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Changes in Physico-Chemical Properties Related to Quality of Kiwifruit (Actinidia deliciosa cv. Hayward) during Cold Storage a

a

Shirin Shahkoomahally & Asghar Ramezanian a

Department of Horticultural Science, Faculty of Agriculture, Shiraz University, Shiraz, Iran Published online: 11 Apr 2015.

Click for updates To cite this article: Shirin Shahkoomahally & Asghar Ramezanian (2015): Changes in Physico-Chemical Properties Related to Quality of Kiwifruit (Actinidia deliciosa cv. Hayward) during Cold Storage, International Journal of Fruit Science, DOI: 10.1080/15538362.2015.1017423 To link to this article: http://dx.doi.org/10.1080/15538362.2015.1017423

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International Journal of Fruit Science, 00:1–11, 2015 Copyright © Taylor & Francis Group, LLC ISSN: 1553-8362 print/1553-8621 online DOI: 10.1080/15538362.2015.1017423

Changes in Physico-Chemical Properties Related to Quality of Kiwifruit (Actinidia deliciosa cv. Hayward) during Cold Storage SHIRIN SHAHKOOMAHALLY and ASGHAR RAMEZANIAN


Department of Horticultural Science, Faculty of Agriculture, Shiraz University, Shiraz, Iran

This research was performed for evaluation of physico-chemical changes of kiwifruit cv. Hayward for 4 months at 0◦ C. The results showed that fruit firmness, dry matter (DM), and starch decreased and weight loss (WL) increased during storage. During the first months of storage, titratable acidity (TA), soluble solids content (SSC), and soluble sugars increased significantly and then decreased toward the end of storage. Results also showed that activity of polyphenol oxidase (PPO) enzyme was increased until 60 days and then decreased. According to these results and sensory analysis, kiwifruit quality decreases with time due to physico-chemical changes during storage period. Results showed that, although fruits will remain edible more than 5 months at 0◦ C, the best quality will remain for 3 to 4 months. KEYWORDS kiwifruit, physiochemical changes, cold storage, quality

INTRODUCTION The kiwifruit was introduced to the world market from New Zealand in the 1950s (Barboni et al., 2010). Kiwifruit represent a source of antioxidant substances, which may intervene in the prevention of human pathologies. In recent years, there has been increasing interest in the production of kiwifruit due to its vitamin C content and high antioxidant capacity (Tavarini et al., 2008). During fruit ripening, several biochemical, physiological, and Address correspondence to Shirin Shahkoomahally, Department of Horticultural Science, Faculty of Agriculture, Shiraz University, 7144165186 Shiraz, Iran. E-mail: shirin. [email protected] 1


2

S. Shahkoomahally and A. Ramezanian

structural modifications happen and these changes determine the final fruit quality attributes. For a good fruit quality, the standard practice for kiwifruit Actinidia deliciosa ‘Hayward’ is to harvest when the soluble solid content (SSC) is minimum 6.2 ◦ Brix and storage at 0◦ C for up to 6 months. In particular, flesh firmness (FF) was lower in fruit collected when the SSC was 10 ◦ Brix and stored for 6 months at 0◦ C (Tavarini et al., 2008). On the other hand, FF is widely used for defining post-harvest quality of kiwifruit (Bonghi et al., 1996). However, during fruit ripening, a series of changes, genetically programmed processes happen: increase in respiration rate and ethylene synthesis, changes in quality characteristics, and fruit softening. This last process is due to structural changes in the cell wall, including a reduction in hemicelluloses, loss of galactose, and solubilization and depolymerization of pectin (Fischer and Bennett, 1991). The storage of fruit is very important for its quality. Sustainability of kiwifruit production is also related to its storage ability in order to feed the market all year round as required by consumers. During cold storage and ripening, kiwifruit undergo biochemical changes, including conversion of starch to sugar, changes in cell wall constituents, and production of characteristic volatiles, which lead to the taste, texture, and aroma desired by consumers. In this research we studied the changes of physico-chemical parameters in ‘Hayward’ kiwifruit, storage capability, and fruit quality.

MATERIALS AND METHODS Plant Material Mature, unripe kiwifruit (Actinidia deliciosa cv. Hayward) of medium sized (80–120 g) fruits, free from visible defects or decay, were harvested from a commercial kiwifruit orchard in Gorgan, Iran with average firmness of 10 kg/cm2 and 7 ◦ Brix. Fruits were immediately transferred to the postharvest laboratory at Shiraz University. Kiwifruits were individually labeled and packaged into ventilated bags made of polyethylene, then stored for 4 months at 0 ± 1◦ C and 90 ± 5% relative humidity (RH) for 4 months. Samples were taken at monthly intervals during storage for quality evaluation and following analyses.

