −20 ◦C for

2 weeks. The extracts were then centrifuged at 12,500 × g for 12 minand an aliquot of the supernatant was used directly for sugar anal-ysis using HPLC. For total phenolics an aliquot of 60 �l supernatantwas prepared according to the Folin–Ciocalteu method, modified

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3 iculturae 129 (2011) 376–381

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0.51–0.63 g/100 g fresh weight, respectively) but in the caseof sucrose the concentration decreased initially from 0.79 to0.54 g/100 g fresh weight from day 0 to day 1 (Table 1). From

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s in Dewanto et al. (2002). After 75 min, the absorbance for totalhenolics was measured at 765 nm using a Varian Cary 50 spec-rophotometer (Agilent Technologies Inc., USA). Quantification wasarried out by comparison against the external standard galliccid, 3,4,5-trihydroxybenzoic acid (Sigma–Aldrich, Germany). Sug-rs were determined by HPLC, with a Waters 515 pump (Watersnc., USA), an autosampler 465 (Kontron, Italy), a RI-detector, IVLDC Analytical, USA). Flow rate was 1 ml/min isocratic running,nd eluent 70:30 acetonitrile:water (v/v). Carbohydrates were sep-rated on a Shodex Asahipak HH2P-50 4E, 250 mm (Showa Denko.K., Japan) and identified and quantified by comparison against thexternal standards d-fructose (Janssen Chimica, Belgium), glucoseSigma Chemical Co., USA.) and sucrose (Sigma Chemical Co., USA).

.6. Statistics

Three replicate samples were used for each storage date. Gen-ral linear model (GLM) was carried out using SAS (SAS Inst. Incv.ary, North Carolina, USA). The mean values by Tukey’s studentisedange test (HSD) were used to investigate the effect of storage onntioxidants. Differences were considered statistically significantt p < 0.05.

. Results

.1. Vitamin C

Vitamin C content in raspberries showed a significant decreaseuring storage from day 0 to day 6, before recovering to the initial

evel. Thus the overall level of vitamin C during 9 days of storageas rather stable. The concentration in raspberries varied between

1.94 and 27.96 mg/100 g fresh weight during storage. In the case oflackberries, there was a small but significant increase in vitamincontent (p = 0.0207) over the whole storage period (Fig. 2). The

oncentration in blackberries ranged from 10.78 to 12.11 mg/100 gresh weight during storage.

.2. Dry matter

The dry matter content in raspberries and blackberries was veryimilar during the whole storage period from 0 to 10 days (data nothown). The mean dry weight (DW) of the raspberry samples forifferent storage times was 8.95% of fresh weight (FW), while for thelackberries it was 12.03%. The seeds were included in dry weightercentage for both types of berries.

.3. Ellagic acid

Ellagic acid content in the raspberries and blackberries didot show much variation during the whole storage period of–10 days (Figs. 3 and 4). Ellagic acid content ranged from03.06 to 113.70 mg/100 g fresh weight in raspberries and72.24–181.59 mg/100 g fresh weight in blackberries, but no sta-istically significant changes were recorded.

.4. Anthocyanins

Cyanidin-3-sophoroside is the major anthocyanin present inaspberries and cyanidine-3-glycoside in blackberries (Mullent al., 2002a; González et al., 2003). In the present study (calcu-ation based on one major peak), the anthocyanins were present

t higher levels in blackberries than in raspberries (Figs. 1 and 2).ignificant differences in anthocyanins content were found in rasp-erries during storage, with the content increasing from 61.92o 76.66 mg/100 g fresh weight with storage time. In blackberries

Fig. 1. Content (mg/100 g FW ± SD) of anthocyanins and vitamin C at different stor-age times (0, 1, 4, 6 and 9 days) in late season raspberries under Scandinavianconditions. Storage temperature 2 ◦C and 75% RH.

there was a gradual and significant decrease in the content of antho-cyanins from 199.37 to 162.35 mg/100 g fresh weight. Some minorpeaks were also detected in both types of berry, but since thesecompounds were present at very low levels they were not includedin the study.

3.5. Total phenolics

The total phenolics in raspberries decreased significantly afterthe first day of storage and then increased from 81.56 to 94.50 mgGAE equivalents/100 g fresh weight from day 1 to day 9 (Fig. 3).In blackberries, the total phenolics content declined during stor-age from 322.11 to 276.52 mg GAE equivalents/100 g fresh weight(Fig. 4).

3.6. Sugars: fructose, glucose and sucrose

The main sugars detected in raspberries and blackberries werefructose, glucose and sucrose. In raspberries, fructose and glu-cose content increased initially during storage (0.68–0.84 and

Storage Time (days)

Fig. 2. Content (mg/100 g FW ± SD) of anthocyanins and vitamin C at different stor-age times (0, 3, 7, and 10 days) in late season blackberries under Scandinavianconditions. Storage temperature 2 ◦C and 75% RH.

