Vanilla

Samira Sarter

Introduction

Natural vanilla is an important ingredient in the food industry all over the world. The vanilla bean, the fruit of the climbing orchid Vanilla planifolia, is the main source for the commercial production of vanilla flavor, which consists of a mixture of vanil-lin and many other flavored compounds (Perez-Silva et al., 2006). However, the development of the vanilla flavor in harvested green beans is obtained only after a curing process comprising four stages in the traditional method; that is, killing, sweating, drying, and conditioning. As vanilla requires a humid tropical climate, the drying step is a key element to prevent microbial development, which might compromise its quality. The curing process, which takes several months, will then determine the vanilla bean quality regarding both commercial and safety standards. Over the past 20 years, the number of standards has grown rapidly due to the globalization and free trade. A very high value added product such as vanilla is very dependent on both the regulatory and private standards to be competitive on the international markets. In addition to the numerous technical regulations on food safety, plant protection, and labeling developed at the national and international levels, the private sector has increasingly established new standards covering the supply chain from farm to table. During these different stages of the vanilla beans preparation and storage, microbial hazards can occur at multiple points and then multiply or cross-contaminate other products once present. Thus, a farm-to-table approach is required to identify the hazards and the most effective points to control their occurrence. Since spices and food ingredients might be a source of contaminations (Scheuer and Gareis, 2002), this chapter focuses on the microbiological hazards associated with the processing and storage of cured vanilla beans and on the preventive measures to control those hazards.

Microbial Hazards of Cured Vanilla Beans

Microbial contaminations (mainly molds and bacteria) of the vanilla beans can occur at the harvest and through the several steps of handling and processing. The curing process, besides enabling the biochemical process of aroma, is essential for the control of these microorganisms, which is beneficial for the preservation of the cured beans.

Curing of vanilla beans is a traditionally well-established process in the main countries of production (Madagascar, Mexico, Comores, Reunion, and Tahiti). It is laborious and takes up to six months, depending on the curing procedures adopted by different producing countries. In general, it is mainly based on the following four steps (Dignum et al., 2001):

• Killing the green beans by a thermal treatment (hot water, oven) to stop the vegetative development of the fresh beans.

• Sweating which takes place during the cycles of sunning and sweating, where the beans are spread out in the sun until they are hot, and then wrapped up in blankets and put into an airtight container overnight to maintain their warmth and moisture.

• Drying the beans slowly to prevent the microbial spoilage and to progressively allow the reactions for the development of aroma.

• Conditioning the dried beans in boxes for 3–4 months to obtain the desired aroma and flavor.

The first stage (killing) reduces the initial microbial load on the surface of the green beans. During curing, the major fungi found on vanilla beans are mainly black Aspergillus and green Penicillium strains (Röling et al., 2001). Several bacterial communities are present on the green beans, but after scalding (immersion in hot water 65–70°C for 2 min), this study has reported only the presence of Bacillus strains (Bacillus subtilis, Bacillus firmus, Bacillus licheniformis, Bacillus pumilis, Bacillus smithii) due to their thermophilic nature as being sporeforming microorganisms. For split beans, which have not been scalded, other genera were found such as Xanthomonas, Cellulomonas, Vibrio, and Staphylococcus. B. subtilis (including B. licheniformis as well) are food-spoilage organisms that have been isolated from other herbs and spices and that have also been implicated in food poisoning (te Giffel et al., 1996). Bourriquet (1954) has identified the presence of Aspergillus niger, Penicillium lividum, Penicillium vanillae, and Penicillium rugulosum on vanilla beans from Madagascar and Comores. Another study has shown that the main mold contaminations of vanilla beans consisted of Penicillium glaucum, Trichoderma sp., Aspergillus oryzae, Aspergillus amstelodami, and Xantochpinirous sp. at a total concentration of 8.4 × 10⁴/g (Bachman et al., 1995).