Physical and Physico-Chemical Assays WEIGHT LOSS (WL) The percentage WL was determined according to the following equation: %WL (t) =

W0 − Wt × 100, W0

3

Physico-Chemical Properties of Kiwifruit

where %WL (t) is the WL percent at time t, W 0 is the initial sample weight, and Wt is the sample weight at time t.

FIRMNESS Firmness was measured on two opposite faces of the equatorial zone using a texture analyzer (Stevens-Lfra, Harlow, Essex, UK) fitted with an 8-mmdiameter cylindrical probe. The penetration depth was 2 mm and the crosshead speed was 2 mm.s−1 . Firmness was expressed as kg/cm2 .


P H,

SSC,

AND TITRATABLE ACIDITY

(TA)

SSC percentages were determined using a hand refractometer (ATAGO, Tokyo, Japan) at 20◦ C. The pH values were determined by using a pH meter (JENWAY 351, Staffordshire, UK). TA was determined by titration with 0.3 N NaOH up to pH 8.1.

EXTRACTION

AND ASSAY OF POLYPHENOL OXIDASE

(PPO)

ENZYME

The PPO activity was performed using the method described by Murr and Morris (1974) with slight modification. One gram of frozen tissue was homogenized in 0.2 mol L−1 sodium phosphate buffer (pH 6.5) containing 1% polyvinylpyrrolidone (PVP) centrifuged at 15,000 rpm for 20 min at 4◦ C in a refrigerated centrifuge. PPO activity was determined in 2 mL total reaction mixture containing 1 mL of aliquot of the supernatant, 200 µl of pyrocatechol solution (0.2 M), and 800 µl of sodium phosphate buffer pH 6.2. One unit of PPO activity was defined as the amount of enzyme that caused the increase in absorbance of 0.01 by a WPA spectrophotometer (WPA, Cambridge, UK) at 410 nm in 1 min under the specified conditions.

SENSORY

EVALUATION

Sensory analysis to compare the quality of kiwifruits were carried out by 10 trained adults, aged 25–40 years (5 females and 5 males). Each judge evaluated four kiwifruits for the following characteristics: crunchiness (amount of noise generated when the fruit was chewed at a fast rate with the back teeth), juiciness (amount of free fluid released from the fruit during chewing), sweetness, sourness, texture preference, and visual appearance on a scale of 1–5 (ranked), where (1) very low, (2) low, (3) medium, (4) high, and (5) very high. The sensorial analyses were made at the time of storage initiation and after 2 and 4 months.

4

DRY

S. Shahkoomahally and A. Ramezanian MATTER

(DM)

Fruit DM was measured by cutting two equatorial slices, of 3-mm thickness, and drying them at 75◦ C for 72 h. The percent of fruit DM was calculated on basis of the final weight/ initial weight of slices. JUICE

DENSITY

To determine the density (D) of fruits, 5 ml of the juice of the fruits were weighed with a milligram scale (0.001) and then was determined using the following equation:


Density (D) = SOLUBLE

weight . volume

SUGARS AND STARCH CONTENT

Soluble sugars were extracted with the phenol–sulfuric acid method of Buysse and Merckx (1993) and measured. One milliliter of phenol solution (5%) was added to one milliliter of extract and immediately 5 ml of concentrated sulfuric acid was added. The resulting solution was shaken for 30 s and next the tubes were transferred into ice water until cooled. Then the absorption was read by a spectrophotometer (WPA, Cambridge, UK) at 490 nm (Buysse and Merckx, 1993). In order to measure the starch content, 2.5 ml of the supernatant extract was added into the test tube, then 10 ml of anthron (2 g L−1 ) solution was added into the test tube and was put into a warm bath for 7.5 min. Test tubes containing the solution were transferred into the ice to be cooled then the absorbance was read at 630 nm with a WPA model spectrophotometer (Cready et al., 1950). FRUIT

DENSITY

Fruit density was measured according to the following relationship: Fruit density = STATISTICAL

Fruit weight . Fruit volume

ANALYSIS

Data for the physical and chemical parameters were subjected to analysis of variance (GLM). Sources of variation were time of storage. All analyses were performed with SAS software package v. 9.1 for windows (SAS Institute Inc., Cary, North Carolina, USA).

