Strawberry Flavor: Diverse Chemical Compositions, a Seasonal Influence, and Effects on Sensory Perception
and Effects on Sensory Perception. PLoS ONE 9(2): e88446. doi:10.1371/journal.pone.0088446
Strawberry Flavor: Diverse Chemical Compositions, a Seasonal Influence, and Effects on Sensory Perception
Michael L. Schwieterman 0
Thomas A. Colquhoun 0
Elizabeth A. Jaworski 0
Linda M. Bartoshuk 0
Jessica L. Gilbert 0
Denise M. Tieman 0
Asli Z. Odabasi 0
Howard R. Moskowitz 0
Kevin M. Folta 0
Harry J. Klee 0
Charles A. Sims 0
Vance M. Whitaker 0
David G. Clark 0
Miyako Kusano, RIKEN PSC Japan
0 1 Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, Florida, United States of America, 2 Department of Environmental Horticulture, University of Florida, Gainesville, Florida, United States of America, 3 College of Dentistry, University of Florida, Gainesville, Florida, United States of America, 4 Horticultural Sciences Department, University of Florida, Gainesville, Florida, United States of America, 5 Food Science and Human Nutrition Department, University of Florida, Gainesville, Florida, United States of America, 6 Moskowitz Jacobs Inc., White Plains, New York, United States of America, 7 Gulf Coast Research and Education Center, University of Florida, Wimauma, Florida, United States of America, 8 Plant Innovation Program, University of Florida , Gainesville, Florida , United States of America
Fresh strawberries (Fragaria x ananassa) are valued for their characteristic red color, juicy texture, distinct aroma, and sweet fruity flavor. In this study, genetic and environmentally induced variation is exploited to capture biochemically diverse strawberry fruit for metabolite profiling and consumer rating. Analyses identify fruit attributes influencing hedonics and sensory perception of strawberry fruit using a psychophysics approach. Sweetness intensity, flavor intensity, and texture liking are dependent on sugar concentrations, specific volatile compounds, and fruit firmness, respectively. Overall liking is most greatly influenced by sweetness and strawberry flavor intensity, which are undermined by environmental pressures that reduce sucrose and total volatile content. The volatile profiles among commercial strawberry varieties are complex and distinct, but a list of perceptually impactful compounds from the larger mixture is better defined. Particular esters, terpenes, and furans have the most significant fits to strawberry flavor intensity. In total, thirty-one volatile compounds are found to be significantly correlated to strawberry flavor intensity, only one of them negatively. Further analysis identifies individual volatile compounds that have an enhancing effect on perceived sweetness intensity of fruit independent of sugar content. These findings allow for consumer influence in the breeding of more desirable fruits and vegetables. Also, this approach garners insights into fruit metabolomics, flavor chemistry, and a paradigm for enhancing liking of natural or processed products.
Funding: This work is supported by grants from USDA Specialty Crop Block Grant. Graduate funding is provided by USDA National Needs Fellowship. The
funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: Howard Moskowitz is co-founder of Moskowitz Jacobs Inc, which is an academic collaborator in this research. Moskowitz is also a
courtesy faculty member at the University of Florida in the Food Science and Human Nutrition Department. Portions of the results are protected by US Patent
20130280400 and International Patent WO 2013/163272 A1 Compositions and Methods for Modifying Perception of Sweet Taste. This does not alter the authors
adherence to all the PLOS ONE policies on sharing data and materials.
Modern fully ripe strawberry (Fragaria x ananassa) fruit is
characterized by its large size , vibrant red color , reduced
firmness , distinct aroma , and sweet fruity flavor . The
flesh of the strawberry is a swollen receptacle, a false fruit, and the
seeds or achenes are the true fruit , which will be collectively
referred to as strawberry fruit. The three stages of non-climacteric,
auxin dependent strawberry fruit development; division,
expansion and ripening, involve gains in diameter and fresh weight;
during which color shifts from green to white to dark red in
roughly forty days following anthesis . Ripening of strawberry
fruit results in the accumulation of multiple sugars and organic
acids, culminating with peak volatile emission .
Flavor is the perceptual and hedonic response to the synthesis of
sensory signals of taste, odor, and tactile sensation . In the case
of strawberry and other fruits, sensory elicitation is the result of
multiple direct interactions between plant and human: sugars and
acids, pigments, turgor and structure, and volatile compounds,
which elicit the senses of taste, vision, tactile sensation, and
olfaction, respectively, in the development of flavor . A
consumer based survey indicated sweetness and complex flavor as
consistent favorable attributes of the ideal strawberry experience
. Much emphasis is placed on sugars, acids, and volatile
compounds as these metabolites are primary sensory elicitors of
taste and olfaction which attenuate the perception and hedonics of
sweetness and flavor. Thus a ripe strawberry is metabolically
poised to elicit the greatest sensory and hedonic responses from
During strawberry fruit development sucrose is continually
imported from photosynthetic tissue. A consistently high sucrose
invertase activity contributes to carbon sink strength in all
developmental stages of fruit . Delivered sucrose is hydrolyzed
into glucose and fructose, and these three carbohydrates constitute
the major soluble sugars of ripe strawberries, a result of their
continual accumulation during fruit development . In fact, an
approximately 150% increase in their sum during ripening has
been observed [8,15]. The influx of carbon initiates a complex
network of primary and secondary metabolism specific to ripening
strawberry fruit . For example, the metabolic activity of
ripening strawberry is visualized by the late accumulation of the
predominant red pigment, pelargonidin 3-glucoside , an
anthocyanin derived from the primary metabolite phenylalanine
The dynamics of fruit development are genetically driven.
Microarray analysis determined nearly 15% of probed expressed
genes exhibit significant differential expression (60% up, 40%
down) in red compared to green fruit . One up regulated gene,
Polygalacturonase 1 (FaPG1), contributes to fruit softening  by
aiding in catalytic cell wall disassembly . Reduction of firmness
is also attributed to dissolution of middle lamella, a pectin rich cell
wall layer that functions in cell-to-cell adhesion . Active shifts in
transcription throughout ripening result in metabolic network
reconfiguration altering the chemical and physical properties.
Metabolic profiling indicates an accumulation of sugars, organic
acids, and fatty acids as well as the consumption of amino acids
during fruit development. Subsequently alkanes, alcohols,
aldehydes, anthocyanins, ketones, esters, and furanones increase
during fruit ripening . Many of these chemical classes serve as
precursors to volatile synthesis , thus facilitating a metabolic
flux through biosynthetic pathways for increased and diverse
volatile emissions in ripe strawberry fruit, predominantly furans,
acids, esters, lactones, and terpenes . Over 350 volatile
compounds have been identified across Fragaria , however
within a single fruit, far fewer compounds are detectable and even
less contribute to aroma perception.
