Abstract

Sweet sorghum (Sorghum bicolor L), which later can be divided into grain sorghum and sweet stalk sorghum are highly water efficient crop that requires low amount of water intake for its biomass growth and grain production. Stalk of sweet sorghum produce juice that has high sugar content, which can be used as a main source of ethanol production, whereas grain of sorghum can also be used  as raw materials for food, feed and functional  food.  The quality feature of sorghum that suitable to be use for bioethanol production is determined by its high sugar content in stalk or the amount of carbohydrate in grain. Whereas the protein content in grain and lignocellulosic in the stalk is an added value. Among many parts of sorghum plant, the stalk gives highest contribution to produce juice as raw material for bioethanol. Ethanol production was determined by the production of biomass and sugar content of the stalk. Stalk biomass; brix level in stalk juice had high correlation to sweet sorghum ethanol production.The primary sugars present  in  grain  of  sweet sorghum  are  fructose,  glucose,  raffinose,  sucrose  and  maltose. In  sorghum leaves,  sucrose  is translocated  and  transformed  into starch  during  the  development  of  grains. Grain plus stem of sweet sorghum has been shown to yield more fermentable carbohydrates than other fuel crops. In addition, the grain can  be  used  for  production  of high  fructose  syrup  and  animal feed. Therefore, sorghum is an excellent crop for biomass production. The high nonstructural carbohydrate content of its vegetative biomass can be fermented to methane or ethanol. Sugar production of sweet sorghum was compared with sugarcane  and sugar  beet  and  the  results  showed  that  sugar  production  from  sweet  sorghum  is  cheaper  than  both sugarcane  and  sugar  beet. The  emerging  enzymatic  hydrolysis  technology  has  not  been proven  on  a  commercial  scale.  One  ton of  corn  grain  produces  387  L  of  182 proof  alcohol  while  the  same  amount  of  sorghum  grain produces  372  L. Sorghum is  used  extensively  for  alcohol  production (,  where  it  is  significantly  lower in  price  than  corn  or  wheat.  The commercial  technology required  to  ferment  sweet  sorghum  biomass into alcohol  has  been  reported  in  China.  One  ton  of  sweet  sorghum  stalks  has  the potential  to  yield 74L of 200- proof  alcohol .Since  Iran  has  dry  and  hot  climatic  conditions therefore  sweet  sorghum  has emerged  as  a  leading  candidate  for  liquid  sugar and  biofuel  production with  minimum  inputs .Sweet sorghum can accumulate juice up to 78% of the total biomass, whereas the Brix content of sweet sorghum has been estimated to range from 14 to 23%.  The sugars in sweet sorghum stalks mainly comprise sucrose (~75%) with some amount (~2.6%) of fructose and glucose. Ethanol produced from sweet sorghum is safer for environment due to low sulfur content, low biological and chemical oxygen demand and high octane rating. During concentration of juice to syrup, the foam and froth produced can be processed and used to feed livestock or as an organic fertilizer. After juice extraction, the fibrous leftover material, known as bagasse, serves as a raw material for handmade paper, electricity generation, and bio-composting. Sweet sorghum is being widely considered to be suitable biofuel feedstock to a tropical country like India as sugarcane is grown primarily for sugar while corn is used in food and poultry industry. No significant changes in pH value, sugar contents, and sugar profiles were observed in juices stored in a refrigerator. The whole sweet sorghum plant used as feed stock for bioethanol production and concluded that both juice extracted from the stem and residual bagasse can be used for fermentation to ethanol. There was a significant difference in the sugar content of the samples extracted in different ways; samples extracted without the leaves showed approximately 20% higher sugar content. This crop has also been included in the list of the best sources of liquid biofuels in terms of the development of renewable energy in China. A large amount of biomass by-products are left after the use of sweet sorghum stalks for juice can be utilized in a number of possible ways: biogas production, soil fertilizers or production of pellets and briquettes for burning. Additionally, both sorghum bagasse and molasses can be potentially used for biobutanol production

Keywords

Sorghum bicolor L,  ethanol, Economical Benefits