Enzymes in Food and Beverage Processing

8 Conversion of Aldehydes to Alcohols in Liquid Foods

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by Alcohol Dehydrogenase C. ERIKSSON, I. QVIST, and K. VALLENTIN SIK, The Swedish Food Institute, Fack, S-40021 Göteborg, Sweden

Enzymic aldehyde-alcohol conversion Aliphatic aldehydes and alcohols are frequently found in the volatile fraction of most kinds of foods, e.g., dairy products, meat, poultry, fish, edible oils, vegetables, potato, fruits, and berries. Aldehydes and alcohols can be formed in a food in the normal or abnormal metabolism of tissues and microorganisms, in Strecker degradation during food processing or in lipid oxidation during storage of fresh, dried or frozen foods or food components. The formation of certain odor-potent aldehydes and alcohols from unsaturated fatty acids under the influence of enzymes and hemoproteins, particularly in vegetables, has been summarized earlier (1) . Aliphatic aldehydes, alcohols and esters can be transformed into each other as scheduled by the reaction route. 12 R-CHO . R-CH OH χ R-COO-R Step 1 is catalyzed by the enzyme alcohol dehydroge nase (ADH) in the presence of reduced or oxidized ni cotinamide-adenine dinucleotides (NADH, NAD ), while in step 2 formation of an ester can be achieved by ester synthetase systems, in the presence of a carboxylic acid (R -COOH), a reaction that is less well known for these types of esters. In step 2 the hydro lysis of aliphatic esters involves carboxylic-ester hydrolases. Green pea skins contain such a hydrolase, which was purified by ammonium sulfate fractionation, gel chromatography and two consecutive steps of ion exchange chromatography. This enzyme was found to hydrolyze ethyl-, η-propyl-, η-butyl-, n-pentyl, n-hexyl-, and η-hex-trans-2-enylacetate in increasing 2

+

132 Ory and St. Angelo; Enzymes in Food and Beverage Processing ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

8.

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Aldehyde-Alcohol Conversion in Liquid Foods

133

rate order, while etylpropionate, -buturate, -valerate, and - h e x a n o n a t e were n o t h y d r o l y z e d b y t h i s enzyme (Yamashita, I . , and E r i k s s o n , C , unpublished results). alco alip alco from The

E a r l i e r investigations have revealed that plant hol dehydrogenases have a wide s p e c i f i c i t y over hatic straight chain saturated and unsaturated h o l s and aldehydes. This is true for the enzyme p e a (2) , o r a n g e (_3 ) , p o t a t o (k) , a n d t e a (5.) · equilibrium constant of the reaction Alcohol

+ NAD ^==± +

Aldehyde

+ NADH

+ H

+

was f o u n d t o f a v o r a l c o h o l f o r m a t i o n at t h e pH a n d coenzyme r e l a t i o n s that are normally found i n plant material. The e q u i l i b r i u m constant also varies due to the nature of the a l c o h o l - aldehyde p a i r (2). This variation is exemplified in Table I, which shows t h e c a l c u l a t e d m o l p e r c e n t a g e of n-hexanal and n-hex-trans-2-enal, each i n e q u i l i b r i u m with the cor responding alcohol for two d i f f e r e n t pH a n d NAD/NADH values. Table

I.

Composition of aldehyde-alcohol equilibrium mixtures. Theoretical figures. 100 100 10 10 NAD/NADH PH 6.0 6. 0 7-0 7· 0 1.4 0. l4 0. i4 n-Hexanal (%) 0 .014 n-Hexanol \^>) 99 .986 98.6 9 9 . 86 99- 86 n-Hex-trans-2-enal ($) n - H e x - t r a n s - 2 - e n o l (°/o)

