The development of process flavors

(Rock~nd,LB. and 8euch~ L.R.,eds),pp. 295-327,MarcelDd/.ker 11 Lop~z-Malo,A., Patou,E.,Welti,I., Co~eP.and Argaiz,A. (1994) FoodRes.Int. 27, 545-553 $ ~ , L (] 992) FoodBes.Int. 25,15|-158 12 Gords,L.G.M.and Bennik,M.H.J.(1994)7-.Lebensmittdwirlsch. 6 Leke~n~,L (1995)in NewM e ~ of FoodPreservat/on 45(11),65-71 (Go~l, G.W.,ed.),pp.1-21,Blackie 13 Gould,G.W. (1988)in ~ t / c Mechanismsh~/~t;c,oorganisms 7 Leism~',L. andGonis,LG.M., eds(! 994)FoodPreserva~onby (Whiflen~, R., Gould,G.W., Banks,I.G. andBoard,R.G.,eds),pp. Comb/nedProcessmg/JR 15776EN),Commissionof the European 220--228,BathUniversityPress,Bath,UK Community,Bm.c~ts,Belgium 8 Gi~'edeni,P., R0del,W. and Dmsel,J. (1994)Fleischwir~schaft74, 14 H~iussinger,D., nd. (ig88) pH Homeostasis:Mechanismsand Contml, AcademicPress 639-642 15 Csonka,L.N. (1989)Microbiol.Rev.53,121-147 9 AguileraR,~ic,I.M., Chidfe,J.,Tapiade Daza,M.S.,Welti Chanes,J. 16 Leislner,L. and garan-Djurdji~,S.(1970)Fleischwirtscha~50, and Par~ Arias,E.(1990)Inven~ar/odeAlimentosde Humedad Trad/c/an,~ de/bero,Yn~r/ca,Imtit~o Polit~nico Nacional, 1547-1549 17 Begh-Serensen,L(1994)inFoodP~vationbyCombinedProcesg.s Unid,~l Prd~ior~l In'mdbciplinadade Bio~-nologia,Mexico (EUR15776EN)(Leislner,L. andGo, is, LG.M., eds),pp. 7-24, 10 Alzanmra,SJvL,Ta~a,M.S.,Argaiz,A.andWelfi, l.(1993)FoodRes. Commissionof the EuropeanCommunity,Brussels,Belgium fat. 26,125--130

Review

The developmentof process flavors CharlesH. Manleyand SajidAhmedi

the cooking of foods and the mechanisms involved. Many excellent reviews covering this area of chemistry have already bean publishedt'~. This article will explore those areas in which chemistry can assist the flavorist in creating flavors that are developed by the use of the 'process' of cooking. The flavorhl's approach

The scientific, artistic and regulatory aspects of process flavors are reviewed. The role of the flevorist, as it relates to the creation of process flavors for commercial purposes, is discussed. An overview of the chemisW and analytical techniques used as tools for the artistic approach is also given. In addition, the development of 'building blocks' for flavor creation is discussed, and comparisons are made between the methods used for the creation of classical flavors versus process flavors. Finally, the regulations relatinp to the safety and labeling of these flavors are considered.

Man's interest in 'cooked' flavors stetted with the evolution of the human species, and m~m Lq the only represen~tive of the ~imal kingdom that has established the ~ c t i c e of conking food before eating it. The use of fire, and subsequandy other heat sources, to render a raw nu~m~d pelamble is one of man's higher intellectual achievements. The cre~on of a 'cooked' flavor presents the flavofisz with a major challenge. Cbendstry, p~ficularly analytical and natural product chcnds~'y, allows for the further development of our basic u ~ e r s t ~ l l n g of the components that arise during H. ~ and ~ Ahng,~are at TakasagoInternationalCorp. (USA),Teted~o, Hi, USA(fax:+1-201-288-1692). ©1995.EIsevi~ScienceLtd0924-2244/95/$09.50

