Food Preservation and Safety of Natural Products

By Helen N Onyeaka and Ozioma F. Nwabor

Food Preservation and Safety of Natural Products addresses the most common causes of food spoilage that create significant loss to global food production while also discussing how food serves as a vehicle for the transmission of pathogenic microorganisms responsible for mild to debilitating health conditions in humans. The book provides essential information for food safety professionals on issues relating to foodborne diseases and offers potential solutions by presenting various methods of incorporating natural products in food production to prevent the spread of foodborne pathogenic organisms.

The demand for green consumerism and consumers general distaste for synthetic food additives poses a serious challenge to food safety and preservation. Natural products are used as green and sustainable source of bioactive compounds that can be applied in various fields including food. The use of plant and other natural products in food preservation is on the rise, hence this book reviews microbial mediated food spoilage, foodborne pathogens and food contamination and offers applications of natural products in food preservation.

• Provides important information on microbial metabolic by-products (natural enzymatic processes) to prevent food spoilage or deterioration
• Includes molecular techniques for antimicrobial and antioxidant applications in food, food packaging and edible films
• Presents the latest evidence-based science on the natural products used as additives in food

• Language: English
• Publisher: Academic Press
• Release date: Jun 15, 2022
• ISBN: 9780323857017

Helen N Onyeaka

Dr. Helen Onyeaka is an Associate Professor at the School of Chemical Engineering at the University of Birmingham. She is a highly qualified industrial microbiologist with over 25 years in the field. She holds a PGCE in Biology from Warwick University, a PhD in Biochemical Engineering from the University of Birmingham, an MSc in Biomedical Sciences from Wolverhampton University, and a BSc in Industrial Microbiology from the Federal University of Technology Owerri. She has gained experience working as a lecturer and researcher in the fields of food microbiology, food safety, and chemical engineering. She received the Bridon postgraduate and IChemE Biochemical Engineering award for her doctorate thesis. Dr. Onyeaka is a member of several professional organizations, including the Institute of Biomedical Science, the Society for General Microbiology, the Biochemical Engineering Subject Group (IChemE), the Institute of Biology, the Society of Chemical Industries and The European Federation of Biotechnology, Society for Applied Microbiology.

Book preview

Chapter 1: Introduction

Abstract

The term food preservation and safety has been used over time to mean different things. In the various chapters of this book, particular focus was placed on food spoilage by microorganisms as a major threat to food preservation and safety. Chapter 2 discusses the interactive behavior of food spoilage microorganisms that contribute to their growth and spoilage ability. It also seeks to report necessary information that will enhance understanding of basic concepts related to microbial spoilage of food, ecology, interactions, and the role of microorganisms in food spoilage. Chapter 3 focuses on the sources of microbial contamination and major foodborne pathogens and their clinical features. Chapter 4 discusses various conventional and novel rapid methods for detecting, isolating, and enumeration of foodborne and spoilage microorganisms. Chapter 5 presents traditional preservation and progress in preservation science and highlights the major conventional preservation techniques as well as synthetic chemical preservatives commonly used in food preservation. Chapter 6 reviews natural products as a reliable source of promising food preservatives, emphasizing antimicrobial and antioxidant plant and microbial compounds. Furthermore, it highlights the safety of natural products and the various mechanisms of action as food preservatives. Chapter 7 presents several encapsulation methods that have been highlighted, and their role in the encapsulation of natural products for food application has been detailed. In Chapter 8, some of the emerging technologies employed in food preservation and safety and quality maintenance are discussed. The use of natural active components in smart food packaging systems is discussed in Chapter 9, while Chapter 10 elaborates on natural polymers as food packaging materials. The concept of biocontrol is then explored. Chapter 11, Chapter 12, and Chapter 13 present lactic acid bacteria and bacteriocins as biopreservatives, bacteriophage as a potential biocontrol agent, and antimicrobial peptides in food preservation, respectively. Chapters 14 and 15 discuss natural polymers and hydrocolloid applications in food and natural products as functional food. In Chapter 16, legislations on the use of natural products are presented, while Chapter 17 focuses on the valorization of natural industrial agro-food byproducts, and in Chapter 18, nanotechnology, and nanomaterial delivery in the food system are elaborated.

Keywords

Food preservation; Food safety; Food spoilage; Microbial spoilage; Food quality

Food is a fundamental necessity of life and until this date a scarce and insufficient resource. The United Nations Food and Agricultural Organization estimates that about 821 million people (1 in 9) of the world’s population still do not have enough to eat, and the prevalence of undernourished people is on the increase (1). Hence, food conservation and security are global emergencies calling for immediate and concerted efforts of stakeholders in the food sectors and government. Preservation is an inevitable part of food production and processing, intended for the purpose of food conservation and shelf-life extension. In addition, factors such as the globalization of trade necessitate the extended use of preservatives to prolong the shelf-life of products. Fresh agricultural produce and processed products are shipped thousands of miles, from producer to consumer countries, spending a long time in transit and thus exposed to various forms of damage including microbial and enzymatic deteriorations. Food spoilage or deterioration is a natural process that results from the accumulation of microbial metabolic by-products or natural enzymatic processes such as redox reactions. However, microbial-mediated food spoilage is presumably the most common form of food spoilage resulting in significant loss to global food production.