1 .4

98 . 6

12. 5 87. 5

12. 5 87- 5

58 42

Other aldehyde-alcohol pairs w i l l produce s t i l l other figures a c c o r d i n g to chain l e n g t h , presence of d o u b l e bonds (number and p o s i t i o n ) , b r a n c h i n g etc. Odor

properties

of

aldehydes

and

alcohols

The importance of the above knowledge f o r the flavor o f a f o o d was f u r t h e r studied in experiments, where the odor d e t e c t i o n concentration i n water of n-hexanal, η - h e x - t r a n s - 2 - e n a l , n-hex-2,^-dienal, n-hept-trans-2-enal, n-oct-trans-2-enal, and the c o r r e s p o n d i n g a l c o h o l s was d e t e r m i n e d (6). It was found that the odor d e t e c t i o n concentration of both the aldehydes and the a l c o h o l s d e c r e a s e d w i t h the chain length of C^-Cg saturated compounds, while it i n c r e a s e d w i t h the number o f d o u b l e bonds i n C5 a l d e hydes and a l c o h o l s . T h i s c a n be seen i n T a b l e I I , which also shows t h a t t h e o d o r d e t e c t i o n concentration

Ory and St. Angelo; Enzymes in Food and Beverage Processing ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

134

E N Z Y M E S IN FOOD A N D B E V E R A G E PROCESSING

of alcohols t h a t of the Table

II.

Compound

i s i n a l l cases aldehydes.

significantly

higher

than

Odor d e t e c t i o n c o n c e n t r a t i o n (ODC) o f some aldehydes and a l c o h o l s (Figures from reference 6) ODC ODC ( M ) ODC aid.

n-Hexan-1-ol n-Hexanal η-H ex- trains-2-en - 1- ο 1 η-Hex-trans-2-enal η - H e x - t r a n s - 2 , t r a n s - 4 - d i e n - 1 - oo l n-Hex-trans-2,trans-4·^dienal n-Hept-trans-2-en-1-ol n-Hept-trans-2-enal n-0ct-trans-2-en-1-ol n-Oct-tran s-2-enal

4.8 1.9 6.7 3.2 4 22..4 5.0 3.7 3.4 6.6 2.9

X X X X X X X X X X

10 10 10 10 10 10 10 10 10 10

5 7 5 6 4 6 5 7 6 8

259 21 49 83

231

The r e s u l t s c o n c e r n i n g the e q u i l i b r i u m and odor properties p r o v i d e d the background of f u r t h e r experi ments to r e d u c e the amount o f a l d e h y d e s i n f o o d s by c o n v e r t i n g them to a l c o h o l s by the a d d i t i o n o f A D H . T h i s r e a c t i o n can f o r i n s t a n c e be a p p l i e d to liquid f o o d s , whose p o l y u n s a t u r a t e d f a t t y a c i d s , although present i n small amounts, have o x i d i z e d sufficiently to g i v e r i s e to o f f - f l a v o r due to a l d e h y d e formation. Such a p p l i c a t i o n studies are d e s c r i b e d l a t e r i n this article. Due t o t h e c o n t r i b u t i o n o f s e v e r a l aldehydes to this kind of off-flavor and to d i f f e r e n c e s in their r e a c t i o n r a t e and e q u i l i b r i u m c o n c e n t r a t i o n as well as i n odor d e t e c t i o n c o n c e n t r a t i o n o f b o t h aldehydes and alcohols, such a r e a c t i o n w i l l , or should, not always merely quench the aldehyde odors. The result might t h e r e f o r e be a changed odor s e n s a t i o n from a complex mixture of d i f f e r e n t aldehydes and a l c o h o l s . T h i s s e n s a t i o n m i g h t t h u s n o t o n l y d e p e n d on presence of o d o r b u t a l s o an p o s s i b l e q u a l i t y c h a n g e s , that o c c u r when a l d e h y d e s a r e c o n v e r t e d t o a l c o h o l s o r vice versa. F o r t h i s r e a s o n an a t t e m p t was made t o find out whether c o r r e s p o n d i n g a l d e h y d e s and a l c o h o l s also differ i n odor quality. Water s o l u t i o n s of n - h e x - t r a n s - 2 - e n o l and n - h e x trans-2-enal of varied strength, as w e l l as f o u r dif f e r e n t m i x t u r e s o f t h e s e compounds were s u b j e c t e d to descriptive odor a n a l y s i s . In performing t h i s analysis a s p e c i a l l y t r a i n e d p a n e l w i t h 12 m e m b e r s w a s u s e d .


