Original article Performance of different drying methods and their effects on the chemical quality attributes of raw cocoa material

1564 International Journal of Food Science and Technology 2010, 45, 1564 1571 Original article Performance of different drying methods and their effects on the chemical quality attributes of raw cocoa material Tagro Simplice Guehi, 1 * Irié Bi Zahouli, 2 Louis Ban-Koffi, 2 Monké Adrien Fae 1 & Jean Gnopo Nemlin 2 1 Unité de Formation et de Recherche des Sciences et Technologies des Aliments (UFR-STA), Université d Abobo-Adjamé. 02 Bp 801 Abidjan 02 Coˆ te d Ivoire 2 Station de Recherche et de Technologie, Centre National de Recherche Agronomique (SRT-CNRA). 08 BP 33 Abidjan 08 Coˆ te d Ivoire (Received 13 January 2010; Accepted in revised form 27 April 2010) Summary Keywords Studies were carried out to investigate the impact of different drying processes on the chemical quality traits of raw cocoa beans. The ph of less fermented cocoa is higher than the well-fermented cocoa s. The sun-dried beans ph ranged from 4.5 to 5.5, while the ph of both oven- and mixed-dried beans was between 3.8 and 5.2. The sun-dried beans contained lower volatile acidity than oven-dried beans. Artificially dried beans resulted in higher free acidity content when compared to both sun- and mixed-dried beans. Ammonium nitrogen content in raw cocoa beans is not influenced by the drying methods. Free fatty acid content increases slowly but remains below the critical value of 1.75% whatever the drying processes. While oven-dried beans show the FFA content above 0.70% both of sun- and mixed-dried beans are associated with FFA content below 0.70%. Chemical quality, cocoa, drying methods. Introduction Cocoa beans are the seeds from fruit pods of a tropical tree botanically known as Theobroma cacao L. (Family Sterculiaceae). Each pod contains 30 40 beans embedded in a mass of mucilaginous pulp within the pod. The bean pulp is rich in fermentable sugars, such as glucose, fructose and sucrose, and has a low ph of 3.0 3.5, mainly because of the presence of citric acid. Cocoa bean is the principal raw material of chocolate manufacture (Ardhana & Fleet, 2003). Theobroma cacao is grown mostly in the wet tropical forest climate which is within 20 of latitude of the equator at countries such as Coˆ te d Ivoire, Ghana, Nigeria, Cameroon, Brazil, Equador, Papua New Guinea, Indonesia and Malaysia (Beckett, 1994). World production of cocoa beans was about 3 888 000 t in 2006 07 crop year, and nearly 70% of this quantity was produced in West Africa (World Cocoa Foundation, 2008). Cocoa is a crop that needs to be fermented and dried before export. The processing of cocoa beans consists of two major steps namely fermentation and drying (Wood & Lass, 1985). Fermentation and drying are both essential steps for the quality of final product. Upon harvesting of ripe cocoa *Correspondent: Fax: +22520374300; e-mail: g_tagro@hotmail.com pods, the beans and associated pulp are removed from the pod and subject to microbial fermentation as the first stage in preparation for chocolate production. Fresh cocoa beans are fermented for 5 7 days and dried immediately after fermentation to safe moisture level of 7.5%. The importance of bean fermentation in contributing to chocolate quality has been recognised for over 100 years, and numerous studies have been conducted in different countries to determine the microbial species associated with this process (Schwan et al., 1995). These fermentations are generally conducted as traditional, indigenous processes, the details of which have been well reviewed (Roelofsen, 1958; Lehrian & Patterson, 1983; Lopez & Dimick, 1995; Thompson et al., 2001). Microbial action during fermentation solubilises the pulp material surrounding the beans and produces a range of metabolic end-products (e.g. alcohols, organic acids) which diffuse into the beans to cause their death. These changes induce an array of biochemical reactions within the beans and generate the chemical precursors of chocolate flavour, aroma and colour (Lehrian & Patterson, 1983; Jones & Jones, 1984; Hansen et al., 1998; Hashim et al., 1998; Thompson et al., 2001). During fermentation the temperature of the beans will rise from ambient to about 50 55 C because of the exothermic oxidation reaction (Wood & Lass, 1985). After the end of fermentation, the moisture content of the whole doi:10.1111/j.1365-2621.2010.02302.x Ó 2010 CNRA-Université d Abobo-Adjamé

