Dry heat popping of amaranth seed might damage some of its essential amino acids

Abstract

Amaranth was a major crop among the Aztecs. In Mexico the seed is popped and eaten with brown sugar. The crude protein content of the seed is 14 +/- 2% but its contents of lysine and tryptophan are 6.2 and 1.6 g/16 g N respectively. We developed a popping method based on a fluid bed system (FBS) whereas the traditional method (TM) is just to pop the seeds manually in a hot plate. Assays carried out were evaluation of racemization of the amaranth protein due to heat treatment, amino acid composition of the raw and heat treated seeds and a biological experiment testing whether leucine was the most limiting amino acid of amaranth protein. Male rats were fed both popped amaranths and roasted amaranth. Parboiled amaranth and casein were controls. The results were: (a) Lys, Arg and Cys were damaged in the heat treated seeds; (b) Asp, Met, Glu, Ala and Phe were racemized in that decreasing order in the seeds popped and roasted by the TM; (c) the estimated net protein retention (NPR) and estimated net protein utilization (NPU) of popped amaranths by either method were not different, but were lower than for the parboiled amaranth. The parboiled amaranth was not different from casein; (d) Leu was not the most limiting amino acid in any of the amaranth seeds tested. After Lys, sulfur amino acids appear to be the next most limiting in severely heat treated amaranth. The FBS seems to be a promising method for popping amaranth at industrial level.

Amino acid contents and biological value of protein in various amaranth species

“…Pant (1985) stated the decrease of lysine level by 36% (from 4.83 to 3.08 g/16 g N) in traditionally popped grain while in commercially popped grain the lysine level decreased by 25%. Tovar et al (1989) found the decrease of lysine, arginine and cystine levels while using both the methods of popping.…”

“…High chemical scores were demonstrated in Cys, Asp, Thr, Glu, Pro, Gly, His, Lys and Arg; lower scores (Tovar et al, 1989;Bressani et al, 1992;Dodok et al, 1997;Jarošová et al, 1997;Gorinstein et al, 2002 Biological values of protein in untreated and heattreated amaranth grain are summarized in Table 5. High values of chemical scores were found in Lys, Thr, His and Arg.…”

“…Heat processing can cause damage of essential amino acids resulting in decreased contents or transfer into a racemic mixture (Bressani et al, 1987b;Tovar et al, 1989). Temperatures above 100°C induce reactions in both bind and free amino acids, and especially in essential amino acids valine, leucine, isoleucine, lysine, threonine, methionine, phenylalanine and tryptophan, which then become non-utilizable for humans, thus decreasing the biological value of foodstuffs (Velíšek, 1999).…”

“…for maize, which is rich in leucine but poor in lysine and tryptophan (Vetter, 1994). Amaranth grain contained (g/16 g N) 7.00 lysine, 4.26 methionine + cystine, 5.56 valine, 7.48 leucine, 4.85 isoleucine, and 13.05 arginine (Tovar et al, 1989). According to Bressani et al (1987a) Gorinstein et al (2002).…”

“…At popping, trypsin inhibitors and other antinutritional substances are denatured (Correa et al, 1986;Imeri, 1987;Stratil, 1993). The conventional way of popping is done on hot plates at a temperature higher than 190°C (Tovar et al, 1989).…”