Spices, dry soups, and oriental flavorings

7 Spices, dry soups, and oriental flavorings

This chapter deals with spices, herbs, and dry vegetable seasonings, and covers some oriental flavorings such as soy sauces, fish pastes, and shrimp sauces. It also outlines the microbiology of dry soups and gravy mixes.

I Spices, herbs, and dry vegetable seasonings

A Definitions The International Standard Organization (ISO) defines spices as “vegetable products or mixtures thereof,

free from extraneous matter, used for flavoring, seasoning, and imparting aroma in foods” (ISO, 1995). In the broadest sense “spices” are any parts of various aromatic plant products, with the exception of the leaves, used primarily to season, flavor, or to impart an aroma to foods. The term applies equally to the spices in the whole, broken, or ground form. Most are fragrant, aromatic, and pungent, consisting of rhizome, root, bark, leaf, flowers, fruit, seed, and other parts of the plant.

The so-called “true spices” are products of tropical plants and may be fruits—peppers, allspice, coriander; arils—mace; flower buds—cloves; rhizomes—ginger; or barks—cassia, cinnamon. Spice seeds (e.g. nutmeg, fenugreek, mustard, caraway, celery, and aniseed) may be from either tropical or temperate areas.

Spice essential oils are the volatile aromatic substances prepared by steam distillation of ground spices. Spice oleoresins comprise both the volatile and non-volatile resins present in spices and prepared by solvent extraction of coarsely ground spices using suitable food grade solvents like hexane and ethylene-dichloride.

Condiments are spices alone, or blends of spices, which have been formulated with other flavor potentiators to enhance the flavor of foods. They can be either simple such as celery, garlic, or onion salt, or complex mixtures such as chili sauces, mustard, or chutney. Compounding flavors are mixtures of essential oils and synthetic aromatics used in flavor compositions for flavoring non-traditional candies, biscuits, and soft drinks.

The characteristics and nomenclature of all recognized spices and condiments were reviewed by Pruthi (1983). Herbs are generally defined as leafy parts of soft-stemmed plants (e.g. oregano, marjoram, basil, curry leaves, mints, rosemary, and parsley) of various perennial and annual plants. Herbs are classified as culinary or medicinal herbs depending on their usage. Culinary herbs may, or may not, be strongly aromatic in character, but those used in flavoring of food have distinctive aromatic characteristic. Herbs in medicinal use refer to all plants with medicinal value.

B Important properties Histologically and chemically, spices and herbs are too diverse to be described here; concise presenta-

tions of these qualities are available (Peter, 2001; Tainter and Grenis, 2001). Spices are of interest to microbiologists for three main reasons. They may (i) exhibit antimicrobial activity and occasionally aid in preservation; (ii) support mold growth if improperly dried or allowed

361 to become moist in storage, leading to spoilage and sometimes mycotoxin production; or (iii) contain

SPICES, DRY SOUPS, AND ORIENTAL FLAVORINGS

excessive numbers of microorganisms that may cause spoilage or more rarely, disease, when introduced into food.

Antimicrobial activities of spices and their effect in foods. The role of spices and herbs as antimicrobial agents is discussed in numerous publications. Such studies can be subdivided into four categories: (i) screening studies, (ii) studies on combinations of specific food-borne bacteria (usually pathogens) and specific spices, (iii) studies on antifungal activities; and (iv) studies on specific active components (Tainter and Grenis, 2001).

Spices and herbs containing the most inhibitory essential oils are cloves, thyme, oregano, cinna- mon, allspice, cumin, and caraway (Table 7.1). Few others such as onions and garlic are also known to contain such compounds. However, most herbs and many spices show only little or no antimicrobial activity. The specific antimicrobial agents vary depending on the spice or herb but are often identical with the most important flavor compounds (Peter, 2001). They are usually related to major compo- nents such as eugenol and eugenol derivatives, but others such as allicin, allyl isothiocyanate, and anethol cinnamic aldehyde have been described and are summarized by Farkas (2000). The composi- tion and content of essential oils vary from spice to spice and even within the same spice depending on agricultural practices, geographic and climatic conditions during the growing season (Lawrence, 1978).

Table 7.1 Concentrations of essential oils in some spices and antimicrobial activity of active components

Antimicrobial compounds

Antimicrobial

Essential oil

in distillate or extract

concentration

(ppm) Spice

in whole spice

lab media Organisms Allspice

Compound

1000 (G) Yeast, (Piementa dioica)

Methyl eugenol

9.6 150 (I) Acetobacter, a Cl. botulinum 67B b

Cassis

10–100 (G) Yeast, (Cinnamomum cassis)

1.2 Cinnamic aldehyde

Acetobacter a Clove

Cinnamyl acetate

1000 (G) Yeast, (Syzgium aromaticum)

150 (I) Cl. botulinum, b V. parahaemolyticus c Cinnamon bark

Eugenol acetate

10–1000 (G) Yeast, Acetobacter, a (Cinnamomum zeylanicum)