Performance of different drying methods T. S. Guehi et al. 1565 beans is approximately 60% and this must be reduced to 7 7.5% before the cocoa can be stored, sold, transported and exported to European countries. So the beans are dried immediately to avoid over fermentation, which could lead to product deterioration. Drying is usually carried out using natural sun and artificial hot air techniques (Mc Donald et al., 1981). Natural or artificial drying methods may be chosen, depending on characteristics of each species, the amount of harvested seeds, and on weather conditions prevailing after seeds were harvested. Natural cocoa bean drying is directly dependent on weather conditions. The disadvantage of the method lies in the need for intensive human labour and in turn leads to poor operational performance. Cocoa smallholders produce in small quantity would prefer sun drying, while for the bigger plantation the hot air (artificial) method is preferred (Wood & Lass, 1985). During drying, the cocoa beans undergo various chemical and biochemical changes that form the necessary flavour and aroma precursors needed during processing. Cocoa beans constitute an inexpensive fat source and are the principal raw material of chocolate from Africa and both Central and South America (Tafuri et al., 2004). Nowadays, one of the most widespread concerns in advanced technological countries is food quality and safety. The economy of most developing countries, based primarily on their agricultural resources, is strongly dependent on the often rigorous and rigid quality standards set by developed countries. Ivorian raw cocoa bean quality did not escape being degraded as the liberalisation of the cocoa-producing chain in 1999 and the reasons were unspecified (DGTCP (Direction Ge ne rale du Tre sor et de la Comptabilité Publique de Coˆ te d Ivoire), 2004). Indeed, as this liberalisation and dislocation of the Ivorian traditional control quality and the cocoa producers framing system, agricultural practices varied on the region and sometimes on the producers in the same area. Thus, in Coˆ te d Ivoire, it is difficult to talk about cocoa post harvest treatments. However, Guehi et al. (2008) have identified the common practices about fermentation and drying methods in Coˆ te d Ivoire. The predominant processing of fermentation for Ivorian raw cocoa production consists of ferment beans in heaps in small farms or in wooden boxes in big farms without turning. In Coˆ te d Ivoire, cocoa fermentation usually lasts between 4 and 5 days on weather conditions and time during the cocoa season. Fermentation generally takes shorter at the start and peak of the cocoa crop but longer towards the end of the crop when there is less mucilage available for fermentation. At the end of fermentation, Ivorian cocoa producers spread freshly fermented beans on a meshed wooden tray with area about 30 90 cm and raised 1 m above ground level, mats, polypropylene sheets or the concrete floor of a cocoa house each day to a depth of not less than 5 cm and mixed constantly to promote uniform drying and to break agglomerates. Although sun drying is the preferred method for Ivorian producers, since some years artificial drying method is more and more employed in the big cocoa farms. Probably such variations in agricultural practices in Ivorian cocoa chain could be explained why the quality of Ivorian raw cocoa is more and more degraded. Therefore, it is important to identify the factors that reduce commercial value by studying the chemical quality of Ivorian beans resulted from different durations of fermentation and dried by different drying processes. The objective of this study did not focus on postharvest handling and technology processing of cocoa beans at the farmer s level in Coˆ te d Ivoire. This study aimed to evaluate the performance of some cocoa drying methods in terms of chemical quality of raw cocoa beans such as acidity (ph, free and volatile acidities, ammonium nitrogen contents and free fatty acids content) during fermentation. Materials and methods Cocoa The ripe cocoa pods (Theobroma cacao L.) of mixedhybrids were harvested by hand during the big 2005 cocoa season (from December to February) in the experimental cocoa station of Centre National de Recherche Agronomique (CNRA) located at Bingerville region of Coˆ te d Ivoire, a moderate hot rainy region with an average of 28 29 C during the harvest season, a low altitude, below 500 m, 70 80 mm month rainfall. 