Lack of Correlation Between Instrumental Firmness Values and Sensory Perception of Fruit Texture In Apples

Textural characteristics of the apple fruit are one of the most important components of eating quality. To estimate textural preference of consumers for apples for fresh consumption, penetrometric measurements are being used. Such measurements are widely accepted for both research and industrial (at retailers/supermarkets) purposes. Present study evaluated the correlation between instrumental firmness measurements (Effegi-type) and consumer preference for fruit texture, and described textural characteristics of the cortex tissue of apple cultivars at the ultrastructural level. Untrained consumer panels with over 100 attendees in each session carried out the sensory assessments (3 different sessions with 4 cultivars each session). Preference ratings given by consumers did not closely correlate with instrumental firmness data (R² = 0.1318), therefore penetrometric firmness values did not seem to be accurate predictors of textural preference of consumers for apples. Scanning electronmicroscopy imaging of broken cortex surfaces (for mimicking a bite into an apple fruit) revealed that in cultivars characterized by crisp texture, such as ‘Candy Crisp’, cells usually broke apart with emptying the entire cell content on the fracture surface when biting into an apple (“Fracture-type”). In contrast, in non-crisp non-firm cultivars, such as ‘Red Delicious’, whole cell separation was observed on the fracture surface of the cortex without apparent cell damage, i.e., breaking, and emptying the cell content (“Cell-to-cell debonding type”). Non-crisp but still firm cultivars, such as ‘Granny Smith’, were characterized by cell rupture on the fracture face of the cortical tissues (“Rupture type”). No close relationships between structural characteristics (cell size, cell wall thickness) of apple cortex and instrumental firmness values or sensory texture preference were found. Within a cultivar, decreasing firmness values were measured with increasing fruit size.  Ultrastructural characteristics of the cortex tissues were essentially the same for both small and large fruit of a cultivar with the difference of larger intracellular spaces in latter case.