Cocoa, chocolate, and confectionery

10 Cocoa, chocolate, and confectionery

I Introduction

A Definitions Cocoa beans are the seeds of the tree Theobroma cacao L. Seeds develop in pods, each containing

about 30 beans surrounded by sterile pulp. The pulp consists of parenchymatous cells composed of 80-90% water, 8-13% fermentable sugars (mostly glucose and sucrose), about 0.5% non-volatile acids, mainly citric, and small amounts of amino acids. The pH ranges from 3.6 to 4.0 (Lehrian and Patterson, 1983; Biehl et al., 1989).

The raw beans are composed of two cotyledons, a radicle (germ) and a seed coat (testa). The cotyledons contain about one-third water and one-third fat (cocoa butter), the remainder being starch, sugars, purine bases, phenolic components and non-volatile acids.

Cocoa powders (cocoas) are defined in the Codex Standard 105-1981 (Codex Alimentarius, 1981) as products obtained by mechanical transformation into powder of cocoa press cake produced by partial removal of the fat from cocoa nibs or cocoa by mechanical means. Cocoa butter is also pro- duced during this operation and is defined in the Codex Standard 86-1981 (Codex Alimentarius, 1981).

Chocolate is defined in the Codex Standard 87-1981 (Codex Alimentarius, 1981) as the homogeneous product obtained by an adequate process of manufacture from a mixture of one or more of the following: cocoa nibs, cocoa mass, cocoa press cake, cocoa powder including fat-reduced powder, with or without permitted optional ingredients and/or flavoring agents.

Confectionery is a term for which meaning is different in every country (Minifie, 1989) and may cover a very large number of different products manufactured in various ways. Chocolate confec- tioneries such as bars, blocks and bonbons, and sugar confectionery such as boiled sweets, toffees, fudge, fondants, jellies and pastilles are discussed here and descriptions and definitions of the most important products can be found in the Codex Standards 142-1983 and 147-1985. A list of all prod- uct categories according to CAOBISCO, the Organisation of Confectionery Trade Association within the EC, is given in Nuttall (1999). Flour confectioneries such as cakes and biscuits are considered in Chapter 8.

B Important properties After preliminary treatments such as fermentation process described subsequently and drying, beans

ready for further processing are composed of 87% cotyledon containing only 4-5% water, 12% shell containing 8-10% water and 1% germ.

Cocoa powder contains 9-36% fat and less than 8% moisture, its pH being 5.5-6.2 (natural cocoa) or 7.0-8.0 (alkalized cocoa). Essential composition and quality factors of chocolate are defined in Table 10.1, which corresponds to earlier-mentioned Codex Standard 87-1981.

Confectionery products are a very heterogeneous group of products made with dried milk and other dairy products; cocoa and chocolate products; sugar, honey, syrups or sweeteners; nuts, fruits or jams; starches, gelatin pectin or other thickeners; egg albumen; spices, colors, flavors or acidulants.

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Table 10.1 Essential composition and quality factors of chocolates (Codex Alimentarius, 1981, standard 87-1981) Constituents (in % milk on the dry matter) Fat free

Total

Fat free Total fat Product

milk solids Sugars Chocolate

Milk fat

– – – Unsweetened chocolate

– – – Couverture chocolate

– – – Sweet (plain) chocolate

– – – Milk chocolate

≥ 2.5 ≥ 25 ≥ 3.5 ≥ 10.5 ≥ 25 ≤ 55 Milk couverture chocolate

≥ 2.5 ≥ 25 ≥ 3.5 ≥ 10.5 ≥ 31 ≤ 55 Milk chocolate with high milk content

≥ 2.5 ≥ 20 ≥ 5 ≥ 15 ≥ 25 ≤ 55 Skimmed milk chocolate

≥ 2.5 ≥ 25 ≤ 0.5 ≥ 14 ≥ 25 ≤ 55 Skimmed milk couverture chocolate

≥ 2.5 ≥ 25 ≤ 0.5 ≥ 14 ≥ 31 ≤ 55 Cream chocolate

≥ 2.5 ≥ 25 ≥ 7 ≥ 3&≤14 ≥ 25 ≤ 55 Chocolate vermicelli or flakes

– – – Milk chocolate vermicelli or flakes

II Initial microflora

Cocoa beans are raw agricultural products that are exposed during harvesting and subsequent fermen- tation to numerous microorganisms, including Salmonella spp.

