E CONTROL (mayonnaise and dressings)

E CONTROL (mayonnaise and dressings)

Summary Significant hazards a r Salmonella spp.

E. coli O157:H7. r L. monocytogenes.

r Staph. aureus.

Control measures

Initial level (H 0 ) r Use pasteurized ingredients (i.e. egg, herbs, spices) or source raw material of appropriate specification from approved suppliers.

Reduction (ΣR) r Pasteurize starch or water phase. r Use stable formulations (dependent mainly on pH, acetic acid) that cause

die-off of infection pathogens.

Increase (ΣI) r Use a stable product formulation (pH ≤4.5; at least 0.2% undissociated

acetic acid in the aqueous phase). r Avoid recontamination; physically separate ingredients and processed

products. r Use suitable, hygienic equipment and process hygienically (incl. proper

cleaning). r Store final product dry; prevent condensation.

Testing

r Ingredients may be contaminated with pathogens of concern at low rates (Salmonella spp., for instance, in raw spices and herbs is about 1%);

sampling and testing using reasonable sample numbers is not feasible. r When a stable product formulation is used, process control is sufficient to

assure consumer safety.

Spoilage

r Spoilage can occur due to acetic-acid resistant microorganisms (i.e. certain yeasts and lactic acid bacteria). The major spoilage problems can

be controlled by selecting suitable stable formulations, by preventing contamination via raw materials and the process environment, by hygienic packaging, and chilled storage, and distribution.

a In particular circumstances, other hazards may need to be considered.

Control measures. To achieve microbiologically safe and stable products, a process design based on

a cold process is generally adequate. With respect to product safety, the formulation should assure that pathogens cannot multiply in case contamination does occur and that viable infectious pathogens are not present in the product at the point of consumption. For microbiologically sensitive products it is most important to prevent contamination originating from raw materials or the processing environment. This means that for each product one should consider whether ingredients used present a potential for contamination. Use of decontaminated ingredients or pasteurization of contaminated ingredients in a starch or water phase will control such a hazard. Chilled storage and distribution could in addition be necessary.

MICROORGANISMS IN FOODS 6

Processing. The production of mayonnaise, dressings, and other emulsified sauces has to be carried out in such a way that (re-)contamination with pathogens is prevented and that spoilage of the final product does not occur. Product and process design and implementation in an actual manufacturing process should follow the principles of HACCP (APHA, 1972; NRC, 1985; ICMSF, 1988). Because of the use of egg and other raw material ingredients in emulsified products, pathogens of concern are in particular Salmonella spp., E. coli O157:H7, L. monocytogenes, and Staph. aureus.

Formulation. To prevent growth of pathogens in emulsified sauces, it is recommended that a com- position is chosen that does not permit growth of any relevant pathogen. pH alone will be inadequate to control pathogen growth in most emulsified products. Under optimal conditions, for instance, Salmonella spp. and L. monocytogenes can grow at pH values as low as pH ± 3.8 and 4.4–4.6, respectively. However, in combination with sufficient acetic acid, multiplication stops at a much higher pH. Stable formula- tions can be selected when the aqueous phase composition of a product is known by calculation or

analysis. The levels of undissociated acetic acid, salt, and sugar can be used to predict stability by using the spoilage prediction chart developed by Tuynenburg Muys (1971). The effects of other acids (e.g. lactic acid), preservatives (e.g. sorbic acid) and natural antimicrobials (e.g. mustard or olive oil) can

be considered as well. When a new formulation is considered that is significantly outside the present boundaries of knowledge, its safety and stability should be established by challenge testing, preferably using selected acetic acid-resistant yeasts and lactobacilli.

Michels and Koning (2000) consider that, as a rule, no growth of pathogens will be possible when the emulsified product has a maximum equilibrium pH of 4.5 and at least 0.2% undissociated acetic acid in the aqueous phase. This corresponds to a total acetic acid level of roughly 0.2% at pH 3.0 or to 0.3% at pH 4.5, which is well below the level used in most commercial products.

Decontaminated ingredients. For the industrial manufacture, the absence of infectious pathogens from the final products can best be ensured by the specific use of pasteurized egg preparations and by pasteurization of all other components that may present a microbiological hazard, such as some dairy ingredients or herbs and spices. Pasteurized egg preparations, sourced from approved suppliers (one that controls pathogen hazards by a validated HACCP-based system), are indeed used as the raw material in most industrial productions; sometimes the egg is pasteurized in-house for a second time directly before processing, because a very low incidence of Salmonella spp. and L . monocytogenes may occur in commercially available pasteurized liquid egg. Recommended pasteurization temperatures for liquid eggs vary from 55.6 to 69 ◦

C and the times of exposure vary from 1.5–10 min. In many countries, a specific minimum time–temperature combination is mandatory. The heat treatment required for cooking of a starch phase is generally a few minutes at 85 ◦

C, which is well above what is needed for microbiological decontamination. Where ingredients are heated in the acetic acid-containing water phase, most lactobacilli and yeasts are inactivated by a few minutes at 70 ◦ and heating to 65 ◦

C is frequently adequate.