Besides microbial-mediated food spoilage, food also serves as a vehicle for the transmission of pathogenic microorganisms responsible for mild to debilitating health conditions. Hence, the goal of preservation is not just to prolong the shelf-life of food, but also to improve food safety by preventing the spread of foodborne pathogens. To ensure global acceptance, food industries must adhere to manufacturing standards and good manufacturing practices, comply with principles such as hazard analysis and critical control point (HACCP), and hazard analysis and risk preventive control (HARPC). Strict adherence to established directives, standard operational procedures, good manufacturing practices, HACCP, and other established standards is a fundamental requirement for quality and effective production of safe food products. Food safety is therefore a paramount factor for consideration since deviation might not only attract sanctions or smear the integrity of producers but might amount to devastating public health consequences. Food recall arising from compromise in the quality of products results in substantial economic losses to producers and loss of consumers’ confidence. Thus, guaranteeing the safety of food product demands strict compliance and enforcement of adequate preservative measures aimed at ensuring that food is free from pathogenic microbes as well as other spoilage mediators. Preservation approach includes all food treatments that prolong the shelf-life, protect nutritional, physical, and sensory properties, inhibit proliferation of spoilage microorganisms, and prevent progression of oxidative reactions.

The art of preservation dates to the origin of man. In ancient times, sun drying, salting, smoking, and fermenting were the choice techniques. For instance, meat and fish were preserved by freezing in a cold climate, while the use of fire in preservation can be traced to the pre-Neolithic period. Sun-dried farm product such as cereals, seeds, and tubers were common in Africa and Asia before the colonial era and is still practiced to date among rural farmers. Also, the South Americans practiced potato drying many centuries before the rise of the Inca Empire, and the Indians of pre-Colombian North America used air-drying, with or without smoking, to preserve deer and buffalo meat. More also, fish was dried, salted, and smoked on the shores of the North Atlantic, and both.

These ancient preservation techniques were effective but had many drawbacks that restrict their industrial and large-scale applications. These shortcomings necessitated the search for new, easy, safe, and effective preservation techniques that would ensure longer preservation of food products without constant retreatment. Therefore, the conventional methods are now being replaced by emerging technologies.

As the science of preservation evolved, chemical, physical/mechanical, and irradiation were employed as alternatives means for food shelf-life extension. Physical methods of preservation remained the choice methods of preservation, not involving the addition of extraneous compounds to food. The commonly used physical methods of preservation are based on the reduction of food moisture content through dehydration and storage temperature control. These methods inhibit the growth of microorganisms by reducing the food water activity (aw) to levels unsuitable for microbial proliferation. Notwithstanding, conventional physical methods are time-consuming as well as energy-intensive.

The use of chemicals in the preservation of food is an effective means to prolong the shelf-life of food. Most chemical preservatives are antimicrobials that target spoilage and foodborne microorganisms through growth inhibition by disruption of their cell membrane integrity, interaction with transport channels, inhibition of functional proteins and interference with metabolic enzymatic processes. Antioxidant preservatives inhibit the generation of free reactive radicals and prevent oxidative phosphorylation of fatty, oily, and protein food components. However, the use of chemicals such as butylated hydroxyanisole, sodium benzoate, sodium nitrite and nitrate, and hydroxytoluene in the preservation of food has recently raised controversy. Consequently, reports on hazardous health effects and interference with normal cell division/development have prompted restricted usage. Following the food additive amendment of the Food and Drug Administration (1958), the concept of generally recognized as safe (GRAS) as a requirement for all food additives and preservatives requires that substance used as food additive or preservative must undergo regulatory scrutiny to attain their safety status. Nevertheless, the use of chemicals in the preservation of food remains one of the most convenient forms of preservation, without limitations and repeated treatments.

Exposing food products to carefully measured ionizing radiation as a preservation technique is effectively similar to chemical preservatives. Irradiation as a food preservation technique consists of the application of electromagnetic waves to food products to confer a longer shelf-life. The application of irradiation has demonstrated effects at retarding food spoilage by insect pest infestations (2,3). In this process, radiation inactivates food spoilage organisms, including bacteria, molds, and yeasts (4–6). It also destroys disease-causing organisms, including parasitic worms and insect pests, that damage food during storage (7,8). However, irradiation might impact alterations to food nutritional and sensory properties (9,10), involves high energy input, and constitute a level of risk to food workers due to exposure to electromagnetic radiation.

