Jing-Nan Ren

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.

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.

Effect of Food Emulsifiers on Aroma Release

This study aimed to determine the influence of different emulsifiers or xanthan-emulsifier systems on the release of aroma compounds. Solid-phase microextraction (SPME) and GC-MS were used to study the effects of varying concentrations of xanthan gum, sucrose fatty acid ester, Tween 80 and soybean lecithin on the release of seven aroma compounds. The effects of the emulsifier systems supplemented with xanthan gum on aroma release were also studied in the same way. The results showed varying degrees of influence of sucrose fatty acid ester, soybean lecithin, Tween 80 and xanthan gum on the release of aroma compounds. Compared with other aroma compounds, ethyl acetate was more likely to be conserved in the solution system, while the amount of limonene released was the highest among these seven aroma compounds. In conclusion, different emulsifiers and complexes showed different surface properties that tend to interact with different aroma molecules. The present studies showed that the composition and structure of emulsifiers and specific interactions between emulsifiers and aroma molecules have significant effects on aroma release.