To cite package ‘ppls’ in publications use:

  Kraemer N, Boulesteix A, Tutz G (2008). “Penalized Partial Least
  Squares with Applications to B-Spline Transformations and Functional
  Data.” _Chemometrics and Intelligent Laboratory Systems_, *94*,
  60–69. doi:10.1016/j.chemolab.2008.06.009
  <https://doi.org/10.1016/j.chemolab.2008.06.009>.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Penalized Partial Least Squares with Applications to B-Spline Transformations and Functional Data},
    author = {Nicole Kraemer and Anne-Laure Boulesteix and Gerhard Tutz},
    journal = {Chemometrics and Intelligent Laboratory Systems},
    year = {2008},
    volume = {94},
    pages = {60–69},
    doi = {10.1016/j.chemolab.2008.06.009},
  }