D CONTROL (primary processing of tree nuts, peanuts, coconut, oilseeds, dried legumes, and coffee)

D CONTROL (primary processing of tree nuts, peanuts, coconut, oilseeds, dried legumes, and coffee)

Summary Significant hazards a r Aflatoxins in oilseeds, coconut, tree nuts, and especially peanuts.

r Ochratoxin A in coffee. r Salmonella spp.

Control measures

Initial level (H 0 ) r Initial hazard levels should be very low for tree nuts, coconut, oilseeds,

dried legumes, and coffee. r Aflatoxin may already be present at harvest during severe drought.

r Segregate immature and damaged nuts from sound nuts. r Harvest tree nuts directly from trees where possible. r Use good agricultural practice.

Increase (ΣI) r Dry rapidly. Field drying of peanuts can increase aflatoxin levels. r Store at moisture levels <8%. r Control rodent and bird access to equipment and stored commodities.

Reduction (ΣR) r Sort to remove damaged and immature tree nuts and peanuts. r Color sort for aflatoxins in peanuts.

Testing

r Testing for aflatoxins, using large samples, is essential for control of tree

nuts, peanuts, and coconut. r Tests for Salmonella spp. is advisable for peanuts, coconut.

r Testing for ochratoxin A is essential for coffee.

Spoilage

r Controls for significant hazards will usually control spoilage. a In particular circumstances, other hazards may need to be considered.

Comments. General controls for tree nuts, peanuts, oilseeds, coconut, oilseeds, dried legumes, and coffee are summarized above. Each commodity has specific controls that are summarized below.

Tree nuts and peanuts. Control of aflatoxin formation in susceptible crops is very difficult indeed. Tree nuts should preferably be harvested directly from trees, or collected from the ground at frequent intervals. Mouldy, insect damaged or immature nuts should be segregated. Color sorting is possible for some types of tree nuts.

Peanuts should be dug before or at physiological maturity and should be threshed and dried as effi- ciently as possible. Aflatoxin testing and segregation of positive loads at sheller intake is recommended (Read, 1989). Storage before shelling should be cool, dry, and free from insects.

After shelling, nuts should be graded to remove immature and damaged kernels; split kernels are often diverted to peanut butter manufacture at this time. Nuts should be color sorted mechanically or by hand or both, then sampled by adequate protocols and tested for aflatoxins (Tiemestra, 1977). Samples testing positive may be color sorted again, and retested. Blanching (skin removal) and roasting may be used to increase the effectiveness of color sorting. It should be kept in mind that roasted peanuts have

a short shelf life unless packaged in inert atmospheres.

MICROORGANISMS IN FOODS 6

Shelled nuts should be stored in good conditions: free from moisture, at or below 65% RH, and preferably at about 10 ◦

C, to retard development of rancidity. Nuts should be packaged in high quality materials to prevent moisture ingress. Sampling peanuts for aflatoxin testing is a very important procedure in control. A few highly con- taminated kernels may result in unacceptable aflatoxin levels in a large lot of nuts, especially when these are homogenized as in peanut butter or satay manufacture. Sampling procedures have been de- veloped in the United States (Whitaker et al., 1972; Tiemestra, 1977), Australia (Brown, 1984; Read, 1989), the United Kingdom (Coker, 1989) and elsewhere. Two-class sampling plans are in use: samples must be large (8 kg or more) to be effective. It is impossible to guarantee freedom from aflatoxins in processed peanuts or peanut products from a single set of samples, even with the best sampling plans. It is therefore good commercial practice to sample peanuts and test for aflatoxins both at the shelling and processing stages. Only in this way can effective control of aflatoxin in retail peanuts and peanut products be assured.

No effective sorting techniques exist for reducing aflatoxin contamination in peanuts in the shell, pistachios, or cottonseed. Unlike the case of maize, where fluorescence under ultraviolet light can be used as a measure of aflatoxin content, non-destructive chemical testing techniques do not exist for any commodity under discussion here (Steiner et al., 1992).

Mycotoxins other than aflatoxin are rarely reported in tree nuts and peanuts. Control of toxins other than aflatoxins is not recommended at the present state of knowledge.

Coconut. Aflatoxin has been found in coconut, and controls listed above, especially rapid drying, can be used to control the problem. Ochratoxin A has also been reported from coconut (Zohri and Saber, 1993).

