Chocolate methods

Several standard methods for the quantitative analysis of food samples are based on measuring the sample s mass following a selective solvent extraction. For example, the crude fat content in chocolate can be determined by extracting with ether for 16 h in a Soxhlet extractor. After the extraction is complete, the ether is allowed to evaporate, and the residue is weighed after drying at 100 °C. This analysis has also been accomplished indirectly by weighing a sample before and after extracting with supercritical GO2. 

Chocolate does not behave as a tme Hquid owing to the presence of cocoa particles and the viscosity control of chocolate is quite compHcated. This non-Newtonian behavior has been described (28). When the square root of the rate of shear is plotted against the square root of shear stress for chocolate, a straight line is produced. With this Casson relationship method (29) two values are obtained, Casson viscosity and Casson yield value, which describe the flow of chocolate. The chocolate industry was slow in adopting the Casson relationship but this method now prevails over the simpler MacMichael viscometer. Instmments such as the Carri-Med Rheometer and the Brookfield and Haake Viscometers are now replacing the MacMichael. 

A stable crystalline form for chocolate depends primarily on the method used to cool the fat present in the Hquid chocolate. To avoid the grainy texture and poor color and appearance of improperly cooled chocolate, the chocolate must be tempered or cooled down so as to form cocoa butter seed crystals (31). This is usually accompHshed by cooling the warm (44—50°C) Hquid chocolate in a water jacketed tank, which has a slowly rotating scraper or mixer. As the chocolate cools, the fat begins to soHdify and form seed crystals. Cooling is continued to around 26—29°C, during which time the chocolate becomes more viscous. If not further processed quickly, the chocolate will become too thick to process. 

In another method of tempering, soHd chocolate shavings are added as seed crystals to Hquid chocolate at 32—33°C. This is a particularly good technique for a small confectionery manufacturer, who does not produce his own chocolate. However, the shavings are sometimes difficult to disperse and may cause lumps in the finished product (20). Most companies use continuous thin-film heat exchangers for the tempering process. 

Similarly, the use of Irish moss extract, as the suspending agent in chocolate milk, has, through the additional thickening of the drink, educated the public to expect and to enjoy a more viscous type of chocolate-flavored dairy drink. Consequently, should a method be devised to stabilize the drink properly without increasing its viscosity, it is probable that it would be considered insufficiently rich and deemed unpalatable. 

HPLC allows a quantitative determination with relatively simple extractions. In many cases, extraction only involves a heating of the commodity with water, followed by filtration and injection onto an HPLC column. In the determination of caffeine, theobromine, and theophylline in cocoa, coffee, or tea, as well as in other foods, there is scarcely a month that passes without a new paper on this assay. Kreiser and Martin provide typical conditions for analysis.28 In their studies, samples were extracted in boiling water and filtered prior to injection onto the HPLC column. The HPLC conditions used a Bondapak reversed phase column and a mobile phase of water methanol acetic acid (74 25 1) with detection at 280 nm. This method is accurate, precise, and conserves time. It has also been adopted by the AOAC as an official method for the determination of theobromine and caffeine in cocoa beans and chocolate products.29... 

Zoumas et al.30 presented work on the use of this method in the determination of caffeine and theobromine in various chocolate-containing products, while Blauch and Tarka31 reported the use of a similar method for the determination of caffeine and theobromine in various beverages containing these methylxanthines. 

Chocolate milk samples prepared from sweetened cocoa powders averaged 58 mg per serving of theobromine and 5 mg per serving of caffeine.28 Analysis of a "home-style" recipe resulted in higher methylxanthine values — 94 mg theobromine and 10 mg caffeine per serving. However, the authors noted that this recipe also had a stronger chocolate flavor. The lower values reported by Zoumas et al. and Blauch and Tarka compared to others was attributed to the inability of older methods to separate theobromine and caffeine, and the lack of precision and accuracy of the older methods. A compendium of theobromine and caffeine values reported for chocolate beverages from both published and unpublished studies has been compiled in Table 8. 

Chemical analysis of the finished food product is a more accurate determination of the methylxanthine content. In studies performed at Hershey Foods Corporation, the methylxanthine content of a large variety of commercially available chocolate foods was measured by HPLC methods.38 These results have been compiled together with other literature values in Table 11. Large methylxanthine variations can be seen among the chocolate foods, as well as within different brands of the same item. 

