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Changes in starch and soluble sugar concentrations in winter squash mesocarp during storage at different temperatures
Scientia Horticulturae 127 (2011) 444–446
Contents lists available at ScienceDirect
Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti
Short communication
Changes in starch and soluble sugar concentrations in winter squash mesocarp during storage at different temperatures Daisuke Kami, Takato Muro, Keita Sugiyama ∗ National Agricultural Research Center for Hokkaido Region, NARO, 1 Hitsujigaoka, Toyohira, Sapporo, Hokkaido 062-8555, Japan
a r t i c l e
i n f o
Article history: Received 7 June 2010 Received in revised form 23 September 2010 Accepted 29 October 2010 Keywords: Cucurbits Raffinose Starch Storage Winter squash
a b s t r a c t The effects of storage at 5, 10 or 15 ◦ C for 6 months on the concentrations of starch and soluble sugar in winter squash (Cucurbita maxima Duch.) cultivar ‘TC2A’ fruits were examined. Starch contents were significantly lower at 15 ◦ C than at the other temperatures, although concentrations decreased throughout the storage period at all temperatures. Total soluble sugar contents increased during the first 3 months of storage regardless of temperature, and decreased at 5 ◦ C or 15 ◦ C, but not at 10 ◦ C after 6 months. Myoinositol and raffinose concentration patterns were more complex, and may reflect some role in regulating fruit metabolism during storage that may be important in maintaining overall squash fruit quality. © 2010 Published by Elsevier B.V.
1. Introduction Cucurbita species (e.g. C. pepo, C. maxima, and C. moschata) are important sources of nutritional carbohydrates, minerals and vitamins worldwide. In Japan, winter squash (C. maxima) is preferred over other Cucurbita species, and maintains good post-harvest quality, allowing storage under ambient conditions for several months (Phillips, 1946; Nagao et al., 1991). A number of classic studies have established storage temperature optima for squash fruits (10 ◦ C; Francis and Thomson, 1964), maintenance of eating quality (Schales and Isenberg, 1963), loss of edible tissue weight (Hopp et al., 1960; Schales and Isenberg, 1963), and decay (Francis and Thomson, 1964). Phillips (1946) reported that the starch content of squashes decreases regardless of squash species during storage. Moreover, glucose, fructose, and sucrose contents of ‘Blue Hubbard’ (C. maxima), increase for three months, then decline over the next six months (Phillips, 1946). However, there has been no comprehensive evaluation of changes in the chemical contents of squash fruits under different storage conditions. Because long term storage is required in both the consumer and food processing markets, it would be advantageous to develop longer storage protocols, particularly if these methods were welltolerated by existing varieties. It may also, however, be necessary to develop varieties with improved storage tolerance. This paper aims to provide a detailed quantitative analysis of starch as a substrate
∗ Corresponding author. Tel.: +81 11 857 9141; fax: +81 11 859 2178. E-mail address: [email protected] (K. Sugiyama). 0304-4238/$ – see front matter © 2010 Published by Elsevier B.V. doi:10.1016/j.scienta.2010.10.025
for depolymerization to sugar, and texture that relates to the eating quality of the starch. As prelude to the development of superior storage methods or varieties, the soluble sugar contents of stored winter squash were compared among different temperatures for varying times. 2. Materials and methods As plant material, squash variety ‘TC2A’ (a representative variety from the Hokkaido region) seedlings were planted in a field at the National Agricultural Research Center (Sapporo, Hokkaido, Japan) on 20 May, and harvested on 6 September 2008. Compound chemical fertilizer (10 kg N, 10 kg P2 O5 and 10 kg K2 O per 10 a) was mixed throughout the top 150 mm of soil as basal dressing. The intra-row spacing was 0.6 m with a row width of 1.5 m. After harvest, fruits were cured for 2 weeks at about 20 ◦ C in the dark. Healthy fruits weighing between 1.8 kg and 2.2 kg were selected and stored at 5 ◦ C, 10 ◦ C or 15 ◦ C in 50–60% relative humidity in the dark. At one, three and six months after storage, six fruits were removed from each storage temperature pool to serve as a sample. Starting at three months, some fruits stored at 5 ◦ C were observed to have black spots, and some fruits rotted at 10 ◦ C or 15 ◦ C. Infected or rotted fruits were discarded. After seeds were removed, fruit mesocarps were sliced laterally into 1 mm sections and randomized. For sugar analysis, 10 g of tissue was flash frozen and stored at −80 ◦ C until use. Frozen mesocarps (10 g fresh weight) were homogenized with a Polytron PT 3100 (Kinematica, Lucerne, Switzerland) for 5 min in 40 ml 80% (v/v) ethanol. Sugars in the homogenate were extracted at 80 ◦ C for 1 h, followed by centrifugation at 10,000 x g at
D. Kami et al. / Scientia Horticulturae 127 (2011) 444–446
12
Starch (g/100g; FW)
10 5 ºC
8 b
10 ºC
ab
6
15 ºC
b
a
b
4
a a a
2
a 0 0
1
2
3
4
5
6
Storage Time (month) Fig. 1. Starch concentrations in winter squash ‘TC2A’ fruit stored at three temperatures. Values represent the mean ± SE of six fruits. Differences in mean values labeled with different letters are significant (Tukey’s HSD at p < 0.05).
