Owing to its high biodegradability, and nontoxicity and antimicrobial properties, chitosan is widely-used as an antimicrobial agent either alone or blended with other natural polymers. To broaden chitosan's antimicrobial applicability, comprehensive knowledge of its activity is necessary. The paper reviews the current trend of investigation on antimicrobial activities of chitosan and its mode of action. Chitosan-mediated inhibition is affected by several factors can be classified into four types as intrinsic, environmental, microorganism and physical state, according to their respective roles. In this review, different physical states are comparatively discussed. Mode of antimicrobial action is discussed in parts of the active compound (chitosan) and the target (microorganisms) collectively and independently in same complex. Finally, the general antimicrobial applications of chitosan and perspectives about future studies in this field are considered.
The risks and benefits of traditional cheeses, mainly raw milk cheeses, are rarely set out objectively, whence the recurrent confused debate over their pros and cons. This review starts by emphasizing the particularities of the microbiota in traditional cheeses. It then describes the sensory, hygiene, and possible health benefits associated with traditional cheeses. The microbial diversity underlying the benefits of raw milk cheese depends on both the milk microbiota and on traditional practices, including inoculation practices. Traditional know-how from farming to cheese processing helps to maintain both the richness of the microbiota in individual cheeses and the diversity between cheeses throughout processing. All in all more than 400 species of lactic acid bacteria, Gram and catalase-positive bacteria, Gram-negative bacteria, yeasts and moulds have been detected in raw milk. This biodiversity decreases in cheese cores, where a small number of lactic acid bacteria species are numerically dominant, but persists on the cheese surfaces, which harbour numerous species of bacteria, yeasts and moulds. Diversity between cheeses is due particularly to wide variations in the dynamics of the same species in different cheeses. Flavour is more intense and rich in raw milk cheeses than in processed ones. This is mainly because an abundant native microbiota can express in raw milk cheeses, which is not the case in cheeses made from pasteurized or microfiltered milk. Compared to commercial strains, indigenous lactic acid bacteria isolated from milk/cheese, and surface bacteria and yeasts isolated from traditional brines, were associated with more complex volatile profiles and higher scores for some sensorial attributes. The ability of traditional cheeses to combat pathogens is related more to native antipathogenic strains or microbial consortia than to natural non-microbial inhibitor(s) from milk. Quite different native microbiota can protect against in cheeses (in both core and surface) and on the wooden surfaces of traditional equipment. The inhibition seems to be associated with their qualitative and quantitative composition rather than with their degree of diversity. The inhibitory mechanisms are not well elucidated. Both cross-sectional and cohort studies have evidenced a strong association of raw-milk consumption with protection against allergic/atopic diseases; further studies are needed to determine whether such association extends to traditional raw-milk cheese consumption. In the future, the use of meta-omics methods should help to decipher how traditional cheese ecosystems form and function, opening the way to new methods of risk–benefit management from farm to ripened cheese.
The burden of diseases caused by food-borne pathogens remains largely unknown. Importantly data indicating trends in food-borne infectious intestinal disease is limited to a few industrialised countries, and even fewer pathogens. It has been predicted that the importance of diarrhoeal disease, mainly due to contaminated food and water, as a cause of death will decline worldwide. Evidence for such a downward trend is limited. This prediction presumes that improvements in the production and retail of microbiologically safe food will be sustained in the developed world and, moreover, will be rolled out to those countries of the developing world increasingly producing food for a global market. In this review evidence is presented to indicate that the microbiological safety of food remains a dynamic situation heavily influenced by multiple factors along the food chain from farm to fork. Sustaining food safety standards will depend on constant vigilance maintained by monitoring and surveillance but, with the rising importance of other food-related issues, such as food security, obesity and climate change, competition for resources in the future to enable this may be fierce. In addition the pathogen populations relevant to food safety are not static. Food is an excellent vehicle by which many pathogens (bacteria, viruses/prions and parasites) can reach an appropriate colonisation site in a new host. Although food production practices change, the well-recognised food-borne pathogens, such as spp. and , seem able to evolve to exploit novel opportunities, for example fresh produce, and even generate new public health challenges, for example antimicrobial resistance. In addition, previously unknown food-borne pathogens, many of which are zoonotic, are constantly emerging. Current understanding of the trends in food-borne diseases for bacterial, viral and parasitic pathogens has been reviewed. The bacterial pathogens are exemplified by those well-recognized by policy makers; i.e. , , and . Antimicrobial resistance in several bacterial food-borne pathogens ( , , and spp., methicillin resistant , and ) has been discussed as a separate topic because of its relative importance to policy issues. Awareness and surveillance of viral food-borne pathogens is generally poor but emphasis is placed on Norovirus, Hepatitis A, rotaviruses and newly emerging viruses such as SARS. Many food-borne parasitic pathogens are known (for example , and ) but few of these are effectively monitored in foods, livestock and wildlife and their epidemiology through the food-chain is poorly understood. The lessons learned and future challenges in each topic are debated. It is clear that one overall challenge is the generation and maintenance of constructive dialogue and collaboration between public health, veterinary and food safety experts, bringing together multidisciplinary skills and multi-pathogen expertise. Such collaboration is essential to monitor changing trends in the well-recognised diseases and detect emerging pathogens. It will also be necessary understand the multiple interactions these pathogens have with their environments during transmission along the food chain in order to develop effective prevention and control strategies.
