Instrumental and Sensory Characteristics of Roasted Peanut Flavor

14 Instrumental and Sensory Characteristics of Roasted Peanut Flavor Volatiles LAWRENCE L. BUCKHOLZ, JR.

Downloaded by FUDAN UNIV on February 21, 2017 | http://pubs.acs.org Publication Date: November 11, 1981 | doi: 10.1021/bk-1981-0170.ch014

International Flavors and Fragrances, 1515 Highway 36, Union Beach, NJ 07735 HENRYK DAUN Rutgers—The State University, Cook College, Department of Food Science, New Brunswick, NJ 08902

Roasted peanuts (Arachis hypogaea) possess a unique and widely enjoyed flavor. In this review we will cover the formation of peanut flavor volatiles, analytical aspects, sensory analysis and correlation of instrumental and sensory results. The roasting process (pyrolysis) subjects the peanut to internal temperatures of 130°C to 150°C (Pickett and Holley) (JL) , during which the typical roasted peanut flavor is produced. The purpose of pyrolytically treating certain foods promotes flavor changes (common to all of them) that ultimately increase their palatability. Flavor volatiles are produced in these products which influence their aroma and taste characteristics. A knowledge of the composition of these volatiles and the organoleptic changes in their taste characteristics would help us better understand their flavor chemistry. There are close to 300 flavor compounds identified in roasted peanuts. Walradt et al {2) identified 187 compounds, 142 of them for the first time. Wu {3), listed a table of 205 compounds with references. The most extensive list of compounds was published in 1973 (4). In this review 270 compounds were reported with references. They included 34 hydrocarbons, 26 alcohols, 60 carbonyls, 29 acids, 15 esters, 59 bases, 15 S-compounds and 32 miscellaneous compounds. Flavor Precursors The most important constituents of peanuts responsible for the flavor formation during roasting are the amino acids, sugars, proteins and lipids. Typical precursor amino acids are aspartic acid, asparagine-glutamine, glutamic acid, phenylalanine and histidine. Mason et al (_5) and Young and Mason (6) noted that the arginine content of Spanish peanut decreased with maturity. Immature nuts contained as much as 50% more arginine than mature nuts. Resultant products (peanut butter) made from immature peanuts were inferior in flavor when compared to peanut butter made from mature nuts. 0097-6156/81/0170-0163$05.00/0 © 1981 American Chemical Society Teranishi and Barrera-Benitez; Quality of Selected Fruits and Vegetables of North America ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Teranishi and Barrera-Benitez; Quality of Selected Fruits and Vegetables of North America ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

oldohexose

+

α-Amino

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1

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(I)

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Figure 1.

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-C-OH

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CH

N=CH

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-C-OH

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Pyrazine formation mechanism

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14.

BUCKHOLZ A N D DAUN

165

Roasted Peanut Flavor Volatiles

Products t h a t possess p y r o l y t i c a l l y formed f l a v o r s such as peanuts, hazelnuts, c o f f e e , cocoa e t c . a l l c o n t a i n many c l a s s e s of compounds r e s p o n s i b l e f o r the roasted nutty notes. I n v e s t i g a t i v e work has been done i n the development o f f l a vor components from r o a s t i n g ; the low molecules weight carbonyls, the p y r a z i n e s and other compounds have a l l been s t u d i e d .


Formation

o f Pyrazines

The a l k y l a t e d p y r a z i n e s formation pathway i n amino a c i d carbohydrate systems was s t u d i e d by Koehler e t a l (7). The e f f e c t o f r o a s t i n g on p y r a z i n e formation was demon s t r a t e d by Koehler and O d e l l (8) who used v a r i a t i o n s o f a model system t o demonstratethis e f f e c t . As f a r back as 1967, Newell (9) proposed a p y r a z i n e forma t i o n mechanism between sugar and amino a c i d p r e c u r s o r s (see F i g u r e 1). The S c h i f f base c a t i o n i s formed by a d d i t i o n o f the amino a c i d t o the anomeric p o r t i o n o f aldohexose followed by a l o s s o f water and hydroxyl i o n . Decarboxylation forms an imine which can hydrolyze t o an aldehyde and dienamine. Enolization occurs and the r e s u l t i n g keto-amine condenses t o amino acetone and glyceraldehyde. The pyrazine (2,5 dimethyl) i s then formed by the condensation o f the two molecules o f amino acetone. Walradt e t a l (2) i n v e s t i g a t e d the p o s t u l a t e d mechanism f o r the formation o f a c e t y l and methyl a c e t y l p y r a z i n e s by Wange et a l (10). Walradt proposed a mechanism f o r the formation o f 6,7-dihdyro-5H cyclopentapyrazine as a r e s u l t o f the i n t e r a c t i o n o f g l y o x a l and pyruvaldehyde with amino a c i d s and 2hydroxy-3-methyl-2-cyclopenten-l-one, a frequently occurring product o f carbohydrate degradation. Carbonyls Various workers have d i s c u s s e d the carbonyl compounds de r i v e d from l i p i d s ; (11, _12, 13) . According t o Wu (_3) , a number of aroma compounds can be t r a c e d t o l i p i d degradation d u r i n g r o a s t i n g . Aldehydes, ketones, f a t t y a c i d s , lactones and a l c o h o l s were formed. The o x i d a t i v e degradation o f a-amino a c i d s t o a l d e hydes o f one l e s s carbon atom by compounds such as a l l o x a n , n i n h y d r i n and 2-furaldehyde was d e f i n e d by Schonberg (14). He demonstrated t h a t the amino group must be alpha t o the c a r b o x y l group and t h a t the carbonyl compound must c o n t a i n a dione. This r e a c t i o n which has been known f o r many years i s i l l u s t r a t e d i n Figure 2. I f the hydrogen on the α-carbon o f the amino a c i d i s s u b s t i t u t e d a ketone i s produced.