A cross comparison of five previous studies which analyze
strawberry volatiles depicts the lack of agreement in defining
chemical constituents of strawberry aroma. Each source considers
a highly variable subset of volatiles, which are determined by
signal intensity and/or human perception of separated compounds
[4,5,2325]. Mutual volatiles across studies include butanoic acid,
methyl ester; butanoic acid, ethyl ester; hexanoic acid, methyl
ester; hexanoic acid, ethyl ester; 1,6-octadien-3-ol,
3,7-dimethyl(linalool); butanoic acid, 2-methyl-; and 3(2H)-furanone,
4methoxy-2,5-dimethyl-, the current consensus of integral
strawberry aroma compounds. Comparisons of consumer preference
among a variety of fresh strawberries and their volatile profiles
describes less preferable varieties as possessing less esters, more
decalactones and hexanoic acid . The breadth of volatile
phenotypes previously reported highlights the diversity across
strawberry genotypes and underscores the complexity of the
aggregate traits of aroma and flavor.
Florida strawberry production is concentrated on ten thousand
acres near the Tampa Bay. Mild winters allow for annual
horticulture which requires continual harvest of ripe fruit from late
November through March. Environmental effects on fruit quality
are partially attributed to gradually increasing temperatures
beginning in mid-January. One result is a late season decline of
soluble solids content (SSC) [26,27]. In fact, increasing
temperature is known to be responsible for increasing fruit maturation
rate and decreasing SSC independent of flowering date .
Previous work also identifies variability of SSC, as well as titratable
acidity (TA) and multiple classes of volatile compounds across
harvest dates . The complex fruit biochemistry, which is
variably affected by genetic, environmental, and developmental
factors, coupled with individuals perceptional biases has made
defining strawberry flavor cumbersome.
Here we exploit the genetic and within-season variability of fruit
to provide as many unique strawberry experiences as possible to a
large sample of consumers. To enhance the range and diversity of
flavors and chemical constituents 35 genetic backgrounds were
included: public and private cultivars representing a large
proportion of commercial strawberry acreage in North America,
University of Florida advanced breeding selections, and European
cultivars (Fig. 1). Parallel assays of ripe strawberry samples
quantify fruit traits of TA, pH, and fruit firmness, as well as the
content of malic acid, citric acid, glucose, fructose, sucrose, and 81
volatile compounds of diverse chemical classes. The contributions
of these attributes to fruit quality is determined by simultaneously
evaluating samples for perceived sensory intensities of sourness,
sweetness, and strawberry flavor, as well as the hedonic responses
of texture liking and overall liking by consumer panelists. Data
analyses determine significant biochemical and consumer response
differences between early and late season fruit, gross variation of
strawberry experiences, and factors influencing hedonics and
sensory perception of strawberry fruit consumption using a
psychophysics approach. Ultimately, an effect of particular volatile
constituents to enhance sweetness intensity independent of sugar
content of fruit was found. These findings have great implications
in the breeding of more desirable fruits and vegetables, as well as
for the food industry as a whole.
All human consumer panels are conducted at the Food Science
and Human Nutrition Department at the University of Florida in
Gainesville, FL. The University of Florida Institutional Review
Board 2 (IRB2) chaired by Ira S. Fischler approved the protocol
and written consent form (case 2003-U-0491), which participants
are required to complete.
Thirty-five strawberry cultivars and selections were grown at or
in the near vicinity of the Gulf Coast Research and Education
Center (14625 County Road 672, Wimauma, FL) during the
20102011 (season 1) and 20112012 (season 2) winter seasons.
Fruit are cultivated according to current commercial practices for
annual strawberry plasticulture in Florida [1,29](Fig. 1A). The
cultivars are chosen to represent a large proportion of commercial
strawberry acreage in North America from both public and
private breeding programs. Additional breeding selections and
European cultivars are added to enhance the range of diversity for
flavors and chemical constituents. Weekly cultivar representation
is determined by fruit availability during a particular harvest week
and attempting to maximize genetic diversity, except for the highly
replicated cultivar Festival. Fully-ripe fruit by commercial
standards, 90100% red compared to white  (Fig. 1B-C), is
harvested from three to five cultivars on Monday mornings,
delivered to the respective laboratories, and stored at 4uC in the
dark overnight for simultaneous analysis of fresh strawberry fruit
volatiles, firmness, and sensory analysis on Tuesdays; as well as
sample preparation for later sugar and acid measurements. Six
harvests in both seasons allows for the complete analysis of 54
samples. Weather data is obtained from the Balm, FL station of
the Florida Automated Weather Network (http://fawn.ifas.ufl.
edu/data/reports) for date ranges January 3, 2011 through
February 28, 2011 and December 26, 2011 through March 13,
2012. Daily maximum and minimum temperature recording
height is 60 cm, and daily average relative humidity, rainfall, and
solar radiation are recorded at 2 m.
At least 100 g or seven berries of each sample are removed from
4uC dark overnight storage prior to volatile collection. Samples are
homogenized in a blender prior to splitting into three 15 g
replicates for immediate capturing of volatile emissions. The
remainder is frozen in N2 (l) and stored at 80uC for later sugar
and acid quantification. A two hour collection in a dynamic
headspace volatile collection system  allows for concentration
of emitted volatiles on HaySep 80100 porous polymer adsorbent
(Hayes Separations Inc., Bandera, TX, USA). Elution from
polymer is described by Schmelz .
