Vitamins and other heat liable ingredients are a topic which is rarely covered. Your product has minimums and usually a test is made to verify the level of each vitamin post-process in relation to the included level pre-process. The difference is the loss if any. Adjustments made to get into range. Note this test would be under the conditions used in the process, vary anything and the results can change. So, tests should be as close to real production settings as possible. There is some published data on expected losses at temperatures which can assist in getting in the ball park.
What can vary the results? Basically, the process conditions and since we are discussing heat liable ingredients this will be the main factor. Extrusion is by heat mainly generated by friction which can be decreased by increasing moisture or oil levels during the process for example. Reduce and the friction goes way up and when factoring in possible screw speed and design changes friction can be high. Steam injection or thermal heat also would be a big effect on vitamin retention but with atmospheric conditioners about 100oC is max and typically when making petfood the extruder reaches in the 125oC area.
Reviewing a few as examples of loss at temperatures, riboflavin 98% retained at 93oC, 93% at 123oC and 91% at 143oC. Vitamin A cross-linked 90% retained at 93oC, 75% at 123oC and 62% at 143oC. This shows what is typically expected, a gradual decrease as temperature increases. All systems vary and thus testing to verify is in order. It should be noted that again running conditions can change results. Testing years ago charted running conditions, feeding results and costs of wear and utilities to see if a sweet spot to make products at that time existed. Turned out to be between about 22 to 32 percent moisture during extrusion gave the best results. Too low moisture was too much frictional heat while too high of moisture retarded cook thus decreased the feeding results. The wear and operational costs were reduced from low moisture extrusion when operating in the mid to upper twenties moisture levels. The dryer is another area of concern as it heats the kibble over a time period and temperature is the factor of concern. Again, depends on the dryer design. The ability to control airflow and temperature along the length of the dyer and relating this to the moisture in the product at any given time creates some special drying effects. When the kibble just enters the dryer, it is high in moisture and higher air or dryer temperature removes the free water or surface water easily. This free water in or near the surface on the kibble has the same cooling effect as sweat on your forehead, a cooling effect. The kibble is not overheated and as it progresses through the dryer the temperatures are decreased to avoid over heating the kibbles if this is desired. It should be noted normally these dryer designs are a bit larger for this effect. Typically, the designed goal was to keep the product at under 80oC through the dryer. Seems to be a magical number for acceptable survival of probiotics, prebiotics, vitamins, carotenoids and other heat liable products.
Published in the May 2024 issue of International Pet Food.
