Microscopic study of proteins, starch and cell walls in potato trimmings

Potato trimmings are an undervalued food industry by-product and represent a potential source of valuable nutrients such as potato proteins. Cryo-scanning electron microscopy, atomic force microscopy, fluorescence microscopy and Raman microscopy were used to define the structural organisation of the protein fraction in this food side stream. The complementarity of the techniques allowed to localise the proteins in potato trimmings but also revealed the microstructure of these proteins, which were mainly present as aggregates in the cytoplasm, near starch granules and within gelatinised starch. Globules in the aggregates ranged in size from 0.1 to 0.25 μm. Upon acid-based stabilisation, differences in the microstructure of both gelatinised starch and cell walls were observed. These were most apparent in samples stabilised by steered fermentation, and it is suggested that these changes have caused the improved protein extractability (+41%) observed in these samples. A multipronged microscopy approach helps to elucidate the impact of acid-based stabilisation techniques and might explain the positive effect of the stabilisations on protein extractability. • Potato proteins were visualised using advanced microscopy. • Globular and irregularly shaped protein aggregates were observed. • Acid stabilisation alters the microstructure of gelatinised starch and cell walls. • Improved protein extractability can probably be linked to microstructural changes.