Influence of potato Variety on Phenolic Content In-vitro Starch Digestibility and Predicted Glycaemic Index of Crisps and Chips from Nyandarua County Kenya
With the changing of lifestyles globally the demand for ready-to-eat RTE foods has increased. However mostrnof these RTE foods have been associated with intermediate 55-70 to high glycaemic index GI 70 linked to highrnincidences of type 2 diabetes. Nyandarua County in Kenya is a major producer and consumer of potato and has the secondrnhighest type 2 diabetes prevalence 10.8.
Thisrnstudy investigated the effects of variety and processing method product form on the levels of TPC dry matter RDS SDS RSrnand GI in chips and crisps prepared from 3 potato varieties Shangi Dera mwana and Dutch Robijn.
Chips and crisps samples were obtained from NyandaruarnCounty which is a major producer and consumer of potatornand has the second highest type 2 diabetes prevalence inrnKenya. It lies between 0 32 59.99N and 36 36 59.99ErnDMS Degree Minute Seconds 24. Stratified randomrnsampling design 25 was used to collect samples from thernrural and urban areas. Samples were collected from a total ofrn10 wards. Two wards were selected each from 5 sub-countiesrnin Nyandarua County one being an urban ward and the otherrnrural. Urban wards selected were Karau Kipipiri KiriitarnGathanji and Engineer while the rural wards selected werernMirangine Githioro Central Weru and Gathara. Thesernsamples were collected during lunch time between 12.00rnnoon and 2.00 pm as this is when they are usuallyrnconsumed packed in sterile airtight containers stored in arncool box 4C and transported to the laboratory for analysis.rnSome chips and crisps samples were also prepared in thernlaboratory under standardized conditions using ShangirnFigure 1 Dera mwana Figure 2 and Dutch Robijn Figurern3 potato varieties. Shangi tubers are oval shaped with whiternflesh deep eyes and creamy skin while Dutch Robijn arernround shaped with red skin pale yellow flesh and medium torndeep eyes 26. Dera mwana tubers are oval shaped withrnwhite flesh creamy white skin and shallow eyes. Theserntubers were obtained from an individual farmer inrnGwakiongo found in Mirangine a rural ward in NyandaruarnCounty and transported to the laboratory for analysis.rnFigure 1. Shangi potato variety.rnFigure 2. Dera mwana potato variety.rnFigure 3. Dutch Robijn potato variety.rn2.2. ChemicalsrnFolin-Ciocalteu reagent and gallic acid standard werernobtained from Sigma Chemical Co. St. Louis MO USA. Arndigestible starch and resistant starch assay kit obtained fromrnMegazyme Megazyme International Ireland Ltd WicklowrnIreland. All other chemicals used were of analytical grade.rn2.3. Preparation of Chips and Crisps Under StandardizedrnConditionsrnTo prepare chips 2 kg of each potato variety Shangi Dera mwana and Dutch Robijn were obtained from farmersrnin Mirangine ward Nyandarua County and washed tornremove the dirt on the surface. These were then peeled usingrna kitchen knife washed and rinsed in clean potable water.rnThe tubers were then cut into strips of approximately 10-15rnmm in terms of thickness. These strips were soaked in coldrnwater for 1 min to remove surface starch and put on a strainerrnto drain off the water and dry. The strips were then fried inrn4.5 l oil for approximately 9-11 min at 120C in an electricrnfryer EF-102 CT/110 Hypermatt Ltd China.rnFor preparation of crisps 2 kg tubers of each potatornvariety were obtained from farmers in Mirangine wardrnNyandarua County and washed to remove the dirt on thernsurface. These were then peeled using a kitchen knifernwashed and rinsed in clean potable water. These were thenrnsliced to a thickness of 0.15 cm and fried in 4.5 l oil at 120Crnin an electric fryer Model EF-102 CT/110 forrnapproximately 8-9 min.rnThe prepared chips and crisps samples were then allowedrnto cool to 25C room temperature. The chips and crispsrnwere then placed in air-tight containers and stored in thernrefrigerator at 4C until they could be analyzed.rn2.4. Determination of Dry Matter Content of Chips andrnCrispsrnTotal dry matter content of chips crisps and raw potatorntubers was determined by National Forage TestingrnAssociation reference method NFTA as describedrnby Shreve et al. 27. Two 2 g chips crisps and raw potatornfrom each variety were crushed and placed in aluminumrnmoisture dishes whose weights had already been recorded.rnThe weight of the aluminum dishes and the sample was alsornrecorded. These were then dried in a hot air oven MemmertrnSchwabach Germany at 105C for 3 h after which theyrnwere removed and allowed to cool in a desiccator. Theirrnweights were then recorded. Dry matter weight was thenrncalculated from the remaining yield and dry matter contentrncalculated as a percentage of the original sample.rn2.5. Determination of Total Phenolic ContentrnTotal phenolic content was