RCOCOR' + R"CH(NH )COOH-» R"CHO + C0 + RCH(NH )COR' 2

Figure 2.

2

2

Strecker degradation mechanism


166

QUALITY

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AND

VEGETABLES

Mason et a l (15, 5) d i s c u s s e d S t r e c k e r degradation as a source of carbonyl formation. He and h i s colleagues i s o l a t e d and i d e n t i f i e d the carbonyls (known to a r i s e from the S t r e c k e r Degradation of t h e i r corresponding amino acids) from roasted peanuts. These i n c l u d e d acetaldehyde, 2 and 3 methyl b u t a n a l , i s o butyraldehyde and phenylacetaldehyde. He found t h a t a l l of the corresponding amino a c i d s were shown to be present i n the raw peanuts and were destroyed d u r i n g r o a s t i n g . Mason showed t h a t phenylacetaldehyde and acetaldehyde are produced i n r e l a t i v e l y l a r g e amounts d u r i n g r o a s t i n g ; t h i s would be expected from the l a r g e amounts of f r e e and peptide bound a l a n i n e and phenylalanine present.


A n a l y t i c a l Aspects C o l l e c t i o n of Peanut F l a v o r Components. Many methods have been used t o e x t r a c t v o l a t i l e s from p y r o l y t i c a l l y processed foods i n c l u d i n g peanuts; atmospheric d i s t i l l a t i o n of peanut o i l , h i g h vacuum d i s t i l l a t i o n (Mason e t a l ) (16), steam d i s t i l l a t i o n , s o l vent e x t r a c t i o n and c o n c e n t r a t i o n , e t c . . . A l l of these t e c h niques have been s u c c e s s f u l l y used to i s o l a t e f l a v o r components from peanuts and s i m i l a r products. Mookherjee e t a l (17) ext r a c t e d monocarbonyls from potato chips by use of s o l v e n t ext r a c t i o n . Herz and Chang (18) developed a unique apparatus, a f a l l i n g f i l m s t i l l which was extremely v e r s a t i l e i n i s o l a t i n g v o l a t i l e s from v a r i o u s food components. Walradt e t a l (_2) used a turbo f i l m evaporator, d i s t i l l i n g v o l a t i l e s from an aqueous ground peanut s l u r r y and c o l l e c t i n g the condensate i n a s e r i e s of traps. Headspace Technique. One of the most recent methods of f l a vor a n a l y s i s which evolved w i t h the development of s e n s i t i v e gas chromatographic instrumentation i s the headspace technique. Withycombe e t a l (19), gave an e x c e l l e n t d e s c r i p t i o n of headspace analysis. In t h i s procedure v o l a t i l e s i n gaseous s t a t e t h a t are i n e q u i l i b r i u m over the food are analyzed. Brown e t a l (20) examined v o l a t i l e s from roasted peanuts by i n t r o d u c i n g g l a s s l i n e r s c o n t a i n i n g ground samples o f r o a s t e d nuts i n t o the i n j e c t i o n p o r t of a gas chromatograph where v o l a t i l e s were v a p o r i z e d i n s i t u . In many instances c o n c e n t r a t i o n of the substances i n the headspace i s necessary. Adsorption polymers have been used f o r c o l l e c t i o n , concent r a t i o n , and subsequent G.C. analyses i n a wide v a r i e t y of app l i c a t i o n s i n recent years. Withycombe e t a l (19) used s e v e r a l a d s o r p t i o n polymers t o t r a p the headspace v o l a t i l e s from hydrol y z e d vegetable p r o t e i n (HVP) and found t h a t of t h r e e polymers i n v e s t i g a t e d , Chromosorb 105, Porapak Q, and Tenax GC, the v o l a t i l e s trapped on Tenax GC contained the most c h a r a c t e r i s t i c HVP aroma.



14.

