Quality assessment of grape juice from integrated, organic and biodynamic viticulture using image forming methods
Jürgen Fritz, Miriam Athmann, Georg Meissner, Randolf Kauer, Uwe Geier, Roya Bornhütter and Hans R. Schultz
ABSTRACT
Aim: The image forming methods biocrystallisation, capillary dynamolysis and circular chromatography are introduced as a complementary tool for grape quality assessment. These methods were used to investigate grape juice samples from a long-term field trial comparing integrated, organic and biodynamic viticultural practices. Methods and Results: Characteristic changes in structures created by the reaction of metal salts with grape juice were evaluated using biocrystallisation, circular chromatography and capillary dynamolysis image forming methods. In particular, this study tested the effects of cultivation method, aging time and juice concentration on structure formation.
To assess grape quality, the images of the encoded grape juice samples were: i) grouped into pairs with similar image features, ii) characterised based on reference images (e.g., high versus low resistance to degradation, or the amount of substance necessary for structure formation), iii) ranked according to structures associated with grape quality, and iv) assigned to the different production methods (classification). In order for similar structural features in the image forming methods to be expressed, all samples of grape juice harvested from integrated production over four years required higher juice concentrations than samples from organic and biodynamic origin. This was interpreted as the latter two production systems having higher structure formation efficacy. Furthermore, juices produced from the integrated management system exhibited more structures, indicative of a lower resistance to aging. In three out of four harvest years, the biodynamic samples exhibited the highest structure forming efficacy and resistance to aging.
Conclusion: These findings are consistent with enhanced form maintenance and thus higher internal product quality of biodynamic and organic grapes compared to grapes from integrated farming.
Significance and impact of the study: Image forming methods may serve as a valuable tool for grape juice and wine quality assessment to complement compound-specific chemical analyses.