A variety of xanthines including caffeine, theobromine, and theophylline have been found from food materials including.coffee, chocolate, and tea (419-420). Theophylline determination in sera has been much studied. The technique allows the determination of theophylline at serum levels of 1.5-20 mg/liter theophylline with sample sizes ranging from 50 to 10 /xl (42 -425). Hill (426) assayed theophylline using 50 /xl of serum and an analysis time of 8 min with good interbatch precision and accuracy. Alternative methods which allow the determination of as little as 0.1 mg/ml (427) or 20 ng theophylline in 10 ml serum have been described (428). 

Adamson, G.E. et al., HPLC method for the quantification of procyanidins in cocoa and chocolate samples and correlation to total antioxidant capacity, J. Agric. Food Chem., 47, 4184, 1999. 

M.Wallerstein 1932 Amylases or papain Method of making chocolate syraps ... 

The initial application of the unit was for the automation of a sample preparation method for the determination of sorbate in chocolate syrup. Table I summarizes the data in this study. Figure 3 outlines the sample preparation scheme for this assay. 

Two students, Denby and Scott, began their quest at the library with a computer search for analytical methods. Searching with the key words caffeine and "chocolate," they uncovered numerous articles in chemistry journals. Reports titled High Pressure Liquid Chromatographic Determination of Theobromine and Caffeine in Cocoa and Chocolate Products 5 described a procedure suitable for the equipment in their laboratory.6... 

Wine, of course, is not the only food that contains phenolics. Phenolics are found in all foods, though at low levels in most. Notable foods that are high in phenolics include coffee and tea, chocolate, fruits and derived products, some oils, spices, and some whole grains. Although the following methods were developed for—and first applied to—analysis of wines and grapes, they can be adapted for other foodstuffs (also see Commentary). 

I would recommend the double boiler as there s less of a chance of overheating the chocolate. Whatever method you choose, you want to remove the chocolate from the heat source as soon as most of it has melted and only a few lumps remain. The residual heat will melt the rest of the chocolate without overheating it. There s nothing sadder than burning fancy organic chocolate when it s late at night and all the grocery stores have closed ... 

Miyazawa et al,143 determined the Amadori compounds from dioleylphos-phatidylethanolamine by normal-phase HPLC as the 3-methyl-2-benzothiazolinone hydrazones (MBTH) through their UV absorption (318 nm) with detection limits of 4.5 and 5.3 ng for the fructosyl (F) and the lactulosyl (L) compound, respectively, and linear ranges of up to about 2 ng. Using their method, they obtained the following results infant formula, F 32-112, L 49-88 ng g mayonnaise, F 12.2 ng g-1 chocolate, F 3.9, L 1.5 ng g-1 cow s milk, L 0.079 /xg mL-1 soybean milk, F 0.24, L 0.13 /tg mL-1 and rat plasma, F 0.23 ng mL-1. Significant amounts were not detected in human milk. 

Evaluating odor and flavor taints is frequently done with water, fatty food simulants (oil, chocolate, unsalted butter), hydrophilic powders (sugar, cornflour), or combined hydrophilic-hydrophobic matrices (milk or cream, biscuits) (Kilcast, 2003). The Robinson test often is used to evaluate materials for tainting potential. This test places the test material in a sealed container separated from the food simulant or test food at a relative humidity between 53% and 75%. After about 48 h, the test food is evaluated for taint compared to a control, using a discrimination method (Lord, 2003). Chocolate is frequently used as the food simulant for this test. Intensity of the taint may be evaluated using a... 

Some degree of enforcement of the rule permitting the addition of up to 5% non-cocoa vegetable fats in chocolate may be based on inspection of factories, recipes and supply records. However, to obtain conclusive evidence of fraudulent addition of non-cocoa fats, a reliable method is required to quantify added fats in chocolate. 

All of the classical analytical techniques applied to oils analysis have been applied to studying the authenticity of cocoa butter and considerable attention has been paid to the issue of detecting and quantifying non-cocoa fats in mixtures with cocoa butter and as incorporated into chocolate. A substantial review of these methods has been published (Lipp and Anklam, 1998b). 

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