Mushroom mycelium as a potential source of food flavour

Review

Mushroom mycelium as a potential source of food flavour Yitzhak Hadarand CarlosG. Dosoretz There is an increasing demand for natural ingredients and flavours by the food industry. Submerged fermentation is a fast and attractive technology for the production of highly flavoured mushroom biomass, which is otherwise produced by traditional time- and labour-consuming methods. Typical flavour compounds synthesized by mushrooms include volatiles derived from the metabolism of fatty acids, especially the 'mushroom alcohol' 1-octen-3-ol. However, biotechnological improvements are requir¢,~li to achieve flavour levels satisfactory for commercial application.

The cultivation of edible mushrooms has increased tremendously in the past decade 1,2, and is now one of the most intensive fermentation processes practiced throughout the world to produce food for human consumption. Some 8-10 funsal species are cultivated commercially, of which Agaricus bisporus is the most important (Table 1). Mushroom production is usually based on solid-state fermentation, and various substrates and cultivation systems are used for the different fungi. These methods have been extensively reviewed-~.4. In addition, wild (uncultivated) mushrooms are in high demand for their flavour. Morchella spp., known as morel mushrooms, are very popular for their flavour. However, the fruiting bodies (see Glossary) of morels are very difficult to produce under controlled conditions. Submerged fermentation is a fast and controlled method for the production of highly flavoured mushroom biomass normally produced by traditional methods involving the growth of fruiting bodies, which is time- and labour-consuming. Because of the large demand for edible mushrooms as a food ar~6 as a flavouring agent, there is research interest in attempting to produce flavour-rich mushroom mycelium in submerged fermentation. Moreover, submerged culture is Yilzhak Hadar is at the Departmentof Plant Pathology and Microbiology, Faculty of Agriculture, Hebrew University of Jerusalem, Rehovot 76100, Israel.Carlos G. Dosorelz is at the Departmentof EnvironmentalEngineering and Water Resources,Technion - The Israel Institute of Technology, Haifa 32000, Israel.

214

©1991.ElsevieScience r PublishersILtd,(UK] 0924-2244/91./$O2.00

the only method of producing, in bulk, fungi that are unable to form fruiting bodies under artificial growth conditions, as is the case with the morels s-~. The technique has been used to produce a wide variety of fungai species, including many edible and inedible species that are of interest for their fragrance; however, this review concentrates mainly on the production of flavour-dch edible mushrooms. The biochemical pathways of the formation of mushroom flavour volatiles are also discussed.

Produclionof mushroomsin submergedculture Mushroom cultivation in submerged culture was first described by Humfelds for Agaricus campestris (the 'field mushroom'). Since then, many studies have been conducted, concentrating mainly on the cultivation of species of the genera Agaricus, Morchella and Pleurotus, and some single species such as Lentinula edodes and Coprinus comatus 9-14. The technology of mushroom fermentation in liquid culture was adopted from the antibiotics industry, where fungal pellets are grown in aerated agitated fermenters under controlled conditions of pH and temperature9.1°. It appears that pellets of submerged mycelium develop more flavour than filamentous mycelium, due to ~he improved theological properties of the culture medium, and the autolysis that occurs in the centres of the pellets 15,16. Such autolysis occurs when the concentration of dissolved oxygen within the pellets drops below a critical limit, which influences cell metabolism at the centre of the pellets and results in an increase in the rate of release of flavour compounds I°. The pellet form also has the advantage of providing a texture resembling that of chopped fruiting bodies. Many diffel~nt media have been used for submerged mushroom fermentation, ranging from defined media to waste materials ~-14. Agitation and aeration rate, special additives, and the time and method of harvest are also important for growth, pellet formation and flavour generation. Several groups have studied the factors that affect the formation, growth and size of pellets6.t3,t4. Choice of appropriate inoculum concentration and propagation procedure require special attention, since mushroom mycelium is multicellular and does not produce spores in submerged culture. High biomass yield is also essential for the commercial implementation of submerged mushroom culture. Fermenter configuration is important. Most studies of submerged mushroom cultures have involved the growth of the mushrooms in shaken flasks. Furthermore, in most studies of mushroom growth in fermenters, the conventional stirred tank reactor (CSTR) was used with minor modifications, such as the exclusion of baffles to reduce shear forces and to eliminate the attachment of mycelium to the baffles. Very little attention has been paid to the use of non-mechanically agitated fermenters, such as air-lift, for mushroom production. Song et al.t4 reported the use of an air-lift fermenter for the growth of L. edodes for the production of spawn. More recently, analysis by gas chromatography

