Mechanisms of microbial inactivation

Initial studies of microbial inactivation have been thoroughly reviewed (Wouters and Smelt, 1997 Barsotti and Cheftel, 1999 Jeyamkondam et al., 1999 Ho and Mittal, 2000 Barbosa-C novas et al., 1999, 2001 Dunn, 2001 Wouters et al., 2001a) and will not be detailed here. The processing conditions and results of recent investigations are summarised in Table 18.1. A comparison between the results of various groups of investigators is often challenging because equipment, processing and or sample...

Determining diffusivities of fruits

Knowledge of the diffusivities of gases in bulky plant organs is essential in understanding physiological changes, gas exchanges and internal gas composition. The internal gas composition of fruits is determined by the diffusivities of skin, flesh and stem (Burg and Burg, 1965 Cameron and Yang, 1982). Burg and Burg (1965) designed a system to determine gas resistance factors which can be used to estimate gas diffusivities in bulky plant organs using the ratio of internal concentration to the...

Other concentration and separation processes

The application of the full range of membrane processes has been investigated in all sectors of the food processing industries, and detailed reviews can be found elsewhere (e.g., Cheryan 1998 Lewis 1996a and b Kosikowski 1986). This section will take an overview of selected applications to illustrate the breadth and scope of the techniques as contributors to food preservation. Membranes are widely incorporated into fermentation or enzyme reactors in the biotechnology industries, UF or MF...

Nonenzymic action of lysozyme

Surprisingly, partially heat-denatured lysozyme exerts antibacterial activity on a number of microorganisms (Ibrahim et al., 1996a and b). The antimicrobial activity of such thermally inactivated lysozyme extends to Gram-negative organisms and appears independent of the lysozyme muramidase activity (Ibrahim et al., 1996a). Two mechanisms have been proposed for this non-enzymic action of lysozyme. The first is that lysozyme acts as a cationic protein that induces cell lysis via puncturing of the...

Effects of high pressure on nutritional value and colour quality

The effect of high pressure on vitamins has been investigated by a number of authors and shows that high pressure treatment has little effect on the vitamin contents of food products. Most authors have reported that the ascorbic acid content is not significantly affected by HP treatment, e.g., 82 ascorbic acid retention in fresh green peas after pressure at 900MPa 20oC for 5-10 min. (Quaglia et al., 1996) no significant decrease of ascorbic acid content in egg yolk, guava puree and fruits...

Ultrasound as a preservation technology

Paniwnyk, University of Coventry, UK and F. Chemat, University of Reunion, France The use of ultrasound within the food industry is an active subject for research and development (Povey and Mason, 1998). As is the case in other areas of processing technology, the sound ranges employed can be broadly divided into high frequency, low energy, diagnostic ultrasound in the MHz range and low frequency, high energy, power ultrasound which is in the kHz range (Fig. 16.1). There is an...

Problems in combining traditional preservation techniques

Combined preservation factors for the control of foodborne pathogens include pH, aw, Eh, competing microflora and added preservatives. The basic concept for ensuring microbiological safety is that growth, survival and inactivation of microorganisms in food are dependent on the cumulative effects of a number of factors such as temperature, pH, aw, antimicrobials, etc. By manipulating more than one of these factors, it is possible to control microbial growth or render the pathogens more sensitive...

Process and equipment

The principle involved in generating high-intensity light is that a gradual increase of low to moderate power energy can be harnessed and released in highly concentrated bursts of more powerful energy. Electromagnetic energy is accumulated in a storage capacitor8 within fractions of a second and then released in the form of light within a millionth or billionth of a second, resulting in an amplification of power with a minimum of additional energy consumption (Dunn et al., 1995). Typically,...

Highintensity light

Swanson, Washington State University, USA In response to the ever-present concern over potential foodborne illness and the universal expectation of consumers for wholesome foods, food scientists, engineers and processors are seeking more efficient, effective and feasible methods of reducing pests, spoilage organisms and pathogens from foods. High-intensity white light treatment, a non-thermal method for shelf life extension and pathogen control, offers food...

