Varietal comparison of the chemical, physical and mechanical properties of five colored table grapes

The visual attributes of table grapes, their chemical constituents and mechanical properties are involved in consumer acceptability because they are correlated to sensory perception. Usually, instrumental measurements are preferred to the sensory evaluations because they reduce variations in subjective judgments and can be carried out more easily. In this work chemical-physical attributes and texture properties of five black table grapes (Alphonse Lavallée, Black magic, Cardinal, Perlon, Regina nera) were studied in order to identify significant varietal differences. Spectrophotometric and HPLC methods and Texture Analysis test were used to evaluate color index, sugars and acid composition, phenolic characteristics and mechanical properties of the skin and the pulp of berries. Many differences were found among varieties in technological maturity indexes, hydroxycinnamic acid, anthocyanin content and profile and relative CIE L*, a*, b* parameters, but the more relevant differences were found in mechanical properties. Principal Component Analysis showed that the TPA parameters (hardness, cohesiveness, gumminess, resilience) and berry skin characteristics (break skin energy, skin modulus of elasticy) were the best indices able to fulfill the aim of this work. Almost all the parameters showed differences among cultivars, confirming their importance in the characterization of the variety as well as in the assessment of potential consumer acceptability. In particular, the cultivars demonstrated different reactions to the compression test; thus, the texture analysis parameters can be appropriate to explain varietal differences and to allow their differentiation.