2.2 Cocoa pod storage and breaking The cocoa pod storage time is 4 days at ambient temperature at the field. The pod storage time is the time that the pods were stored after harvesting but before breaking using a piece of wood billet as a bludgeon as reported earlier (Meyer et al., 1989). Pod breaking using wooden billet involves one or two sharp blows with the edge of the billet. The distal portion of the pod falls away and the beans remain attached to the placenta from which they can be easily extracted. The beans were removed from placenta being careful to exclude any germinated, black or diseased beans or pieces of shell or placenta fragments. Cocoa fermentation Cocoa beans were fractioned into seven same subsamples (about 25 kg). One type of fermentation was studied as reported earlier by Mounjouenpou et al. (2008): six boxes fermentation, where the beans of each fraction were put in banana leaves placed in wooden boxes measuring 35 35 35 cm 3. Fermentation was Ó 2010 CNRA-Université d Abobo-Adjamé International Journal of Food Science and Technology 2010, 45, 1564 1571

1566 Performance of different drying methods T. S. Guehi et al. carried out in each box using 25 kg of fresh beans during 1, 2, 3, 4, 5 and 6 days respectively for the boxes no. 1, 2, 3, 4, 5 and 6. The heap of wet cocoa beans was then covered in the box with other fresh banana leaves and other banana leaves were used to insulate the top of box. Initial turning during fermentation was done after 48 h and additional turning 48 h thereafter to facilitate adequate aeration of fermenting mass and to ensure that beans from the top and bottom are thoroughly mixed together. A fresh layer of banana leaves were added to the original leaves after each turning to ensure adequate insulation. Fermentation experimentations were conducted triplicate. Drying methods After fermentation, cocoa beans were fractioned into three same parts. Fermented beans of each fraction were dried according to a specific method. All drying methods processing is stopped when the moisture content of cocoa beans reached 7 8%. Sun drying methods Natural or sun drying process consistent to expose cocoa beans from 9 am until to 6 pm (C9) is considered as standard drying method. So characteristics of dried beans resulted from both other experiments were compared against this sun-dried beans. Two batches, one of whom is respectively unfermented and fermented beans were separately spread thinly on a meshed wooden tray with area about 30 90 cm and raised 1 m above ground level and sun-dried until they reached moisture content of about 7%. The beans were mixed each 1 h to ensure uniformity. Artificial hot air drying methods Raw cocoa beans were artificially dried using an airventilated oven at temperature of 60 C (EV34) until moisture content of 7% as reported (Hii et al., 2009). The beans were spread thinly in single layer (about 2 cm thick) on a meshed sample tray with square openings. Heat was generated by the heater integrated into the side walls of the oven and the hot air flowed through the samples. The exhaust air escaped through a ventilation hole (diameter 4 cm) at the back of the oven. The beans were mixed every 2 h to ensure uniformity. Drying was conducted for 8 h daily, and the beans were left to temper at room temperature overnight. The tempering step is a common routine in cocoa drying, and the purpose is to redistribute the internal moisture to the outer beans layer after each drying cycle. Combination of sun and artificial drying process The unfermented and fermented cocoa beans were dried by a mixed drying process consisting primarily sun drying from 9 am to 6 pm daily until moisture of 25% and consecutively by artificial drying process using an air-ventilated oven (C9 EV18) until moisture content of 7%. Analytical methods Moisture content The beans used in each experiment were weighed prior to mixing during drying by using an analytical balance. The moisture content (%) of the beans was determined with reference to the dry weight of the beans as early reported (Guehi et al., 2007). The measurement was performed in triplicates. Chemical acidities and ph The methods used to quantify, volatile and free acidity, and ammonium nitrogen contents, and to determine ph were described by Pontillon & Cros (1998). Five grams of ground nibs was homogenised in 45 ml boiled distilled water. The mixture was filtered with Whatman No. 4 filter paper and cooled to 20 25 C. The resulting filtrate was measured for ph using a ph meter (Consort P 107) which had been calibrated with buffers at ph 4 and 7 as described by Hii et al., 2009). A further 25-ml aliquot was titrated to an end point ph of 8.1 with 0.01 N solution of NaOH. Titratable acidity was calculated using the formula proposed by Hamid and Lopez (2000). The values reported as meq of sodium hydroxide per 1 g of dry nibs. Acidities were measured in triplicates to check the good fermentation and conservation of the samples. Free fatty acids content. About 15 g of dried cocoa beans