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135


T h e p a n e l was t h e same a s t h e o n e u s e d e a r l i e r for d e s c r i p t i v e odor a n a l y s i s of soy and rape seed p r o t e i n (7_) · T h e o d o r n o t e s u s e d i n t h e a n a l y s i s w e r e selected from the l i t e r a t u r e and from other i n v e s t i g a t i o n s in o u r l a b o r a t o r y on o d o r p r o p e r t i e s of pure chemicals. T h e s e o d o r n o t e s w e r e p r e - t e s t e d w i t h some o f the samples to be a n a l y z e d . F i n a l l y the i n t e n s i t y o f thir teen odor notes ( T a b l e I I I ) were e s t i m a t e d , u s i n g a 0 - 9 point scale. T h e maximum s c o r e , 9> represents the strongest i n t e n s i t y one w o u l d e x p e c t i n n o r m a l , everyday l i f e , w h i l e the minimum s c o r e , 0, meant ab sence of that p a r t i c u l a r odor note. The samples, containing varying concentrations of either n-hex-trans-2-enol or η - h e x - t r a n s - 2 - e n a l or mix t u r e s o f t h e m , w e r e p r e s e n t e d a s 20 m l p o r t i o n s a t r o o m temperature i n 50 m l E r l e n m e y e r f l a s k s provided with clear-fit stoppers. D e t a i l e d procedures f o r the puri fication of the compounds and sample p r e p a r a t i o n have been p u b l i s h e d elsewhere (6). Table

III.

Selected

odor

notes for

n-hex-trans-2-enol Odor strength Sharp pungent Green, l i k e grass Green, leafy Sour, acid Fruity, citrus Fruity, other In the a n a l y s i s were e v a l u a t e d (Table session three differen each sample had been Table

IV.

1 2 3 4 5 6 7 8 9 10

No.

water

solutions

of

n-hex-trans-2-enal.

Sweet Musty Floral Nut-like Oily, fatty Rubber Candle-like

samples a l t o g e t h e r 10 d i f f e r e n t IV) i n random order. In each u n t i l t samples were a n a l y z e d , evaluated four times.

Concentration trans-2-enol samples used

Sample

and

in and for

mg p e r

l i t r e

(ppm) of

n-hex-

n-hex-trans-2-enal in ten odor d e s c r i p t i o n analysis.

n-Hex-trans-2-enol

n-Hex-tran s-2-enal

10 40 100 -

0.5 5 20 0.5 5 0.5 5

—

10 10 40 4o


136

ENZYMES

IN FOOD A N D B E V E R A G E

PROCESSING

A c o m p u t e r p r o g r a m was u s e d t o c a l c u l a t e t h e mean and standard deviation o f the i n t e n s i t y of each odor note f o r each sample and a l s o to t e s t significant dif f e r e n c e s between the samples. I t was f o u n d t h a t t h e most t y p i c a l o d o r n o t e s of n - h e x - t r a n s - 2 - e n ο 1 were "Rubber" and " C a n d l e - l i k e " while those of n-hex-trans-2-enal were " F r u i t y , other" and "Green, l e a f y " and to a l e s s e r extent "Green, like g r a s s " and " F l o r a l " . Odor notes which were perceived e q u a l l y f o r b o t h compounds were "Sour, a c i d " , "Fruity, c i t r u s " and " O i l y , f a t t y " (cf. Table III). The r e s u l t s are e x e m p l i f i e d i n F i g u r e 1 where the changes i n six of the i n i t i a l l y selected thirteen odor n o t e s as i n f l u e n c e d by c o n c e n t r a t i o n are shown. It is o b v i o u s t h a t an i n c r e a s e in concentration of the single compounds e x p e c t e d l y i s f o l l o w e d b y an i n c r e a s e i n per ceived odor i n t e n s i t y of each i n d i v i d u a l of the six notes (samples 1-3 and 4-6). This is also true for the mixtures ( s a m p l e s 7-10) except for the odor note "Rub ber" which decreased i n i n t e n s i t y on i n c r e a s i n g the aldehyde concentration alone (cf. sample 7 and 8, 9 and 10 r e s p e c t i v e l y ) . Most p r o b a b l y , the odor note " R u b b e r " , p r o d u c e d p r i m a r i l y b y t h e a l c o h o l , was mas ked by the increased i n t e n s i t y of other odor notes i n troduced by the i n c r e a s e d aldehyde concentration. In c o n c l u s i o n , a c o n v e r s i o n between this parti c u l a r a l d e h y d e and a l c o h o l w i l l r e s u l t i n an overall change i n odor i n t e n s i t y with l i t t l e change i n odor quality. Application