BUCKHOLZ AND DAUN

167


A method d e s c r i b e d by Buckholz e t a l (_21) employs the use o f the a d s o r p t i o n polymer Tenax GC (para 2,6 diphenylene oxide) t o c o l l e c t v o l a t i l e s from roasted peanuts. Two types o f peanuts Runner #1 and Spanish were roasted. The temperature was h e l d a t a constant 163°C and r o a s t i n g times o f 7 minutes, 8 minutes and 9 minutes were used t o o b t a i n l i g h t r o a s t , medium r o a s t and dark r o a s t peanuts. Optimal c o n d i t i o n s f o r the a d s o r p t i o n polymer method c o l l e c t i o n o f v o l a t i l e s were as f o l l o w s . Four hundred grams o f peanuts were placed i n a 50°C jacketed g l a s s column and e x t r a c t e d w i t h n i t r o g e n f o r 4 hours a t a flow r a t e o f 40 mls/min. Volatiles were adsorbed onto e i g h t h i n c h t r a p s packed w i t h Tenax GC which were attached t o the top o f the column v i a a t e f l o n thermometer adapter. Three t r a p s were used i n s e r i e s . S i x c o l l e c t i o n s were made f o r each r o a s t i n g c o n d i t i o n . Gas Chromatography - Mass Spectrometry. The development o f gas chromatography g r e a t l y i n c r e a s e d the a n a l y t i c a l chemists a b i l i t y t o separate, i s o l a t e and i d e n t i f y components. Gas chro matography (GC) has been used i n c o n j u n c t i o n w i t h mass spectrom e t r y , n u c l e a r magnetic resonance spectrometry and i n f r a red spec troscopy as evidenced by Mason e t a l (16) i n h i s peanut f l a v o r work. Bondarovich e t a l (22) used mass spectrometry i n conjunc t i o n w i t h GC t o i d e n t i f y p y r a z i n e s i n c o f f e e , van Praag e t a l (23) used s i m i l a r i n s t r u m e n t a l techniques on cocoa which i s a l s o h i g h i n p y r a z i n e s . Pattee e t a l (24) analyzed raw peanut essence by GC mass s p e c t r a l means. Raw peanut essence i s h i g h i n carbon y l s . Walradt e t a l {2) used a 500 f t . s t a i n l e s s s t e e l c a p i l l a r y column .03 inches i n diameter coated w i t h Carbowax 20M coupled to a mass spectrometer t o i d e n t i f y the v o l a t i l e s i n h i s peanut essence. Johnson e t a l (25, 26) used h i g h and low r e s o l u t i o n mass spectrometers coupled t o open t u b u l a r columns and C r a i n and Tang (27) i d e n t i f i e d components i n Macadamia nuts by GC mass spectrometry and compared t h e i r f i n d i n g s t o GC r e t e n t i o n i n d i c e s and mass s p e c t r a l reference data. So GC mass s p e c t r a l a n a l y s i s has proved t o be an e x c e l l e n t t o o l f o r the s e p a r a t i o n , i d e n t i f i c a t i o n o f peanut v o l a t i l e s . In a recent work, Buckholz e t a l (21) , the t r a p s c o n t a i n i n g ad sorbed v o l a t i l e s were i n s e r t e d d i r e c t l y i n t o the m o d i f i e d i n j e c t i o n p o r t o f a V a r i a n 2700 gas chromatograph (GC) f o r analy sis. A 400 f t . by 0.032 i n c h g l a s s c a p i l l a r y column coated w i t h SE-30 was used. The column was temperature programmed from 50°C t o 190°C a t 2°/min. Mass s p e c t r a l a n a l y s i s was used t o i d e n t i f y the GC peaks present i n the peanut headspace v o l a t i l e s . Seven new compounds were t e n t a t i v e l y i d e n t i f i e d by GC mass spectral analysis. The newly i d e n t i f i e d compounds were η-ethyl p y r r o l e , 1,2dimethyl p y r r o l e , l - o c t e n - 3 - o l , 2 , 4 - d i m e t h y l - 3 - t h i a z o l i n e e t h y l decanoate, decane and indane. /



168

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E f f e c t of Roasting Time on the Amount and Composition of Volatiles. Buckholz et a l (28) s t u d i e d the i n f l u e n c e of r o a s t i n g time on the chemical composition of the aroma of f r e s h roasted peanuts. A n a l y t i c a l d e t a i l s of t h i s work w i l l be p u b l i s h e d i n the near f u t u r e . Peaks were q u a n t i t a t e d by a chromatography computer u s i n g an I n t e r n a l Standard method (Buckholz et a l ) (21). E t h y l nonanoate was used as the I n t e r n a l Standard. The amount of peanut headspace v o l a t i l e s adsorbed onto the t r a p s was expressed as e t h y l nonanoate. Table I shows the t o t a l amounts of v o l a t i l e s c o l l e c t e d f o r a l l r o a s t i n g times and both peanut types. Q u a n t i t i e s are expressed i n 10"^ gms. The G.C. p r o f i l e s were separated i n t o 3 b o i l i n g p t . zones; Most V o l a t i l e (pks 1-10); Medium V o l a t i l e (pks 11-19) and Least V o l a t i l e (pks 20-32). F i g u r e 3 shows GC p r o f i l e f o r L i g h t , Medium and Dark roasted samples f o r Runner #1. The same peaks were found to be present i n both peanut types (Runner #1 and Spanish) and under a l l r o a s t i n g c o n d i t i o n s , but d i f f e r e d q u a n t i t a t i v e l y . Thirty-two peaks were s e l e c t e d f o r e v a l u a t i o n based on an i n i t i a l composition of 0.1% o r more. The carbonyls are represented by peaks 4, 6, 7, 11 and 16 on F i g u r e 3. They were i d e n t i f i e d as isobutyraldehyde, i s o v a l e r aldehyde, 2-methyl b u t a n a l , pentanal and hexanal. The pyrazines are represented by peaks 13, 18, 20, 25 and 26. They were i d e n t i f i e d as p y r a z i n e , 2-methyl p y r a z i n e , 2,5-dimethyl p y r a z i n e , 2ethyl-5-methyl p y r a z i n e and 2-ethyl-3-methyl p y r a z i n e . The authors observed a decrease i n carbonyls (which are r e s p o n s i b l e f o r harsh green f l a v o r notes) and i n c r e a s e i n pyrazines (which are r e s p o n s i b l e f o r roasted notes) with longer r o a s t i n g time. 2-Methyl butanal i s a t y p i c a l carbonyl which has been prev i o u s l y i d e n t i f i e d i n peanuts, Mason e t a l (15). 2,5-Dimethyl pyrazine i s a l s o a t y p i c a l compound which has been p r e v i o u s l y r e ported i n peanuts (Mason et a l ) (16). A decrease i n aldehyde and subsequent i n c r e a s e i n pyrazine w i t h increased r o a s t i n g time was demonstrated by these authors. This supports Mason and Johnson's f i n d i n g s (15, 16). They reported t h a t the low molecular weight carbonyls, p a r t i c u l a r l y aldehydes, were r e s p o n s i b l e f o r the harsh green notes present i n roasted peanuts while the a l k y l a t e d pyrazines were r e s p o n s i b l e f o r the roasted nutty c h a r a c t e r of roasted peanuts (15, 16). Sensory A t t r i b u t e s of Roasted Peanuts Few foods have a f l a v o r and t e x t u r e t h a t i s as u n i v e r s a l l y l i k e d as peanuts. T y p i c a l peanut f l a v o r , n u t t i n e s s , sweetness and b i t t e r n e s s can be a l t e r e d by v a r i e t y , growing c o n d i t i o n s , methods of h a r v e s t i n g , s t o r i n g and p r o c e s s i n g ( r o a s t i n g ) . The b i t t e r f l a v o r i n peanuts i s due to a t l e a s t four components o f saponins which are about 20 times as concentrated i n