To understand why may persist in food industry equipment and premises, notably at low temperature, scientific studies have so far focused on adhesion potential, biofilm forming ability, resistance to desiccation, acid and heat, tolerance to increased sublethal concentration of disinfectants or resistance to lethal concentrations. Evidence from studies in processing plants shows that the factors associated with the presence of are those that favor growth. Interestingly, most conditions promoting bacterial growth were shown, in laboratory assays, to decrease adhesion of cells. Good growth conditions can be found in so-called harborage sites, shelters due to unhygienic design of equipment and premises or unhygienic or damaged materials. These sites are hard to eliminate. A conceptual model of persistence/no persistence based on the relative weight of growth outcome of cleaning and disinfection is suggested. It shows that a minimum initial bacterial load is necessary for bacteria to persist in a harborage site and that when a low initial bacterial charge is applied, early cleaning and disinfection is the only way to avoid persistence. We conclude by proposing that there are no strains of with unique properties that lead to persistence, but harborage sites in food industry premises and equipment where can persist. ► Persistence of in equipment and premises ► No strains with unique properties that lead to persistence ► Most significant factor is the ability to grow, possible in harborage sites ► Cleaning and disinfection not effective in harborage sites ► Harborage sites should be combated, hygienic design crucial.
Enterococci belong to the lactic acid bacteria (LAB) and they are of importance in foods due to their involvement in food spoilage and fermentations, as well as their utilisation as probiotics in humans and slaughter animals. However, they are also important nosocomial pathogens that cause bacteraemia, endocarditis and other infections. Some strains are resistant to many antibiotics and possess virulence factors such as adhesins, invasins, pili and haemolysin. The role of enterococci in disease has raised questions on their safety for use in foods or as probiotics. Studies on the incidence of virulence traits among enterococcal strains isolated from food showed that some can harbour virulence traits, but it is also thought that virulence is not the result of the presence of specific virulence determinants alone, but is rather a more intricate process. Specific genetic lineages of hospital-adapted strains have emerged, such as clonal complex (CC) 17 and CC2, CC9, CC28 and CC40, which are high risk enterococcal clonal complexes. These are characterised by the presence of antibiotic resistance determinants and/or virulence factors, often located on pathogenicity islands or plasmids. Mobile genetic elements thus are considered to play a major role in the establishment of problematic lineages. Although enterococci occur in high numbers in certain types of fermented cheeses and sausages, they are not deliberately added as starter cultures. Some and strains are used as probiotics and are ingested in high numbers, generally in the form of pharmaceutical preparations. Such probiotics are administered to treat diarrhoea, antibiotic-associated diarrhoea or irritable bowel syndrome, to lower cholesterol levels or to improve host immunity. In animals, enterococcal probiotics are mainly used to treat or prevent diarrhoea, for immune stimulation or to improve growth. From a food microbiological point of view, the safety of the bacteria used as probiotics must be assured, and data on the major strains in use so far indicate that they are safe. The advantage of use of probiotics in slaughter animals, from a food microbiological point of view, lies in the reduction of zoonotic pathogens in the gastrointestinal tract of animals which prevents the transmission of these pathogens via food. The use of enterococcal probiotics should, in view of the development of problematic lineages and the potential for gene transfer in the gastrointestinal tract of both humans and animals, be carefully monitored, and the advantages of using these and new strains should be considered in a well contemplated risk/benefit analysis. ► The use of enterococci as probiotics has implications in terms of food safety. ► Enterococci may possess virulence factors or transferable antibiotic resistances. ► Current applications of enterococcal probiotics in humans include treatments for diarrhoea and IBD. ► Enterococcal probiotics are used for increasing growth and health. ► Mobile genetic elements influence diversity and hence strain safety.
