SHORT CHAIN FATTY ACID SCFA

3 II. LITERATURE REVIEW

A. RESISTANT STARCH RS

Resistant starch RS has been defined as t otal amount of starch, and the products of starch degradation that resists digestion in the small intestine of healthy people then enter the large bowel. It occurs for various reasons including chemical structure, cooking of food, chemical modification, and food mastication Topping and Clifton 2001. There are four types of resistant starch. Starch found in plant cell walls that is inaccessible to amylase activity is one type of resistant starch, designated type 1 resistant starch RS1. Food sources of RS1 include partially milled grains and seeds. Resistant starch also may be formed during food processing. Ungelatinized granules of starch are typically resistant to enzymatic digestion and are designated type 2 resistant starch RS2. This type of starch can be found in potatoes and unripe green bananas. Cooking and cooling starchy foods by moist heat or extrude starchy foods, for example, generates retrogade starch called type 3 resistant starch RS3. Chemical modifications of starch, such as formation of starch esters, or cross-bonded starches, also result in resistant starch, called type 4 resistant starch RS4. RS3 and RS4 may be partially fermented by colonic bacteria Gropper, et. al 2009 . Interestingly, if RS2 granules are heated to over 100ºC, the granularity is lost and starch is gelatinized or the granules swell thereby increasing the availability of the starch to amylase. However, when the starch cools, there is some recrystallization of the starch. This is called retrogradation, which is resistant to α–amylase hydrolysis Medeiros and Wildman 2012. Starch that is trapped within whole plant cells or within the food matrix, and some starch granules that have not been fully gelatinized, are hydrolysed only very slowly by a-amylase and therefore may escape complete digestion in the small intestine. The energy yield to the body from this source is less than that provided if starch is digested and absorbed in the small intestine Englyst, et. al 1996. The glycemic effects of starch is therefore lowered, which decreases insulin secretion. In addition to glycemic management resistant starches may play role in weight management as well Medeiros and Wildman 2012. The material included in the definition of RS reaches the human large intestine and thus becomes a substrate for microbial fermentation. The end-products are H 2 and CO 2 , CH 4 in about half the population, and short-chain fatty acids. SCFA consist primarily of butyrate, propionate and acetate Englyst, et. al 1996. SCFA contribute to normal large bowel function and prevent pathology through their actions in the lumen and on the colonic musculature and vasculature, through their metabolism by colonocytes Topping and Clifton 2001.

B. SHORT CHAIN FATTY ACID SCFA

Short chain fatty acids SCFA are end-product of luminal microbial fermentation of predominantly non-digestible dietary carbohydrates. SCFA with different carbon chain lengths acetate C2, propionate C3, butyrate C4, valerate C5, and caproate C6 are produced in 4 varying amounts depending on the diet and the composition of the intestinal microbiota Marleen, et. al 2003. SCFA constitute approximately two-thirds of the colonic anion concentration 70-130 mmoll, mainly as acetate, propionate, and butyrate Mortensen and Clausen 1996. Various population data show that SCFA production is in order of acetate propionate butyrate in a molar ratio of approximately 60:20:20 or 3:1:1, respectively in the proximal and distal colon Cummings, et. al 1987; Topping and Clifton 2001. The major source of this in the human colon is thought to be plant cellwall polysaccharides such as cellulose, pectins, and hemicelluloses, currently referred to in human nutrition as dietary fibre. Starch would also be a suitable substrate if it were to reach the colon in significant quantities. Plant cell-wall polysaccharides are composed of hexose glucose and galactose, pentose xylose and arabinose, and uronic acid monomers which are fermented by gut micro- organisms along a variety of pathways. The important feature to remember of this metabolism is that it is anaerobic. Many lines of evidence therefore support the idea that fermentation occurs in the colon but, because of the difficulties in obtaining access to the human large bowel during normal digestion, most of the evidence for fermentation has, of necessity, been indirect Cummings, et. al 1987. There are several bacterial species which produce butyric acid. Most butyric acid-producing bacteria form acetic acid in addition to butyric acid as their major fermentation products. Clostridium butyricum, C. tyobutyricum, C. thermobutyricum, C. beijerinckii, and C. populeti are of interest for the production of butyrate. There are some benefits using Clostridium butyricum. These bacteria needs simple growth medium, produces high metabolite, and easy to isolate. Therefore, Clostrium butyricum also has butyrogenic activity, produce more butyric acid than acetic acid and propionic acid. C. butyricum had the highest specific growth rates compared with other genera. On the other hand, Clostridium spp. are generally less dominant in the human colon and hence the role of Clostridium in the production of butyrate in humans is unclear Wang 1999. SCFA will be absorbed and contribute about 3 kilocalories per gram Medeiros and Wildman 2012. SCFA are rapidly absorbed and have shown to have distinct bioactivity depending on their chain length. With regard to maintenance of colonic health and barrier function, butyrate has drawn most attention as this fatty acid is the major energy source for the colonocytes Roedriger 1990. Furthermore, butyrate has been shown to have anti-carcinogenic effects mainly by affecting proliferation, differentiation, and gene expression of colonocytes Scheppach, et. al 1995. Butyrate concentration didn‟t show a significant correlation with pH or propionic concentration McIntyre, et. al 1993. The production of propionate is by two main, but circuitous, routes, firstly, involving fixation of CO 2 , to form succinate which is subsecquently decarboxylated the decarboxylic acid pathway or secondlly, from lactate and acrylate the acrylate pathway. Acetate is usually formed by the oxidative decarboxylation of pyruvate and butyrate by reluction of acetoacetate formed from acetate Cummings, et. al 1981. Short chain fatty acids are metabolized at 3 major sites in the body Hijova and Chmelarova 2007: 5 1. Cells of the ceco-colonic epithelium that use butyrate as a major substrate for the maintenance of energy producing path-ways; 2. Liver cells that metabolize residual butyrate with propionate used for gluconeogenesis; 50 to 70 of acetate is also taken up by the liver; 3. Muscle cells that generate energy from the oxidation of residual acetate. In ruminants and other herbivores, SCFA are absorbed and transported via the portal vein to the liver, and the fraction not absorbed is distributed to the other body organs and tissues for metabolism. In herbivores, peripheral venous SCFA concentrations are high due to comparatively low visceral extraction and high rates of absorption into the circulation. However, human peripheral venous blood concentrations are normally low, and only acetate is present in measurable amounts. This profile reflects the lower SCFA production rates and greater visceral extraction in omnivores, meaning that human peripheral venous SCFA are not representative of those in the portal circulation. Human experimentation has been confined largely to fecal measurements, which are also limited as 95 of SCFA are produced and absorbed within the colon Topping and Clifton 2001. Purwani, et. al 2012 study revealed that type 3 resistant starch RS3 derived from sago and rice starch that treated with pullulanase could be well utilized as substrate by Clostridium butyricum and showed good proportion of acetate: propionate: butyrate in the bacterial culture filtrate. The fermentation of resistant starch type 3 RS3 derived from sago starch treated with pullulanase RSSP by C. butyricum produced 17.65 mM of butyrate, and fermentation of RS3 derived from rice starch treated with pullulanase RSRP by C. butyricum produced 21.76 mM, higher concentration than fermentation of RSSP. This study implied that difference of starch source resulted difference of SCFA concentration.

C. APOPTOSIS