determined using FolinCiocalteu method for the chips crisps and raw potatornfollowing the procedure described by Karim et al. 28 withrnmodifications. One 1 g raw potato crisps and chip wererndried at 60C for 1 h after which 0.2 g sample was weighedrninto 20ml plastic digestion tubes. Ten 10 ml 70 ethanolrnwas then added and mixed vigorously for 1.5 h in a vortexrnmixer Fisher Scientific USA. The mixture was therncentrifuged using a Z382K centrifuge Hermle LabnetrnGermany with a speed of 5000 g for 10 min. Supernatantrn1 ml was then pipetted into a 100 ml volumetric flask. Tenrn10 ml 0.35 M sodium carbonate was then pipetted into eachrnflask. Folin-Ciocalteu reagent 5ml was then pipetted intornthe flasks in intervals of 2 min between each flask and thernmixtures topped up to the mark 100 ml. The absorbancernwas measured at 765 nm using a spectrophotometer LW-V200 RS UV/VIS Germany after calibration with the blankrn70 ethanol. A gallic acid standard curve was generatedrnand used to determine the concentration of phenols in thernsamples.rn2.6. Determination of RDS SDS and TDSrnRDS SDS and TDS were determined according thernmethod described by McCleary 14. The potato chips andrncrisps were first defatted followed by enzyme digestion.rnApproximately 0.5 g sample was weighed using a weighingrnbalance TX323L Shimadzu Corporation Kyoto Japan intorn50 ml Kirgen polypropylene tubes and a cylindrical 206rnmm magnetic stirrer bar added to each tube. Ethanol 0.5mlrn95 v/v and 17.5 ml sodium maleate buffer were then addedrnto the sample. The tubes were then capped and placed in arnpolypropylene tube holder and placed in a water bath ModelrnW26 Haake Germany set at 37C and the contents allowedrnto mix for 5 min with stirring at 170 rpm on a vortex mixerrnMX-S Biobase Jinan Shandong China. Pancreaticrnamylase/amyloglucosidase solution 2.5 ml was added torneach tube and the mixture incubated at 37C in a water bathrnModel W26 Haake Germany equipped with a temperaturernprobe EN13485 Hanna Woonsocket U.S.A withrnintermittent stirring on a vortex mixer MX-S Biobase JinanrnShandong China. Digested mixture 1 ml was drawn usingrnan eppendorf positive displacement pipette for RDSrndetermination after 20 min and 120 min for SDSrndetermination then after 240 min for TDS determination.rnThe aliquots were immediately added to 20 ml 50 mM aceticrnacid solution and mixed thoroughly to stop the enzymerndigestion. Each solution 2 ml was transferred to 2 mlrnpolypropylene microfuge tubes and centrifuged at 15871 grnfor 5 min using a microfuge centrifuge Mikro 200 HettichrnTbingen Germany. Aliquot 0.1 ml was then transferredrnto cylindrical 16100 mm glass test tubes and 0.1 ml dilutedrnamyloglucosidase added to each tube and mixed thoroughlyrnto hydrolyze any remaining maltose. The mixture was thenrnincubated at 50C for 30 min. Glucoserndetermination/Glucose oxidase/peroxidase GOPOD reagentrn3 ml was added to each tube and the mixture incubated atrn50C for 20 min. A reagent blank was also prepared byrnmixing 0.2 ml 100 mM acetic acid with 3ml GOPODrnreagent. D-glucose standards were also prepared inrnquadruplicate by mixing 0.1 ml D-glucose provided in thernMegazyme kit with 0.1 ml 100 mM acetic acid and 3 mlrnGOPOD reagent. These were both incubated with thernsamples at 50C for 20 min. The absorbance was thenrnmeasured at 510 nm using the reagent blank as the referencernusing a spectrophotometer UV-1900 Model 01304rnShimadzu Kyoto Japan. RDS SDS and TDS contents werernthen calculated as follows:rnRDS SDS or TDS g/100g A F EV/WD/0.1100rn1/106rn162/180rnwhere: A absorbance read against the reagent blank after 20rnmin RDS SDS 120 min and TDS 240 min F factor to convert absorbance to g88.9284rnEV extraction volume ml Method 120.5rnrnW weight of sample in grnD dilution of sample 1 ml of the sample was added to 20rnml acetic acid21rn0.1 vol. of sample analyzedrn100 conversion to g/100grn106rn conversion from g to grn162/180 factor to convert from free D-glucose tornanhydrous D-glucose found in starchrnMethod 1 involved the procedure where 0.5 g of the samplernwas used in the analysis. An alternative method uses 1 g.rn2.7. Determination of Resistant StarchrnAfter 240 min of enzyme digestion in section 2.6 abovern4ml suspension was removed using a positive displacementrnpipette and transferred into 50ml polypropylene tubesrncontaining 4ml 95 v/v ethanol and the contents mixedrnthoroughly by inverting the tubes. The tubes were thenrnplaced in a centrifuge CN-2060 MRC Israel and therncontents centrifuged for 10min at 2000 g. The supernatantrnsolution in each tube was decanted immediately and thernpellet suspended in 2 ml of 50 v/v ethanol and mixed on arnvortex mixer MX-S Biobase Jinan Shandong China. Thern50 v/v ethanol 6 ml was then added to the each tube andrnthe tubes capped. The contents were centrifuged at 5096 grnfor 10 min and