The maturity of sweet sorghum is subdivided into many stages. The sugar accumulation in the sweet sorghum stalk juice differs in each stage so it is difficult to know the optimum harvesting time. Many studies have already reported that sugar accumulation in the sweet sorghum stalk juice starts from booting stage. The sugar content in the sweet sorghum stalk increases between the milk stages and dough stages. It then starts to decline during the physiological maturity. Since no study has made a conclusion on the exact harvesting time of sweet sorghum stalk where the sugar content is at the maximum, thus, the main core of this study is to determine the optimum harvesting time between the milk stage and physiological maturity where the sugar content of the sweet sorghum stalk is at the highest.
As the sweet sorghum approaches maturity, the stem juice composition and the quality of the stalk changes (Prasad et al, 2007, p.2418). As the sweet sorghum becomes mature, the sugar content of the stem juice increases and the stalk becomes bigger (Prasad et al, 2007, p. 2418). High amount of sugar can be found in its stem or stalk (Food and Agriculture Association, 2010 Prasad et al, 2007, p. 2417 Almodares et al, 2007, p. 424 Matei and Nicolescu, n.d., p.167 Woods 200 p.6). Sweet sorghum stems sugar content is mainly 70-80 saccharose and the rest are fructose and glucose (Food and Agriculture Association, 2010).
The sugar in the sweet sorghums stem or stalk can be obtained through the extraction of juice by means of milling (Tsuchihashi and Goto, 2004, p. 442). Sugar is expressed as degree Brix (Brix) and is measured through the use of Brix hydrometer or sugar refractometer (Bitzer and Fox, 2000, p.2).
The different stages of maturity also affect the sugar content of sweet sorghums stem juice. The steps in the stages of maturity of the seed are early-flowering, flowering, late-flowering, early-milk, late-milk, soft-dough, hard-dough, and ripe (Bitzer and Fox, 2000, p.2).
Matei and Nicolescu (n.d., p.170) stated in their study that sugar starts to build up during the early stage of sweet sorghum development. At the beginning of the harvest, the sugar concentration in sweet sorghum s stem juice is approximately 12.5 Brix and as sweet sorghum reaches maturity the sugar concentration increases up to 17 Brix (Prasad et al, 2007, p. 2418).
Almodares et al (2007, p. 424) stated that during flowering, the sugar content is lowest. This mainly because of the presence of high acid invertase enzyme during the flowering stage (Almodares et al, 2007 p.424).
Hills (1990, p.14) reported that sugar concentration in sweet sorghums stalk juice starts to increase during the milk stage to the soft dough stage of the seed and then decreases as the seeds become more mature.
Also, Matei and Nicolescu (n.d., p.170) declared with experimental results that sugar content in sweet sorghum increases during milk maturity stage (14.29 grams100 ml juice) and decreases after the physiological maturity (13.67 grams100 ml. juice). Hunter and Anderson (1997, p.82) cited that sugar content of sweet sorghums stalk juice is almost double between the dough stage and physiological maturity compared to the sugar content between the milk and dough stages.
Muminov (1997, p.353) stated in his study that at the beginning of the milky ripeness period, the monosaccharides and disaccharides in the sweet sorghum stalk juice continue to increase and the ratio of dry matter to sweet sorghum stalk juice stabilizes. The high acidic characteristic of sweet sorghum stalk juice in the flowering stage remains in the milky ripeness period which is presented by Muminov (1997, p.353) as pH 3.2 and titratable acid of 4.7gliter tartaric acid. As the sweet sorghum reaches maturity, the acid declines while the sugar content increases. Beyond the full ripeness of the sorghum, the pH value and titratable acidity of the sweet sorghum stalk juice decreases to pH 5.4 and 2.4 gliter tartaric acid, respectively (Muminov, 1997, p.353).
Bitzer and Fox (2000, p.2) devised a simple method in order to determine the maturity of the sweet sorghum. As per Bitzer and Fox (2000, p.2), as the stalk reaches its full size, the seed heads also reaches its maturity, thus, by merely looking at the seed head, one can determine if the sweet sorghum plant is already matured.
Sweet sorghum stalks can be harvested within ten days after harvesting the grains but the total soluble sugar content expressed as Brix will only be 14 Brix to 20 Brix and the juice content will only be 48 to 50 (International Crops research Institute for the Semi-Arid Tropics, 2010). If the sweet sorghum is mainly cultivated for sugar and sorghum syrup, therefore, the stalk should be harvested without grains or 20 days prior to physiological maturity (International Crops research Institute for the Semi-Arid Tropics, 2010). By harvesting the stalk before physiological maturity, the total soluble sugar content will be 16 Brix to 23 Brix and the juice content will be approximately 55 to 60 International Crops research Institute for the Semi-Arid Tropics, 2010).