Control of bongkrek poisoning in tempeh bongkrek requires process control. Toxin production appears to be related to the concentration of coconut fat in the product (Garcia et al., 1999). Acidifying the coconut press cake to pH 4.5 to 5 with vinegar and incubating at 37 ◦

C, the op- timum temperature for Rhi. stolonifer, is the most appropriate way to suppress toxic bacteria. If Burk. cocovenenans contaminates the product, mould growth is inhibited, so product showing poor mould growth should be treated as suspect and not consumed (Arbianto, 1979; Cox et al., 1997).

NaCl (0.5–0.6%) neutralizes the inhibitory effect of Burk. cocovenenans on growth of R. oligosporus, and greatly reduces production of bongkrek acid (Ko et al., 1979). Higher levels of NaCl inhibited bongkrek acid production even in the presence of 10 7 Burk. cocovenenans. Levels of bongkrek acid and toxoflavin were not detectable in tempeh bongkrek made with a high inoculum (10 4 –10 5 spores per gram) of R. oligosporus in the presence of high NaCl (2%) and pH 4.5–5.5 (Buckle and Kartadarma, 1990).

Oilseeds. Pressing of oilseeds distributes aflatoxin between the oil and the press cake in about equal proportions (Sashidhar, 1993). Aflatoxins are effectively removed from oil by the refining process. Alkali used to remove free fatty acids and other refining processes also detoxify or remove aflatoxins (Parker

and Melnick, 1966). The presence of aflatoxins in sesame oil (Dawar and Ghaffar, 1991) and linseed oil (Sahay et al., 1990) indicates that some food oils are unrefined.

Removing aflatoxin from press cakes is not so simple. Physical techniques such as heating are relatively ineffective. Temperatures above 100 ◦

C are needed to reduce aflatoxin levels appreciably (see Samarajeewa et al., 1990 for a review).

A variety of chemical techniques have been proposed for detoxification. The earliest effective method was solvent extraction, using acetone–hexane–water, 54:44:2 (Gardner et al., 1968) or 80%

457 aqueous isopropanol (Rayner and Dollear, 1968), but it was expensive and impractical. Chlorine is

NUTS, OILSEEDS, AND DRIED LEGUMES

effective for decontamination of aflatoxin from contaminated surfaces and glassware (Trager and Stoloff, 1967) but is of little value in foods, where organic material rapidly denatures the chlorine. Concerns over the safety of chlorine decontamination still exist (Samarajeewa et al., 1990); how- ever, reduction in aflatoxin by more than 75% was achieved using chlorine gas (Samarajeewa et al., 1991).

Hydrogen peroxide (0.5%) at pH 4 will detoxify peanut protein isolates (Rhee et al., 1976), but peanut meal required 6% H 2 O 2 at pH 9.5 to be detoxified (Sreenivasamurthy et al., 1967). Relatively little change occurred in foods so treated, suggesting H 2 O 2 may be a useful treatment under some circumstances. The most commonly recommended method for aflatoxin detoxification has been ammoniation (see reviews by Park et al., 1988; Samarajeewa et al., 1990). Two techniques have been established: atmo- spheric pressure ammoniation at ambient temperature, where product is sealed in plastic bags or bins for 2–3 weeks; and ammoniation at high temperature and pressure, where a 1 h treatment is sufficient (Park, 1993).

Ammoniation has been approved for commercial use on contaminated cottonseed meal or maize in certain states of the United States and for some types of animal feeds in other countries (Park, 1993). However, neither ammoniation nor any other procedure has been widely used commercially. The most effective aflatoxin decontamination technique so far found is to feed the contaminated food, press cake or feed to ruminant animals, other than dairy cows. Up to 400 µg/kg of aflatoxin can be tolerated by beef cattle without appreciable reduction in growth rate or contamination of meat (Pohland and Wood, 1987). Also, mixing of feed ingredients to produce feeds with less than 200–300 µg/kg aflatoxin in total is now widely practised.

It is emphasized that feeds contaminated with aflatoxin must not be fed to dairy cows. Aflatoxins are hydroxylated by mammals as a detoxification mechanism and some of the hydroxylated compounds pass into milk. Aflatoxin M 1 , the hydroxylated derivative of aflatoxin B 1 , is less toxic than B 1 , but still sufficiently so to be unacceptable above trace amounts in the diets of young children. Very low limits have been set for aflatoxin M 1 in milk: in Europe limits of 0.1 µg/kg are common (van Egmond, 1992). As about 1% of aflatoxin B 1 in feed is converted to aflatoxin M 1 (Frobish et al., 1986), such a limit requires that dairy rations contain less than 10 µg/kg aflatoxin in the total diet. Mycotoxins other than aflatoxins have been reported only rarely from oilseeds.