were carefully shelled manually. Cocoa nibs were frozen in liquid nitrogen before finely grinding in a kitchen-scale coffee grinding (Moulinex, France) to the smallest particle (size < 500 lm). Ten grams of cocoa powder was put in Whatman cartridge and soaked in 350 ml of petroleum ether (Prolabo Normapur, type 40 60 C) for one night. Cocoa butter was extracted on a Soxhlet apparatus for 8 h. After eliminating the solvent in a rotary evaporator, FFA contents were quantified in triplicates by the official method 42-1993 (IOCCC, 1996) as reported earlier (Guehi et al., 2008). Statistical methods All analytical experiments treatments were conducted in three replicates. The experimental data were analysed by using one-way anova using the SAS software GLM procedure (SAS Institute, 2002) and mean comparison using the Newman Keuls test at 95% confidence level (P < 0.05). International Journal of Food Science and Technology 2010, 45, 1564 1571 Ó 2010 CNRA-Université d Abobo-Adjamé

Performance of different drying methods T. S. Guehi et al. 1567 ph 6 5 4 3 2 dried cocoa beans. Indeed these results were not significantly different (P < 0.05) from the ph values of both best fermented beans sourced from West Africa which is around 5.5 (Franke et al., 2008) and the standard Malaysian estate beans, which is about 4.4 4.7 (Nazaruddin et al., 2006). In conclusion, the ph of Ivorian cocoa beans resulted from each treatment was found to be acid as well as all current raw cocoa beans whatever the duration of fermentation. 1 0 Results and discussion C9 EV34 C9EV18 Figure 1 Effect of drying methods on ph of raw cocoa beans. C9: sun drying method EV34: artificial hot air drying method, C9EV18: combination of sun and artificial drying methods. Effect of drying methods on ph of raw cocoa material Figure 1 illustrates the influence of drying processes on the ph of raw cocoa beans. In term of ph, whatever the duration of fermentation process, comparison was also made against the sun-dried beans obtained from other experiments. For fresh beans (0 day fermentation) and cocoa beans fermented during 2 and 4 days, the ph of mixed-dried beans is not significantly different from that of sun-dried beans except the day 6 fermented beans. The sun-dried beans ph ranged from 4.5 to 5.5, while for the oven- and mixed-dried beans registered ph was comprised between 3.8 and 5.2. The differences may be explained by several factors such as exposure times to drying air, drying air temperature, relative humidity in the drying site, nature of drying air flow and the speed with which moisture migrated from the inner cocoa beans structures to their surface as previously indicated by Franke et al. (2008). Indeed artificial and mixed drying processes are faster with little time needed for the cocoa beans to have their moisture reduced from about 60% to around 8% than the natural drying process. So the ph value for sun-dried beans is usually higher (less acidic) than artificially and mixed-dried beans because of the slow and gentle drying process that enable the evaporation of more acetic acid (Hii et al., 2009). The lower ph of unfermented cocoa beans could be explained by the bean pulp which has a low ph of 3.0 3.5, mainly because of the presence of citric acid (Ardhana & Fleet, 2003). Generally, the ph of fermented beans falls within the values reported for most Effect of drying methods on volatile acidity of raw cocoa material The impact of drying processes on the volatile acidity of raw cocoa beans is shown in Fig. 2. The results show that the changes in volatile acidity content of cocoa beans depend on drying methods. Indeed sun-dried beans contain lower volatile acidity than oven-dried beans for both fresh beans and fermented beans. Solardried beans present a volatile content below 1.0 meq of NaOH g while that of oven-dried beans ranged from 1.0 to 2.4 meq of NaOH g whatever the duration of fermentation. For the beans fermented during 6 days, the volatile acidity content of sun-dried beans is not significantly different from the content both of oven and mixed-dried beans. Highest volatile acidity in beans fermented during 2 days could be explained by the accumulation of acetic acid which is mainly produced through oxidation of ethanol in the presence of oxygen by acetic acid bacteria from the second day of fermentation processing (Hii et al., 2009). The lowest volatile acidity content in both sun- and mixed-dried beans is because of the fact that generally volatile acidity is removed as acetic acid from Volatile aicdity content (meq of NaOH per g) 3 2 1 0 C9 EV34 C9EV18 Figure 2 Effect of drying methods on volatile acidity of raw cocoa beans. C9: sun drying method EV34: artificial hot air drying method, C9EV18: combination of sun and artificial drying methods. Ó 2010 CNRA-Université d Abobo-Adjamé International Journal of Food Science and Technology 2010, 45, 1564 1571

