Ghanaian Cocoa Bean Fermentation Characterized by Spectroscopic and Chromatographic Methods and Chemometrics

Abstract: Export of cocoa beans is of great economic importance in Ghana and several other tropical countries. Raw cocoa has an astringent, unpleasant taste, and flavor, and has to be fermented, dried, and roasted to obtain the characteristic cocoa flavor and taste. In an attempt to obtain a deeper understanding of the changes in the cocoa beans during fermentation and investigate the possibility of future development of objective methods for assessing the degree of fermentation, a novel combination of methods including cut test, colorimetry, fluorescence spectroscopy, NIR spectroscopy, and GC-MS evaluated by chemometric methods was used to examine cocoa beans sampled at different durations of fermentation and samples representing fully fermented and dried beans from all cocoa growing regions of Ghana. Using colorimetry it was found that samples moved towards higher a* and b* values as fermentation progressed. Furthermore, the degree of fermentation could, in general, be well described by the spectroscopic methods used. In addition, it was possible to link analysis of volatile compounds with predictions of fermentation time. Fermented and dried cocoa beans from the Volta and the Western regions clustered separately in the score plots based on colorimetric, fluorescence, NIR, and GC-MS indicating regional differences in the composition of Ghanaian cocoa beans. The study demonstrates the potential of colorimetry and spectroscopic methods as valuable tools for determining the fermentation degree of cocoa beans. Using GC-MS it was possible to demonstrate the formation of several important aroma compounds such 2-phenylethyl acetate, propionic acid, and acetoin and the breakdown of others like diacetyl during fermentation. Practical Application: The present study demonstrates the potential of using colorimetry and spectroscopic methods as objective methods for determining cocoa bean quality along the processing chain. Development of objective methods for determining cocoa bean quality will be of great importance for quality insurance within the fields of cocoa processing and raw material control in chocolate producing companies.     

Simultaneous Measurement of Titratable Acidity and Fermentation Index in Cocoa Beans by Electronic Tongue Together with Linear and Non-linear Multivariate Technique

Titratable acidity (TA) and fermentation index (FI) are important quality indicators of cocoa beans. This paper attempted the simultaneous analysis of these indicators by electronic tongue (ET) and two multivariate calibrations. ET was used for data acquisition, while partial least squares (PLSs) and principal component support vector machine regression (PC-SVMR) were used to build the calibration models. Some parameters were optimized simultaneously by leave-one-out cross-validation (LOOCV) in calibrating the model. The performance of the model was tested according to root mean square error of prediction (RMSEP) and correlation coefficient (R _pre) in the prediction set. The results revealed that PC-SVMR model was superior to PLS model in this work. The optimal PC-SVMR model for TA was R _pre?=?0.960 and RMSEP?=?0.0077, while for FI, this was R _pre?=?0.954 and RMSEP?=?0.058. This study demonstrated that ET together with SVMR could be used to analyze titratable acidity and fermentation index in cocoa beans for quality control purposes.     

A closed-loop electronics cooling by implementing single phase impinging jet and mini channels heat exchanger

This paper reports our works in the design and testing of a closed-loop electronics cooling system that adopts bi-technologies: single phase impinging jet and mini channels heat exchanger. The system has the cooling capacity of 200 W over a single chip with a hydraulic diameter of 12 mm. The equivalent heat flux is 177 W/cm². The cooling system maintains the chip’s surface temperature below 95 °C maximum when the ambient temperature is 30 °C. De-ionized water is the working fluid of the system. For the impinging jet, two different nozzles are designed and tested. The hydraulic diameters (d_N) are 0.5 mm and 0.8 mm. The corresponding volume flow rates are 280 mL/min and 348 mL/min. Mini channels heat exchanger has 6 (six) copper tubes with the inner diameter of 1.27 mm and the total length of about 1 m. The cooling system has a mini diaphragm pump and a DC electric fan with the maximum power consumptions of 8.4 W and 0.96 W respectively. The coefficient of performance of the system is 21.4.     

CMOS compatible bistable electromagnetic microvalve on a single wafer

This paper presents our work in the bistable electromagnetic actuated microvalve. The microvalve is entirely fabricated by surface micromachining on top of a single Si (silicon) substrate. The microvalve has an overall diameter of 1600 μm and the overall height of 600 μm, including the wafer thickness. The bistable mechanism is achieved by integrating an electroplated micro CoNiMnP magnet on the membrane. The microvalve was tested in the flow of deionized (DI) water at 0-50 μL/min. The latching/unlatching of the microvalve was performed to control the flow DI water at 30 μL/min, it required the operational current of 0.38 A and the power of 1.17 W. The latching/unlatching response time of the microvalve is 10 ms, with the leaking rate of 0.16-0.8 μL/min.     

