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Sep 30, 2010

Microbiological Spoilage of Bakery Products

There are both microbiological and non-microbiological food safety concerns associated with bakery products and grains. The microbiological concerns are fewer in number and traditionally have involved spoilage issues and have not been associated with food borne illness. I would like to discuss these microbiological concerns initially and then discuss a more extensive list of non-microbial food safety concerns later in this paper.

 There are a few microbial spoilage and pathogen concerns that have been historically associated with bakery products and grains. The most common cause of bakery product spoilage is the growth of mold on the product surface before the end of shelf life. The causes of this problem are primarily associated with poor sanitation and improper handling and storage of the finished products in high humidity environments. There are a number of species shown to be responsible for this problem. Among the most common are species of the genus Rhizopus and Neurospora. Bacterial spoilage of bakery products by Bacillus subtilus can also occur. Growth of this organism to high numbers results in a ropy product defect. The spores are often present in the flour and may grow in the product when the dough is held for an extended period of time prior to baking and/or when the product is improperly or inadequately cooled following baking. This problem has been effectively eliminated through improved baking practices.

Bacterial spoilage of grains is not typically a problem if the grains are properly handled and remain dry. Fungal spoilage can be common. There are a number of mold genera responsible for this, among them Alternaria, Cladosporium, Penicillium, Fusarium and Aspergillus. Infection and growth can occur in the field depending upon prevailing climatic conditions or agricultural practices or it may occur post harvest if the grains are not properly dried and maintained dry. Mycotoxin production is a possibility when these organisms are present.

 There have been some food safety incidents and illnesses associated with certain bakery products such as cream filled pastries, cakes and pies. The causative agent of these illnesses has been Staphylococcus aureus. This organism is a common contaminant of the skin and nasal passages and becomes a contaminant of the product filling through the food handler. This contamination, combined with improper formulation (high water activity and/or neutral pH) and handling of the products (temperature abuse) results in high levels of growth of the organism and production of a heat stable toxin. It is this toxin that is responsible for illness. There have also been a number of reported cases of illness associated with the consumption of bakery products contaminated with viral pathogens. Finished product contamination with Norovirus and Hepatitus A has occurred through the poor personal hygiene practices of infected food handlers. Overall, the incidence of food borne illness related to bakery products is quite low with the primary causes associated with human errors in sanitation, handling, storage and personal hygiene.

While bacterial pathogens may be found in grains at low levels and the processing or milling of the grains does not eliminate these organisms, there have not been any documented cases of food borne illness linked directly to grains. Interestingly, many ingredients used in bakery products have been associated with pathogen contamination and occasionally food borne illness. Eggs, whey protein, NFDM, soy flour, nuts and chocolate have all been known to be contaminated with Salmonella and implicated as the sources of illness. So then why haven’t there been higher numbers of outbreaks associated with bakery products? It is because the baking industry uses heating processes (baking and frying) that ensure consistent destruction of pathogens when present in ingredients. Knowing this, is it of value to conduct pathogen testing on these ingredients and on milled grains intended for use in bakery products? In fact, it is of little value to conduct such testing. Food safety cannot be “tested into” an ingredient. Ingredients are made safe through their processing. Testing of ingredients can at best be considered a verification that the appropriate processes have been carried out to reduce or eliminate pathogens but it adds little to ensure the finished products produced from those ingredients will be safe. Testing has many potential pitfalls that make it unreliable for ensuring safety. Test samples typically only represent evaluations of a single point in time. As such they may not be representative of the entire production lot. From a statistical perspective, testing a single sample or a limited number of samples will not be adequate to find a pathogen when present at low levels. Some additional reasons why testing cannot be de pended upon are: contaminants are not homogeneously distributed, sample collection, sample size and test methods can influence results, microbial growth or die-off can occur during handling, storage and shipping of samples, and poor laboratory practices or errors can occur during sample preparation and testing. Since finished product testing is of only minimal value in assuring ingredient safety what other ways can this be managed? The most effective way for an ingredient purchaser to assure safety is to require their suppliers to manage ingredient safety through the implementation of appropriate prerequisite programs and a scientifically validated HACCP program. When properly established these programs will provide continuous management of safety concerns throughout the ingredient manufacturing process.

 In some cases there is no step in the traditional processing of an ingredient to ensure it is pathogen free. This is true for wheat flour. Wheat can be contaminated at some low level with Salmonella. Studies have shown milling of wheat into flour does not eliminate Salmonella. As a result 1- 2 percent of wheat flour is contaminated with Salmonella. What are the implications of this? There has never been a recall traced to the presence of Salmonella in flour used in a bakery product associated with food borne illness. This historical lack of food borne illness associated with bakery products proves traditional bakery product processing methods are the most important steps in eliminating this pathogen. Therefore even in this instance asking a flour ingredient supplier to conduct testing for Salmonella can provide little assurance the organism is absent and therefore adds little value to ensuring food safety. The processing steps followed by the bakery product manufacturer are critical for the destruction of Salmonella and these steps alone assure the safety of these products.

 I would now like to discuss the non-microbial food safety concerns associated with bakery products and grains. Among the most prominent of these concerns is the presence of undeclared allergens in bakery products. In 2006 the FDA will require the eight allergens of greatest concern be properly declared on finished product labels. These allergens are: wheat (flour, bran, vital wheat gluten), eggs (whole, whites, yolks, albumin), dairy (milk, cream, whey powder, NFDM), peanuts (groundnuts), tree nuts (almonds, brazil nuts, hazelnuts, pistachios, walnuts, pecans), soy (protein, flour, isolate), shellfish (mussels, clams, scallops), and fish. In order to manage this allergen concern properly many facilities should implement a prerequisite program focused on allergen control. Among the many aspects of this will be the need to: conduct allergen surveys to determine what allergens are in the facility; ensure the HACCP hazard analysis includes allergens as potential hazards; store allergen and non-allergen ingredients separately; manage and sequence production runs in a manner to exclude the possibility of cross contamination; establish other measures to prevent cross contamination; verify the effectiveness of sanitation; ensure all allergens are declared on the label; and work with purchasing to determine what allergens may be present in incoming ingredients. Allergen related recalls will become a bigger concern for the industry unless action is taken to properly implement and manage the steps mentioned above.

