Effects of Increase in .ALPHA.-Amylase and Endo-Protease Activities during Germination on the Breadmaking Quality of Wheat.

Abstract

The effects of increase in ␣-amylase and endo-protease activities during germination on the deterioration of the breadmaking quality of hard wheat were examined using three varieties with different strengths of gluten: VictoriaINTA, Harunoakebono, and Leader. The results are summarized as follows: (1) The degradation of the breadmaking quality of flour damaged in germination differed greatly according to the gluten strength of each variety. VictoriaINTA, which has extra-strong gluten, was more tolerant of the germination damage than the other varieties with strong gluten. (2) The degradation of specific loaf volume, which is caused by lowering the gas retention of the dough, was the result of the softening of the dough that was observed as a decrease in the mixing peak time and the breaking force of the dough. (3) The ␣-amylase and endo-protease activities of flours did not seemed to influence the breadmaking quality, although there was a considerably high correlation between endo-protease activity of whole wheat flour and breadmaking quality. From these results, it would seem that the main reason that flour damaged during germination degrades breadmaking quality is the endo-protease in the wheat grain, which already causes partial gluten decomposition. Accordingly, it might be better to examine the endo-protease activity of whole wheat flour at harvest ripeness in order to estimate the value of breadmaking quality within the hard-wheat breeding system. Keywords: extra-strong variety, breadmaking quality, endo-protease activity, ␣-amylase activity Most Japanese hard wheat used for bread is grown in Hokkaido; however, pre-harvest sprouting often occurs as grain develops due to unfavorable weather. This problem is serious because wheat flour that is damaged during germination has a maximum viscosity (MV) of Amylograph that is below 300 B.U. and is unsuitable for industrial processing. Many studies on germination damage in wheat deal with starch degradation, i.e., MV of Amylograph, Falling number, ␣-amylase activity and the quality of bread (MacGregor & Matsuo, 1972; Meredith & Pomernz, 1985;MacGregor & Dushnicky, 1989). However, the deterioration of breadmaking quality in flour that has been damaged during sprouting cannot always be explained by low MV values (Yamauchi et al., 1998;Sato et al., 1999). Therefore, another practical index to estimate the value of breadmaking quality is required within the hard-wheat breeding system. On the other hand, there is some evidence that the degradation of storage protein also greatly contributes to the loss of breadmaking quality during germination. (Kruger, 1971;Bushuk & Lukow, 1987;Lukow & Bushuk, 1984;Janssen et al., 1996b;Weegels et al.,1996). Studies show that an increase in ␣-amylase and endoprotease activities in wheat may lead to degradation of endosperm starch and protein during germination and may have a deleterious effect on the quality of bread (Kiribuchi & Nakamura, 1973; Preston & Kruger, 1979;Meredith & Pomeranz, 1985;Salomonsson et al., 1989; Sun & Henson,19...

The Pasting Properties of Flour and Starch in Wheat Grain Damaged by .ALPHA.-Amylase

“…2. ␣-Amylase activity of flour was low (32-69 mU/g) until 12 h and began to increase sharply after that, reaching as high as 4512 mU/g after 48 h. According to the report of Ichinose et al (2001), higher ␣-amylase activity (536-3821 mU/g) was observed in the flours from wheat grain of three cultivars preserved for 24 h at 20˚C after soaking in water for 24 h at 5˚C. From the results of flour pasting properties, there was little change in peak viscosity (214-231 RVU) and breakdown (102-110 RVU) up to 12 h. Distinct decreases in peak viscosity and breakdown were observed between 12 and 48 h. Thus, there was a correspondence of decreases in peak viscosity and breakdown with an increase in ␣-amylase activity.…”

“…Seeds were stored at 4˚C and used within 2 months. A wetting treatment was performed by the method of Ichinose et al (2001). Distilled water was poured on the wheat seeds.…”

Dough and Breadmaking Properties of Various Strong Wheat Grains Cultivated in Japan

“…18) The low resistance value of Haruyutaka as shown in Tables 3 indicates the increasing activity of endo protease rather than amylase during the pre harvest sprouting damage as mentioned above, 3) since the viscosity was not distinctly lowered (Table 4). Thus, the close protein content (9.7%) of Haruyutaka to the soft type wheat flour suggested the inferior and weak protein qualities, which were partially decomposed or damaged by the endo protease, followed by the poor baking properties as compared with other samples tested.…”

“…2) Sprouting has been reported to bring about partial gluten decomposition through the increased activity of endo protease, leading to the softening of gluten and inferior breadmaking quality. 3) In breadmaking, the functional properties of starch have considerable effects on the quality of wheat based food products. The different amylose to amylopectin ratio in wheat starch influences the texture, stability and elasticity of dough and bread.…”

“…However, growing environments and pre harvest sprouting damage also significantly affect the quality of wheat flours. 3,11,12) Therefore, the quality of wheat flours is usually evaluated by suitability for a particular end use product. The objective of this study is to evaluate dough properties and baking qualities of various new kinds of strong wheat grains grown in some parts of Japan to provide useful information for milling and breadmaking factories about the quality of these new domestic wheat cultivars.…”