33.39

LEAST VOL. 20-32

6

316.57

50.83

99.46

166.28

RUNNER MEDIUM

352.74

74.21

124.94

153.59

DARK

338.04

39.94

126.29

171.80

LIGHT

371.85

60.68

161.26

149.91

SPANISH MEDIUM

* - T h i s represents 6 c o l l e c t i o n s and subsequent GC a n a l y s i s p e r r o a s t i n g c o n d i t i o n . Q u a n t i t i e s expressed i n 10~ gms.

324.67

117.65

MED. VOL. 11-19

TOTAL

173.63

LIGHT

MOST VOL. 1-10

CHROMATOGRAM SECTIONS

COMPARISON OF THE TOTAL VOLATILES ADSORBED UNDER STANDARD CONDITIONS FOR VARIOUS ROASTING TIMES IN THE MOST ( I ) , MIDDLE (II) AND LEAST (III) VOLATILE AREAS OF THE GC CHROMATOGRAM

TABLE I


366.26

68.95

161.41

145.90

DARK

QUALITY

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Runner..

Runner

mediul

LU CO

ο ClCO LU

VI

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or Ο ο

Runner.

LU

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3

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4

40

30

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5

6

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50

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I

7

8

9

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GC profiles for light, medium, and dark roasted samples for Runner #1



14.

BUCKHOLZ A N D DAUN


111

the hearts of peanuts as i n the cotyledons according t o F i s h e r (29) and D i e c h e r t and Morris ( 3 0 ) . Peanut f l a v o r i s c l o s e l y r e l a t e d to the o i l , and on separat i o n the f l a v o r goes w i t h the o i l r a t h e r than w i t h the meal. In p r a c t i c a l l y a l l cases o f heating the f l a v o r i s accentuated. T h i s i s p a r t i c u l a r l y t r u e w i t h dry r o a s t i n g . The p y r a z i n e s were r e s p o n s i b l e f o r the r o a s t e d nutty f l a v o r of f r e s h roasted peanuts (Mason e t a l ) (15, 1 6 ) , (Johnson 2 5 , 2 6 ) . According to Mason et a l (15), the low molecular weight a l d e hydes are r e s p o n s i b l e f o r the harsh aroma a s s o c i a t e d w i t h f r e s h roasted nuts. Sensory e v a l u a t i o n i s i n d i s p e n s a b l e f o r e v a l u a t i n g food and f l a v o r m a t e r i a l s . Peanuts and peanut products have been extens i v e l y evaluated using sensory a n a l y s i s alone and i n combination w i t h instrumental a n a l y s i s ; ( M i l u t i n o v i c et a l ) ( 3 1 ) , (Fore e t a l ) ( 3 2 ) , (Dupuy e t a l ) (_33, J34,) and (Young e t a l ) ( 3 5 ) . Dravnieks et a l (32) evaluated corn u s i n g sensory e v a l u a t i o n i n combination w i t h G.C. M i l u t i n o v i c used a 9" p t . hedonic s c a l e to r a t e and determine s i g n i f i c a n t d i f f e r e n c e s among tomato j u i c e blends and peanut samples from v a r i o u s r o a s t i n g times. The sensory scores were then c o r r e l a t e d w i t h instrumental f i n d i n g s . Fore et a l (32) r a t e d peanut b u t t e r samples u s i n g hedonic s c a l i n g and c o r r e l a t e d these r e s u l t s to gas chromatographic (G.C.) r e s u l t s . G.C. v o l a t i l e p r o f i l e s were determined f o r 14 peanut b u t t e r s which had been f l a v o r scored. When s e l e c t e d peak area r a t i o s were p l o t t e d a g a i n s t f l a v o r scores 9 of the 14 p o i n t s were almost on the r e g r e s s i o n l i n e , the r e s t were w i t h i n one u n i t . Dupuy a l s o used hedonic s c a l i n g on vegetable o i l s and v a r i o u s peanut b u t t e r s and Young e t a l (J35) evaluated peanut b u t t e r s from roasted peanuts prepared by d i f f e r e n t r o a s t i n g methods u s i n g a nine p o i n t hedonic s c a l e . T r i a n g l e t e s t i n g can be used p r i o r to hedonic r a t i n g , to e l i m i n a t e p s y c h o l o g i c a l i n f l u e n c e s from a f f e c t i n g judges s c o r i n g . The i n f l u e n c e of r o a s t i n g time on sensory a t t r i b u t e s of roasted peanuts was examined by Buckholz e t a l (36). Sensory methods mentioned below are d e s c r i b e d i n d e t a i l i n t h i s p u b l i c a tion. Peanut samples from each r o a s t i n g c o n d i t i o n were evaluated o r g a n o l e p t i c a l l y f o r s t r e n g t h and d e s i r a b i l i t y of aroma and f l a vor using a 9 p o i n t hedonic s c a l e . S t a t i s t i c a l a n a l y s i s was then done u s i n g the Tukey Test to determine s i g n i f i c a n t d i f f e r e n c e s among r o a s t i n g c o n d i t i o n s . Table 2 shows the r e l a t i v e rankings of a l l four f l a v o r a t t r i b u t e s namely s t r e n g t h and d e s i r a b i l i t y of aroma and f l a v o r as i n f l u e n c e d by r o a s t i n g time. T h i s t a b l e i l l u s t r a t e s the average f l a v o r score f o r each a t t r i b u t e . The optimum samples chosen on the b a s i s o f the mean value f o r d e s i r a b i l i t y of aroma and f l a vor were Runner #1 Medium and Spanish Dark. The Tukey Test of s i g n i f i c a n c e at . 0 5 l e v e l showed s i g n i f i cant d i f f e r e n c e s i n r o a s t i n g c o n d i t i o n s w i t h respect to s t r e n g t h of odor and f l a v o r but no s i g n i f i c a n t d i f f e r e n c e s w i t h respect t o