 A second food safety concern that is receiving greater regulatory scrutiny of late is mycotoxin contamination. This is of greatest concern in grains and to a much lesser extent a concern in bakery products. Mycotoxins are low molecular weight, toxic secondary metabolites produced by molds.

The Limitations of Testing

Statistically unreliable

                                                                        Probability of Lot Acceptance

                                                                       Number of Samples Analyzed


% Defective Units





















 They are naturally occurring compounds and virtually unavoidable contaminants of grains. They may enter the food chain both directly and indirectly. Mycotoxins are stable to heat and other physical and chemical processes and therefore are not easily removed during processing although typically some reduction in levels does occur. More than 300 mycotoxins have been identified and there are six primary groups that have been identified as being of greatest concern.

 Among the most well known of these six groups is the aflatoxins. Aflatoxins are produced by two molds, Aspergillus parasiticus and A. flavus. They are produced primarily during harvest and storage but can also be present pre-harvest. Fungal growth and toxin production can occur on a variety of products and it is commonly present on nuts, seeds and cereals. The toxin has been identified as potent hepatocarcinogen and currently the FDA action level for aflatoxin B1 in food for human consumption is 20 ppb.

 A second group receiving increasing government attention is the trichothecenes. There are four types of toxins within this group, referred to as A-D. Group A contains T-2 toxin and Group B contains deoxynivalenol (DON) often referred to as vomitoxin. This is the most common trihcothecene found. The trichothecenes are produced by several common molds but the most important molds of concern are Fusarium spp. These mycotoxins react with DNA, RNA and other cellular organelles and are considered to be highly toxic. The presence of DON is an ongoing concern in wheat and the FDA has created an advisory for DON in wheat products for human consumption of 1 ppm.

 The third group of concern is zearalenone. This mycotoxin is produced primarily by Fusarium graminearum and F. semitectum. Ingestion of this mycotoxin can induce estrogenic effects (hyperestrogenism) in humans. The toxin can be found in corn, wheat, barley, sorghum and rye and currently there are no regulatory standards or guidelines although the critical level of concern is considered to be 0.5 ppm.

 The fourth group of interest is the fumonisins. The major producers of these mycotoxins are Fusarium verticillioides and F. proliferatum. It is believed there may be a possible link between consumption of these toxins and an increased incidence of human esophageal cancer. Recent studies have also shown a potential link to neural tube defects. In the US, it is estimated 80-100 percent of all harvested corn is contaminated by F.verticillioides, however, it may or may not contain fumonisin. Currently the FDA guidance level for fumonisin in products intended for humans and animals is between 2-4 ppm.

 The fifth group of concern is the ochratoxins. This group of related compounds is produced by Penicillium verucosum, other Penicillium spp. and Aspergillus ochraceus. Ochratoxin A is the toxin of most concern. It is found in wheat, corn, barley, soy, coffee, oats, beans, peas, grapes and is very stable. Therefore it is often found in further processed products. There is currently no US regulatory standard or guideline for the presence of this toxin, however the consensus level of concern in ingredients for human use is 10–20 ppm.

 The sixth and final group involves the mycotoxin, patulin. This mycotoxin is not a concern in grains, however it could be a concern for fruit filled bakery products. It is produced by a number of Penicillium, Aspergillus and Byssochlamys species and is primarily found in fruits such as apples, pears and grapes. This mycotoxin induces intestinal damage and is considered to be a potential carcinogen. The FDA has issued a compliance policy guideline and in some countries the recommended maximum concentration in fruit juice is 50 ppb.

 The next area of great interest and food safety concern involves the presence of pesticides applied to grains and carry over from grains into bakery products. Pesticides are chemicals intended to kill insects, fungi, weeds, rodents and other pests. The greatest public health risk from pesticides is absorption of large doses through the skin, by inhalation or by oral ingestion. Food borne illness may result through exposure by the oral route. There are three types of pesticides that have been associated with food borne illness: organophosphorus, carbamate and chlorinated hydrocarbons. All three forms affect the neurological system within 30 minutes to a few hours after ingestion. Symptoms vary based on level of exposure but if untreated death may occur.

 There are some food safety concerns involving intentional additives used in bakery products. Potassium bromate which is used as a dough conditioner and processing aid is believed to be a potential human carcinogen. This compound has been banned in many countries however the FDA currently permits its use. The concern occurs when not all the bromate is converted to bromide during processing. This has been determined to be likely to occur if initial bromate usage levels are greater than 75 ppm. The FDA has recommended and the industry has adopted a voluntary “safe use” residue limit of 20 ppb. In 1999 a consumer a complete prohibition of the use of this chemical. The FDA’s response to this petition is still pending but could result in a complete ban on the use of potassium bromate. A second intentional additive, which poses a minor food safety concern, is niacin (also referred to as nicotinic acid). This is a vitamin added to provide nutritional fortification to some baked products. Excessive levels or lack of proper mixing resulting in localized areas of product with high levels of niacin can cause problems. If niacin is consumed at levels in excess of 100-300 mg it can cause a short duration food borne illness generally described by a disconcerting flushing feeling, itching and stomach pain. Fortunately, with time these symptoms will subside and there appear to be no lasting effects.