Microbial food cultures have directly or indirectly come under various regulatory frameworks in the course of the last decades. Several of those regulatory frameworks put emphasis on “the history of use”, “traditional food”, or “general recognition of safety”. Authoritative lists of microorganisms with a documented use in food have therefore come into high demand. One such list was published in 2002 as a result of a joint project between the International Dairy Federation (IDF) and the European Food and Feed Cultures Association (EFFCA). The “2002 IDF inventory” has become a de facto reference for food cultures in practical use. However, as the focus mainly was on commercially available dairy cultures, there was an unmet need for a list with a wider scope. We present an updated inventory of microorganisms used in food fermentations covering a wide range of food matrices (dairy, meat, fish, vegetables, legumes, cereals, beverages, and vinegar). We have also reviewed and updated the taxonomy of the microorganisms used in food fermentations in order to bring the taxonomy in agreement with the current standing in nomenclature. ► Up to date inventory of microbial species used in production of fermented foods. ► The inventory covers species of starter cultures and “natural floras”. ► Species with a documented beneficial technological purpose are included. ► We present a history of use also for newly established taxonomic units. ► The inventory consists of 195 bacterial species and 69 species of yeasts and molds.
The microbial safety of foods continues to be a major concern to consumers, regulatory agencies and food industries throughout the world. Many food preservation strategies have been used traditionally for the control of microbial spoilage in foods but the contamination of food and spoilage by microorganisms is a problem yet to be controlled adequately. Although synthetic antimicrobials are approved in many countries, the recent trend has been for use of natural preservatives, which necessitates the exploration of alternative sources of safe, effective and acceptable natural preservatives. Plants contain innumerable constituents and are valuable sources of new and biologically active molecules possessing antimicrobial properties. Plants extracts either as standardized extracts or as a source of pure compounds provide unlimited opportunities for control of microbial growth owing to their chemical diversity. Many plant extracts possess antimicrobial activity against a range of bacteria, yeast and molds, but the variations in quality and quantity of their bioactive constituents is the major detriments in their food use. Further, phytochemicals added to foods may be lost by various processing techniques. Several plant extracts or purified compounds intended for food use have been consumed by humans for thousands of years, but typical toxicological information is not available for them. Although international guidelines exist for the safety evaluation of food additives, owing to problems in standardization of plant extracts, typical toxicological values have not been assigned to them. Development of cost effective isolation procedures that yield standardized extracts as well as safety and toxicology evaluation of these antimicrobials requires a deeper investigation. ► A comprehensive review of literature on plant extracts has been presented. ► Application of plant extracts for food preservation has been emphasized. ► Various antimicrobial phytochemicals present in plant extracts have been tabulated.