The second key step is the drying step as the moisture content is a major factor in the preservation of cured vanilla beans because low moisture content is essential to prevent microbial growth. The beans should be well aerated while drying to avoid bacterial fermentation, which leads to undesirable flavor, as creosoted vanilla. When properly cured, the water content of beans must be sufficiently low to prevent the growth and activity of microorganisms. Actually, combination of low water with high phenolic content of which vanillin is the major compound, provide an inhibitory effect of the spoilage in cured beans (Havkin-Frenkel and Frenkel, 2006). According to ISO 5565-1:1999 (ISO, 1999), the maximum moisture specification in cured beans is 38% for classes 1 and 2, 30% for class 3, and 25% for class 4. The water content in cured vanilla beans correspond to water activity (a_w) values of, respectively, 0.89, 0.86, and 0.84 (J.M. Méot, pers. comm.). The presence of appropriate water content ranging from 25% to 30% has been reported to result in the desirable texture and appearance of the cured beans (Sreedhar et al., 2007).

Immature beans have been reported to be more susceptible to mold infestation by Penicillium and Aspergillus species (Sasikumar et al., 1992). As Aspergillus and Penicillium are, with Fusarium, the most important genera containing toxigenic isolates, prevention measures based on Good Agricultural Practices and Good Manufacturing Practices should be observed to mitigate preharvest and postharvest contaminations by mycotoxins (FDA, 2009). Mycotoxins are toxic secondary metabolites produced by fungi under specific conditions related to the physiological (microbial growth) and environmental (pH, temperature, a_w, preservatives) conditions. The toxigenic fungi may be eliminated during processing, while their corresponding extracellular mycotoxin remains in the food. The most important mycotoxins for human health risk are described in Table 14.1 (FAO, 2001). Among the fungi reported in vanilla beans, A. niger does not have the ability to produce aflatoxins (Schuster et al., 2002). However, this specie has been reported to produce ochratoxin A (Blumenthal, 2004). A. oryzae does not produce aflatoxins despite its very close taxonomic relatedness to Aspergillus flavus group, a major group that produces aflatoxins in food (Blumenthal, 2004). A. oryzae might produce other myc-otoxin such as 3-nitropropionic acid. P. lividum has been reported to produce citrinin and penicillic acid (Frisvad, 1986). However, the risk, if any, of mycotoxin contamination of vanilla beans needs a detailed assessment (Codex Alimentarius Commission (CAC), 1999). A few research papers have reported the contamination of vanilla beans by mycotoxins. Analyzing a total of 681 samples of spices for the natural occurrence of ochratoxin A (OTA) and ochratoxin B (OTB), Scheuer and Gareis (2002) found one sample of vanilla extract that was positive for OTB at 156 ng/g.

Source: From FAO. 2001. Manual on the Application of the HACCP System in Mycotoxin Prevention and Control. FAO, Rome. With permission.

Immaturity has been linked also to a poor yield of vanillin in the cured beans (Saltron et al., 2002, 2003). Cured beans contain about 2.5% of vanillin when properly prepared. Molds attack the bean from the fruit base, where the vanillin concentration is the least (Bourriquet, 1954). It should be stressed that vanillin has been reported to have antimicrobial properties against different food-related microorganisms (Nakazawa et al., 1982) and some pathogenic, indicator, or spoilage microorganisms: Escherichia coli, Enterobacter aerogenes, Pseudomonas aeruginosa, Salmonella enterica, Candida albicans, Lactobacillus casei, Penicillium expansum, and Saccharomyces cerevisiae (Rupasinghe et al., 2006). In vitro studies have shown that vanillin is effective in molds growth inhibition. The addition of 1000 ppm of natural vanillin for instance inhibited Aspergillus ochraceus growth for more than two months at 25°C, while growth of A. flavus, A. niger, and Aspergillus parasiticus was inhibited by 1500 ppm (Lopez-Malo et al., 1995, 1997). Vanillin has been proposed by these authors for hurdle technology in combination with other antimicrobial factors such as reduced pH and a_w to prevent mold spoilage in fruit purées. Another study using different food-spoilage molds and yeasts have suggested that the aldehyde moiety plays a key role in the antifungal activity of vanillin (Fitzgerald et al., 2005). These authors (Fitzgerald et al., 2004) have also investigated the mode of action of vanillin against Escherichia coli, Lactobacillus plantarum, and Listeria innocua. The antimicrobial activity of vanillin was dependent on the time of exposure, concentration, and the target organism. The in vitro minimum inhibitory concentrations of vanillin were 15, 75, and 35 mmol/L for the three tested strains. This inhibitory action of vanillin was found bacteriostatic rather than bactericidal for all. This study demonstrated that the vanillin disturbs the integrity of the cytoplasmic membrane, leading to the loss of ion gradients, pH homeostasis, and inhibition of respiratory activity of the tested bacteria.