Sound, undamaged beans have few, if any, microorganisms inside the cotyledons (Meursing and Slot, 1968). Immediately after cutting and breaking of the pods and removal of the sterile pulp, beans are contaminated with bacteria and fungi originating mainly not only from soil and air but also from the surface of pods, and the hands and tools of harvesters (Ostovar and Keeney, 1973). Microbial contamination with particular microorganisms occurs from fermentation boxes, baskets or trays, which are constantly reused.

Cocoa fermentation is performed in many ways throughout the world depending on the scale of the plantation and traditions. The principal formats include fermentation in piles, in heaps, in baskets, in wooden boxes or in trays (Shaugnessy, 1992).

A very diverse range of raw materials is used in chocolate and confectioneries. The respective chapters should be consulted for data on the initial flora that are introduced into these products.

III Primary processing

A Effects of processing on microorganisms The fermentation of the pulp residues surrounding the beans involves external microbial, as well as

internal enzymatic, processes and is an important step in the formation of flavor precursors (Schwan et al., 1995). During fermentation, the combination of heat and acids leads to the destruction of the germ, thus avoiding degradation of cocoa fat associated with germination.

More than 60% of the microorganisms isolated do not seem to be essential for successful fermentation (Rombouts, 1952). Although differences in the composition of the microflora can be found due to different sampling methods, inhomogeneities of the fermenting mass, mixing of the beans, etc.; three main stages can be differentiated: (i) production of alcohol; (ii) production of acids; and (iii) utilization of acids. In most cases, this succession is not clear-cut and transitional phases or overlaps occur (Hansen and Welty, 1970; Ostovar and Keeney, 1973).

469 Yeasts. During the first few days (1–2 days), yeasts form the predominant population, rapidly me-

COCOA, CHOCOLATE, AND CONFECTIONERY

tabolizing sugars to ethanol, breaking down the mucilaginous pulp by means of excreted pectinolytic enzymes, thus facilitating draining off the sweating fluids (Schwan et al., 1997). Catabolism of cit- ric acid leads to an increase of the pH to about 4.0 (Gauthier et al., 1977; Sanchez et al., 1984, 1985).

By the third day, fermentative yeasts decline and the conditions found, i.e. low oxygen concentration or high concentrations of carbon dioxide, favor the development of lactic acid bacteria (Passos et al., 1984a,b).

Bacteria. In well-aerated portions of the fermenting mass, acetic bacteria become dominant, trans- forming ethanol to acetic acid (Carr et al., 1980, Passos et al., 1984a,b). Both acetic and lactic acids can

be further oxidized to carbon dioxide and water, with a concomitant increase in pH. These exothermic oxidation reactions lead to an increase in temperature of the fermenting mass to 45-50 ◦

C, a temperature that is optimal for spore-forming bacilli. Their development is also promoted by the steadily increas- ing pH value. An important aroma component of cocoa flavor, tetramethyl-pyrazine, was found to be synthesized by Bacillus subtilis (Ostovar and Keeney, 1972; Zak et al., 1972).

Microorganisms found in fermenting cacao in Ghana and Malaysia included yeasts Kloeckera, Can- dida, Saccharomyces, Hanseniaspora, Rhodotorula, Debaryomyces, Pichia and Schizosaccharomyces; acetic acid bacteria-Aerobacter rancens, Aer. xylinum, Aer. ascendens and Gluconobacter oxydans; lactic acid bacteria-Lactobacillus collinoides, Lb. plantarum, Lb. fermentum and Lb. mali; and Bacillus species-Bacillus cereus, B. licheniformis and B. coagulans (Carr et al., 1979). Fermentation is a complex process and it is not always well understood which microorganisms are essential. Few attempts have been carried out with directed fermentations using cocktails of established strains (Schwan, 1998).