Trends in Food Science & TechnologySeptember 1991

Table 1. Commercial world production of edible mushrooms~

Glossary

Species

Common name

Agi,ricusbisporus Lentinulaedodes Volvariellavolvacea Flammulinavelutipes Pleurotus spp. Pholiota nameko Auriculariaspp. Tremella spp.

Champignon Shiitake Chinesemushroom Wintermushroom Oyster mushroom Winter mushroom Ear mushroom Jelly mushroom

Mycelium: A mass of filamenls that make up the vegetative form of many types of fungi and certain bacteria. During the vegetative phase, the organism grows, rather than reproduces. During the cultivation of Agaricus bisporus,the mycelium is normally grown in compost, and regular 'crops' of fruiting bodies (see below) are harvested.

Tonnesper annum

Other species aAdaptedfromRefs1 and 2

750 000 180000 65 000 65 000 40 000 20 000 12 000 3 000 9 000

Fruiting bodies: Specialized structures containing reproductive spores. Usually it is the fruiting bodies of mushrooms that are eaten. Pellet: Spherical colony of fungal mycelium grown in a liquid medium. Spawn: Mycelium used as an inoculum in mushroom :ultivation. In typical solid-state fermentation, spawn is grown in manure and derived either from an existing mycelial culture or from inoculation of the manure with spores.