Quantification of volatiles in an elution is performed on an
Agilent 7890A Series gas chromatograph (GC) (carrier gas; He at
3.99 ml min21; splitless injector, temperature 220uC, injection
volume 2 ml) equipped with a DB-5 column
((5%-Phenyl)methylpolysiloxane, 30 m length 6250 mm i.d. 6 1 mm film
thickness; Agilent Technologies, Santa Clara, CA, USA). Oven
temperature is programmed from 40uC (0.5 min hold) at 5uC
min21 to 250uC (4 min hold). Signals are captured with a flame
ionization detector (FID) at 280uC. Peaks from FID signal are
integrated manually with Chemstation B.04.01 software (Agilent
Technologies, Santa Clara, CA). Volatile emissions (ng1 gFW21
h21) are calculated based on individual peak area relative to
sample elution standard peak area. GC-mass spectrometry (MS)
analysis of elutions are performed on an Agilent 6890N GC in
tandem with an Agilent 5975 MS (Agilent Technologies, Santa
Clara, CA, USA) and retention times are compared with authentic
standards (Sigma Aldrich, St Louis, MO, USA) for volatile
identification . Chemical Abstract Services (CAS) registry
numbers were used to query SciFinderH substances database for
associated chemical name and molecular formula presented in
Sugars and Acids Quantification
Titratable acidity, pH, and soluble solids content  are
averaged from four replicates of the supernatant of centrifuged
thawed homogenates . An appropriate dilution of the
supernatant from a separate homogenate (centrifugation of 1.5 ml at
16,000 x g for 20 min) is analyzed using biochemical kits (per
manufacturers instructions) for quantification of citric acid,
Lmalic acid, D-glucose, D-fructose, and sucrose (CAT#
10-139076-035, CAT# 10-139-068-035, and CAT# 10-716-260-035;
R-Biopharm, Darmstadt, Germany) with absorbance measured at
365 nm on an Epoch Microplate Spectrophotometer (BioTek,
Winooksi, VT, USA). Metabolite average concentration (mg1 100
gFW21) is determined from two to six technical replicates per
pooled sample. Derived sucrose concentrations via D-glucose and
D-fructose are mathematically pooled.
Firmness of the strawberries is determined as the resistance of
the fruit to penetration at its equator with a TA.XTPlus Texture
Analyzer (Texture Technologies Corp., Scarsdale, NY, USA;
Stable Micro Systems, Godalming, Surrey, UK). The Texture
Analyzer is equipped with a 50 kg load cell and an 8 mm diameter
convex tip probe. Whole fruit is penetrated on the side to 7 mm
down from the epidermis at a test speed of 2 mm1 sec21; a flap cut
off the opposite provides stability. Maximum force in kg for eight
fruit is averaged and reported as a measure of firmness.
Over the course of two annual seasons, 166 recruited strawberry
consumers (58 male, 108 female) evaluate strawberry cultivars.
Ages of panelist ranged from 18 to 71, with a median age of 24.
Panelists self-classified themselves as 98 White or Caucasian, 11
Black or African-American, 1 Native American, Alaska Native or
Aleutian, 41 Asian/Pacific Islander, and 15 Other. An average of
106 (range of 98113) panelists evaluated between three and five
cultivars per session . Fresh, fully-ripe strawberry fruit is
removed from overnight 4uC dark storage and allowed to warm to
room temperature prior to sensory analysis. Each panelist is given
one to two whole strawberries for evaluation, depending on
cultivar availability. Panelists bite each sample, chew, and swallow
it. Ratings for overall liking and texture liking are scaled on
hedonic general labeled magnitude scale (gLMS) from 100 to +
100, i.e. least to most pleasurable experience . Perceived
intensity of sweetness, sourness, and strawberry flavor are scaled in
context of all sensory experiences using sensory gLMS that ranges
from 0 to +100, i.e. none to most intense sensory stimulus .
Scales are employed to mediate valid comparisons across subjects
Means and standard errors for consumer, physical, and
metabolite measurements are determined from all replicates using
JMP (Version 8, SAS Institute Inc., Cary, NC, USA). One-way
analysis of early and late season fruit quality and consumer
response measures was subjected to mean comparison using
Tukeys HSD (a = 0.05). Bivariate analysis among individual
measurements of samples allows for linear fit, which includes
summary of fit, analysis of variance, t-test, and correlation analysis
for density ellipse. Two-way Ward hierarchical cluster analysis of
all quantified metabolite and strawberry samples is accomplished
in JMP. Amounts of individual volatile compounds are regressed
using the enter method in SPSS (IBM Corp., Armonk, NY,
USA). This is done individually for each of the three sugars:
glucose, fructose or sucrose to identify which compounds have an
effect on sweetness intensity  independent of each of the
sugars. For p-values # 0.05, the volatile makes a contribution to
perceived sweetness that is independent of the sugar tested.
The inventory of 54 fully ripe (Fig. 1C) unique strawberry
samples (35 cultivars, 12 harvests, two seasons) assayed for TA,
pH, firmness, as well as the concentrations of malic acid, citric
acid, glucose, fructose, sucrose, and quantity of 81 volatile
compounds is reported (Table S2). Cluster analysis of relative
chemical composition of all samples and derived hierarchy of both
cultivar and metabolite relatedness is displayed (Fig. 2). The
vertical dendrogram (Fig. 2) demonstrates the lack of relatedness
among volatile compound quantities through large distances of
initial segments, as well as the high number of clusters. Slightly
more structure is observed among the samples, horizontal
dendrogram (Fig. 2), due to genetic or environmental effects.
Progression of Harvest Season Affects Perceived Quality
and Metabolite Content of Strawberry
Overall liking is a measure of pleasure derived from consuming
a strawberry sample. The two samples with the greatest overall
liking ratings are of cultivar Festival. Fruit harvested early in the
season, week 2 of season 1 and week 1 of season 2, elicit overall
likings of 36.1 and 36.6, respectively (Table 1). Five weeks
following both early samplings of Festival the overall liking of the
same cultivar decreases below the sample set median of 23.5
(Table S2) to 17.3 in season 1 week 7 and to 23.1 in season 2 week
6 (Table 1). Therefore the earlier season samples elicit a greater
hedonic response than late season samples. Overall likings are
determined using the hedonic general labeled magnitude scale that
ranges from 100 to +100, i.e. least to most pleasurable experience
. Conversely, sweetness, sourness, and strawberry flavor
are measured using the sensory intensity general labeled
magnitude scale that ranges from 0 to +100, i.e. none to most intense
sensory stimulus . Consumer perception of sweetness and
strawberry flavor intensity decrease significantly between the same
pairs of early and late season Festival fruit (Table 1). Significant
biochemical differences between early and late samples include
decreased content of glucose, fructose, sucrose, and total volatiles.
The early Festival from the first season contains 88% more total
sugar and 65% more total volatiles than the late Festival of the
same season (Table 1), demonstrating the disparity between early
and late harvest week fruit quality and its effect on consumer
sensory perception and acceptability.
Solar radiation, minimum temperature and maximum
temperature increase gradually within the limits of similar ranges in
season 1 and season 2 (Fig. S1 A-D). Relative humidity remains
constant during and across seasons (Fig. S1 E, F). Slightly more
rain fell in early season 1 than season 2 (Fig. S1 G-H) One
manifestation of these environmental changes over a harvest
season is the negative relationship between total sugar and harvest
week (Table 1). The content of all individual sugars measured
decreases between early and late season Festival samples;
however there is a significant decrease in the proportion of
sucrose to total sugar (Table 1). The disproportionate decrease is
observed for the collection of samples as well (Fig. S2A-C) (Table
S3). Also, a significant correlation is observed across all 54 samples
among total volatiles and sucrose (R2 = 0.305*) (Fig. S2E) but not
glucose (R2 = 0.005) (data not shown) or fructose (R2 = 0.001) (Fig.