A common source of acetic acid-resistant spoilage organisms is improperly or inadequately cleaned equipment used for manufacturing mayonnaise and dressings. The same may hold for the processing environment. During process design, appropriate hygienic equipment well suited for CIP should be selected. The lay-out of the process line should also be such that the environment is easily cleaned and that cross-contamination from raw ingredients to decontaminated product is prevented. Proper manual cleaning may still be required for traditional colloid mills, fillers, and other equipment that are difficult to clean by CIP alone because of for example crevices in the equipment construction.

Hygienic processing.

493 Packaging. The glass jars, tubs or other containers used for packaging mayonnaise and dressings are

OIL- AND FAT-BASED FOODS

normally free of acetic acid-resistant spoilage organisms and thus there is no need for decontamination or for extremely clean packaging materials.

Distribution. For ambient stable mayonnaise and dressings, distribution is not a problem. For chilled products, temperature of distribution and retail is a point to control and monitoring of temperatures in the chilled chain will help to find and correct deviations.

Consumer use. Most emulsified sauces discussed are only spoiled by acetic acid-resistant organ- isms, which are not widespread in the consumer’s home. Consequently, these products will not easily spoil during consumer use. However, when mild compositions with low acetic acid levels are put on the market, the possibility of spoilage during consumer use should be considered. Such spoilage can be controlled largely, but not completely, by limiting the shelf-life at ambient temperatures of open prod- ucts or by recommending chilled storage after opening. Labeling instructions can thus be important for vulnerable products.

III Mayonnaise-based salads

A Definitions Mayonnaise-based salads or dressed salads are simply mixtures of a variety of foods described in other

chapters of this book with a mayonnaise base. The components may consist of chicken, meat, egg, fish, shellfish, potato, vegetables, herbs, pasta, fruits, or nuts. Apart from the mayonnaise and the main components mentioned, starch, sugar, spices, organic acids, preservatives, and flavors/colors may be present. A specific definition does not exist.

B Important properties Due to the vinegar of the mayonnaise base or the additional acids used, the dressed salads generally have

between pH 4.0–5.5; the acetic acid level in the aqueous phase (often between 0.2–0.5%) is typically much lower than that of mayonnaise itself. Most mayonnaise-based salads are kept refrigerated to extend their shelf-life.

C Methods of processing and preservation Mayonnaise-based salads are made by mixing ingredients at ambient or chill temperatures with a

special thick mayonnaise or dressing. Some ingredients, like chicken or meat, are cooked but others may not be. Typical ingredients that are used without a heat treatment are raw vegetables. Because they could introduce a very broad spectrum of microorganisms, vegetables are well cleaned and sometimes marinated in special brines to reduce their microbial load. When the complete salad has been mixed, it is packed in consumer-sized tubs or in larger containers for sale by a retailer. When prepared from chilled components in a well-chilled environment, salads can be packed and palletized directly; otherwise quick chilling after packing is required. Acetic acid levels in the aqueous phase of mayonnaise based-salads are still quite low, and therefore these products may be quite vulnerable to spoilage; preservatives (i.e. sorbic acid and benzoic acid) may help to improve stability. The refrigerated shelf-life of a typical mayonnaise-based salad may vary between 2–8 weeks, depending on initial contamination, pH, level of inhibitory acid, and level/type of preservatives (if any) present.

MICROORGANISMS IN FOODS 6

D Microbial spoilage and pathogens The initial microflora of mayonnaise-based salads is made up of the microbial load of the raw materials

used. Raw materials used should not introduce pathogens or significant numbers of spoilage organisms. Control of the possible proliferation of the initial microflora depends on the formulation of the product, whether pasteurization is used and whether hygienic conditions are adhered to. A low pH and a suitable level of organic acids in the product formulation, minimize the growth of most spoilage bacteria and pathogens. It is preferred to use pasteurized, or even sterilized, raw materials. Pasteurized materials may

be put into an acid brine or salted to render them ambient stable. Several raw materials (e.g. hand-peeled cooked shrimps, vegetables, herbs, and spices) are difficult to obtain with sufficiently low counts and in-house measures (e.g. steam decontamination of herbs and spices) should be taken to reduce their counts upon arrival at the manufacturing site. When it is not possible to effectively eliminate spoilage organisms (e.g. yeasts and lactobacilli in raw herring), the absence of infective pathogens must be ensured by selecting raw materials from approved suppliers. In addition to GAP and other specific control measures for the raw materials, product formulation, processing and expected shelf-life should all be adequate to control the expected level of initial contamination.