The flavorist's approach to flavor development is a creative one, bm with a scientific foundation. Let us first review how the flavorist sets about the task of creating flavors from scratch. The most important step is to first evaluate the target flavor in descriptive terms. A commonly used method is to describe the flavor's character in terms of its top, middle and base 'notes'. The flavorist draws upon experience gained from past work on different flavor blends. An ingredient that might be suitable for providing a eartaln top note may adversely affect the middle and base notes; therefore, a vast amount of expefieuce as well as a degree of artistry arc needed to effectively combine these notes to produce a well-balanced flavor. Sensory evaluation methods may help define the flavor in terms of its attributes and strength. A small 9~nel of sensory e x p e ~ (5-8 flavorists) is needed to do this. Efforts are focused on selecting appropriate descriptive terms (usually 6 - 8 ) that relate to the character and quality of the flavor or taste. A more in-depth evaluation may be accomplished by using analytical methods such as the extraction of volatilas,followed by their separation using gas chromatography end aroma evaluation of the separated components (olfactometry). A number of good reviews on such methods for evaluating a flavor can be found in a recent Imbrication4. By the use of these methods, the important volatile flavor components can be identified. Once the basic formula of a flavor has been obtained using the analytical methods, the flavorist is ready to put artistry to worL The aroma components that have Trends in Food Science & Technology February i 995 [Vol. 61

TaMe 1..f~nificaM arenu~c f~tvor conqpe~m~ fe~d in pre¢~s i ~ n ~

c.0~m~type

s~:~e~e

Aldehydes

2,4-Dodecadienal

3670

Furans

H y d m ~

2491

Fumnones

4-Hydroxy.2,s-dimelhyl-3(2H)-furanone

3635

Sweetc.~m~

Pyrazines

2-Ethyl-3,5-dimethylpyrazine

3149

I~ed, ~,

Thiazoles/thiazolines

4-Methylthiazole

3716

Roastecl,c o ~ d onion, me,W

Thiophenes

2-Mercapl~hiophene

3062

Fried onion, mustard-like

2718

Onion, gadic

Pol~ulfides (thi~.~es) 3-Methyl-l,2,4-tdd~iane

cac~sse.

lOppm-O.03 ppb nuuy, popcorn

2S pm-O.O~ppb 3pFm-O.OO3ppb 0.2 pgm-ll~0b o ~ ppm-2 ~0b

' DatatakenfromRef.6 b1ppb repre~,m~1 pelt in I0' FF.MA,Flavo¢and Extra~,Manufacturers,~smcJafion GRAS,'Generallyrecosnizedassafe' which occur during thermal treatment, the been identified are assembled for the formulation of the flavor compound. Missing components can he replaced flav~ is more related to cooing flum to chemical s y m l u ~ by selecting chemicals that possess similar notes or by or to reaction chemistry. This basic chemisey of gecess synthesizing the specific chemical. Additional notes may flavors has bean reviewed in a recent tcxts. A list of a few significant flavor components and their be needed to complete the flavor profile and also to apply the finishing touches that make the flavor unique. aroma characters that ate found in cooked food flavors The addition of these extra notes is a true example of is given in Table 1. Note the chemical complexity of the list and the l~esence of certain L,etemcyclic oxygen-, the creativity of the flavorist. Also note A different approach, which does not use analytical nitrogen- and sulfur-containing c ~ the widely varying nmge of the aroma rhomboids of methods, is taken for the development of certain flavors O f ~ ~ m e d Ueterecy¢~compothat require a 'natural' label claim. Different raw ma- these ~ t s . terials that possess similar notes, such as floral absolutes, nents,the sulfur-containing ones conuibute most signiliessential oils, oleoresios, botanical extracts and es- candy to flavors such as mast beef~. The tla'ee sulfursences, are needed to produce such flavors. Flavorists containingcomponcntsnotedin Rg. I possessbetharoma have to rely entirely on their artistic ability and experi- char~tor and s~ength rarely found in other food flavors. ence when using these types of raw materials. Efforts The classical approach would be to have these ma~'ials involve a trial-and-error approach together with the use available in their synthetic form for the flavorist to use. of combinations of the flavo~ raw materials as building However, this may not be possible owing to their cony blocks to create the necessary flavor profile. It is quite plexity, potency, manufacturing costs and/or regulatory likely that the chemical analysis of the flavorist's final considerations. Instead, the flavodst builds these maflavor will be different from that of the target flavor, and teriais by creating 'building blocks' for process flavors by subjecting known ~ to thermal lm~-,ssing. yet the flavor profile may be a near match.