Cinnamic aldehyde

Cl. botulinum 67B, b

100 (I) L. monocytogenes d,e Garlic

Eugenol

10–100 (I) Cl. botulinum 67B, b (Allium sativum)

Allyl sulfonyl

Allyl sulfide

L. monocytogenes, d-f Yeast, bacteria e

Mustard

90 22–100 Yeast, Acetobacter, a (Sinapis nigra)

Allyl isothionate

L. monocytogenes d Oregano

100 (G) V. parahaemolyticus, g (Origanum vulgare)

Thymol

100–200 (I) Cl. botulinum A, B, E f Paprika

Carvacrol

100 (I) Bacillus (Capsicum annuum) Thyme

Capsicidin

100 (G) V. parahaemolyticus, g (Thymus vulgaris)

2.5 Thymol

Carvacrol

100 (I) Cl. botulinum 67B, b Gram + bacteria, h Asp. parasiticus, Asp. flavus, c,d,i

aflatoxin B 1 and G 1 a Blum and Fabian (1943). b Ismaiel and Pierson (1990a,b). c Farag et al. (1989b). d Karapinar and Aktug (1987). e Tynecka and Gos

(1973). f Bahk et al. (1990). g Beuchat (1976). h G´al (1968, 1969). i Farag et al. (1989a).

(G) = Germicidal; (I ) = Inhibitory

MICROORGANISMS IN FOODS 6

The degree of inhibition depends on several factors such as the concentration of the active sub- stance(s), the food matrix, the method used to determine the inhibitory activity, the solubility of the components in the different components of the food or the target microorganisms. In view of the very large number of specific studies (hundreds) published, it is certainly not possible to provide an exhaus- tive and balanced summary here. However, Shelef (1983) reviewed publications prior to the 1980s, and more recent reviews by Hirasa and Takemasa (1998), Smith-Palmer et al. (1998), Hammer et al. (1999), Dorman and Deans (2000), Tainter and Grenis (2001) and Kalemba and Kunicka (2003) provide good summaries of older and recent research and a starting point to access more detailed and specific papers.

There is little available literature on the practical utilization of spices as antimicrobials in foods. This is probably due to the fact that, in general, the concentrations needed to achieve efficient inhibition frequently impact negatively on the organoleptic characteristics of the food. Consequently, the concen- trations of essential oils in spiced foods (Table 7.1) are generally too low to prevent microbial growth (Salzer et al, 1977; Zaika, 1988) and levels found inhibitory in laboratory media are often insufficient to cause inhibition in food matrices (Evert Ting and Deibel, 1992).

The mechanisms of inhibition of germination of spores, or of growth of vegetative forms, by active components of essential oils are varied, reflecting their chemical diversity. Most studies have been de- voted to the effect of phenolic compounds such as thymol, carvacrol, or eugenol (Ultee et al., 1998,1999; Lambert et al., 2001; Walsh et al., 2003).

C Methods of processing and preservation Herbs and spices have traditionally been traded as dry products allowing for easy transportation and

storage. This is still the case today. Numerous herbs and spices are, however, grown in humid tropical regions, which can make drying difficult, in particular if there is limited availability of equipment for mechanical drying.

The main steps of processing are cleaning, curing, drying, grinding, and pulverizing. Other steps, such as fermentation, are applied in a few instances, for example, for cassia bark to facilitate removal of outer layers, or for allspice berries to develop color and appearance.

Cleaning is required to remove insects, stones, twigs, and soil. Equipment used for this operation utilizes the physical differences between spices and foreign material. Magnets, sifters, de-stoners, air tables and separators, indent and spiral separators are the most frequently used pieces of equipment. Depending on the herbs and spices handled, several items of equipment are used in combination to eliminate different types of foreign material. A detailed description of the different possibilities, as well as of the subsequent grinding operations, is provided by Tainter and Grenis (2001).

In addition to dried products, fresh or frozen herbs are commercialized as well. In the case of fresh products, distribution is often restricted to local areas utilising refrigeration or freezing of herbs, wider distribution is possible. Spices such as garlic are also processed into shelf stable products, using usually mild heat processing, alone or in combination with acidification.

D Types of final products Spices are frequently used whole or ground. For many industrially prepared foods, concentrated spice

extracts, either volatile oils or oleoresins, are used. These extracts have numerous advantages: they can be standardized for flavor strength or color, they do not represent a problem in terms of foreign materials, and are almost sterile. Such extracts are generally obtained by grinding the spice, extracting with water or solvents which are then removed by drying or distillation. Such extracts are either used as solutions or dried, or encapsulated on carriers such as salt, dextrose, maltodextrin, or gum arabic. The manufacture of such extracts is described in detail by Tainter and Grenis (2001) and Peter (2001).

SPICES, DRY SOUPS, AND ORIENTAL FLAVORINGS

E Initial microflora There is little information on the initial microflora of herbs and spices in the field before harvest. In the

absence of such data, it is assumed that the initial microflora is similar to that of other agricultural prod- ucts harvested under similar soil and climate conditions. The relatively few studies of the microbiology of spice plants are largely restricted to the etiological agents of diseases.

