II. Applications of Novel Biocompounds in Quality and Safety of Foods
Antifungal Lactic Acid Bacteria (LAB): Potential Use in Food Systems
Fungal spoilage in food is one of the principal causes of food deterioration and wastages. Although, considerable advancements have been made in the traditional methods of fungal control, alternative methods using antifungal LAB and its metabolites offer a more natural solution in the wake of demand for minimally processed, natural foods. LAB produces an array of antifungal metabolites (such as organic acids, phenyllactate, fatty acids, proteinaceous compounds, volatiles, reuterin, etc.), which either act individually or in synergism with each other in different food systems. Many research reports have elucidated the desired inhibition of fungal contaminants present in various foods such as daily, breads, fruits, and vegetables, animal feeds, etc., by LAB. Although, commercial antifungal formulations based on LAB are presently available for application in different food formats, more detailed research is still needed in terms of final food quality, stability during processing, mechanism of action, synergism activities, safety, etc. to fully harness their potential for commercial food exploitation.
Fungi are common food contaminants that play a pivotal role in the spoilage and reduction of marketable quality, hygiene, and safety of food materials to an unacceptable level. The fungal spoilages are responsible for significant food waste and contribute enormously to the postharvest losses of food products. In addition, fungal contaminants also compromise safety of the foods by generating poisonous secondary metabolites called mycotoxins. Hence, the control and elimination of fungal contaminants has become a major challenge for food producers and processors including scientists, who are continuously seeking for newer and effective remedies to avert or control fungal spoilage in foodstuffs. Apart from the advances in the existing technologies in the control of fungal spoilages, recently, new biopreservation strategies by utilizing bioprotective potentials of Lactic acid bacteria (LAB) and its antifungal metabolites have also gathered a lot of attention.
LAB is a multifarious class of microorganisms characterized by standard criteria of lactic acid production in major amounts as an end-product during carbohydrate fermentation. The group composed of members with distinct characteristics as Gram-positive, aerotolerant, non-motile, non-sporulating having either rod or coccus morphology. At present, about 17 bacterial genera are categorized as LAB . LAB has a complex nutritional requirement due to which they are found mostly in nutrient-rich habitats, naturally occurring in food products like daily, cereal, meat, vegetables, etc., and many others in the intestinal linings of humans and other animals. Traditionally, the fermentative metabolism of LAB has been a very important attribute of these microbes in yielding variety of fermented foods across the globe.
The LAB causes rapid acidification of food products, which is followed by many changes in the flavor, body, and texture. In addition to the change in the organoleptic properties of the food material, LAB also acts as a biopreservative microorganisms and the final product has an enhanced shelf-life than the raw material. During its growth in the food products, LAB produces variety of antimicrobial metabolites that exert significant antagonistic activity against many related and unrelated microorganisms, thereby provides advantage of in situ shelf-life extension of fermented food products.
Nowadays, there is an increase in the demand of minimally-processed natural foods due to which LAB and its biopreservative metabolites have been looked up as a possible alternative to chemical preservatives added to foods. LAB is ideal candidates for commercial exploitation since many of them have been attributed to GRAS and QPS status by US-FDA and EU, respectively. Hence, LAB possess healthy and natural image. Recently, the beneficial health effects of certain LAB have also been recognized by many researchers due to which many LAB are now commonly used as Probiotics.
The biopreservative potential of LAB is well known and many of the earlier reports have exclusively elaborated on the various antimicrobial substances derived from LAB. These metabolites are diverse in nature depending on the producing LAB species and can have a narrow to a wide spectrum of antimicrobial activity. The metabolites of LAB can inhibit both bacterial as well as fungal contaminants, however, in this chapter, we are going to discuss only the antifungal metabolites derived from LAB although the same metabolites may also have antibacterial activity.
This chapter focuses on the antifungal potential of LAB derived via specific metabolites, which are secreted through various biochemical pathways, their modes of action, and their applications as bioprotective cultures or metabolic mixes in a wide variety of food materials.