References

1 Pradhan P., Kropp J. Climate Change and Food Security: Highlighting Urban Food System and Regional Specificities. In: United Nations Expert Group Meeting on Population, Food Security, Nutrition and Sustainable Development 16th-17th September 2019, New York; 2019.

2 Sileem T.M., Mohamed S.A., Mahmoud E.A. Efficiency of the Gamma Irradiation in Controlling the Red Flour Beetles, Tribolium Castaneum Herbst, and Preventing Its Secondary Infestations. Egypt Acad. J. Biol. Sci. 2019;11:87–96.

3 Eyssa H.M., Sawires S.G., Senna M.M. Gamma Irradiation of Polyethylene Nanocomposites for Food Packaging Applications Against Stored‐Product Insect Pests. J. Vinyl Addit. Technol. 2019;25:E120–E129.

4 Tawema P., Han J., Vu K.D., Salmieri S., Lacroix M. Antimicrobial Effects of Combined UV-C or Gamma Radiation with Natural Antimicrobial Formulations against Listeria Monocytogenes, Escherichia coli O157: H7, and Total Yeasts/Molds in Fresh Cut Cauliflower. LWT Food Sci. Technol. 2016;65:451–456.

5 Gabriel A.A., David M.M.C., Elpa M.S.C., Michelena J.C.D. Decontamination of Dried Whole Black Peppercorns Using Ultraviolet-c Irradiation. Food Microbiol. 2020;88:103401.

6 Choi E.J., Park H.W., Yang H.S., Chun H.H. Effects of Combined Treatment with Ultraviolet-C Irradiation and Grape Seed Extract Followed by Supercooled Storage on Microbial Inactivation and Quality of Dongchimi. LWT Food Sci. Technol. 2017;85:110–120.

7 Lacombe A., Breard A., Hwang C.-A., Hill D., Fan X., Huang L. Inactivation of Toxoplasma Gondii on Blueberries Using Low Dose Irradiation without Affecting Quality. Food Control. 2017;73:981–985.

8 Feliciano R.J., Gabriel A.A. Juice Composition, Physicochemistry, and Efficacy of Ultraviolet Radiation Against Cryptococcus Albidus. J. Food Compos. Anal. 2019;84:103313.

9 Boylston T.D., Reitmeier C.A., Moy J.H., Mosher G.A., Taladriz L. Sensory Quality and Nutrient Composition of Three Hawaiian Fruits Treated by X‐irradiation. J. Food Qual. 2002;25:419–433.

10 Ahmad T., Butt M.Z., Aadil R.M., Inam‐ur‐Raheem M., Bekhit A.E.D., Guimarães J.T. Impact of Nonthermal Processing on Different Milk Enzymes. Int. J. Dairy Technol. 2019;72:481–495.

Chapter 2: Food ecology and microbial food spoilage

Abstract

Food spoilage, an organoleptic change in food, can occur at any stage along the food chain. This spoilage may be influenced by insect and physical damage, indigenous enzyme activity, or microorganisms. Besides perishable foods with a limited lifespan, food generally has a considerably longer lifespan, but it spoils eventually. In the course of microbial food spoilage, substrates such as organic acids, esters, carbonyls, diamines alcohols, sulfur compounds, hydrocarbons, and fluorescent pigments are generated as by-products. Although chemical and physical variables are the key factors for detecting spoilage microorganisms, food contamination by microbial toxins or spores is often unsuspected until the outbreak of foodborne infections. Thus, notwithstanding the enormous health and economic impacts associated with food spoilage, the mechanisms and interactions leading to food spoilage are still, to a considerable extent, very unclear. This chapter discusses the interactive behavior of food spoilage microorganisms that contribute to their growth and spoilage ability. It also seeks to report necessary information that will enhance understanding of basic concepts related to microbial spoilage of food, ecology, interactions, and the role of microorganisms in food spoilage.

Keywords

Food spoilage; Microbial contamination; Food ecology; Spoilage organisms

Overview

As global population continues to increase, there is a growing concern for food shortage and sustainability. Hence, food spoilage resulting in wastage of agricultural produce and food products, and contributing to shortage in supply is a global challenge. Also, the lack of proper and modern storage facilities is a problem for global food production and security, with preservative failures and resistance of spoilage microorganisms as contributing factors. The lack of detailed and accurate understanding regarding the process and mechanism of spoilage, associated microorganisms, and the ecology of food is a drawback to addressing these issues. To address this, it is essential to confront the drawbacks to shelf-life extension of food products as well as proper packaging, in order to guarantee food security globally. This chapter dwells on information that will enhance better understanding of basic concepts related to microbial spoilage of food, ecology, interactions, and role of microorganisms in food spoilage. Proper comprehension of these mechanisms is needed for preservation method and storage design. Factors including food-specific spoilage organism, as well as intrinsic and extrinsic factors that enhance the proliferation of food spoilage microorganisms and the role of storage parameters in food spoilage should be understood.