Spices and herbs are presumed to contain those microorganisms indigenous to the soil and plants in which they are grown and that are capable of surviving the drying process. Sources of contamination are dust and soil, fecal material from birds, rodents, and other animals, and possibly the water used in some processes such as the soaking of peppercorns to prepare white pepper.

Microbial counts vary according to the region of origin, the year of production, and the harvest and storage conditions prior to drying. Observed counts are thus a reflection of the original bioload, of growth, as well as of die-off. Drying as well as subsequent storage reduces the number of vegetative cells and this die-off is probably enhanced by oxidation and the presence of active compounds in herbs and spices (Farkas, 2000). The remaining flora consists mainly of spore-forming bacteria and molds because of their ability to survive over prolonged periods in dry materials.

Results of surveys of microbial contamination of untreated spices sampled in processing establish- ments or at import are shown in Table 7.2 or in an updated version published by Farkas (2000), which,

Table 7.2 Distribution (%) of Aerobic Plate Counts (APC) and mold counts in untreated spices a,b

Mold count (cfu/g) Spice

Aerobic Plate Count (cfu/g)

35 34 29 26 11 – – Capsicum (chili)

11 9 62 18 61 44 44 7 5 – – Pepper (black)

3 5 50 42 82 32 10 28 5 2 23 Pepper (white)

21 46 29 32 87 3 6 3 – – a Spices not treated with microbiocidal agents.

b Collated from published and unpublished data for dried spices analyzed in North America, Europe, the Middle East, and Japan c N = number of samples: APC = 962, mold count = 808: most of the samples examined for mold count were also examined for

APC. d Numbers are log 10 : <2 = <100; 2–3 = 100–999; 3–4 = 1000–9999, etc.

MICROORGANISMS IN FOODS 6 Table 7.3 Total aerobic bacterial counts and spore counts in

various spice samples a

log 10 (cfu/g) at 30 ◦ C

Spice

Aerobic count

Spore count

Allspice

Caraway seed

Coriander I

Coriander II

Paprika I

Paprika II

Paprika III

Paprika IV

Paprika V

Pepper, Black I

Pepper, Black II

Pepper, Black III

Pepper, White I

Pepper, White II

Pepper, White III

Mixed Spices

a From Neumayr et al. (1983).

however, does not differ greatly. Similar contamination patterns have been shown in other surveys per- formed in different regions (Hartgen and Kahlan, 1985; Shamshad et al., 1985; Pafumi, 1986; Garcia et al., 2001).

In many spices, most of the microbial flora consists of aerobic mesophilic spores, often representing > 50% of the mesophilic aerobic counts (Table 7.3). Species most frequently found include Bacillus subtilis, B. licheniformis, B. megaterium, B. pumilus, B. brevis, B. polymyxa, and B. cereus (Goto et al., 1971; Julseth and Deibel, 1974; Palumbo et al., 1975; Seenappa et al., 1979; Baxter and Holzapfel, 1982; F´abri et al., 1985; Ito et al., 1985; Shamshad et al., 1985). For example, Sheneman (1973) reported that the bacterial flora of dried onions consists mainly of Bacillus species, such as B. subtilis,

B. licheniformis, B. cereus, and B. firmus. The proportion of obligately anaerobic spore-formers is usually small (Inal et al., 1975; F´abri et al., 1985; Kov´acs-Domj´an, 1988). Thermophilic anaerobes and aerobes are found occasionally, sometimes in moderate numbers (Kadis et al., 1971, Pruthi, 1983, Kov´acs-Domj´an, 1988). Consequently, some spices are potentially prolific sources of high heat-resistant spores of bacteria, including thermoduric flat sours, putrefactive anaerobes, and “sulfide stinkers” (Krishnaswamy et al., 1973), which reduce the stability of canned foods stored at tropical ambient temperatures.

Psychrotrophic or psychrophilic spore-formers are not common in spices or herbs, even in those having high mesophilic counts (Michels and Visser, 1976). Psychrotrophic non-spore-forming bacteria (i.e. capable of growth at <7 ◦

C) are generally less numerous in spices and herbs than mesophiles.

de Boer et al. (1985) found that the psychrotrophic count was <10 5 cfu/g in 88% of 143 samples and < 10 3 cfu/g in 53% of samples. Psychrotrophic counts of ≥10 6 cfu/g were found in some samples of thyme, dill, coriander, basil, chervil, and liquorice.

