Terahertz Non-Contact Monitoring of Cocoa Butter in Chocolate

Chocolate is widely enjoyed in many sweets and foods all over the world. In cocoa butter, fatty acids combine together and give cocoa butter 6 different types of crystals: γ, α, β’(III), β’(IV), β(V) and β(VI). In the industry, the β(V) form that is required, is metastable and gives chocolate its marketable properties. The β(VI) form is also stable but not desirable, because of fat bloom. The objective of this study is to characterize these polytypes by terahertz (THz) spectroscopy. THz spectroscopy is expected to be a new tool in food industry, as THz energy corresponds to collective molecular macro-vibrations. Two chocolates from different factories were inspected with optical microscope, X-ray diffraction (XRD) and THz spectroscopy. Optical microscope showed different surface aspects, XRD showed the same species in the two brands and THz spectroscopy showed different features. These differences may be due to fatty acids combination of chocolate.


Introduction
Chocolate is an organic edible compound that is made from cocoa bean. It is widely preferred in many sweets and foods all over the world. The average composition of the chocolate is 54% carbohydrates, 27% fats, 9% fiber, 6% proteins and 1% water [1]. These fats come from cocoa butter, which is mainly made of three fatty acids: 34.5% of oleic acid O (mono-unsaturated), 26% of palmitic acid P (saturated) and 34.5% of stearic acid S (saturated). Around 85% of the total fats are a combination of these three fatty acids in triglyceride fats: POP, POS *Novel terahertz spectroscopy enables us to identify fatty acids combination of chocolate.
How to cite this paper: Weiller, S., Ta late, its polytypes properties. 6 different crystals can be distinguished, with several varieties: γ, α, β'(III), β'(IV), β(V) and β(VI). Because the γ, α and β' are not thermodynamically stable, they are therefore not an issue. In the industry, the β(V) form that is required, is metastable and gives chocolate all of the properties that make it marketable: brilliant, appetizing, melting in the mouth and brittle.
The β(VI) form is also stable and has a melting point higher than the β(V) form.
However, it is not desired, because of the aspect if giving to the chocolate: fat bloom. Chocolate tempering can overcome this issue. Until now, X-ray diffraction (XRD) was used to characterize the crystal structure of chocolate [5]. Terahertz (THz) wave bridges microwave and light, and its frequency corresponds to the weak molecular bonding. THz spectroscopy has promising potential for the identification of macromolecules such as polymer and biomolecules. Unlike XRD, THz spectroscopy is not hurting for human tissues, due to its low energy. It is also a non-destructive analysis tool. THz time-domain spectroscopy (THz-TDS) has been used on chocolate, but only for non-destructive detection of contaminations in chocolate [6]. The non-destructive evaluation can therefore be a new tool for in-line quality monitoring of chocolate in factories. The goal of this study is to try to characterize the different polytypes combination of cocoa butter in chocolate with THz spectroscopy.

Materials and Methods
The optical system used for THz spectroscopy was composed with a 1064 nm Q-switch pulsed Nd:YAG laser as pump for Cr:Forsterite lasers, as shown in

Results and Discussion
Type 1 samples surface morphology showed significant differences between the factories. Visually, factory L samples appear to be smoother. This is confirmed where ΔA and Δλ are the differences of the absorbance and wavelength at the beginning and the end of the slope. Baseline correction and peaks separation that highlighted two peaks in common for the two brands, at 2.05 THz and around 2.88 THz.
In addition to that, Figure 4  Terahertz spectroscopy can therefore be a new tool to control tempering in chocolate factories. The control is important for cocoa butter crystallization [13].
Even packed in films such as paper with high transmittance of terahertz wave, chocolate can still be monitored by using terahertz spectroscopy. Elucidation of terahertz vibrational modes should be elucidated for terahertz applications of food and pharmacy [14].

Conclusion
The cocoa butter polymorphs of β(V) and β(VI) have been determined in chocolate by XRD. Surface morphology analysis highlighted fat bloom deposit on factory H samples. Terahertz spectroscopy showed difference between factories L and H. These differences may be due to formation and migration of β(VI) crystals on the surface of factory H samples, which can be elaborated more by terahertz measurements of chocolate at each step in the tempering process.