It is well known that microbial food spoilage is a natural phenomenon mediated by food autochthonous microbiota. The spoilage of food product through microbial activities could result in the accumulation of malodorous by-products. These metabolites from the growth of microorganisms can alter the products organoleptic, nutritional, and sensory qualities, making them distasteful to consumers. Annually, the economic losses resulting from microbial mediated food spoilage account for millions of dollars in monetary terms, with millions of tons worth of products. The United Nations Food and Agricultural Organization estimated that 1.3 billion tons of food products are lost annually to spoilage (1). This is mostly attributed to microbial spoilage, leading to final products with unacceptable properties and quality (2). It is estimated that approximately 25% of all foods produced globally are lost due to microbial spoilage (3).

Efforts at containing microbial mediated food spoilage have significantly succeeded at extending products shelf-life while concurrently reducing the prevalence of foodborne infections and intoxications. However, recent consumers craving for minimal preserved food and green consumerism challenge the current state of preservation. Effective design and implementation of a reliable preservation regime in conformity with changing consumers taste and regulations must incorporate a basic understanding of the microbial metabolism and ecology. Such knowledge of food from a natural perspective, vis-à-vis food ecosystem and ecological influence on spoilage and the deteriorative process is required for effective and healthy preservation of food.

Food ecology

Food products are frequently contaminated by microorganisms present along the food production chain. During production and harvesting, soil microorganisms can contaminate food crops and vegetables. Likewise, microorganisms present in water could contaminate most processed food products if not treated. During processing, the microbial load of agricultural products are significantly reduced, but not completely eliminated. Factors including noncompliance to regulations, standard operating procedures as well as poor manufacturing practices, are implicated in processed food contamination. Poor hygienic practices by food handlers might also result in the contamination of the food production line, and cross-contamination of finished products. The presence of microorganisms in finished products facilitates spoilage.

Food spoilage is a complex ecological phenomenon triggered by the biochemical activity of specific groups of microorganisms (4). It involves microbial interaction and communication, at individual, population and community levels within the food matrix. It also includes microbial diversity and dynamics, community structure, ecological function, response to alterations in the food environment, and presence of antimicrobial molecules. These activities are modulated by food structure and composition, as well as the inherent microbial population. These food hurdles present a defense barrier against the proliferation of diverse potential spoilage microorganism. However, certain organisms termed specific spoilage organisms surmount food hurdles, and act as first-line colonizers and a scaffold for progressive food invasion and deterioration. Diversity of the microbial food consortia determines the rate and pattern of degradation. Single specie degradations mostly examined in experimental settings are slow, unlike the natural multicultural food spoilage process. Fig. 1 illustrates the kinetics of food spoilage in a monocultural and multicultural condition. Multicultural food spoilage proceeds faster than monocultural food spoilage. Natural food spoilage is a multicultural phenomenon involving multiple microbial species and subpopulations. Microbial communication (quorum sensing) modulates gene expression within the community (5), resulting in the production of spoilage enhancing metabolites. At a certain threshold, microbial populations induced gene expression effectuates the synthesis of food spoilage enzymes.

Fig. 1

Fig. 1 Rate of spoilage by single and mixed microbial population.

Quorum sensing regulates natural selection during the spoilage process (6,7). Predominant microbial populations’ controls gene expression and modulates the synthesis of enzymes/metabolite (8). Members of the community communicate by exchange and sensing of signaling molecules (9). Microbial communication promotes synergism between various population within the community (10). Auto induction facilitates communication through the binding of signaling molecules to cellular receptors, triggering changes in gene expression. Coexisting microbial populations engage in inter-species and intra-specie communication within the community (7). However, the mechanism of quorum sensing differs between species. Expression of transcriptional regulator (Lux R) proteins and autoinducer synthase I (Lux I) controls quorum sensing in Gram-negative bacteria (11). In Gram positives, quorum sensing is controlled by the agr system and the Lux S auto-inducer peptide AI-2. Microbial community structure shades populations from the detrimental effect of food antimicrobials, preservative, and sanitizers (6,12). Alteration of the quorum-sensing pathway controls microbial gene expression and thus might be employed for successful modulation of communication enhanced spoilage. Development of inhibitors targeted at blocking microbial signaling networks will prolong shelf-life and preventive spoilage. The microbial community, serves as an adaptive strategy to environmental fluctuations and promotes population stability (6). However, despite the benefits of communal living, the interspecies competition promotes negative interactions and natural selection.