Dried legumes. Storage in conditions below 65% relative humidity in conditions free from insects should be adequate for control of microbiological problems with dried legumes. There is no history of significant microbiological safety issues with dried legumes other than peanuts.

Coffee. Control of ochratoxin A production in coffee can be achieved by quality control measures and good practice. As it appears that infection of coffee beans with fungi capable of producing ochratoxin

A does not occur on the tree to any real extent, careful control of drying and storage can reduce or eliminate this problem. Reduce contamination of fresh cherries by toxin producing fungal species by harvesting cherries only from the tree; do not harvest cherries from the ground. Reduce damage to fresh cherries as far as possible.

Segregate cherries that fall from washers or other equipment. Ensure that rapid drying takes place, by mechanical means where necessary. Avoid leaving cherries exposed to moisture ingress, due to either mist or rain, in the drying yard. Turn over cherries frequently during sun drying. Ensure layers of drying cherries are only 1–2 cm deep.

MICROORGANISMS IN FOODS 6

Careful cleaning procedures to eliminate defectives and husk material from dried green coffee can reduce ochratoxin A levels effectively. The use of gravity sorters and color sorters is recommended.

IV Tree nut, peanut, and coconut processing

A Effects of processing on microorganisms Tree nuts and peanuts. The most important step in further processing of nuts from the microbiological

viewpoint is roasting. Most kinds of nuts used as snack foods are roasted before packaging for retail sale. Large reductions in numbers and kinds of microorganisms occur during this high temperature process. Roasting is accompanied by drying and by some production of inhibitory compounds due to Maillard browning, so that roasted nuts are an inhospitable environment for microorganisms. This can

be an effective method for destroying enteric pathogens such as salmonellae. Due to the low a w of the roasted nuts, the heat generated during grinding in peanut butter manufacture provides little change in microbial numbers, but has the effect of distributing cells or toxins throughout

a large product bulk. This is particularly important for aflatoxins, where high levels in a few nuts can cause unacceptable contamination in a whole batch.

Coconut. Dried coconuts (copra) are commonly further processed only by shredding, which affords no reduction in bacterial load, and indeed may lead to an increase in bacterial counts. Sterilized coconut milk with or without preservatives was found to support the growth of Bacillus spp., Ps. fluorescens, E. coli, Streptococcus faecalis, Saccharomyces cerevisiae, Clostridium spp., Lactobacillus plantarum and Salmonella Typhimurium. Preservatives delayed but did not prevent microbial growth. Some commercial samples of coconut milk were found to contain Bacillus and Clostridium species (Uboldi-Eiroa et al., 1975).

B Spoilage Microbial spoilage is not a serious problem with most nut products. Inadequate drying before packaging,

or poor storage associated with inadequate packaging can lead to visible spoilage from mould growth, or in extreme cases, aflatoxin production.

C Pathogens Problems with mycotoxins in processed nut products are similar to those detailed above for dried

unprocessed nuts. No increases in toxins such as aflatoxin are to be expected, but neither do significant reductions occur. High levels of contamination in a few nuts can lead to contamination of a large batch of peanut butter or similar product during manufacture. This problem can result in considerable losses of processed product.

Contamination with pathogens can occur between roasting and packaging from improperly cleaned and/or maintained equipment. Low levels of contamination of peanuts with salmonellae have been known to occur in this way (Oliver, 1996; Scheil et al., 1988). Pathogens on processed nuts can also be important when the nuts are used as ingredients in high a w products such as yoghurts. Food poisoning due to walnuts incorporated into yoghurt has occurred (O’Mahoney et al., 1990).

Salmonella has been frequently isolated from desiccated coconut (Schaffner et al., 1967; McCoy, 1975; Gilbert, 1982). The source of contamination was traced to animal excreta found on the mill premises, especially in the yard where the coconuts were stacked. Contamination was then passed

459 through the successive stages of manufacture. Two strains of S. Senftenberg were found to be the most

NUTS, OILSEEDS, AND DRIED LEGUMES

frequent contaminants of desiccated coconut from Sri Lanka (Coconut Board, 1969). Contamination with levels of coagulase positive Staphylococcus aureus exceeding 10 2 /g have been reported in com- mercially produced dehydrated coconut from Brazil (Leitao et al., 1973, 1974).