S2F). A harvest week associated decrease in total sugars,
predominantly sucrose, results in a decrease in volatile content,
which ultimately undermines late season overall liking
(R2 = 0.422*) (Fig. 3E) through sweetness and strawberry flavor
Overall Liking is Subject to Ratings of Sweetness, Flavor,
and Texture but not Sourness
In order to elucidate factors contributing to a positive
strawberry experience, overall liking of strawberry samples is fit
against the hedonic measure of texture liking and the sensory
intensities of sweetness, sourness, and strawberry flavor intensity
(Fig. 3A-D). High correlation with significant fit exists for texture
liking (R2 = 0.490*) (Fig. 3A), sweetness intensity (R2 = 0.742*)
(Fig. 3B), and strawberry flavor intensity (R2 = 0.604*) (Fig. 3D).
However, sourness intensity shows no correlation to overall liking
(R2 = 0.008) (Fig. 3C). Increasing firmness contributes to greater
texture liking (R2 = 0.358*) (Fig. 3I), and texture liking has a
significant influence on overall liking. Sweetness intensity is the
strongest driver of overall liking measured in this study. The
correlation between total sugar and overall liking (R2 = 0.488*)
(Fig. 3F) demonstrates the aggregate sugar metabolites effect on
hedonic response to strawberry fruit. Total sugar concentration
accounts for nearly half of the observed overall liking variation but
is far from a complete measure. Sourness intensity appears to have
no influence on the hedonic response to strawberry fruit, but fit of
TA to overall liking is significant, even if minor (R2 = 0.099*) (Fig.
3G). Total volatiles is the second aggregate metabolite measure
having a significant enhancing effect on the overall liking of
strawberry (R2 = 0.179*) (Fig. 3H). This is not surprising, as
strawberry flavor intensity exhibits the second highest correlation
to overall liking (Fig. 3D).
Texture Liking Correlates to Fruit Firmness
The upper limit for hedonics of texture is comparable to that of
overall liking and is observed in Festival (sn 1, wk 2) with an
average of 35.7, however, the low texture liking value of 5.8 for
Mara Des Bois (sn 1, wk 7) indicates a more drastic disliking of
off textures than the overall liking of even the lowest rating fruit
(Table S2). Firmness of samples is assayed by measuring the force
required for a set penetration of the fruit, acting as a proxy for
texture. The firmness of the fresh strawberry exhibited nearly a
five-fold difference in force, 0.2 kg for Mara des Bois (sn 1, wk 7)
and 1.0 kg for Festival (sn 1, wk 5) (Table S2). Increasing force of
penetration, i.e. increasing firmness of berries, is positively
correlated with texture liking, indicating a hedonic response to
firmer fruit (Fig. 3I). However, the texture liking is less than the
expected rating for the two samples with greatest firmness (Fig. 3I).
Sweetness Intensity is a Result of Sugar Content
Perceived sweetness intensity is the greatest predictor of overall
liking. In fact, the same samples scoring the highest and lowest for
overall liking, Festival (sn 2, wk 1) and Red Merlin (sn 1, wk 6),
elicit the greatest (36.2) and least (14.59) intense sensations of
sweetness (Table S2). The early and late harvest week samples
support the observable decline in perceived sweetness intensity
across harvest weeks, which is also observable for multiple sugar
measures (Fig. S2A-C) (Table 1).
In the 54 samples assayed, the total sugar concentration ranged
from 2.29 7.93%, a 3.5-fold difference (Table S2). Glucose and
fructose concentrations exhibit highly similar ranges to each other,
0.66 2.48% and 0.75 2.61%, respectively (Table S2), and
nearperfect correlation (R2 = 0.984*) (data not shown) within a sample.
However, the concentration of glucose or fructose is not predictive
of sucrose concentration (R2 = 0.011 and 0.004, respectively) (data
(mg1 100 gFW21) 1903
(mg1 100 gFW21) 2048
(mg1 100 gFW21) 1218
(mg1 100 gFW21) 5169
not shown). Sucrose demonstrated a more dynamic state as its
concentration dips as low as 0.16% and up to 2.84%, nearly a
seventeen-fold difference among all samples.
Sucrose is the single metabolite with the most significant
contribution to overall liking (R2 = 0.442*) (Table S4).
Individually, sucrose (R2 = 0.445*) (Fig. 3N), glucose (R2 = 0.337*) (Fig.
3O), and fructose (R2 = 0.300*) (Table S4) all significantly
influence the variation in sweetness intensity. However, total
sugar actually only accounts for slightly more than two-thirds of
sweetness intensity variation (R2 = 0.687*) (Fig. 3M) likely a result
of covariation of glucose and fructose. Interestingly, the total
volatile content of a sample correlates positively with sweetness
intensity, potentially accounting for up to 13.9%* of variation in
sweetness intensity (Fig. 3P).
Sourness Intensity is Partially Explained by Titratable
Cultivar Red Merlin (sn 1, wk 6) elicited the most intense
sourness response at 24.6 (Table S2). This same sample rates as the
lowest in terms of overall liking and sweetness. Acidity of
strawberry fruit is assayed using measures of pH, TA, citric acid
and malic acid. The pH of strawberry samples ranges from 3.35 to
4.12, while TA ranges from 0.44% to 1.05%. The range of malic
Comparison of means for temperature (mean of 7 days prior to harvest), consumer ratings, and biochemical measures between early and late season strawberry fruit
cultivar Festival from season 1 and season 2. Mean comparison accomplished in JMP 8 using Tukeys HSD. Mean marked A is significantly greater than mean marked B
(a = 0.05).
acid across samples is 0.078% to 0.338% while citric acid ranged
from 0.441% to 1.080% (Table S2). TA has the greatest
correlation to sourness intensity (R2 = 0.314*) (Fig. 3J), when
compared to pH (R2 = 0.118*), malic acid (R2 = 0.189*) (Fig. 3K),
or citric acid (R2 = 0.146*) (Fig. 3L) concentration. Citric acid
concentration is approximately three-fold greater than malic acid
and has a significant effect on TA (R2 = 0.49*) (data not shown).
There is no correlation of malic acid to TA (R2 = 0.01) (data not
shown). The lack of relationship among sourness intensity and
overall liking (Fig. 3C) is shadowed by the strong correlations of
sweetness intensity (Fig. 3B) and flavor intensity (Fig. 3D) to overall
liking. Deficiencies in perceived sweetness and flavor intensity as
observed in Red Merlin can result in a fruit that is negatively
perceived as intensely sour.
