While bacteria and yeast are used for the production of rather simple proteins, mammalian cells are generally required for the production of more complex proteins (i.e. post-translational modifications and, in particular, complex glycosylations). In order to boost cell growth and protein production, cultivation media are commonly supplemented with plant peptones, which are hydrolysed plant proteins. Therefore; plant peptones consist mainly of an undefined mixture of peptides, but also contain carbohydrates, phenolic compounds, salts, etc. To increase biosafety, the current trend is the use of chemically defined media. The straightforward idea that only a small number of compounds from peptones are biologically active is attractive, but their identification remains challenging. We first characterised global chemical families of compounds present in a soy peptone. The main constituents of this batch were peptides (60%) and carbohydrates (20%). The addition of this peptone or derived fractions to the culture medium was then tested on Chinese hamster ovary cells, CHO-320 line, expressing gamma-interferon (gamma-IFN), cultivated in BDM. Its presence did not increase the time-integral of the viable cell density, it increased slightly that of the gamma-IFN concentration, but significantly the product/cell yield. Upon fractionation of this peptone by anion exchange chromatography and gel filtration, beneficial and detrimental fractions were obtained. The antioxidant activity of detrimental fractions was higher than that of beneficial fractions. Whereas the chemical nature of antioxidants contained in the detrimental fractions remains unknown, it may be assumed that they could inhibit the proliferation of CHO cells. Although the beneficial compounds were not identified, a fraction exhibiting the same effect as the peptone, but less complex, was obtained. (C)2010 Elsevier Ltd. All rights reserved.