Clostridium butyricum Short chain fatty acid (SCFA) profile produced by Clostridium butyricum grown on medium containing type 3 resistant starch (RS3) of sweet potato

5 Some benefits of resistant starch are the slow hydrolysis of RS makes it useful for the slow release of glucose, which can be especially useful in controlling glycaemic plasma responses, increase faecal bulk, lower faecal pH, and increase excretion of butyrate and acetate Philip et al. 1995. Besides physiological benefits in human, RS has been reported to have potential as a unique ingredient that can yield high-quality foods. For example, application tests of RS showed improvement of crispiness and expansion in certain products and better mouthfeel, colour and flavour as compared with products produced with traditional, insoluble fibres. The process of making resistant starch is consisted of gelatinizing a slurry of the starch, treating the gelatinized starch with a debranching enzyme, deactivating the enzyme, cooling and isolating the starch product Schmiedel et al., 2003. Gelatinization process is purposed to make debranching enzyme easier to hydrolize α-1,6 glicosidic bond. Cooling process will stimulate retrogradation which form crystalline structures. The crystalline structure of granules may cause starch to be resistant to enzyme hydrolysis. Starch product can be isolated by hot air dyring, freeze drying, and spray drying. Pullulanase pullulan 6-glucanohydrolase, EC 3.2.1.41, an important debranching enzyme in starch processing, can cleave α-1,6 linkages in pullulan, amylopectin and other related polysaccharides Lin et al. 2006. Debranching of amylopectin will provide an increased opportunity to molecule alignment or aggregation, to form crystalline structures, and is, hence, helpful in RS formation. The pullulanase enzyme preferably reacts with a pH from 4.5 to 5.5 at temperature of 40°C to 60°C. Berry 1986 reported a substantially increased RS3 content during monitoring the debranching effect of pullulanase on potato amylopectin, and attributed this effect to an increase in linear starch chains resulting from debranching.

C. Clostridium butyricum

The bacterial population of the human cecum and colon is numerically large with at least 1.0 x 10 3 cfug, which, with an estimated mass of 250–750 g of digesta, gives a calculated total of 1.0 x 10 3 cfu in the whole hindgut Hill, 1995. More than 50 genera and over 400 species of bacteria have been identified in human faeces. Colonic microflora predominantly comprises facultative anaerobes e.g. Enterobacteria, Streptococci, Staphylococci, Lactobacilli, Propionibacteria and Bacilli in the upper part of the colon but lower down these change to strict anaerobes e.g. Bacteroides, Bifidobacterium, Eubacterium, Peptococci, Fusobacterium and Clostridium Roberfroid, 2001. One of colon bacteria is Clostridium butyricum which has characteristics such as spore former, positive gram bacteria, obligate anaerob and lives in human or animal colon and soil. It has rod shaped with the dimension of 0.5-1.7 x 2.4-7.6µm Mitsuoka, 1990. Clostridium butyricum plays important role in supporting other beneficial bacteria in gastrointestinal like Bacillus bifidus, Acidophilous bacterium, and Streptococcus faecium. There are some benefits using Clostridium butyricum in the fermentation, these bacteria needs simple growth medium, produces high metabolite, and easy to isolate. Beside that, Clostrium butyricum also has butyrogenic activity, it means these bacteria produce more butyric acid than acetic acid and propionic acid. Bacteria from genus Clostridium and Bifidobacterium can ferment high amylose starch, but bacteria from genus Clostridium has higher activity in fermentation Wang, 1999. Several factors which influence bacteria growth are temperature, oxygen, nutrition, and pH. In general, the medium pH not only affects cell growth and fermentation rate, but also changes final product yield and purity. Changing the medium pH also may induce a metabolic shift Zhu, 2004. Several studies were performed to determine the optimal cultivation conditions for the butyric acid production by Clostridium butyricum: temperature 35-37 o C, pH 4.5-7 and atmosphere of pure CO 2 or 6 pure N 2 or N 2 and CO 2 in ratio of 1 : 9; temperature 37 o C, pH 6-7.5, medium flushed with oxygen-free nitrogen gas Zigova Sturdik 2000.

D. SWEET POTATO