Amylase is the general name of a kind of enzymes that can hydrolyze starch. According to the different hydrolysis methods of starch, amylase can be divided into four types: endo-type, exo-type, debranching and transfer. Among the amylases, a- amylase has the characteristics of rich sources and diverse catalytic characteristics, and has extremely important applications in the industrial process of starch processing.
the sources of a-amylase are extremely rich, including animals, plants and microorganisms. Among them, microorganism-derived a- amylase can meet the needs of various industrial applications and plays an extremely important role in industry. In the process of starch treatment in modern industry, the hydrolysis method of microbial a- amylase has completely replaced the traditional chemical hydrolysis method.
There are many kinds of fungal a- amylases. At present, almost all fungal a- amylases used in industry are from Aspergillus microorganisms in filamentous fungi, such as Aspergillus oryzae, etc. Most fungal a- amylases have mild action temperature and pH, such as the optimal action pH is between 5. and 5.5, the optimal action temperature is between 5 and 55℃, and when the temperature exceeds 6℃.
Noguchi A et al. (28) in Japan first reported that the cDNA sequence of a-amylase homologue TRa2 was cloned from a strain of T.viride JCM22452, and its amino acid sequence was highly homologous to other ascomycetes' a- amylases, and catechin glycosides (EGCG) could also be produced. TRa2 produced by this Trichoderma strain can saccharify natural flavonoids such as catechin and hydrolyze maltooligosaccharide into maltotriose and maltotetraose.
Mohamed et al. (211) studied the purification method and enzymatic properties of a- amylase A3 produced by T.harzianum fermentation with kumquat peel as culture medium. Through gel filtration and SDS-PAGE electrophoresis analysis, it was found that the purified enzyme was 7kDa, and the enzyme activity was the largest for potato soluble starch at pH 4.5 and 4℃, and it could keep stable at 4℃ for 3min. However, at 5℃ and 6℃, only 7% and 5% of the enzyme activity can be maintained. Ca2+ can significantly improve the enzyme activity, while other metal ions and metal chelating agents, EDTA, sodium citrate and sodium oxalate can inhibit the enzyme activity.
Khan et al. (212) found that T.viride can produce a large amount of a- amylase. When cultured at 3℃ for 12 d in a medium with 3% bran and 1% glucose as carbon source, the yield of a- amylase reached the best, reaching 6 u/ml. If 1% starch is used as carbon source, under the same culture conditions, it shows that the amount of a- amylase produced by this Trichoderma strain is very low, and the maximum amount occurs on the fourth day, and the yield is only 1.36U/mL.
Denniso American Company applied for the invention patent "Trichoderma reesei a- amylase enhances saccharification of corn starch" in the United States and China respectively (China patent number: zl2888186.8；; U.S. PatentNo.: 212129226) shows that raw maltose a- amylase (TrAA) from T.reesei can be used alone or combined with pullulanase in maltose production process, and TrAA can catalyze maltose production at low pH and high temperature. In the process of producing high glucose syrup from liquefied starch, TrAA can effectively inhibit glucose from being converted into maltooligosaccharide, so that the grape concentration in the processed corn starch mixture reaches about 96%(w/v).