Energy conservation during the milling process of main carbohydrates used during dry pet food processing

When purchasing raw materials, we are often focusing only on the final price and nutritional performance. It is our goal to get the minimal price for maximal nutritional uptake. Often, it is forgotten to evaluate possible performance during the processing.  One of such forgotten spots is milling efficiency, Harder and fattier raw material is harder, and thus less efficiently ground, Energy consumption during the grinding increases with the hardness of materials (Healy et al. 1994). Improperly ground raw materials will results in nonhomogeneous particle size distribution and thus effect kibble appearance and final kibble quality (dust increase) (Thomas, 1996).

Evaluation of hardness and elasticity of the raw materials is done by texture analyses, a simple method to capture differences.  For this purpose, it was evaluated four standard carbohydrate sources used in wheat-free diets/ non-grain diets (with an exception of maize, which is in use in many pet foods due to its higher digestibility values). Hardness is a measure of the compression weight while elasticity shows distance probe travels before the material is crushed. Less distance shows quicker and more effective crushing of raw materials.

The test showed that the whole peas need the highest energy to be broken, followed by corn and tapioca pellets. Pea starch flour pellets were softer compared with other materials tested (Fig.1). In addition, pea starch pellets expressed less variation during the testing.

Hardness Pea starch

Figure 1. Interval plot for the Hardness expressed in Kg, where 95% of the area of a normal distribution is within standard deviations of the mean.

Table 1. Analyses of the samples, total sample repetitions N. 15. Table shows mean value, standard error of the mean, standard deviation, and median values.

Ingredient Hardness, Kg
Mean SE Mean St.Dev. Median
Corn, cracked 27.3 3.98 12.6 24.7
Pea starch flour, pellet 11.7 2.02 6.7 11.1
Pea, whole 37.9 3.48 11 39.8
Tapioca pellets 27.3 2.44 7.71 29.05

Pea starch flour as expressed lowest deformation length which indicates most efficient crushing (Fig.2).

Such efficient crushing of pea starch is attributed to very fine particle size during the extraction and gentle pelleting process.

Elasticity Pea starch

Figure 2. Interval plot for the elasticity of raw materials expressed in mm, where 95% of the area of a normal distribution is within standard deviations of the mean.


In conclusion, pea starch flour is easy to grind and can act as energy preserver during the milling process. Equally important is also a fact that among all tested raw materials pea starch pellets are significantly different compared to others and with least variations between same sample group.