How do I calculate plsda residuals for new data?

Hello,

I was wondering what exactly the “mat.c” value in a plsda object is. In documentation, it is listed as " matrix of coefficients from the regression of X / residual matrices X on the X-variates, to be used internally by predict", but in both the predict and predict.mixo_pls the value cannot be found.
I ask because I am interested in calculating the residuals of new data after a plsda object has been computed. Perhaps this can be done by means of the predict function?

Looking forward to your response,
Nick