Biological Control of Molds and Mycotoxins in Foods and Feeds

Non-Technical Summary: Mold and yeast (fungal) deterioration of foods and agricultural commodities is a serious problem in the U.S. and worldwide. Molds may be a problem in cereal grains, cereal products, oilseeds, nuts and various processed foods such as intermediate moisture food products, natural cheeses, cured and smoked meats, jams, jellies and various refrigerated and frozen foods, as well as livestock feeds and petfoods. Yeasts may spoil salad dressings, cottage cheese, fruit juices and juice concentrates. Mold deterioration of these products causes damage that reduces quality, grades and prices, resulting in economic loss. In addition, the presence of molds in these commodities poses hazards to human and animal health. A serious hazard associated with mold growth in foods and feeds is the possible production of mycotoxins, substances which are toxic, potentially carcinogenic, and which may adversely affect immune systems. Mold growth with accompanying potential mycotoxin production makes foods and feeds unfit for human or animal consumption. Lactic acid bacteria (LAB), propionic acid bacteria (PAB) and Bacillus pumilus are potential food-grade biological control agents that can be used to prevent growth of mold and yeasts and mycotoxin production in stored acidic and refrigerated foods, stored cereal grains, grains in the field, livestock feeds and petfoods. This project is designed to discover and isolate these antifungal biological control agents and develop them into food grade biological control agents that can be used to prevent mold and yeast spoilage of stored foods, feeds and grains and prevent mycotoxin contamination in these products. The outcomes of this project are expect to be the development of novel, new food and feed perservation systems using freindly, not-toxic bacteria to prevent mold and yeast spoilage and mycotoxin production. The impacts of this will be safer foods and feeds and economic savings. <P> Approach: Lactic Acid Bacteria (LAB) cultures will be obtained from sources such as probiotic and sourdough cultures and fermented plant foods. Cultures will be evaluated for antifungal activity. Propionic acid bacteria (PAB) obtained from ATCC and commercial culture companies will also be studied for antifungal activity. Pure and mixed LAB cultures and PAB cultures will be screened for antifungal activity against a set of molds and yeasts. Preliminary screening will be carried out by growing the bacterial cultures in modified MRS (mMRS) broth and mixing the fermented mMRS (less bacteria) with Potato Dextrose Broth in 96 well plates, inoculating the wells with the different molds and incubating at room temperature. Presence or absence of mold growth will be determined visually and by measuring the optical density (OD) of the wells. Absence of mold growth will be interpreted as inhibition and defined as antifungal activity. Those cultures, pure and mixed with demonstrated antifungal properties will be studied further. Cultures will be grown in a suitable liquid substrate such as cheese whey, tomato juice broth or other suitable food grade broth substrate to produce a fermented liquid or "fermentate". This fermentate will be mixed with double strength culture broths, both with and without the bacterial cells. These broths will be inoculated with the same mold and yeast species that were previously used to detect antifungal activity. Mold growth will be measured by increase in mold mycelial mass over time. Yeast growth will be determined by optical density measurements and plate counts over periods of time. Propionic acid bacteria produce propionic acid, a known antifungal substance. Lactic acid bacteria produce lactic acid and may co-exist or even stimulate the growth of PAB. These combined LAB and PAB fermentate cultures would be expected to have strong antifungal activity. The most strongly antifungal LAB, PAB and fermentates will be studied in combination with each other and with Bacillus pumilus and Lactobacillus rhamnosus which have been previously studied. These cultures will also be combined with known antimycotic food additives such as potassium sorbate and calcium propionate and naturally occurring substances, with known antifungal properties, such as mustard and ground flaxseed. These combinations will be studied for the ability to inhibit growth and mycotoxin production by known mycotoxigenic molds. Mold growth will be measured by determining mycelial dry weights. Mycotoxin concentrations will be measured using commercially available quantitative ELISA test kits. Quantitation of mycotoxin levels will also be done by high performance liquid chromatography (HPLC). Experimental designs for this work will be developed based on advice from a statistician.