Protein oxidation of soy protein isolate (SPI) is induced by heating, and oxidised protein may negatively affect the immune function of broilers.

That is the conclusion reached by D.W. Wu and colleagues at Nanjing Agricultural University after a study looking at the effects of heat treatment of SPI on the growth performance and immune function of broiler chickens.

In their paper in Poultry Science, they explain that the SPI was heated in an oven at 100°C for one, four or eight hours and resultant oxidative status was evaluated.

A total of 320 one-day-old Arbor Acres chickens were randomly divided into four treatment groups with eight replicates of 10 birds, and fed diets supplemented with the unheated SPI or one of the three heat-treated SPI for 21 days.

The results showed that heat exposure of SPI for four and eight hours caused an increase in protein carbonyl, and a simultaneous decrease in sulfhydryl and free amine groups compared with unheated SPI.

The bodyweight of broilers fed diets supplemented with SPI heated for eight hours were significantly lower than that of broilers fed diets supplemented with unheated SPI.

Compared with unheated SPI, heat-treated SPI (heated for eight hours) reduced liver weight at 14 days of age, spleen and bursa weights at 21 days of age.

The content of IgG in serum and duodenal mucosa of broilers (at 14 days) was decreased when diets supplemented with heat-treated SPI (heated for eight hours).

No significant differences were observed in the mucosa secretory IgA contents of broilers among the treatment groups.

Compared with unheated SPI, a significant increases were observed in the content of adrenocorticotropic hormone and cortisol in serum of broilers fed the heat-treated SPI (heated for eight hours) at 21 days.

The myeloperoxidase activities in serum (at 14 days) and mucosa of broilers were increased when diets supplemented with heat-treated SPI (heated for eight hours).

Reference

Wu D.W., X. Chen, X. Yang, Z.X. Leng, P.S. Yan and Y.M. Zhou. 2014. Effects of heat treatment of soy protein isolate on the growth performance and immune function of broiler chickens. Poultry Science. 93(2):326-334. doi: 10.3382/ps.2013-03507