The health impact of carbohydrates is often debated in questions regarding nutrition and health. One reason is that intake of carbohydrates affect the blood glucose level to different extent depending on the characteristics of the carbohydrate. Starch is the most common carbohydrate and it can be categorized as rapidly digested starch (RDS), slowly digested starch (SDS) and resistant starch (RS) where the speed parameter refers to how easily enzymes hydrolyze the starch is and thus how fast the blood glucose level is affected. However, RS does not affect the blood glucose level but instead becomes substrate for microbial fermentation of the gut microbiota. Long term consumption of resistant starch decreases the risk of intestinal diseases. The aim of this project was therefore to investigate different in vitro methods for determination of RS content in samples. The impact which particle size and extrusion have on the amount of RS were investigated since the factors can increase or decrease the amount of RS. Sorghum and cowpea were of interest to analyze since the crops are important nutrient sources in both Africa and Asia. Two methods were investigated for determination of RS content where the method developed by Megazyme International Ireland Ltd. was more stable than the method developed by Goñi et al. Modifications of the Megazyme method were performed in order to obtain more reliable values which was achieved when enzymes from Sigma-Aldrich were used. Samples of sorghum of the particle sizes 125 µm and 250 µm resulted in values ranging between 11.44 – 11.94 g RS/100 g sample and 8.49 – 9.02 g RS/100 g sample after extrusion was performed. Samples of the larger particle size resulted in lower amount of RS, most likely due to starch-protein associations. Cowpea resulted in 11.05 g RS/100 g sample and 9.20 g RS/100 g sample before and after extrusion. Determination of the amylose and amylopectin ratio showed that sorghum contained 53.3 – 59.3 % (w/w) amylose and cowpea 53.2 % (w/w) amylose. A ratio favoring amylose also favors the formation of RS. However, the particle size has larger impact on the RS content than the amylose content and sorghum of particle size 125 µm was shown to be the healthiest regarding amount of RS. Cowpea showed the lowest amount of amylose yet the highest amount of RS among the extrudates and the lowest set back value of -0.5 which leads to an assumption towards unstable methods. Further development of the methods should be carried out in forms of modifications. Optimization of treatments regarding sorghum of particle size 125 µm should be continued in order to obtain even higher RS content.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:ltu-68886 |
| Date | January 2018 |
| Creators | Ngo, Carolin |
| Publisher | Luleå tekniska universitet, Industriell miljö- och processteknik |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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