Teranishi and Barrera-Benitez; Quality of Selected Fruits and Vegetables of North America ACS Symposium Series; American Chemical Society: Washington, DC, 1981. 5.26 5.80 6.02

0.85

5.46 6.01 6.21

0.81

LIGHT

MEDIUM

DARK

TUKEY (0.05) Q

5.30 5.10 5.19

0.93

5.28 5.56

0.89

5.11

4.94

6.74

6.84

DARK

5.24

5.45

5.32

5.69

6.07

MEDIUM

SPANISH

4.96

FLAVOR

4.83

ODOR

4.78

FLAVOR

4. 98

ODOR

DESIRABILITY OF

LIGHT

RUNNER #1

STRENGTH OF

RELATIVE RANKING OF SAMPLES USING AVERAGE SCORE

TABLE I I


14.

BUCKHOLZ AND DAUN


173

d e s i r a b i l i t y o f odor and f l a v o r Table 3. D e t a i l s on the Tukey Test as a method o f s t a t i s t i c a l a n a l y s i s can be found i n (Steel et a l ) (37). The Tukey Test i s a r a t h e r c o n s e r v a t i v e s t a t i s t i c a l c a l c u l a t i o n that demonstrates only severe d i f f e r e n c e s and ignores s u b t l e ones that might be considered s i g n i f i c a n t by other means of c a l c u l a t i o n . In t h i s method as shown i n Table 3 any two sam p l e s t h a t are not d i r e c t l y connected by a bar are d e c l a r e d s i g n i f i c a n t l y d i f f e r e n t from each other.


C o n t r i b u t i o n o f Newly I d e n t i f i e d Compounds t o Peanut F l a v o r To determine the importance o f the newly i d e n t i f i e d com pounds i n t h e i r o v e r a l l c o n t r i b u t i o n t o peanut f l a v o r , t h e f o l lowing sensory e v a l u a t i o n was conducted by s i x experienced f l a v o r chemists i n a l a b s p e c i f i c a l l y designed f o r sensory a n a l y s i s . A good q u a l i t y t y p i c a l peanut f l a v o r was evaluated i n d i s t i l l e d water a t 50 ppm. T h i s l e v e l o f f l a v o r provided o p t i m a l aroma and t a s t e c h a r a c t e r i s t i c s . The new compounds were then added i n d i v i d u a l l y t o the peanut f l a v o r i n s o l u t i o n and evaluated o r g a n o l e p t i c a l l y f o r t h e i r o v e r a l l c o n t r i b u t i o n t o the aroma and f l a v o r o f the peanut f l a v o r . The peanut f l a v o r c o n t a i n i n g the new compound was then evaluated against the peanut f l a v o r alone to determine enhancement o r d e t r a c t i o n from the e x i s t i n g f l a v o r . Concentrations o f the added chemicals were adjusted u n t i l optimal o r g a n o l e p t i c c o n t r i b u t i o n was p e r c e i v e d . Table 4 shows the pea nut f l a v o r c o n c e n t r a t i o n i n d i s t i l l e d water p l u s a l i s t o f t h e compounds, optimal c o n c e n t r a t i o n i n the d i l u t e d peanut f l a v o r and a d e s c r i p t i o n o f the o r g a n o l e p t i c c o n t r i b u t i o n o r d e t r a c t i o n from the f l a v o r . I t was found that the chemicals i n d i v i d u a l l y enhanced s e l e c t e d areas o f the o v e r a l l peanut f l a v o r . The η-ethyl p y r r o l e and e t h y l decanoate enhanced the nut meat area o f the f l a v o r which c o n t r i b u t e d t o the o v e r a l l sweet n u t t i n e s s . The e t h y l decanoate a l s o added sweet f a t t y notes which c o n t r i b u t e d t o the o v e r a l l f l a v o r body. The 2,4-Dimethyl-3-thiazoline added deep roasted notes and c o n t r i b u t e d t o the nut s k i n c h a r a c t e r . Some people d e s c r i b e these notes as the s h e l l y notes. The l - 0 c t e n - 3 - o l added t o the earthy green notes i n the background, some f a t t i n e s s and a l s o enhanced the sweet nut s k i n portion. Decane - the hydrocarbon c o n t r i b u t e d t o the f u l l n e s s o r body of the f l a v o r adding some f a t t y o r waxy notes and rounding o f f the f l a v o r i n general which imparted a f u l l n e s s o r r i c h n e s s t o the o v e r a l l f l a v o r c h a r a c t e r . Indane - added some harsh solventy notes c o n t r i b u t i n g t o the green area and c o n t r i b u t e d t o the f u l l n e s s o f the f l a v o r . 1,2Dimethyl p y r r o l e was not evaluated s i n c e a reference sample was not a v a i l a b l e .