studies.

B e e r , m i l k and apple j u i c e are well-known examples of l i q u i d foods which have been r e p o r t e d to develop o x i d a t i v e f l a v o r due to l i p i d o x i d a t i o n , a l t h o u g h b o t h beer and a p p l e j u i c e c o n t a i n o n l y m i n o r amounts of l i p i d s . At t h i s stage these products contain alde hydes l i k e n-hexanal, n-hex-trans-2-enal, n-hepttrans-2-enal, etc. I n i t i a l studies revealed that the p r o d u c t s m e n t i o n e d c o n t a i n e d no a c t i v e ADH and no or v e r y s m a l l amounts o f NAD and NADH. I t was also found that n-hexanal added to beer, m i l k , and apple j u i c e c o u l d r a p i d l y and e f f e c t i v e l y be c o n v e r t e d into n - h e x a n o l by the a d d i t i o n o f ADH and NADH. M i l k was c h o s e n as t h e f i n a l o b j e c t of investiga t i o n s i n c e the pH o f a p p l e j u i c e , b e e r and m i l k is a r o u n d 3·5> 4 . 1 , and 6 . 2 , r e s p e c t i v e l y , a n d on t h e fact t h a t p a r t i c u l a r l y A D H , but a l s o NADH, i s l e s s stable a t a p H l o w e r t h a n 6. T h e m i l k u s e d was p r o d u c e d b y a fistulated cow t h a t h a d b e e n f e d s u n f l o w e r o i l in +


ERIKSSON E T A L .


Intensity

Intensity

"FRUITY, CITRUS"

"FRUITY,OTHER"

Intensity

intensity

"GREEN, LEAFY

"GREEN,UKE GRASS"

Sample

Sample

Intensity

Intensity

"FLORAL"

"RUBBER"

Sample

0

12 3

M L

4 56

J l l i

7 8 910

.Sample

Figure 1. Mean panel intensities of selected characteristic odor notes used in descriptive analysis of 10 water solutions containing n-hex-trsais-2-enol (samples 1-3), n-hex-trans-2-enal (samples 4-6), and mixtures of the two compounds (7-10). The concentration of the odor substances are listed in Table IV.