A wide variety of mesophilic non-sporing bacteria may be present in spices (Julseth and Deibel, 1974). Coliforms are often found (Pafumi, 1986; see also Table 7.4) but Escherichia coli is less frequent (Baxter and Holzapfel, 1982; Schwab et al., 1982). However, ∼30% of black and white peppercorns

SPICES, DRY SOUPS, AND ORIENTAL FLAVORINGS

Table 7.4 Frequency of occurrence of coliforms and Escherichia coli in untreated spices a–c

Coliforms

Escherichia coli

cfu/g

Number of samples

Number of samples

a Whole and ground spices. b E. coli was found in the following untreated spices: basil, bay, capsicum, celery seed, coriander, cumin, dill, fennel, garlic, ginger, onion, oregano, parsley, pepper (black), rosemary, sage, and thyme. c

Collated from published and unpublished data for dried spices analyzed in North America, Europe, the Middle East, and Japan.

contained E. coli (Pafumi, 1986). Of 64 samples of parsley from retail and manufacturing outlets and market gardens in Germany, 30 contained E. coli (K¨aferstein, 1976). In a British survey, 42% of 100 samples from 10 different spices and herbs contained E. coli at levels of less than 10 cfu/g (Roberts et al., 1982). In another study, 23% of 53 samples of spices and herbs contained more than cfu/g 10 4 Enterobacteriaceae (de Boer et al., 1985). A survey on four selected spices (black peppercorns, white peppercorns, coriander, and fennel seed) imported into the United States did not show any relationship between the enteric microflora found in spices and that found in associated fecal pellets (Satchell et al., 1989).

Fecal streptococci occur in about half of spice samples, usually in low numbers, and rarely exceeding

10 4 cfu/g (Masson, 1978; Baxter and Holzapfel, 1982). Staphylococci and lactic acid bacteria are rare in spices (Baxter and Holzapfel, 1982; Masson, 1978). Flannigan and Hui (1976) found up to 4 × 10 3 cfu/g thermophilic actinomycetes (mainly Thermoactinomycetes vulgaris) in 6 of 20 samples of ground spices. Spices can play a major source of mold contamination in meat products (Eschmann, 1965; Christensen et al., 1967; Hadlok, 1969). Mold counts of spices are not correlated with aerobic plate counts (Table 7.2). White pepper, black pepper, chili, and coriander seem to be most heavily contami- nated with molds. Although the types of molds isolated from spices can vary greatly, Eurotium species, Aspergillus niger, and Penicillium spp. are usually most prevalent (Table 7.5).

Yeasts have been found in spices in low numbers only (Masson, 1978; Baxter and Holzapfel, 1982). Candida huminicola, Can. parapsilosis, and Can. tropicalis were reported to be the main yeast species in Indian spices (Krishnaswamy et al., 1973).

F Primary processing Harvesting and initial processing. The various spices require widely diverse harvest and post-harvest

methods, which have an impact on the initial microbial content. The main processing factor influencing the microbiological quality of spices is the rapidity of drying to prevent spoilage while retaining their desirable characteristics.

Descriptions, characteristics, production, harvesting and initial processing, usage and functional properties of all major herbs and spices are discussed in great detail by Tainter and Grenis (2001) and Peter (2001).

MICROORGANISMS IN FOODS 6

Table 7.5 Main components of the mold flora of untreated spices as percentage of mold count a,b

Asp. Asp. Asp. Asp. Asp. Asp. Asp. Asp. M.p Pen. Rhiz. (cfu/g)

Mold c Absidia Asp.

terr. ver. spp. spp. spp. Allspice

spp.

can. flav.

– – – – 9 Capsicum (chili)

– – – 18 18 Pepper (black)

– 1 – 2 – Pepper (white)

– – – – – a From Flannigan and Hui (1976); see also Pal and Kundu (1972), Moreau and Moreau (1978), Dragoni (1978).

b Minor components were Thermoascus crustaceus in black pepper; Talaromyces dupontii in fenugreek; Thermomyces lanuginosus in white pepper, Alternaria altenata in red pepper, Fusarium poae in fennel, Syncephalastrum racemosum in ginger and nutmeg.

c Asp., Aspergillus; can., candidus; flav., flavus; fum., fumigatus; gl., glaucus (group); nid., nidulans; nig., niger; tam., tamarii; terr., terreus; ver., versicolor; M.p, Mucor pusillus; Pen., Penicillium; Rhiz., Rhizopus.

d + , present; −, not present.

A Codex Alimentarius Code of Hygienic Practice for Spices and Dried Aromatic Plants has been published. It describes requirements for environmental hygiene in the production/harvesting area, estab- lishment design and facilities, personnel hygiene and health requirements, hygienic processing require- ments, and end-product specifications. It is emphasized that, in addition to good agricultural practices, raw spices should be protected from contamination by human, animal, and other wastes which might constitute a hazard to health of the consumer through spices.

Spoilage Spoilage of spices. Virtually no bacterial spoilage of spices occurs subsequent to harvesting and

drying. However, fungal spoilage may occur prior to drying, or during storage and shipping if relative humidity and temperature are high, or localized wetting occurs.

Mold counts of untreated spices (turmeric, rosemary, and white pepper) held in polyethylene pouches with humidities >80% increased up to 10 8 cfu/g during 1–3 months of storage at 30–35 ◦

C (Ito et al., 1985). Seenappa and Kempton (1980a,b) observed that during storage of dried whole red peppers at 70% relative humidity, Eurotium species grew and colonized stalks, pods, and seeds. At 85% relative humidity, Eurotium species were replaced by Asp. niger, Asp. flavus, and Asp. ochraceus. At 95% relative humidity, Asp. flavus and Asp. ochraceus or Asp. flavus alone were the predominant fungal contaminant.