Specific spoilage organism concept

Most nutrient-rich food products are prone to microbial deterioration (13). Micorbial metabolic activities and accumulation of metabolic by-products facilitate food spoilage with altered sensory and organoleptic qualities (14). This is commonly, initiated by native microorganisms that elude processing steps and cross contaminants. However, the survival and proliferation of a microorganism within food substrate depend on its physiology and metabolism. Although several microorganisms can survive in food products, predominant species associated with specific food are described as the food’s specific spoilage organisms. This classification attributes to organisms that possess the ability to produce spoilage mediating metabolites associated with food quality alteration sufficiently to result in rejection (15). The spoilage microbiota or specific spoilage organisms constitute a minute fraction of the food microbial population and often involve specific species or genera (15). Species of lactic acid bacterial, including Leuconostoc, Lactobacilli, and Lactococci, are frequently associated with spoilage of food with high sugar content. Thus, the metabolic substrate demand of an organism is an important determinant of the food type the organisms mediates its spoilage. Pseudomonas spp., Shewanella, and Enterobacteriaceae are associated with spoilage of protein-rich food substrates. Fungi and molds including Aspergillus, Fusarium, Penicillium, Stachybotrys, and Saccharomycetes are responsible for the spoilage of food with water content low enough to inhibit the growth of bacteria. Although constituting a population minority in food, the specific spoilage organisms multiplies rapidly during storage producing spoilage mediating enzymes (16). These organisms dismantle food hurdles, prompting compromise, and create conducive environment for competent organisms to thrive. In contrast, the production of acidic and antimicrobial by-products by certain bacteria groups inhibits the growth of nontolerant microbial species. Food spoilage microbiota possess the necessary metabolic machinery required to deteriorate the initial food hurdles. Like the primary colonizers, specific spoilage organisms initiate colonization of food environment, resulting in cascade of successional changes in microbial community and population during spoilage. Food spoilage climaxes in the complete deterioration of products by a multicommunal mixed population. Table 1 presents various types of food and food products with detailed list of specific spoilage organisms as contained in published articles. Fig. 2 shows the succession in microbial spoilage of food from initiation to deterioration. Several species and microbial class colonize the food product at different times leading to the complete deterioration of the food product. Fig. 3 presents the growth pattern of individual groups of food spoilers. The specific spoilage organisms exhibit rapid growth rate, while the scavengers show slow or delayed growth.

Table 1

Fig. 2

Fig. 2 Food spoilage progression.

Fig. 3

Fig. 3 Transformational changes in food spoilage microflora.

Factors affecting microbial food spoilage

Extrinsic (environmental) and intrinsic (inherent) properties of food are the major determinant of the food spoilage microbiota Fig. 4. The food spoilage microbiota is dynamic, and changes from stage to stage during the spoilage process (130), in response to alterations in food properties and storage environmental conditions. Spoilage initiator microbiota might not necessarily constitute the microbiota at degradation and decay (131). Chemical and enzymatic transformation of food components regulates the microbial population variation and dynamics, resulting in the formation of compounds that alters the sensory and nutritional qualities. To effectively initiate the spoilage process, food spoilers must be able to survive and metabolize within the food environment. Thus, psychrotrophs and psychrotolerants, including Pseudomonas spp. (132), Brochothrix thermosphacta(133), Bacillus spp. (134), Pantoea agglomerans, Serratia spp., Hafnia alvei, and Yersinia enterocolitica(135), frequently mediate spoilage at refrigerator temperatures. Acid-tolerant spore-forming bacterium Alicyclobacillus acideoterrestris is a primary spoilage organism of pasteurized juice (136) and withstands environmental acidic content. The pH and water activity (aw) of food limits the range of microbial colonizers. Optimum pH and water activity (aw) for microbial activity are between 6 and 7.5 and 0.98–0.99 (131), respectively. Food intrinsic factors are determinant of food spoilage microbiota. Decreased aw below the minimum tolerant level inhibits the growth of bacteria except for extremophiles and filamentous fungi capable of growing on dried matrix. Spore formers such as Bacillus and Clostridia spp. play a notable role in the spoilage of mild heat-treated food products. This is due to their ability to form spores in the presence of heat and subsequently revert to vegetative growth under favorable conditions. Clostridium spp. are implicated in blown pack spoilage of vacuum-packed products (137,138), favoring the demand for anaerobic/facultative aerobic growth requirement. Nutrient content and class are important for microbial colonization and deterioration of food products. Most Enterobacteriaceae can effectively degrade protein rich products owing to the ability to convert amino acids to malodorous volatile compounds, such as diamines and sulfuric compounds.

Fig. 4

Fig. 4 Factors contributing to food spoilage.

Extrinsic or environmental factors are important attributes of every ecosystem, with tremendous effects on the life and survival of inhabiting populations. They include storage temperature, light, humidity, gaseous condition, and packaging. Implicit factors relating to microbial factors including growth rate, tolerance, physiological characteristics, adaptation, and interactions, are important parameters to the rate of food spoilage.