138

E N Z Y M E S IN FOOD A N D B E V E R A G E PROCESSING

order to i n c r e a s e the p r o p o r t i o n of polyunsaturated f a t t y acids i n the milk f a t . Such milk undergoes rapid l i p i d o x i d a t i o n i m m e d i a t e l y a f t e r m i l k i n g , much larger amounts of n - h e x a n a l and s i m i l a r aldehydes b e i n g formed than i n ordinary milk. The sunflower o i l was admini strated t o t h e cow t h r o u g h a t u b i n g d i r e c t l y i n t o the abomasum i n o r d e r t o p r e v e n t the unsaturated fatty acids from b e i n g hydrogenated i n the rumen, which is the case a f t e r o r a l i n t a k e of unsaturated f a t . The fatty acid fraction of the milk produced contained 2k°/o o l e i c , 19°/o l i n o l e i c a n d λ°/ο l i n o l e n i c a c i d . The m i l k was p a s t e u r i z e d a t 6 3 ° C f o r 30 m i n , 2 . 5 mg o f tetracycline ( D u m o c y c l i n , Dumex, C o p e n h a g e n , Denmark) b e i n g added per l i t r e of milk to i n c r e a s e the m i c r o biological stability. T h e s t a b i l i z e d m i l k was then d i v i d e d i n t o two b a t c h e s , one w h i c h was a l l o w e d to c o n t a i n t h e o r i g i n a l 3·5 per cent of fat (whole milk), and another where the f a t c o n t e n t was r e d u c e d t o ap proximately Λ°/ο ( r e d u c e d f a t milk). The f o l l o w i n g two e x p e r i m e n t s were made. In the f i r s t experiment one hundred ml p o r t i o n s of f u l l fat milk and reduced fat m i l k were s t o r e d f o r k days at 4°C i n s t e r i l i z e d stoppered flasks. E v e r y day f o u r samples each of e i t h e r whole milk or reduced fat m i l k were withdrawn f o r gas chromatographic n-hexanal a n a l y s i s . I n two of t h e s e s a m p l e s f r o m e a c h b a t c h , 3 mg o f y e a s t A D H (300 U / m g , B o e h r i n g e r , M a n n h e i m , W . G e r m a n y ) a n d 50 m g o f N A D H (789ε β - N A D H , B o e h r i n g e r , M a n n h e i m , W . G e r m a n y ) per 100 m l w e r e a d d e d 30 m i n p r i o r t o t h e n-hexanal analysis. T h e r e m a i n i n g two s a m p l e s o f e a c h b a t c h were not t r e a t e d and u s e d as c o n t r o l s . The r e a c t i o n t o o k p l a c e at 20°C. The n - h e x a n a l a n a l y s e s were per f o r m e d on d a y s 1 a n d 3 w i t h t h e w h o l e m i l k and on days 2 and k w i t h the r e d u c e d f a t milk. In t h e s e c o n d e x p e r i m e n t 3 m g o f A D H a n d 50 m g o f NADH p e r 100 m l w e r e a d d e d t o b o t h t h e w h o l e m i l k and reduced fat m i l k on t h e s e c o n d d a y a f t e r m i l k i n g a n d pasteurizing. The samples were then s t o r e d f o r 9 days a t k C· C o n t r o l s w i t h no enzyme and coenzyme a d d e d were run p a r a l l e l . T h e n - h e x a n a l a n a l y s e s were made o n d a y s 3> 5> 79 a n d 9 w i t h b o t h t h e enzyme-coenzyme treated and the u n t r e a t e d milk. F o r n - h e x a n a l d e t e r m i n a t i o n t w o 100 m l s a m p l e s of m i l k a n d 200 m l o f d i s t i l l e d w a t e r f o r d i l u t i o n w e r e transferred on e a c h o c c a s i o n t o a p e r v i o u s l y described head space sampling device connected to a Perkin-Elmer 900 g a s c h r o m â t o g r a p h (8). Three hundred ml of heads p a c e g a s was f o r c e d t h r o u g h a p r e c o l u m n c o n c e n t r a t i o n a c c e s s o r y by a i r pressure f o r 30 m i n w h e r e b y t h e volat i l e o r g a n i c compounds i n the head space gas were c o n -


8.