Grapes have a complex microbial ecology including filamentous fungi, yeasts and bacteria with different physiological characteristics and effects upon wine production. Some species are only found in grapes, such as parasitic fungi and environmental bacteria, while others have the ability to survive and grow in wines, constituting the wine microbial consortium. This consortium covers yeast species, lactic acid bacteria and acetic acid bacteria. The proportion of these microorganisms depends on the grape ripening stage and on the availability of nutrients. Grape berries are susceptible to fungal parasites until after which the microbiota of truly intact berries is similar to that of plant leaves, which is dominated by basidiomycetous yeasts (e.g. spp., spp. spp.) and the yeast-like fungus . The cuticle of visually intact berries may bear microfissures and softens with ripening, increasing nutrient availability and explaining the possible dominance by the oxidative or weakly fermentative ascomycetous populations (e.g. spp., spp., spp., spp.) approaching harvest time. When grape skin is clearly damaged, the availability of high sugar concentrations on the berry surface favours the increase of ascomycetes with higher fermentative activity like spp. and , including dangerous wine spoilage yeasts (e.g. spp , spp.), and of acetic acid bacteria (e.g. spp., spp.). The sugar fermenting species is rarely found on unblemished berries, being favoured by grape damage. Lactic acid bacteria are minor partners of grape microbiota and while being the typical agent of malolactic fermentation, has been seldom isolated from grapes in the vineyard. Environmental ubiquitous bacteria of the genus spp., spp., spp., spp., spp., spp., among others, have been isolated from grapes but do not have the ability to grow in wines. Saprophytic moulds, like , causing grey rot, or spp., possibly producing ochratoxin, are only active in the vineyard, although their metabolites may affect wine quality during grape processing. The impact of damaged grapes in yeast ecology has been underestimated mostly because of inaccurate grape sampling. Injured berries hidden in apparently sound bunches explain the recovery of a higher number of species when whole bunches are picked. Grape health status is the main factor affecting the microbial ecology of grapes, increasing both microbial numbers and species diversity. Therefore, the influence of abiotic (e.g. climate, rain, hail), biotic (e.g. insects, birds, phytopathogenic and saprophytic moulds) and viticultural (e.g. fungicides) factors is dependent on their primary damaging effect. ► Yeasts and other microbiota (bacteria, moulds) of grapes are reviewed. ► Grape health status is the main factor affecting the microbial ecology of grapes, increasing both microbial numbers and species diversity. ► Accurate berry sampling is essential to understand grape microbial ecology. ► Microbial dissemination and persistence during the annual vineplant cycle is discussed.
Significant losses in harvested fruit can be directly attributable to decay fungi. Some of these pathogenic fungi are also the source of mycotoxins that are harmful to humans. Biological control of postharvest decay of fruits, vegetables and grains using antagonistic yeasts has been explored as one of several promising alternatives to chemical fungicides, the use of which is facing increasingly more stringent regulation. Yeast species have been isolated over the past two decades from a variety of sources, including fruit surfaces, the phyllosphere, soil and sea water, and their potential as postharvest biocontrol agents has been investigated. Several mechanisms have been proposed as responsible for their antagonistic activity, including competition for nutrients and space, parasitism of the pathogen, secretion of antifungal compounds, induction of host resistance, biofilm formation, and most recently, the involvement of reactive oxygen species (ROS) in defense response. It has been recognized that a biocontrol system is composed of a three-way interaction between the host (commodity), the pathogen and the yeast, all of which are affected by environmental factors. Efficacy and consistent performance in controlling postharvest diseases are the hurdles that must be overcome if the use of yeast biocontrol agents and other alternatives are to be widely used commercially. Therefore, attempts have been made to combine alternative treatments in order improve their overall performance. The current review provides a brief overview of the topic of the use of yeasts as postharvest biocontrol agents and includes information on the sources from which yeast antagonists have been isolated, their mode of action, and abiotic stress resistance in yeast as it relates to biocontrol performance. Areas in need of future research are also highlighted.
Recent outbreaks of food-borne diseases highlight the need for reducing bacterial pathogens in foods of animal origin. Animal enteric pathogens are a direct source for food contamination. The ban of antibiotics as growth promoters (AGPs) has been a challenge for animal nutrition increasing the need to find alternative methods to control and prevent pathogenic bacterial colonization. The modulation of the gut microbiota with new feed additives, such as probiotics and prebiotics, towards host-protecting functions to support animal health, is a topical issue in animal breeding and creates fascinating possibilities. Although the knowledge on the effects of such feed additives has increased, essential information concerning their impact on the host are, to date, incomplete. For the future, the most important target, within probiotic and prebiotic research, is a demonstrated health-promoting benefit supported by knowledge on the mechanistic actions. Genomic-based knowledge on the composition and functions of the gut microbiota, as well as its deviations, will advance the selection of new and specific probiotics. Potential combinations of suitable probiotics and prebiotics may prove to be the next step to reduce the risk of intestinal diseases and remove specific microbial disorders. In this review we discuss the current knowledge on the contribution of the gut microbiota to host well-being. Moreover, we review available information on probiotics and prebiotics and their application in animal feeding.
