Viscosity of cooking oils affects dishwasher cleaning performance

Edible oil is a primary energy source in human diets. This study investigates the effects of heating temperature on the physicochemical properties of edible oils and their impact on dishwasher cleaning performance. First, the density and dynamic viscosity of peanut oil, rapeseed oil, and soybean oil were measured at room temperature and after heating to 50, 100, 150, 200, and 250 °C. Accordingly, two oils with the greatest viscosity difference-soybean oil at room temperature (SO_25) and peanut oil heated to 250 °C (PO_250)-were selected for dishwasher cleaning performance tests. Residue penalty score (RPS) and re-deposition penalty score (RDPS) were defined to characterize the cleaning ability and anti-redeposition performance of dishwashers. The results indicated that PO_250 generally exhibited lower cleaning scores. In the quick wash mode, the RPS and RDPS of PO_250 and SO_25 were relatively similar; however, in the standard wash mode, both RPS and RDPS of PO_250 were higher than those of SO_25. Statistical analysis further revealed that changes in washing mode have a greater impact on cleaning scores for high-viscosity oil than for low-viscosity oil. Moreover, low-viscosity oil exhibited greater inter-machine variability in dishwasher cleaning scores compared with high-viscosity oil. Scanning electron microscopy (SEM) imaging showed that PO_250 formed an oil film on the ceramic surface, whereas SO_25 appeared as discrete particles. This study provides a scientific basis for developing regionally applicable dishwasher testing standards, contributing to the optimization of cleaning technologies.