The potential hazards for cured vanilla beans can thus be categorized as follows:

• Microbial spoilage due to bacterial fermentation or molds development

• Contaminations from microbial toxins (mycotoxins from molds)

• Bacterial contaminations related to poor hygienic conditions

To prevent these microbial hazards of cured vanilla beans, the relevant factors that should be controlled are the maturity of the green beans at harvest, the a_w of the processed beans, and the overall postharvest hygienic conditions. To preserve the quality of the beans during the storage that could last several months or up to one year, other parameters such as temperature, humidity, gas composition, and type of packaging should also be taken into consideration.

Microbial Hazards Management and Control

Control measures aim to prevent, eliminate, or reduce food safety hazards to a tolerable level by either controlling initial levels of a hazardous agent, or preventing an increase in its levels, or reducing its levels. An important role of Hazard Analysis Critical Control Point (HACCP) is to help the food producer and processor build safety into processes through identification of key or critical control measures that prevent, eliminate, or reduce hazards to acceptable levels.

The control of microbiological hazards of cured vanilla beans is particularly dependent on effective drying and the subsequent prevention of postprocess contamination and/or growth. The most effective microbial control measure in vanilla beans processing is to dry the commodity such that a_w is very low to support the microbial development, and in particular, the mold growth and/or prevent myco-toxin production from toxinogenic species. a_w is a measure of the water that is available to microorganisms. To prevent the growth of most molds, a_w needs to be ≤0.70. Each toxigenic mold has its own minimum a_w for growth and mycotoxin production and these translate into moisture contents for each commodity. These moisture contents are termed “safe” and would be the critical limit for the control measure. Most spoilage bacteria cannot grow at an a_w ≤ 0.91. Staphylococcus aureus has, however, been found to grow at a_w as low as 0.84. Since molds are able to grow over a wide range of pH values, moisture conditions, and wider temperature range than bacteria, they are more susceptible for contaminating vanilla beans. A critical control point could be placed at the end of the drying process and one critical limit would be the water content or a_w of the beans, which would be easy to monitor in an HACCP system.

Poor hygienic conditions are a major source of contamination of the beans during the whole process. Since the majority of microorganisms are located onto the surface of the beans, the education of handlers is a priority. Hands as well as contaminated gloves and blankets can serve as vectors for the transmission of microorganisms. As reported in the literature, the hands of food workers are of major importance in the transfer of contaminants from person to person, from person to surfaces or vice versa, and from person to food (Guzewich and Ross, 1999). Good housekeeping procedures are necessary to minimize the levels of insects and fungi in storage facilities. Moldy beans should be discarded immediately because they lead to off-odors and lead to cross-contaminations between different lots of the vanilla beans.