of the n-pentane extract of Pleurotus pulmonarius grown About 150 different volatile compounds have been identas pellets in submerged culture has shown that levels of ified in various mushroom species, representing a wide total volatiles and of l-octen-3-01 (the main volatile variety of chemical structures 25-32 including simple compound responsible for the characteristic fiavour of aliphatic alcohols, aldehydes, ketones, esters, lactones, mushrooms) are approximately twice as high when the mono- and sesquiterpenes, and aromatics such as cinpellets are grown in an air-lifi fermenter than when namyl derivatives. grown in a CSTR fermenter; however, the levels of The acyclic sesquiterpene alcohols trans-nerolidol mushroom flavour volatiles in pellets grown in both and fokienol have been identified as the main volatile types of fermenter were lower than levels in fruiting components of Lentinellus cochleams 33. The bicyclic bodies (Hadar, Y. and Dosoretz, C.G., unpublished). sesquiterpene alcohol drimenol and a linalool derivative Pleurotus ostreatus ('oyster mushroom') pellets have been identified as the main aroma components of grown in submerged culture in a CSTR fermenter L~,and the fungus Gioephyllum odoranmm 34. The brown-rot P. pulmonarius pellets grown in submerged culture in fungus Lentinus lepideus produces a typical anise-like either a CSTR or an air-lift fermenter (Hadar, S. and odour that has been identifed as a cinnamic acid derivaDosoretz, C.G., unpublished) had similar levels of crude tive33. Polyporus resinosus produced predominately protein, fat, carbohydrate and organic matter as the benzaldehyde and 4-methoxybenzaldehyde ('anise aldefruiting bodies of the respective species; thus, the com- hyde') when grown on a synthetic medium, with moderposition and nutritional value of the biomass is not ate agitation 3°. A series of pyrazine compounds, which adversely affected by the choice of culture method. provide the characteristic 'roasted' or 'nutty' flavours However, at present, the low yield of flavour remains a associated with heated foods, were identified in Boletus limiting factor to the commercial viability of the sub- edulis:°'2L The characteristic almond-like flavour of merged culture of edible mushrooms. Therefore, the Agaricus subrefences is primarily due to henzyl alcohol, remainder of this article will discuss the formation of with minor contributions from benzaldehyde, benzothe volatiles that give mushrooms their flavour. nitrile, methyl benzoate and phenylacetic acid ~~. The shiitake mushroom, L. edodes, produces the cyclic Mushroom flavour sulphur-containing compound lenthionine as the primary Flavours stimulate human senses with their odour and aroma component3°. Various compounds, including taste. Their interactions and mechanisms of action are 3-methylbutanal, butanol, 3-methylbutanol, pentanol, complex and are still not fully understood. Fiavour is hexanol, fuffural, phenylaeetaldehyde and ct-terpineol, probably one of the most important reasons why we have been identified as minor volatile components of consume wild and commercially grown edible mush- mushrooms25.3~. rooms 17. Currently, it is generally thought that a series of eightIt is not yet certain how the various components com- carbon (Ca) compounds are the primary volatiles that bine to give the characteristic flavour of mushrooms. contribute to the characteristic flavour of edible mushCertain non-volatile substances may contribute to the rooms; less volatile C9 and C,o compounds are occharacteristic flavour, including L-glutamic acid, short- casionally present in edible mushrooms:4J7. The Ca chain fatty acids, carbohydrates, proteins, and non- compounds seem to be widely distributed among fungi, protein nitrogenous substances such as nucleotides including inedible species and moulds. (mainly guanosine monophosphate) 7.~8-2°. Some unusual amino acids may also make important contributions to The 'mushroom alcohol' 1-octen-3-ol, and other Cs mushroom flavuur, especially to the flavour of heated volatiles The flavour characteristics of several mushroom mushrooms. The profile of flavour compounds can vary drastically among species and even among varieties, and volatiles are given in Table 2. Trans~2-octenal has the lowest threshold value, but does not possess a typical can also be influenced by culture conditions. The chemical composition of the volatile fraction, 'mushroom' odour, whereas l-octen-3-ol, l-octen-3-yl which is considered to make the major contribution to acetate and 1-octen-3-yl propionate have low thresholds mushroom flavour, has been extensively reviewed 2~-24. that produce characteristic mushroom-like flavours. The Trends in Food Science & Technology September 1991

215

characteristic flavour compound of cooked mushrooms is 1-octen-3-one, which also has a low threshold value, and which is present at very low concentrations during mushroom fermentation. Overall, the most important volatiles associated with commercially available fresh, proceshed or cooked mushrooms are 1-octen-3-one and 1-octen-3-ol. Owing to its intense characteristic flavour, l-octen-3-ol [CH3(CH2)4CH(OH)CH--ICH2] is known as 'mushroom alcohol'. It occurs as two optically active isomers; the (-) form has the stronger fiavour and is more abundant; it is considered to be the most important component of the mushroom volatiles m'38. Thus, 1-octen-3-ol constitutes 78% of the volatile fraction of A. bisporus, 66% that of Cantharellus cibarius (the 'chanterelle' mushroom), 72% that of Gyroraitra esculenta, 49% that of B. edulis, 70% that of Lactarius trivialis, 90% that of Lactarius torminosus, 67% that of P. ostreatus, and 72% that of P. puirnonarius 2~'39.Dijkstra4° found that the level of l-octen-3-ol in the headspace of 14 mushroom species ranged from less than 0.02Bl/l in B. edulis to 190~t1/1 in Calvatia gigantea (the 'giant puffball'). Evaluation uy s~nsol-'y pml~;t~-ute th~ flfiVOUi'Svt-'ert~;u,t.u~A ---." .... t,s,u, ~ ,...... o z ' : :~ and A • bispo r u $ ]llOlCal.~,O. . . . . . . . . . . . . .H. .i n. .t . ..-'~. . . . . .UilOI(~OIi,~ l l t t U U L ~ stronger mushroom flavour, which could be correlated with its higher level of l-octen-3-ol (Ref. 41). The 'mushroom alcohol' was also a major volatile component of pure cultures of Penicillium caseicolura, Penicillium roqueforti and Aspergiilus niger grown on a defined complex organic mediumz4,4', and is present in several species of white rot3L Ney and Freytag~ evaluated the sensory properties of a series of alcohols with the general structural formula RCH(OH)CH=CH2, with R varying from methyl to pentyl. They found that both l-octen-3-ol and l-hepten3-ol have a characteristic mushroom odour. In addition,