Ultrasonic enzyme inactivation

To prevent denaturation, an enzyme has to maintain its native structure. Hydrophobic interactions, hydrogen bonding, van der Waals interactions, ion pairing, electrostatic forces, and steric constraints stabilise the three-dimensional molecular structure of globular proteins. Enzyme inactivation is a requisite for stabilisation of some food materials. Although it can be easily achieved by heat treatment, there are some cases where the high heat resistance of some enzymes can adversely influence...

Virus resistance

Viral resistance was the first successful example of plant disease resistance obtained by biotechnological means. To date, most of the available examples used genes from the pathogens in order to confer resistance in what is known as 'pathogen-derived resistance' (PDR). Transgenic tobacco plants resistant to the tobacco mosaic virus (TMV) were obtained by overexpression of the viral coat protein gene in what was named coat-protein-mediated resistance (CPMR) (Abel et al., 1986). Subsequently,...

Modified atmosphere packaging MAP

Ooraikul, University of Alberta, Canada The agri-food industry has undergone a profound change during the 20th century. Early in the century efforts were concentrated on finding ways to increase agricultural production in order to feed the world's rapidly growing population. Not many people foresaw the effectiveness of the two-pronged attack on the problems mounted by scientists, bureaucrats and politicians around the world. The average population growth rate in the past 30 years has been...

Microbial growth in solid food systems colony dynamics

In the following sections, the process of colony development is discussed. First of all, a general introduction on colony dynamics is presented after which the direct consequences of diffusion limitation in solid media, namely, concentration gradients within and around the colony, are demonstrated. Then, the strategies bacterial cells exploit to optimize their growth performance are then discussed. This is denoted as the microscopic viewpoint or cell bed. Depending on these cell level,...

Chitosan

Chitosan, (1 4)-2-amino-2-deoxy- -D-glucan, is a natural constituent of fungal cell walls (Ruiz-Herrera, 1992). It is produced commercially from chitin, a by-product of shellfish processing, by alkaline deacetylation. Chitosan is the designated name for the series of polymers with different ratios of glucosamine (GlcN) and V-acetyl glucosamine (GlcNAc). Most commercial chitosans have less than 30 acetylated units (referred to as degree of acetylation less than 30 ) and molecular weights between...

Combining traditional and new preservation techniques

In general, preservation by a single factor is not sufficient to ensure completely safe products, and multiple hurdles are advised (Leistner and Gorris, 1995). Likewise, to avoid the undesirable effects of heat, one approach is to use mild heat in combination with other emerging preservation technologies. The use of multiple preservation techniques incorporating mild treatments, e.g., mild heat, can result in enhanced preservative action by having an additive or synergistic effect on microbial...

Effects on enzymes

Initial studies on enzyme inactivation have been reviewed by Barsotti and Cheftel (1999), Yeom and Zhang (2001), Van Loey et al. (2002) and Bendicho et al. (2002a), and will not be detailed here. It is clear that enzymes (and food proteins) are much more resistant to PEF than vegetative microbial cells. However, a striking observation is that some investigators did not observe notable enzyme inactivation by PEF, while others, probing the same or other enzymes, often reported 30 to 95...

Methods of food preservation

The five basic historical methods of food preservation still in use today comprise desiccation or drying, heating, freezing, fermentation, and chemical preservation (Grierson, 1997). 1. Desiccation. Desiccation (dehydration, or drying) prevents the rotting of meat, the germination of stored grains, and the sprouting of certain vegetables. It also inhibits the growth of micro-organisms, but some of these dormant microorganisms can become dangerous with rehydration of the food. The Chinese and...

Fungal and bacterial resistance

Obtaining fungal-resistant crops has proved to be more difficult than for viruses and insects. Most of the difficulties are due to our lack of understanding of the molecular mechanisms controlling the interactions between the plant host and the fungus. In recent years, there has been an explosion in our knowledge of this interaction and several promising strategies are now being developed. One of the most promising resistance strategies is the use of cell wall lytic enzymes to degrade or damage...

