flavor and aroma biology - ucanr.edu

1

Flavor and Aroma Biology

Florence Zakharov Department of Plant Sciences

David ObenlandUSDA/ARS

Outline

Introduction to our sensory system and the perception of flavor

Relationships between fruit composition and flavor perception

Fruit biology and development of flavor components (influence of genetic and environmental factors)

Perception of Quality

• Our sensory systems are responsible for generating an internal representation of the outside world, including its chemical (taste and olfaction) and physical(mechanical, sound, vision and temperature) features.

• When evaluating the quality of the foods we eat, we use the complete array of our sensory system (chemical and physical senses) and integrate this information to formulate a judgment.

• From an evolution standpoint, chemical senses are the most primal of the senses.

Varies depending on protagonist in PH chain

Consumer-centric “quality” ultimately drives marketability and sales

Overall consumer acceptance (and repeat buy) strongly correlated with “Flavor acceptance”

Perception of Quality

Sensory Attributes of Foods

Appearance

Taste

Odor/smell/aroma

Irritation/pain

Texture/mouthfeel

Temperature

• Our sense of taste is in charge of evaluating the nutritious content of food and preventing the ingestion of toxic substances.

• Taste is a sensation perceived in the mouth, more specifically on the tongue. We have innate likes and dislikes for it.

• Sweet

• Salty

• Bitter

• Sour (acidic)

• Umami (protein – savory)

5 TASTE MODALITIES

Taste

Obenland-Zakharov "Flavor & Aroma Biology" Postharvest Technology of Horticultural Crops Short Course 2015 (c) Postharvest Technology Center, UC Davis

2

Quality Class of compound Examples

Sweet Sugars Sucrose, fructose, glucose

Some proteins Monellin, thaumatin

Sour Acids Citric acid, malic acid, tartaric acid

Bitter Alkaloids, Phenolics, Terpenoids, some proteins

Naringin, cucurbitacins, limonoids

Salty Ions Sodium, calcium

Umami Amino acids Glutamate, aspartate

Fruit Composition and Taste

Astringency (tannins, calcium oxalate)

Sense of touch (mechanoreceptors)

Texture and Mouthfeel

Aroma (or smell or odor) is the sensation perceived when volatile compounds are drawn into the nose.

We have learned likes and dislikes for it.

Aroma Taste and Aroma

• Taste and aroma are very closely linked.

• If you want to onlyTASTE something, you need to pinch your nose to avoid perceiving the volatiles in foods or drinks.

What is a volatile compound?

• A small molecule which has a high tendency to evaporate.

• Volatiles are naturally produced by plants(flowers, fruits, vegetables, herbs…) and animals. They can also be made artificially (by chemical reactions designed for their production).

linalool

OH

OH

nerolidol

linalool

OHCH2

OH

phenylethanolCH2

O H

phenylacetaldehyde

OH

O OCH3

methylsalicylate

linalool

OH

CH2

OH

phenylethanol

linalool

OH

OH

geraniol

linalool

OH

CH2

O H

phenylacetaldehyde

O H

benzaldehyde OHOCH3

eugenol

limonene

limonene

linalool

OH

CH2

OH

phenylethanol

neral

O

geranial

O


3

What does a volatile compound smell like?

• Each single volatile compound has a distinct smell.

Floral, woody, sweet, fruity, berry, green

Sulfurous, vegetable,

cabbage, onion

-ionone Dimethyl disulfide Myrcene

Peppery, spicy

O H3C

CH3

S

S

“Character-impact” volatilesVanillin 2-isobutyl

3-methoxypyrazineO

OH

HO

OCH3

N

H3CH3C

N

Complexity of Fruit Aromas

• A natural aroma, smell or odor is typically made up of tens or sometimes hundreds of different volatile compounds.

• A mixture of volatile compounds is not perceived as “the sum of its parts”: volatiles interact to create a unique, distinct, aroma.

Over 200 volatile compounds !!

The aroma of a strawberry…

GC olfactometry is used to help determine which volatiles contribute to flavor

Tomato GC Olfactometry chromatogram

0 2 4 6 8 10 12 14 16 18 20

hexa

nal

cis-

3-he

xena

l

tran

s-2-

hexe

nal

met

hion

al

1-oc

ten-

3-on

e

6-m

ethy

l-5-

hept

en-3

-one

2-is

obut

ylth

iazo

leph

enyl

acet

alde

hyde

fura

neol

lina

lool

met

hyls

alic

ylat

e

citr

al

E,E

-2,4

-dec

adie

nal

gera

nyla

ceto

ne

beta

-ion

one

Elizabeth Baldwin, USDA/ARS


4

• We have different sensitivity levels for different volatiles.