Table 2. Main ilavour volatilescommonlyfound in ediMe mushrooms,and their orsanolepticcharacteristics" Threshold level Compound

(pg/ml)

Flavourdescription Sweet,detergentor soap

l-Octanol

0.480

3-Oct~nol

0.018

Like cod-liver oil, weakly nutty

i-Octen-3-ol

0.010

Mushroom-like, raw mushroom,general mushroom,butter-like, fungal, resinous

Trans-2-octen-l-ol

0.040

Medical, oily, sweet

Trans.2.octenal

0.003

Sweet, phenolic

1-Octen-3-one

0.004

Like boiled mushroom, metallic, wild mushroom

3-Octanone

0.050

Sweet,ester-like,fruity, musty,floral

1-Octen.3.yl acetate

0.090

Mushroom.like, soapy

1-Octen-3-yl propionate 0.022 aAdaptedfromRefs23, 27 and 31

216

Herbaceous,sweet, fruily, mushroom-like

a weak mushroom odour was noted for the saturated compound 3-octanol, but no such odour was registered for 1-octanol, 2-octanol or l-heptanol, suggesting that mushroom aroma is highly dependent on the presence of the double bond and on the configuration of the hydroxyl group at C3. However, Hanssen and Klingenberg tg, who compared 12 different commercial mushroom concentrates by both chemical analysis and sensory evaluation, concluded that mushroom flavour cannot be explained satisfactorily merely on the basis of chemical analysis. Since mushrooms contain numerous chemically reactive compounds, conventional processir,g, and especially drying or heating, can lead to significant change~ in the overall flavour composition*7"*9'zL Volatiles and guanosine monophosphate may be lost, or new compounds originating from reactive precursors in the raw material may be formed's.43. The weak or atypical flavour of dried or canned mushrooms may be explained by their decreased concentrations of 1-octen-3-ol and guanosine monophosphate m. The main changes in the profile of volatUes of A. bisporus during cooking were an increase in the content of l-octen-3-one and a correspondLn_g loss (due to oxidation) of l-octen-3-ol, an •

"

t-l.. . . . . . . . .

:n~

O6"

h,~r..-..d,4~,h~rl,a

.ar,~

3-octanone, and the formation of furfural and methylfurfural:s.44. Drying of mushrooms can result in major losses (as much as 90%) of l-octen-3-oP°. Some manufacturers of commercial mushroom concentrates enhance flavour intensity, and compensate for potential losses of the flavour compounds of fresh mushroom, by preserving and adding genuine mushroom fiavour compounds but, often, mixtures of artificial substances are added to obtain a 'mushroom-like' flavouP9.

Biosynthesis of flavour volatiles in mushrooms The ability to biosynthesize volatile metabolites is nearly as widespread among fungi as it is among higher plants. However, compared with the amount of available knowledge on the components of essential oils derived from higher plants, relatively little is known about the volatiles of fungi 'z2s.4s. Typical mushroom fiavours tend to be due to volatile C8 compounds derived enzymatically from unsaturated fatty acid precursors. The differences in flavour sensations among fungi may be attributed to the different enzymes involved in th~ oxidati¢c degradation of the fatty acids. The main precursors for tile short-chain volatile compounds responsible for the typical flavour of fungi are C,6 to Cue unsaturated fatty a,'.ids, which contain one or more double bonds. Under physiological conditions, they are enzymatically degraded m a number of volatile compounds, some of which have very low odour and ~ste threshold levels 46. Minor compounds such as hydroxy- and oxo-fatty acids, carotenoids, and sterols have also been reported. The metabolic pathway involves three major steps. The first step is the hydrolysis of lipids to free fatty acids (mainly linoleic and linolenic acids) by acyl hydrolases. The second step involves the hydroperoxidation of frends in Food Science& TechnologySeptember 1991

