Effect of hypobaric storage on quality, antioxidant enzyme and antioxidant capability of the Chinese bayberry fruits
© Chen et al.; licensee Chemistry Central Ltd. 2013
Received: 15 November 2012
Accepted: 10 January 2013
Published: 14 January 2013
The Chinese bayberry (Myrica rubra Sieb. and Zucc.) is a subtropical fruit native to China, with unique flavor, sweet and sour taste, and high nutrition and health values. The fruit is highly perishable and susceptible to mechanical injury, physiological deterioration and fungal decay once harvested. This study was to investigate the effect of hypobaric storage on the quality of Chinese bayberry fruit and then develop storage technology to prolong the supply of the fruit.
The fruit stored under hypobaric conditions exhibited lower decay, higher titratable acidity and total phenolics compared with those stored under normal atmospheric conditions. Hypobaric storage significantly reduced malonaldehyde accumulation, respiratory rate and maintained high catalase and peroxidase activities of Chinese bayberry fruit. Ferric reducing antioxidant power was also higher in the fruit stored under hypobaric condition than those under normal atmospheric conditions.
Hypobaric storage improved the metabolism, antioxidant system and postharvest quality of Chinese bayberry fruit and provided an effective alternative method to prolong the storage life of this fruit.
The Chinese bayberries (Myrica rubra Sieb. and Zucc.) are a subtropical fruit native to China. In terms of the unique flavor, sweet and sour taste, attractive red color, and high nutrition and health values; Chinese bayberries have been cultivated in eastern and southern China for more than 2000 years and are being introduced to other countries. The fruit mature in early summer season and are praised as the “precious southern Yangtze fruit of early summer” [1–3]. The Chinese bayberries contain abundant anthocyanins, flavonoids and other phenolic compounds, with high antioxidant capacity [3–5]. Unfortunately, the fruit are highly perishable and susceptible to mechanical injury, physiological deterioration and fungal decay, resulting in a short postharvest life of 1−2 days at ambient temperature . Some methods, including low temperature storage [7, 8], high oxygen atmosphere treatment [9, 10], hot air treatment [6, 11], combined treatment of ethanol vapor with hot air , have been used to investigate postharvest physicochemical and physiological attributes and storage life extension of the Chinese bayberry fruit. However, due to the delicate nature of the fruit, poor handling practices and inadequate storage facilities, the shelf life of the Chinese bayberry is still short, which markedly limits its market. As this fruit is further commercially developed, it is important to develop effective storage methods to prolong the shelf life.
Among these techniques for controlling postharvest decay of fruit and vegetables, the use of sub-atmospheric pressure exhibits a potential to store fresh Chinese bayberries. Hypobaric storage can quickly remove heat and reduce oxygen level . During storage, water spray could be used to solve the problem of insufficient environmental humidity . It has been reported that hypobaric treatment delayed ripening of some climatic fruits such as apples, avocados, bananas, mangoes, tomatoes, apple, sweet cherry, asparagus, and peach [14–17]. With the development of storage technology, different models of hypobaric storage machine have been developed and tested for the storage of fruit and vegetables. However, little information is available in the literature about this storage technology for Chinese bayberry fruit.The objective of this present study was to investigate the effects of different hypobaric storage treatments on postharvest life and quality of the Chinese bayberry fruit. The antioxidant enzyme activities and antioxidant capacity were also evaluated. Finally, the optimal condition of hypobaric storage to extend the shelf life of the Chinese bayberry fruit was determined.
Results and discussion
Effect of hypobaric storage on fruit decay of Chinese bayberries
Effects of hypobaric storage on skin colour and pulp TSS and TA
Effects of hypobaric storage on respiration and ethylene production rates
The respiratory rate of the Chinese bayberry fruit was around 9 mg CO2 kg-1 h-1 before storage and decreased gradually with increasing storage (Figure 3A). By the end of storage, respiratory rates of the Chinese bayberry stored under 101.3, 85±5, and 55±5 kPa conditions were 4.75, 3.72, and 3.16 mg CO2 kg-1 h-1, respectively. The respiratory intensity of the fruit under hypobaric storage was significantly (P<0.05) inhibited, as compared with under normal atmospheric pressure. Ethylene production rates of the Chinese bayberries decreased gradually, from 0.52 before storage to 0.042 μL kg-1 h-1 by the end of storage (Figure 3B). However, no significant differences in ethylene production rates were observed between the hypobaric storage and normal storage.
