Enzymatic Hydrolysis of starch in tigernut (Cyperus Esculentus L.) milk using two enzymes and its sensorial effects

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JULY, 2015
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The aqueous beverage of Cyperus esculentus L. also known as tigernut milk has been considered as substitute to cow milk. But its starch content imparts an undesirable organoleptic attribute: chalkiness. In order to improve tigernut milk sensorial quality, the enzymes α-amylase and glucoamylase was used at 5 different combinations (1% α-amylase, 0.8% α-amylase+0.2% glucoamylase, 0.5% α-amylase+0.5% glucoamylase, 0.2% α-amylase+0.8% glucoamylase, 1% glucoamylase) for starch hydrolysis at 50°C for 4 hours. Physico-chemical properties (starch and glucose contents, pH and °Brix) were analyzed hourly. Two hydrolyzed samples with the most effective enzyme combinations were subjected to sensory analyses with the raw sample as control. The initial starch content was 33.08 ± 3.82% and decreased hourly to 19.36 ± 0.39% after four hours. However, glucose content increased from 3.66 ± 0.16% to 6.00 ± 0.5%. The pH of the fresh sample was 5.48 ± 0.02. It increased throughout hydrolysis up to 6.13 ± 0.01. The °Brix was initially between 3.17 and 4.27 and this increased to 6.13 ± 0.06. It was shown that 1% α-amylase and 0.8% α-amylase+0.2% glucoamylase have the closest and highest physico-chemical results but reduction in starch content was higher in 1% α-amylase than 0.8% α-amylase+0.2% glucoamylase. The optimum time for hydrolysis was found to be 3 hours. Sensory analyses showed that hydrolysis resulted in the browning of the samples, but did not affect the chalky mouthfeel to the extent that it could not be effectively noticed by respondents. Raw tigernut milk sample had the highest consumer preference, followed by 0.8% α-amylase+0.2% glucoamylase hydrolyzed tigernut milk. More work should be done to meet the need of the industry in terms of chalkiness reduction by targeting enzymatic hydrolysis of cellulose and pectinase. Key words: tigernut milk, starch, enzymatic hydrolysis, sensory attributes
A thesis submitted to the Department of Food Science and Technology, Kwame Nkrumah University of Science and Technology in partial fulfilment of the requirements for the degree of Master of Science.