4 ◦ C for 20 min. The supernatant was passed through a 5 m filter paper (Toyo Roshi Kaisha, Tokyo, Japan), and the resultant ethanolic extract was dried under a vacuum, dissolved in 5 ml distilled water, and filtered through a 0.4 m Omnipore membrane filter (Millipore, Tokyo, Japan). Glucose, fructose, sucrose, myo-inositol and raffinose concentrations were determined by high performance liquid chromatography (HPLC) with a TSK gel Amide-80 column (Tosoh, Tokyo, Japan). The mobile phase was 75% (v/v) acetonitrile/water at a flow rate of 0.8 ml/min. Quantification of sugars was performed by comparison with external standards. For starch analysis, tissue slices were dried at 80 ◦ C for 7 days and stored at room temperature until analysis as proposed by Sugiyama and Ooshiro (2001). A 0.1 g sample of dried mesocarp was suspended in 10 ml distilled water and autoclaved at 115 ◦ C for 15 min. The mixture was cooled at room temperature for 60 min, and centrifuged at 10,000 x g at 4 ◦ C for 20 min. The supernatant was passed through filter papers as above, then mixed with 150 l HCl (6.0 mol/l) and 2.0 ml of iodine solution (0.05 mol/l) to obtain a colorimetric reaction. The mixture was adjusted to 50 ml, and the Abs660 of the solution was measured with a spectrophotometer (Shimadzu MP-3000, Tokyo). A calibration curve was constructed with standard solutions of potato starch. Results are expressed as the mean ± standard error (SE) of six fruits per treatment. Statistically significant differences were established using Tukey’s HSD at the 5% level. 3. Results and discussion Mesocarp starch contents decreased fastest during the first month at all temperatures, but especially at 15 ◦ C (Fig. 1). The rates of further reductions were about the same under all conditions through the end of the experiment. Wu et al. (1999) reported that ␣-amylase activities were higher at 21 ◦ C than at 16 ◦ C in sugar apple fruits (Annona squamosa L.). It is likely that starch is converted to soluble sugar for use as a respiratory substrate. However, it is unclear whether the difference between the cooler temperatures is due to greater respiratory demand or to higher enzyme activity at 15 ◦ C. Five soluble sugars (fructose, glucose, sucrose, myo-inositol and raffinose) were detected by HPLC in stored fruits. Total sugar contents increased from 3.37 g/100 g fresh weight (FW) to around 7 g/100 g in the first month of storage, and to nearly 8 g/100 g FW by the third month (Fig. 2A). Total sugar then decreased over the next three months at 5 ◦ C and 15 ◦ C, but continued to increase at 10 ◦ C. The increase in total sugar is presumably due to depoly-
445
merization of starch. Enzymatic breakdown of starch via amylases should yield an equal weight of glucose. However, glucose only increases slightly from its T0 weight of about 0.6 g/100 g FW at all three temperatures (Fig. 2C). The bulk of individual sugar increase is due to sucrose, which nearly triples during the first month from its T0 weight of 2 g/100 g FW (Fig. 2D). This indicates that fructose isomerases and sucrose synthase must be present and active in stored winter squash fruits to provide the equimolar amount of d-fructose required for disaccharide sucrose production. Fructose and glucose weights did not significantly differ except for fructose at three months after storage (Fig. 2B and C), presumably due to the metabolic balance between starch catabolism and sucrose synthesis. The sucrose content was higher in all three storage temperatures at three months, but was lower six months after storage, particularly at 15 ◦ C. Carbon dioxide production rises and Brix decreases as storage temperatures increase in cherimoya (Yonemoto et al., 2002) and melon (Aguayo et al., 2004), presumably because of higher metabolic rates. This result is reflected in the increased total sugar and sucrose present in tissues at three months of storage at 15 ◦ C, but