1568 Performance of different drying methods T. S. Guehi et al. fermented beans during a slow and gentle drying process as natural process contrary to artificial drying process which would dry faster and break the diffusion path of the acetic acid during moisture removal because of its high drying rate (Jinap et al., 1994a,b). Indeed during drying, acetic acid is evaporated off along with the moisture removal process because of its volatile nature. However, the lactic acids contained inside cannot be evaporated off as it is not a volatile compound (Hii et al., 2009). In conclusion, beans solar-dried from 9 am to 6 pm daily for 1 week and subsequently dried in an oven at 60 C were of comparable quality to sun-dried beans. Both of these were of better quality than beans oven-dried at 60 C as previously concluded by Jinap et al. (1994a,b). A large number of reports have referred to the high acidity and poor flavour development of artificially dried beans compared to sun-dried beans with similar levels of fermentation (Shelton, 1967; Jinap et al., 1994a). Effect of drying methods on free acidity of raw cocoa material Figure 3 shows the effect of drying methods on free acidity of raw cocoa beans. The changes in free acidity content show that artificially dried beans have resulted in high acidity when compared to both sun- and mixeddried beans whatever the duration of fermentation. Indeed, artificially dried cocoa contains 2.5, 4.5, 4.2 and 3.4 meq of NaOH g respectively for fresh beans and beans fermented during 2, 4 and 6 days. If the fermentation is stopped after 4 days, there is a danger of a winning of acidity and flavour acidity (Chong et al., 1978; Duncan et al., 1989) because of the important Free acidity content (meq of NaOH per g) 6 5 4 3 2 1 0 C9 EV34 C9EV18 Figure 3 Effect of drying methods on free acidity of raw cocoa beans. C9: sun drying method EV34: artificial hot air drying method, C9EV18: combination of sun and artificial drying methods. production of acetic acid in the presence of oxygen by acetic acid bacteria from the oxidation of ethanol initially produced by yeasts (Schwan & Wheals, 2004) and other organic acids such as lactic acid. The slight free acidity content of beans fermented during 2 days could be explained by the fact that biochemical changes in the sugar of the pulp around the beans lead to the formation of only the ethylic alcohol and not of acidic compound. Acidity of beans is influenced by several factors and fermentation method is known to be crucial. Meyer et al. (1989) found that fermentation in boxes has been shown to produce more acid beans than either heap or tray fermentation. The lower free acidity content in beans fermented during 6 days might be because of biochemical changes in the heap of fermented beans leading to the formation of slight concentration of lactic acid because of the turnings made at 48 and 96 h of fermentation causing the slowing of lactic bacteria growth, the probable loss of these acidities during fermentation by exudation of acidic liquid and not by chemical degradation (Jinap et al., 1994a). After all, most studies have shown that removal of moisture from beans increases their acidities (Hii et al., 2009). Free acidity content of mixed-dried beans is similar to the quality of sun-dried beans as previously found by Jinap et al. (1994a) which clearly demonstrated that beans air blown for 72 h and subsequently dried in an oven at 60 C were of comparable quality to sun-dried beans. Both of these cocoa were of better quality than beans oven-dried at 60 C (Jinap et al., 1994a). As previously concluded, sun-dried beans and mixed-dried beans have resulted in low free acidity when compared to artificially dried beans because of the sun drying process sufficient time for the volatilisation of acids (acetic acid) from the beans and thereby reducing the acidity. Indeed, during drying, acetic acid is evaporated off along with the moisture removal process because of its volatile nature. However, the lactic acids contained inside cannot be evaporated off as it is not a volatile compound (Hii et al., 2009). So sun drying, if done properly, produces the best quality beans (Crespo, 1985). According to Bonaparte et al. (1998), this method, however, is inefficient and produces beans of inconsistent quality when drying conditions are unfavourable. Furthermore, it appears that drying of fermented beans at higher temperature such as artificially or oven drying process resulted in inferior quality cocoa with respect to beans acidity. High acidic beans are always associated with oven drying process. Effect of drying methods on ammonium nitrogen of raw cocoa material The effect of drying processes on ammonium nitrogen of raw cocoa material is presented in Fig. 4. Ammonium nitrogen content increases according to the duration of International Journal of Food Science and Technology 2010, 45, 1564 1571 Ó 2010 CNRA-Université d Abobo-Adjamé