Flavor Intensity Is Influenced by Total and Specific
In this study, strawberry flavor intensity accounts for the
retronasal olfaction component of chemical senses, which
compliments sourness and sweetness intensities contribution to taste. The
overall highest sensory intensity is 37.5 (Table S2) for strawberry
flavor of Festival (sn 2, wk 1), which also rates highest for overall
liking and sweetness intensity. Opposite this, FL- 05-85 (sn 1, wk 6)
delivers the least intense strawberry flavor experience with a score
of 19.4 (Table S2). Total volatiles in Festival (sn 2, wk 1) is over
50% greater than in FL 05-85 and seven more volatiles
compounds are detected (Table S2). Total volatiles within a
sample contribute to strawberry flavor intensity (R2 = 0.167*) (Fig.
3Q), but it is not simply the sum of volatile constituents that
explain the effect. For instance, the maximum total volatile
content detected within a sample, 27.3 mg1 gFW21 hr21 from
Camarosa (sn 1, wk 2), does not result in the greatest flavor
intensity (30.5) and the minimum, 8.5 mg1 gFW21 hr21 from
Sweet Anne (sn 2, wk 9), does not rate as the least flavorful (25.8)
The chemical diversity of the resources analyzed allows for the
identification of 81 volatile compounds from fresh strawberry fruit
(Fig. S3). The majority of compounds are lipid related esters, while
lipid related aldehydes account for the majority of volatile mass.
Terpenes, furans, and ketones are also represented in the
headspace of strawberry. Forty-three of the 81 volatile compounds
are not detected (,0.06 ng1 gFW21 hr21) in at least one sample.
Therefore, 38 volatiles are measured in all samples; appearing to
be constant in the genetic resources analyzed (Table S2). No
cultivar has detectable amounts of all 81 volatiles. Samples of
Festival, Camino Real, PROPRIETARY 6, and FL 06-38 are
the most volatile diverse, but are lacking detectable amounts
benzoic acid, 2-amino-, methyl ester (134-20-3) . This methyl
ester of anthranilic acid is detectable in only Mara des Bois and
Charlotte from the final harvest (wk 7) of season 1 (Table S2).
Chandler (sn 2, wk 4) and Red Merlin (sn 1, wk 6) are the least
volatile diverse samples lacking detectable amounts of 19 and 17
compounds, respectively (Table S2).
The most abundant ester, butanoic acid, methyl ester
(623-427)is measured at over 7 mg1 gFW21 hr21 from PROPRIETARY 2
(sn 1, wk 3) and has a significant correlation to flavor (R2 = 0.097*)
(Fig. 3S). A terpene alcohol, 1,6,10-Dodecatrien-3-ol,
3,7,11trimethyl-, (6E)- (40716-66-3) (nerolidol), with maximum content
of over 600 ng1 gFW21 hr21 in Sweet Charlie is not detected in
Red Merlin. The nerolidol rich Sweet Charlie garners greater
flavor intensity at 32.2 than deficient Red Merlin at 23.95. The
impact on flavor intensity by nerolidol (R2 = 0.112*) (Table S4) is
greater than butanoic acid, methyl ester despite having maximum
contents lower by one order of magnitude. Hexanal (66-25-1) is
the second most abundant individual compound, an aldehyde
detected in all samples, exceeds 11 mg1 gFW21 hr21(Table S2),
and does not have a significant correlation to flavor intensity
(R2 = 0.016) (Table S4). Hexanoic acid, ethyl ester (123-66-0)
exhibits over 200-fold difference across samples, and also has no
bearing on sensory perception (Table S4). Conversely, two minor
level aldehydes demonstrate a disparity in effect: 2-pentenal,
(2E)(1576-87-0) is enhancing toward flavor intensity (R2 = 0.239*) (Fig.
3R), while pentanal (110-62-3) is the only compound that
negatively correlates to flavor (R2 = 0.079*) (Fig. 3T). The
significant contribution of the 1,6-octadien-3-ol,
3,7-dimethyl(78-70-6) (linalool) to flavor intensity positively correlates with
increasing content (R2 = 0.074*) (Table S4). In Chandler
3(2H)furanone, 4-methoxy-2,5-dimethyl- (4077-47-8) is not detectable,
and only has maximum content of 40 ng1 gFW21 hr21 in
Treasure (sn 1 wk 3). The level of this characteristic strawberry
furan is significantly impactful on perceived flavor intensity
(R2 = 0.108*) (Table S4). In total, thirty volatile compounds
diverse in structure have a positive relationship to flavor intensity
and their significance cannot be derived from content alone.
Specific Volatiles Enhance Sweetness Intensity
Independent of Sugars
Multiple regression of individual volatile compounds against
perceived intensity of sweetness is performed independent of
glucose, fructose, or sucrose concentration (Table S5). Twenty four
volatile compounds show significant correlations (a = 0.05) to
perceived sweetness intensity independent of glucose or fructose
concentration, twenty-two of which are mutual between the two
monosaccharides. Twenty volatiles are found to enhance
sweetness intensity independent of sucrose concentration; only six of
these volatiles are shared with those independent of glucose and
fructose: 1-penten-3-one (1629-58-9); 2(3H)-furanone,
dihydro-5octyl- (2305-05-7) (c-dodecalactone); butanoic acid, pentyl ester
(540-18-1); butanoic acid, hexyl ester (2639-63-6); acetic acid,
hexyl ester (142-92-7); and butanoic acid, 1-methylbutyl ester.
Only three compounds are found to be negatively related to
sweetness independent of at least one of the sugars: octanoic acid,
ethyl ester (106-32-1) exclusively independent of glucose;
2pentanone, 4-methyl- (108-10-1) mutually independent of glucose
and fructose; and 2-buten-1-ol, 3-methyl-, 1-acetate (1191-16-8)
exclusively independent of sucrose.
Exploitation of genetic diversity and environmental variation
allows for a wide range of consumer hedonic and sensory
responses. The cultivars in this study represent a large proportion
of commercial strawberry acreage in North America, advanced
breeding selections, and European cultivars. A genetic collection
aimed at enhancing the diversity of physical and chemical
constituents, as well as consumer experiences. Despite the
perennial life cycle of strawberry much commercial production
uses annual methods, which in sub-tropical Florida allows for
continual harvest of ripe fruit from late November through March.