CHa-(CH2)a-CH=CH-CHs-CH=CH-(CH2)7-COOH (11nolelc acld) polyunsaturated fatty acids, in which lipoxygenase is the key enO= 1 l i p o x y g e n a s e zyme37"47'48.'Lipoxygenase' refers to a group of iron proteins that catalyse CHa-(CH=)~-CH=CH-CH2-HC(OOH)-CH=CH-(CH2)7-COOB the oxidation of fatty acids con(lC-h~droperoxy-trans-8.cts-12-octadecad~enoic acid) taining a cis,cis- 1,4-pentadiene system to produce conjugated hydroperoxidiene derivatives. The third hydroNroxide lyases step is postulated to involve lipoxygenase in combination with other enzymes, such as cleaving enzymes (e.g. hydroperoxide lyases), CH3-ICH=I4-CH(OHI-CH=CH2 OCH-CH2-CH=CH-ICH=)7-COOH oxidoreductases (e.g. alcohol de(1-octen-3-ol) (10-oxo-trans-8-deceflolc acid) hydrogenase), isomerases (e.g. cistrans isomerases), double-bond re- Fig.1 ducing enzymes, and ester-forming Postulated pathway for the biosynthesis of the 'mushroom alcohol' 1-octen-3-ol from linoleic acid in enzymes46,4s. mushrooms (adapted from Ref. 49). The mechanism by which hydroperoxides are cleaved to form volatile alcohols and aldehydes still remains unclear. flavour synthesis, and the effects of medium compoThe lipoxygenase-catalysed formation of 13-hydro- sition, the addition of specific precursors, genetic peroxides, and their cleavage by aldehyde lyases and manipulation of the fungus, and the use of molecular hydroperoxide lyases was proposed as the mechanism biology approaches; studying the fate of flavoar comby which fat,_%¢a~,d~ break d,~-,n ;o. f~rm volatile pounds during postharvest treatments; developing a carbonyl compounds and unsaturated alcohols37,47,'9. fermentation technology, such as mycelium immobilizWorking with crude enzymes extracted from A. bisporus, ation, appropriate to continuous (versus batch) produc.Wurzenberger and Grosch4~.49-~' reported the formation tion of flavour; and developing economically viable of a 10-hydroperoxide isomer derived from the hydro- methods of extracting and concentrating the flavour. peroxidation of iinoleic acid by lipoxygenase, and its Biotechnological production of mushroom flavour for subsequent cleavage by hydroperoxide lyases to form the food industry has been the subject of research for lO-oxo-trans-8-decenoic acid and l-octen-3-ol. The many years. The combination of a strong demand for pathway is outlined in Fig. 1. 'natural' foods and recently developed technologies Preliminary studies in our laboratory have analysed may lead to a breakthrough in the production of flavourthe levels of biomass, total fatty acids, linoleic acid, rich mushroom biomass. lipoxygenase activity and I-oeten-3-ol during the growth of P. puimonarius in a 10-1itre CSTR fermenter References containing a complex organic medium. The results 1 Taulorus,T.E. (1985) Adv. Biotechnol. Proc. S, 227-273 sugges', that, in actively growing mushrooms, levels of 2 Wood, D.A.(1989) Mushroom]. 201,272-275 total fatty acids and of linoleic acid decrease, while total 3 Flegg,P.B.,Spencer,D.M. and Wood, D.A., eds (1985} The Biology and Technology of the Cultivated Mushrooms, JohnWiley & Sons biomass, lipoxygenase activity and l-octen-3-ol levels 4 Wood,D.A. and Smith,J.F,(1987)in Essaysin Agricultural and Food increase (Hadar, Y. and Dosoretz, C.G., unpublished). Microbiology (Norris, J.R.and Pettipher,G.L., cads),pp. 309-343, More detailed studies of the production of I-octen-3-ol John Wiley & Sons in mushrooms grown in various well-defined chemical $ Martin,A.M. (1982) Biotechnol. Lett. 4, 13-18 media are required.

