Quantification of grittiness of yogurt using flow characteristics indexes

The grittiness of a food product is quantified mainly by sensory evaluation since it is difficult to use a measuring instrument for perceived texture. In this study, we examined a method for quantitatively evaluating the grittiness of yogurt according to its flow characteristics. Three categories of yogurt (15 types in total) were used as samples. Sensory evaluation (QDA: qualitative data analysis) and flow characteristics evaluation were conducted. Four trained panels evaluated the smoothness of samples using a 15-cm scale method. Distance from the left edge to the plot on a 15-cm scale was expressed using a score of 0 (smooth) to 15 (gritty) points. The mean score of the four panels (sensory evaluation score) was used for the analysis. For the flow characteristics evaluation, the yogurt was pressurized until it flowed from the reservoir and through the pipe (needle). Flow velocity and pressure of the yogurt were measured. The fluctuation frequency of the flow velocity was defined as F [1/s]. The difference between the maximum and minimum flow velocity was defined as Δvmax [L/s]. Grittiness was evaluated using these flow characteristics indexes. The logarithm of (average particle size × concentration) was proportional to the sensory evaluation score. F and Δvmax increased in proportion to the concentration of dispersed particles. There was a correlation between F and the sensory evaluation score. There was also a correlation between Δvmax and the sensory evaluation score. The relationship between the sensory evaluation score and the flow characteristics indexes was examined using all the yogurts. The sensory evaluation score was a linear function of the logarithm of (F × Δvmax). Therefore, it was shown that quantitative evaluation of the grittiness of yogurt was possible using the flow characteristics indexes.