A nearly three-fold difference in overall liking of strawberry is
observable within all samples. The highest and lowest rating
samples are Festival of the first week in the second season and
Red Merlin of the sixth week in the first season. These two
cultivars are the product of separate breeding programs, have
distinct genetic backgrounds, and therefore distinct biochemical
inventories. Harvested at opposite ends of the seasons the early
and late season fruit are subjected to different environmental
conditions, further attenuating genetic differences. The diversity of
strawberries samples assayed and range of consumer liking
captured (Fig. 2) indicates the chemical diversity of strawberry
cultivars is not only perceivably different but certain profiles are
more highly preferable.
Elevated texture liking, sweetness intensity, and strawberry
flavor intensity significantly increases overall liking, while sourness
intensity alone has no detectable relationship to overall liking (Fig.
3A-D). Integration and synthesis of response to sensory signals of
taste, olfaction, and tactile sensation constitute an eating
experience  and drive overall liking. The senses of taste and olfaction
sample the chemicals present in food e.g. sugars, acids, and volatile
chemical compounds. These elicitors attenuate the perception and
hedonics of food [38,39]. Ratings of strawberry fruit are correlated
to specific chemical or physical attributes, especially sweetness (Fig.
3B) and flavor intensity (Fig. 3D), the two greatest drivers of overall
Much work has been done to measure sugars and volatile
compounds in strawberry fruit in an attempt to understand
sweetness and flavor, and these aims are in line with consumer
demand. A consumer survey using 36 attributes of strawberry
determined sweetness and complex flavor as consistent
favorable characteristics of the ideal strawberry experience .
Previous work in tomato  and this current study on strawberry
surveyed participants for ideal ratings of the respective fruits.
Using the same gLMS scales employed in the current study, scores
for ideal strawberry and tomato overall liking, sourness intensity,
and flavor intensity are highly similar. Ideal flavor evoked the
highest mean response of 45 for both, exemplifying its importance
to the consumer. Interestingly, a large disparity for ideal sweetness
intensity is found; 42 and 33 for strawberry and tomato,
respectively. Ideal sweetness intensity is much greater in
strawberry, potentially due to differences in consumption. Strawberry is
often consumed fresh and is a delicacy or dessert fruit, while
tomato is savory and often an ingredient in complex recipes.
Therefore, the desire for sweetness may be greater in strawberry.
The overall liking of strawberry fruit is significantly related to
texture liking (Fig. 3A), and increasing fruit firmness accounts for
more than a third of increasing texture liking (Fig. 3I). The
fivefold variation in firmness can be attributed to variation in fruit
development or softening (Table S2). Strawberry fruit
development consists of division, expansion, and ripening .
Developmentally regulated, ripening associated fruit softening is
multifaceted , including catalytic cell wall disassembly  and
dissolution of cell-to-cell adhesion . The relationship between
texture liking and firmness does not appear entirely linear, because
the two firmest samples are close to average texture liking (Fig. 3I).
Excessively firm fruits may be perceived as under ripe while those
with less firmness may be considered over ripe; affecting texture
liking. Fruit can progress through ripening, from under to over
ripe, in ten days , exemplifying the narrow window in which
multiple facets of fruit quality must synchronize.
Despite a moderate range of intensity, perceived sourness has
little to no bearing on overall liking (Fig. 3C). Just over 30% of
sourness intensity variation can be accounted for by positive
correlation with TA. The concentrations of citric acid and malic
acid metabolites are likely additive toward the effect of TA on
sourness intensity, and in fact both organic acids have significant
correlations to sourness intensity (Fig. 3K-L). Despite a lack of
influence by sourness intensity on overall liking, metabolites of
sourness have a critical role in fruit biochemistry. Increased TA
shows a significant minor correlation with overall liking (Table S4)
and correlates significantly with total sugar (data not shown). This
co-linearity may be due to accumulation of sugars and subsequent
biosynthesis of organic acids during ripening of fruit [7,8,16].
Citric acid is the predominant organic acid in ripe fruit  and its
concentration is fairly stable during ripening. Also, it is known to
act as an intermediate between imported sucrose and fatty acid
biosynthesis , which may facilitate enhancement of overall
liking through volatile biosynthesis.
The consumer rating of sweetness intensity is the primary factor
contributing to overall liking, and sweetness is the component of
taste perception facilitating the detection of sugars. Sugars are
simple carbohydrates, a readily available form of energy, and the
degree of correlation among sweetness and overall liking is due to
hedonic effect . Variation in sweetness intensity is best
explained by sugar content (Fig. 3L). Previously, soluble solid
content (SSC) has been used as a valid indicator of sweetness in
strawberry [1,28]. However this is an aggregate measure, as
previous quantification of individual sugars within a strawberry
identifies sucrose, glucose, and fructose as the predominant soluble
solids [1,8,15,40]. Sucrose concentrations observed across samples
is responsible for more variation in total sugar, sweetness intensity
and overall liking than any other individual compound (Table S4).
Metabolites contributing to perceived sweetness intensity have the
greatest influence on the overall hedonics of strawberry. A
significant decrease in sweetness intensity occurs between early
and late season fruit, and unfortunately overall liking decreases as
well (Table 1) (Fig. 3E).
Drastic fruit quality differences between early and late season
fruit result in lower consumer response (Table 1) (Fig. 3E), which is
likely due to environmental changes (Fig. S1) or plant maturity. A
significant difference in the mean temperature one week prior to
harvest is likely a causative factor (Table 1). Monitored
development of Festival fruit under elevated temperature decreases the
fruit development period from 36 days at 15uC to 24 days at 22uC.
Also, a simultaneous decrease in SSC is observed, both
independent of flowering date i.e. plant maturity [26,27]. The
mean temperature of the week prior to harvest for early and late
season Festival fruit are 15uC and 20uC for the first season and
14uC and 19uC for the second season (Table 1). These differences
in environment likely alter whole plant physiology and more
specifically fruit biochemistry during development and ripening,
affecting fruit quality. During strawberry fruit development
sucrose is continually translocated from photosynthetic tissue,
while a consistently high sucrose invertase activity in fruit
hydrolyzes sucrose into glucose and fructose, maintaining sink
strength of fruit  and in turn feed biosynthetic pathways .
Total and individual sugars decrease in ripe fruit during both
seasons as the plant is subjected to increasing temperatures (Table
1). Increased maturation rate hastens fruit development,
potentially decreasing cumulative period sucrose is imported to fruit,
and inhibiting sucrose accumulation to affect other fruit quality
attributes. These factors are likely causative of the observable
decrease in sweetness and flavor intensity as the season progresses.
