A Study of the texture of ‘Gala’ apples: the relations between the grade of maturity, measured with Time-resolved reflectance spectroscopy, and mechanical, acoustical and sensory properties

Vanoli Maristella1,2, Anna Rizzolo2, Maurizio Grassi2, Fabio Lovati2, Marina Buccheri2, Angelo Zanella3, Nadja Sadar3, Alberto Dalla Mora4, Edoardo Martinenghi4, Alessandro Torricelli4, Lorenzo Spinelli1
[email protected]
1 Istituto di Fotonica e Nanotecnologie (IFN), Consiglio
Nazionale delle Ricerche, Milano
2 Unità di ricerca per i processi dell’industria agroalimentare
(IAA), Consiglio per la ricerca in agricoltura e l’analisi
dell’economia agraria, Milano
3 Research Centre for Agriculture and Forestry Laimburg,
Ora, Bolzano
4 Dipartimento di Fisica, Politecnico di Milano

The consumers of apples prefer crunchy and juicy fruits over mealy ones. These sensory characteristics define the texture of a fruit and are related to the mechanical and acoustic properties of the pulp. The texture depends on the ripening stage and varies according to the softening of the fruit due to the modifications of the cell walls and the intermediate lamella. The scope was to study the texture variations of ‘Gala’ apples on different ripening stages through the analysis of the mechanical, acoustic, and sensory properties. In order to do so, 180 fruits have been measured at harvest through the time-resolved reflectance spectroscopy (TRS) at 670nm. Then, the fruits were arranged according to their decreasing coefficient (increasing ripeness) of absorption (μa670) in three classes of maturation (little, medium, very ripe) and randomized in 6 samples. At harvest and after 2 months of storage in controlled atmosphere, the fruits were exposed to shelf life of 1, 7, and 14 days at 20°C. After each period of shelf life, they have undergone sensory analysis and have been analysed individually for mechanical properties. These properties were measured in a non-destructive way (pressure on the entire apple) and with destructive methods through the contemporary acquisition of the mechanical and the acoustic profile through a penetrometic measurement combined with acoustic-measuring equipment.
The sensory data underwent a cluster-analysis which led to 4 sensory profiles (W1, W2, W3, W4), characterized by crunchiness, juiciness and decreasing consistency and increasing mealiness. The W1 profile, typical for the fruits that are part of the TRS class “less ripe”, were characterized at harvest and at the begin of shelf life of elevated penetrometic and compression levels and of an elevated number of sounds >60dB. The profile W4 (mealy), typical for the fruits of the TRS classes “medium and very ripe”, showed at the end of shelf life an elevated number of sounds between 40 and 50 dB, larger intercellular spaces and lower levels of firmness and of compression.

Key words: TRS, compression, intercellular space, firmness, crunchiness
Activity type
Participation in scientific conference
Activity work package
Fruit quality; improvement of fruit handling/storage
Activity number
Activity contact
Dr. Angelo Zanella
Laimburg Research Centre
Laimburg 6 - Pfatten
I-39040 Post Auer (BZ), Italy
[email protected]
Activity partner
Activity country
Last edit
The EUFRUIT thematic network has received funding from the
European Union's Horizon 2020 research and innovation programme
under grant agreement No 696337.