Answers:
Some of the main types of modification in polysaccharides include the following;
- Chemical
- Physical
- Enzymatic
The two principle targets of the below polysaccharide are;
- Acetylation
- Carboxymethylation
Cross-linking in the polysaccharide is forming a tridimensional network where the chain of the polymer is linked by noncovalent or covalent bonds. A quantified amount of citric acid as a catalyst. Phosphate (sodium phosphate having 50% w/w on the weight of the citric acid employed) is employed with the catalyst ( acid). The solution of starch having the catalyst and cross-linking agents heated up to about 363 K, this temperature is maintained for about 2 minutes. After that, the mixture is cooled to 338K and then poured it to Teflon coated a plate of glass (Woods, 2013). The cast films were then permitted to air dry and this cooling is conducted within 2 days (48 hours) after that it will be peeled off from the plates. The film of starch is then treated in a hot air at about 438K for about 8 hours for the reaction of cross-linking to occur. Immediately after heating, the film was moved to a conditioning chamber controlled at 296K and about relative humidity of 50%. The below chemical equation shows the cross-linking of starch (Barnett, 2010).
Uses of the citric acid
- Citric acid is employed as a catalyst hence it will help to speeds up the chemical reaction.
- Citric acid also helps to improve mechanical properties. Using the citric acid in the cross-linking to improve their stability and strength.
Uses of the phosphate
- The sodium phosphate helps to reduce the size of granule employed in the crosslinking.
The formation of the starch acetates having a relatively high degree of substitution can be produced using acetic anhydride and use the sodium hydroxide (NaOH) as a catalyst. The degree of substitution increases with the increased reaction time. The substitution reaction occurs through the addition-elimination (Booker, 2014). The OH in the C6 readily react and is acetylated readily than the secondary ones on the C3 and C2 because of its steric hindrances. The main OH at the exterior of the starch molecule will react readily with the acetic group, at the same time the two secondary which are at the interior surface will form a hydrogen bond with the OH group on the adjacent glucose unit. This method is employed to synthesise starch acetate and the below chemical equation shows how the reaction occurs.
Uses of phosphates
- Phosphates are used in making the baking powder
- Some phosphate is used for processing the several ceramic
- Phosphates are employed as cleaning solution which is used by the mildew and the stubborn stains.
Uses of starch acetates
- Starch acetate is employed in developing fibre for the potential use as tissue.
- They are also used as an ingredient in various food.
The physical modification is the modification of the starch impacted through physical treatment which does not lead to any modification of starch by the chemical. (Robinson, 2011) The physical modification is subdivided into two, that is the nonthermal and thermal treatment. Thermal treatment comprises of that treatment which generates pregelatinized and angular cold-water-swelling starches, annealing, heat-moisture treatment, heating of dry starch and microwave heating. The nonthermal comprises of instantaneous controlled pressure drop, dynamic pulsed pressure, thawing, pulse electric field and freezing.
Uses of physically modified starches
- Used as food product as a thickening agent
- Such starch is used as a stabilizer
- They are used in pharmaceuticals as disintegrant
- They are as well used as a binder in paper coated.
Some of the common type of modified food starch includes;
- Corn
- Wheat
- Tapioca
- Potato
References
Barnett, A. (2010). Examining Food Technology. London: CRC.
Booker, J. (2014). Food Technology. Manchester: Nelson Thornes.
Robinson, J. (2011). Food Technology. Washinton DC: Nelson Thornes.
Woods, L. (2013). Food Technology. Chicago: Heinemann.
