Effects Of Polyphenol And Ph On Cocoa Flavour Precursors And Flavour Compounds Using Lipidic Model System
Sofian Seng, Noor Soffalina (2009) Effects Of Polyphenol And Ph On Cocoa Flavour Precursors And Flavour Compounds Using Lipidic Model System. Masters thesis, Universiti Putra Malaysia.
Polyphenol is a naturally occurring compound in cocoa beans reported to reduce the concentration of flavour compounds, mainly pyrazines after cocoa roasting. This study was carried out to determine the effect of polyphenol concentrations and pH on cocoa flavour precursors (i.e. reducing sugars and amino acids) and flavour compounds (i.e. alkylpyrazines) during roasting. The study was conducted using a lipidic model system at roasting temperature 1200C for 45 min. The concentration of amino acids and reducing sugars incorporated in the model systems was based on the results of the concentration found in fermented Malaysian cocoa beans. To determine the effect of polyphenol concentration, crude polyphenol extracted from cocoa bean was added into the lipidic model system at 0, 58, 116 and 174 g kg-1. Results showed that the higher concentrations of polyphenols (174 g kg-1) significantly (p<0.05) decreased the concentration of reducing sugars and amino acids during roasting. As the concentration of polyphenol increased from 58, 116 to 174 g kg-1, fructose was degraded at 33, 35, and 41% and glucose at 29, 30 and 33% respectively. Seventeen individual amino acids were detected, among all; alanine, tyrosine, valine and isoleucine were significantly (p<0.05) degraded higher than the others. These amino acids which are in the hydrophobic group were degraded at 41, 44, 45 and 43 % respectively at polyphenol concentration 174 g kg-1. Changes in procyanidins monomeric and polymeric constituents were correlated with the reduction of the precursors. High polyphenol concentration (174 g kg-1) significantly decreased the formation of alkylpyrazines in the model system. The Response Surface Methodology (RSM) plots revealed that lower concentration of amino acids and reducing sugars was obtained at higher polyphenol concentration (120 g kg-1) and lower pH value (4.5). Based on the constraints set on the obtained surface plots, the optimum region for polyphenol concentration of 43 – 58 g kg-1 and pH of 7.0 -7.5 was obtained for the optimum production of flavour precursors; while the optimum region polyphenol concentration of < 75g kg-1 and pH of > 6.0 was obtained for the production of alkylpyrazines. The optimum point was determined using response optimizer and it was found that the optimum polyphenol concentration of 49.5 g kg-1 and pH of 7.2 for flavor precursors and polyphenol concentration of 52.3 g kg-1 and pH of 7.0 for generated alkypyrazines.Thus, it is recommended that the acidity of the beans should be controlled during processing and extracting the excessive amount of polyphenol higher than 52.3 g kg-1 from the cocoa beans should be considered to lower its negative effect on reducing sugars and amino acids.
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