Feed & Additive Magazine Issue 3 April 2021

ARTICLE FEED & ADDITIVE MAGAZINE April 2021 73 ibility of amino acids in raw soybean flake, proper- ly cooked soybean meal and over-cooked soybean meal in caecectomised roosters (Figure 2). The study demonstrated that ileal digestibility of all amino ac- ids are compromised when soybean meals are either undercooked or overcooked. TRADITIONAL METHODS TO CHECK THE IMPACT OF SOYBEAN MEAL PROCESSING CONDITIONS ON QUALITY Common tests for feed producers to check soybean meal quality include: • Trypsin inhibitor activity (TIA) – the destruction of TIA during D-T operation is highly correlated with the destruction of urease activ- ity and can be used as a method to detect under-processed material. • Urease activity (UA) – the most common method to detect un- der-processed soybean meal, this test involves analysing the pH change due to the presence of urease. If the soy- bean meal is under-processed, there should be more urease enzyme pres- ent and there will be a greater pH rise. It is an indirect method com- monly used in the industry to rough- ly estimate the TIA, as detection of the TIA is difficult and expensive. UA correlates with TIA as both enzymes are similarly deactivated at a range of heat treatment. Typically UA is quot- ed in urease index units (U), and in- dustry expectation is 0.05-0.3U. • KOH solubility – used to detect over-cooked soybean meal by measur- ing nitrogen solubility in 0.2% KOH solution. Raw soybean meal is 100% soluble in 0.2% KOH but the opti- mum quality lies between 78% (over- cooked) and 84% (undercooked). • Protein dispersibility index (PDI) - The amount of soybean meal protein dispersed in water after blending a soybean meal sample in water with a high-speed blender. Optimum quality is PDI value of 40-45%. • Reactive lysine – total and reactive amino acid con- tent and digestibility are reduced during the toasting process. Lysine is a sensitive marker of overprocessing as the free amino group on its sidechain is exposed and reacts readily with sugars and fats if the temperature and moisture allow, making the lysine unusable by the animal. The reactive lysine content is a measure of the Figure 2: Ileal digestibility of soybean meal amino acids (raw flake, cooked and overcooked form) when fed to caecectomised roosters (2) Figure 1: Typical soybean meal production process (1) 0 20 40 60 80 100 120 ThrC ys Val MetI le Leu PheH is LysA rg Trp Ileal digestibility, % Raw flake Cooked Over-cooked