Interactions and adaptation of an organism to its immediate environment determine its survival or extinction. Food as an ecosystem involves a complex interplay of abiotic storage environmental factors referred to as extrinsic factors. These factors include, the food storage temperature, humidity, processing pressure, light, and aeration. Stability of food inert components and maintenance of organoleptic and sensory properties of food products relies on strict adherence to appropriate storage conditions. Modulating food storage environmental conditions against the optimum growth requirements of food-specific spoilage organisms truncates microbial metabolism, hence ensuring prolonged shelf-life. Storage of food at ≤  4 °C as obtained in refrigeration has been employed sustainably as a preservation technique. Relative humidity affects products shelf-life by promoting microbial growth, altering food composition and destruction of the food packaging. Hygroscopic food products absorb water from the environment leading to altered food composition that might facilitate the growth of food spoilage microorganism. Thus, ensuring appropriate relative humidity within the food storage environment is key to food stability and preservation. A previous research concluded that relative humidity was the most important factor affecting the relative abundances of microbial communities and had a 38.98% and 15.74% contributions to the variation of bacterial and fungal communities, respectively, in a food product (139). Lipid oxidation is one of the main mechanism of deterioration in food products such as edible oils and beverages, affecting their chemical, physical, and sensory properties. Auto-oxidation and photo-oxidation are commonly responsible for the induction of lipid oxidation (140,141). Photo oxidation is a chemical reaction, where, a substance reacts with oxygen under the influence of light. Exposure of food products to light mediates photo-oxidation of photo reactive components, leading to alterations in the food organoleptic, sensory, and chemical compositions. Hence, protection of food from direct exposure to light ensures prolongation of shelf-life. These factors consciously optimized and applied in food processing and storage helps retain the ambient conditions of the food storage environment without impacting negatively on the food properties.

Microbial interactions

Food constitutes a distinctive ecosystem of multidynamic microbial populations characterized by an abiotic matrix of abundant nutrients (142). The relationship between foods and inherent microbial community is essential to food quality and safety. The presence of undesirable microbial population affect food quality, and as a consequence cause spoilage or foodborne disease (143). Therefore, the knowledge of microbial food community and their interactions within the food matrix will contribute to managing the menace of microbial food spoilage and guide food handlers, scientist and producers. Unfortunately, microbial associations in food communities are poorly investigated (142) not minding the less complex nature of the food communities compared to other environment (144). Food microbial interactions are important to spoilage (14) as in fermentation (145). In Table 2, microbial associations within specific food products are reported together with the intended application in the food system. Like every environment, the microbial food communities are in constant competition for both space and nutrient. Thus, positive as well as negative interactions dominate this microenvironment. Fig. 5 shows a diagrammatic representation of the various interactions between food microbial populations. Specific classes of organisms are used to represent distinct populations in the food systems and the arrows are used as a linkage between populations and the type of interaction between them.

Table 2

Fig. 5

Fig. 5 Schematic representation of microbial interactions in food ecosystem.

Negative interactions

Microbial interactions that affect adversely the participating population are classified as negative. The commonly encountered negative interaction includes amensalism, predation, competition, and parasitism. Certain groups of the food spoilage microbiota secrete metabolic by-products with antimicrobial properties. Lactic acid bacteria like L. lactis and Pediococcus spp. produce antimicrobial (bacteriocin), namely nisin and pediocin, that inhibits the growth of other groups of Gram-positive food spoilers (163). Other antimicrobial bacteriocin produced by LAB includes plantaricin, bulgaricin, acidophilin, pediocin, and lactocin. Majority of Gram-negative bacteria are resistant to the effect of bacteriocins, probably due to the structure and composition characteristics. Yeasts involved in the spoilage of wine are also able to inhibit malolactic bacteria by secreting several bioactive compounds and often involving combinatory effects (164,165). Production of ethanol by S. cerevisiae adversely affect non-ethanol-tolerant bacteria and yeast species (165,166), leading to a decline in biodiversity (167,168). Classical predation in the food ecosystem is exemplified by the activity of the aerobic predatory bacteria, Bdellovibrio bacteriovorus on many species of Gram-negative bacteria, causing the lysis of the invaded prey. This organism, found in many food spoilage environments preys on Gram-negative spoilage bacteria such as E. coli and Salmonella spp. (169). Parasitism in the food microenvironment is demonstrated by bacteriophages present in the food. Most phages found in food infect, multiply. and lyse both spoilage and foodborne pathogenic bacteria host. Food bacteriophage play significant roles in specie elimination during microbial succession in food deterioration, and cross transfer of genetic information through transduction. Applications of competent lytic phage inhibits the growth of spoilage bacteria and extend food shelf-life (170–172). Incorporation of the T4, P100, and P7 phage in food will inactivate the foodborne pathogenic bacteria E. coli, L. monocytogenes and S. enterica respectively. Host specificity and sensitivity are major advantage of phage. Biotechnological attempt exploiting this unique property in food biocontrol for the inhibition of spoilage and foodborne microorganism is presumably a recent advancement in food biocontrol and preservation science. However, this might also be a major drawback to industrial application of phage as biocontrol agents, given the narrowed range of susceptible bacterial species. In addition, application of bacteria species as bio-protective cultures against targeted food spoilage organisms attempts to explore natural negative interactions coexisting between different bacteria species and genera as a foundation for the design of alternative control strategy.

