Effect of pressure and temperature on the availability of lysine in meat and bone meal as determined by slope-ratio assays with growing pigs, rats and chicks and by chemical techniques.

1. The availability of lysine for pigs, rats and chicks was determined using samples of meat and bone meal (MBM) subjected to different pressure and temperature treatments during dry-rendering processing. The relation between slope-ratio estimates and three chemical tests for estimating 'available' lysine was assessed. 2. The availability of lysine (proportion of total) for pigs was 0.97 in the control. Pressure (275 kPa gauge, 141 degrees, for 30 min) in the early stage of rendering reduced availability to 0.74 and, in the late stage, to 0.46. Maintaining the final temperature at 125 degrees for 4 h had little effect (0.84) whereas a higher temperature of 150 degrees for 4 h reduced availability to 0.38. 3. Availability estimates for rats were lower than those of the pig, ranging from 0.88 in the control to 0.21 for the high-temperature treatment (150 degrees for 4 h). The effects for temperature were similar to those for the pig, whereas the effect of pressure was equally detrimental in both the early and late stages (0.45 and 0.43 respectively). 4. For chicks, availability estimates were similar to those for the pig for the control (0.93) and the two temperature treatments (0.86 and 0.31 for the 125 degrees and 150 degrees treatments respectively). The chick was less susceptible to the effect of pressure applied to the MBM (0.78 and 0.63 for the early- and late-stage treatments respectively). 5. Values for the indirect- and direct-1-fluoro-2,4-dinitrobenzene-(FDNB)-'available'-lysine assays decreased from 0.86 and 0.74 to 0.57 and 0.54 for the control and 150 degrees for 4 h treatments respectively, indicating that approximately half the reduced availability involved reactions with the epsilon-amino group of lysine. There was little relation between the FDNB values and lysine availability for the treatments involving changes in pressure. 6. There was little or no relation between dye-binding capacity of the meals, as assessed by the Acid Orange-12 dye-binding procedure (Hurrell et al. 1979), and lysine availability for the three species.