Effect of heat treatment on the nutritive value of proteins: Chemical and balance studies

Abstract

21 h. a t 110" showed losses of dry weight, nitrogen, sulphur and all the amino-acids. The protein value of the heated material as shown by bioassay fell by a greater extent t h a n could be accounted for by losses of lysine, available lysine or the sulphur amino-acids. The limiting amino-acids in both original and heated material were the sulphur amino-acids. Balance stuJies of nitrogen, sulphur and lysine carried out concomitantly showed that the fall in the utilisation of lysine was largely accounted for by a reduction in its digestibility : the falls in utilisation of nitrogen and sulphur were mainly due to a reduced retention of the absorbed elements. The results are discussed in relation to possible types of reaction involved in the heat damage of proteins.

Nutritional effects of food processing

“…The other amino acids showed full retention when analysed after acid hydrolysis but only 35-50y0 were available. Pork heated in water at 110°C for 24 hr and then dried at 100°C for 16 hr showed a fall in net protein utilization from 76 to 41 (Donoso et al, 1962). The net protein utilization was partially restored to a value of 60 by adding methionine.…”

Effect of Heat Treatment on the Digestibility and Utilization of Proteins

“…Some other authors [2,7,12] also observed much smaller changes in protein digestibility coefficients in the case of products containing Maillard proteins than it could be expected from the results of the changes in protein efficiency ratio, NPU or biological values.…”

“…Although the adverse effect of heat treatment on the nutritive value of protein has been frequently demonstrated in animals [2,[7][8][9][10]12], the actual mechanism which produces this reduction is not quite understood. On the one hand, the in vitro studies show that proteins which undergo Maillard reaction are not completely digested by the digestive enzymes [1,4,9,14,16] but, on the other hand, the digestibility coefficients of protein, evaluated with the use of animals, arc not decreasing to the ex tent expected [2,7,12,16].…”

“…On the one hand, the in vitro studies show that proteins which undergo Maillard reaction are not completely digested by the digestive enzymes [1,4,9,14,16] but, on the other hand, the digestibility coefficients of protein, evaluated with the use of animals, arc not decreasing to the ex tent expected [2,7,12,16]. Changes of the protein digestibility coefficients are much smaller than the relative changes in the protein nutritive values as evaluated by means of growth tests or net protein utilization (NPU) [2,7,12].…”

The effect of processing on the nutritive value of flesh foods

“…Heat processing is known to be responsible for reductions in protein value as a result of the destruction or unavailability of the constituent amino acids. Broadly speaking, three types of reaction are responsible for the nutritional changes which occur (Donoso, Lewis, Miller & Payne, 1962):…”