5


RESULTS AND DISCUSSIONS


pH, TA, and SSC The pH of fruits increased slightly until storage at day 60 and then fell slightly toward the end of the storage period (Table 1). TA tended to decline slightly. The results of fruit acidity showed a tendency to rise in the first month (0.60%), and then decreased significantly up to month 4 (0.29%) of storage (Table 1). TA is directly related to the amount of organic acids in fruit, which is an important parameter in fruit quality. A correlation between enhanced respiration and a decrease in TA has been suggested by Lurie and Klein (1990) to be due to the use of organic acids as respiratory substrates in the respiratory cycle in fruits. SSC mainly depends on storage time (p < 0.05). Fruits that were subjected to longer storage time evidenced an accelerated consumption of sugars from the 60th day of storage and SSC decreased significantly after 60 days of storage at 0◦ C (Table 1). The highest (15.5%) and lowest (13.12%) SSC were recorded after 60 and 120 days of storage. When fruits are subjected to ripening, an increase of fruit respiration rates, and consequently sugar consumption also increases. On the other hand, a SSC increase in the fruit is probably due to the solubilization of sugars, from pectic polymer residues (Varoquaux et al., 1990).

WL Fruit lost weight linearly with increasing duration of the storage. Fruits showed a significant increase of WL during storage (Table 1). The increased WL in fruits could be due to either increased respiration associated with accelerated ripening or increased evaporation, or both processes (Jacobi et al., 2000).

Firmness Fruits lost their firmness gradually during the storage period (Table 2). Fruits underwent faster softening, attaining to minimum value 1.30 (kg/cm2 ) at TABLE 1 Changes in Quality Parameters of ‘Hayward’ Kiwifruit during 120 Days Storage at 0◦ C Storage time (d) 0 30 60 90 120 z Means

TA (%)z 0.48 0.6 0.47 0.35 0.29

± ± ± ± ±

0.006b 0.012a 0.015b 0.036c 0.018d

SSC (%)z 7.87 13.72 15.55 13.55 13.12

± ± ± ± ±

0.41d 0.19b 0.18a 0.26bc 0.34c

WL (%)z 2.23 5.05 6.77 9.73

0a ± 0.32b ± 0.43c ± 0.42d ± 0.4e

pHz 3.10 3.19 3.29 3.20 3.24

± ± ± ± ±

within a column followed by the same letter are not significantly different at P ≤ 0.05.

0.07b 0.04ab 0.05a 0.10a 0.05a

6

S. Shahkoomahally and A. Ramezanian TABLE 2 Changes in Firmness of ‘Hayward’ Kiwifruit during 120 Days Storage at 0◦ C Firmness (kg/cm2 )z

Storage time (d)

10.21 ± 0.53a 5.45 ± 0.45b 3.75 ± 0.33c 3.00 ± 0.12d 1.30 ± 0.12e

0 30 60 90 120


z Means within a column followed by the same letter are not significantly different at P ≤ 0.05.

120 days. Cell wall disassembly is a key ripening-associated event that determines the extent of fruit softening and contributes to the ultimate deterioration of the fruit (Fischer and Bennett, 1991). Firmness maintenance could be related to cell wall degrading enzyme activity reduction of polygalactoronase (PG) and pectinemethylestrerase (PME), glucanase, and galactosidase (Lurie, 1998).

Fruit Density, Fruit Juice Density and DM Fruit density was fairly constant between the 30th and 90th days of storage (P > 0.05). These density changes suggest mean fruit volume decreases, between the first and last storage time but fruit mass is constant against storage time. For example, cell wall softening and gas escape might facilitate the shrinkage and/or collapse of intercellular air spaces. Gases are produced when fruit ripens, total gas volumes appear reasonably constant in fruit at similar points of their development: storage life (Jordan et al., 2000) and therefore do not affect the usefulness of the density: DM relationship. The mass per volume unit (densities) of the juices were generally increased as storage time progressed (Table 3), which could be due to the effect of moisture loss through evaporation but it was reasonably constant over the different storage times. The DM loss during storage was slight (Table 4), but fruits showed a sudden decrease in the DM at the early stage of storage (18.24%). Most TABLE 3 Changes in Density of ‘Hayward’ Kiwifruit during 120 Days Storage at 0◦ C Storage time (day) 0 30 60 90 120 z Means

Fruit juice density (g/mL)z

Fruit density (g/mL)z

0.959 ± 0.013c 1.030 ± 0.0026ba 1.01 ± 0.036ba 1.052 ± 0.047a 1 ± 0.007bc

1.068 ± 0.012a 1.06 ± 0.014ab 1.062 ± 0.007a 1.05 ± 0.007ab 1.041 ± 0.012b


7


TABLE 4 Changes in Sugar, Starch, and DM of ‘Hayward’ Kiwifruit during 120 Days Storage at 0◦ C Sugar (g/100 g DW)z

