Product Description
Bok choy (Brassica rapa subsp. chinensis) is a leafy Chinese vegetable with green leaves and lighter, fibrous stalks. Its flavor is slightly sweet with a mild peppery undertone, with the leaves being more flavorful than the stalks. Usually sold fresh in bunches, it is commonly used in stir-fries, soups, and lightly cooked dishes. Bok choy is also widely known by other names, including pakchoi, pak choy, and bakchoi.
Maturity and Quality
True leaves typically reach about 10-15 cm (3.9-5.9 in) long, and with the petiole or stalk, leaves can reach up to 20 to 70 cm (7.8 to 27.6 in) long at harvest.
Basal leaves, or broadly obovate, are 20-30 cm (7.8-11.8 in) long, firm, dark green, and glossy. The base narrows into a broad stalk, and the whole margin may have inconspicuous rounded or undulated teeth.
Visual Appearance: Leaves should remain intact without mechanical damage, disease spots, or insect infestations. Leaves must be free of yellowing, wilting, or blemishes.
Color: Leaves should display a uniform dark green color, while petioles should be pale green or white.
Freshness: Leaves should appear glossy and firm and retain adequate moisture to ensure a crisp texture.
Figure 1. Freshly harvested bok choy at three different maturity stages: immature, mature, and overmature. Photo Credit: Postharvest Team, Jiangsu Academy of Agricultural Sciences (JAAS), China.
Postharvest Handling and Storage
Bok Choy stored at 0°C (32°F) can maintain freshness for up to 40 days. Increasing the temperature accelerates leaf yellowing, water loss, aging, and decay. However, storing at 0°C (32°F) poses a high risk of freezing, thus the recommended storage temperature is 2°C (36°F). When stored at 15°C (59°F), the shelf life of Bok Choy is reduced to less than 7 days, and at temperatures above 15°C (59°F), it drops to less than 4 days.
Rapid postharvest initial cooling is crucial for preserving the quality of Bok Choy. Forced air, vacuum, and hydro-vacuum are effective initial cooling methods, and hydro-vacuum cooling is particularly recommended.
Figure 2. Shelf life of bok choy under varying storage temperatures. This image highlights the impact of temperature on the shelf life of bok choy. Photo Credit: Postharvest Team, Jiangsu Academy of Agricultural Sciences (JAAS), China.
＞95%
25°C (77°F): 15 to 50 mg CO2/(kg·h); 0°C (32°F): 0.5 to 2 mg CO2/(kg·h)
The respiration rate may vary as it is closely related to the season and harvest timing. Generally, bok choy harvested in the summer exhibits a higher respiration rate than in the winter.
Ethylene production rates are generally low, only 2-5 μL/(kg·h) at 25°C (77°F).
Although the ethylene production rate in bok choy is relatively low, it's sensitive to ethylene. Exposure to 5 ppm ethylene can accelerate leaf yellowing and promote disease development.
Bok choy is not commonly stored under controlled atmosphere (CA) conditions for retail. However, if extended preservation beyond 40 days is required—such as for long-distance maritime transport—CA storage or other preservation methods like controlled freezing-point preservation or individual quick freezing can be among the most effective strategies for maintaining freshness. At optimal storage temperatures, a CA containing 2% oxygen and 2-5% carbon dioxide can help preserve bok choy's color and overall quality.
Hydro-vacuum cooling to a final temperature of 4 oC (39.2°F), final pressure of 0.9 kPa, and watering rate of 5% (weight of the product) can effectively mitigate quality loss and accelerate the initial cooling process, thereby delaying senescence in bok choy.
Figure 3. Comparison of bok choy quality and shelf life under different postharvest treatments: control, vacuum cooling, and hydro-vacuum cooling. The image also features internal and external scenes of the cooling process in operation. Photo Credit: Postharvest Team, Jiangsu Academy of Agricultural Sciences (JAAS), China.
Red LED irradiation at 6.5 μmol/(m²·s) from 9:00 AM to 9:00 PM, which has been experimentally explored to simulate retailer shelf lighting exposure time under laboratory conditions, can delay the yellowing of postharvest pak choi, maintaining its quality and extending its shelf life.
Figure 4. Phenotypic response of bok choy to red light irradiation. Performed under controlled conditions in a lighting-preservation chamber, demonstrating the effect of light treatment on postharvest quality. Photo Credit: Agricultural Products Preservation Technology and Equipment Innovation Team, JAAS.
Microporous Film Packaging. Microporous film (Water Vapor Transmission Rate, WVTR: 5.0245 g/m2·d; Oxygen Transmission Rate, OTR: 3.355E-3cm3/m2·d·Pa; Carbon Dioxide Transmission Rate, CO2TR: 1.063E-3cm3/m2·d·Pa; Micropore Spacing: 2 cm; Micropore Diameter: 100 μm) packaging can help maintain an appropriate atmospheric composition within the packaging, effectively delaying senescence in bok choy. At 15℃ (59°F), the bok choy packed in microporous film can retain its quality, particularly reducing color loss, for up to 8 days.
Figure 5. Comparison of bok choy packaged using supermarket bags, perforated film, and microporous film. This image highlights the differences in the quality and shelf life of bok choy, attributed to the use of different packaging materials. The image also portrays the microstructure and appearance of the microporous film packaging material. Photo Credit: Postharvest Team, Jiangsu Academy of Agricultural Sciences (JAAS), China.
Physiological and Physical Disorders
Freezing Injury. Bok choy freezes at about -0.2°C (31.64°F). The most common symptom of freezing injury is a water-soaked appearance of the stalks and leaves, followed by rapid decay due to bacterial soft rot.
Figure 6. Frost-damaged packchoi. Water-soaked regions caused by freezing injury are indicated with red arrows. Photo Credit: Postharvest Team, Jiangsu Academy of Agricultural Sciences (JAAS), China.
Physical Injury. Due to its delicate tissues and harvesting methods involving cutting, bok choy is prone to physical injuries during harvest. Such injuries increase the risk of decay.
Leaf yellowing. Chlorophyll degradation leads to diffuse yellowing of the leaves, a primary issue affecting bok choy quality during postharvest storage and transportation.
Figure 7. Bok choy exhibiting leaf yellowing. Leaf yellowing is a common sign of senescence and quality deterioration during storage. Photo Credit: Postharvest Team, Jiangsu Academy of Agricultural Sciences (JAAS), China.
Pathological Disorders
Bacterial Soft-Rot (Pectobacterium carotovorum) usually begins at the base of the leaves and can also infect the leaves, causing tissue softening, water-soaked regions, and emission of foul odor.
Figure 8. Bacterial soft rot in bok choy. This image highlights symptoms of bacterial infection, including a dark water-soaked region. Photo Credit: Postharvest Team, Jiangsu Academy of Agricultural Sciences (JAAS), China.
Fusarium wilt (Fusarium spp.) primarily infects older leaves, causing the affected areas to turn yellow and develop black spots. This pathogen is mainly soil-born and can cause infection during postharvest storage.
Figure 9. Fusarium wilt in bok choy. Characteristic symptoms include discoloration and wilting. Photo Credit: Postharvest Team, Jiangsu Academy of Agricultural Sciences (JAAS), China.
References
References from scientifically validated sources will be added in the future.