Study On The Method Of Adulteration Detection Of Cocoa Powder

Cocoa powder has intense aroma of cocoa and can be used for producing chocolate, icecream, candy, pastry and other foods containing cocoa powder. Cocoa powder contains kindsof active ingredient, like dietary fiber, protein, cocoa butter, flavonoid and vitamin, whichcould help to stabilize blood sugar, control appetite, and use as mood stabiliser. Since themiddle of1990s, with the expansion of the application and the development of cocoa productsin foreign trade, the cocoa products processing industry has developed rapidly in China.However, at the same time, a lot of adulteration cocoa powder began to appear in the domesticmarket which not only has serious hazard to food safety, but also has negative influence onthe image of our international trade and the interest of normal manufacturer of cocoa products.Therefore, for the current common phenomenon of adulteration cocoa powder, this studyextracted lipid with soxhlet extraction method and measured the fatty acid composition ofcocoa butter by gas chromatography with hydrogen flame ionization detector (GC-FID) andestablished fingerprint. After the lipid was removed, the sample was proceeded to extractepolysaccharide components by ultrasonic-assisted extraction method. The polysaccharide washydrolyzed with sulfuric acid and derivatizated by PMP reagent after protein removal, andthen which was analysed by high performance liquid chromatography (HPLC) to obtain thefingerprint of monosaccharide compositions of the polysaccharides. Based on the fingerprintsof lipid and polysaccharide, adulteration cocoa powder was successfully analyzed byhierarchical cluster analysis and principal component analysis methods.This study analysed the fatty acid composition of cocoa butter from eleven samples ofcocoa powder by GC-FID, and then established gas chromatographic fingerprint by the"Chromatography Fingerprint Evaluation System (2004A Edition)" software, which includedtwenty-five common peaks and part of the peaks were determined by reference standards. Thesimilarity analysis of fingerprint of cocoa butter from eleven samples of cocoa powdershowed that the similarity was not less than0.999. Based on the fingerprint, hierarchicalcluster analysis and principal component analysis methods were used for analyzing thesimulating adulteration samples of cocoa powder which mixed with cocoa butter replacer(CBR), hydrogenated soybean oil or palm oil. The results showed that the detection limit ofthe adulteration cocoa powder mixed with lauric acid-cocoa butter replacer, hydrogenatedsoybean oil or palm oil was0.6%, and the detection limit of the adulteration cocoa powdermixed with non lauric acid-cocoa butter replacer was1.5%.Futhermore, this thesis measured the monosaccharide composition of polysaccharidesfrom eleven samples of cocoa powder that was derivatizated using the PMP by HPLC andbuilded the HPLC fingerprint which contained twleve common peaks. The similarity analysisresults of fingerprint showed that the similarity was more than0.995. And the hierarchicalcluster analysis and principal component analysis method was used to analyze adulterationcocoa powder mixed with cocoa husk powder or several kind of exogenous powder (includingchestnut shell powder, longan shell powder, peanut shell powder, sweet potato starch, wheatstarch, corn starch and wheat powder). The results indicated that the cocoa powder mixed with15%or more cocoa husk powder and mixed with10%or more kind of exogenouspowder (including chestnut shell powder, longan shell powder, peanut shell powder, sweetpotato starch, wheat starch, corn starch and wheat powder) could be identified by this method.In order to eliminate the interference of maillard reaction on polysaccharide fingerprint,it was necessary to remove the protein in the coarse polysaccharide sample. By comparedseveral protease enzymatic effects on enzymolysis protein, the alkaline protease was selectedto remove the proteins. The protein content of the sample was measured by Kjeldah method,which was used as an indicator of protein hydrolysis conditions. In order to find the bestconditions of enzymatic hydrolysis, an orthogonal test was adopted to investigate hydrolysistemperature, enzyme concentration, pH value, hydrolysis time and substrate concentration.The optimal hydrolysis conditions were as follows: enzyme concentration was5500U/g,hydrolysis temperature was60℃, hydrolysis time was4h, the pH value was8.0, and thesubstrate concentration was1%.