Oe~lep~ fl~ pmceB flaver

The~Uod,

In the development of process flavcws, flavorists must rely both on their creativity and on a basic understanding of chemistry when creating and u "ldizing rather complex mixtures of volatile and non-volatile components. The main difference is in the raw materials needed to create a process flavor. Most of the components of cooked flavors do not occur in nature; they are, after all, p~odncts of the heat process. Such flavors have gencrally been referred to as either process flavors of reaction flavors. The flavor industry prefers the term process flavors, as it relates to the ~ used to create the flavor. The term 'process' refers to cooking, roasting, baking, frying or any other word that describes a heat process to make food more acceptable. Although the development of a process flavor relies on basic chemical reactions between

The cooked flavor is not the effect of just one or two aroma ~ n t s , but the sum of the seusory effects of

Trends in Food Scienc= & Technology Februap/1995 [Vol. 61

Fig.l Examplesof three sulC~--containin8a,'ema~ cen~0eendsand their odor ~ , given in brackets.(a), 2-methyl-3-(methyithio)(uran(0.03 ppm); (b), bis(2-methyl-3-fmyI)dbulfide (0.02 × 10-61~m) and (c), 2,5-dimethyl-3-furanth~ (unknown).

l

47

all of the components together and in a very defined way. Even though many compounds are thought m be important to either process or me~ flavors, a delicate blend of

these componeats and otber ingredients is needed to create a chara~-~i~c flavor. Therefore, precursors that produce the ~ mixture of volatiles when heated using co~troUed ~ z e and temperature conditions are needed. Meat extracts, for example, when analyzed are reported m contain a complex mixture of precursors ine|nding nucleic acids, nucleo~des, nucleosides, pop~des, amino ~ d s , free sugars, llpids, and nu'cronutrients such as vit~nins. If such a mixture of precursors were put togother, the flavor of the meat would be reasonably well duplicated. However, because of the limitations of cost, availability or labelling resections, this list either has to be compromised or different mixtures of precursors have to be found. It is not always possible to produce a single mixture and set o f processing conditions that wou~ result in a finished flavor. Thus, it may be necessary to develop the flavor in parts or building blocks, using thermal reaction chemistry. This is done by first establishing the important odor-active components of the cooked meat, utilizing the gas chromatography olfactometry techaique~. Once these have been identified, the next step is m determine possible precursor materials that would generate these components. It may be possible to select some of these precursors, particularly the amino acids, using the analyrical data of the non-volatile compounds in meat extractse'9. A series of experiments is then carried out to optimize the combinations, processing conditions and the molar ratios for the generation of these key edoractive compounds. Several reaction bases may thus be produeed, each one rich in one set of odor-active compounds and therefore possessing a particular note. These are evaluated by the flavorist for their strength and charucter, and may be utilized as building blocks to develop a sophisticated and complete flavor. Figure 2 provides an overview of the pathway involved in the production of these building blocks.

One very impmtant aspect of the development of process flavors is outside the realm of reaction chemistry. This aspect involves the use of non-volatila flavor enhancers, the most important ones being monosodium glutamate (MSG), salt, and the nucleotides disodium geanylate and ~ u m inosinate. Acidulants and buffers are also important to the overall flavor. These flavor enhancers are, however, considered to be nonflavor ingredients even though the skillful use and blending of such substances contributes significantly to the overall taste and flavor impression of meat flavor. This is because, as important as the flavor enhancers are, the flavor industry is based on selling flavors that generally equate to the aromatic part of the food or its top note.