Although total sugar decreases between early and late fruit, a
disproportionate amount of the decrease is attributed to sucrose
(Table 1), which indicates sucrose as the waning constituent of
sugar content (Fig. S2A-C). Glucose and fructose concentrations
are tightly correlated to each other, show less seasonal influence
than sucrose, and lack correlation to sucrose. These observations
are indicative of tighter biochemical regulation of glucose and
fructose than sucrose, which has the greatest variability in
concentration among the three sugars. Total volatile content has
an indirect dependence on sucrose concentration (Fig. S2E), and a
decrease in total volatiles is observed between early and late season
strawberry (Table 1). Influence of harvest date on headspace of
fresh strawberry fruit is known [41,42]. Increased volatile content
is likely dependent on more free sucrose, i.e. a larger imported
reserve, facilitating greater flux through primary and secondary
metabolism. Generation of glucose and fructose initiates a
complex network of primary and secondary metabolism specific
to ripening strawberry fruit, in which sucrose is principal and
limiting to the strawberry fruit biosynthetic pathways .
Upregulation of biosynthetic genes associated with volatile
secondary metabolites  and the consumption of primary
metabolite classes of fatty acids and amino acids, precursors of
volatile compounds, happens in the final stages of ripening .
This sucrose dependent metabolic shift culminates in peak volatile
content and diversity .
Strawberry flavor intensity is the second greatest determinant of
overall liking (Fig. 3D) and accounts for perception of volatile
compounds through retronasal olfaction. A significant positive
relationship exists among total volatile content and the flavor
intensity for a given sample, however, total volatile content is not
entirely explanatory of flavor intensity. The maximum rating for
strawberry flavor intensity by Festival (sn 2, wk1) is the greatest
consumer response evoked within this study (Table S2),
highlighting the significance of sensory perception of aroma. However, this
sample only has slightly more than 60% of total volatile mass of
the greatest sample. The extent of volatile phenotype diversity is
great enough across strawberry fruit to not only be discerned but
Within the genetic resources of Fragaria x ananassa analyzed in
this study 81 compounds are reproducibly detected, but not one
cultivar has detectable amounts of all compounds. The amount of
individual volatile compounds within fruit can have a significant
influence on flavor intensity, but which volatiles are determinant of
flavor has a lack of consensus. Previous determination of flavor
relevance relied on approaches in which importance of volatiles is
at least initially based on abundance. Determination of flavor
descriptors or thresholds of isolated compounds were determined
using human perception via orthonasal olfaction [4,5,2325],
negating the complex system of strawberry fruit or actual flavor
relevant retronasal olfaction.
Of the forty-six volatile compounds cited as relevant to
strawberry flavor in five studies [4,5,2325] only seven are mutual
to at least three of the studies, exemplifying the lack of agreement
in defining flavor-relevant constituents. This consensus includes
butanoic acid, methyl ester; butanoic acid, ethyl ester; hexanoic
acid, methyl ester (106-70-7); hexanoic acid, ethyl ester; linalool;
butanoic acid, 2-methyl- (116-53-0); and 3(2H)-furanone,
4methoxy-2,5-dimethyl-, all of which are quantified in this report.
These compounds exhibit adequate variability in fruit samples to
discern dose dependent effect on flavor intensity. However, only
linalool; butanoic acid, ethyl ester; butanoic acid, methyl ester; and
3(2H)-furanone, 4-methoxy-2,5-dimethyl- show significant positive
correlation with flavor intensity (Table S4). These compounds that
are found to influence flavor intensity represent diverse classes,
terpene alcohol, two esters, and a furan, respectively, while the
three compounds not fitting to flavor are all esters. With esters
accounting for the majority of chemical compounds detected in
strawberry it is possible that too much emphasis is placed on the
chemical class for flavor, or that in a complex mixture less are
perceivable than when smelled individually.
Over one third of volatiles in this study significantly correlate
with strawberry flavor intensity, potentially enhancing perception
of a complex and highly variable volatile mixture (Table S4),
seventeen of which are not of previous strawberry flavor focus.
Two of these unrecognized compounds, 1-hexanol (111-71-7) and
butanoic acid, 3-methyl-, butyl ester (109-19-3), are present in the
most flavorful strawberry sample but undetected in the least
flavorful (Table S2). This pair of compounds as well as pentanoic
acid, ethyl ester (539-82-2) and butanoic acid, 3-methyl-, octyl
ester (7786-58-5), also present/absent in the most/least flavorful,
have relatively minor amounts but show evidence of enhancing
perceived sweetness intensity independent of individual sugars.
Relatively low abundance volatiles are indicated as new impactful
components of strawberry flavor.
Thirty-eight volatile compounds are observed to significantly
enhance the perceived intensity of sweetness; twenty-two mutually
independent of glucose and fructose, fourteen uniquely
independent of sucrose, and six compounds mutually independent of all
three sugar: 1-penten-3-one; 2(3H)-furanone, dihydro-5-octyl-
(cdodecalactone); butanoic acid, pentyl ester; butanoic acid, hexyl
ester; acetic acid, hexyl ester; and butanoic acid, 1-methylbutyl
ester (Table S5). In tomato, similar analysis of a volatile subset
identifies three compounds enhancing sweetness intensity
independent of fructose: geranial; 1-butanol, 3-methyl- (123-51-3); and
butanal, 2-methyl- (96-17-3) . These compounds are not
identified in the current study; therefore the effect cannot be
confirmed in a second system. Botanically, tomato is considered a
true fruit and demonstrates climacteric ripening, while strawberry
fruit is non-climacteric and considered an aggregate accessory
fruit. The developmental origin of the flesh which is consumed is
divergent, exhibiting unique biochemistries, but the observance of
volatile compounds potentially enhancing perceived sweetness
appears to be widespread in fruit.
Orthonasal olfaction is the result of smelling i.e. bringing odor in
through the nose, while retronasal olfaction is elicited by odorants
traveling from oral cavity or esophagus up to nasal cavity .
Orthonasal olfaction introduces volatile compounds to the nasal
epithelium via inhalation, while retronasal olfaction is achieved
during exhalation . Specifically, the path of odorants
distinguishes the manner of interaction between consumer and
potential food, with orthonasal contributing to aroma and
retronasal to flavor. Integration of sensory stimuli relies on
projection of signals to various structures of the brain.
Interestingly, portions of orthonasal (smell) and retronasal (flavor) olfaction
project to different brain areas for processing , while taste
activation partly overlaps that of retronasal olfaction for
integration to produce flavor . Co-activation of taste and retronasal
olfaction, but not orthonasal, is shown to elicit responses at
otherwise independently sub-threshold levels, exemplifying the
ability of multiple sensory integration to intensify one another
. Mechanical blockage of retronasal olfaction during tasting of
solutions significantly reduces the ability to correctly identify
solute, including sucrose . Combination of taste and retronasal
olfaction results in a sensory system more adapt at analyzing the
chemical content of food, but cross communication also facilitates
manipulation of the system.