From this point of view, the HACCP system is a widely recognized food safety management. It is a systematic approach in identifying, evaluating, and controlling food safety hazards. It is based on a preventive approach from the primary production till the end product sold on the market rather than relying solely on conventional inspections by regulatory agencies. Once an HACCP plan has been developed and introduced into a food operation it must be maintained on a continuous basis. The seven principles are: (1) identifying any hazards that must be prevented, eliminated, or reduced to acceptable levels; (2) identifying the critical control points (CCPs) at the step(s) at which control is essential to prevent or eliminate a hazard or to reduce it to acceptable levels; (3) establishing critical limits at CCPs, which separate acceptability from unacceptability for the prevention, elimination, or reduction of identified hazards; (4) establishing and implementing effective monitoring procedures at CCPs; (5) establishing corrective actions when monitoring indicates that a CCP is not under control; (6) establishing procedures, which shall be carried out regularly, to verify that the measures outlined are working effectively; and (7) establishing documents and records commensurate with the nature and size of the food businessto demonstrate the effective application of the measures outlined. CCP, as defined in the Food Code, means a point at which loss of control may result in an unacceptable health risk (FDA, 2009). These principles have international acceptance and their application have been described by the food hygiene code of the Codex Alimentarius Commission (CAC, 2003), the National Advisory Committee on Microbiological Criteria for Foods (NACMCF, 1992), the ISO 22000 (ISO, 2005), the Food Code of the Food and Drug Administration (FDA, 2009), and the European regulation No 852/2004 (JO, 2004). Since 2006, this new European regulation on the hygiene of foodstuffs has been applied and it is also applicable to foreign operators who produce export food to the European Union. The new hygiene rules take particular account of the following principles:

• Primary responsibility for food safety borne by the food business operator.

• Food safety ensured throughout the food chain, starting with primary production.

• General implementation of procedures based on the HACCP principles.

• Application of basic common hygiene requirements, possibly further specified for certain categories of food.

• Development of guides to good practice for hygiene or for the application of HACCP principles as a valuable instrument to aid food business operators at all levels of the food chain to comply with the new rules.

The Recommended International Code of Practice—General Principles of Food Hygiene (CAC, 2003) is a basis for the implementation of Good Hygienic Practices as it gives the basic rules for the hygienic handling, storage, processing, distribution, and final preparation of food along the production chain. This code contains the Annex on HACCP system and guidelines for its application. In addition, the Code of Hygienic Practice for spices and dried aromatic plants (CAC, 1995) is more specific to our purpose and includes the minimum requirements of hygiene for harvesting, postharvest technology (curing, bleaching, drying, cleaning, grading, packing, transportation, and storage, including microbial and insect disinfestation), processing establishment, processing technology, packaging, and storage of processed products.

Conclusion

Standard specifications are important criteria determining the market value of a high value-added product highly demanded on the international market such as natural vanilla beans. During the postharvest preparation and processing of vanilla beans, microbiological hazards can occur at any stage and could compromise both safety and quality standards of cured vanilla beans. Key common factors for the beans preservation include (1) the maturity of the harvested beans to optimize the vanillin yield as having antimicrobial activity against molds and bacteria, (2) the killing and drying steps of curing to control the microbial development on the beans, (3) the hygienic conditions during the whole postharvest process to control the occurrence of contaminations and cross-contaminations between different batches of beans, and (4) the conditioning step and postprocess storage to control the microbial growth and activity (production of mycotoxins from molds). To help producers and processors implementing these controls along the processing chain, it is necessary to build HACCP system based on sound Good Hygienic Practices (GHP), Good Agricultural Practices (GAP), and Good Manufacturing Practices (GMP) achieving an integrated approach to food safety management. Nevertheless, the most important restrictions for the implementation of HACCP throughout the whole supply chain of vanilla production might be organizational, since the actors chain involve farmers, collectors, processors, and exporters that do not necessarily comply with a vertical coordination, which has been reported to be more efficient for this purpose (Hobbs and Kerr, 1992). In this context, HACCP might face the problem of small operators with limited resources in developing countries.

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