The process flavor top note We have discussed the role that building blocks play in creating a good flavor, but it should be noted that many of the aromatic flavor components may also be added to a flavor. The classical method o~ creating a flavor relics on the skillful combination o, natth-al extracts and artificial aromatic chemicals. The components listed in Table 1 have been synthesized by the flavor industry m be used for creating final flavors. As noted before, beterocyclic chemicals have been isolated from meats or similar foods that have been cooked, roasted, fried, and so on. All of these chemicals have been evaluated as being safe by a group of experts in the field of food safety and are, therefore, considered 'generally recognized as safe' (GRAS) for use in food or beverage products in the USA m. The GRAS registration numbers given to each of the components by the Flavor and Extracts Manufacturers Association's (FEMA) Expert Panel are noted in the table. Any of these components would be used by the flavorist in concert with building blocks end flavor enhancers. The final flavor is a complex mixture of ingredients and as such does not fit into the existing concept of a 'classical flavor'.

The classical flavor Proteins

] r Carbohydrates

The basic difference between a process flavor and a classical flavor is that a classical flavor is created by using volatile chemical compounds or volatile extracts of natural materials (see Fig. 3). Such natural materials are defined by the US Food and Drug Regulations under the Code of Federal Regulationstt. Typically, the classical flavor approach reproduces the aroma of fruit-type flavors, which find their way into many food and beverage applications. H conditions For instance, the flavor that is characteristic of fruit I Ttme/ter~,eratureConditions is a direct product of the natural biological processes occurring in fruit, and comprises the volatile materials developed during the ripening or natural fermentation of fruit. The methods for the creation of classical flavors have been in place since tt-e flavor industry was estabiisbed some 150 years ago; however, the establishment of the art and science for the creation of the process F~Z flavors is only a recent development. Therefore, the Pathwayfor creatinga buildingblock. manner in which flavors have neen regulated in the

Lo

48

Trendsin FoodScience& TechnologyFebruary1995KVoL6]

USA has been based mainly on the mgulato~ body's ~ g ofthe i r ~ of cls~icat-flavor chem/s~.

~

regu~on of pn~cm nmmm

Basically, process tiave~s a ~ generally regulated under the definition of the GRAS ~ n . Process flavors are included in the h ~ u n diet at very low levels and are, therefore, not viewed as food additives. Under the GRAS con~p~ used in the USA, an ingredient may be added to the food system if there is general tecognitinn that it possesses no health risk to the consumer. Unlike food additives (ingredients that ~ e used in high amounts f~r functionality), GRAS substances do not need pre-market clearance by the Food and Drug Administration (FDA). Because process flavors a~e ated from foods, food in~llents or R~rov~l food additives or GRAS substances, and are processed under conditions similar to those used to prepare food at home or using traditional c o r a m ~ i ~ l foed t e d m o l o ~ Wac-

( 2 - a n n o - S - ~ 4 , 5 . ~ and 2-minot-nm~V6-p~ylin~zoH,.S.b~) in me or 0.001 pizn of ~ ¢ m in fl~e f i ~ d flavemi foed lzrodnct (Fig. 4). Al~ungh the first ~ a ~ m is ~ of s ~ , tim r e g u l a ~ nmst also ~ t ~ l~OCedu~ f ~

labeling the tlavor and tbe ~ ! food pnxluct

labeling or tha L~eting of It~ food t l ~ th~ flavor is I~t as simple as that for a e l m ~ a l flavor. Under US law and r e g , ~ the classical flavor is labeled as either a uatusal flavor or un mificial flavor (or ~ thag is called 'with other natural flavor'). All c o m i m n e ~ .chat cem~ tribute to the flavc~ am exempt from dilclesum on tha p~ges ~oel, und may ha inmped t o ~ h ~ u ~ o r tha term 'flavor'. However, those components not considered as flavor components, tinned n o n - l ~ r hunts, must be listed individeally on the label. The

