Effect of milk protein concentrate (MPC80) quality on susceptibility to fouling during thermal processing

•Increasing storage temperature decreased milk protein concentrate solubility.•Poor-soluble milk protein concentrate resulted in higher-amount of foulant.•Calcium content in foulant was not significantly different.•More air bubbles were observed in foulant by poor-soluble powder.

This study aims to understand the effect of milk protein concentrate (MPC80) solubility on its susceptibility to initiate fouling on stainless steel (SS) surfaces during thermal processing. In order to generate powders with different dissolution characteristics, a part of powder was stored at 25 °C (well-soluble powder) and the remaining part was stored at 40 °C (poor-soluble powder) for 2 weeks. Fouling characteristics of reconstituted MPC80 powder with 80 g protein per 100 g powder were studied using a custom-built benchtop plate heat exchanger. Exposing the MPC80 powder to a higher temperature during storage (40 °C) significantly decreased the solubility and increased the amount of foulant on SS coupons (P < 0.05). Microscopic investigations (scanning electron microscopy and laser scanning confocal microscopy) of resulted fouled layers revealed heterogeneous fouling layers of varying tomographies consisting of lipids, proteins, and calcium. The energy dispersive X-ray spectroscopy helped in visualizing the spatial distribution of the elements (Ca, N, O, C, etc.) throughout the fouled layer. Thus, the study can be useful in understanding the fouled layer characteristics during thermal processing of MPC80 and help in designing effective cleaning protocols.