Plants extracts as natural antifungals

VIRGINIA FERNÁNDEZ PINTO, ANDREA PATRIARCA, GRACIELA POSE

Novel technologies in Food Science, Their impact on product, consumers trends and environment

ISEKI (Mundus and Food) Task 5.2 Book 9) Elsevier.

Año: 2008;

Fungi can contaminate foods in the field, at harvest and in the different stages of storage and processing. Common deterioration symptoms are rotting and the development off- odors and off-flavors. The most important aspect of spoilage caused by fungi is the formation of toxic secondary metabolites called mycotoxins, which may have harmful effects on human and animal health. Fungal spoilage is an increasing economic problem in the food industry. Chemical antifungals are becoming less attractive as food preservatives due to the development of resistance and due to the stricter legal regulations concerning the permitted concentrations. Finally, consumers tend to demand more naturally preserved products. Food preservation is a continuous fight against microorganism spoiling the food or making it unsafe. The food industry investigates the replacement of traditional food preservation techniques like hat treatments, salting, acidification, drying and chemical preservation, by new techniques due to the increased consumer demand for natural, nutritious and tasty food products. In spite of the intensive research efforts and investments, very few of these new research methods are until now implemented by the food industry The ban of chemical additives by consumers has driven the food industry and food research towards the investigation of natural antimicrobial compound. Numerous antimicrobial agents that exist in plants are often evolved as host defense mechanisms. This antimicrobial character has been demonstrated mainly in vitro and in liquid or solid media. These in – vitro experiments are often elaborated but the feasibility of new preservatives technologies is generally too late validate by in vivo or in situ experiments. However, two aspects that are crucial for the practical application of the natural compounds are often overlooked: 1- The changes in organoleptical  and textural properties of the food when added  and 2- The interaction with food ingredients and the influence of this interaction on its efficacy. In many cases, concentrations of the antimicrobial compounds in herbs and spices are too low to be effectively without adverse effects on the sensory characteristics of the food products. More over the lipophilic  character of  these phyto-antimicrobials hampers the practical use of them (Devlieghere et al 2004) Fungicides are the primary means of controlling postharvest diseases. About 23 million kg of fungicides are applied to fruit and vegetables annually, and it’s generally accepted that production and marketing of these `products would not be possible without their use. However, as harvested fruit and vegetables are commonly treated with fungicides to retard postharvest diseases, there is a greater  likelihood of direct human exposure to them than to chemicals that are applied solely to protect foliage. In addition, synthetic fungicides can leave significant residues in treated commodities. Development of resistance to common used fungicides within populations of postharvest pathogens has also become a significant problem. For example, many synthetic fungicides are currently used to control blue mould rot of citrus fruit. However, acquired resistance by Penicillium italicum and Penicillium digitatum to fungicides used on citrus fruit has become a matter of concern in recent years. The side effects of synthetic fungicides means that alternative strategies need to be developed for reducing looses due to postharvest decay that are perceiving as safe by the public and pose negligible risk to human health and environment.   The use of non- chemical methods and non- selective fungicide  treatments may provide a part of this need. Inoculum reduction achieved trough sanitation, the use of non-selective fungicides (sodium carbonate, sodium bicarbonate, active chlorine and sorbic acid) and physical treatments as heat therapy, low temperature storage, hot water treatments and radiation can significantly lower the disease pressure on harvested commodities. Harvesting and handling techniques that minimize injury to the commodity, along with storage conditions that are optimum for maintaining host resistance will also aid in suppressing disease developing after harvest, However none of these treatments are consequently effective and many cause damage to the commodities. Thus, replacements of synthetic fungicides by natural products, particularly of plant origin, which are non toxic and specific in their action is gaining considerable attention.  Biological compounds because of their natural origin are comparatively biodegradable and most of them are almost non-residual in nature. Several plants have thousands years of history and their non-toxicity, at least at oral level, is proven. This safety feature is very important in formulations of such products because it has an impact on the cost of development and registration of  new pesticide. The research and development costs of botanicals fungicide from discovery to marketing is much less compared to that of chemical fungicides. This expense is in large part due to the concern over possible high toxicities of chemical fungicides that necessitate long term toxicological testing on experimental animals. Biologicals, because of their target specificity typically require only short term toxicological. Although the exploitation of natural products to protect the postharvest decay of perishable products is just beginning, these products have the potential to be safe fungicides and will replace the synthetic ones. Keeping in view the merits of botanicals as postharvest fungitoxicants, the products that found efficacious during in vitro tests, should be properly tested for their practical potency based on in vivo trials, organoleptic test and safety limit profile. (Tripathi, P. ; Dubey, N, 2004) A promising recent development involves incorporating antimicrobials into packaging materials, rather than the food itself. This concentrates the antimicrobial at the surface of the product which is where noxious organisms grow and reduces interference from food constituents. Whatever the delivery system, selection of an antimicrobial should be based on the sensory and chemical compatibility of the antimicrobial with the target food, its stability given the type of primary preservation system used, its effectiveness against the expected undesirable microorganisms, its safety and its cost effectiveness (Holley and Patel, 2005) Another possibility is to incorporate the antimicrobial into and edible film or coating by dipping or spraying. The use of edible films and coatings in food protection and preservation has recently increased since they offer several advantages over synthetic materials, such as being biodegradable and environmentally friendly. Currently studies with edible films with antimicrobial properties are on increase. This films could prolong the shelf life and safety of foods by preventing growth of pathogenic and spoilage microorganisms because of their lag phase extension and /or their growth rate. Moreover, antimicrobials imbedded in films can be gradually released on the food surface requiring smaller amounts to achieve the target shelf life. The ability of edible films to retard moisture, oxygen, aromas and solute transport may be improved by including additives such as antioxidants, antimicrobials, spices, colorants, flavors and fortifying nutrients in film formulations (Ponce et al 2008)