Other lactic acid bacteria present in fermenting cacao beans were Lb. casei, Lb. lactis, Lb. bulgaricus, Lb. acidophilus and Streptococcus lactis. Other Acetobacter species included Acetobacter lovaniensis and (from Malaysia) Aceto. aceti and Aceto. roseum. Other bacteria reported were B. sphaericus, Arthrobacter spp., Micrococcus spp. and Sarcina spp. All of these bacteria produced different organic acids associated with cacao fermentation, the major ones being acetic and lactic acids (Jinap, 1994). Malaysian and Brazilian cocoa suffered from excessive acidity and much work has been carried out to overcome this quality problem, thought to be microbiological (Carr et al., 1979, 1980; Chick et al., 1981).

Spoilage of fermenting beans may be due to the development of Aerobacter spp. and Pseudomonas spp. if the pH rises above 5.0 during fermentation (Ostovar and Keeney, 1973).

Molds. Molds may spoil beans at the outer surfaces of the fermenting heap, in particular if the beans remain unturned for 2-3 days (Roelofsen, 1958). However, after degradation of pulp residues and decrease of temperature, mycelia may penetrate the mass if sufficient oxygen is supplied, causing compositional changes, in particular of fatty acids (Hansen et al., 1973; Hansen, 1975).

Aspergillus fumigatus, the most commonly found mold during fermentation, is particularly harmful in destroying testa and permitting penetration by other molds, such as Asp. niger, Asp. flavus, Asp. tamani, Eurotium spp., Penicillium spp. and Mucor spp. (Chatt, 1953; Roelofsen, 1958). However, the presence of mycotoxins has been reported only rarely (Lenovich, 1979). This is probably due to the presence of inhibitors such as methylxanthines (Buchanan and Fletcher, 1978) or due to the fact that contaminated layers, such as shells, are eliminated during further processing.

During subsequent drying the water content of the beans decreases from about 60% to 6-8%. Ar- tificial drying is very quick and does not permit mold growth, whereas sun drying may take 7 days or more, depending on the atmospheric conditions. Populations of microorganisms normally found

on the surface of dried beans consist mainly of mesophilic and thermophilic spores (10 6 –10 7 /g).

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Heat-sensitive bacteria, such as Enterobacter spp., Flavobacterium spp., Microbacterium spp., Strep- tococcus spp., Micrococcus spp. and Streptomyces spp. (about 10 5 cfu/g) as well as yeasts and molds (10 3 –10 7 cfu/g) have been found (Hansen and Welty, 1970; Barrile et al., 1971; Niles, 1981).The only xerophilic mold species isolated from cocoa beans was Asp. glaucus, which may be due to the isolation techniques applied.

Storage in jute bags or silos under unsuitable conditions may cause spoilage of the beans. Molds, in particular xerophilic forms, are able to develop if beans are damaged, improperly dried, or when moisture increases above 8% (Maravalhas, 1966; Hansen and Welty, 1970). Moldy beans are at the origin of off-flavors.

Fungi, especially Asp. flavus, commonly found in cacao ferments, were reported to have remarkable lipolytic activity, and to be the main contributors to spoilage of fermented cacao beans (Kavanagh et al., 1970; Hansen et al., 1973).

Aspergillus and Penicillium were also reported to cause large increases in carbonyl compounds, methyl ketones, 2-enals and 2,4-dienals in moldy beans (Hansen and Keeney, 1970). Most of the carbonyls were dissolved in the fat phase and remained in butter when the beans were pressed (Hansen and Keeney, 1969).

B Methods of processing Before processing, beans are cleaned by screening, air currents and magnets to remove extraneous

materials. Sound, undamaged beans have few if any microorganisms inside the cotyledons (Meursing and Slot, 1968).

