What kinds of microbes inhabit the food that we eat?


Food scientists and and real people have very different concepts of the microbes that inhabit our foods. As I have stated before, we are obsessed with shelf life. From the first day of any food microbiology course students become scared witless as they learn that food kills, or at least the nasty microbes in food kill. Food-micro students also learn that other non-lethal microbes in our food induce chemical reactions that can either delight or dismay us. Then there are numerous species that just happen to be present that have no effect on the food itself. At least, until recently those were the four categories—pathogens, fermenters, spoilers and free riders. Now we have a fifth category—the colonizers. Any food technologist must consider the consequences a food process will have on these types of microbes.

Food technologists process food to extend shelf life. The main cause of food spoilage is the presence and growth of microbes. Fruits, vegetables and other plant-based, food materials carry microbes on their surface that can lead to decay and waste. While most plant materials are resistant to these microbes, cuts and bruises permit entry into vulnerable tissue. Raw meat is generally assumed to be contaminated, high in a protein, and susceptible to rapid microbial rotting. Edible plant or animal tissue spoils when it becomes unsightly, smells or tastes bad, or exudes slime turning the food to mush. Processing can slow spoilage. Canning kills all spoilage microbes. Pasteurization slows spoilage but does not stop it. Drying and freezing keep microbial populations from multiplying as long as the food stays dry or frozen. Fermenting encourages growth of favorable microbes to outcompete those that cause undesirable changes. Addition of preservatives, the most widely used are sugar and salt, also limits growth of spoilage organisms. Despite its reputation the Twinkie will not last forever. The sugar present and its low moisture level allow it to live longer than other foods.

Food technologists process food to prevent food poisoning. An estimated 3,000 Americans die each year out of 48 million who become sick from a food-related illness.  These deaths and illnesses are primarily caused by naturally occurring microbes called human pathogens. It is important to note that spoiled foods are not necessarily unsafe foods, and that unsafe foods are not necessarily spoiled foods. Smelling foods that are suspect is NOT a reliable indicator of food safety. Those human pathogens that don’t kill us can give us wicked-bad stomach trouble. And that is not all! Other symptoms of food poisoning can include double vision, fever, flu-like conditions, slurred speech and paralysis. The presence of a pathogen in a food may not cause an illness, but mishandling of food can allow the organism to grow in the food and cause that food to become a hazard.

Food poisoning can occur as an infection, an intoxication or a toxicoinfection. The offending microbe in an infection grows in the food, is ingested and then grows inside the person. Pathogens causing intoxications produce a toxin in the food which causes the illness even if the organism is killed by cooking or processing but the toxin remains active. Agents of toxicoinfections can serve as either infective or intoxicant pathogens. The last meal is not always responsible for a food-related illness. The time between ingestion of the contaminated food and the first symptoms tends to be at least 12 hours for many pathogens and even as long as a week for others.

Food technologists process food to create new products. Fermented products are among the oldest types of processed foods. Beer, bread, cheese, kombucha, pickles, wine and yogurt are popular fermented foods. A raw, whole food is transformed chemically by fermentative microbes. Grains, fish, fruits, milk, and vegetables can all serve as raw materials for finished fermented products. Commercial fermentations are carefully controlled from the introduction of defined microbial cultures to the selection of ingredients and manipulation of the environmental conditions. Food technologists also create formulated foods by mixing numerous ingredients. These foods can vary from highly sugared or salted junk foods to sophisticated medicinal foods to meet very specific nutritional needs.

Food technologists don’t process food to eliminate all microbes. Heat is the most effective way to kill spoilage and pathogenic microbes, but it also can damage flavor and harm nutrients. Heat is responsible for many desirable flavor combinations, but too much heat can lead to loss of delicate aromas or development of off-flavors. Likewise, heat can destroy vitamins and cooking in water can drive minerals and water-soluble vitamins into the cooking liquid. Milk is pasteurized to kill pathogens without killing off all the spoilage ones, keeping it safe at a sacrifice of a shorter shelf life. Other products undergo minimal processing to preserve flavor and nutrients but may require other techniques, such as refrigeration, to slow spoilage and decrease the chances of food poisoning. Also, there is no need to kill the free riders as they don’t affect food safety or quality.

Probiotics redo

Food scientists are now working to develop ways to colonize our guts. I show my age as I realize that the microbiome was not on the radar in any of my food microbiology courses. There was some mention of eating yogurt to replace harmful microbes in our gut with beneficial microbes, but that was the extent of it. Now, probiotics (the microbes), prebiotics (food to keep them happy) and synbiotics (combinations of pro- and prebiotics) are appearing in food micro textbooks and in food products. Foods are being developed as vehicles to increase diversity of our microbiome and provide us with the beneficial microbes we need for a healthy gut. It is becoming clear that occasional doses of these biotics will not be enough to maintain the types of populations that could benefit health. Many studies have been published that focus on use of pro- and prebiotics to protect us from various chronic diseases, but the biochemical mechanisms are not clear.

Contrary to popular belief, food technologists do not process food to create a sterile food supply. Most of the food we eat has microbes. Canned fish, fruit and vegetables may have some free riders, but they are essentially microbe free. Food technologists process food to extend shelf life by killing many but not necessarily all spoilage microbes so the food will last longer and less food is wasted. Food processors modify raw food materials to keep products safe. Food product developers design foods to expose their customers to new sensory sensations. Food technologists do not want to over-process foods as too much processing can compromise the nutritional value and flavor of products. Food processors have been using the special process fermentation for centuries to use beneficial microbes to outcompete human pathogens and spoilage microbes to produce safe, flavorful foods.

The new challenge for food science and technology is to develop foods that will contribute to a more diverse microbiota for healthier guts without compromising safety and shelf life. It is not difficult to get these microbes into food. It is more challenging to make sure that such products appeal to Americans so that they will be eaten. The biggest challenge will be to make sure that such microbes actually make it through the stomach to the gut and stay there long enough to promote human health.

Next week:  Gut health and the internet

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