Synthesis and accumulation of amylase-trypsin inhibitors and changes in carbohydrate profile during grain development of bread wheat (Triticum aestivum L.)

Abstract

Background: Recent studies indicate that amylase-trypsin inhibitors (ATIs) and certain carbohydrates referred to as FODMAPs (fermentable oligo-, di-, monosaccharides and polyols) play an important role in promoting wheat sensitivity. Hitherto, no study has investigated the accumulation of ATIs during the development of the wheat caryopsis. We collected caryopses of common wheat cv. 'Arnold' at eight different grain developmental stages to study compositional changes in ATI and FODMAP content.

Results: The harvested caryopses were analysed for their size, protein and carbohydrate concentrations. ATIs were further characterized by MALDI-TOF MS, and their trypsin inhibition was evaluated by an enzymatic assay. The results showed that ATI accumulation started about 1 week after anthesis and subsequently increased steadily until physiological maturity. However, the biological activity of ATIs in terms of enzyme inhibition was not detectable before about 4 weeks after anthesis. Carbohydrate analysis revealed the abundance of short-chain fructans in early stages of grain development, whereas non-water-soluble carbohydrates increased during later developmental stages.

Conclusions: The results provide new insights into the complex metabolisms during grain filling and maturation, with particular emphasis on the ATI content as well as the inhibitory potential towards trypsin. The time lag between ATI accumulation and development of their biological activity is possibly attributed to the assembling of ATIs to dimers and tetramers, which seems to be crucial for their inhibitory potential.

Keywords: ATI metabolism; FODMAPs; Grain development; Trypsin inhibition; Wheat sensitivity.

Fig. 1

Spike and kernel development in bread wheat cv. ‘Arnold’ during grain filling and maturation. The reported values are mean values obtained from the measurement of at least 20 kernels

Fig. 2

Changes of grain characteristics during seed development of bread wheat cv. ‘Arnold’. a Crude protein (green line and circles and 95% confidence interval, n = 3 per developmental stage) and starch content (red line and diamonds, n = 2) displayed as percentage and b mg per kernel, respectively

Fig. 3

MALDI-TOF MS spectra of proteins from developing wheat kernels extracted with chloroform-methanol after SPE purification in the range of 5–70 kDa. a AAI standard (in the range of 7–35 kDa). b PWG gliadin. c-j ‘Arnold’ grains sampled 7, 11, 14, 18, 25, 33, 39, and 46 days after anthesis, respectively

Fig. 4

Relative distribution of the major kernel components (i.e., crude protein content (PROT), small water-soluble carbohydrates (SWSC) and non-water-soluble carbohydrates (NWSC)) during grain development of bread wheat cv. ‘Arnold’