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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.

The effects of the interaction of xanthan and sugar on the release of aroma compounds (α‐pinene, ethyl acetate, ethyl butyrate, perillaldehyde, hexenal, and d‐limonene) were investigated in model solutions (xanthan, sugar and xanthan‐sugar solutions). The released aroma compounds were analysed by solid‐phase microextraction and gas chromatography‐mass spectrometer (SPME/GC‐MS). The results showed that the six aroma compounds decreased differently in the 0.4 g·L‐1 xanthan solution. A slightly stronger release of these aroma compounds in glucose solution was observed than that in sucrose solution. The release of these aroma compounds increased in the xanthan solution after the addition of the sucrose. This indicated that the release of these aroma compounds was inhibited in the xanthan solution. But the addition of sucrose in the xanthan solution could promote the release of the aroma compounds. Additionally, the rheology results showed that the xanthan solution exhibited a gradual shear thinning and the C* of xanthan was 2 g·L‐1. However, the concentrations of the xanthan solution which could inhibit the release of the six aroma compounds were not fully consistent with C*. And this indicated that viscosity was not the main factor influencing the release of aroma compounds in the xanthan solution. Copyright © 2016 John Wiley & Sons, Ltd.

The changes in the physicochemical characteristics of raspberry juice during storage were studied. Free aroma compounds during storage 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. The content of the ascorbic acid was reduced by 47 and 31% in fresh and processed juice after 20 days of storage, respectively. A total of 23 free aroma compounds were identified in the raspberry juice. Only 12, 10, 9 and 10 free aroma compounds were found in this juice after 5, 10, 15 and 20 days of storage, with total contents of 1,614, 696, 806 and 1,103 μg/L. C13-norisoprenoids were the predominant compounds during storage. In total, 14 bound aroma compounds were found in this juice. Benzoic acid was the most abundant benzene compound. Most of the bound fractions were missed during storage. PRACTICAL APPLICATIONSAroma attribute is one of the most important factors to the quality of the fruit juice. It changed seriously during hot processing or storage. The main reason was that the aroma compounds in the juice were transferred, degraded or evaporated. Nevertheless, glycosidically bound aroma compounds might be released during processing or storage. The findings of this research revealed that most of the physicochemical characteristics remained stable during storage, except ascorbic acid. The free and bound aroma compounds of the raspberry juice changed a lot during storage. Most of these compounds decreased or were missed during hot processing and storage. The information gained from this research could be further applied in the raspberry and food industry to improve the quality of the juice during processing and storage.

The concentration of bound volatiles in pulp and peel decreased with the rise in β-glucosidase activity in pulp and peel during maturation. This indicated that bound volatiles in Jincheng oranges were released during maturation owing to the increase in β-glucosidase.

Abstract: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.

The present study focused on the effect of olive oil on Ostwald ripening of flavor nanoemulsions. The release of the aroma compounds from the nanoemulsion system was also investigated. The results showed that the droplets size of the nanoemulsions decreased sharply first and then kept stable with the increase of Tween 80. The optimum surfactant/cosurfactant (Km) ratio was determined at 7:1. The average particle size of nanoemulsion was 39.22 nm. The polydispersity index (PDI) was 0.242 nm, and the particle size distribution was in the range of 20-150 nm at the optimum Km. The stability of the nanoemulsions was improved after the addition of olive oil, and it increased noticeably with the increase of olive oil. The addition of olive oil could help to stabilize the emulsions and hamper Ostwald ripening. All the 11 aroma compounds in the nanoemulsions were detected after 24-h storage. While only 5 aroma compounds were found after 48-h storage, and α-pinene and β-myrcene were the only two aroma compounds detected after 72-h storage with low contents of 1.41 and 0.5 mg/L. The addition of olive oil inhibited the release of the aroma compounds from the nanoemulsion system. The released ethyl acetate was reduced by 48% after the addition of 10% olive oil. Significant decrease on the release of α-pinene and nonanal was observed after the addition of 3% olive oil. And the decrease was also observed on the release of β-myrcene, D-limonene, α-terpineol, decanal and eugenol when the olive oil content was ≥ 5%. However, benzyl alcohol, β-ionone and 1-octanol showed no significant changes with the increase of olive oil. This indicated that the addition of olive oil could provide greater retention of the aroma compounds in the nanoemulsions.