Grainy properties of post–heating fermented milk with different particle sizes

Post–heating operation is crucial to produce ambient yogurt, which is also a direct cause of sensory defects, especially graininess. Consumers’ perception of graininess varies based on individual sensitivities. Accurate evaluation of graininess is a prerequisite for improving the sensory quality of ambient yogurts. The purpose of this study was to propose a method to discriminate consumers' sensitivity to grainy perception of post–heating (55 °C–85 °C, 25 s) fermented milk, and to further determine the volume proportion threshold required to produce different graininess intensities by blending fermented milk with different particle sizes. The results suggested that increasing the post–heating temperature induced various graininess by promoting different microgel aggregation. Fermented milks with microgel aggregate sizes of ∼14–∼20 μm, ∼27 μm, and ∼46–∼65 μm were classified as “weak”, “moderate”, and “strong” graininess, respectively. This result was obtained by approximately 81% of the panelists with moderate and high sensitivity on the perception of graininess. Furthermore, the graininess can be modulated by regulating the fermented milks with larger microgels and with smaller microgels; however, the blending volume of the latter must exceed 50% to reduce the graininess of the former by 1–2 sensory intensity ranks.