It was reported that hypobaric packaging reduced the respiration rates of strawberry and curled lettuce . He et al.  also reported that hypobaric storage conditions could reduce greatly the ethylene production rate in both lettuce and wheat. The removal of ethylene production could delay senescence of fruits and vegetables and, indirectly, reduce their susceptibility to pathogens . The inhibition of the respiratory rate in the Chinese bayberry fruit by hypobaric treatment can help to extend the shelf life.
Effect of hypobaric storage on malondialdehyde (MDA) content
Effect of hypobaric storage on antioxidant enzyme activities
Effects of hypobaric storage on total phenolic content and total antioxidant capacity
Materials and methods
The Chinese bayberries (Myrica rubra Sieb. & Zucc., cv. Dongkui) fruit were harvested manually from a commercial orchard in Xianju county of Zhejiang Province, China on June 28, 2010, and then transported to the laboratory by a refrigerated car within 3 hours. Fruit were selected for uniformity of shape and color and the blemished and diseased fruit were discarded.
Fruit treatments were performed in a hypobaric storage system with storage chambers whose pressure could be set independently (Model XL-5, Xianlv Low-pressure Fresh Keeping Equipment Co. Ltd., Shanghai, China). Each replicate containing 2 kg fruits was put in a plastic basket and placed into the hypobaric chamber. The applied pressures were set to be 85±5, 55±5 and 15±5 kPa, respectively. The normal atmospheric pressure (101.3 kPa) was used as control. These fruit were stored at 1±0.5°C and 85–90% relative humidity (RH). Fruit samples were taken for analysis every 3 days in the storage period of 15 days.
Evaluations of fruit decay and skin colour
Fruit decay was visually evaluated. Fruit with visible mold growth with about 2% of the surface affected was considered rotten. The severity of fruit decay was expressed as percentage of fruit showing decay symptoms. Skin colour of 20 fruit from each replicate was measured using a colorimeter (Konica Minolta, CR-400, Japan) with a 6-mm aperture size, which provided L* and a* values according to the system established by the Commission Internationale de L’Eclairage (CIE, International Commission on Illumination). A reference white tile was used for calibration.
Measurements of respiration and ethylene production rates
Ten fruit were enclosed in 250 mL glass jars at 5°C for 2 h and then 2 mL of headspace gas were taken from each jar. CO2 amount was measured by gas chromatography (Rainbow, SP-9890, China) equipped with flame ionization detector and a packed column (GDX-502, Zhonghuida Inc., China). Ethylene concentration was analysed by gas chromatography using a flame ionization detector. Respiration and ethylene production rates were expressed as mg CO2 and μg per hour on fresh weight basis, respectively.
Measurements of total soluble solids and titratable acidity
Fifty fruit from each treatment were taken. Juice was obtained by a juicer (HR1861, Philips Co. Beijing, China), followed by filtration through cheesecloth. The juice was analyzed for total soluble solids (TSS) and titratable acidity (TA). TSS concentration was determined by a portable refractometer (Atago PAL-1, Japan) while TA content was measured by titrating 20 mL of the juice to pH 8.2 using 0.1 mol L-1 NaOH.
MDA content determination
MDA content was determined according to the method described by Li et al.  with some modification. Fruit tissues (1 g) were extracted for 2 h with 5 mL of trichloroacetic acid (10%). Three milliliters of 0.5% thiobarbituric acid (TBA) in 10% trichloroacetic acid were added to 1 mL of the extract. The solution was heated in a boiling water bath for 20 min, then immediately cooled, and finally centrifuged at 6000 × g for 10 min to clarify the solution. Absorbance was measured at 532 and 600 nm. MDA content was expressed as μmol/g FW by the method of Li et al. .