concentrations were lower three months later, a trend which is less apparent at 5 ◦ C and 10 ◦ C. The myo-inositol content was significantly different between the three storage temperatures after three months of storage, but at six months only the 10 ◦ C storage treatment was significantly higher than 5 ◦ C and 15 ◦ C (Fig. 2E). Ferree and Streeter (2004) reported a decrease in myo-inositol of grape leaves with water stress. It is not clear from the experiments performed what mechanism could account for the relative changes in myo-inositol concentrations. However, inositol acts as a signaling compound in eukaryotic cells, including, presumably in squash fruits, low temperature stress response. Some chilling damage was observed in fruits stored at 5 ◦ C. Inositol can occur in a number of isomeric forms, and HPLC separation is unlikely to differentiate between isoforms. Further, these results do not account for conversion to or interconversion between inositol and phytic acid, which could account for some of the differences observed at different temperatures. In any case, inositol accounts for only about 3% of the sugar at the beginning of the experiment, and is thus unlikely to play a major role in the apparent fruit quality, though it may be extremely important as a signaling molecule for other metabolic activity. Raffinose content was significantly higher at three months of storage at 5 ◦ C and 10 ◦ C than at 15 ◦ C (Fig. 2F). After six months, however, raffinose concentrations were significantly different at each temperature, with about three times the raffinose with storage at 5 ◦ C than at T0 . Storage at 10 ◦ C apparently caused a transient increase in raffinose such that by six months the concentration was only slightly higher than at T0 . On the other hand, raffinose content did not change appreciably at 15 ◦ C. Because low raffinose content has been associated with cultivars that do not maintain fruit quality with storage (unpublished), raffinose, like inositol, may play a regulatory role in maintaining storage quality. Lyons (1973) suggested that chilling injury can be the consequence of oxidative stress resulting from excess reactive oxygen species that induce peroxidation and breakdown of membrane fatty acids. Indeed, Karpinski (2002) found that low temperature increases reactive oxygen species and induces oxidative stress. Nishikawa et al. (2008) reported oligosaccharides like raffinose have a role in scavenging reactive oxygen in Arabidopsis thaliana. Therefore, mesocarp tissues may have increased raffinose concentrations to control reactive oxygen species produced at low temperatures. In the next study, it will be necessary to study the relationship between antioxidant activity and raffinose. Since there may be a relationship between the storage capacity of a squash variety and its inositol and raffinose contents,
D. Kami et al. / Scientia Horticulturae 127 (2011) 444–446
Total sugar (g/100g; FW)
A
10 8
B
a a a
a a a
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6
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Raffinose (g/100g; FW)
Myo-inositol (g/100g; FW)
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C
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0.08 0.04
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a 0
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0 0
1
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0
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Fig. 2. Sugar concentrations in winter squash ‘TC2A’ fruit stored at 5, 10 or 15 ◦ C. (A) Total sugar, (B) fructose, (C) glucose, (D) sucrose, (E) myo-inositol, and (F) raffinose. Values represent mean ± SE of six fruits. (A) Sum of concentrations of fructose, glucose, sucrose, inositol and raffinose. Values represent mean ± SE of six fruits. Significant differences in mean values are labeled with different letters (Tukey’s HSD at p < 0.05).