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Fig. 3. Content (mg/100 g FW ± SD) of ellagic acid and total phenolics at differentstorage times (0, 1, 4, 6 and 9 days) in late season raspberries under Scandinavianconditions. Storage temperature 2 ◦C and 75% RH.

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Fig. 4. Content (mg/100 g FW ± SD) of ellagic acid and total phenolics at differentstorage times (0, 3, 7, and 10 days) in late season blackberries under Scandinavianconditions. Storage temperature 2 ◦C and 75% RH.

Table 1Content of total soluble solids (TSS) and sugars (fructose, glucose and sucrose) inlate season raspberries and blackberries in Scandinavian conditions, stored at 2 ◦Cfor different storage periods (0–10 days).

Storage time (days) TSS (soluble solids) Sugars (g/100 g fresh weight)

Fructose Glucose Sucrose

Raspberries0 7.46a 0.68b 0.51d 0.79a1 7.10d 0.84a 0.63a 0.54c4 7.3b 0.86a 0.54c 0.42d6 7.20c 0.65c 0.43e 0.42d9 6.50e 0.86a 0.57b 0.55bHSD 0.06 0.015 0 1.25Blackberries0 8.60a 2.23a 2.08a 0.12c3 7.16b 2.15b 1.86b 0.20a7 6.90c 2.25a 1.92b 0.18b10 7.13b 2.09b 1.73c 0.17bHSD 0.16 0.06 0.05 0.00032

Mean Tukey’s HSD values for all determinants, based on n = 3. HSD = highly sig-nificant difference (p < 0.05). Different letters within columns indicate significantdifferences between storage periods (p < 0.05).

rae 129 (2011) 376–381 379

day 4–6 of storage the fructose/glucose ratio decreased (ratio notshown), while the level of sucrose did not change. On the lastday of storage, the sum of the total sugars analysed was thesame as the initial level in raspberries. In blackberries, signif-icant changes were recorded. Fructose concentration decreasedfrom 2.23 to 2.09 g/100 g fresh weight and glucose from 2.08 to1.73 g/100 g fresh weight during storage, though sucrose showeda minor increase initially, from 0.12 to 0.20 g/100 g fresh weight(Table 1). At harvest, the fructose and glucose levels were almostthe same, but the sucrose content comprised only 7–10% or less ofthe total sugars. Total soluble solids decreased during storage inboth raspberries and blackberries (Table 1).

4. Discussion

Late season production of raspberries and blackberries did notcause any major changes during storage in the content of differ-ent antioxidants analysed in this investigation, confirming previousinvestigations on stored berries (Kalt et al., 1999; Perkins-Veazieand Kalt, 2002). Climate conditions in Scandinavia, such as lowlight intensity, short day length and low temperature in late season,could be expected to affect the content and biological metabolismof various antioxidants during post-harvest storage of the berries.Vitamin C is an important parameter in relation to the nutri-tional and health-promoting qualities of stored berries. Previousstudies have reported slightly higher levels of vitamin C at har-vest in raspberries and blackberries (Józef and Ireneusz, 2007;Pantelidisa et al., 2007). The somewhat lower levels found in thisinvestigation might be explained by decreasing ascorbic acid syn-thesis from sugars originating from photosynthesis in the plant.The decreasing light and temperature due to late season couldhave negatively affected the vitamin C content, as reported inprevious studies (Kalt et al., 1999; Lee and Kader, 2000; Wangand Zheng, 2001). The fluctuations in vitamin C content duringstorage in raspberries and blackberries (Figs. 1 and 2) suggestthat only limited ascorbic acid synthesis took place, and suchsynthesis could have been affected by temperature and lengthof storage, as reported in previous studies (Agar et al., 1997;Haffner et al., 2002). The low pH values (i.e. acidic medium) pre-viously found in berries (de Ancos et al., 2000; Reyes-Carmonaet al., 2005; Wold and Opstad, 2007) may influence vitamin Cstability positively (Skrede, 1996; Agar et al., 1997). The antho-cyanins may also protect the vitamin C content (Davies et al.,1991).