174

QUALITY

TABLE

OF SELECTED

FRUITS

A N D

VEGETABLES

III

TUKEY TEST FOR SIGNIFICANT DIFFERENCES BETWEEN SAMPLES


STRENGTH

ODOR

R-L*

S-L*

4.98

5.46

S-M *

R-M *

S-D*

R-D*

6.01

6.07

6.21

6.84

1

1

I 1

1

I 1

r-—

STRENGTH R-L

S-L

4.78

1

FLAVOR

5.26

R-M

S-M

S-D

5.69

5.80

6.02

1

1

R-L

R-D

4.83

4.93

6.74 I L

1 DESIRABILITY

R-D

1

ODOR

S-L

S-M

R-M

5.24

5.28

5.31

S-D

5.56 •

DESIRABILITY S-M

R-L

4.96

5.10

FLAVOR R-D

5.11

I1

S-D

5.19

S-L

R-M

5.30

5.44 I

R

=

RUNNER

S

=

SPANISH

L

=

LIGHT

M

=

MEDIUM

D

=

DARK


14.

B U C K H O L Z AND DAUN

175


TABLE IV EVALUATION OF NEWLY IDENTIFIED FLAVOR CHEMICALS FOR THEIR OVERALL CONTRIBUTION TO PEANUT FLAVOR


STANDARD TEST SOLUTION - PEANUT FLAVOR 50 PPM

CHEMICAL

IN DISTILLED WATER

OPTIMUM LEVEL PPM

N-ETHYL PYRROLE

1.0

ADDS TO SWEET MEATINESS OF PEANUT AND ENHANCES OVERALL NUTTINESS.

ETHYL DECANOATE

.01

ADDS SWEET FATTY NOTE WHICH CONTRIBUTE TO OVERALL FULLNESS OF FLAVOR

2,4-DIMETHYL-3THIAZOLINE

.05

ADDS TO PEANUT ACTER ENHANCES SKIN NOTES AND TO THE ROASTED

1-OCTEN-3-OL

.01

ADDS EARTHY SWEET NUTTINESS. ALSO ADDS FULLNESS TO FLAVOR CHARACTER.

SHELL CHARROASTED NUT ADDS DEPTH NOTES.

DECANE

2.0

CONTRIBUTES A UNIQUE FATTINESS ALMOST A WAXY NOTE ROUNDING OFF FLAVOR AND ENRICHING THE FLAVOR BODY.

INDANE

0.1

ADDED SOME HARSH SOLVENTY NOTES CONTRIBUTING TO THE GREEN AREA AND CONTRIBUTED TO THE FULLNESS OF FLAVOR.

- T h i s was found t o be the optimum l e v e l f o r t h i s i n d i s t i l l e d water.