rices, proces~ flavors, provided ~ y are used at their appropriate flavor levels, a~e considered safe. With the advent of very sophisficami mudyfical insu'umentation, chemists have been able to identify comonly in trace amounts in alnmat ponentsthat are ~ t any chemical mixture; such mixtures include foods, food additives, food ingredients and GRAS materials. Some of the components found in trace amounts have been shown by testing their effects in animalg to be toxic at certain level~. Needless to say, such findings, when published, present the regulators with the problem of evaluating the safety to humans of exposure to these ingredients containing toxic components. One can eliminate or reduce the use of the component, or monitor its use to establish tbe magnitude of the problem und establish a safe limit of use. Substances known as ehlomwopunols have been identified in hydrolyzed vegetable proteins (HVP) .3, which may be used as a major component in process finv~s or in a final flavor compound. Because of the widespread use of HVP, some governments in Europe have established a maximum level of chlompmpenols allowed in HVP (for example, the Genmm Health Agency has established l ppm for the monnchleropropanol and 0.005 ppm for the diehloropmpanols). The industry that manufactures HVP-containing materials has voluntarily modified its processes to reduce the levels of chlorowotmnols they contain to well below the limit. Another aw.a of health concern relates to the reports on the isolation of certain haten~ydk: amines from cooked meats and meat extracts, as these subs!ances have been shown m be matagenic, producing cancers in anin~ls ~ s . Because meat extracts may be incmporated in some process flavors, them is concern about the levels of heterocyclle amines in these flavors. Recent scientific g e p o ~ indicate that process flavors are free of detectable levels of haterocyclle amines, except where meat exlracts are used in the formulation oftbe flavor ~e. Europe appears to be establishing a maximum level of 0.05ppm for two specific heterocyclic amines

Trendsin FoodScience& TechnologyFebruary1995[Vol.6]

flavor approach

I

Food/spic~

1--

Flavmingredient

Flavorsubstance Flavorenhancers

Process

II

chemical

l

Flavorsuheamce

Buildin8block

~

pmces~

approach

Fig.3 Coml~isond thecn~iond a flavorusing~e classicalflavorapproachand

(a)

NHz

[ ~

N~H3

r-~.4 l . ~ l i c mines:{a),2-amino-3-mehytimidazo[4,541quin~ine; and(b),2-amino-1-me~yl-6-phenylimidazo[4,S-~plnidine. 49

ncn-fl~vc¢ ccmpceents comprise any functional material, such as ~ i o ~ t , cenier, food dye, water binder or ~ v e ~ As ~.rc~y mentioned, flavor enhancers such as MSG m'e not consk~'ed as flavor ingredients and must, also, be lis~e~ on the packaging label of the flavor by ~ common or ~ na~e. The process flavor, being more complex and composed of a n ~ e of foods, food ingredients or eddi~ives, is more dfl~cuR to label. Many of the ingredients used must t ] ~ f c f e appear on the label. The US D c p m ' ~ a t of Agricolu~re (USDA) has developed g u l c h e s for the I~be]ing of procass flavors used in me~t cad poultry p~odectst~. Box 1 presents a sumn~ry of these geide~es. Those n~erials that are used in the process to create a flavor profile and are not specifically identified as having to be labeled may be considered e ~ e n ~ fxom individual labeling disclosure. Unlike H)A.~egu~ed food products, USDA-regulated products and ~bels must have a pre-markat clearance. A label r~view conm~ttce has been established by the USDA in W ~ b i n ~ DC, USA. It t~vJews a n~nufacturer's formu~ o n and indicates the labeling requirements for the flavor. By using this procedure, the flavor's formulation can be kep~ c c ~ d e n f i ~ ~ l ~ l i n g information is issued in the form of a ~ Mix Committee letter. This leV~cris genor~y needed by the food company using the flavor before the flavor is a~owed to be brought into a p~nt under USDA ~u~rvision. In Europe, these flavors have been identified as a sopclass of flavorings and designated as 'process

