This study analyzed the color and polyphenolic content of canned California-style black ripe olives over 27 months of storage. Color measurements using a colorimeter showed a decrease in redness and yellowness over time. Tyrosol concentration was positively correlated with redness and yellowness measurements. Tyrosol levels were lowest of the measured polyphenols and were the only compound linearly correlated with color values. The study suggests tyrosol concentration may be used to predict olive color changes during prolonged storage.

1. Kelly Phang, Rebecca Johnson, Alyson Mitchell PhD
1 Shields Avenue, University of California, Davis.
Acknowledgements
Alyson Mitchell, PhD. Rebecca Johnson. Food safety
and Measurement Facility. Micheal Clegg. Musco
Family Olive Co.
Conclusions
• Of the polyphenolics measured, only tyrosol
demonstrated a trend between phenolic content and
color measurements.
• Tyrosol concentration was found to be positively
correlated with the a* color value [degree of red (+) vs
green(-)] and b* color value [degree of yellow (+) vs
blue (-)] on the insides of CBROs.
• Color values do not have linear trends for a* or b* color
value over time, but group similarly due to processing
and/or storage.
• In comparison, the two other prominent polyphenols
tyrosol and hydroxytyrosol 4-O glucoside are much
higher in concentration in CBROs and do not correlate
to any linear model to colorimetry measurements.
Abstract
Consumers expect a particular shade of black in
California-style black ripe olives [CBROs] indicative of
olive quality. During prolonged storage, the color of
CBROs may degrade and lead to consumer rejection of
the product. Herein, the color of canned CBROs over
27 months was quantified using a Hunter Lab
colorimeter. The levels of twelve polyphenols
associated with olive bitterness and/or health (i.e.
tyrosol, hydroxytyrosol, and hydroxytyrosol 4-O
glucoside [HT4-O]) were quantified using ultra high
performance liquid chromatography (UHPLC)
electrospray mass spectrometry (ESI/MS). Preliminary
data indicate that olives are initially darker with shades
of red and yellow which diminish in intensity during
prolonged storage time. Hunter L*a*b color values were
correlated with polyphenolic levels. Colorimetry data
indicates a non-linear trend of L*a*b color values over
time. A linear trend between tyrosol and a* and b* color
values was observed. Tyrosol was the only polyphenol
with a linear correlation to L*a*b* color value. Levels of
tyrosol were lowest (< 20 mg/kg) relative to
hydroxytyrosol (20-102 mg/kg) and HT4-O glucoside
(3-260 mg/kg).
Introduction
L*a*b Color Space
Andy Williams. Newspaper Color Quality Club 2002-2004.
L* values on the z-axis, and represent lightness.
a* values on the x-axis, representing green (-a) to red (+a).
b* values on the y-axis, and represent blue (-b) to yellow (+b).
–
–
Results Correlation of a* color values on the
inside of olives to tyrosol levels
The above diagram shows the formation of phenolic compounds
hydroxytyrosol from oleuropein, and tyrosol from ligstroside. Herein we
measured the three chemicals highlighted in red.
Color Trends in California-Style Black Ripe
Olives in Correlation to Polyphenolic Content
y = 3.2963x + 3.5965
R² = 0.9499
0
5
10
15
20
25
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
Tyrosolmg/kg
a inside
Tyrosol
Plotting phenolic concentration against a* color value
demonstrates that there is a correlation between tyrosol
levels and a* values.
The b* values have a similar linear correlation to tyrosol
concentration.
This model may be potentially be used to link a* values
and b* values of the inside of olives, to their tyrosol
levels.
0
50
100
150
200
250
300
0 5 10 15 20 25 30
mg/kgolive
Months
Hydroxytyrosol 4-O Glucoside
0
2
4
6
8
10
12
0 1 2 3 4 5
binside
a inside
a* and b* inside value
3 Months
9 Months
15 Months
27 Months
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0 5 10 15 20 25 30
ainside
Months
a value of olive inside value vs month
0
5
10
15
20
25
30
35
0 5 10 15 20 25 30
Lvalue(L:ightness)
Months
L value of olive inside vs month
Hydroxytyrosol content ranges
from 20-102 mg/kg olive.
Tyrosol content was in a range
of <20 mg/kg olive.
*Tyrosol’s values correlate with
a* values and b* values in
colorimetry measurements,
show in the box to the right.
Hydroxytyrosol 4-O glucoside
levels were at 3-260 mg/kg
olive.
Colorimetry
a* values and b* values of the
inside the olive have similar
values per month, with clear
separation between time points.
The a* inside values do not have
a linear trend, but are
comparable to tyrosol levels.
Therefore a model was created,
linking tyrosol levels to a values
of the insides of olives.
a* values refer to red (+a) vs
green (-a).
L values did not vary much over
time.
L values refer to lightness
values. A higher value
corresponds to a lighter color.
Method
Canned olives were processed on a single date and canned olives
were stored for 27 months. Olives were sampled at 3, 9, 15, 27
months. Three cans were measured, with three composites per
can, and with ten olives in each composite.
L*a*b values measured
using a Hunter
Colorimeter inside and
outside each olive.
Homogenized using a
professional spice grinder.
Olives were defatted using
a hexane removal of 40mL.
Olives were dehydrated for 48 hours
and homogenized every 24 hours.
0.1g of sample
was sieved and
weighed out.
Sample extraction
with 4mL of 60%
methanol solution
in water.
Filtered with
a nylon 0.22
micron filter.
920uL injected with 80uL O-
coumeric acid internal standard
0
20
40
60
80
100
120
140
0 5 10 15 20 25 30
mg/kgOlive
Months
Hydroxytyrosol
0
5
10
15
20
25
0 5 10 15 20 25 30
mg/kgOlive
Months
Tyrosol