Gang Fan

Characterisation of free and bound volatile compounds from six different varieties of citrus fruits.

Free volatile compounds in six varieties of citrus juices were analyzed by solid-phase microextraction-gas chromatography-mass spectrometry. Bound fractions were isolated and extracted with methanol and Amberlite XAD-2 resin and then hydrolyzed by almond β-glucosidase. A total of 43 free and 17 bound volatile compounds were identified in citrus. Free volatile contents in sweet orange were the most abundant, followed by those in grapefruits and mandarins. Among free volatiles, terpenes were the most abundant in citrus juice. Sensory analysis results showed that the flavor of the same citrus cultivars was similar, but the flavor of different cultivars varied. Among bound volatiles, benzenic compounds were the most abundant in these citrus juices. Bound volatiles also significantly differed among cultivars. In addition, only p-vinylguaiacol were detected in all of the samples.

Antifungal activity and action mode of pinocembrin from propolis against Penicillium italicum

The antifungal activity and possible mode of action of pinocembrin isolated from propolis against Penicillium italicum were investigated. Pinocembrin exhibited strong antifungal activity against P. italicum in a dose-dependent manner. Respiration rates of P. italicum during spore germination and mycelial growth were significantly inhibited when exposure to pinocembrin. The respirations of mitochondria in state 2 and state 3 from mycelia were significantly inhibited in the presence of this compound. The phosphorylated adenosine nucleotides levels in hyphae of P. italicum treated with pinocembrin were significantly low and energy charge value became unstable. Unltrastructure of hyphae was seriously damaged with pinocembrin incubation for 24 h, which was further confirmed by the increase of relative ionic leakage and soluble protein loss of P. italicum mycelia treated with pinocembrin. It was concluded that pinocembrin inhibited the mycelial growth of P. italicum by interfering energy homeostasis and cell membrane damage of the pathogen. Pinocembrin would be a promising bioactive compound for treatment of P. italicum infections on postharvest citrus fruit.

Optimisation of α-terpineol production by limonene biotransformation using Penicillium digitatum DSM 62840

BACKGROUND In this study, (R)-(+)-limonene biotransformation using three fungal strains was compared. Penicillium digitatum DSM 62840 was distinguished for its capacity to transform limonene into α-terpineol with high regioselectivity. Growth kinetics in submerged liquid culture and the effects of growth phase and contact time on biotransformation were studied using this strain. Substrate concentration, co-solvent selection, and cultivation conditions were subsequently optimised. RESULTS The maximum concentration of α-terpineol (833.93 mg L(-1)) was obtained when the pre-culture medium was in medium log-phase by adding 840 mg L(-1) substrate dissolved in ethanol and cultivation was performed at 24 °C, 150 rpm, and pH 6.0 for 12 h. Addition of small amounts of (R)-(+)-limonene (84 mg L(-1)) at the start of fungal log-phase growth yielded a 1.5-fold yield of α-terpineol, indicating that the enzyme was inducible. CONCLUSION Among these three strains tested, P. digitatum DSM 62840 was proved to be an efficient biocatalyst to transform (R)-(+)-limonene to α-terpineol. Further studies revealed that the optimal growth phase for biotransformation was in the medium log phase of this strain. The biotransformation represented a wide tolerance of temperature; α-terpineol concentration underwent no significant change at 8-32 °C. The biotransformation could also be performed using resting cells.

Physiological and Quality Changes of Postharvest Strawberries at Different Storage Temperature and Their Relationships to Fruit Discoloration

The changes in fruit color development, fruit quality, reactive oxygen species (ROS) metabolism, and phenolic metabolism of strawberries during storage at 15°C, 25°C and 35°C were evaluated to explore the key internal factors resulting in the fruit discoloration. The high storage temperatures aggravated fruit discoloration as indicated by the decrease of L*, a* and b* values, and accelerated weight loss of postharvest strawberry fruit. The fruit under higher temperature treatments induced more productions of superoxide anion (O2•) and hydrogen peroxide content (H2O2), more accumulation of Malondialdehyde (MDA) and lower antioxidant enzyme activities including Superoxide Dismutase (SOD) and Catalase (CAT). For phenolic metabolism, the high storage temperature increased the levels of anthocyanins, total flavonoids and phenolics, and enhanced the activities of relative enzymes including Polyphenol Oxidase (PPO) and Peroxidase (POD) in postharvest strawberry fruit. Further data correlation analysis indicates that anthocyanins accumulation was the most important factor leading to fruit discoloration of post harvest strawberries, followed by ROS and weight loss. Based on present study, the results suggest that fruit color of post harvest strawberry could be maintained through the ways including delay of the anthocyanins accumulation, maintenance of antioxidant activity and reduction of the water loss during storage. *Corresponding author: Dr. Litao Peng, Key Laboratory of Environment Correlative Dietology, Ministry of Education, College of food science and technology, Huazhong Agricultural University, Wuhan 430070, China, Tel: +86(27)8728211; Fax: +86(27)87288373; E-mail: penglt12@mail.hzau.edu.cn Received Date: May 09, 2017 Accepted Date: November 28, 2017 Published Date: December 02, 2017