flavor



176

QUALITY

OF

SELECTED

FRUITS

AND

VEGETABLES

More and more work i s being done i n c o r r e l a t i n g instrumental a n a l y s i s with sensory e v a l u a t i o n . McCarthy e t a l (38) and Heinz et a l (39) d i d e a r l i e r c o r r e l a t i o n s t u d i e s on f r u i t . More recent works were done by Dupuy e t a l (40) and Warner e t a l (41). They c o r r e l a t e d sensory score vs G.C. a n a l y s i s on vegetable o i l s obtaining excellent results. Powers (42) provided a general d e s c r i p t i o n o f a computer a s s i s t e d method f o r c o r r e l a t i n g v o l a t i l e s from foods with sensory impressions u s i n g the gas chromatograph and o r g a n o l e p t i c data. F i r s t , p r o f i l e curves a r e t r e a t e d t o y i e l d peak h e i g h t s , peak areas o r r a t i o s between peaks based on area o r height. A computer program then p i c k s out these v a r i a b l e s which a r e the most d i s c r i m i n a t i n g f a c t o r s between p r o f i l e samples. These f a c t o r s are then mathematically r e l a t e d back t o the o r g a n o l e p t i c scores o f the samples from which the p r o f i l e curves were prepared. Weighting f a c t o r s f o r each peak v a r i a b l e are then c a l c u l a t e d . When t h e d i s c r i m i n a t i n g peak v a r i a b l e s and weightings a r e known, a d i s criminant equation can be used t o p r e d i c t the o r g a n o l e p t i c scores of samples which are r e l a t e d t o , but not n e c e s s a r i l y p a r t o f the i n i t i a l sample s e t examined. The l a r g e r the i n i t i a l s e t o f samp l e s from which p r o f i l e s a r e a v a i l a b l e , the c l o s e r the c o r r e l a t i o n between p r e d i c t e d o r g a n o l e p t i c scores and peak v a r i a b l e s becomes. This c o r r e l a t i o n i s s t r i c t l y mathematical and has no r e l a t i o n t o f l a v o r compounds a f f e c t i n g o r g a n o l e p t i c scores. T h i s technique has been modified by other authors. Biggers et a l (43) on c o f f e e , M i l u t i n o v i c e t a l (31) on peanuts and tomato products, Powers e t a l (44) on peanuts and Dravnieks e t a l (45) on corn. Blumenthal e t a l (46) c o r r e l a t e d G.C. chromatograms w i t h o r g a n o l e p t i c scores on v a r i o u s f a t s and o i l s a f t e r simulated deep f a t f r y i n g . A computerized s t a t i s t i c a l approach showed e x c e l l e n t c o r r e l a t i o n between G.C. peaks and o r g a n o l e p t i c scores. C o r r e l a t i o n o f Instrumental

and Sensory Data

Buckholz e t a l (36) s e l e c t e d t h i r t y - t w o peaks from the GC p r o f i l e s t o be q u a n t i t a t e d and c o r r e l a t e d t o o r g a n o l e p t i c f l a v o r scores. The chosen peaks were determined t o be important t o peanut f l a v o r and common t o a l l p r o f i l e s f o r both types o f peanuts and a l l three r o a s t i n g c o n d i t i o n s . T h e i r averaged i n d i v i d u a l areas were entered onto punch cards along with o r g a n o l e p t i c panel scores f o r the four f l a v o r a t t r i b u t e s f o r a l l peanut r o a s t samples. Stepwise m u l t i p l e r e g r e s s i o n was then used t o c o r r e l a t e instrumental q u a n t i t a t i o n t o f l a v o r score. Figures 4 and 5 show i n d i v i d u a l peaks c o r r e l a t e d t o f l a v o r score. Peak 11 was i d e n t i f i e d as pentanal. This was a t y p i c a l carbonyl which had been i d e n t i f i e d i n peanuts. O r g a n o l e p t i c a l l y t h i s compound represented harsh, green solventy notes. The negat i v e c o r r e l a t i o n -0.9770 ( C o e f f i c i e n t o f Determination) showed



4.8

Θ 'R-D

5.4

0

β.Ο

* DARK

M » MEDIUM

6.6

SPANISH

» LIGHT

S *

L

RUNNER

R»

1

— ι — 7.8

Figure 4.

7.2

R-M

Θ

— ι — 9.6

10.2

Ο

H

10.8

M.4

S 'M

WEIGHT, grams χ I0

— ι — 9.0

Θ

12.0

-0.90770

NO II

Correlation of peak 11 (pentanal) to flavor score

8.4

^

r=

PEAK



L

1

Νδ 2 4

θ!τ 0*8

Γ!Ο

TU

K2

1Τ3 6

WEIGHT, grams χ ΙΟ"

θ!θ

,S'M

sΌ

TÎ4

*

'LIGHT

ΓΤβ

D

ΐΤβ

'DARK

M * MEDIUM

Ζ.

SPANISH

R m RUNNER 5 *

Figure 5. Correlation of peak 24 (2-ethyl-6-methyl pyrazine) toflavorscore

θΪβ

R "M"

r= +0.98129

PEAK


14.

BUCKHOLZ A N D D A U N


179

t h a t sensory preference i n c r e a s e d as c o n c e n t r a t i o n decreased. Peak 24 was i d e n t i f i e d as 2-ethyl-6-methyl p y r a z i n e . T h i s was a t y p i c a l pyrazine which had been i d e n t i f i e d i n peanuts. O r g a n o l e p t i c a l l y t h i s compound represented roasted, nutty, earthy notes. The p o s i t i v e c o r r e l a t i o n of +0.98129 (CD.) showed that sensory preference i n c r e a s e d with c o n c e n t r a t i o n . These p l o t s i n d i c a t e d t h a t a decrease i n carbonyls with a subsequent increase i n pyrazines were important to good q u a l i t y peanut f l a vor. T h i s supported the work of Mason et a l (15, 16) and Johnson (25, 26).


