Germination Vigour versus Delayed Luminescence of Coffee Seeds

Preliminary Series

Cristiano M. Gallep

, Evelyn M. do Amaral

, Geovana C. Alonco

Mirian P. Maluf

and Lilian Padilha

Applied Photonics Lab., School of Technology, University of Campinas, Limeira, SP, Brazil

EMBRAPA Café, Parque Estação Biológica, Brasilia, DF, Brazil

Keywords: Delayed Luminescence, Coffee Seed, Germination Vigour, Post-Harvest Treatment.

Abstract: Nine coffee seeds samples submitted to different post-harvest treatments were tested in terms of ultra-weak

delayed luminescence and induced to germinate afterwards. Hyperbolic decay function was used to quantify

the time profiles and their fitting parameters were correlated to the correspondent germination vigour (total

seedlings’ elongation). Good linear relation was found (R

> 0.85) for the initial value parameter as well as

for the decay velocity parameter. These preliminary results point to further tests in order to validate a

photonic, non-invasive, non-destructive test for coffee seed’s viability analyses.

1 INTRODUCTION

THE coffee seed normally presents high germination

potential just after appropriate harvest and

desiccation. However, it loses its physiological

quality very rapidly under common storing

conditions. Therefore, it is not possible to have

feasible seeds, i.e. able to germinate, for more than

some months (Eira, 2006). Some techniques may

improve seed’s viability on long term, by improving

storing conditions (Couturon, 1980; Hong & Ellis,

1992), or controlling the re-hydration process

(Dussert et al., 2000) or even inducing low-

temperature hibernation (Dussert et al., 2001).

Although some progress was achieved, the usual

way for checking seeds’ viability and vigour is to

allow them to germinate, losing so the hibernation

condition. In order to distinguish between feasible

and not feasible seeds, and so enable an optimization

of seed’s storage conditions, a quick and non-

destructive method is demanded, as well for other

types of sensitive seeds.

The biophotonic phenomena, i.e. the ultra-weak

delayed luminescence and spontaneous emission

found in living organisms, with detected intensity of

10-1000 photons/cm

.s, has been studied by many

multi-disciplinary groups all over the world, in a

broad variety of themes (Kobayshi and Inaba, 2000).

This peculiar luminescence holds much longer than

the usual bio-fluorescence, and is found far from

normal thermal emission, covering the entire visible

spectrum and the near IR and UV (Popp, 2000).

Correlation between the ultra-weak delayed

luminescence (DL) behaviour and the germination

capacity was found for barley (Yan, 2003), soya

(Lanzanò, 2009; Costanzo, 2008), rice (Yong, 2010),

and wheat (Wang, 2009) seeds.

A first, small trial with coffee seeds were

performed by the first author ten years ago at IIB

facilities (Neuss, Germany), with some indicative

results of good correlation between the DL

parameters and the germination capacity of tested

seeds (Gallep, 2004).

Here, preliminary series of ultra-weak DL of

coffee seeds are presented in relation to their

germination vigor – germination rate and total

seedling elongation measured in the hypocotyl root

axis. Seeds submitted to different post-harvest

treatments were tested for delayed luminescence,

and induced to germinate afterwards.

The germination performance was established

after 15 days and 30 days and correlated to DL

parameters. Good correlation (R

>0.85) was found

between the germination vigor and the initial

intensity and the decay velocity.

147

M. Gallep C., M. do Amaral E., C. Alonco G., P. Maluf M. and Padilha L..

Germination Vigour versus Delayed Luminescence of Coffee Seeds - Preliminary Series.

DOI: 10.5220/0004677401470151

In Proceedings of 2nd International Conference on Photonics, Optics and Laser Technology (PHOTOPTICS-2014), pages 147-151

ISBN: 978-989-758-008-6

 2014 SCITEPRESS (Science and Technology Publications, Lda.)

2 MATERIAL AND METHODS

The DL of nine groups of coffee seeds (Coffea

arabica), harvested in 2011 and treated in different

conditions, were analysed in terms of hyperbolic

decay in May/2013 and further induced to germinate

in controlled conditions.

The different seed groups are presented on Table

1 – if mucilage is removed mechanically or by

fermentation, if drying was done in drying machine,

in shadow or under sun-light, and the moisture

content achieved after drying (12% or 35%).

