الفهرس 
Introduction
Structure and properties of starchy substancesOnly 14 pages are availabe for public view
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Abstract
Starch degrading enzymes like amylases have received a great deal of attention because of their perceived technological significance and economic benefits.
Amylases hydrolyze starch molecule into glucose, maltose and dextrin. They can be classified into α-amylase (EC 3.2.1.1), β-amylase (EC 3.2.1.2) and glucoamylase (EC 3.2.1.3). They have many applications in bread and baking industry, starch liquefaction and saccharification, textile desizing, paper industry, detergent industry, analysis in medical and clinical chemistry, food and pharmaceutical industries.
Amylase enzymes could be obtained from several sources, such as plants, animals and microorganisms.
Microbial enzymes are preferred for their stability over plant and animal enzymes which increases their spectrum of industrial applications. They also have the advantages of cost effectiveness, consistency, less time and space required for production and ease of process modification and optimization. Evidences of amylase in yeast, bacteria and moulds have been reported and their properties are documented.
Starch hydrolyzing ability is reasonably widely distributed among genera and species of yeasts and that explains why several laboratories have been involved in recent years in the isolation, evaluation and/or the eventual construction of amylolytic yeast strains.
Because most of yeasts from environments are safe (GRAS, generally regarded as safe), interest in amylolytic yeasts has increased in recent years as their potential value for conversion of starchy biomass to single-cell protein and ethanol has been recognized.
Yeast strains are known to produce α -amylase and glucoamylase except a few, which produce only α -amylase or glucoamylase or pullulanase. These enzymes are produced extracellularly.
A fermentable yeast that produces amylase is important to produce ethanol economically from starch without the need for a previous saccharifying process.
This investigation was aimed to study the following topics:-
1- Isolate and identification of a large number of yeast strains from bagasse, Wastes of potato chips manufacturing, bread dough, fermented local products such as kishk and posa and the surfaces of various types of fruits such as apple, grape, plum and fig with special attention given to rotting and decayed fruits obtained from the local market of Assiut city, Assiut, Egypt and screening of these yeast strains isolates for their amylolytic activity.
2- Use of the most potential strains for studying the optimal environmental conditions (incubation temperature, , pH value, inoculum size and incubation period) as well as the nutritional factors (carbon sources and nitrogen sources) that required for the maximum production of Total amylase, α-amylase and Amyloglucosidase activities.
The obtained results could be summarized as the following:-
1- 77 out of 198 yeast isolates proved to have amylolytic activity. Only the four isolates which proved to possess the highest amylolytic activity were subjected to standard tests and classification schemes.
2- Data of the identification program indicated that these isolates represent four strains belonging to four species appertaining to two genera of yeasts. It could be observed that, Candida was the first predominant genus encountering in 75% of the total identified isolates of yeast cultures. Three species of Candida were identified as Candida tropicalisHA147, Candida sakeHA124and Candida membranifaciensHA19. The second identified genues was Cryptococcus and represented by Cryptococcus heimaeyensisHA7.
3- With respect to amylase(s) production, the highest enzymatic activity were obtained using Candida tropicalisHA147, Candida sakeHA124, Candida membranifaciensHA19 and Cryptococcus heimaeyensisHA7. So, these yeast strains were selected to study the environmental and nutritional factors affecting the production of total amylase, α-amylase and amyloglucosidase activities.
4- from studying the environmental and nutritional factors affecting total amylase, α-amylase and amyloglucosidase production by Candida tropicalisHA147, Candida sakeHA124, Candida membranifaciensHA19 and Cryptococcus heimaeyensisHA7, it could be concluded that production of total amylase, α-amylase and amyloglucosidase are affected by several fermentation conditions as follow:
A- The optimum incubation temperature for total amylase, α-amylase and amyloglucosidase production by Candida tropicalisHA147, Candida sakeHA124, Candida membranifaciensHA19 and Cryptococcus heimaeyensisHA7 was 25˚C.
B- The optimum incubation period was 48 hour for Candida tropicalisHA147, Candida sakeHA124 and Candida membranifaciensHA19 while it was 72 hour for Cryptococcus heimaeyensisHA7.
C- The optimum pH that can secure the highest production of these enzymes was 4.5 for Candida tropicalisHA147 and Candida membranifaciensHA19 and pH 6 for Candida sakeHA124 and Cryptococcus heimaeyensisHA7
D- It was found that, the 1% was selected as the best economical inoculum sizes for all tested yeast strains.
E- Various carbon sources namely: starch, maltose sucrose and glucose were tested. Data showed that starch was the best carbon source for total amylase, α-amylase and amyloglucosidase production followed by maltose for all tested yeast strains. Also, it was found that, the maximum enzyme(s) production was attained at 4% concentration of starch for Candida tropicalisHA147, Candida membranifaciensHA19 and Cryptococcus heimaeyensis HA7 while it was 5% incase of Candida sakeHA124.
F- Among the four nitrogen sources tested, yeast extract exhibited the best results for inducing total amylase, α-amylase and Amyloglucosidase production especially at concentration of 1% for Candida sakeHA124, Candida membranifaciensHA19 and Cryptococcus heimaeyensisHA7 and 2% for Candida tropicalisHA147