It is well known that fresh-cut processors usually rely on wash water sanitizers to reduce microbial counts in order to maintain quality and extend shelf-life of the end product. Water is a useful tool for reducing potential contamination but it can also transfer pathogenic microorganisms. Washing with sanitizers is important in fresh-cut produce hygiene, particularly removing soil and debris, but especially in water disinfection to avoid cross-contamination between clean and contaminated product. Most of the sanitizing solutions induce higher microbial reduction after washing when compared to water washing, but after storage, epiphytic microorganisms grow rapidly, reaching similar levels. In fact, despite the general idea that sanitizers are used to reduce the microbial population on the produce, their main effect is maintaining the microbial quality of the water. The use of potable water instead of water containing chemical disinfection agents for washing fresh-cut vegetables is being advocated in some European countries. However, the problems of using an inadequate sanitizer or even none are considered in this manuscript. The need for a standardized approach to evaluate and compare the efficiency of sanitizing agents is also presented. Most new alternative techniques accentuate the problems with chlorine suggesting that the industry should move away from this traditional disinfection agent. However, the use of chlorine based sanitizers are presented as belonging to the most effective and efficient sanitizers when adequate doses are used. In this review improvements in water disinfection and sanitation strategies, including a shower pre-washing step and a final rinse of the produce, are suggested.
Chitosan was used as a coating material to improve encapsulation of a probiotic and prebiotic in calcium alginate beads. Chitosan-coated alginate microspheres were produced to encapsulate (L) and (B) as probiotics and the prebiotic quercetin (Q) with the objective of enhancing survival of the probiotic bacteria and keeping intact the prebiotic during exposure to the adverse conditions of the gastro-intestinal tract. The encapsulation yield for viable cells for chitosan-coated alginate microspheres with quercetin (L + Q and B + Q) was very low. These results, together with the study about the survival of microspheres with quercetin during storage at 4 °C, demonstrated that probiotic bacteria microencapsulated with quercetin did not survive. Owing to this, quercetin and or were microencapsulated separately. Microencapsulated and microencapsulated were resistant to simulated gastric conditions (pH 2.0, 2 h) and bile solution (3%, 2 h), resulting in significantly ( < 0.05) improved survival when compared with free bacteria. This work showed that the microencapsulation of and with alginate and a chitosan coating offers an effective means of delivery of viable bacterial cells to the colon and maintaining their survival during simulated gastric and intestinal juice.
To inform risk management decisions on control, prevention and surveillance of foodborne disease, the disease burden of foodborne pathogens is estimated using Disability Adjusted Life Years as a summary metric of public health. Fourteen pathogens that can be transmitted by food are included in the study (four infectious bacteria, three toxin-producing bacteria, four viruses and three protozoa). Data represent the burden in the Netherlands in 2009. The incidence of community-acquired non-consulting cases, patients consulting their general practitioner, those admitted to hospital, as well as the incidence of sequelae and fatal cases is estimated using surveillance data, cohort studies and published data. Disease burden includes estimates of duration and disability weights for non-fatal cases and loss of statistical life expectancy for fatal cases. Results at pathogen level are combined with data from an expert survey to assess the fraction of cases attributable to food, and the main food groups contributing to transmission. Among 1.8 million cases of disease (approx. 10,600 per 100,000) and 233 deaths (1.4 per 100,000) by these fourteen pathogens, approximately one-third (680,000 cases; 4100 per 100,000) and 78 deaths (0.5 per 100,000) are attributable to foodborne transmission. The total burden is 13,500 DALY (82 DALY per 100,000). On a population level, , thermophilic spp., rotaviruses, noroviruses and spp. cause the highest disease burden. The burden per case is highest for perinatal listeriosis and congenital toxoplasmosis. Approximately 45% of the total burden is attributed to food. and spp. appear to be key targets for additional intervention efforts, with a focus on food and environmental pathways. The ranking of foodborne pathogens based on burden is very different compared to when only incidence is considered. The burden of acute disease is a relatively small part of the total burden. In the Netherlands, the burden of foodborne pathogens is similar to the burden of upper respiratory and urinary tract infections. ► DALYs are proposed for risk ranking of foodborne pathogens. ► The burden of and spp. is highest in the population. ► The burden of spp. and is highest for individuals. ► Foodborne accounts for approximately half of the total disease burden. ► Foods of animal origin cause two-thirds of the burden by foods.
