Chemistry of Chocolate
Swiss… Belgian… Pure… Milk…
Here we are in mid-February again, bombarded by chocolate from all sides in preparation for Valentine’s Day on the 14th. Whether in a solid bar, as a chewy truffle, or as a luxurious drink, chocolate has completely infiltrated our lives. Most people can agree that this confectionary treat is fantastic for any occasion – to be given as a gift, to recover after having a bad day, as well as to celebrate a good one – chocolate is certainly meant to be enjoyed.
Even if you don’t like the taste, the chances are high that someone close to you does. So how can you be certain of its quality?
Components of a chocolate bar
For the sake of this article, let us consider the humble chocolate bar, without any extra additions (not to mention any Golden Tickets). This form can be found worldwide in nearly any grocery store or candy shop, generally designated as white, milk, or dark.
All of this variability comes from the edible seeds in the fruit of the cacao tree, which grows in hot, tropical regions around the equator. They must be fermented and then roasted after cleaning. From this, cocoa mass is produced, which is a starting base for several uses. Cocoa butter and cocoa solids are prepared from the cocoa mass and are utilized in products ranging from foods and beverages to personal care items.
As for chocolate bars, these are generally sweetened and modified from the pure form, which is very bitter. Milk (liquid, condensed, or powdered) is added to many types, but does not necessarily have to be present. Varying the content of the cocoa solids and cocoa butter in chocolate to different degrees results in the classifications of dark to white. While some dark chocolates do not contain any milk, white chocolates do to add to the significant amounts of cocoa fat used to produce them.
In general, dark chocolate contains a high ratio of cocoa solids to cocoa butter and may or may not contain any milk. It may be sweetened or unsweetened. Milk chocolate is a much broader category, containing less cocoa solids but not necessarily a different cocoa butter content compared to dark chocolate, as milk fats are also introduced. Milk chocolate is also sweetened, either with sugar or other substitutes. White chocolate contains no cocoa solids at all, but a blend of cocoa butter and milk, along with sweeteners.
Depending on the country, there are different regulations in place regarding the classification of the type of chocolate. If you are interested, you can find a selection of them here.
What makes your favorite chocolate unique?
Of course, more ingredients are added to chocolate bars to affect a number of things like the aroma, texture/mouthfeel, and certainly to enhance the flavor. The origin of the cacao beans, much like coffee, can impart certain characteristics to the resulting chocolate. The manufacturing process also plays a major part in determining e.g., whether the chocolate has a characteristic snap or has a distinct scent, setting it apart from other brands.
In some cases, vegetable fats are used to replace a portion of the cocoa fats, although this may not legally be considered «chocolate» in some countries. The adjustment of long-standing recipes for certain chocolate brands has sometimes led to customer backlash, as quality is perceived to have changed. Truly, chocolate is inextricably tied to our hearts.
Applications for chocolate quality analysis
Nobody wants to give their Valentine a bad gift, especially out-of-date chocolate from a dubious source. Here, we have prepared some interesting analyses for different chocolate quality parameters in the laboratory.
Sugar analysis via Ion Chromatography (IC)
Most types of chocolate contain sugars or sugar substitutes to sweeten the underlying bitterness. Considering different regulations regarding food labeling and also nutritional content, the accurate reporting of sugars is important for manufacturers and consumers alike.
Sugar analysis in chocolate can be performed with Metrohm IC and Pulsed Amperometric Detection (PAD). An example chromatogram of this analysis is given below.
A small amount of commercially produced sweetened milk chocolate was weighed and dissolved into ultrapure water. After further sample preparation using Metrohm Inline Ultrafiltration, the sample (20 µL) was injected on to the Metrosep Carb 2 – 150/4.0 separation column and separated using alkaline eluent. As shown, both lactose and sucrose elute without overlap in less than 20 minutes.
Learn more about Metrohm Inline Ultrafiltration for difficult sample matrices and safeguard your IC system!
In this example, the sugar content was listed on the label as 47 g per 100 g portion (470 g/kg). Lactose was determined to be 94.6 g/kg, and sucrose was measured at 385.6 g/kg. To learn about what other carbohydrates, sweeteners, and more can be determined in chocolate and other foods with Metrohm IC, download our free brochure about Food Analysis and check out the table on page 25!