~ h u n ~ con~mpeon an~ aeeproduced f ~ n in~diems or mi',eures~ t :

flavors'. This term is also used on retail food package la~ls. The Europe~ Union (EU) is working on a reguL~ry definition of the process flavor, which includes identification of the precursors, the processing conditions, the processing aide and the maximum levels of trace toxic components allowed. The definition has been drawn up by the European flavor industry, which has developed guidelines for the n u m u f ~ r e of process flavorsis. Once this document is accepted by the EU, as a DLrective, it will become the regulatory definition for process flavors in the EU.

comerc~ preducu~ Process flavors have been in commercial use in the world since the company Unilever patented such a flavor in the early 1960s (Ref. 19). Before that time, both hydrolyzed proteins and autolyzed yeast extracts were the major sources of meat-type flavorings used by the industry. Since then, the scieuce and art o f making

process flavors has expanded from Europe to the rest of the world. Most flavor companies now offer some type of flavor that has been developed using the concepts outlined in this article. Although the precise amount of process flavors being produced is not exactly lmo-~m,it has been asfimated that R approechas 15 × 10eb(-675 × I06 k~in the USA, with a sinfilar quantity being manufeetured in Europe. These figures do not include hydrolysates or autolyzed yeast used either alone or as flavor enhancers in food produc~. Major progress in flavor development continues with more superior process flavors appearing on the market every year. Much of the development is within the context of regarding the total food product as a flavor system. Certain processes such as canning and retorting, which were previously deemed to be detrimental to the flavor, can now be utilized for positive flavor generation. Such developments allow the food manufacuw~ to launch food products with improved flavor atlrihates, sbeff life, nutrition and cost savings. Refe~es

~. Unc~ the ~

~

~

'Ac~e~

50

~

spec~iec~ [~e re~e~n cora~n~ an~no ac~{s),

;

Rd. 17

1 Padiment,T.H., ~-,o~in, R.I.and Ho, C-T.,eds(1989)~ 1 Generatonof Aromas(ACSSymposiumSeries409),~ n ChemicalSocie~/,Washington,DC, USA 2 Tetanishi,R.,TakeoEa,G.R.and Gun~ M. eds(1992)F/avor Precursors,ThermalandE n ~ Convers/ons(AC~Symposium Ser~s49O),AmedcanChem~l Sock, Washington,DC, USA 3 ~nley, C.H. (1994)in .ToteceBookofF/avo~(Reineccius,G., ed.), pp.139-154,Chapman&Hall 4 Ho, C.T.andManley,CH., eds(1993)FtavorMeasurement OFTBasicS~poc,iumSeries),Marcel S SchRier,P.andW~lter, P,,eds(1993)l~inFlavor P~ecunor,~t~J/es,Nlu~edPebti~n~ We~on, IL, USA 6 Fors,S.(1981)Senso~l~ofVola~leMaillardReaction ~ and ge/a~ed~ (SIKSen,'ice5edes1'.'~.71), Sw~l~ Insetmefor FoodRes~rch,~ Sweden 7 Acr~e,T.E.(1993)in f l a v o e ~ ( I F T BasicSympo~um5edes) ~ l e y , C.H. and Ho, C-T.,eds),pp. 77-94, MarcelD ~ 8 ArJsmy,M.C. andToldra,F. (1991)./.A~/c. FoodC/~at 39, pp. 1792-1795 Trends in Food Science& Technology Febmaw 1995 [Vol. 6]

