Urease Activity and Other Chemical Criteria as Indicators of Inadequate Heating of Soybean Oil Meal

Chemical methods of evaluating protein quality

“…review by Rice & Beuk, 1953). The heat treatment required also inactivates most of the enzyme urease that occurs in raw soya beans (Bird, Boucher, Caskey, Hayward & Hunter, 1947). This inactivation has been widely used as a test for inadequate heating; the test material has only to be digested in the presence of urea, which will be hydrolysed to a varying extent to ammonia and CO,.…”

“…Carpenter et al 1957). But this effect may not apply when the same raw material is treated by different processes such as 'solvent extraction' and 'expeller' processing of oilseeds (Bird et al 1947), or the 'hot-air' and 'steam-jacket' drying of fish meals. Also changes in the raw material may change the colour of the product without necessarily affecting the nutritive value, as, for example, the difference between fish meals made from white fish or from herring.…”

Urease activity in soybean meal products

“…Many test methods for control of toasting have been proposed (4), but the two which have been used most are 1) the modified Caskey-Knapp (2,3), an assay for urease, and 2) the nitrogen-solubility method, a measurement of the water-soluble nitrogen compounds (8), often referred to as the nitrogen-solubility index or NS,I value. The modified Caskey-Knapp (2) is a method which measures a change in the pH, for a given reaction time, of a weakly buffered system of soybean oil meal and urea.…”

Evaluation of heat processing on soy proteins using a pH stat to monitor tryptic hydrolysis

“…The meals that gave the poorest growth response exhibited the highest urease activity. Bird et al (1947) also found that the urease assay was acceptable in detecting inadequately heated meals, in a study comparing urease values with the growth response of chicks.…”

“…Measurement of urease activity in toasted soy meal is the official method used in the soybean processing industry. This method measures a change in pH for a given reaction time of a weakly buffered system of soybean meal and urea (Caskey and Knapp, 1944;Bird et al, 1947). A meal that gives a pH increase of 0.02 to 0.25 at 30°C is usually accepted by soybean processors as properly toasted for good nutrition (Croston et al, 1955).…”