Insect infestation may contribute to the biodeterioration of spices, by serving as a source of mold spores (Seenappa et al., 1979). Emulsions of mixed essential oils can sometimes support bacterial growth to 10 7 –10 8 cfu/mL in the aqueous phase when inhibitory molecules (e.g. cinnamic aldehyde in oil of cinnamon) partition into a non-inhibitory oil phase (e.g. oil of nutmeg). Adjustment to pH 4 with lactic acid effectively controls this problem (Pirie and Clayson, 1964).

Spoilage of foods by microorganisms from spices. Spices containing excessive numbers of bacterial spores have been associated with the spoilage of canned foods (Bean and Salvi, 1970; Julseth and Deibel,

367 off-flavors and enzymes that impact the textural properties of foods (e.g. pectinase and protease). The

SPICES, DRY SOUPS, AND ORIENTAL FLAVORINGS

quality of processed meats may be adversely affected by the bacteria and molds introduced with spices (Palumbo et al., 1975). However, the potential for spoilage depends on whether the meat is canned and pasteurized or heated to obtain a shelf stable product; fermented; or cooked and refrigerated. Even when there is little likelihood of contaminated spice causing spoilage (e.g. in dry gravy bases or dehydrated soups), spices may introduce microorganisms considered undesirable to industrial or regulatory interests (Kadis et al., 1971; Surkiewicz et al., 1972, 1976).

Pathogens. Herbs and spices are not major contributors to food-borne disease. However, they occa- sionally contain bacteria that can cause infections. Spices are frequently contaminated with toxigenic molds and may sometimes even contain mycotoxins.

Bacteria. Spore-forming microorganisms that are capable of causing gastroenteritis when ingested in large numbers are found in spices, but usually in low numbers. A typical example is B. cereus, which is often reported (de Boer et al., 1985; Powers et al., 1976; Roberts et al., 1982; Pafumi, 1986;

5 Kov´acs-Domj´an, 1988), and which must multiply to at least 10 6 –10 cfu/g in the food to which the spice is added. From 110 samples of various spices tested for prevalence and levels of B. cereus, the organism

was found in 53% of the samples (50–8500 cfu/g) with 89% of the isolates being enterotoxigenic (Powers et al., 1976). In extreme cases, counts up to 10 5 cfu/g have been found (Baxter and Holzapfel, 1982; Pafumi, 1986). B. subtilis and B. licheniformis commonly found in many spices have been linked to food-borne gastroenteritis in a few cases (Kramer et al., 1982) but none of them directly to spices.

A relatively high incidence of Clostridium perfringens has also been found in several spices (Powers et al., 1975; Leitao et al., 1973–1974; de Boer et al., 1985; Roberts et al., 1982; Salmeron et al., 1987) but usually with numbers <500 cfu/g and rarely >1000 cfu/g. Since spores of Cl. perfringens can survive cooking temperatures and will grow in foods held at room temperatures or up to 50 ◦

C, spices must be considered as a potential issue for such foods. Clostridium botulinum has been at the origin of outbreaks related to spices in oil such as garlic (St. Louis et al., 1988; Morse et al., 1990; Lohse et al., 2003) or mustard prepared with fried lotus rhizomes (Otofuji et al., 1987).

Salmonellae have been found in several herbs and spices (Guarinao, 1972; Leitao et al., 1973–1974; Bockem¨uhl and Wohlers, 1984; Pafumi, 1986; Satchell et al., 1989; Bruchmann, 1995) with prevalences ranging between 2% and7% being reported. The presence of salmonellae is of particular concern when herbs and spices are consumed raw or added to prepared foods without further cooking (D’Aoust, 1994, 2000). An oubreak was caused by S. Thompson fresh cilantro (Campbell et al., 2001). The closely related Citrobacter freundii was at the origin of an outbreak with sandwiches prepared with green butter containing contaminated parsley (Tschappe et al., 1995). Black and white pepper have been implicated as vehicles for the spread of Salmonella Weltevreden causing serious cases of salmonellosis (Laidley et al., 1974; Severs, 1974; WHO, 1973, 1974). Black pepper contaminated with S.Oranienburg was also at the origin of an outbreak in Norway in 1981–1982 involving over 120 patients and causing one fatality (CDC, 1982; WHO, 1982; Gustavsen and Breen, 1984).

In 1993, a nationwide outbreak of salmonellosis occurred in Germany, which was traced to con- taminated paprika originating from South America, and paprika-powdered potato chips with as few as

ca. 0.04 salmonellae per gram (Lehmacher et al., 1995). Of the estimated 1000 cases, children below

14 years of age were principally affected. S. Saint Paul, S. Rubislaw, S. Javiana, and monophasic and non-motile strains of rare Salmonella O-groups were isolated from both paprika products and patients. Staphylococcus aureus is rarely found in dry spices (Julseth and Deibel, 1974; Powers et al., 1976). This is true also for Listeria monocytogenes, which was found only at levels <0.04 cfu/g in different

MICROORGANISMS IN FOODS 6

The levels of pathogenic microorganisms reported for a number of spices probably reflects an under reporting of bacteria of public health importance, due to methodological limitations. The presence of inhibitory compounds in a number of spices require special techniques (e.g. resuscitation of injured cells and overcoming inhibition at low dilutions), but still may underestimate the prevalence (Wilson and Andrew, 1976). It has been suggested that diluted spice pre-enrichment ratios of 1:1000 are necessary for cloves, pimento, cinnamon, oregano, and mustard seed to isolate Salmonella with confidence (Pafumi, 1986).

