Heat shock treatment maintains the quality attributes of postharvest jujube fruits and delays their senescence process during cold storage.

The effects of heat shock (HT), 1-methylcyclopropene (1-MCP), or their combination (HT + 1-MCP) on the quality of fresh jujube fruits during cold storage were studied. Among them, HT showed the best preservation effect on jujube fruits, which was more effective than others in inhibiting the increase of red index, decay incidence, and weight loss and delaying the decrease of firmness, soluble solids content (SSC), titratable acidity (TA), and ascorbic acid (AsA) content. Besides, it could delay the degradation rate of the cell wall to maintain the integrity of cell membrane, and keep the high activity of active oxygen scavenging enzymes. During cold storage, malondialdehyde (MDA) content and relative electrolyte leakage (REL) of the HT group were significantly lower than those of the control group, 1-MCP, and HT + 1-MCP group (p < .05), while superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activities were significantly higher than those of other groups (p < .05). It was concluded that the postharvest HT treatment could effectively delay the senescence and decay of jujube fruits. PRACTICAL APPLICATIONS: Jujube fruits have high nutritional value used for food and medicine. However, they are not tolerant to storage after harvest, resulting in high economic losses. Therefore, it is of great significance to find a suitable method to maintain the quality of jujube fruits. Our results revealed the effect of HT, 1-MCP, and their combination on the quality maintenance of jujube fruits, and found that HT could effectively maintain the quality of them, which could be used as an effective method for keeping jujube fruits fresh.

Comparison of the biochemical properties and thermal inactivation of polyphenol oxidase from three lily bulb cultivars.

The biochemical properties and thermal inactivation of polyphenol oxidase (PPO) from three main planted lily cultivars in China, namely, Lilium lancifolium Thunb, Lilium brownie var. viridulum, and Lilium davidii var. unicolor cotton were evaluated. Data indicate that the PPO from three cultivars showed two optimum pH levels of 4.0 and 6.5-7.0 and temperature of 15°C and exhibited the highest affinity toward 4-methylcatechol. However, this enzyme did not exhibit monophenolase activity. Thiourea and L-cysteine were more effective than other inhibitors. The enzymatic activity of L. lancifolium Thunb PPO crude extract was higher than that of L. brownie var. viridulum and L. davidii var. unicolor cotton. For thermal inactivation, L. davidii var. unicolor cotton PPO showed the best thermal resistance at 65-75°C, and L. lancifolium Thunb showed stability at 45°C. The deactivation of the three types of PPO followed the first-order reaction kinetics, and the activation energy (Ea) was 144.28, 138.00, and 107.12 kJ/mol for L. lancifolium Thunb PPO, L. brownie var. viridulum PPO, and L. davidii var. unicolor cotton PPO, respectively. PRACTICAL APPLICATIONS: Lilium is an ornamental and edible plant typically used for food and traditional Chinese medicine. Its flowers are used for decoration, and its underground bulbs are rich in various bioactive substances. Fresh lily bulbs easily turn brown and lose economic value during storage and processing. Polyphenol oxidase (PPO) is a crucial molecule involved in the enzymatic browning of fruit and vegetables. In this study, PPO was extracted from three main planted lily cultivars in China. Namely, Lilium lancifolium Thunb, Lilium brownie var. viridulum, Lilium davidii var. unicolor cotton and was partially characterized. The results are of considerable importance to further understand the PPO of lily bulbs and provide guidance for the inactivation of enzymes and the processing of lily bulb juice.