Total phenolics in raspberries declined after one day of storagebut increased thereafter. Phenolic compounds have been suggestedto be released from their complexes with other components suchas proteins and carbohydrates, as observed in a study on prunes(Hamauzu and Kume, 2005), which might be one possible expla-nation for the results found in the present study. However, denovo synthesis cannot be excluded. The present results are in linewith previous findings that the antioxidant capacity of raspber-ries at 0 ◦C increases due to the increase in total phenolics andanthocyanins (Kalt et al., 1999; Mullen et al., 2002b). In contrast,in blackberries there was a linear decrease with increasing stor-age time, which conflicts with the results of some previous studies(Perkins-Veazie and Kalt, 2002) and might be due to the late seasonproduction. The concentrations of total phenolics in blackberries atharvest in the present study, 322 mg GAE equivalents/100 g freshweight, were at the same level or somewhat higher than previouslyreported results, ranging from 275 to 320 mg GAE equivalents/100 g

fresh weight (Wang and Lin, 2000; Perkins-Veazie and Kalt, 2002).Fruiting order has also been suggested to influence the total phe-nolics level, as it has been found to increase from primary totertiary fruits in raspberries and blackberries (Perkins-Veazie and

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alt, 2002; Anttonen and Karjalainen, 2009). The levels of totalhenolics found in raspberries at harvest in this study, 92.1 mgAE equivalents/100 g fresh weight, were lower than previous

eported results, 192–359 mg GAE equivalents/100 g fresh weighty Anttonen and Karjalainen (2005), or approximately the same,9.5–187.47 mg GAE equivalents/100 g fresh weight, as found bye Ancos et al. (2000).

Changes in the content of anthocyanins during storage showedignificant differences between different storage periods in bothaspberries and blackberries. A linear increase during post-harvesttorage was noted in raspberries, with only one statistically sig-ificant change for the last storage period. This might be due toiosynthesis during storage or to increased availability of the freenthocyanins with increased storage time, as previously found inlackberries and red oranges (Basiouny, 1995; Lo Piero et al., 2005).uring storage the organic acids, through interconversion witharbohydrates, may provide carbon skeletons for the synthesis ofhenolics, including anthocyanins (Kalt et al., 1999). The level andhemical composition of anthocyanins observed here during stor-ge in raspberries are in agreement with previous work (Kalt et al.,999; Wang and Lin, 2000). Changes in anthocyanins content inlackberry were also highly significant, with a linear decrease with

ncreasing storage time up to 10 days. These results are also ingreement with previous findings (Perkiins-Veazie. et al., 1999;ang and Lin, 2000; Perkins-Veazie and Collins, 2002; Pantelidisa

t al., 2007).The ellagic acid content of raspberries and blackberries was

ound to be relatively high, but no statistically significant changesere found during different storage periods in the late season

erries. The stability during storage might be explained by the facthat ellagic acid is a phenolic compound that is strongly linked tohe cell walls of the fruit and cannot be easily extracted withoutydrolysis (Clifford and Scalbert, 2000). The high contents of ellagiccid in both types of berry at harvest could be due to pre-harvestrowing conditions, including cultural and climate conditions suchs the temperature during the berry growing season, harvestingate and day length effects. The fruiting order has been shown toave a significant effects on ellagic acid content, with the phenolicsontent including ellagic acid generally increasing from primary toertiary fruits (Anttonen and Karjalainen, 2009). The high levels ofllagic acid observed here in late season berries, primarily tertiaryruit, might therefore at least partly be explained by fruiting order.

There is little information in the literature concerning storageffects on sugars in raspberries and blackberries. In this study theontents of different sugars were comparatively low, but quite sta-le, during storage. There were some fluctuations in the profile ofifferent sugars in raspberries and blackberries, which might bexplained by unbalanced consumption of these reducing sugarsuring storage. Another explanation is that the fructose and glu-ose content increased as a result of sucrose hydrolysis, which haseen reported in other fruit (Akhavan and Wrolstad, 1980). Theydrolysis of sucrose during post-harvest storage is very dependentn the concentration of the reactants, temperature, storage timend acid concentration (catalyst) induced by pre- and post-harvestruit conditions (Perkiins-Veazie. et al., 1999; Ayala-Zavala et al.,004). There are three possible carbon sources for soluble sugarynthesis after harvest: starch, organic acid and cell wall disassem-ly. Cell wall disassembly has been reported to play a vital role inugar accumulation during cool storage of berry fruits (Plowman,991; Cordenunsi et al., 2003). The data indicate that pre-harvestonditions such as light intensities, harvesting date and averageemperature affect the levels and chemical composition of sugars

n berries. The somewhat lower levels of sugars in this study mighte due to the lower amount and intensity of light during the fruitrowing season (Watson et al., 2002). Total available heat and lightre important factors in determining the sugar level and chemical

rae 129 (2011) 376–381

composition of berry crops (Lee and Kader, 2000; Watson et al.,2002).

5. Conclusions

This study showed that late season production generallyresulted in minor changes in the sugar content of raspberriesand blackberries and did not negatively influence their antioxi-dant levels. Analyses of the effects of storage on berry chemistryand antioxidant content suggested that storage at 2 ◦C positivelyaffected phenolic metabolism, enhancing the antioxidant contentand therefore the health-promoting function of berry fruits.

Acknowledgements

Our thanks to research engineer Karl-Erik Gustavsson for skilfultechnical assistance during HPLC-analysis. The Higher EducationCommission (HEC) of Pakistan is gratefully acknowledged for a PhDscholarship.

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