References On Preservation And Storage Of Food With Publishing

ALLI I (1993), 'Quality control of MAP products', in Parry R T, Principles and Applications of Modified Atmosphere Packaging of Food, London, Blackie Academic & Professional, an imprint of Chapman & Hall, 101-114. AMANATIDOU A (2001) High oxygen as an additional factor in food preservation, PhD thesis, Wageningen University, The Netherlands. ARANGO H, VAILLANT F, VELEZ C, MILLAN P and REYNES M (1999), 'Evaluation of post-harvest performance of naranjilla (Solanum quitoense Lam.) fruits...

Herbs and spices as sources of antioxidants

Herbs are stems or leaves from various plants, used for the preparation of infusions, extracts, dressings, soups or sauces. Many species of this class of food ingredients are active antioxidants, mainly because of the content of phenolic compounds. The most important representatives of this group are tea leaves obtained from both green or fermented tea (Camellia sinensis L. or Camellia assamica L.) or dust left after their preparation. Green tea is particularly rich in catechins and related...

Methods for reducing spoilage in vegetables

Edible vegetables come in all shapes, developmental stages and colours. Leafy vegetables are arguably the most economically important type and include Lettuce (Lactuca sativa), Spinach (Spinacea oleracea), Endive (Cichorium endivia), Radicchio and Witloof (Cichorium intybus). In order to increase the life of these vegetables it is important to understand the mechanisms of leaf senescence. Contrary to the popular belief that senescence is a chaotic process, there is plenty of evidence to prove...

Inactivation of spoilage microorganisms

The preservation of food that is already produced, i.e., control of food spoilage on minimally processed fruits and vegetables, is a current area of extensive research interests (Salunkhe and Desai, 1984 Shewfelt and Prussia, 1993). High-intensity light treatments for control of food spoilage and shelf life extension of smooth surface, non-opaque foods is proving to be an effective and versatile application of high-intensity light technology. Key spoilage organisms involved in the deterioration...

References

A. 1999 , 'Microbial stress response in minimal processing', Int. J. Food Microbiol. 50, 65-91. ACMSF Advisory Committee on the Microbiological Safety of Food 1995 , 'Report on Verocytotoxin-producing Escherichia coli', HMSO, London. AGATA, N., OHTA, M. and YOKOYAMA, K. 2002 , 'Production of Bacillus cereus emetic toxin cereulide in various foods', Int. J. Food Microbiol. 73, 23-27. AKBAR, S., GAIDENKO, T.A., KANG, C.M., O'REILLY, M., DEVINE, K.M. and PRICE, C.W. 2001 ,...

Colony morphology

Schematic Diagram Circular Colony

When the evolution of one single colony grown on an agar plate is monitored, some typical morphological changes can be observed. For colonies of Aerobacter Klebsiella aerogenes, Cooper et al. 1970 made colony drawings from the negatives of photographs with the aid of an enlarger magnifying 10 to 15 times. lnitially, nutrient supply is sufficient for all the cells in the colony, resulting in a young circular colony. As the colony ages, the nutrient concentration in the agar beneath the colony is...

Wettability and coating effectiveness

The effectiveness of edible coatings on fruits and vegetables depends primarily on controlling the wettability of the coating solutions, which affects the coating thickness of the film Park, 1999 . Edible coating formulations must wet and spread on the fruit's surface uniformly and upon drying form a coating that has adequate adhesion, cohesion and durability to function properly Krochta and Mulder-Johnston 1997 . Hershko and Nussinovitch 1998 indicated that suitable hydrocolloid coatings could...

Measurement and prediction of water activity in foods 861 Measurement of water activity

Fast, convenient and reliable laboratory analytical methods of measuring aw are demanded in the food industry and in research laboratories for quality assurance, process design, food formulation and selection of storage conditions. This is particularly true for those foods in which control of aw is critical for determining microbiological activity and safety. Diverse reviews and collaborative studies about the methods used to measure aw in foods have been published Stoloff, 1978 Labuza et al.,...

Organic acids mode of action

The principal mode of action of organic acids is the release of protons from carboxylic groups, thus lowering the pH of their environment. Proton release means dissociation of the acid molecule, with the degree of dissociation depending on the pKa value. Strong acids tend to be fully dissociated and thus produce a strong drop in pH, while weak acids are only partially dissociated. This has two important consequences a organic acids with two or three carboxylic groups react on changes of pH by...

