Rheological characterisation of juices obtained from transgenic pectate lyase-silenced strawberry fruits

The present study is focused on the characteristics of juice made from transgenic strawberry fruits with a 90% reduction on pectate lyase mRNA expression. No differences of soluble solids, pH or solid volume fraction were found between control and transgenic juices. Total sugar content of the serum fraction was also similar but a slightly higher content of large molecular mass polyuronides was observed in transgenic juice. The solid fraction of transgenic juice contained larger particles than did the control. The dynamic shear analysis of the juices showed higher values of the storage (G′) and loss (G′′) moduli versus strain for the transgenic samples, with G′ over G′′ within the linear viscoelastic range (LVR). For both samples, G′ and G′′ increased with frequency, showing a weak-gel response, whereas complex viscosity (η∗) decreased with frequency, denoting a shear-thinning behaviour. Overall, the transgenic juices showed higher values of G′, G′′ and complex viscosity than did the control within the frequency range assayed and a more solid-like character. These results suggest that effects of pectate lyase-silencing in tissue integrity increased the content of large particles in juice, its viscoelastic properties being modified and its viscosity increased.