I

Conclusionsand future prospects The world market for natural flavours is expanding. Microorganisms have been widely studied as a potential source of f[avours 2°'23"24.4s.52,53.The technology of growing mushrooms in submerged culture for the production of flavours has been developing since the 1950s. Yet, mushroom flavour products derived from submerged fermentation are still not widely available. While the technique gives good yields of fungal biomass, the biomass is low in flavour. Thus, the key to successful implementation of submerged culture is the ability to produce biomass that is rich in mushroom flavour. To achieve this goal, more research should be conducted along several routes: enhancing the production of flavour compounds by studying the biochemistry of Trends in Food Science & Technology September 1991

6 7 8 9

Kosaric,N. and Miyata, N. (1981)I. Dairy Res. 48, 149-162 Litchfield,J.H. (1967) Biotechnol. Bioeng. 9, 289-304 Humfeld,N. (1948) Science 107, 373 Litchfield,J.H. (1967) in Microbial Technology (Peppier,H.J.,ed.), pp. 107-144, Reinhold 10 Solomons,G.L. (1975) in The FilamentousFungi(Smith, I.E.and Berry, D.R.,eds),pp. 249-264, EdwardArnold 11 Bukhalo,,~.5.and Soiomko, E.F.(1978)Mushroom 5ci. 10, 833-841 12 Martin,A.M. and Bailey,V.I. (1985)AppL Environ. MicrohioL 49,

1502-1506 13 Hadar,Y. and Cohen-Arazi,E. (1986)AppL Environ. Microbiol. 51, 1352-1354 14 Song,C.H., Cho, K.Y.and Nair, N.G. {1987)Mycologia 79,

866-876 15 Melz,B. and Kossen,W.F. (1977) giotechnol, gioeng. 19, 781-799 16 Sch~igerl,K., Wittier, R. and Lorenz,T. (1983) TrendsBiotechnol. 1, i 20-123

217

Manning,K. (1985) in The Biology and Technology of the Cultivated Mushroom (Flegg,P.B.,Spencer,D.M. and Wood, D.A., eds), pp. 211-230, JohnWiley & Sons 18 Dijkstra, F.I. and Wilken, TO. (1976) Z. Lebensmiit. Untersuch. Forsch. 160, 255-262 19 Hanssen,H.P. and Klingenberg,A. (1983) Z. Lebensmift. Untersuch. Forsch.177, 333-335 20 Kempler,G.M. (1983)Adv. AppL Microbiol. 29, 29-51 21 Maga,J.A. (1981) J. Agfic. Food Chem. 29,1-4 22 Sprecher,E. and Hans.sen,H.P. (1985) in Topics in Flavour Research (Berger,R.G., Nitz, S. and Schreier,H.P., eds), pp. 387-403, H. Eihhom, Marvling-Hangenham 23 Gross,B. and Asther, M. (1989) $cL Aliment. 9, 427-454 24 Kiderlerer,J.L. (1989)J. Appl. Bacleriol. Syrup. Suppl. 18,1335-1445 25 Picardi,S.M. and Issenberg,P. (1973)J. Agric. FoodChem. 21, 959-962 26 Ney,K.H. and Freytag,W.G. (1978) Gordian 78, 144-152 27 I~/salo, H. and Suihko,M. (1976) Lebensm. Wiss. Technol. 9, 371-376 28 DraweR,F., BerBer,R.G.and Neuhauser,K. (1983) Eur.J. AppL Microbiol. Biotechnol. 18, 124-127 29 Berger,R.G., Neuhauser,K. and Drawert, F. (1986) Flavour FragranceJ. 17