Enzymatic activity assay
Five grams of fruit tissues were homogenized in 25 mL of 100 mmol L-1 Tris-HCl buffer (pH 7.8) containing 2 mmol L-1 EDTA and 2 mmol L-1 1,4-dithiothreitol at 4°C. The homogenate was centrifuged at 15,000 × g for 15 min at 4°C, and then the supernatant was collected for the enzymatic activity assay. Protein was measured according to the method of Bradford , using bovine serum albumin (BSA) as the standard.
CAT was analyzed according to the method of Beers & Sizer  with some modifications. The disappearance of H2O2 was monitored by measuring the decrease in absorbance at 240 nm of a reaction mixture containing 100 mmol L-1 Tris-HCl buffer (pH 7.8), 25 mmol L-1 H2O2, and 0.2 mL of crude enzyme extract. One unit of enzymatic activity was defined as 0.01 change of absorbance at 240 nm per minute. Specific CAT activity was expressed as units per mg protein. POD activity was assayed according to the method described by Yang et al. . The reaction mixture (2 mL) consisted of 50 mmol L-1 sodium phosphate buffer (pH 6.5), 6 mmol L-1 guaiacol and 4.5 mmol L-1 H2O2 prior to the addation of 1 mL of crude enzyme extract. Increase in absorbance at 470 nm at intervals of 30 s was recorded. One unit of enzymatic activity was defined as the amount of enzyme that catalyzed the peroxidation of 1 mmol of guaiacol per minute. Specific POD activity was expressed as units per mg protein.
Total phenolic content determination
One gram of lyophilized fruit tissues was extracted with 25 mL of ethanol for 3 h. Total phenolic contents were estimated colourimetrically using the Folin-Ciocalteu method . The extract was appropriately diluted, and then 1 mL of the dilution was oxidized with 0.5 mL of Folin-Ciocalteau reagent. The reaction was neutralized with 5 ml of 5% Na2CO3. The solution was immediately diluted to a final volume of 25 mL with distilled water and then mixed thoroughly. The absorbance was read at 765 nm after 1 hour of incubation in dark at 25°C using a spectrophotometer (Shimadzu UV-2550, Japan). Gallic acid was used as a standard, and phenolic contents were expressed as mg gallic acid equivalents (GAE)/g FW.
The ferric reducing ability of the Chinese bayberry was measured according to the method of Benzie & Strain . To prepare the FRAP reagent, a mixture of 0.3 mol L-1 acetate buffer (pH 3.6), 10 mmol L-1 tripyridyltriazine (TPTZ), and 20 mmol L-1 ferric chloride (10:1:1, v/v/v) was made. One gram of lyophilized fruit tissues was extracted for 12 hours with 20 mL of ethanol. The FRAP reagent (3.9 mL) was added to the extract solution sample (0.1 mL) and then mixed thoroughly. The reaction was then monitored for 10 min at 37°C and the absorbance was recorded at 593 nm on the Shimadzu UV-2550 spectrophotometer. The ferric reducing ability of the Chinese bayberry fruit was expressed as mmol FeSO4 per litre crude extract.
All samples were prepared and analysed in triplicate. Statistical analysis was done with one-way analysis of variance using the SAS statistical software package.
Previous studies indicated that hypobaric storage reduced commodity respiration and prevented wilting and senescence during storage [17, 30]. In the present study, application of hypobaric pressure to the Chinese bayberries significantly reduced fruit decay and loss in total acids, inhibited respiratory rate, decreased MDA accumulation and maintained total phenolic content, antioxidant capacity and CAT and POD activities. These data suggested that hypobaric storage could be an effective technology in maintaining postharvest quality and prolonging shelf life of Chinese bayberry fruit.
The work was supported by the National High Technology Research and Development Program of China (863 Program) (grant No. 2012AA101606), The International Cooperation Project of China (grant No. 2013DFA31450) Special Fund for Agro-scientific Research in the Public Interest (grant No. 201303073) and The International Cooperation Project of the Science and Technology Department of Zhejiang Province, China (grant No. 2011C14003).
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