The spoilage of raw meat is mainly due to undesired microbial development in meat during storage. The type of bacteria and their loads depend on the initial meat contamination and on the specific storage conditions that can influence the development of different spoilage-related microbial populations thus affecting the type and rate of the spoilage process. This review focuses on the composition of raw meat spoilage microbiota and the influence of storage conditions such as temperature, packaging atmosphere and use of different preservatives on the bacterial diversity developing in raw meat. In addition, the most recent tools used for the detection and identification of meat microbiota are also reviewed. ► The most important microbial species occurring during meat storage are described. ► The effect of different storage conditions on microbial composition of meat is highlighted. ► The principal tools used for the identification of meat microbiota are reviewed.
Bacteriocins are ribosomally-synthesized peptides or proteins with antimicrobial activity, produced by different groups of bacteria. Many lactic acid bacteria (LAB) produce bacteriocins with rather broad spectra of inhibition. Several LAB bacteriocins offer potential applications in food preservation, and the use of bacteriocins in the food industry can help to reduce the addition of chemical preservatives as well as the intensity of heat treatments, resulting in foods which are more naturally preserved and richer in organoleptic and nutritional properties. This can be an alternative to satisfy the increasing consumers demands for safe, fresh-tasting, ready-to-eat, minimally-processed foods and also to develop “novel” food products (e.g. less acidic, or with a lower salt content). In addition to the available commercial preparations of nisin and pediocin PA-1/AcH, other bacteriocins (like for example lacticin 3147, enterocin AS-48 or variacin) also offer promising perspectives. Broad-spectrum bacteriocins present potential wider uses, while narrow-spectrum bacteriocins can be used more specifically to selectively inhibit certain high-risk bacteria in foods like without affecting harmless microbiota. Bacteriocins can be added to foods in the form of concentrated preparations as food preservatives, shelf-life extenders, additives or ingredients, or they can be produced in situ by bacteriocinogenic starters, adjunct or protective cultures. Immobilized bacteriocins can also find application for development of bioactive food packaging. In recent years, application of bacteriocins as part of hurdle technology has gained great attention. Several bacteriocins show additive or synergistic effects when used in combination with other antimicrobial agents, including chemical preservatives, natural phenolic compounds, as well as other antimicrobial proteins. This, as well as the combined use of different bacteriocins may also be an attractive approach to avoid development of resistant strains. The combination of bacteriocins and physical treatments like high pressure processing or pulsed electric fields also offer good opportunities for more effective preservation of foods, providing an additional barrier to more refractile forms like bacterial endospores as well. The effectiveness of bacteriocins is often dictated by environmental factors like pH, temperature, food composition and structure, as well as the food microbiota. Foods must be considered as complex ecosystems in which microbial interactions may have a great influence on the microbial balance and proliferation of beneficial or harmful bacteria. Recent developments in molecular microbial ecology can help to better understand the global effects of bacteriocins in food ecosystems, and the study of bacterial genomes may reveal new sources of bacteriocins.
Food decay by spoilage fungi causes considerable economic losses and constitutes a health risk for consumers due to the potential for fungi to produce mycotoxins. The indiscriminate use of synthetic antifungals has led to the development of resistant strains which has necessitated utilization of higher concentrations, with the consequent increase in toxic residues in food products. Numerous studies have demonstrated that plant extracts contain diverse bioactive components that can control mould growth. The metabolites produced by plants are a promising alternative because plants generate a wide variety of compounds, either as part of their development or in response to stress or pathogen attack. The aim of this article is to summarize the results from the literature on and experiments regarding the effects of plant-derived products for controlling fungal growth. Data from research work on the mode of action of these metabolites inside the fungal cell and the influence of abiotic external factors such as pH and temperature are also covered in the present review. Furthermore, an analysis on how the stress factor derived from the presence of plant extracts and essential oils affects secondary metabolism of the fungus, specifically mycotoxin synthesis, is developed. Finally, the effectiveness of using plant-derived compounds in combination with other natural antimicrobials and its application in food using novel technologies is discussed.