1,181-185

BerBer,R.G., Neuhauser,K. and Drawert, F. (1987) BiotechnoL Bioeng. 30, 987-990 31 Gallois, A., Gross, B., Langlois,D., $pinnler, H.E. and Brunerie,P. (1990) M¥col. Res.94, 494-504 32 Hanssen,H.P. (1985) Phytochemistry24,1293-1294 33 Hanssen,H.P. and Abraham,W.R. (1986) Z. Naluffoesch.41c, 959-962 34 Hanssen,H.P., Sinnwell,V. and Abraham,W.R. (1986) Z. Naturforsch. 41c, 825-829 30

Chen,C.C. and Wu, C.M. (1984)]. Food Sci. 49, 1208-1209 Chen,C.C., Liu, S.E.,Wu, C.M. and Ho, C.T. (1986)Am. Chem. SOc. Syrup. Set. 317, 176-183 37 Tress],R., Bahri, D. and Engel,K.H. (1982)J. Agric. Food Chem. 30, 89-93 38 Mosandl,A., Hensinger,G. and Gessnor,~.i. (1986)J. Agric. Food Chem. 34, 119-121 39 Hon8, J.S.,Lee,J.Y., Kim, Y.H., Kim, M.K., Jung,G.T. and Lee, K.R. (1986) KoreanJ. MycoL 14, 31-36 40 Dijkslra, F.I. (1976)Z. Lebensmitt. Untersuch Forsch. 160, 401-405 41 Karahdian,C., Josephson,D.B. and Lindsay,R.C.(1985) J. Agric. Food Chem.33, 339-343 42 Abbott,J.A.and San Antonio, J.P.(1974)J. Food Sci. 39, 411-417 43 MacLeod,A.I. and Panchasara,S.D. (1983) Phytochemistry22, 705 44 Card,A. andAvisse,C. (1977) Ann. lechnoI.Agfic. 26,287-293 45 Garfield,I.L. (1986) Am. Chem. SOc.SFmp.Set. 317, 310-322 46 Grosch,W. (1982) in Food Flavours, PartA (Morton, I.D. and MacLeod,A.J.,eds),pp. 325-398, Elsevier 47 Wurzenberger,M. and Grosch, W. (1984) Biochim. Biophys. Acta 795, 25-30 48 Josephson,D.B., Lindsay,R.C and Stuiber,D.A. (1984)J. Agric. Food Chem. 32, 1347-1352 49 Wurzenberger,M. and Grosch,W. (1982) Z Lehensmitt. Untersuch. Fo~sch.175, 186-190 SO Wurzenberger,M. and Grosch,W. (1986) Lipids 21,261-266 51 Wurzenberger,M. and Grosch,W. (1984) Biochim. Biophys. Acta 794, 35 36

18-24

52 53

5charpf,L.G.0Seitz, E.W., Morris, J.A. and Farbond,M.I. (1986) Am. Chem. Sec. Syrup. Set. 317, 326-346 Armstrong,D.W. and Yamazaki,H. (1986) TrendsBio~ochnol.4, 264-268

Cross-disciplinary trends Trends in Food Science & Technology is one of ten Trends journals published in Cambridge, UK. The following selection of recently published Trends articles may be of interest to food scientistsand nutritionists. Long-range interactions in proteins, by Norma Allewell, Trends in Biochemical Sciences 16, 239-240 Sniffing out odorant receptors, by Sigrun Korsching, Trends in Biochemical Sciences 16, 277-278 Evaluation of two assumptions:single straight line, and single normal distribution, by Laszlo Endrenyi and Mayank Patel, Trends in Pharmacological Sciences 12, 293-296 Stabilizing proteins ... with hybrid vigour, by Michael I. Geisow, Trends in Biotechnology g, 25%260 pH gradients and membrane transport in liposomal systems, by RR. Cullis, M.B. Bailey, "I.D. Madden, L.D. Mayer and M.J. Hope, Trends in Biotechnoiogy9, 268-272 The kineticsof plasmid loss, by David K. Summers, Trends in Biotechnology9, 273-278 Strategiesfor improving plasmid stability in genetically modified bacteria in bioreactors, by P.K.R. Kumar, H-E. Maschke, K. Friehsand K. SchOgerl, Trends in Biotechnology9, 27%284

218

Trends in Food Science & Technology September 1991