René Siret

Instrumental Texture Analysis Parameters as Markers of Table-Grape and Winegrape Quality: A Review

Texture analysis is a well-established analytical technique in the food industry for evaluating the mechanical and physical characteristics of both raw ingredients and finished products. Instrumental mechanical properties of table grapes, acquired using universal testing machines equipped with specific probes, may be of interest in the viticulture and postharvest sectors to recognize the potential of each variety and help satisfy market requirements. The measured parameters are related to some sensory properties and, therefore, indirectly to consumer acceptability of the product. As texture analysis is a rapid and low-cost analytical technique, it can also be favorably applied in enology as a routine tool for monitoring winegrape quality. Among the different mechanical parameters measurable, berry skin thickness and hardness are indices that reflect anthocyanin extractability and dehydration kinetics with adequate reliability. This review collects the most recent research results from grape texture studies, emphasizes the potentiality and limits of this analytical technique when applied to grape studies, and highlights trends that require further understanding.

Physical and Physiological Heterogeneity within the Grape Bunch: Impact on Mechanical Properties during Maturation

Mechanical properties are emerging as complementary criteria to evaluate grape berry quality for winemaking. As texture is evaluated on a berry per berry basis, it is important to assess the impact of the within grape heterogeneity on mechanical properties. Evolution of textural maturity of Cabernet franc was assayed throughout ripening using double compression 20% tests. Berries were sampled from whole grape bunches rather than randomly picked in the vineyard. Results showed coherent and significant evolution of double compression parameters: F1, Grad0, Grad1, W1, and gumminess significantly decreased whereas cohesiveness significantly increased during maturation. Variations in mechanical parameters were related with major physiological and physical traits. Mechanical parameters differed significantly according to berry position. Among these parameters, Grad1 was highly correlated with berry density and Brix (r = −0.91 for both), and W1 was highly correlated with water content (r = 0.87). Within-bunch heterogeneity was illustrated by different distributions of physical, physiological, and mechanical parameters. A negative gradient was shown from the top to the bottom of bunches for dry weight, density, Brix, cohesiveness, and gumminess. Berries at the distal part of the bunch were more advanced in maturity and were softer than berries at the top. Results are discussed with regard to the sampling strategy in the assessment of grape berry quality based on mechanical properties.

Cryo-laser scanning confocal microscopy of diffusible plant compounds

BackgroundThe in vivo observation of diffusible components, such as ions and small phenolic compounds, remains a challenge in turgid plant organs. The analytical techniques used to localize such components in water-rich tissue with a large field of view are lacking. It remains an issue to limit compound diffusion during sample preparation and observation processes.ResultsAn experimental setup involving the infusion staining of plant tissue and the cryo-fixation and cryo-sectioning of tissue samples followed by fluorescence cryo-observation by laser scanning confocal microscopy (LSCM) was developed. This setup was successfully applied to investigate the structure of the apple fruit cortex and table grape berry and was shown to be relevant for localizing calcium, potassium and flavonoid compounds.ConclusionThe cryo-approach was well adapted and opens new opportunities for imaging other diffusible components in hydrated tissues.