it would be highly beneficial to compare the relative contents of these sugar contents among winter squash cultivars with differing storage capacities. It is possible that breeding for good storage can be selected or engineered by altering raffinose and inositol or phytic acid contents, or possibly the raffinose/inositol ratio. References Aguayo, E., Escalona, V.H., Artés, F., 2004. Metabolic behavior and quality changes of whole and fresh processed melon. J. Food Sci. 69, SNG148–155. Ferree, D.C., Streeter, J.G., 2004. Response of container-grown grapevines to soil compaction. HortScience 39, 1250–1254. Francis, F.J., Thomson, C.L., 1964. Optimum storage conditions for butternut squash. Proc. Am. Soc. Hort. Sci. 86, 451–456. Hopp, R.J., Merrow, S.B., Elbert, E.M., 1960. Varietal differences and storage changes in -carotene content of six varieties of winter squashes. Proc. Am. Soc. Hort. Sci. 76, 568–576. Karpinski, S., 2002. Low temperature stress and antioxidant defense mechanism in higher plants. In: Inze, D., Van Montagu, M. (Eds.), Oxidative Stress in Plants. Tayler & Francis, London and New York, pp. 69–103.
Lyons, J.M., 1973. Chilling injury in plants. Annu. Rev. Plant Physiol. 24, 455–466. Nagao, A., Teruhiko, I., Dohi, H., 1991. Efects of curing condition and storage temperature on postharvest quality of squash fruit. J. Jpn. Soc. Hort. Sci. 60, 175–181 (In Japanese with English summery). Nishikawa, A., Yabuta, Y., Shigeoka, S., 2008. Galactinol and raffinose constitute a novel function to protect plants from oxidative damage. Plant Physiol. 147, 1251–1263. Phillips, T.G., 1946. Changes in the composition of squash during storage. Plant Physiol. 21, 533–541. Schales, F.D., Isenberg, F.M., 1963. The effect of curing and storage on chemical composition and taste acceptability of winter squash. Proc. Am. Soc. Hort. Sci. 83, 667–674. Sugiyama, Y., Ooshiro, A., 2001. A simple and rapid method analysis of starch content in root and shoot of Satsuma mandarin using colorimetric determination. Jpn. J. Soil Sci. Plant Nutr. 72, 81–84 (In Japanese with English summery). Wu, M.C., Chen, C.H., Chen, C.S., 1999. Changes in sugars, starch and amylase activity during ripening of sugar apples at different storage temperatures. Food Preservation Sci. 25, 57–61. Yonemoto, Y., Higuchi, H., Kitano, Y., 2002. Efects of storage temperature and wax coating on ethylene production, respiration and shelf-life in cherimoya fruit. J. Jpn. Soc. Hort. Sci. 71, 643–650.
Contents lists available at ScienceDirect
Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti
Short communication
Changes in starch and soluble sugar concentrations in winter squash mesocarp during storage at different temperatures Daisuke Kami, Takato Muro, Keita Sugiyama ∗ National Agricultural Research Center for Hokkaido Region, NARO, 1 Hitsujigaoka, Toyohira, Sapporo, Hokkaido 062-8555, Japan
a r t i c l e
i n f o
Article history: Received 7 June 2010 Received in revised form 23 September 2010 Accepted 29 October 2010 Keywords: Cucurbits Raffinose Starch Storage Winter squash
a b s t r a c t The effects of storage at 5, 10 or 15 ◦ C for 6 months on the concentrations of starch and soluble sugar in winter squash (Cucurbita maxima Duch.) cultivar ‘TC2A’ fruits were examined. Starch contents were significantly lower at 15 ◦ C than at the other temperatures, although concentrations decreased throughout the storage period at all temperatures. Total soluble sugar contents increased during the first 3 months of storage regardless of temperature, and decreased at 5 ◦ C or 15 ◦ C, but not at 10 ◦ C after 6 months. Myoinositol and raffinose concentration patterns were more complex, and may reflect some role in regulating fruit metabolism during storage that may be important in maintaining overall squash fruit quality. © 2010 Published by Elsevier B.V.