Prasad et al (2007, p.2418) and Bitzer and Fox (2000, p.2) suggested that sweet sorghums should be harvested before maturity where the sugar content is approximately in the range of 15.5 Brix to 16.5 Brix Almodares et al (2007, p.424) reported that during physiological maturity and before chilling the sugar content is about 15.97 Brix. The findings of Almodares el al (2007) are in parallel with that of the findings of Prasad et al (2007). During physiological maturity, the high acid invertase enzymes which are present in the flowering stage are being replaced by the natural invertase enzymes that catalyze sugar production (Almodares et al, 2007, p. 424). Harvest time should not exceed the physiological maturity because the starch content of sweet sorghums stem juice increases beyond maturity (Bitzer and Fox, 2000, p.2). The starch content increases during maturity because of the enzymes that are naturally present in sweet sorghum and other plants. These enzymes catalyze the conversion of sugar in the sweet sorghum stalk juice which is mainly composed of monosaccharides and disaccharides like glucose and fructose into a polysaccharide which is starch. Also, crystallization and gelling of sweet sorghum syrup might occur if the stalk will be harvested beyond maturity (Bitzer and Fox, 2000, p.2).
Muminov (1997, p.354) suggested that sweet sorghum stalk should be harvested before the technological ripeness period and should be processed during the technological ripeness period if the sweet sorghum is cultivated for the purpose of obtaining edible concentrated glucose-fructose syrup.
But in a recent study by the Maryland researchers, delaying the harvest time of sweet sorghum by one month beyond the soft-dough stage gives beneficial effects in places with cool climate (Austin, 2010). Delayed harvest time resulted to decrease in biomass and juice volume but an increase in sugar content (Austin, 2010).
The time of harvesting and determination of maturity of sweet sorghum are very crucial in obtaining sweet sorghum with high sugar content. Since ethanol production also depends on sugar content, therefore knowing the right time of harvesting and determining maturity are also beneficial in obtaining high ethanol yield.
Again, the studies being mentioned didnt exactly gave the optimum harvesting time of sweet sorghum stalk therefore, this study is made for the reason of determining the optimum harvesting time of sweet sorghum stalk with the highest sugar content.
As the sweet sorghum approaches maturity, the stem juice composition and the quality of the stalk changes (Prasad et al, 2007, p.2418). As the sweet sorghum becomes mature, the sugar content of the stem juice increases and the stalk becomes bigger (Prasad et al, 2007, p. 2418). High amount of sugar can be found in its stem or stalk (Food and Agriculture Association, 2010 Prasad et al, 2007, p. 2417 Almodares et al, 2007, p. 424 Matei and Nicolescu, n.d., p.167 Woods 200 p.6). Sweet sorghum stems sugar content is mainly 70-80 saccharose and the rest are fructose and glucose (Food and Agriculture Association, 2010).
The sugar in the sweet sorghums stem or stalk can be obtained through the extraction of juice by means of milling (Tsuchihashi and Goto, 2004, p. 442). Sugar is expressed as degree Brix (Brix) and is measured through the use of Brix hydrometer or sugar refractometer (Bitzer and Fox, 2000, p.2).
The different stages of maturity also affect the sugar content of sweet sorghums stem juice. The steps in the stages of maturity of the seed are early-flowering, flowering, late-flowering, early-milk, late-milk, soft-dough, hard-dough, and ripe (Bitzer and Fox, 2000, p.2).
Matei and Nicolescu (n.d., p.170) stated in their study that sugar starts to build up during the early stage of sweet sorghum development. At the beginning of the harvest, the sugar concentration in sweet sorghum s stem juice is approximately 12.5 Brix and as sweet sorghum reaches maturity the sugar concentration increases up to 17 Brix (Prasad et al, 2007, p. 2418).
Almodares et al (2007, p. 424) stated that during flowering, the sugar content is lowest. This mainly because of the presence of high acid invertase enzyme during the flowering stage (Almodares et al, 2007 p.424).
Hills (1990, p.14) reported that sugar concentration in sweet sorghums stalk juice starts to increase during the milk stage to the soft dough stage of the seed and then decreases as the seeds become more mature.