Roasting is an important step in the development of chocolate flavor since basic chemical reactions occur during this process (Zak, 1988; Cros, 1995). Roasting (treatments of 15 min to 2 h at 105–150 ◦ C) is the only processing step in the chocolate production allowing for complete destruction of vegetative microorganisms, in particular pathogens such as Salmonella spp.

The oldest and most used method starts with cleaned whole beans. Depending on the type of equip- ment used, and the product characteristics aimed for, roasting of shell-free cocoa nibs or of raw ground (liquid) cocoa mass can also be performed (Heemskerk, 1999). A substantial decrease of the number of spores, i.e. of the total viable count, is achieved mainly by the elimination of shells during winnowing (Lindley, 1972).

Preliminary treatments such as infrared heating (micronizing) or steam-treatment, primarily designed to allow for a better separation of shells and a minimization of fat losses also have a certain bactericidal effect (Minson, 1992, Heemskerk, 1999).

After roasting of the beans, spore-formers such as B. subtilis, B. coagulans, B. stearothermophilus,

B. licheniformis, B. megaterium, may be found (Barrile et al., 1971; Ostovar and Keeney, 1973).

IV Processed products

A Effects of processing on microorganisms Chocolate. The subsequent processing steps of the roasted beans, nibs or liquor such as milling and

refining, mixing, conching, tempering or molding, have only a small influence on the final flora of chocolate. Even if temperatures of 60-80 ◦

C are reached during milling or conching, microorganisms are protected by the low water activity and the high fat content. The final flora is mainly composed of Bacillus spp. (Collins-Thompson et al., 1981), the levels being very much dependent on the original spore load of the raw beans and the type of roasting applied. Slight

471 changes in the distribution of species may be observed after the addition of ingredients such as milk

COCOA, CHOCOLATE, AND CONFECTIONERY

powder or sugar. The presence of non-sporing bacteria such as faecal indicators or salmonellae is due to recontami- nation from the environment or from added ingredients.

Cocoa powder. In the production of cocoa powder, alkalization or dutching is a process developed in the early 1800s whereby nibs, less commonly cocoa liquor, cocoa powder or press cake are heated with alkali (usually sodium hydroxide or potassium carbonate) at temperatures of 85–1l5 ◦

C to obtain desired physicochemical changes (flavor, color) as summarized by Kleinert (1988) or Meursing and Zijderveld (1999). This treatment has a strong sterilizing effect due to the combined effect of water, alkali and heat (Minifie, 1989, Meursing and Zijderveld, 1999).

In the case of cocoa powder, the final flora is almost exclusively introduced during further processing of the almost sterile alkalized liquor, i.e. pressing to extract cocoa butter, breaking of the cake and subsequent grinding of the kibbles, cooling and packaging of the powder (Minifie, 1989). The major recontaminants are sporeformers (Gabis et al., 1970; Mossel et al., 1974). During grinding, heat is evolved and cooling air must be dry to prevent growth of molds in ducts and conveyors (Minifie, 1989). Total aerobic count is therefore very appropriate as an indicator of recontamination of cocoa

powder. Products with <10 3 cfu/g are normal, whereas counts exceeding 10 4 cfu/g may indicate poor manufacturing practices (Meursing and Slot, 1968; Collins-Thompson et al., 1978). Irradiation of cocoa powder has been shown to kill microorganisms effectively, but the organoleptic quality was no longer acceptable (Gr¨unewald and M¨unzner, 1972).

Confectionery products. Due to the wide range of products, processing may include very weak treat- ments allowing for little or no killing effect on microorganisms to very strong treatments, such as boiling, allowing for the complete destruction of vegetative bacteria (Slater, 1986; Vendrell et al., 2000).