Developments in conventional freezer technology

Impingement technologies are being used to increase heat transfer during freezing Newman, 2001 . Impingement heat transfer is typically 3-5 times that of a conventional tunnel utilising axial flow fans. The increased heat transfer is achieved by forcing air at high velocity to impinge on the food perpendicular to the food surface. This breaks up the boundary layer of air, which would normally provide some insulation to the food when air is blown tangentially across the surface. With the...

Treatment chambers

A treatment chamber usually consists of two electrodes held in position by an insulating material which also forms an enclosure containing the sample to be processed. The design of the treatment chamber is an important parameter for microbial inactivation and must conform to several specifications 1. The treatment chamber should resist high current intensity. 2. The distribution of electric field in the treatment chamber should be as uniform as possible. 3. 'Dead zones' absence of electric...

Second stage

This stage of model construction demonstrates the interdependence between the parameters derived from the first stage of modelling and the environmental conditions. The Arrhenius relationship, where the natural logarithm of the growth rate is inversely proportional to the absolute temperature, can be used and this relationship can be extended to include other factors such as pH and aw. Belehradec or square root models are based on the linear relationship between the square root of the growth...

Ultrasonic inactivation of microorganisms spores and enzymes

Ultrasonic Food Preservation

There are many examples of microorganisms inactivated using ultrasound Table 16.4 . Some of these have been studied in culture media and others in food. The most frequently studied microorganisms, not only in the field of power ultrasound, but also among other methods of food preservation are Saccaromyces cerevisiae and Escherichia coli. The former has been found to be less resistant to ultrasound than other vegetative cells, which is mostly attributed to its larger size. The inactivation of...

Using MAP and other techniques to preserve fresh and minimally processed produce

Whenever possible, fresh produce is usually preferred to processed products by the consumers because of its freshness, which implies higher sensory and nutritional quality. Thus, fresh markets will always be with us despite the fact that most foods are now available in many convenient, processed forms, and their quality continues to improve with new processing and preservation technologies. Unfortunately, freshness is normally parallel with perishability, which implies short shelf life and...

With a bactericide in surface cleaning

One of the major long-established industrial applications of power ultrasound is in surface cleaning and it has proved to be an extremely efficient technology. Ultrasound is particularly useful in surface decontamination where the inrush of fluid that accompanies cavitational collapse near a surface is non-symmetric Fig. 16.5 . The particular advantage of ultrasonic cleaning in this context is that it can reach crevices that are not easily reached by conventional cleaning methods. Objects that...

Using plastic packaging in retort operations

Food packaging is evolving, conventional cylindrical cans are changing shape and becoming thinner and so more susceptible to damage by inappropriate differential pressure during retorting. Retortable plastics are becoming commonplace and a growing number of new products are appearing in heat sealable semi-rigid plastic containers with multi-layer plastic lids or multi-layer, heat-sealed flexible pouches. Consequently, retort technology is evolving to match. Process styles and process control...

Regulatory and safety issues

In the European community, the legal basis for organic acids as food additives is the directive 87 107 EEC. Lactic acid European designation E270 , acetic acid E260 , and acetates, such as potassium acetate E261 , calcium acetate E263 and sodium acetates E262 are generally permitted food additives under EC directive 95 2 EC. Sodium lactate E325 , potassium lactate E326 and calcium lactate E327 are food additives, which may be added on a quantum satis basis to foods Directive 92 5 EC annex 1 ....

Preservation Of Food Through Osmotic Method

BARAT, J, CHIRALT, A and FITO, P 2000 'Structural change kinetics in osmotic dehydration of apple tissue', Proceedings of the 12th International Drying Symposium, Elsevier Science, Amsterdam. BOGH-SORENSEN, L 2000 'Maintaining safety in the cold chain', in Kennedy, C ed. , Managing Frozen Foods, Woodhead Publishing Limited, Cambridge. BOWATER, F J 2001 'Rapid chilling plant compared to conventional systems', in Rapid Cooling of Food, Meeting of IIR Commission C2, Bristol UK . BOWLING, R A,...