Performance of different drying methods T. S. Guehi et al. 1569 Ammonium nitrogen content (ppm) 800 700 600 500 400 300 200 100 0 C9 EV34 C9EV Free fatty acids content ( ) 2.00 1.80 1.60 1.40 1.20 1.00 0.80 0.60 0.40 0.20 0.00 Figure 4 Effect of drying methods on Ammonium Nitrogen of raw cocoa beans. C9: sun drying method EV34: artificial hot air drying method, C9EV18: combination of sun and artificial drying methods. C9 EV34 C9EV18 fermentation whatever the drying method. Low ammonium nitrogen content is expected to the short duration of fermentation especially in the early stages, and high ammonium nitrogen content is found in cocoa beans fermented during long duration. Indeed ammonium nitrogen content varies from about 200 to above 600 ppm from the beginning to the end of fermentation. These observations demonstrate clearly that drying methods show no significant differences in ammonium nitrogen content because of the fact that ammonium nitrogen is not a volatile compound. However, ammonium nitrogen might be produced during fermentation from the degradation of cocoa beans nitrogen compounds, such as total polyphenols, flavonoids, epicatechin, catechin; the formation of precursors of pyrazines (Jinap et al., 1994b; Hashim et al., 1997); and the proteolysis of proteins and the oxidation of amino acids and peptides by the suppression of nitrogen under the control of amino acid oxidase and glutamine synthesis enzyme. The presence of relative high concentration of ammonium nitrogen in all samples could be because of the storage of cocoa pods during 4 days before breaking and to the boxes fermentation method. In addition probably, long duration of fermentation could lead to the production of much ammonium nitrogen through amino acid oxidase enzymes activities as previously described by Jinap et al. (1994a) and glutamine synthesis enzyme and then cocoa beans becomes dark in appearance. These enzymes activities originated from both endogenous source (beans) and microbial source such us Bacillus sp. could generate ammonium nitrogen during fermentation (Jinap et al., 1994b). Effect of drying methods on free fatty acids of raw cocoa material Free fatty acids (FFA) content increases slowly but remains below the critical value of 1.75% in cocoa beans Figure 5 Effect of drying methods on free fatty acids of raw cocoa beans. C9: sun drying method EV34: artificial hot air drying method, C9EV18: combination of sun and artificial drying methods. whatever the duration of fermentation (Fig. 5). FFA content varies from 0.4% to 1% for both fresh and fermented cocoa beans. Among three dried samples studied, oven-dried cocoa beans show higher FFA content than both solar- and mixed-dried beans. Indeed artificial drying process leads to the FFA content above 0.70%, while both sun and mixed drying processes produce raw cocoa beans with FFA content below 0.70%. Slighter increasing in changes FFA depending on the fermentation duration indicates no significant difference (P < 0.05) within fermented cocoa beans. So limitation of cocoa beans fermentation duration to 6 days does not seem to be critical to increase the chances for FFA formation. FFA content of mixeddried beans is similar to the quality of sun-dried beans demonstrating that beans air blown for 7 days and subsequently dried in an oven at 60 C were of comparable quality to sun-dried beans. Both of these cocoas were of better quality than beans oven-dried at 60 C. This result is probably because of the break of triglycerides obtained from the liquefaction and the diffusion of cocoa butter during the faster process of oven drying method. Higher variations of FFA content corresponding high standard deviations observed in the same cocoa beans sample are probably because of a high heterogeneity of beans qualities and certainly to the growth of some lipolytic fungi such as Mucor sp. and Rhizopus sp. Indeed circumstantial evidence presented the FFA formation in cocoa beans is because of microbial enzymatic activities in the combination with certain factors such as the quality and the physical integrity of beans and not to endogenous plant lipases as previously demonstrated by Gue not et al. (1976) and Guehi et al. Ó 2010 CNRA-Université d Abobo-Adjamé International Journal of Food Science and Technology 2010, 45, 1564 1571