B Spoilage Chocolate. Due to its low water activity of 0.4-0.5 (Richardson, 1987), microbial spoilage of chocolate

is not possible. Development of molds on the interface of product and packaging material at very high relative humidities and for chocolate prepared with different types of sugars, thus modifying the a w characteristics of the product, have been reported by Ogunmoyela and Birch (1984). Some xerophilic molds such as Bettsia alvei, Chrysosporium xerophilum and Neosartorya glabra have been isolated from spoilt chocolate and chocolate confectionery. The spoilage of chocolate by Chrysosporium species has been studied and described by Kinderlerer (1997).

Soapiness is a chemical defect of unsweetened or white chocolate (Table 10.1) and is most common in products containing coconut and palm oil, which are rich in short- and medium-chain fatty acids. High levels of lipolytic enzymes from Bacillus spp. or molds persisting in raw materials such as cocoa liquor or powdered milk may also adversely affect fats used in chocolate and confectionery products (Witlin and Smyth, 1957).

Cocoa powder. Spoilage of cocoa by molds is only observed in case of moisture uptake. Cases of development of off-flavors, i.e. the presence of trichloranisole and derivatives, due to mold contamination of packaging material have been reported (Whitfield et al., 1984).

Confectionery product. Microbial spoilage of confectionery products is best considered within the framework presented in Table 10.2.

MICROORGANISMS IN FOODS 6 Table 10.2 Water activity of various

types of confectionery products a Type of product

Water activity

Wafer biscuits

Hard candy

Roasted nuts

a From Richardson (1987).

Confectionery products with water activities ranging between 0.5 and 0.8 are prone to spoilage by xerophilic yeasts or molds due to the formation of gas causing fractures or bursting of products, to the formation of slime, color changes or off-odors and off-flavors, or the secretion of enzymes causing liquefaction of products (Mossel and Sand, 1968; Blaschke-Hellmessen and Teuschel, 1970; Windisch, 1977; Pitt and Hocking, 1985; Miller et al., 1986; Jermini et al., 1987). The most important spoilage yeast is Zygosaccharomyces rouxii, which is capable of growing in sugar syrups of very high soluble solids content (Pitt and Hocking, 1985).

Spoilage fungi may be introduced through raw materials such as dairy products, flours and starches, sugars, nuts and dried fruits or jams (Zeller, 1963; Mossel and Sand, 1968; Legan and Voysey, 1991; Finoli et al., 1994). They may survive due to processing failures as in the case of preserved fruits (Walker and Ayres, 1970) or from recontamination due to their presence in the environment (Dragoni et al., 1989).

C Pathogens The only pathogen of concern in chocolate and cocoa powder is Salmonella spp., as found in different

product surveys (D’Aoust, 1977) and confirmed by epidemiology up to recent years. These products were not recognized as causes of salmonellosis until 1970 and 1973, after two outbreaks. Cocoa powder contaminated with Salmonella Durham and used in confectionery products was at the origin of an outbreak affecting 110 people in Sweden (G¨astrin et al., 1972). In Canada and in the United States 200 people, mostly children with an average age of 3 years, suffered an intoxication from chocolate contaminated with S. Eastbourne (Craven et al., 1975; D’Aoust et al., 1975). Contamination was shown to be due to cross-contamination in the factory due to inadequate separation of clean and unclean zones.

In l982–l983 an outbreak involving 245 people in the UK, again mostly children, was quickly traced to two types of chocolate bars produced in Italy and contaminated with S. Napoli (Gill et al., 1983). Contaminated water penetrating through microleaks of equipment was discussed as a possible source of contamination. Some cases due to S. nima reported in Canada were traced back to chocolate coins imported from Belgium (Hockin et al., 1989). Another case involved more than 300 children in an outbreak linked to chocolate contaminated with S. Typhimurium (Kapperud et al., 1989a). Epidemio- logical studies have shown that the strain was identical to strains isolated from birds in the same region (Kapperud et al., 1989b, 1990). Although for a prolonged period of time no outbreak has been reported,

a survey in Mexico has shown that Salmonella can still be found in finished products (Torres-Vitela et al., 1995). The most recent outbreak has been reported in 2001 involved a few hundreds of consumers and

473 was traced to chocolate manufactured in Germany and contaminated with S. Oranienburg (Anonymous,

COCOA, CHOCOLATE, AND CONFECTIONERY

2002). There are relatively few data on the economical impact of most outbreaks, but available figures compiled by Todd (1985) and Roberts et al. (1989) show they can have a fatal outcome for involved companies.