• Some volatiles, like furaneol, can be detected by our olfactory system at extremely low levels; while others, like acetic acid (vinegar!), we can detect only at higher levels.

• Even though acetic acid is much more abundant than furaneol in strawberries, it is furaneol that is more important for determining the characteristic aroma of the strawberry (because of its low odor threshold value).

Odor Thresholds What the nose knows…

O

OHO

O

OH

OT ≈ 10 ppb

OT ≈ 60 ppm

Studying Fruit Flavor

How do plants produce these flavor compounds?

How do internal and external factors influence the production of these compounds?

What kinds of flavor compounds are present in fruits?

Develop varieties with novel flavor properties based on knowledge of genetic determinants of volatile formation

Control fruit flavor quality throughout production and postharvest handling

Define commodity- and variety-specific compositional characteristics that can be related to sensory attributes

CO2

Calvin Cycle Sugars Sugars

Glycolysis

More carb.

AcidsProteins

Pigments

Volatiles

Flavor Development: Diversity and Complexity

A B C D E

K L

M

J

N O P

Q

R

G H I

F

Climactic factors Temperature, light, atmospheric gases…

Genetic factors Pathways, hormones, regulatory mechanisms…

Agricultural factors Soil type, irrigation, fertilization…

Taste Development Sugars

• Starch accumulation is an important factor for determining the final sugar content of many fruits.

• In tomato, cultivars that accumulate higher levels of starch in young fruits eventually contain more soluble sugars at the ripe stage.

Sugars from leaves (photosynthesis)

Starchin the fruit

Starchin the fruit

Soluble Sugars(sweet)

Soluble Sugars (sweeter)

How are aroma volatiles made in plants?

• There are more than 2,000 volatiles known to date in plants. About 900 different volatiles have been reported in fruits andvegetables.

• Research has identified genes involved in the synthesis of less than 10% of all volatiles known.

Aroma Development Volatiles


5

Alcohol Acyl Transferase: a gene involved in fruit aroma

formation

+ +

Alcohol Acyl-CoA Volatile Ester (Aroma)

CoA

SAAT

VAAT

CM-AATs

BanAAT

AAT

Octyl Acetate Hexyl Acetate

R1 OH

R2

O SCoA

R2

OOR1

HS CoA

H3C H3CO

O

H3C H3CO

O

How is aroma (volatile) production controlled in fruits/vegetables?

• In climacteric fruits, ethylene plays an important role in triggering aroma formation during fruit ripening.

Aroma Development Volatiles

Regulation of Aroma Formation

Ayub et al., 1996 El-Sharkawy et al., 2005

Regulation of Aroma Formation

Ethylene

Aroma-forming gene

Normal Transgenic

Aroma Biology

What are the impacts of cultivation practices and postharvest storage on aroma formation?

• Pre-harvest factors

Supply of carbon (sugars) to the fruit, water stress, light, temperature, plant diseases…

• Postharvest factors

Temperature

• Cold slows down metabolism (less volatiles made).

• Cold slows down evaporation of volatiles from fruit surface.

Ethylene

• In climacteric fruits, aroma cannot form without ethylene.

Modified or controlled atmosphere

• MA or CA alters plant metabolism – risk of anaerobic metabolism which can cause off-odors.

Aroma Biology


6

An example of the impact of temperature on flavor…mandarins

0

1

2

3

4

5

6

7

8

0 1 2 3 4 5 6Weeks after packing

He

do

nic

sc

ore

41F 0 weeks 2 weeks 4 weeks

Some taste panel comments on warm temp fruit

Spoiled, rancid

Really old

Off-flavor

Strange aftertaste

Not fresh

Over ripe

Warm temperaturemain cause offlavor loss

Time in cold storageinfluences response68°F

Modified atmospheres can form within fruit as a result of coating application

Waxed Unwaxed

Effect of modified atmosphere as a result of surfacecoating on mandarin ethanol concentration

ethanol ethyl estersHarvest Coating + 68°F 1 week

Is there hope?...

Quality-oriented practices

• Understand the physiology of commodity, select cultivars with optimum flavor quality.

• Harvest at maximum flavor potential (riper) to attain (and retain) maximum flavor quality.

More Research needed…

• Improving techniques to slow down metabolism when fruits already start to ripen.

• Developing rapid, non-destructive methods for objective flavor quality determination (beyond “Brix”…)


flavor and aroma biology - ucanr.edu

Documents