1. Introduction Cucurbita species (e.g. C. pepo, C. maxima, and C. moschata) are important sources of nutritional carbohydrates, minerals and vitamins worldwide. In Japan, winter squash (C. maxima) is preferred over other Cucurbita species, and maintains good post-harvest quality, allowing storage under ambient conditions for several months (Phillips, 1946; Nagao et al., 1991). A number of classic studies have established storage temperature optima for squash fruits (10 ◦ C; Francis and Thomson, 1964), maintenance of eating quality (Schales and Isenberg, 1963), loss of edible tissue weight (Hopp et al., 1960; Schales and Isenberg, 1963), and decay (Francis and Thomson, 1964). Phillips (1946) reported that the starch content of squashes decreases regardless of squash species during storage. Moreover, glucose, fructose, and sucrose contents of ‘Blue Hubbard’ (C. maxima), increase for three months, then decline over the next six months (Phillips, 1946). However, there has been no comprehensive evaluation of changes in the chemical contents of squash fruits under different storage conditions. Because long term storage is required in both the consumer and food processing markets, it would be advantageous to develop longer storage protocols, particularly if these methods were welltolerated by existing varieties. It may also, however, be necessary to develop varieties with improved storage tolerance. This paper aims to provide a detailed quantitative analysis of starch as a substrate
∗ Corresponding author. Tel.: +81 11 857 9141; fax: +81 11 859 2178. E-mail address: [email protected] (K. Sugiyama). 0304-4238/$ – see front matter © 2010 Published by Elsevier B.V. doi:10.1016/j.scienta.2010.10.025
for depolymerization to sugar, and texture that relates to the eating quality of the starch. As prelude to the development of superior storage methods or varieties, the soluble sugar contents of stored winter squash were compared among different temperatures for varying times. 2. Materials and methods As plant material, squash variety ‘TC2A’ (a representative variety from the Hokkaido region) seedlings were planted in a field at the National Agricultural Research Center (Sapporo, Hokkaido, Japan) on 20 May, and harvested on 6 September 2008. Compound chemical fertilizer (10 kg N, 10 kg P2 O5 and 10 kg K2 O per 10 a) was mixed throughout the top 150 mm of soil as basal dressing. The intra-row spacing was 0.6 m with a row width of 1.5 m. After harvest, fruits were cured for 2 weeks at about 20 ◦ C in the dark. Healthy fruits weighing between 1.8 kg and 2.2 kg were selected and stored at 5 ◦ C, 10 ◦ C or 15 ◦ C in 50–60% relative humidity in the dark. At one, three and six months after storage, six fruits were removed from each storage temperature pool to serve as a sample. Starting at three months, some fruits stored at 5 ◦ C were observed to have black spots, and some fruits rotted at 10 ◦ C or 15 ◦ C. Infected or rotted fruits were discarded. After seeds were removed, fruit mesocarps were sliced laterally into 1 mm sections and randomized. For sugar analysis, 10 g of tissue was flash frozen and stored at −80 ◦ C until use. Frozen mesocarps (10 g fresh weight) were homogenized with a Polytron PT 3100 (Kinematica, Lucerne, Switzerland) for 5 min in 40 ml 80% (v/v) ethanol. Sugars in the homogenate were extracted at 80 ◦ C for 1 h, followed by centrifugation at 10,000 x g at
D. Kami et al. / Scientia Horticulturae 127 (2011) 444–446
12
Starch (g/100g; FW)
10 5 ºC
8 b
10 ºC
ab
6
15 ºC
b
a
b
4
a a a
2
a 0 0
1
2
3
4
5
6
Storage Time (month) Fig. 1. Starch concentrations in winter squash ‘TC2A’ fruit stored at three temperatures. Values represent the mean ± SE of six fruits. Differences in mean values labeled with different letters are significant (Tukey’s HSD at p < 0.05).
