Influence of feeding alikaline/heat processed proteins on growth and protein and mineral status of rats

Abstract

Effects of feeding alkaline (0.1 N NaOH) and heat treated (75°C for 3 h) proteins (lactalbumin and soybean protein isolate, SPI) on growth, and protein and mineral status of rats have been determined. The untreated and alkaline/heat treated lactalbumin contained 0.10 and 4.42 g lysinoalanine (LAL)/100 g protein, respectively. Similarly, the untreated and treated SPI contained 0.03 and 1.94 g LAL/100 g protein, respectively. The formation of LAL in the treated proteins was accompanied with a loss of cystine (73-77%), threonine (35-45%), serine (18-30%) and lysine (19-20%). The alkaline/heat treatments caused significant (P < 0.05) reductions in protein digestibility of lactalbumin (99 vs. 73%) and SPI (96 vs. 68%). The processing treatments also caused a drastic negative effect on protein quality, as measured by rat growth methods such as relative protein efficiency ratio (RPER) and relative net protein ratio (RNPR). The RPER and RNPR values of untreated lactalbumin and SPI were 89-91 and 56-64%, respectively. But the RPER and RNPR values of the treated lactalbumin and SPI were 0%. The mineral status of rats was also compromised by feeding alkaline/heat treated proteins. Liver iron levels in male rats (165-180 μg/g dry weight) and female rats (306-321 μg/g dry weight) fed the treated proteins were about half the levels in male rats (229-257 μg/g dry weight) and female rats (578-697 μg/g dry weight) fed the untreated proteins. The kidney iron contents of rats fed the treated proteins were also lower than that of rats fed the untreated proteins. Liver copper levels of male and female rats fed the treated proteins were up to three fold higher than those found in rats fed the untreated proteins. The data suggested that LAL, an unnatural amino acid derivative formed during processing of foods, may produce adverse effects on growth, protein digestibility, protein quality and mineral bioavailability and utilization. The antinutritional effects of LAL may be more pronounced in sole-source foods such as infant formulas and formulated liquid diets which have been reported to contain significant amounts (up to 2400 ppm of LAL in the protein) of LAL.