A relatively high incidence of toxigenic molds, including Asp. flavus, Asp. parasiticus, Asp. fumigatus, Asp. ochraceus, Penicillium citrinum, and Pen. islandicum, has been reported in some spices (Christensen, 1972; Mislivec et al., 1972; Pal and Kundu, 1972; Shank et al., 1972a,b; Bhat et al., 1987; Anisa Ath-kar et al., 1988).

Molds.

Aflatoxins have been detected in a range of spices, e.g. black pepper, ginger, turmeric, celery seed, nutmeg, coriander, red pepper, cumin seed and mustard seed (Scott and Kennedy, 1973, 1975; Flannigan and Hui, 1976; Seenappa and Kempton, 1980a,b; Awe and Schranz, 1981; Emerole et al., 1982; Misra, 1987; Misra et al., 1989; Sahay and Prasad, 1990), although the levels recorded were generally low. While certain spices and herbs, especially cinnamon, cloves, and possibly oregano, inhibit mycelial growth and subsequent toxin production, others, particularly sesame seed, ginger, and rosemary, appear to be conducive to aflatoxin production (Llewellyn et al., 1981; Buchanan and Shepherd, 1982).

Nutmeg and red pepper appear to be especially prone to aflatoxin production (Seenappa and Kempton, 1980b), but levels reported are usually <25 µg/kg (Beljaars et al., 1975). In a survey of 21 different imported spices by the U.S. Food and Drug Administration (FDA), nutmeg and chili were found to contain detectable levels of aflatoxins most frequently (Wood, 1989). Total aflatoxin levels as high as 700 µg/kg in Nigeria (Emerole et al., 1982) and 966 µg/kg in Thailand (Shank et al., 1972b) have been reported. A French survey implicated pepper as a source of toxigenic Asp. flavus, which produced high levels of aflatoxin in sausages and pepper cheese (Jacquet and Teherani, 1974). Care must to be taken when extrapolating the results of laboratory studies in which spices were crushed and/or sterilized because this may make them more susceptible to toxigenic molds than when in the natural state.

Although the widespread use of spices makes it important to control contamination by aflatoxigenic and other mycotoxin-producing fungi, the actual ingestion of mycotoxins with spices is generally low in relation to that which occurs in staples such as cereals.

G Processing Large quantities of herbs and spices are traded without further processing. However, depending on the

final use, for example, in ready-to-eat products or in products where growth is possible, spices free of pathogens and very low counts may be required. A number of technologies are known and are, or have been, applied to destroy pathogens, in particular vegetative pathogens such as Salmonella, and to reduce microbial loads.

Summaries of available technologies are provided by Gerhardt (1994), Hirasa and Takemasa (1998), Peter (2001), and Tainter and Grenis (2001).

Gas treatment. In some countries, treatment of spices with low levels of methyl bromide or ethylene oxide has been applied to destroy insects. For many years, the most widely used method to destroy microorganisms in dry food ingredients was fumigation with ethylene oxide or, to a much lesser extent, propylene oxide (Mayr and Suhr, 1972; Gerhardt and Ladd Effio, 1982, Farkas, 1998). Because of the extreme flammability of ethylene oxide, various non-flammable mixtures of ethylene oxide in inert gases (carbon dioxide or a chlorinated hydrocarbon) were applied. These inert gases do not add to or detract

369 from the biocidal activity of ethylene oxide. Such fumigation treatments were normally carried out in

SPICES, DRY SOUPS, AND ORIENTAL FLAVORINGS

specially designed vacuum chambers. The concentration range of ethylene oxide used in treatments for microorganisms in dry food commodities is 400–1000 mg/L. Spices thus treated are frequently, but erroneously, termed “sterile”.

Under industrial conditions, ethylene oxide treatment reduces the aerobic plate count (per gram) of spices by 10 1 –10 4 -fold, depending on the type of spice, the composition of the microflora, and conditions of the treatment. Bacterial spores are only marginally more resistant than vegetative cells (Blake and Stumbo, 1970; Werner et al., 1970). Decreases in mold counts are usually in the range of

10 2 –10 3 -fold per gram, and occasionally greater. The rate of destruction of microbial cells depends on the concentration of the fumigant, temperature, relative humidity of the atmosphere in the fumigation chamber, the moisture content of the product treated (degree of dryness of the microbial cells), the porosity of the product, and the permeability of the packaging material (Hoffman, 1971; Russell, 1971).

