Physical and Biochemical Changes in Broccoli That May Assist in Decision-Making Related to International Marine Transport in Air or CA /

In conducting a supply chain project for the US Army, we learned that broccoli is one of the most commonly rejected items during marine transport of mixed loads of fresh fruits and vegetables in the Pacific region. Preliminary MAP experiments with freshly harvested broccoli indicated that temperature control alone is sufficient to maintain broccoli quality during shipping for up to 3 weeks. Those results suggested that the broccoli in the shipments being simulated is not always freshly harvested at the time of container loading. Therefore, in this research we investigated potential indicators of broccoli freshness (i.e., physiological age) using delayed establishment of CA conditions. Fresh broccoli was obtained locally and held overnight in air at 0.5°C prior to the start of each experiment. Broccoli was placed into air or CA (1 kPa O2 plus 10 kPa CO2) at 0.5°C immediately or after 5 or 10 days in air at 0.5 or 5°C. Color changes on the florets and the cut surface of the stalks, weight loss, chlorophyll fluorescence, and overall subjective visual quality were evaluated after 10 and 20 days of storage at 0.5°C and after 20 days of storage plus 2 days shelf life at 20°C. Additional samples were stored for later analyses of vitamin C, chlorophyll a, chlorophyll b, total chlorophyll, total sugars, total amino acids, total phenolics and total protein. Although there were changes during storage and differences between treatments, none of the indices could be used as a ‘freshness indicator’ due to variability between different lots of broccoli that precluded determination of the physiological age. Optimum temperature conditions during transport can prevent rapid deterioration of freshly harvested broccoli for 3 weeks without further benefit from the use of CA/MA, but without specific knowledge of the product’s prior temperature history, such shipments remain risky. INTRODUCTION Broccoli is a very perishable commodity with limited shelf life after harvest. Quality loss is usually due to dehydration of the cut surface and loss of green color in the florets and is related to respiration rate, ethylene production and lipid peroxidation processes (Toivonen and Sweeney, 1998). The floret yellowing is a result of chlorophyll breakdown (King and Morris, 1994; Zhuang et al., 1995). Broccoli can be kept in excellent condition for 2 to 3 weeks if it is stored at low temperature (0°C) with 98-100% relative humidity (RH). Broccoli may be shipped for up to 3 weeks in mixed load marine containers to supply US military bases in the Pacific region but it is reportedly one of the most commonly rejected fresh vegetable items upon arrival. Preliminary experiments with fresh broccoli indicated that temperature control during simulated shipping could maintain the product’s quality for 30 days, which is longer than the time required to transport the crop by sea within the Pacific region. Thus, we considered that the products might not always be freshly harvested before shipping. The purpose of this research was to investigate potential indicators of broccoli freshness Proc. XI Int. Controlled and Modified Atmosphere Research Conf. Eds.: M.L. Amodio and G. Colelli Acta Hort. 1071, ISHS 2015 652 (i.e., physiological age) using delayed establishment of CA conditions. MATERIALS AND METHODS Fresh ‘Green Magic’ broccoli heads were obtained from a packinghouse in Palatka, FL within 1 h of harvest. The broccoli (14-count, in 24-lb waxed fiberboard cartons) was transferred in an air-conditioned vehicle to the Postharvest Horticulture Laboratory at UF in Gainesville and stored overnight at 0.5°C. Broccoli was equally divided into three groups. The first group was immediately placed into a flow-through storage system of humidified air or CA (1 kPa O2 plus 10 kPa CO2) at 0.5°C. The second and third groups were first placed into humidified air at 0.5 or 5°C, respectively, for 5 or 10 d before being transferred to air or CA at 0.5°C. The broccoli heads were naked inside the chambers. Color changes, weight loss, chlorophyll fluorescence, and overall visual quality were evaluated after 10 and 20 d of storage in air or CA at 0.5°C and after 20 d of storage plus 3 d shelf life at 20°C. Respiration rate and ethylene production were determined by GC. Chlorophyll fluorescence was determined from the Fv/Fm fluorescent measurement parameter using a chlorophyll fluorometer (model OS1p, Opti-Sciences, New Hampshire, USA). Chlorophyll concentration in the florets was determined as described by Lichententale (1987). The visual color was related to the transition from green to yellow, which was determined by the a* and L* values using a Minolta Colorimeter CR-400. Vitamin C content of the florets was determined as described by Teranda (1978). Ethanol extraction of the florets was used to determine the concentration of total amino acids and sugars as described by Lee and Takahashi (1966) and Dubois et al. (1956), respectively. The BSA assay was used to determine the concentration of total proteins according to Lemoine et al. (2007). We used three heads of broccolli per replicate and four replicates per treatment. The experiment was repeated three times. RESULTS AND DISCUSSION Αir-stored broccoli had higher ethylene production than CA-stored broccoli in all treatments (Fig. 1A), which was probably related to faster senescence of the florets that were stored in air compared to CA-stored florets. Ethylene production increased during shelf life at 20°C, with broccoli from the 10-d delay treatments having the highest ethylene production (Fig. 1B). Respiration did not differ significantly among treatments and remained low during storage, but there was also a significant increase in respiration rate during the 3 d of shelf life at 20°C (data not shown). These results are in agreement with the literature, confirming that broccoli shows a climacteric pattern of respiration and ethylene production (Makhlouf et al., 1989; Rushing, 1990), with increased ethylene and carbon dioxide production associated with tissue senescence. Vitamin C decreased during storage at 0.5°C in all treatments (Fig. 2). After 3 d of shelf life at 20°C, the concentration of vitamin C had decreased by 30 to 50% from the initial concentration (Fig. 2). For the 10-d delay treatment, vitamin C in broccoli heads stored at 0.5°C was significantly higher than in the heads stored at 5°C (Fig. 2C). It has been reported that temperature management after harvest is the most important factor to maintain the vitamin C content of fruits and vegetables; losses are accelerated at higher temperatures and with longer storage durations (Lee and Kader, 2000). Chlorophyll fluorescence did not differ among the treatments, with the Fv/Fm ratio decreasing during storage in all treatments (data not shown). Chlorophyll concentration changed as expected during storage, with total chlorophyll remaining stable in most of the treatments during the low-temperature storage period (Fig. 3). However, after 3 d of shelf life at 20°C, chlorophyll concentration had decreased by 50% (Fig. 3B and C) or more from the initial values in the delay treatments. In the no delay treatment, the decrease in total chlorophyll concentration during shelf life was around 20% (Fig. 3A). In agreement with the chlorophyll measurements, there were no differences in the color indices a* and L* between the treatments during storage at 0.5 or 5°C (Fig. 4). No significant changes in weight occurred during the storage period in any treatment; however, after 3 d of shelf life at 20°C weight loss was about 30% in all