The book begins with a general discussion of microbial hazards and their public health ramifications. It then moves on to survey the production processes of different food types, including dairy, eggs, beef, poultry, and fruits and vegetables, pinpointing potential sources of human foodborne diseases. The authors address the growing market in processed foods as well novel interventions such as innovative food packaging and technologies to reduce spoilage organisms and prolong shelf life. Each chapter also describes the ormal flora of raw product, spoilage issues, pathogens of concern, sources of contamination, factors that influence survival and growth of pathogens and spoilage organisms, indicator microorganisms, approaches to maintaining product quailty and reducing harmful microbial populations, microbial standards for end-product testing, conventional microbiological and molecular methods, and regulatory issues.
Microbiologically Safe Foods
Other important topics include the safety of genetically modified organisms (GMOs), predictive microbiology, emerging foodborne pathogens, good agricultural and manufacturing processes, avian influenza, and bioterrorism.
Norma Heredia, ScD, is Professor of Food Safety at the University of Nuevo Leon in Mexico. Her research focus is the epidemiology and control of microorganisms in foods. She serves the industry and government as a consultant and in laboratory analysis of food microbiology. She has served on the editorial boards and as an ad hoc reviewer for several journals.
Irene Wesley, DPH, is a microbiologist at the National Animal Disease Center, part of the USDA's Agricultural Research Service, in Ames, Iowa. Her research focus is the on-farm detection of microbial foodborne pathogens in livestock and poultry. She is a member of the American Academy of Microbiology and has served on national food safety committees and editorial boards.
Santos Garcia, ScD, is Professor and Consultant of Food Safety at the University of Nuevo Leon in Mexico. His research focus is the physiology and control of microbial food-borne pathogens. He has served on international food safety committees and editorial boards for several journals. He is a coeditor of Guide to Foodborne Pathogens (Wiley).
Dried foods are low water activity foods with water activity ranging from 0.03 to 0.7. They are commonly misconstrued to be inherently safe from food borne pathogenic bacteria. However, there are many reported cases where many food borne illnesses were caused by the consumption of dried foods contaminated with Salmonella spp., Cronobacter spp., Staphylococcus spp. and E. coli. In this work, we have systematically reviewed the literature dealing with the effect of drying/dehydration on the survival of pathogenic microorganisms with special focus on Salmonella spp. We have also reviewed and synthesized the literature dealing with the effect of drying process on microorganisms in dried vegetables, meat, fish, spices, mushroom and powdered foods. This review concludes that dried foods are not inherently safe microbiologically and required other hurdles to achieve microbial safety.
The relatively low number of bacteria present in a food sample limits the sensitivity of all of the various types of tests available to evaluate food safety, including those based on culture. A preliminary step called enrichment culture may be used to amplify the number of bacterial pathogens, by pre-incubating the food sample in a non-selective medium that promotes growth of any bacteria that might be in the sample.
We will be conducting our own investigation of food safety using a modified and scaled down adaptation of the standard laboratory methods, beginning with a pre-enrichment culture of food samples, followed by plated on several types of selective and differential media. Our determination of food contamination will be based on (a) growth of bacteria on the selective media and (b) observation of a specific biochemical reaction (usually a color change) characteristic for a particular type of pathogen. Note that these methods are based on bacterial phenotypes (traits), and more than one species of bacteria may have the same selective/differential traits. Therefore, definitive identification of a bacterium isolated from food requires additional testing.
The major determinants for the incidence of FBD are unsafe raw food, abused temperature, inadequate storage, improper handling, undercooking and cross contamination [4]. Food from animal sources, fresh produce and ready-to-eat (RTE) foods are the most at risk. In particular, RTE foods are an emerging issue concerning food safety. Furthermore, they have been demonstrated to contain antimicrobial-resistant strains. Since these products are consumed without any further treatment, they could serve as a vector for the spread of antibiotic-resistant microorganisms, posing a significant threat to public health [5].