1570 Performance of different drying methods T. S. Guehi et al. (2008). Microbial lipase activities hydrolysed the ester bonds between fatty acids and hydroxyl functions of glycerol in triglycerides of cocoa butter and liberated free fatty acids which content increased. As the quality of our beans and their integrity were high, a little amount of free fatty acid was formed. Indeed, whatever the drying process, cocoa beans resulted showed FFA content below critical content of 1.75% according to European directive (EEC, 1973). According to Gue not et al. (1976), high FFA contents above 1.75% were mostly observed in poor-quality raw cocoa beans. This observation confirms that all samples obtained from our study are of best quality in term of FFA content and indicates clearly that any appropriate cocoa drying processing do not have an appreciable impact on FFA formation. Conclusion Although drying processes has shown no great effect on ammonium nitrogen and free fatty acids formation in cocoa beans, the changes in acidic characteristics such as ph, free and volatile are largely dependent on the drying methods. Among cocoa samples resulted from our study, sun-dried beans and beans air blown for 7 days and subsequently dried in an oven at 60 C were of better quality than beans oven-dried at 60 C. So sun drying method of cocoa beans is best for optimal quality. Fermentation duration has a significant impact on the formation of ammonium nitrogen which originated from the decomposition of polyphenol compounds. The results obtained from this study are essential in understanding and solving the problems associated with the quality of raw cocoa beans material. Further research is needed to carry out the effect of the storage time before breaking pods and their sanitary quality on physico-chemical and microbial quality attributes of industrial raw cocoa material aimed to improve globally the quality of raw cocoa beans sourced from Coˆ te d Ivoire. Acknowledgments This research was supported by Centre National de Recherches Agronomiques (CNRA) cocoa program of Coˆ te d Ivoire. The authors are grateful particularly to Dr. Firmin ABOUA, Senior Researcher and to the support given by the Unity of Research and Formation in Food Sciences and Technologies (UFR-STA) of Universite d Abobo-Adjame. References Ardhana, M.M. & Fleet, G.H. (2003). The microbial ecology of cocoa bean fermentations in Indonesia. International Journal of Food Microbiology, 86, 87 99. Beckett, S.T. (1994). Industrial Chocolate Manufacture and Use, 2nd edn. Blacki Academic & Professional, Glasgow. Bonaparte, A., Alikhani, Z., Madramootoo, C.A. & Raghavan, V. (1998). Some Quality Characteristics of Solar-Dried Cocoa Beans in St Lucia. Journal of the Science of Food and Agriculture, 76, 553 558. Chong, C.F.Shepherd, R. & Poon, Y.C. (1978). Mitigation of cocoa bean acidity Fermentary investigations. In: Cocoa Biotechnology (edited by P.S. Dimick). Pp. 387 414. Department of Food Science. Pennsylvania State University, USA. Crespo, S. (1985). Judging the quality of cocoa beans. The Manufact Confectioner, May, 59 63. DGTCP (Direction Générale du Trésor et de la Comptabilité Publique de Coˆ te d Ivoire) (2004) Commercialisation du cacao: La Coˆ te d Ivoire s apprête à relever le de fi de la certification. Article 140 online http://www.tresor.gov.ci/actualités. Accessed 08 02 2006. Duncan, R.J.E., Godfrey, G., Yap, T.N., Pettipher, G.L. & Tharumarajah, T. (1989). Improvement of Malaysian cocoa bean flavour by modification of harvesting, fermentation and drying methods The Sime Cadbury Process. Cocoa Growers Bulletin, 42, 43 57. EEC (1973). Directive 73 241 EEC by European Parliament and the European Council relating to cocoa and chocolate products intended for human consumption. Official Journal of the European Communities L 228 of 16 08 1973, pp. 0023 0035. Franke, L.B., Torres, M.