Positive interaction

Positive microbial interactions, including mutualism, commensalism and cooperation involving both intraspecies and interspecies, dominate the food ecosystem. Mutualism or synergism between two or more microbial populations enhances the breakdown of complex, recalcitrant food components. Microbial populations involved in mutualistic relationship are indispensable partners, hence the absence of one population negatively affects the other. This natural cooperation is important in diverse biotechnological and industrial applications, for the formation of desired products such as yogurt, wine, and sauerkraut. Mixed cultures of diverse yeasts and bacteria populations are important in the production of wine, and improving aroma and flavor profile of the finished product (173,174). However, irrespective of the industrial benefits associated with mixed microbial cultures, unregulated presence in food enhances the rate of spoilage. Mixed culture of LAB and Enterobacteriaceae enhanced the spoilage of vacuum-packed beef with the accumulation of putrescine when compared to single microbial cultures (175). Food ecological microbial populations show inter-dependence for nutrients, which are necessary for effective product deterioration (175,176). Microbial interactions in the food deteriorative process have not received much research attention, as seen by the paucity of literature. However, a plethora of research dedicated to the role played by multiple microbial populations and cocultures in controlled deteriorative processes like fermentation gives credence to the importance of microbial cooperation. Symbiotic relationships among microorganisms in the food microenvironment enhances microbial diversity of the food ecosystem, thus promoting the spoilage of food. Certain populations of the ecosystem depend on other for survival without hurting or posing any threat to them. Metabolic activities of member of the food ecosystem might alter environmental conditions like pH or generate metabolites required for the survival of another population. This relationship is demonstrated by the removal of oxygen by groups of Gram-negative bacteria, creating an anaerobic environment suitable for the proliferation of Clostridium spp. in meat spoilage (14). LAB also ensures the breakdown of sugar in high sugar-containing products, promoting the growth of Staphylococcus spp. and other Gram-positive spoilers. Lipase producers, such as Bacillus cereus, secrets phospholipase enzyme that degrades food lipid contents, encouraging the growth of nonlipase producing strains and enhancing the rate of microbial food spoilage.

Bacteria in food spoilage

Food shortage caused by microbial activities could lead to starvation. The spoilage of food can arise from different sources and manifest in various forms. Microbial mediated food spoilage is the most predominant form of food spoilage seconded by enzymatic deteriorations resulting from oxidative and reduction reactions. Due to the ubiquitous nature and diversity of bacteria, bacterial food spoilage contributes immensely and probably the most common form of microbial mediated food spoilage. Bacterial mediated spoilage is often characterized by production of slimy off-odor metabolites and food texture alterations. Food contamination by bacteria results in spoilage, food intoxication/poisoning, or foodborne disease. Consumption of bacteria or exogenous bacterial metabolites in food is a major cause of food poisoning, intoxication and foodborne disease, resulting in mild illness such as diarrhea, vomiting and stomach cramp and in severe cases might lead to hospitalization and death if not properly handed. Staphylococcal food contamination is a common cause of food poisoning resulting from the ingestion of staphylococcal enterotoxins (SEs) preformed in food by enterotoxigenic strains of S. aureus(177). Food and food products are often contaminated by bacterial during production, processing and handling. Food service workers play a key role in the contamination of food and finished products. Several meat contaminating bacteria such as coliforms, micrococci, pseudomonads (8,14) are frequent colonizers of animals, whereas vegetables are often contaminated by soil bacteria such as Bacillus spp. Most food spoilage bacteria are inactivated during storage. However, few storage condition–persistent species might thrive either in viable active forms or as inactive spores in food products, resulting in the compromise of products.