A particular characteristic of salmonellae in chocolate products is its survival over very long periods of time, up to several years in the case of naturally contaminated products (Dockst¨ader and Groomes, 1971; Rieschel and Schenkel, 1971; Tamminga, 1979). Furthermore, salmonellae show a very high heat resistance in chocolate, which is due to the low water activity and the protective effect of fat. Increased tolerance to heat may also be due to habituation to reduced water activity (Mattick et al., 2000). S. Anatum was found to be the most heat-resistant species isolated from chocolate (Barrile et al., 1970).

C reached during milling, refining or conching do not provide effective destruction (Goepfert and Biggie, 1968) and even considerable overheating (>100 ◦

Temperatures of 70–80 ◦

C) could not achieve complete destruction of small numbers of S. Senftenberg (Rieschel and Schenkel, 1971). Addition of 2% of water allowed decontamination at 71 ◦

C (Barrile and Cone, 1970).

One remarkable aspect is the very low infective dose reported: an average of 1.6 cells/g was de- termined for S. Napoli (Greenwood and Hooper, 1983); of 0.2–1.0 cells/g for S. Eastbourne (D’Aoust and Pivnick, 1976) and as low as 0.005–0.025 cells/g for S. Nima (Hockin et al., 1989). The levels of S. Oranienburg detected in the contaminated chocolate were of the order of 1 cfu/g or less.

The very low infective doses reported may be a consequence of the short intragastric residence and the protective effect conferred by the fat present in chocolate towards gastric acids (Tamminga et al., 1976; D’Aoust, 1977).

Few outbreaks have been traced back to contaminated confectionery products such as traditional torrone (nougat) in Italy (De Grandi et al., 1987), marshmellows (Lewis et al., 1996). In the first two cases the egg preparation used to manufacture the products were identified as the source of contamination. Recently halva, a popular low moisture confectionery in eastern Mediterranean countries and in Middle East, contaminated with S. Typhimurium (Anonymous, 2001) has caused an outbreak. An outbreak of salmonellosis caused by S. Mbandaka in 1996 in several states in Australia has been traced back to peanut butter contaminated with as low as 3 cfu/g (Ng et al., 1996; Scheil et al., 1998). Contaminated peanut butter used to flavor extruded snacks had already been at the origin of an outbreak in the UK and the US a few years earlier (Killalea et al., 1996; Shohat et al., 1996). The behavior of the pathogen in peanut butter is similar to that in chocolate (Burnett et al., 2000).

Staph. aureus survives for several months in chocolate, but is not likely to produce significant levels of toxins as it cannot grow (Ostovar, 1973).

Confectionery does not support the growth of disease-causing bacteria and, only rarely, supports that of mycotoxigenic molds. Salmonellae are unable to grow at the a w of common confections. However, if they enter a confection through the ingredients, they may survive for long periods–up to 8 days in chocolate and egg liqueur stored at 4 ◦

C (Warburton et al., 1993). At the low a w of confections, these bacteria may survive a heating step (Goepfert et al., 1970; Gibson, 1973; De Grandi et al., 1987). Mycotoxins may be introduced through the use of contaminated ingredients as shown by Bresch et al. (2000). Various confection ingredients may contribute to salmonellae–primarily nuts and coconut (Chap- ter 9), 1 chocolate (this chapter), milk (Chapter 16), egg albumen (Chapter 15), flour and starches (Chapter 8), spices (Chapter 7) and gelatin (Chapter 1). Moldy nuts could introduce mycotoxins (Chapter 9).

1 A very recent outbreak due to contaminated almonds has been reported by Chan et al. (2002) underlining the risks related with raw materials of agricultural origin, particularly where unprocessed.

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