The moisture content of the spice to be treated should be as high as possible but compatible with keeping quality (Guarino, 1972). The temperature should be elevated slightly to ∼25–30 ◦

C, to increase the rate of destruction of microorganisms (Coretti and Inal, 1969). At 20–25 ◦

C, fumigation for 6–7 h is required, although this varies depending on the microflora present (Hadlok and Toure, 1973). Chamber temperatures of 50–60 ◦

C may be used; but it is unlikely that the center of bags or barrels of spice in the chamber attain these temperatures. A mixture of ethylene oxide and methyl formate was recommended for those few spices (turmeric and mustard seed) whose color and flavor are adversely affected by ethylene oxide (Mayr and Suhr, 1972).

In some countries, propylene oxide is used in preference to ethylene oxide. On a weight basis, it is less bactericidal than ethylene oxide, but it is less likely to form toxic by-products. Due to toxicological considerations, the use of these gases is more and more discouraged (Gerhardt and Ladd Effio, 1983; Neumayr et al., 1983; OSHA, 1984; EEC, 1989). For a more ex- tensive discussion of gas treatment, see also ICMSF, (1980a, Vol. 1, Chapter 10).

Irradiation. Ultraviolet irradiation has little penetrating power and has limited effectiveness in re- ducing bacteria on spices (Walkowiak et al., 1971) even with continuous agitation to expose surfaces (Eschmann, 1965).

Research and development over some 40 years on a large variety of dry food ingredients and herbs has proved that ionizing radiation is an effective process for destroying contaminating organisms (Farkas, 1988; Steele, 2001). For practical reasons, ionizing radiation applied to food is limited to gamma rays

from isotopic sources such as 60 Co and 137 Cs, machine produced X-rays (of energies up to 5 MeV), or accelerated electrons (with energies up to 10 MeV). Gamma rays and X-rays have a high penetrating capacity when compared with accelerated electrons. Penetration depends on the kinetic energy of photons or electrons and on the density of the product to be treated. Except for differences related to penetration and exposure time, electromagnetic ionizing radiations and electron beams are equivalent in food irradiation and can be used interchangeably (Josephson and Peterson, 1982–1983; Urbain, 1986).

Depending on the design of the irradiation facility and requirements, products can be treated in bulk. Spices are best packaged before irradiation to avoid re-contamination after radiation treatment. Because treatment of food with ionizing radiation causes almost no temperature rise in the product, irradiation can be applied through packaging materials including those that cannot withstand heat.

The primary aim of radiation processing of spices is the inactivation of bacterial and mold spores. Depending on the number and type of microorganisms and the chemical composition of the commodity,

a radiation dose of up to 20 kGy may be required to achieve commercial “sterility” (i.e. a total viable cell count of <10 cfu/g) in natural spices and herbs. However, doses of 3–10 kGy can reduce viable cell counts to a satisfactory level (from 10 5 –10 7 cfu/g to <10 3 –10 4 cfu/g) without affecting quality attributes (Zehnder and Ettel, 1982; Sugimoto et al., 1986; Munasiri et al., 1987; Farkas, 1988; Singh

MICROORGANISMS IN FOODS 6

et al., 1988; Narvaiz et al., 1989; Ito and Islam, 1994, Nieto-Sandoval et al., 2000). The number of bacterial spores normally decreases by at least 10 2 -fold after irradiation with 5 kGy. There is little difference in the radiation resistance of aerobic spores most frequently occurring in spices (with an apparent overall D-value varying between <1.7 and 2.7 kGy). This is not much affected, at least from the practical point of view, by the water activity of the spice. In fact, D-values derived from irradiation of spice samples are similar to those obtained for related pure strains of aerobic spore-formers in aqueous

systems (Briggs, 1966; H¨arnulv and Snygg, 1973). Slightly higher D 10 values were obtained for electron beams or converted X-rays irradiation than for gamma-ray irradiation which was explained by the much higher dose rate of machine sources imparting less oxidation damage to microorganisms (Ito and Islam, 1994).

Sulfite-reducing clostridia, usually present in low (<10 3 cfu/g) populations, can be eliminated by

4 kGy (Neumayr et al., 1983). Thermophilic spore-forming bacteria, of great importance to the canning industry, can be essentially eliminated with the same radiation doses as those necessary to cause a sufficient reduction of the total aerobic viable counts. Bacteria of the family Enterobacteriaceae are relatively radiation sensitive, even in dry ingredients, and in most cases a dose of ∼5 kGy is sufficient for their elimination. A dose of 4–5 kGy can eliminate molds at least as effectively as ethylene oxide treatment. The germicidal efficiency of irradiation is much less dependent on moisture content or humidity than is ethylene oxide (Farkas et al., l973; Farkas and Andr´assy, 1984).