Water activity microbial growth death and survival

The optimum aw for growth of the majority of microorganisms is in the range 0.99-0.98. Every microorganism has limiting aw values below which it will not grow, form spores, or produce toxic metabolites Beuchat, 1987 . Considering aw in relation to microbial stability, the minimum aw values that permit microbial growth for different types of microorganisms are of great concern. Table 8.1 presents the aw values of various foods and their associated microbial spoilage, showing also the...

Low temperatures enhance resistance to dehydration

Experiments in our laboratory with S.cerevisiae help to clarify the role played by cell membranes in the combined effects of temperature and hydration Beney et al., 2001 . The extent of S.cerevisiae survival by exposure to osmotic stress of 100 MPa was increased by a factor of 2.5 after cooling of cells from 250C to 10 C prior to osmotic stress Fig. 10.10 . Such enhancement of yeast osmoresistance was attributed to the fact that that the cooling step at 10 C reduced the osmotic destabilisation...

Removal of microorganisms by microfiltration

Microfiltration is a well-established laboratory technique for the removal of micro-organisms both vegetative and spore forms , and hence the production of sterile fluids, without the application of heat. The advent of cross-flow MF has enabled the same concept to be applied on a commercial scale. The technique has been widely applied to the production of clarified beverages such as beer and cider Finnegan and Skudder, 1989 , wine Palacios et al., 2002 or fruit juices Short, 1988 ....

Natural antioxidants

Pokorny, Prague Institute of Chemical Technology, Czech Republic 3.2 Classifying natural antioxidants 3.3 Antioxidants from oilseeds, cereals and grain legumes 3.4 Antioxidants from fruits, vegetables, herbs and spices 3.5 Using natural antioxidants in food 3.6 Improving antioxidant functionality 3.7 Combining antioxidants with other preservation techniques 3.9 Sources of further information and advice

Sources of further information and advice 981 Batch retort system suppliers

The following list of batch retort suppliers is intended as a guide and is not exhaustive. Breedstraat 3 B-9100 Sint Niklaas Belgium Tel 32 3 780 1398 http www.fmcfoodtech.com Breedstraat 3 B-9100 Sint Niklaas Belgium Tel 32 3 780 1398 http www.fmcfoodtech.com H G Molenaar amp Co Ltd Water immersion PO Box 5, Paarl 7622 South AfTica Tel 27 21 868 2210 Hermann Stock Maschinenfabrik GmbH Rendsburger Strasse 93, D - 24537 Neumunster Germany Tel 49 4321 1880 http www.stocksterilisation.com Water...

Methods for reducing spoilage in fruits

The dependence of climacteric fruits on ethylene to regulate the ripening rate have made them the focus of much biotechnological research aimed at Fig. 13.1 Ethylene biosynthetic pathway Yang and Hoffmann, 1984 . Met, methionine SAM, S-adenosyl methionine ACC, 1-aminocyclopropane-1-carboxylic acid. increasing the shelf life while not affecting other quality characteristics. Most of the approaches have been aimed at controlling the amount of ethylene synthesised by the fruits or the sensitivity...

Other lytic enzymes

Apart from lysozyme, two other types of hydrolytic enzymes may work bacterio-lytically. Firstly, as already covered above, the N-acetylmuramoyl-L-alanine amidases catalyse cleavage of the junction between the peptidoglycan polysaccharide backbone and the peptide crosslinks additionally certain endopep-tidases are known to catalyse the hydrolysis of the peptide sidechains. Knowledge is lacking on enzymatic cleavage of the interpeptide bridges in peptidoglycan, however. Streptomyces spp. express...

Spices and their essential oils

Spices and their essential oils have varying degrees of antimicrobial activity. Among the spices, cloves, cinnamon, oregano, thyme, sage, rosemary, basil and vanillin have the strongest antimicrobial activity. The major antimicrobial components of clove Syzygium aromaticum and cinnamon Cinnamomum zeylanicum essential oils are eugenol 2-methoxy-4- 2-propenyl -phenol and cinnamic aldehyde 3-phenyl-2-propenal , respectively. Smith-Palmer et al. 1998 determined that the 24 hr minimum inhibitory...