Storage time (day) 0 30 60 90 120 z Means

25.18 37.33 43.36 36.57 34.96

± ± ± ± ±

0.99d 1.23b 1.05a 1.08bc 1.48c

Starch (g/kg DW)z 6.75 4.33 3.38 3.10 2.21

± ± ± ± ±

DM (%FW)z

0.49a 0.57b 0.07c 0.54c 0.38d

21.02 18.24 19.03 17.52 16.24

± ± ± ± ±

1.10a 0.52bc 0.49c 0.91dc 0.96d


Sugar and Starch Soluble sugar content fluctuated during 4 months. Soluble sugars increased up to 2 months (43.36 g/100 g dw) and then similar to SSC, decreased with time in storage and the lowest (34.92 g/100 g dw) were recorded after 120 days of storage (Table 4). A positive linear correlation between the soluble sugar content and soluble solid content was determined that showed high regression coefficients (Fig. 1). Apparently, this increase is a result of the ripening process. The lower levels of sugars were probably related to the breakdown of tissues in fruits (Wang and Buta, 2003). The increases in sugar could be attributed mainly due to breakdown of starch into simple sugars during ripening alone with a proportional increase in percent of sugars, which was attributed to the increased activity of amylase and other enzymes, 18 16 Soluble solid content


probably this result is directly related to the evaporation of moisture from fruit during storage. The fate of the imported carbohydrate is different in different periods of fruit storage.

y = 0.432x – 2.567 R2 = 0.968

14 12 10 8 6 4 2 0

0

10

20

30

40

50

Total natural sugar

FIGURE 1 Correlation between total natural sugar and soluble solid content in ‘Hayward’ kiwifruit during 120 days storage at 0◦ C.

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A

Visual appearance 4

Texture preference

3 2

Sourness

1 0 Crunchiness

Sweetness

B Downloaded by [ETH Zurich] at 03:15 12 April 2015

Juiciness

Visual appearance 4

Texture preference

3 2

Sourness

1 0 Crunchiness

Juiciness

Sweetness

C Texture preference

Visual appearance 4 3 2 1 0

Crunchiness

Sourness

Juiciness Sweetness

FIGURE 2 Radial graph of the sensory analysis of ‘Hayward’ kiwifruit at the beginning of the storage (t = 0 days) (A), after 60 days (B), and 120 days (C) of the storage at 0◦ C.

resulting in gluconeogenesis and converted into sucrose, glucose, and fructose during storage. Further hydrolysis decreased the level during storage (Rathore et al., 2009). Starch content decreased linearly with increasing duration of the storage (Table 4), attaining a minimum value 2.21 (g/kg dw) at 120 days. Maximum amount of soluble sugars in fruits might be due to rapid

9


conversion of starch to sugars as a result of moisture loss and decrease in acidity by physiological changes during storage (Wills and Rigney, 2007).

Following 120 days of storage, eating quality diminished, but all fruit were considered to be of good eating quality. Fruit visual quality and the taste scores decreased with time in storage (Fig. 2). When prolonging the storage time from 0 to 120 days, losses in sourness and texture were enhanced. Texture decreased during the storage period showing a similar trend to appearance values. Kiwifruit showed significantly lower scores for appearance at the end (120 days) of storage than from day 0 to day 60. The results of sweetness showed an increasing trend first and then decreasing significantly (Fig. 1). It might be due to fluctuations in acids and pH (Malundo et al., 1997).

PPO Results pertaining to monthly intervals showed that activity increased during 2 months and then decreased toward the end of the experiment (Fig. 3). At the end of storage, the activity of PPO was 1.21 (unit/min/g). A similar result was observed by Tareen et al. (2012). Internal browning of fruit is probably related to the increase in PPO and POD (peroxidase) activities, which could oxidize phenolic compounds to quinone or quinine-like compounds, finally appearing as polymerized brown pigments (Lill et al., 1989). Phenolic compounds represent the main substrates used by oxidative enzymes with consequences in terms of color and quality changes, as well 1.8

PPO activity (unit/min/g FW)


Sensory Evaluation

1.6 1.4 1.2 1 0.8 0.6 0.4

PPO

0.2 0

0

1

2

3

4

5

Storage time (days)

FIGURE 3 Changes in polyphenol oxidase (PPO) of ‘Hayward’ kiwifruit during 120 days storage at 0◦ C. Least significant difference is at a level of 5% of significance. Vertical bars represent standard deviations of the means.

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as being associated with plant defense mechanisms against stress situations that can affect the postharvest period (Tomás-Barberán and Espín, 2001).


CONCLUSIONS The results of the changes in the physico-chemical attributes indicate that TA, SSC, and soluble sugars increased significantly and then decreased toward the end of storage. Also, the activity of PPO enzyme was increased until 60 days and then decreased. But fruit firmness, DM, and starch decreased and WL increased during storage. Taken together, this study showed that although fruits will remain edible more than 5 months at 0◦ C, the best quality will remain for 3 to 4 months. Therefore, storage times were found to be crucial factors, determining the changes in physico-chemical properties of kiwifruit during cold storage. Further experiments are required to explore the mechanism of the physico-chemical changes and find methods, which maintain quality of kiwifruit during storage period.

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