Interesting results that bring to light the issues concerning unsatisfactory levels of microbiological contamination of food intended for consumption came from the first systematic nationwide analysis of food safety conducted in Lebanon by Kharroubi et al. [6]. During the campaign launched by the Lebanese MoPH, in the period from 2015 to 2017, 11,625 food samples were randomly collected in unannounced inspections in different food facilities, with 28.7% of them resulting unacceptable for consumption. Raw matrices such as red meat and poultry together with dairy products and spices displayed higher rejection rates. As for pathogens, E. coli, Staphylococcus aureus and Salmonella were detected in several samples, highlighting an unacceptable risk for consumers.
Positive results come instead from the work of Aduah et al. [8], which studied the prevalence of antibiotic-resistant Salmonella enterica in RTE meats in Ghana and investigated the food safety knowledge among food vendors and consumers. The study revealed that 98% of the RTE meats were satisfactory and safe to eat regarding Salmonella and highlighted how these results are certainly linked to the good knowledge of meat safety and the proper handling practices of meat vendors and consumers.
Schill et al. [9] studied the microbiological and sensory quality of cultivated mushrooms available at the Austrian retail level on the day of purchase and after storage. The majority of mushrooms displayed high microbiological and sensory quality at the day of purchase while differences in the microbial load and sensory characteristics have been observed especially in re-packed mushrooms with long transport distances. The shelf life of these products appears to be affected by various aspects, including raw material quality, the processing environment and postharvest and storage conditions, and studying these intrinsic and extrinsic factors is important to guarantee safe products that maintain their microbiological and sensory qualities throughout shelf life.
An interesting study has been conducted by Maio et al. [11], who evaluated the microbiological quality of different food products sold in supermarkets at the expiry date. It was observed that 70.21% of the samples analyzed at the expiry date failed in at least one microbiological criterion, resulting, however, as safe given the absence of pathogenic microorganisms. These data point out the issues concerning shelf life and the challenges that food manufacturers face in order to minimize decrease in product quality due either to spoilage by bacteria or to biochemical processes.
As mentioned above, apart from microbiological risk, pluricellular parasites (e.g., nematodes) also represent an important public health issue that affect food quality and safety. Ahuir-Baraja et al. [12] have evaluated the effectiveness of gutting Blue Whiting in Spanish supermarkets as an Anisakidosis safety measure. The results show that the prevalence of ascaridoid larvae infection found in ungutted blue whiting was considerably high. However, if gutting reduces the larval burden, it cannot be considered an effective method for the total removal of ascaridoid larvae. Larger and heavier fish present higher infection levels. The time until evisceration is also an important factor.
These results confirm the need to develop and improve new strategies to achieve safe and healthy food; currently, in this context, novel technologies are being investigated in many different countries. Alternative agricultural practices, such as hydroponic culture, represent an interesting example. Hydroponic vegetables are cultivated in the absence of soil and rely on the use of balanced nutrient solutions to support their development. Given the more controlled environment and the feasibility, hydroponic culture is an attractive alternative to increase the quality and safety of produce. Currently, the literature lacks significant reports on the benefits of this technique, but there is a general belief that it can provide healthy and more hygienic products, and for this reason, it is becoming more and more popular. In the work by Lam et al. [13], this issue has been addressed. Researchers investigated the microbiological contamination and the presence of antibiotic resistant bacteria in hydroponic lettuce, compared to conventional and organic lettuce in retail. As expected, hydroponic lettuce contained the least number of resistant bacteria among the three groups. However, antibiotic-resistant bacteria contamination also appears to be an issue not to be underestimated in this particular type of product, and water appears to be the crucial element to control in order to obtain microbiologically safe products and reduce the spread of AMR.
Alternatives to conventional processing procedures are also taking place. An alternative to classic thermal sterilization of liquid foods is the use of ultrasounds. This technique has been applied primarily to milk and fruit juices, with the aim of increasing shelf life due to the reduction of contaminating microorganisms, still improving the quality of products, that display increased levels of antioxidants and bioactive compounds. Ma et al. [14] studied the effect of ultrasound-combined sterilization technology on the safety and quality of grape juice. Ultrasound treatment is often more effective when combined with moderate heat and is known as thermosonication. These authors found that thermosonication (TS) and TS combined with nisin (TSN) are very promising alternatives to conventional thermal sterilization; they are able to improve the nutritional and functional characteristics of grape juice, increasing the total phenolic content and antioxidant capacity, and at the same time ensure microbiological safety. 2ff7e9595c
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