Conclusions The aroma of f r e s h roasted peanuts i s i n f l u e n c e d by the r o a s t i n g time and i s a r e f l e c t i o n of the changes i n the r a t i o s of carbonyl d e r i v a t i v e s t o p y r a z i n e s . A knowledge of the mechanism of formation o f these v o l a t i l e s i s t h e r e f o r e not only d e s i r a b l e , but necessary t o optimize q u a l i t y and o v e r a l l f l a v o r acceptance; or where d u p l i c a t i o n and/or m o d i f i c a t i o n of the p a r t i c u l a r f l a v o r i s d e s i r e d . By changing r o a s t i n g time customized f l a v o r s can be c r e a t e d to provide the d e s i r e d type of peanut q u a l i t y . Peanuts roasted f o r v a r i o u s lengths of time can be successf u l l y r a t e d by hedonic s c a l i n g i f the e v a l u a t i o n i s separated i n t o four sensory a t t r i b u t e s ; namely s t r e n g t h and d e s i r a b i l i t y of aroma and f l a v o r . P a n e l i s t s d i d r e a d i l y agree on the i n t e n s i t y of aroma and f l a v o r but not d e s i r a b i l i t y . C o r r e l a t i o n of i n s t r u m e n t a l and sensory data showed t h a t a decrease i n carbonyls w i t h a subsequent increase i n p y r a z i n e s i s important f o r good q u a l i t y peanut f l a v o r . I t was demonstrated t h a t the newly i d e n t i f i e d compounds a l l had a s i g n i f i c a n t i n f l u e n c e on the aroma and f l a v o r o f f r e s h roasted peanuts. E v a l u a t i o n i n an e x i s t i n g f l a v o r showed t h a t a l l the compounds with the exception of indane produced a marked i n c r e a s e i n the q u a l i t y o f the peanut f l a v o r .

Abstract The roasting process subjects peanuts to internal temperatures of 130°-150°C during which the typical roast peanut flavor is produced. The most important constituents of peanuts responsible for flavor formation are the amino acids, sugars, protein and l i p i d s . There are close to 300 flavor compounds i d e n t i f i e d in roasted peanuts. Pyrazines contribute roasted nutty aroma and aldehydes are responsible for harsh green aroma. Recent development in the research include application of an absorption polymer Tenax GC to c o l l e c t v o l a t i l e s , quantitation of flavor components and computer aided correlation of instrumental and sensory data.


180

QUALITY OF SELECTED FRUITS AND VEGETABLES

Literature Cited


1.

Pickett, T. A.; Holley, Κ. T. 1952, Ga. Agr. Exp. Sta. Tech. Bull. 1. 2. Walradt, J. P.; Pittet, A. O.; Kinlin, T.E.; Muraldihara, R.; Sanderson, A. J. Agr. Food Chem. 1971, 19, 972. 3. Wu, C. The Isolation and Fractionation of Volatile Flavor Constituents of Roasted Peanuts, Ph.D. Thesis, Rutgers University, New Brunswick, New Jersey. 4. van Straten, S.; de V r i j e r , F., (Eds.), "Lists of Volatile Compounds i n Food", 3rd Edition, Central Institute for Nutrition and Food Research, Zeist, Netherlands, 1973. 5. Mason, M. E.; Newell, J.Α.; Johnson, B.R.; Koehler, P.E.; Waller, G. R. J . Agr. Food Chem. 1969,17,728. 6. Young, C. T.; Mason, M. E. J . Food Sci. 1972, 37, 722. 7. Koehler, P. E.; Mason, M. E.; Newell, J. A. J . Agr. Food Chem. 1969,17,393. 8. Koehler, P. E.; Odell, M. E. J. Agr. Food Chem. 1970, 18, 895. 9. Newell, J . Α.; Mason, M. E.; Matlock, R.S. J. Agr. Food Chem. 1967, 15, 767. 10. Wange, P. S.; Kato, H.; Fujimaki, M. Agr. Biol. Chem. (Japan) 1969,33,1775. 11. Forss, D. A. Progr. Chem. Fats Other Lipids 1972, 13, 177. 12. Dismick, P. S. "The Formation and Characteristics of Flavor Components Derived from Food Lipids", 29th P.M.C.A. Production Conference, 1975; p 25-31. 13. Erikkson, C. J . Agr. Food Chem. 1975,23,126. 14. Schonberg, Α.; Moubacker, R.; Mostofa, A. J . Chem. Soc. 1948, 176. 15. Mason, M. E.; Johnson, B. R.; Hamming, M. C. J . Agr. Food Chem. 1967, 15, 66. 16. Mason, M. E.; Johnson, B. R.; Hamming, M. C. J . Agr. Food Chem. 1966, 14, 454. 17. Mookherjee, B. D.; Deck, R. E.; Chang, S. S. J. Agr. Food Chem. 1965, 13, 131. 18. Herz, Κ. O.; Chang, S. S. J . Food Sci. 1967, 31, 937. 19. Withycombe, D. Α.; Mookherjee, B. D.; Hruza, A. "Analysis of Foods and Beverages Headspace Techniques", Academic Press, New York, 1978; p 81. 20. Brown, D. F.; Dollear, F. G.; Dupuy, H. P.; J . Am. O i l Chem. Soc. 1972, 49(1), 81. 21. Buckholz, L. L., Jr.; Withycombe, D. Α.; Daun, H. J. Agr. Food Chem. 1980A, 28, 760. 22. Bondarovich, Η. Α.; Friedel, P.; Krompl, V.; Renner, J . A.; Shepherd, F. W.; Gianturco, M. A. J. Agr. Food Chem. 1967, 15(6), 1093. 23. van Praag, M.; Stein, H. S., and Tibbetts, M.S. J . Agr. Food Chem. 1968, 16, 1005.


14. BUCKHOLZ AND DAUN Roasted Peanut Flavor Volatiles 181

24. 25. 26. 27. 28.


29. 30. 31. 32. 33. 34. 35. 36. 37.

38. 39. 40. 41.

42. 43. 44. 45. 46.

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RECEIVED April 7, 1981.


Instrumental and Sensory Characteristics of Roasted Peanut Flavor

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