Also, Matei and Nicolescu (n.d., p.170) declared with experimental results that sugar content in sweet sorghum increases during milk maturity stage (14.29 grams100 ml juice) and decreases after the physiological maturity (13.67 grams100 ml. juice). Hunter and Anderson (1997, p.82) cited that sugar content of sweet sorghums stalk juice is almost double between the dough stage and physiological maturity compared to the sugar content between the milk and dough stages.
Muminov (1997, p.353) stated in his study that at the beginning of the milky ripeness period, the monosaccharides and disaccharides in the sweet sorghum stalk juice continue to increase and the ratio of dry matter to sweet sorghum stalk juice stabilizes. The high acidic characteristic of sweet sorghum stalk juice in the flowering stage remains in the milky ripeness period which is presented by Muminov (1997, p.353) as pH 3.2 and titratable acid of 4.7gliter tartaric acid. As the sweet sorghum reaches maturity, the acid declines while the sugar content increases. Beyond the full ripeness of the sorghum, the pH value and titratable acidity of the sweet sorghum stalk juice decreases to pH 5.4 and 2.4 gliter tartaric acid, respectively (Muminov, 1997, p.353).
Bitzer and Fox (2000, p.2) devised a simple method in order to determine the maturity of the sweet sorghum. As per Bitzer and Fox (2000, p.2), as the stalk reaches its full size, the seed heads also reaches its maturity, thus, by merely looking at the seed head, one can determine if the sweet sorghum plant is already matured.
Sweet sorghum stalks can be harvested within ten days after harvesting the grains but the total soluble sugar content expressed as Brix will only be 14 Brix to 20 Brix and the juice content will only be 48 to 50 (International Crops research Institute for the Semi-Arid Tropics, 2010). If the sweet sorghum is mainly cultivated for sugar and sorghum syrup, therefore, the stalk should be harvested without grains or 20 days prior to physiological maturity (International Crops research Institute for the Semi-Arid Tropics, 2010). By harvesting the stalk before physiological maturity, the total soluble sugar content will be 16 Brix to 23 Brix and the juice content will be approximately 55 to 60 International Crops research Institute for the Semi-Arid Tropics, 2010).
Prasad et al (2007, p.2418) and Bitzer and Fox (2000, p.2) suggested that sweet sorghums should be harvested before maturity where the sugar content is approximately in the range of 15.5 Brix to 16.5 Brix Almodares et al (2007, p.424) reported that during physiological maturity and before chilling the sugar content is about 15.97 Brix. The findings of Almodares el al (2007) are in parallel with that of the findings of Prasad et al (2007). During physiological maturity, the high acid invertase enzymes which are present in the flowering stage are being replaced by the natural invertase enzymes that catalyze sugar production (Almodares et al, 2007, p. 424). Harvest time should not exceed the physiological maturity because the starch content of sweet sorghums stem juice increases beyond maturity (Bitzer and Fox, 2000, p.2). The starch content increases during maturity because of the enzymes that are naturally present in sweet sorghum and other plants. These enzymes catalyze the conversion of sugar in the sweet sorghum stalk juice which is mainly composed of monosaccharides and disaccharides like glucose and fructose into a polysaccharide which is starch. Also, crystallization and gelling of sweet sorghum syrup might occur if the stalk will be harvested beyond maturity (Bitzer and Fox, 2000, p.2).
Muminov (1997, p.354) suggested that sweet sorghum stalk should be harvested before the technological ripeness period and should be processed during the technological ripeness period if the sweet sorghum is cultivated for the purpose of obtaining edible concentrated glucose-fructose syrup.
But in a recent study by the Maryland researchers, delaying the harvest time of sweet sorghum by one month beyond the soft-dough stage gives beneficial effects in places with cool climate (Austin, 2010). Delayed harvest time resulted to decrease in biomass and juice volume but an increase in sugar content (Austin, 2010).
The time of harvesting and determination of maturity of sweet sorghum are very crucial in obtaining sweet sorghum with high sugar content. Since ethanol production also depends on sugar content, therefore knowing the right time of harvesting and determining maturity are also beneficial in obtaining high ethanol yield.
Again, the studies being mentioned didnt exactly gave the optimum harvesting time of sweet sorghum stalk therefore, this study is made for the reason of determining the optimum harvesting time of sweet sorghum stalk with the highest sugar content.
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Invertase is an enzyme that catalyzes the hydrolysis (breakdown) of sucrose (table sugar). The resulting mixture of fructose and glucose is called inverted sugar syrup. Related to invertases are sucrases. invertase
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