Influencing cocoa flavour using Pichia kluyveri and Kluyveromyces marxianus in a defined mixed starter culture for cocoa fermentation

The potential impact of aromatic and pectinolytic yeasts on cocoa flavour was investigated using two defined mixed starter cultures encompassing strains of Pichia kluyveri and Kluyveromyces marxianus for inoculating cocoa beans in small scale tray fermentations. Samples for microbial and metabolite analysis were collected at 12–24 hour intervals during 120 h of fermentation. Yeast isolates were grouped by (GTG)₅-based rep-PCR fingerprinting and identified by sequencing of the D1/D2 region of the 26S rRNA gene and the actin gene. Pulsed Field Gel Electrophoresis (PFGE) was conducted on isolates belonging to the species P. kluyveri and K. marxianus to verify strain level identity with the inoculated strains. Furthermore, Denaturing Gradient Gel Electrophoresis (DGGE) was performed to follow yeast and bacterial dynamics over time including the presence of the bacterial inoculum consisting of Lactobacillus fermentum and Acetobacter pasteurianus. Yeast cell counts peaked after 12 h of fermentation with the predominant species being identified as Hanseniaspora opuntiae and Hanseniaspora thailandica. P. kluyveri and K. marxianus were found to compose 9.3% and 13.5% of the yeast population, respectively, after 12 h of fermentation whilst PFGE showed that ~ 88% of all P. kluyveri isolates and 100% of all K. marxianus isolates were identical to the inoculated strains. Despite never being the dominant yeast species at any stage of fermentation, the un-conched chocolates produced from the two inoculated fermentations were judged by sensory analysis to differ in flavour profile compared to the spontaneously fermented control. This could indicate that yeasts have a greater impact on the sensory qualities of cocoa than previously assumed.     

Shock synthesis of GaAs from elemental powders

Stoichiometric mixtures of Ga and As powders were explosively shocked to create GaAs. The reactants were loaded into stainless steel capsules, which were, in turn, fitted into Sawaoka fixtures. The sample assemblies were struck with flyer plates traveling at 1.3 to 2.5 Km/s. The shocked samples were analyzed by specific gravity measurements, X-ray diffraction (XRD), optical microscopy, and scanning electron microscopy (SEM). The density of the poly crystalline product ranged from 79 to 95 pct of theoretical. The XRD patterns showed only the presence of GaAs; however, small amounts of gallium-rich and arsenic-rich regions were found by energy-dispersive X-ray spectroscopy (EDS) analysis. This paper is based on a presentation made in the symposium “Reaction Synthesis of Materials” presented during the TMS Annual Meeting, New Orleans, LA, February 17–21, 1991, under the auspices of the TMS Powder Metallurgy Committee.     

Fermentation of cocoa beans: influence of microbial activities and polyphenol concentrations on the flavour of chocolate

BACKGROUND: Spontaneous cocoa bean fermentation is characterised by a succession of microbial activities. Cocoa flavour precursors are developed during fermentation and drying of cocoa beans. Polyphenols and alkaloids contribute to astringency and bitterness of cocoa and chocolate. RESULTS: Population dynamics, metabolite target analyses, and chocolate production were performed for seven independent spontaneous cocoa bean heap fermentations in Ghana. Although the same micro‐organisms were involved in these heaps, carried out at different farms or in different seasons, heap temperatures and microbial metabolite concentrations were different. This could be due to heterogeneity and size of the heaps, but was mainly ascribed to microbial variability. Indeed, differences in microbial activity could be linked with the flavour of chocolates made from the corresponding dried, fermented cocoa beans. Whereas the polyphenol and alkaloid contents of cocoa beans were crop‐ and heap‐dependent, epicatechin and theobromine levels decreased during fermentation due to diffusion out of the bean cotyledons and polyphenol oxidation and condensation. Residual levels were responsible for the degree of bitterness of the final chocolates. CONCLUSION: Differences in microbial activities between different heap fermentations can result in dried fermented cocoa beans and chocolates with different flavour characteristics. Hence, fermentation control may direct the flavour of chocolate. Copyright © 2008 Society of Chemical Industry     

Synthesis and characterization of H-bonded side-chain and crosslinking LC polymers containing donor/acceptor homopolymers and copolymers

Side-chain copolymers consisting of proton acceptors (stilbazoles) and proton donors (benzoic acids) connected to polyacrylate backbones with different methylene spacer lengths are prepared by tuning their donor/acceptor molar ratios. The H-bonded copolymer networks are formed once they were synthesized, and showed more homogenous phase behavior than the physical blending supramolecular networks composed of donor and acceptor homopolymers. Analogous monomer–monomer and polymer–monomer (H-bonded side-chain polymer) complexes of similar structures are also investigated. According to DSC, POM, and XRD studies, it reveals that the copolymers with various spacer lengths and donor/acceptor molar ratios show the smectic A (S_A) phase. The d spacing values of XRD results suggest that the H-bonded copolymers may be constructed by either a monolayer or an interdigitated bilayer structure. Generally, the d spacing values of copolymers (in the S_A phase) increase with higher H-bonded crosslinking density between benzoic acids and stilbazoles, i.e. decrease with higher molar ratios of benzoic acids, which may be owing to the formation of hydrogen bonds between benzoic acids from different backbones. The isotropization temperatures of the H-bonded blends and copolymers increase as the molar ratios of benzoic acids increase, while the higher H-bonded crosslinking density between benzoic acids and stilbazoles stabilizes the liquid crystalline phase.