Fouling mechanisms of coconut milk foulants formed during pasteurization

Abstract

This work aimed to study mechanisms of coconut milk fouling by studying major components found in coconut milk foulants, namely proteins and fats, generated at various pasteurization times. Both batch (BP) and continuous pasteurizations (CP) were studied. Similar results were observed from the BP and CP. Mass of foulants increased with pasteurization times (5–25 min). In addition, masses of proteins and fats increased with pasteurization time. Although, the mass of fats found in CP foulants increased slightly, mass of both types of foulants linearly correlated with masses of proteins and fats. SEM images of coconut milk foulants showed that fouling occurred within one minute of pasteurization. The images together with content analysis of the foulants demonstrated that the foulants may composed of few layers together and an initial layer of foulants was composed of proteins, carbohydrates, fats, and minerals. Emulsion sizes of pasteurized coconut milk increased with the pasteurization time. Hence, the coconut milk fouling mechanisms may initially start by deposition of denatured protein and other components in water phase of the milk onto heat transfer surfaces. The deposition of proteins together with denaturation of proteins, which act as emulsifiers of the milk, caused instability of the coconut emulsion. Therefore, the increased coconut oil droplet sizes during pasteurization were observed. Consequently, fat and carbohydrate attached to fat could deposit into and onto the fouling layers. Although fouling mechanisms of BP and CP foulants were similar, the different flow schemes affected the compositions, appearances, and strengths of the two foulants. These in turn affect cleaning behaviours of the two foulants.