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139

densed i n a cool trap. The condensed m a t e r i a l was allowed to enter the i n j e c t o r o f the gas chromâtοgraph, kept at 110°C b y s u d d e n h e a t i n g o f t h e t r a p w i t h an oil b a t h at 140°C. T h e s e p a r a t i o n was p e r f o r m e d on an tubular stainless steel c o l u m n , Ο . 7 6 mm I . D . χ 181 mm, c o a t e d w i t h S F 9 6 / l g e p a l CO88O ( 9 5 / 5 ) . The oven tem p e r a t u r e was p r o g r a m m e d 2 0 - l 4 0 ° C a t 2°/min after an i n i t i a l 3 min i s o t h e r m a l p e r i o d , and the n i t r o g e n gas f l o w was 12 m l / m i n . T h e F I D s i g n a l was f e d i n t o an Infratronics CRS-101 electronic integrator, with d i g i tal print-out equipment. The i n t e g r a t o r values of the h e x a n a l peak ( p r e v i o u s l y i d e n t i f i e d by mass spectro metry) were used to r e p r e s e n t the n - h e x a n a l content of the head space. The r e s u l t s g i v e n i n T a b l e s V a n d V I show that boih discontinuous (first experiment) and continuous (second experiment) t r e a t m e n t o f t h e two k i n d s o f m i l k e i t h e r reduced the concentration of the i n i t i a l l y formed n-hexanal instantaneously or kept i t reduced throughout the experiment. In the gas chromatograms one c o u l d a l s o see t h a t the n - h e x a n o l peak r o s e along w i t h the d e c l i n e of the n - h e x a n a l peak and t h a t other aldehydes and a l c o h o l s behaved s i m i l a r l y . The i n i t i a l n - h e x a n a l c o n c e n t r a t i o n was i n t h e r a n g e of 0.5 1 ppm, as compared to e a r l i e r studies on m i l k with added n-hexanal. Table

V.

Concentration of over milk stored of added a l c o h o l coenzyme (NADH).

n-hexanal i n the headspace a t k°C. Immediate effect dehydrogenase (ADH) and (integrator values).

Days

Τ Skim no

no

30

min

5

860

910

130

125

milk

addition

Whole

milking

3

milk

ADH+NADH, Whole

after

milk

addition

Skim

2

810

85Ο

100

120

milk

ADH4-NADH,

30

min


ENZYMES

140 Table

V I .

I N FOOD A N D B E V E R A G E

Concentration o f n-hexanal i n the headspace o v e r m i l k s t o r e d a t k°C f o r 9 d a y s . Long term e f f e c t o f a l c o h o l d e h y d r o g e n a s e (ADH) and c o e n z y m e (NADH) a d d e d on d a y 2. (integrator values). Days

Skim no

no

added

day

2

800

910

1030

125

125

125

76Ο

820

875

100

100

100

1035

125

milk

addition

Whole

milking

milk

ADH+NADH

Whole

after

milk

addition

Skim

PROCESSING

930

milk

ADH+NADH

added

day

2

130

The f u r t h e r a p p l i c a t i o n of enzymic conversion of aldehydes and a l c o h o l s b y t h e A D H - N A D H system must probably await the development of suitable reactors. In m a t e r i a l c o n t a i n i n g enough NADH o r N A D i n correct concentration ratios this coenzyme content can be u t i l i z e d i n the reaction. When, however, the c o enzyme i s i n s u f f i c i e n t o r l a c k i n g , coenzyme from an external source, such as spent brewer's y e a s t , must be u s e d . By a standard procedure (9) we f o u n d that b r e w e r ' s y e a s t c o n t a i n s a b o u t 2 . 5 mg N A D + N A D H / g d r y yeast i n a NAD /NADH ratio f r o m a p p r o x i m a t e l y 2/1 t o 10/1 d e p e n d i n g o n t h e w a y o f p r e p a r a t i o n . A high pro p o r t i o n o f NADH can be obtained by r e d u c t i o n ofN A D either chemically, electrolytically (_K)) o r e n z y m a t i c a l iy. S i n c e t h e number o f m o l e c u l e s o f coenzyme needed w i l l b e t h e same a s t h e n u m b e r o f c o n v e r t i b l e aldehyde or a l c o h o l m o l e c u l e s , i t w i l l i n most c a s e s be b o t h i m p r a c t i c a l and uneconomical to apply the A D H - N A D ( H ) technique without disposal of re-usable enzymecoenzyme systems. I m m o b i l i z a t i o n o f enzymes and c o enzymes on s u i t a b l e carriers seems t o b e a f r u i t f u l evolution to enable future conversions of this type. In t h e c a s e o f A D H a n d N A D H b o t h t h e enzyme a n d a c o enzyme a n a l o g u e have been i m m o b i l i z e d on S e p h a r o s e k B, which allowed the formation of a binary ADH-NADH complex. T h e i m m o b i l i z e d b i n a r y complex was a l s o shown t o b e f u n c t i o n a l i n t h e same w a y a s t h e soluble one (11). T h e o x i d i z e d a n d r e d u c e d coenzymes c a n e a s i l y be t r a n s f e r r e d into each other i n s i t u by a p p l y i n g


