Studies on Postharvest Physiology and Handling Techniques of Mulberry Fruits (Morus atropurpurea Roxb.)
Date Issued
2010
Date
2010
Author(s)
Tseng, Wei-Bo
Abstract
Mulberry fruit (Morus spp.) a newly raised fruit crop in Taiwan. It is so perishable that there is serious loss after harvest, and it is a strong limitation for the expansion of mulberry industry. Researches in the postharvest physiology and technology of mulberry are limited; therefore, the objective of this thesis is to establish the basic postharvest physiology data as well as to assess various handling technologies for extending shelf-life of fresh mulberry fruits.
Mulberry fruits (Morus atropurpurea Roxb.) should be harvested at fully mature (dark-purple color) stage to achieve maximum quality; since full ripe fruits had the highest values of total soluble solids to titratable acidity ratio (7.75 ± 0.89) and anthocyanin content (1244.18 ± 43.64 mg•L-1 cyanidin-3-glucoside equivalent). The patterns of respiration rate and ethylene production of ‘Miaoli No.1’ and ‘46C019’ mulberry fruits, harvested at fully mature (dark-purple) stage exhibited typical characteristics of nonclimacteric fruits. The respiration rate at 5℃ was 19.14~21.62 mg CO2∙kg-1∙hr-1 and the ethylene production rate at 20℃ was 4.90~6.85 μL C2H4∙kg-1∙hr-1, therefore, mulberry fruit can be categorized as high respiration rate and moderate ethylene production rate. Temperature was the most important environmental factor influencing the respiration and ethylene biosynthesis in mulberry, the rates of respiration and ethylene production were enhanced by 18 and 6 folds, respectively, when temperature was raised from 0℃ to 20℃.
Decay was the major cause of postharvest loss in mulberry fruits. The shelf-life of ‘Miaoli No. 1’ mulberry was only 1~2 days at 20℃; however, it was extended to 10~12 days when the fruits were stored at 0℃ due to significant suppression of pathological decay. Furthermore, lowering the storage temperature to 0~5℃ also reduced the percentage of weight loss in mulberry. There were no changes in total soluble solids and titratable acidity of mulberry fruits stored at 0℃ or 5℃. On the other hand, the anthocyanin content of mulberry gradually declined to 50% after 8 days storage at 0℃or 5℃.
‘Miaoli No. 1’ mulberry fruits cooled by forced-air cooling immediately after harvest reduced the decay incidence, decay severity index, and prolonged shelf-life. Precooled fruits maintained higher titratable acidity during storage at 5℃, but there were no significant benefits on preservation of fresh weight, total soluble solids, pH, and anthocyanin content of the product. Storing ‘Miaoli No. 1’ mulberry fruits in controlled atmosphere with 22% CO2 + 6% O2 or 11% CO2 + 5% O2 at 5℃ also effectively restrained decay percentage and decay severity index. Fruits treated with 22% CO2 + 6% O2 at 5℃ for a week show no visible decay and maintained better total soluble solids maintenance when compared with the air control fruits. However, high CO2 concentration in controlled atmosphere storage enhanced the degradation of anthocyanin of mulberry fruits during storage at 5℃, but affected neither weight loss nor titratable acidity of the fruits.
Pre-storage irradiation ‘Miaoli No. 1’ mulberry fruits with 2.40 kJ∙m-2 ultraviolet-C (UV-C) induced the accumulation of the phytoalexin trans-resveratrol and reduced the percentage of decay, but not the decay severity index during storage at 5℃. The trans-resveratrol content of UV-C irradiated mulberry fruits rose to 2.83 μg.g-1dw after 4 days storage at 5℃, obviously higher than that of control (2.21μg.g-1 dw), and then declined. The content of trans-piceid, another phytoalexin in mulberry, was not induced by UV-C irradiation. Therefore, the accumulation of trans-resveratrol may be one of the factors that inhibit postharvest decay in ‘Miaoli No. 1’ mulberry fruits treated with UV-C. The efficacy of UV-C irradiation on mulberry was affected by the storage temperature and irradiation dose. Lower UV-C irradiation dosage (0.48 kJ∙m-2) and higher storage temperature (10℃) did not significant inhibit decay of mulberry fruits. In addition, the effect of UV treatment did not last long enough to protect the fruit from decay.
Subjects
mulberry fruit
postharvest physiology
postharvest handling technology
controlled atmosphere storage
precooling
UV-C irradiation
resveratrol
Type
thesis
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