Effects of pericarp alpha‐amylase activity on wheat (Triticum aestivum) Hagberg falling number

Abstract

Pericarp alpha-amylase activity in wheat has largely been ignored as a potential cause of low Hagberg falling number (HFN) in the UK, because pericarp alpha-amylase enzymes have been thought too temperature-sensitive to affect HFN and are usually degraded by harvest. Nevertheless, there are several circumstances where immature grains may be present in harvested grain. Therefore, we tested the hypotheses that pericarp alpha-amylase enzymes in immature grains could lower HFN, but also that inactivation of the enzymes during drying and storage could ameliorate the effect. The first hypothesis was tested by addition of large amounts of pericarp alpha-amylase activity from freeze-dried, defrosted or fresh green grains to high HFN flours of low alpha-amylase activity, followed by HFN measurement. Enzyme assay and HFN analysis assessed the effect of drying on pericarp alpha-amylase activity after different storage treatments. Addition of pericarp alpha-amylase, from all three sources, to high HFN flours caused an exponential decrease in HFN. A drop in HFN from over 470 s to below 250 s resulted from addition of 5-10% by weight of green grains. Between 35-70% of the a-AMY-2 activity in immature grains was eliminated by air-drying at 20ºC over 8-10 days, although the residual activity could still lower HFN. Thus, pericarp alpha-amylase activity may be a cause of low HFN in some UK wheat crops.

Significance of kernel moisture content in determination of Hagberg Falling Number in wheat

“…(Olered & Jönsson, 1970). Lunn et al (2001) confirmed that the presence of pericarp isozymes has an effect on the HFN of wheat but more alpha-AMY-2 activity is required to reduce HFN compared with the alpha-AMY-1 activity due to the different adsorbent properties of alpha-AMY-1 and alpha-AMY-2.…”

“…During germination or sprouting alpha-AMY-1 isozyme [also referred to as 'malt', high pI, Group 1 and GIII (Marchylo et al, 1980)] and alpha-AMY-2 to a lesser extent, are produced (Sargeant, 1980;Mrva & Mares, 2001b). The alpha-AMY-2 isozyme [also referred to as 'green', low pI, Group 2, GI and GII (Marchylo et al, 1980;Lunn et al, 2001)] is expressed in high concentrations in the pericarp of immature, green grains (Gale, 1989). The alpha-AMY-3 isozyme is also transiently expressed (Daussant & Renard, 1987).…”

“…This differs from the pat-tern of enzyme production during germination or sprouting where initial enzyme synthesis is concentrated at the embryo end of the grains (Mares et al, 1994;Mrva & Mares, 1996a). LMA appears to be limited to specific genotypes under certain environmental conditions, is completely independent of pre-harvest sprouting and can be expressed in sprouting tolerant and dormant genotypes (Lunn et al, 2001). Genotype (Gale et al, 1983) and temperature shocks (Mrva & Mares, 1996b) have been listed as some of the factors that induce the phenomenon.…”

“…The negative perception surrounding HFN was enhanced when numerous reports of low HFN wheat, without visual sprouting were received in the following seasons throughout the summer rainfall wheat producing areas of South Africa. Due to the association between sprouted wheat and HFN (Hagberg, 1960;Lunn et al, 2001), producers try to minimize the risk of low HFN by harvesting their wheat at a relatively high kernel moisture content to avoid possible preharvest sprouting. Within the current South African wheat quality evaluation system, producers are allowed to deliver wheat with kernel moisture content (KMC) ranging between 16-18%, depending on infrastructure, silo and company policy.…”

“…Late maturity alpha-amylase (LMA), also known as prematurity amylase (Lunn et al, 2001), refers to the synthesis of high pI alpha-amylase isozymes throughout the entire aleurone layer and its deposition in the endosperm cavity of the grain (Mrva & Mares, 1996a). This differs from the pat-tern of enzyme production during germination or sprouting where initial enzyme synthesis is concentrated at the embryo end of the grains (Mares et al, 1994;Mrva & Mares, 1996a).…”