Stephan Trautzsch

Investigation on Key Molecules of Huanglongbing (HLB)-Induced Orange Juice Off-flavor

Orange fruits from huanglongbing (HLB)-infected trees do not fully mature and show a severe off-flavor described as bitter-harsh, metallic, and less juicy and fruity. The investigation of juice from HLB-infected (HLBOJ) and healthy control oranges (COJ) by gas chromatography-mass spectrometry showed higher concentrations of fruity esters, such as ethyl butyrate and ethyl 2-methylbutyrate, and soapy-waxy alkanals, such as octanal and decanal, in the COJ, whereas the HLBOJ showed higher concentrations of green aldehydes such as hexanal and degradation compounds of limonene and linalool such as α-terpineol. Application of aroma extract dilution analysis on terpeneless peel oil led to the identification of long-chained aldehydes such as ( E, E)-2,4-decadienal, ( Z)-8-tetradecenal, trans-4,5-epoxy-( E)-2-decenal, ( Z)-4-decenal, and octanal with the highest flavor dilution factors among 25 odor-active volatiles in the peel oil of healthy oranges. Taste-guided fractionation and identification of the HLBOJ secondary metabolites followed by sensory validation revealed that flavanoids such as hesperidin may modulate the flavor to evoke the unacceptable harsh/metallic taste impression. Quantitation of the bitter components showed good correlation between the limonoid and flavanoid concentrations with the off-flavor and quality of the oranges obtained throughout the season.

Chapter 45 – Studies on Stability of Citrus Flavors and Insights into Degradation Pathways of Key Aroma Compounds

Model studies have been performed with individual citrus related aroma compounds such as citral, α-terpineol, α-terpinene, and others, in order to de-couple the complexity of citrus flavors. Degradation pathways and transformation rates have been determined for the most relevant compounds leading to the most prominent off-note compound p-methyl acetophenone. Citral is one of the main precursors. Catechins (flavan-3-ols) are often used as antioxidants for stabilization of flavor mixtures. The reactivity of catechins towards aldehydes is underestimated. In our study, we demonstrate the formation of covalent catechin–citral adducts – a reaction that might influence the aroma stability of citrus flavors in the presence of catechins. As a result, the freshness of citrus flavors and stability of key aroma-active substances can be improved, on the result of this study.