Â.P. & Lopes, R.R. (2008). Performance of different drying methods and their effects on the physiological quality of grain sorghum seeds (S. bicolor (L.) Moench). Revista Brasileira de Sementes, 30, 177 184. Guehi, T.S., Konan, Y.M., Koffi-Nevry, R.N Dri, D.Y. & Manizan, N.P. (2007). Enumeration and Identification of Main Fungal Isolates and Evaluation of Fermentation s Degree of Ivorian Raw Cocoa Beans. Australian Journal of Basic and Applied Sciences, 1, 479 486. Guehi, T.S., Dingkuhn, M., Cros, E. et al. (2008). Impact of cocoa processing technologies in free fatty acids formation in stored raw cocoa beans. African Journal of Agricultural Research, 3, 174 179. Guénot, M.C., Perriot, J.J. & Vincent, J.C. (1976). Evolution de la microflore et des acides gras des fèves de cacao au cours du stockage: e tude préliminaire. Cafe Cacao The, 20, 53 58. Hansen, G.E., Olmo, M.D. & Burns, C. (1998). Enzyme activities in cocoa beans during fermentation. Journal of the Science of Food and Agriculture, 77, 273 281. Hamid, A. & Lopez, A.S. (2000). Quality and weight changes in cocoa beans stored under two warehouses conditions in East Malaysia. The planter, Kuala Lumpur, 76, 619 637. Hashim, P., Selamat, J., Ali, A. & Kharidah, S. (1997). Pyrazines formation in cocoa beans: changes during fermentation. Journal of Food Science and Technology, 34, 483 487. Hashim, P., Selamat, J., Muhammad, S.K.S. & Ali, A. (1998). Changes in free amino acid peptide-n, sugar and pyrazine concentration during cocoa fermentation. Journal of the Science of Food and Agriculture, 78, 535 542. Hii, C.L., Law, C.L., Cloke, M. & Suzannah, S. (2009). Thin layer drying kinetics of cocoa and dried product quality. Biosystems Engineering, 102, 153 161. IOCCC: International Office of Cocoa, Chocolate and Sugar Confection (1996). Determination of free fatty acids (FFA) content of cocoa fat as a measure of cocoa nib acidity. Analytical Method no 42 1993. Jinap, S., Thien, J. & Yap, T.N. (1994a). Effect of drying on acidity and volatile fatty acids content of cocoa beans. Journal of the Science of Food and Agriculture, 65, 67 75. Jinap, S., Siti, M.H. & Norsiati, M.G. (1994b). Formation of Methyl Pyrazine during Cocoa Bean Fermentation. Pertanika Journal of Tropical Agriculture Science, 17, 27 32. Jones, K.L. & Jones, S.E. (1984). Fermentations involved in the production of cocoa, coffee and tea. Progress in Industrial Microbiology, 19, 411 433. International Journal of Food Science and Technology 2010, 45, 1564 1571 Ó 2010 CNRA-Université d Abobo-Adjamé

Performance of different drying methods T. S. Guehi et al. 1571 Lehrian, D.W. & Patterson, G.R. (1983). Cocoa fermentation. In: Food and Feed Production with Microorganisms. Biotechnology, vol. 5. (edited by G. Reed). Pp. 529 575. Verlag Chemie, Weinheim, Germany. Lopez, A.S.F. & Dimick, P.S. (1995). Cocoa fermentation. In: Enzymes, Biomass, Food and Feed, 2nd edn. Biotechnology, Vol. 9. (edited by G. Reed & T.W. Nagodawithana). Pp. 561 577. VCH, Weinheim, Germany. Mc Donald, C.R., Lass, R.A. & Lopez, A.S.F. (1981). Cocoa drying a review. Cocoa Growers Bulletin, 31, 5 41. Meyer, B., Biehl, B., Said, M.B. & Samarakoddy, R.J. (1989). Post harvest pod storage: a method of pulp preconditioning to impair strong nib acidification during cocoa fermentation in Malaysia. Journal of the Science of Food and Agriculture, 48, 285 304. Mounjouenpou, P., Gueule, D., Fontana-Tachon, A., Guyot, B., Tondje, P.R. & Guiraud, J.-P. (2008). Filamentous fungi producing ochratoxin a during cocoa processing in Cameroon. International Journal of Food Microbiology, 121, 234 241. Nazaruddin, R., Seng, L.K., Hassan, O. & Said, M. (2006). Effect of pulp preconditioning on the content of polyphenols in cocoa beans (Theobroma Cacao) during fermentation. Industrial Crops and Products, 24, 87 94. Pontillon, J. & Cros, E. (1998). Me thodes analytiques pour le cacao et produits dérivés. In: Cacao et chocolat (edited by J. Pontillon). Pp. 447 545. Paris, France: Lavoisier. Roelofsen, P.A. (1958). Fermentation, drying and storage of cacao beans. Advances in Food Research, 8, 225 296. SAS Institute, Inc. (2002). JMP Software Version 5, Cary, NC. Schwan, R.F. & Wheals, A.E. (2004). The microbiology of cocoa fermentation and its role in chocolate quality. Critical Reviews in Food Science and Nutrition, 44, 205 221. Schwan, R.F., Rose, A.H. & Board, R.G. (1995). Microbial fermentation of cocoa beans, with emphasis on enzymatic degradation of the pulp. Journal of Applied Bacteriology, 79, 96S 107S (symposium supplement). Shelton, B. (1967). Artificial drying of cocoa beans. Tropical Agriculture (Trinidad), 44, 125 131. Tafuri, A., Ferracane, R. & Ritieni, A. (2004). Ochratoxin A in Italian marketed cocoa products. Food chemistry, 88, 487 494. Thompson, S.S., Miller, K.B. & Lopez, A.S.F. (2001). Cocoa and coffee. In: Food Microbiology Fundamentals and Frontiers (edited by M.P. Doyle, L.R. Beuchat & T.J. Montville). Pp. 721 736. ASM Press, Washington, DC, USA. Wood, G.A.R., Lass, R.A. (1985). Cocoa, 4th edn. Longman Inc., New York. World Cocoa Foundation (2008). Cocoa market. Available from: http://www.worldcocoafoundation.org. Accessed 17 04 2009. Ó 2010 CNRA-Université d Abobo-Adjamé International Journal of Food Science and Technology 2010, 45, 1564 1571