4 ◦ C for 20 min. The supernatant was passed through a 5 m filter paper (Toyo Roshi Kaisha, Tokyo, Japan), and the resultant ethanolic extract was dried under a vacuum, dissolved in 5 ml distilled water, and filtered through a 0.4 m Omnipore membrane filter (Millipore, Tokyo, Japan). Glucose, fructose, sucrose, myo-inositol and raffinose concentrations were determined by high performance liquid chromatography (HPLC) with a TSK gel Amide-80 column (Tosoh, Tokyo, Japan). The mobile phase was 75% (v/v) acetonitrile/water at a flow rate of 0.8 ml/min. Quantification of sugars was performed by comparison with external standards. For starch analysis, tissue slices were dried at 80 ◦ C for 7 days and stored at room temperature until analysis as proposed by Sugiyama and Ooshiro (2001). A 0.1 g sample of dried mesocarp was suspended in 10 ml distilled water and autoclaved at 115 ◦ C for 15 min. The mixture was cooled at room temperature for 60 min, and centrifuged at 10,000 x g at 4 ◦ C for 20 min. The supernatant was passed through filter papers as above, then mixed with 150 l HCl (6.0 mol/l) and 2.0 ml of iodine solution (0.05 mol/l) to obtain a colorimetric reaction. The mixture was adjusted to 50 ml, and the Abs660 of the solution was measured with a spectrophotometer (Shimadzu MP-3000, Tokyo). A calibration curve was constructed with standard solutions of potato starch. Results are expressed as the mean ± standard error (SE) of six fruits per treatment. Statistically significant differences were established using Tukey’s HSD at the 5% level. 3. Results and discussion Mesocarp starch contents decreased fastest during the first month at all temperatures, but especially at 15 ◦ C (Fig. 1). The rates of further reductions were about the same under all conditions through the end of the experiment. Wu et al. (1999) reported that ␣-amylase activities were higher at 21 ◦ C than at 16 ◦ C in sugar apple fruits (Annona squamosa L.). It is likely that starch is converted to soluble sugar for use as a respiratory substrate. However, it is unclear whether the difference between the cooler temperatures is due to greater respiratory demand or to higher enzyme activity at 15 ◦ C. Five soluble sugars (fructose, glucose, sucrose, myo-inositol and raffinose) were detected by HPLC in stored fruits. Total sugar contents increased from 3.37 g/100 g fresh weight (FW) to around 7 g/100 g in the first month of storage, and to nearly 8 g/100 g FW by the third month (Fig. 2A). Total sugar then decreased over the next three months at 5 ◦ C and 15 ◦ C, but continued to increase at 10 ◦ C. The increase in total sugar is presumably due to depoly-
445
merization of starch. Enzymatic breakdown of starch via amylases should yield an equal weight of glucose. However, glucose only increases slightly from its T0 weight of about 0.6 g/100 g FW at all three temperatures (Fig. 2C). The bulk of individual sugar increase is due to sucrose, which nearly triples during the first month from its T0 weight of 2 g/100 g FW (Fig. 2D). This indicates that fructose isomerases and sucrose synthase must be present and active in stored winter squash fruits to provide the equimolar amount of d-fructose required for disaccharide sucrose production. Fructose and glucose weights did not significantly differ except for fructose at three months after storage (Fig. 2B and C), presumably due to the metabolic balance between starch catabolism and sucrose synthesis. The sucrose content was higher in all three storage temperatures at three months, but was lower six months after storage, particularly at 15 ◦ C. Carbon dioxide production rises and Brix decreases as storage temperatures increase in cherimoya (Yonemoto et al., 2002) and melon (Aguayo et al., 2004), presumably because of higher metabolic rates. This result is reflected in the increased total sugar and sucrose present in tissues at three months of storage at 15 ◦ C, but concentrations were lower three months later, a trend which is less apparent at 5 ◦ C and 10 ◦ C. The myo-inositol content was significantly different between the three storage temperatures after three months of storage, but at six months only the 10 ◦ C storage treatment was significantly higher than 5 ◦ C and 15 ◦ C (Fig. 2E). Ferree and Streeter (2004) reported a decrease in myo-inositol of grape leaves with water stress. It is not clear from the experiments performed what mechanism could account for the relative changes in myo-inositol concentrations. However, inositol acts as a signaling compound in eukaryotic cells, including, presumably in squash fruits, low temperature stress response. Some chilling damage was observed in fruits stored at 5 ◦ C. Inositol can occur in a number of isomeric forms, and HPLC separation is unlikely to differentiate between isoforms. Further, these results do not account for conversion to or interconversion between