The food industry knows of the intensification of volatile
sensations by the addition of small amounts of sweeteners to
solutions containing volatiles . The ability of volatiles to
enhance taste is also a known phenomenon . Enhancement of
perceived sweetness is demonstrated by addition of volatiles amyl
acetate (banana)  and citral . Multiple studies show the
ability of strawberry aroma to intensify the sweetness of a sugar
solution [52,53], as well as pineapple, raspberry, passion fruit,
lychee, and peach [53,54]. Also, sweetness enhancement has been
achieved with vanilla , caramel [53,56], and chocolate 
indicating this phenomenon is not only associated with fruit
volatiles. Studies to determine perceptional differences when
tomato is spiked with sugars, acids, and volatiles indicates cross
talk between taste and olfaction, in which volatiles impact
perception of sweetness and vice versa . Individual volatile
compounds have been implicated in tomato to intensify perceived
sweetness independent of sugar content [34,58]. The results here
narrow the previous effect of enhanced sweetness by strawberry
aroma, a variable mixture, to individual compounds in the fruit.
These volatiles are not present at the highest amounts in fruits and
most have not been targets of flavor analysis. Also, most appear to
be associated with lipid metabolism, like many other volatiles
quantified in this work, yet their presence or increased content has
an enhancing effect on perceived sweetness independent of sugars.
Technically, sweetness is a facet of taste . Therefore a means
to convey sweetness via aroma can serve as an attractant to seed
dispersers of wild strawberry, or perhaps it is a result of artificial
selection  to enhance a limited sugar capacity in commercial
Strawberry fruit ripening culminates as the flesh softens, volatile
emission peaks, and sugars accumulate. This highly coordinated
process results in fruit with strong liking due primarily to texture,
flavor, and sweetness. However, cultivar, environmental
conditions, and their interactions influence fruit attributes, altering the
composition of strawberry. This diversity allows for a spectrum of
experiences such that the hedonics and intensities of these
sensations can vary greatly. The importance of sucrose to
sweetness intensity is evident, and the correlation of total volatiles
to sucrose highlights the dependence of secondary metabolism to
primary metabolism. Individual volatiles correlate to strawberry
flavor intensity, helping to better define distinct, perceptually
impactful compounds from the larger mixture of the fruit. The
dependence of liking on sweetness and strawberry flavor is
undermined by environmental pressures that reduce sucrose and
total volatile content. A cultivar that exhibits minimal seasonal
environmental influence presents itself as a breeding ideotype, as
maintenance of sucrose concentration may alleviate loss of overall
liking. Selection for increased amounts of volatile compounds that
act independently of sugars to enhance sweetness can serve as an
alternate approach. The volatiles described herein are sampled
mainly from current commercial cultivars and are therefore
feasible targets for varietal improvement in the short-term,
whereas future studies will be necessary to identify
sweetenhancing volatiles not already present in elite germplasm.
Figure S1 Season Environmental Conditions. Daily
maximum and minimum temperatures (A and B), daily average solar
radiation (C and D), daily average relative humidity (E and F), and
daily total rain fall (G and H) during the 2011 (A, C, E, and G) and
2012 (B, D, F, and H) seasons. Data for Balm, FL obtained from
Florida Automated Weather Network (http://fawn.ifas.ufl.edu/
data/reports). Data spans three weeks prior to first harvest through
last harvest of each season with individual harvests indicated by
dotted vertical line and harvest week number. Dashed horizontal
lines represent means of environmental measures. Solid lines are
the bivariate fit of environmental measure across season.
Coefficients of determination (R2) and p-value of fit is listed above
individual scatterplots and are calculated using bivariate fit in JMP
Figure S2 Individual sugars and total volatiles
regressed against season progression. Regression of sucrose
(A), glucose (B), fructose (C), and total volatiles (D) by harvest week
during the seasons. Total volatile content is regressed against
sucrose (E) and fructose (F). Sucrose (A) and total volatiles (D)
demonstrate a significant negative fit to harvest week, unlike
glucose (B) and fructose (C). A strong relationship between total
volatile emmission and sucrose concentration is found (E) that is
not observed between total volatiles and glucose (data not shown)
and fructose (F). Coefficient of determination (R2) and p-value of fit
is listed above individual scatterplots and is calculated using
Figure S3 Chemical structure of volatile compounds.
Chemical structure of volatile compounds quantified in
strawberry. Sorted by increasing retention time (left to right, top row to
bottom row), identified by CAS Registry Number.
Table S1 CAS registry number, chemical name, and
formula index. Chemical Abstract Services (CAS) registry
numbers were used to query SciFinderH substances database for
associated chemical name and molecular formula.
Table S2 Full data table. Means and standard errors of
replicates for all measures for each sample assayed. Includes
consumer panel measures, internal and external color, puncture
force, organic acids, sugars, SSC, pH, TA, and volatile
compounds. High and low value, median, and fold difference for
each column displayed above means table.
Table S3 Fruit attributes bivariate fit during season.
Regression of harvest week during season (X) on panel responses
and metabolite concentration (Y). Coefficient of determination
(R2), correlation coefficient, p-value, sample size (n), mean and
standard deviation of X and Y derived from bivariate fit in JMP 8.
Table S4 Fruit quality bivariate fit. Regression of chemical
and physical measures of fruit (X) to panel responses (Y).
Coefficient of determination (R2), correlation coefficient, p-value,
sample size (n), mean and standard deviation of X and Y derived
from bivariate fit in JMP 8.
Table S5 Multiple regression for identification of
sweetness enhancing volatiles. Individual volatile compound
concentrations are regressed against perceived sweetness intensity
independent of effect from glucose, fructose, or sucrose, separately.
Thirty compounds (*) (a = 0.05) were found to enhance intensity of
sweetness independent of at least one of the three sugars. Six
compounds (bold) were found to significantly enhance intensity of
sweetness independent of all three sugars.
The authors wish to acknowledge David Moore for fruit transport, Yanina
Perez for assistance with fruit chemical data collection, and Timothy
Johnson for assistance with volatile collection. Portions of the results are
protected by US Patent 20130280400 and International Patent WO 2013/
Conceived and designed the experiments: MLS TAC LMB DMT KMF
HJK CAS VMW DGC. Performed the experiments: MLS JLG AZO.
Analyzed the data: MLS EAJ LMB HRM. Contributed reagents/
materials/analysis tools: DMT HJK VMW. Wrote the paper: MLS.
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