Spoilage. Because of the low pH and the presence of a particular level of organic acids, certain yeasts, lactic acid bacteria, and molds are the most frequent cause of spoilage of mayonnaise-based salads. Characteristic spoilage yeasts in, for instance, coleslaw are Saccharomyces exiguus and Sacc. dairensis (Brocklehurst et al., 1983). Many other yeasts (e.g. Sacc. cerevisiae, Pichia membranaefaciens, Z. bailii, Z. rouxii, Sporobolomyces odorus, Trichosporon beigelli, Torulaspora delbrueckii, Can. sake, Can. lambica, Can. Vini, and Yarrowia lipolytica have also been isolated from salads (Baumgart et al., 1983; Brocklehurst and Lund, 1984; Bonestroo, 1992). Molds produce visible spoilage, whereas yeasts produce off-flavor, gas formation, or colonies visible as surface growth.

Multiplication of lactobacilli in mayonnaise-based salads may lead to high counts, which are not always accompanied by spoilage. Gas-producing lactobacilli or rope-forming strains produce more evident signs of spoilage. The most frequent lactic acid bacteria that grow in dressed sal- ads are Lb. plantarum, Lb. buchneri, and Lb. brevis. Less common types are Lb. leichmannii, Lb. delbrueckii, Lb. casei, Lb. fructivorans, Lb. confusus, Leuconostoc mesenteroides, and Pediococcus damnosus (Baumgart et al., 1983; Erickson et al., 1993). All of these organisms come primarily from vegetables and pickles or the processing environment. Although sorbic and benzoic acids inhibit yeasts, they have little effect on lactobacilli. In the case of benzoic acid, this is because a significant proportion of benzoic acid added partitions into the oil phase of a salad. The rather high pH of salads may decrease the amount of undissociated benzoic acid in the aqueous phase.

A significant consideration for both stability and safety is that large pieces of meat may remain at a relatively high pH within the salad tissues, because the acids diffuse very slowly through solid foods. The equilibrium pH value may be higher than that of the freshly made product, so that a variety of organisms can grow. Marinating pieces of meat or fish (such as herring) to reach a sufficiently low pH before mixing and proper chilling immediately after production may adequately reduce growth of spoilage organisms or pathogens.

Pathogens. Food-borne illness caused by eating contaminated mayonnaise-based salads has occurred when raw materials or ingredients used contain toxins (e.g. potato salad with botulinum toxin, Seals et al., 1981) or that are contaminated with infectious pathogens. An outbreak of typhoid fever in 1974 in Germany, which resulted in 417 cases and five deaths, was associated with contaminated potato salad (H¨upper, 1975). Two related incidents of salmonellosis were caused by S. Indiana in a salad product served at a European Union Summit Conference in Maastricht and in a cold buffet eaten at a family dinner

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495 (Beckers et al., 1985). In the first incident, numbers of S. Indiana reached levels of 10 7 cfu/g, whereas in

the latter incident mainly cross-contamination with S. Indiana at a low infective dose without significant multiplication was suspected. Evidently, food-borne bacterial pathogens can survive well in chilled salads. In salads with an elevated pH, held at 22 or 32 ◦

C, Salmonella and Staph. aureus grew well within

C (Doyle et al., 1982). Kurihara et al. (1994) demonstrated rapid growth of S. Enteritidis at 25 ◦

24 h in chicken salad (pH 6.1) and in ham salad (pH 5.2), whereas no growth occurred at 4 ◦

C in potato, egg, and crab salads (pH was 5.72, 7.11, and 6.51, respectively) made with 15% of homemade mayonnaise (pH 4.75). This mayonnaise contained 0.1% of acetic acid which, assuming a dry matter level of 30%, results in only 0.02% of total acetic acid in the salad’s aqueous phase and thus only a trace of undissociated acetic acid to prevent pathogen multiplication (0.002% at pH 5.7 and even less at the other pH values).

Pathogens other than salmonellae also have been associated with food-borne illness from mayonnaise-based salads. In 1981, enteroinvasive E. coli was associated with eating potato salad on a cruise ship (Snyder et al., 1984). Shigella is another significant cause of illness and Smith (1987) refers to at least 11 outbreaks in the United States within the period 1975–1981; there were 1500 cases of illness then due to Shigella flexneri or Shig. sonnei caused by various types of salads of which eight were potato salads. Ten cases of staphylococcal food poisoning occurred in the United States due to potato salad (Bryan, 1988). A total of 41 outbreaks caused by potato salad are listed in Bryan (1988). This high rate of food-borne illness may have been due to the relatively large proportion of neutral potato in these salads and a low level of acetic acid, permitting extended survival and growth of pathogens, particularly when temperature abuse had taken place. In 1981 in Canada, coleslaw was identified as the vehicle of transmission of L. monocytogenes, causing 34 peri-natal cases and seven adult cases of listeriosis (Schlech et al., 1983). Erickson et al. (1993) studied home-style chicken salad with mayonnaise (pH

5.7) and observed significant growth of Salmonella spp. and L. monocytogenes at 12.8 ◦

C, but not at

4 ◦ C; in macaroni salad at pH 4.6, no growth was observed.