Table 7.6 illustrates the effect of irradiation on the microbial content of spices and the effectiveness of radiation for the treatment of black pepper. No post-irradiation recovery of surviving microorganisms has been observed during storage of irradiated spice samples. On the contrary, a further decrease of survivors has been observed in some cases (Bachman and Gieszczynska, 1973). The surviving microflora of spices treated with “pasteurizing” doses of ionizing radiation has lower heat and salt resistance, and is more fastidious relative to pH, moisture, and growth temperature requirements than that of untreated spices, which reduce the microflora’s ability to survive and grow in processed food products (Farkas et al., 1973; Kiss and Farkas, 1981; Farkas and Andr´assy, 1985). The heat-sensitizing effect of irradiation increases with increase in radiation dose, and the weakening of the surviving microflora in irradiated dry ingredients is permanent and does not diminish during normal storage of the ingredients (Farkas and Andr´assy, 1984).

A code of good irradiation practice for the control of pathogens and other microflora in spices, herbs, and other vegetable seasonings has been prepared by the International Consultative Group on Food Irradiation (ICGFI, 1988). For a more extensive discussion of irradiation treatments, see ICMSF (1980a, Vol. 1, Chapters 2 and 3).

Table 7.6 Microbial decontamination of black pepper by gamma radiation a

log 10 cfu/g at a dose of (kGy)

Group of microorganisms 0 2 4 6 8 10 Total aerobic mesophiles

8.0 6.2 5.2 3.9 2.1 < 1.8 Aerobic mesophilic spores (a) Surviving 1min at 80 ◦ C 7.7 6.6 4.7 3.0 1.8 < 1.8

– – Anaerobic mesophilic spores (a) Surviving 1min at 80 ◦ C 7.5 6.1 3.1 < 1.8 < 1.8 < 1.8 (b) Surviving 20min at 100 ◦ C 5.9 < 1.8 < 1.8 < 1.8 < 1.8 < 1.8

(b) Surviving 20min at 100 ◦ C 6.0 2.9 0.2 –

Enterobacteriaceae 4.7 2.8 1.7 1.1 < − 0.5 Lancefield Group D streptococci

4.9 1.7 0.4 < − 0.5 < − 0.5 Molds

– a From Soedarman et al. (1984).

371 Other decontamination methods. Because of heat sensitivity of the delicate flavor and other essential

SPICES, DRY SOUPS, AND ORIENTAL FLAVORINGS

components of many spices and herbs or some other specific functional properties, the normal heat sterilization process cannot be applied (Thiessen and Hoffmann, 1970; Thiessen, 1971; Maarse and Nijssen, 1980). Hot ethanol vapor has been suggested as an alternative “gaseous sterilization” treatment of natural spices and other foods (Wistreich et al., 1975). This treatment may result in the desired antimicrobial effect with whole seeds, i.e. whole pepper, but it is not feasible for ground or leafy spices (Neumayr and Leistner, 1981). Another chemical method is the reduction of viable cell counts by acidification with hydrochloric acid followed by neutralization, i.e. in situ salt formation (Scharf, 1967). Although such a procedure has been examined for decontaminating paprika, and the resultant paste is suitable for use in some meat products (Huszka et al., 1973), this treatment is applicable only over a very limited range of conditions and commodities.

Microwave treatment has little practical utility because microwave heating is seriously hampered at the low moisture content of dry commodities (Vajdi and Pereira, 1973). Due to the heterogeneity of products and the dielectric field, the heating effect is very uneven in these materials. This results in significant adverse changes in sensory quality (Neumayer et al., 1983; Dehne et al., 1990).

A process utilizing superheated steam created interest in the treatment of spice seed, berries, and roots or rhizomes (Dehne et al., 1992a,b). However, heat/steam is less useful for products such as leafy herbs, which lose flavor and color, and ground products such as onion and garlic, which cake and must

be re-milled. Another thermal method proposed to decontaminate spices is to treat them in an extruder (USP, 1985). Different pressure–time–temperature combinations have been tested, and the method is in commercial operation. Cooking extrusion according to a UK patent (G.B. 2236 6588, published 1993)

achieves >10 4 -fold reduction of viable counts by virtue of shear force, temperature shock, pressure differential, and probably the antimicrobial effect of spice oils within a high stress environment. This process can successfully handle color-sensitive materials, e.g. herbs and paprika, due to the short time at high temperature in the extruder (Tuley, 1991). Studies performed by Almela et al. (2002) have made use of HTST treatments under overpressure to treat paprika with only minimal losses in color.

A steam treatment has been developed for whole spices (Sorensen, 1987, 1989), which utilizes

a specific fraction of extract from food grade beef bones as coating material to prevent losses of volatiles during the thermal process. The treatment is claimed to be feasible for most spices, with some exceptions where excessive darkening (paprika and garlic), loss of green color (dill), or development of roasted/cooked taste (onion) may cause problems.

Because thermal treatments required for a large reduction of viable cell counts result in serious losses of sensory or functional properties of products (Modlich and Weber, 1993), the various alternative modern heat processing methods described in this chapter are suitable mostly for cell-count reduction of slightly to moderately contaminated and unground spices, or, for special cases such as a reduction of molds. As noted by Dehne and B¨ogl (1993), the problem of highly contaminated natural spices cannot be addressed simply through the decontamination processes, and must include the introduction of suitable hygiene measures in the producer countries.