Changes in fat during pet food machine extrusion
Extrusion will partially hydrolyze triglyceride, producing monoglycerides and free fatty acids. Therefore, from the simple treatment, the extrusion process will reduce the stability of the oil, but for the whole product, the extruded products are in the process of storage.
The increase in free fatty acid content is significantly lower than that of unsqueezed samples, which is mainly due to the inactivation of factors that promote fat hydrolysis, such as lipohydrolase and lipoxygenase in the feed. The fat and its hydrolyzate can form a complex with the gelatinized starch during extrusion, so that the fat cannot be extracted by petroleum ether. The formation of such a complex makes it difficult for the fat to exude from the product to give the product a good appearance.
This pet food machine complex dissociates in the acidic digestive tract and therefore does not affect the digestibility of fat. Fat has a greater effect on the texture, shape and palatability of the feed, but the overall presence of fat not only affects the quality of the final extruded product (mainly the degree of expansion), but may even affect the smooth progress of the entire extrusion process. For example, for the extrusion of defatted soybean powder, the fat content should not exceed 1%; in the production of bulk material in the feed industry, when the amount of grease added to the single-screw extruder is 0-12%, there is no effect on the extrusion effect. When the addition amount is 12-17%, the weight of the product increases by 16g/l for every 1% increase, and the effect is even worse when the addition amount continues to increase. When the amount exceeds 22%, the product loses the general extrusion characteristics. .
Therefore, the pet food machine extrusion should be based on raw materials with low oil content.