the supernatant decanted. The pellets werernrecovered and free liquid removed by inverting on absorbentrnpaper. The pellets were then re-suspended in 2ml and mixedrnon a vortex mixer. Ethanol 6ml 50 v/v was added and thernmixture centrifuged at 5096g for 10 min. The supernatantrnsolution was decanted and the tubes covered with parafilmrnuntil resistant starch determination.rnCylindrical magnetic stirrer bars 515 mm and 2mlrn1.7M NaOH were added to each tube and the tubes placed inrnan ice bath. The ice bath was then placed on magnetic stirrerrnMSH-20A Daihan Scientific Seoul Korea for 20 min.rnBuffer 8 ml 1M sodium acetate was added to each tubernwhile still on the magnetic stirrer and 0.1ml diluternamyloglucosidase as indicated by the manufacturer addedrnimmediately. The mixture was then incubated in a water bathrnat 50C for 30 min with intermittent vortex mixing. Therncontents in control sample tube were transferred to a 100 mlrnvolumetric flask and a wash bottle containing distilled waterrnused to ensure all the contents had been transferred and thernvolume topped up to the mark with distilled water. An aliquotrn2ml of the solution was centrifuged at 15581 g for 5 minrnin a microfuge. For the other samples 2ml of the solutionrnapproximately 10.3ml was centrifuged at 15581 g for 5rnmin in a microfuge. Aliquots 0.1 ml of the centrifugedrnsamples were transferred into 16 100 mm glass test tubesrnafter which 3 ml of GOPOD reagent was added. A reagentrnblank was also prepared by mixing 3ml GOPOD reagent withrn0.1ml 100 mM sodium acetate buffer. The samples andrnreagent blank were then incubated in a water bath at 50C forrn20 min. The absorbance was then read at 510 nm against thernreagent blank using spectrophotometer UV-1900 Modelrn01304 Shimadzu Kyoto Japan. Resistant starch wasrncalculated using the formula below:rnResistant starch g/100g A FEV/4rnFV/0.11/106100/W162/180rnwhere: A absorbance read against the reagent blankrnF factor to convert absorbance to g88.9284rnEV extraction volume ml Method 120.5rn4 volume of solution taken after 4h digestionrnFV10.3ml method 1rn0.1 aliquot taken from the final volume to which GOPODrnreagent was addedrnW weight of sample in grn100 conversion to g/100grn106rn conversion from g to grn162/180 factor to convert from free D-glucose tornanhydrous D-glucose found in starchrn2.8. Determination of Glycaemic Index GIrnGlycaemic index GI was determined as described byrnGermaine et al. 29 using a GI prediction equation. Thernequation uses the hydrolysis index at the 90th min which hasrnbeen found to have the best correlation with the actualrnincrease in blood sugar in the in vivo method. The hydrolysisrnindex at the 90th min was determined by plotting a graph ofrndigestible starch w/w against incubation time min. GIrnwas then determined using the hydrolysis at the 90th minrnusing the formula below.rnGIH90 39.21 0.803H90 0.7rnwhere: GIH90 glycaemic indexat the 90th minrnH90 hydrolysis index at the 90th minrn39.21 and 0.803 are constantsrn0.7 conversion factor found to give GI values closer tornthe in vivo valuesrn2.9. Statistical AnalysesrnData were analyzed using two-way ANOVA followed by arnTukeys Honest Significant Difference HSD test to comparernmeans. Pearson correlation was run to study correlationrnamong variables. All statistical analyses were carried outrnusing SPSS Version 22. Values of p 0.05 were consideredrnsignificantly different.
Potato varietyrnsignificantly affected TPC RDS SDS and GI but did not significantly affect RS p0.05. Processing method results inrndifferent product forms which significantly affected dry matter content and GI p0.05. Higher levels of TPC and lower scoresrnof GI were found in chips and crisps prepared from Dera mwana variety. Significant positive correlation relationships werernobserved between GI and RDS and SDS p 0.05 and RDS and SDS p0.05.
This study demonstrates that potato chips and crispsrnprepared from Shangi Dera mwana and Dutch Robijn potatornvarieties have different amounts of total phenolic contentrnTPC RDS SDS and dry matter which significantly affectsrnthe rate and extent of starch digestibility and predictedrnglycaemic index. The findings of this study also show thatrnthe glycaemic index of potato chips and crisps lie in thernintermediate range 55-70. Comparatively Dera mwanarnvariety results in the highest amount of retained TPC andrnlower levels of RDS and SDS and thus is recommended forrnprocessing of chips and crisps as it has the best potential inrnglycemic control. Dutch Robijn variety has the highestrnpotential to raise blood glucose and its consumption mayrnhave to be reduced for glycemic control.
Publication Information
Focus County(s):
Nyandarua County
Programme Area(s):
Non-Communicable Diseases
Research Priority Area(s):
Disease Domain(s):
Document History:
Publication Date: 27.May.2021
Conference Title: