The Genetics of Kiwifruit Flavor and Fragrance

TPS-b family genes involved in signature aroma terpenes emission in ripe kiwifruit

Aroma is a critical factor influencing consumer acceptability of ripe fruit. When fruit are eaten, the aroma travels retronasally from the mouth into the olfactory receptors located in the nose after exhaling. In kiwifruit (Actinidia spp.), terpene volatiles such as α-terpinolene and 1,8-cineole have been shown to contribute to the characteristic aroma of ripe fruit. Notably, 1,8-cineole contributes a key floral/eucalyptus note to the aroma of ripe A. chinensis 'Hort16A' kiwifruit, based on sensory descriptive and discriminant analysis. Emission of α-terpinolene and 1,8-cineole in kiwifruit is induced by ethylene, and production peaks when fruit are at eating ripeness. Two monoterpene synthase TPS-b family genes have been isolated from the fruit of A. arguta and A. chinensis that produce α-terpinolene and 1,8-cineole, respectively. Here we discuss terpene volatiles with respect to fruit aroma and consumer sensory evaluation, analyze the gene structure and conserved motifs of TPS-b genes in published kiwifruit genomes and then construct a transcriptional regulatory network based on Actinidia TPS-b. These data provide further insights into the potential molecular mechanisms underlying signature monoterpene synthesis to improve flavor in kiwifruit.

Effects of Penicillium expansum infection on the quality and flavor of yellow flesh kiwifruit during cold storage

This study aimed to assess the effects of Penicillium expansum (P. expansum) infection on the quality and flavor of Jinmi (JM) and Jinyan (JY) kiwifruit. Kiwifruit were inoculated with P. expansum and stored at 0 ± 1°C, and the changes in quality indicators and volatile substances (VCs) at different stages of disease were determined. Results showed that in wound-inoculated kiwifruit, the soluble solid content (SSC) increased. Conversely, their titratable acidity and vitamin C (VC) content, firmness, lightness, and saturation decreased. The taste-related parameters and nutritional value of kiwifruit declined after infection. VCs such as ethanol, 3-methyl-1-butanol, and 2-methylisoborneol were detected only in the diseased fruit and gradually increased as the disease aggravated, suggesting that they may be the main sources of odor during P. expansum infection. Therefore, VCs detection can be used to determine possible P. expansum infection, as well as the degree of infection in kiwifruit. PRACTICAL APPLICATIONS: In practical application, we can use the results of this study to determine possible Penicillium expansum infection, as well as the degree of infection in kiwifruit according to the indicators such as volatile substances. Kiwifruit enterprises can use the nondestructive detection model established in this study to screen out the kiwifruit infected with P. expansum more efficiently, quickly, and accurately, in order to prevent harm to the health of consumers.

Tracing internal quality and aroma of a red-fleshed kiwifruit during ripening by means of GC-MS and E-nose

'Hongyang' kiwifruit is a new breed of red-fleshed cultivar that has become broadly popular with consumers in recent years. In this study, the internal quality and aroma of this kiwifruit during ripening were investigated by means of gas chromatography-mass spectrometry (GC-MS) and electronic nose (E-nose). Results showed that the green note aldehydes declined, the main fruity esters increased, and the terpenes had no obvious changes during ripening. Correlations between quality indices, volatile compounds, and E-nose data were analyzed by ANOVA partial least squares regression (APLSR), and the results showed that firmness and titratable acidity (TA) had highly positive correlations with (E)-2-hexenal and hexanal, while soluble solids content (SSC) and SSC/TA ratio had positive correlations with ester compounds. The E-nose sensors of S7, S10, S8, S6, S9, and S2 were positively correlated with ester compounds, S1, S3, and S5 were mainly correlated with hexanal, and S4 was correlated with terpene compounds. Partial least squares regression (PLSR) and support vector machine (SVM) were employed to predict the quality indices by E-nose data, and SVM presented a better performance in predicting firmness, SSC, TA, and SSC/TA ratio (R ² > 0.98 in the training set and R ² > 0.94 in the testing set). This study demonstrated that the E-nose technique could be used as an alternative to trace the flavor quality of kiwifruit during ripening.

Historical Review on the Identification of Mesifurane, 2,5-Dimethyl-4-methoxy-3(2 H)-furanone, and Its Occurrence in Berries and Fruits

Mesifurane, 2,5-dimethyl-4-methoxy-3(2 H)-furanone, is a natural compound used a worldwide as a flavoring for foods, beverages, and cosmetics. Global sales of mesifurane are around $100 million. Its significance as a flavor-impact compound in some Nordic berries was discovered in the early 1970s in Finland. Synthesized mesifurane was used as a key compound in aroma mixes exploited in a Finnish patent. Mesifurane is a significant flavorant in arctic brambles, mangoes, strawberries, and many other fruits and berries and is an enzymatic methylation product of 2,5-dimethyl-4-hydroxy-3(2 H)-furanone. Because of the obscurity of the information on the history of the commonly used trivial name, mesifurane, it is time to lift the veil and reveal the background of the present situation. The key player was a northern berry, arctic bramble ( Rubus arcticus), the Finnish name of which is mesimarja. Forty years ago, aroma research was limited by technical factors, but nowadays there is a surplus of information.