Using membranes in food preservation

Membranes were first developed commercially as a means of purifying water by RO, and for purifying waste water. Applications in food processing have since widened considerably. Membrane techniques can contribute to food preservation in two ways. Firstly, membranes reject all micro-organisms within the retentate and thus the permeate will be sterile on production. Hence, provided that the relevant components of the food fluid permeate the membrane, then membrane processing can be used per se as...

Applications of natural antioxidants for the stabilization of essential oils and cosmetics against oxidation

Essential oils are not lipids because they do not contain bound fatty acids, but they are as easily oxidized as lipids are and their oxidation proceeds along similar lines. Many essential oils contain components resistant to oxidation or even possessing antioxidant properties, but other essential oils are very sensitive to oxidation, especially citrus essential oils. During their oxidation, citrus odour notes disappear, and intensities of woody, acidic and heavy odour notes develop Pokorny et...

Prediction of water activity in practical applications

Aw can be influenced in at least three ways during the preparation of dried, intermediate and high moisture foods 1. Water can be removed by a dehydration, evaporation or concentration process. 2. Additional solute can be added. The impregnation of solute can be performed by moist infusion or by dry infusion. Moist infusion consists in soaking the food pieces in a water-solute solution of lower aw while dry infusion involves direct mixing of food pieces and solutes in required proportions. When...

A historical view of edible coatings

Wax was the first edible coating used on fruits and vegetables. The Chinese applied wax coatings to oranges and lemons in the twelfth and thirteenth centuries Hardenburg, 1967 . Although the Chinese did not realize that the full function of edible coatings was to slow down respiratory gas exchange, they found that wax coated fruits could be stored longer than non-waxed fruits. In the 1930s hot-melt paraffin waxes became commercially available as edible coatings for fresh fruits such as apples...

Factors that influence the efficiency of the lactoperoxidase system

Addition of nisin together with lactoperoxidase and glucose glucose-oxidase to pre-sterilised milk inoculated with L. monocytogenes was demonstrated to exert a pronounced synergistic and lasting bacteriocidal effect on L. monocytogenes as no cells were detected in the inoculated milk during 15 days of incubation of the milk at 250C Boussel et al., 2000 . Likewise, designed additions of nisin and bacteriocin-producing lactic acid bacteria in conjunction with activation of the lactoperoxidase...

Effects of lysozyme in real food product trials

The presence of egg white lysozyme inhibits the outgrowth of C. tyrobutyricum in ripened, yellow cheeses such as Edam or Gouda Bester and Lombard, 1990 Wasserfall and Teuber, 1979 . When the lysozyme is added just before the addition of rennet in cheese making, lysozyme both kills resting vegetative C. tyrobutyricum cells, delaying the outgrowth of spore cells into vegetative cells, and retards proliferating vegetative cells Wasserfall and Teuber, 1979 . As discussed in more detail in section...

Applications fully dehydrated intermediate and high moisture foods

Improved knowledge of the relation of water in foods led to the rediscovery and optimization of old preservation techniques and to a renewed interest in foods that are shelf-stable by control of water activity. This applies for fully dehydrated, intermediate and high moisture traditional foods with inherent empiric hurdles, and also for novel products, especially high water activity foods, for which the hurdles are intelligently selected and intentionally applied. Traditional fully dehydrated...

The use and effect of enzymes as antibacterial agents

Enzymes may exert antibacterial activity by a number of different mechanisms Table 4.1 . Lysozymes and other antimicrobial, lytic enzymes mainly elicit their antibacterial activity by inducing bacteriolysis via catalytic cleavage of cell-surface polymers or cell-wall junctions. As will be discussed later in this chapter, lysozyme may also work bacteriocidally by mechanisms that are independent of its catalytic activity. Lactoperoxidase, and other peroxidase systems, work antimicrobially via...

Lactoferrin

In milk and colostrum, the primary iron-binding protein is lactoferrin. Lactoferrin has two iron binding sites per molecule. Lactoferrin is inhibitory by itself to a number of microorganisms including Bacillus subtilis, B. stearothermophilus, Listeria monocytogenes, Micrococcus species, E. coli and Klebsiella species Oram and Reiter, 1968 Korhonen, 1978 Reiter, 1978 Mandel and Ellison, 1985 Payne et al., 1990 . The compound has no activity against Salmonella Typhimurium, Pseudomonas fluorescens...