The results given in the literature are conflicting when considering the relationship between antimicrobial activity and chitosan characteristics. To be able to clarify, we prepared fifteen homogeneous chitosans with different acetylation degrees (DA) and molecular weights (MW) by reacetylation of a fully deacetylated chitin under homogeneous conditions. They were tested at different pH values for their antimicrobial activities against four Gram-negative bacteria ( , , and ), four Gram-positive bacteria ( , , and ) and three fungi ( , and ). Chitosans markedly inhibited growth of most bacteria and fungi tested, although the inhibitory effect depends on the type of microorganism and on the chitosan characteristics (DA and MW) with minimum inhibitory concentrations in the range of 0.001 to 0.1 w%. Considering chitosan efficiency on bacteria, our series of data clearly show that the lower DA and the lower pH give the larger efficiency. Antibacterial activity was further enhanced for Gram-negative bacteria with decreasing MW, whereas, opposite effect was observed with the Gram-positive. Concerning the antifungal activity, the influence of chitosan characteristics was dependent on the particular type of fungus. Fungal growth decreased with increasing MW for and decreasing DA for but no MW or DA dependences were observed with .
The objective of this study was to evaluate the efficacy of plant essential oils (EOs) in combination and to investigate the effect of food ingredients on their efficacy. The EOs assessed in combination included basil, lemon balm, marjoram, oregano, rosemary, sage and thyme. Combinations of EOs were initially screened against , , and using the spot-on-agar test. The influence of varying concentrations of EO combinations on efficacy was also monitored using . These preliminary studies showed promising results for oregano in combination with basil, thyme or marjoram. The checkerboard method was then used to quantify the efficacy of oregano, marjoram or thyme in combination with the remainder of selected EOs. Fractional inhibitory concentrations (FIC) were calculated and interpreted as synergy, addition, indifference or antagonism. All the oregano combinations showed additive efficacy against , and oregano combined with marjoram, thyme or basil also had an additive effect against and . The mixtures of marjoram or thyme also displayed additive effects in combination with basil, rosemary or sage against . The effect of food ingredients and pH on the antimicrobial efficacy of oregano and thyme was assessed by monitoring the lag phase and the maximum specific growth rate of grown in model media. The model media included potato starch (0, 1, 5 or 10%), beef extract (1.5, 3, 6 or 12%), sunflower oil (0, 1, 5 or 10%) and TSB at pH levels of 4, 5, 6 or 7. The antimicrobial efficacy of EOs was found to be a function of ingredient manipulation. Starch and oils concentrations of 5% and 10% had a negative impact on the EO efficacy. On the contrary, the EOs were more effective at high concentrations of protein, and at pH 5, by comparison with pH 6 or 7. This study suggests that combinations of EOs could minimize application concentrations and consequently reduce any adverse sensory impact in food. However, their application for microbial control might be affected by food composition, therefore, careful selection of EOs appropriate to the sensory and compositional status of the food system is required. This work shows that EOs might be more effective against food-borne pathogens and spoilage bacteria when applied to ready to use foods containing a high protein level at acidic pH, as well as lower levels of fats or carbohydrates.
Mycotoxins likely have existed for as long as crops have been grown but recognition of the true chemical nature of such entities of fungal metabolism was not known until recent times. Conjecturally, there is historical evidence of their presence back as far as the time reported in the Dead Sea Scrolls. Evidence of their periodic, historical occurrence exists until the recognition of aflatoxins in the early 1960s. At that time mycotoxins were considered as a storage phenomenon whereby grains becoming moldy during storage allowed for the production of these secondary metabolites proven to be toxic when consumed by man and other animals. Subsequently, aflatoxins and mycotoxins of several kinds were found to be formed during development of crop plants in the field. The determination of which of the many known mycotoxins are significant can be based upon their frequency of occurrence and/or the severity of the disease that they produce, especially if they are known to be carcinogenic. Among the mycotoxins fitting into this major group would be the aflatoxins, deoxynivalenol, fumonisins, zearalenone, T-2 toxin, ochratoxin and certain ergot alkaloids. The diseases (mycotoxicoses) caused by these mycotoxins are quite varied and involve a wide range of susceptible animal species including humans. Most of these diseases occur after consumption of mycotoxin contaminated grain or products made from such grains but other routes of exposure exist. The diagnosis of mycotoxicoses may prove to be difficult because of the similarity of signs of disease to those caused by other agents. Therefore, diagnosis of a mycotoxicoses is dependent upon adequate testing for mycotoxins involving sampling, sample preparation and analysis.