Mold and yeast in food deterioration

The versatility and tolerance to harsh environmental conditions makes yeast and molds ubiquitous environmental microflora and regular contaminants of food and agricultural products. These organisms can grow on virtually any kind of food but frequently implicated in grain, cereal, nuts and fruit spoilage. Yeast constitutes the dominant spoilage microbiota in food with low water activity and high sugar content. Fungi-mediated food spoilage often results in the formation of deadly mycotoxins by toxin-producing species (178). Generally, optimum water activity aw requirement for most yeast range from 0.87 to 0.94, molds grow at lower aw of 0.70–0.80 with some osmotolerant species growing at aw of 0.60 (179). Food spoilage fungi can originate from various sources, including the atmosphere, soil, plants, and sea water. Mycotoxin-producing mold from sea salt was implicated in the spoilage of dry-cured meat in a Slovenian production facility (180). Spoilage mediated by yeast and molds are often visible as patches or discolorations that destroys visual appeal. Molds and yeast contamination are challenging to management due to resistance and tolerance to various preservatives. Mycotoxin such as aflatoxin produced by Aspergillus flavus and Ochratoxin A (a potent nephrotoxin and carcinogen) are primary concern to mold/yeast contamination. Heat stable mycotoxin are a major cause of food-related intoxications and in mild situations might result in allergy. Although rare, consumption of yeast/mold in contaminated food might elicit opportunistic infections in immunocompromised and aged individuals (181,182). Enzymes produced by yeast and mold such as protease, lipase, hydrolase, cellulase, pectinase, and other carbohydrate degrading enzymes are potent degraders of food hurdles. In the food ecosystem, interactions of yeast/molds with bacteria enhances the rate of spoilage and deterioration. Purposeful and regulated interaction of filamentous fungi, yeasts, and LAB are a crucial biotechnological strategy for the production of several fermented food products, with improved organoleptic characteristics (183). However, in the natural environment, unregulated interactions between yeast/molds and bacteria negatively impact microbial diversity with the possibility of spoilage enhancement (184,185).

Phage in the food ecosystem

Bacteriophages are ubiquitous biological entities recognized as the most diverse and abundant on the biosphere, outnumbering the bacteria by 10-fold (186,187). Bacteriophages have been isolated from various environments and samples including: food and food products (188–192) as well as animal feed (193). Although rarely associated with spoilage, bacteriophages are important in the food ecosystem as they play a crucial role in shaping microbial diversity of the food spoilage process. Lytic phage infects bacteria, leading to lysis. The presence of phage in the food significantly reduces or eliminates susceptible bacteria species. Food spoiler such as Campylobacter jejuni, E. coli, Salmonella enteritidis, Shigella flexneri, Yersinia enterocolitica, Bacillus cereus as well as foodborne pathogens like Listeria monocytogenes are susceptible to phage lysis (189,190,194–196). Phage in addition increases the genetic diversity of its immediate ecosystem through horizontal gene transfer referred to as transduction. Phage-mediated transduction is thus, an important driver of ecological and evolutionary processes in microbial communities (197). For instance, Stx phage vector transferred Shiga toxin gene from pathogenic foodborne entero-toxigenic E. coli to nontoxigenic strains of E. coli(198) leading to the evolution of strains with a different set of genes. Hence, bacteriophage-mediated gene shuffling in the food ecosystem might be a source of concern that might lead to cross-resistance to preservatives and conferment of deteriorative potentials to nonspoilage strains. As such, widening the horizon of the spoilage microbiota.

Nonmicrobial food spoilage

This chapter focus on microbial food spoilage; however, it is important to highlight that food spoilage is not restricted to microbial spoilage. Factors broadly classified as physical and chemical factors contribute or facilitate spoilage of food. Physical spoilage involves damage of food due to physical changes and product instability. This might result from improper handling during storage and transportation of products. Physical spoilage does not necessarily render the food unfit for consumption but might reduce consumers appeal and acceptance of the product. Some of the common physical spoilage involves bruises of fresh products like fruits, breaking and crushing of crispy food products such as chips and cookies, decoloration of products, package damage, loss of water content, and breakage/leakage of sealed content. Food spoilage can also occur as a result of the chemical breakdown of food components. The rate of degradative chemical reaction in food depends on physical conditions such as the storage temperature, light intensity, and humidity. Chemical reaction mainly oxidative and reduction reaction in food can alter the natural organoleptic and nutritional qualities of food, making them unacceptable. Oxidative browning is a common chemical spoilage of food observed in fruits and fresh vegetables. Lipid oxidation or oxidative rancidity is the most common chemical degradative spoilage observed in products with rich fat and oil content. Unlike physical spoilage, most chemical spoilage renders the food unfit for consumption with characteristic alterations in taste, appearance and production of off-odor and sometimes toxic by-products.

Conclusion

Food spoilage remains a global threat to food security and safety, with microbial mediated spoilage on the lead. Control of microbial proliferation in food and food products requires an understanding of the spoilage microbiota and the food storage environment. To eliminate or retard the rate of food spoilage requires conscious optimization and alterations in food intrinsic and environmental factors. Regulation of microbial interactions through growth monitoring and inhibition of undesirable microbial species might also be a useful approach in the management and control of food spoilage.

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