9 Ka{o,H., Rime,M.R.andN ~ ,

T. (19B9)in/he Ro/eofFree 14 Ohgaki,H.,T~kayama,S.and S u ~ , T.(1991)Mu~. R ~ Se~es388) 259,pp.399-410 (Teranishi,R.,6utm~,R.G.andShahidi,F.,eds),pp. 158-174, aS ~umo, LC, ~nneoo~, E.,raick~m,~ , roaosSm, r~., AmedcanChemicalSociety,Washir,~on,DC,USA Wagner,aM., ~ , O.O. and/vl~m/,C.H.(ICJ93)Re~L 10 wood,LA. andOoull,I. (1991)Re~/.Tox/co/.lxnannaco/.14,pp.48-58 Tox/co/./~amtaco/.17,pp.s1.-5109 11 Codeof~ l Re~ul~ians(1994)[21CF.R.§lOI.221,US 16 ~kson, LS.,H~raves,W.A.,S~mup,W.H.andOiachen~,G.W. GovernmentPrintingOffice (Ig94)M~a~ ges.320,pp.113-124 12 Lin,LI. (i 993)in "/~e'~l (.,e~rA~ F/av~ (ACSSymposiumSeries 17 ~A-/:S/S/~.~e to.~pp//ers( 1 0 1 ~ , 1~0), USDep~mme~ 543)(Padinmm,T.H.,Morello,M.J.andMcGonin,R.,eds),pp.33-41, AmericanChemicalSocieP/,Washin~on,OC,USA 18 /OFIF/avorCu/o~nes(1993),Intemal~ O~-~ion of Flair 13 VanRillaer,W. andBeemae~,H. (1,389)Z. ~.-Un~e~s. Farx~. IndusU~,Geneva,~ 188,pp. 343-345 !~ May,CG. (1%0) US Pa~ent2 934 435 AminoAcids~ I P e ~ i~ FoodT ~ (ACS~

Review

The potential of dielectrophoresis for the real-time detection of microorganisms in foods

There are major social, economic and sometimes political implications of food poisoning but methods for the early determination of causative microbes are very limited. Conventional microbiological methods are slow, largely because incubations in cultural stages are required to generate detectable concentrations of cells. Recent developments have shown the potential of dielectmphoresis [a phenomenon observed when neutral or charged particles ate placed in a non-uniform altemating current (a.c.) electric field] for the rapid concentration, separation and identif, cation of microbes found in foods. The aim is to utilize cells already present in samples and therefore avoid testing delays because of slow bacterial growth phases. Many biological, chemical and physical factors can reduce the efficiency and sensitivity of TradillonaJ m e d a l s ~ r the ~ ana~s dielectrop~ic techniques, and these are under intense offoods investigation. Expanding research activities, particulady into Conventional microbiological techniques require dielectrophoretic enrichment methods, the rapid differentiation tlme-comuming and laborious pmp~umion procedm., of viable cells and the analysis of very low microbial concen- such as resuscitation, pre-emiclmtent, selective enrichment and isolation of colonies, to be perfonued before a trations, should provide major improvements in the analysis specific detection or idenl~cadon can be established of fond microorganisms in the future. using yet further wocedmes. Although these detect/~ and identification stages often rely on genetical, biochemical or serological methods, which can be rapid relative to the pgocedmes used to prepare the colonies, The microbiological content and contamination of foods they nevertheless add to the overall time taken to have acquired increased importance and priority,owing complete an analysis. MaWr improvements in analytical standards, eslargely to a greater public awareness of the potential harmful effects of certain microorganisms and the tight- pecially in terms of the sample numbers examined, the ening of legislation on food quality. Food poisoning ~liabiHty of results and tl~ rapidity of reporting, ate not using traditional methods. often has a significant social impact and, although death fe~ible for most a p e s is rare, considerable distress and disruption to individuals and the community are conunon. Food poisoning There hive been many attempts to modify traditional can also cause m j o r financial loss tO ilglividuals, food raicrobiological techniques in order to facilitate a more companies and the nation as a whole. extensive and quicker turnover of sample analysis. w. gemmd~ is at the Oepamnemof Biol%,y,U n i ~ of York, Rapid methods for the detection of fondbor~ pathogens I-leflin~0n,Yetc,UK VO15DD(~ +44-1904-432923;emag:~dx.~ .have largely emerged in the areas of elecltoaics '-~, immunology4-7 and DNA teehnolog~9, alfllough some ac.uk).

W. Bernard Betls

Trendsin FoodScience& TechnologyFebruary1995 IVol. 61

©ms, um,,t~sc~.,ceudo924.~4,~rvso9.so

51