Lactose content in lactose-free chocolate
The accurate measurement of lactose in lactose-free products, including chocolate, is of special importance to consumers who are lactose-intolerant and suffer from digestive issues after eating it. Foods which are labelled as lactose-free must adhere to guidelines concerning the actual non-zero lactose content. Foodstuff containing less than 0.1 g lactose per100 g (or 100 mL) is most frequently declared as lactose-free.
Determination of lactose in chocolate is possible with IC. Here is an chromatographic overlay of a dissolved chocolate sample with lactose spikes which was analyzed via Metrohm IC using the flexiPAD detection mode.
Milk chocolate, labelled lactose-free measured via Metrohm IC (0.57 ± 0.06 mg/100 g lactose, n = 6).
The sample contained 0.6 mg lactose per 100 g, with measurement of the lactose peak occurring at 13.2 minutes. The black line is the unspiked lactose-free chocolate sample, red and blue are spiked samples of increasing concentration. To prepare the samples, approximately 2.5–5 g chocolate was dissolved in heated ultrapure water, using Carrez reagents to remove excess proteins and fats from the sample matrix. Afterward, centrifugation of the samples was performed, followed by the direct injection of the supernatant (10 µL) into the IC system. Measurement was performed with the Metrosep Carb 2 – 250/4.0 separation column and an alkaline eluent.
Interested in lactose determinations with ion chromatography? Download our free Application Notes on the Metrohm website!
Water determination with Karl Fischer Titration
The amount of water in foods, including chocolate, can affect their shelf life and stability, as well as contribute to other physical and chemical factors. Aside from this, during the processing stage, the amount of water present affects the flow characteristics of the chocolate mass.
AOAC Official Method 977.10 lists Karl Fischer titration as the accepted analysis method for moisture in cacao products.
The determination of moisture in different chocolate products is exhibited in the following downloadable poster. As an example, several samples (n = 10) of dark chocolate (45% cocoa content) were analyzed for their moisture content with Metrohm Karl Fischer titration. Results were found to be 0.96% water with a relative standard deviation (RSD) of 2.73%. More information about this analysis can be found in our poster about automated water determination in chocolate, or in chapter 11.6 of our comprehensive Monograph about Karl Fischer titration.
Oxidation stability with the Rancimat test
Oxidation stability is an important quality criterion of chocolate as it provides information about the long-term stability of the product. Cocoa contains various flavonoids that act as antioxidants. Although the flavonoid content may vary amongst chocolate type, in general, the greater the content of cocoa solids in the chocolate, the greater its antioxidant effect.
The 892 Professional Rancimat from Metrohm determines the oxidation stability of fat-containing foods and cosmetics. The Rancimat method accelerates the aging process of the sample and measures the induction time or oxidation stability index (OSI).
Chocolate cannot be measured directly with the classical Rancimat method, as no evaluable induction time is obtained. There are many reasons for this: e.g., the fat content is too low. Traditionally, extraction of the fat from the chocolate is necessary, but not always.
Learn more about the Rancimat method on our website, and download our free Application Note about the oxidation stability of chocolate. In this Application Note, the oxidation stability of white, milk and dark chocolate is determined without extraction.
Cadmium in chocolate by Voltammetric analysis
The toxic element cadmium (Cd) can be found in elevated concentrations with high bioavailability in some soils. Under such conditions, cacao trees can accumulate cadmium in the beans. Chocolate produced from the affected beans will contain elevated cadmium levels.
Typical limit values for Cd in chocolate in the European Union are between 100 µg/kg and 800 µg/kg (EU Commission Regulation 1881/2006) depending on the cocoa content of the chocolate. Anodic stripping voltammetry (ASV) can be used to accurately determine trace quantities of cadmium in chocolate down to approximately 10 µg/kg. The method is simple to perform, specific, and free of interferences.
Chocolate samples are first mineralized by dry ashing in a furnace at 450 °C for several hours. The remaining ash is then dissolved in an acidified matrix. The cadmium determination is then carried out on the 884 Professional VA instrument from Metrohm. To learn more about how to perform the analysis, download our free Application Note.
Happy Valentine’s Day from us all at Metrohm!
Post written by Dr. Alyson Lanciki, Scientific Editor at Metrohm International Headquarters, Herisau, Switzerland.