inositol and phytic acid, which could account for some of the differences observed at different temperatures. In any case, inositol accounts for only about 3% of the sugar at the beginning of the experiment, and is thus unlikely to play a major role in the apparent fruit quality, though it may be extremely important as a signaling molecule for other metabolic activity. Raffinose content was significantly higher at three months of storage at 5 ◦ C and 10 ◦ C than at 15 ◦ C (Fig. 2F). After six months, however, raffinose concentrations were significantly different at each temperature, with about three times the raffinose with storage at 5 ◦ C than at T0 . Storage at 10 ◦ C apparently caused a transient increase in raffinose such that by six months the concentration was only slightly higher than at T0 . On the other hand, raffinose content did not change appreciably at 15 ◦ C. Because low raffinose content has been associated with cultivars that do not maintain fruit quality with storage (unpublished), raffinose, like inositol, may play a regulatory role in maintaining storage quality. Lyons (1973) suggested that chilling injury can be the consequence of oxidative stress resulting from excess reactive oxygen species that induce peroxidation and breakdown of membrane fatty acids. Indeed, Karpinski (2002) found that low temperature increases reactive oxygen species and induces oxidative stress. Nishikawa et al. (2008) reported oligosaccharides like raffinose have a role in scavenging reactive oxygen in Arabidopsis thaliana. Therefore, mesocarp tissues may have increased raffinose concentrations to control reactive oxygen species produced at low temperatures. In the next study, it will be necessary to study the relationship between antioxidant activity and raffinose. Since there may be a relationship between the storage capacity of a squash variety and its inositol and raffinose contents,
D. Kami et al. / Scientia Horticulturae 127 (2011) 444–446
Total sugar (g/100g; FW)
A
10 8
B
a a a
a a a
Fructose (g/100g; FW)
446
b a
6
a
4
5 ºC 10 ºC 15 ºC
2
1.4 1.2
a
1.0 0.8
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0.6
1
2
3
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5
6
0
1
2
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2.0
a
1.6
a 1.2
a
a
a
a a
0.8
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4
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6
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Sucrose (g/100g; FW)
Glucose (g/100g; FW)
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Storage period (month)
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4
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Storage period (month)
Raffinose (g/100g; FW)
Myo-inositol (g/100g; FW)
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0 0
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a a
0.08 0.04
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0.3
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0.1
a 0
a
0 0
1
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3
4
5
6
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0
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4
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Storage period (month)
Fig. 2. Sugar concentrations in winter squash ‘TC2A’ fruit stored at 5, 10 or 15 ◦ C. (A) Total sugar, (B) fructose, (C) glucose, (D) sucrose, (E) myo-inositol, and (F) raffinose. Values represent mean ± SE of six fruits. (A) Sum of concentrations of fructose, glucose, sucrose, inositol and raffinose. Values represent mean ± SE of six fruits. Significant differences in mean values are labeled with different letters (Tukey’s HSD at p < 0.05).
it would be highly beneficial to compare the relative contents of these sugar contents among winter squash cultivars with differing storage capacities. It is possible that breeding for good storage can be selected or engineered by altering raffinose and inositol or phytic acid contents, or possibly the raffinose/inositol ratio. References Aguayo, E., Escalona, V.H., Artés, F., 2004. Metabolic behavior and quality changes of whole and fresh processed melon. J. Food Sci. 69, SNG148–155. Ferree, D.C., Streeter, J.G., 2004. Response of container-grown grapevines to soil compaction. HortScience 39, 1250–1254. Francis, F.J., Thomson, C.L., 1964. Optimum storage conditions for butternut squash. Proc. Am. Soc. Hort. Sci. 86, 451–456. Hopp, R.J., Merrow, S.B., Elbert, E.M., 1960. Varietal differences and storage changes in -carotene content of six varieties of winter squashes. Proc. Am. Soc. Hort. Sci. 76, 568–576. Karpinski, S., 2002. Low temperature stress and antioxidant defense mechanism in higher plants. In: Inze, D., Van Montagu, M. (Eds.), Oxidative Stress in Plants. Tayler & Francis, London and New York, pp. 69–103.
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