8.

ERIKSSON E T A L .


alternative substrates. and r e g e n e r a t e coenzyme and membrane t e c h n i q u e

Other suggestions to are microincapsulation (13)·

141

retain ( 12)

Abstract. Enzymic interconversion of a l i p h a t i c aldehydes, alcohols, and carboxylic esters i s b r i e f l y surveyed. Odor properties are presented, both quantitative ones, as odor detection concentration and q u a l i t a t i v e ones, as odor descriptions of certain aldehydes and a l c o h o l s , which are normally found i n foods after lipid oxidation. Experiments were performed to reduce the amount of preformed aldehydes, p a r t i c u l a r l y n-hexanal i n milk containing polyunsaturated f a t , by addition of alcohol dehydrogenase and NADH. Acknowledgment. The authors are indebted to Mrs. M. Knutsson, M. Sc., Astra-Ewos AB, Södertälje, Sweden, f o r d e l i v e r i n g polyunsaturated cow's milk for t h i s study. Literature cited. (l)

E r i k s s o n , C., i n "Industrial Aspects of B i o chemistry", e d . , Spencer, B., V o l . 30, part I I , p. 865, North Holland/American E l s e v i e r , Amsterdam, 1974.

(2)

E r i k s s o n , C.E., J. Food

(3)

Bruemmer, J.H. and Roe, B., J. Agr. Food Chem. (1971) 19, 266. Davies, D.D., Patil, K.D., Ugochukwu, E . N . and Towers, G.H.N., Phytochemistry (1973) 12, 523. Hatamaka, A. and Oghi, T., Agr. Biol. Chem. (1972) 36, 2033. E r i k s s o n , C.E., Lundgren, Β and V a l l e n t i n , Κ., Chemical Senses and Flavor (1976) 2, 3.

(4) (5) (6)

Sci.

(1968) 33,

525.

(7)

Q v i s t , I . and von Sydow, Ε., Lebensm.-Wiss. u. Technol. (1976) i n press.

(8)

von Sydow, Ε., Andersson, J., Anjou, Κ., Karlsson, G., Land, D. and G r i f f i t h s , Ν., Lebensm.-Wiss. u. Technol. (1970) 3, 11. Klingenberg, Μ., i n "Methoden der enzymatischen Analyse", e d . , Bergmeyer, H . U . , V o l . 2, p. 1975, Verlag Chemie, Weinheim, 1970.

(9)


142

(10)

(11) (12) (13)

E N Z Y M E S I N FOOD A N D B E V E R A G E PROCESSING

Alizawa, Μ., Coughlin, R.W. and Charles, Μ., Biotechnology and Bioengineering (1976) 18, 209. Gestrelius, S., Månsson, M-O. and Mosbach, Κ., Eur. J. Biochem. (1975) 57, 529. Campbell, J. and Ming Swi Chang, T., Biochim. Biophys. Acta (1975) 397, 101. Chambers, R.P., Ford. J.R., A l l e n d e r , J.H., Baricos, W.H. and Cohen, W., i n "Enzyme E n gineering", ed., Kendall Pye, Ε., and Wingard, J r , L. B., V o l . 2, p. 195, Plenum Press, New York, 1974.


Enzymes in Food and Beverage Processing

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