Table 1: Coffee seed groups - different post-harvest

treatment.

group

post-harvest treatment

Moisture

content

mechanical removal of

mucilage,

mechanical dryer

12%

mechanical removal of

mucilage, dried in shadow

12%

A11

mechanical removal of

mucilage, sun-dried

12%

A13

removal of mucilage by

fermentation, mechanical dryer

12%

A14

removal of mucilage by

fermentation, mechanical dryer

35%

A15

removal of mucilage by

fermentation, dried in shadow

12%

A16

removal of mucilage by

fermentation, dried in shadow

35%

A17

removal of mucilage by

fermentation, sun-dried

12%

A18

removal of mucilage by

fermentation, sun-dried

35%

The seeds were harvest, processed and stored in

controlled conditions at Federal University of Lavras

(UFLA, MG, Brazil) in June/2011. Random

samples of 50 grams were taken from each seed

group for the ultra-weak DL measurements and

stored in dark to avoid artefacts.

The experimental setup for DL tests are shown at

Figure 1; it is a dark chamber with photon-count

module (photomultiplier tube + electronics) and

fiber optic ring connect to external light source

(halogen lamp) by fiber cable and electrical-

mechanical shutter, all automatic controlled by

software; it includes also temperature control for

samples using fluid flow (Bertonha, 2011).

Each group of seeds was arranged in the chamber

in order to complete the sample holder, which was

stabilized in temperature (T = 21

C +/- 1) to avoid

seed stress. The DL measurements used photon-

count mode in 100 s time-windows for 20 thousand

points (total = 2 s) and were taken after twenty-

second exposure to white light (160 lux), and

repeated sequentially ten times for each sample. A

delay of 370 ms occurs between the end of

excitation and photon-count start due technical

limitation.

The 10-repetition DL data was averaged and the

curve was fitted by generic hyperbolic-like decay,

formulated by:

/1.



(1)

where t is related to time, a+b is the curve’s initial

value (t = 0), a is its final value (t = ∞), c is related

to the decay velocity for small t and d is related to

enhancement in velocity decay, more pronounced

for great values of t.

Figure 1: Setup for DL measurements in biosamples -

(top) chamber, illumination and controls schematics;

(bottom) picture of prototype.

After all samples were measured two hundread

seeds were taken from each sample and induced to

germinate in a controlled chamber (T = 30

C +/- 1,

humidity > 70%) for 30 days. For that, each group of

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200 were divided in 4 x 50 seeds, and each sub-

group disposed in rolls of paper towels moistened

with water equivalent to 2

times the dry paper

substrate weght. At the 15

day after start and at the

end, at the 30

day, each group was analysed in

terms of hypocotyl root axis growth, measuring

each seedling elongation.

3 RESULTS AND DISCUSSION

The DL time profiles of all groups are shown at

Figure 2, as well as their correspondent hyperbolic

decay fitting (R

>0.995) parameters: a, b, c and d. It

is clear from Figure 2 that groups A7, A11 and A13

present higher initial value than the other groups.

Group A17 time profile is also distinguishable from

the remaining curves, with small increase from 1 ms

to 100 ms.

Figure 2: DL data for groups A7 to A18– (top) 10 test

average time profile; (bottom) paramenters of hyperbolic

decay fitting (R

>0.995).

These facts are so reflected in the b parameter of

their. It is also noted that the c parameter is also

higher for the A7, A11 and A13 samples, meaning

that their DL intensity decay faster that the other

groups, as can be seen also in the time profiles form

10 ms to 100 ms. The A15 time profile is also

noticed to have small increase at the beginning, ie. t

< 1ms, as occurring for the curves of A7, A11 and

A13.

The remaining groups – A9, A14, A16 and A18

– have similar time profiles, with small initial value

(~3) and regular decay velocity, ie. similar c factor.

The germination data – seedling’s elongation

incidence, in a total of 200 seeds/group – at the 15

and 30

day are presented at Figure 3 for the viable

groups; the ones not displayed had no seedling

development at all, ie. zero seeds alive. It is noted

that groups A7 and A13 present the higher

development of all, followed by A11 and, with much

lower development, by A15 and, much lower, A17.

The A9 had few seedlings developed.

By summing all seedlings’ length the total

elongation is obtained for each group, for both the

and 30

day after imbibition. This numbers

were so plotted against the correspondent b and c

parameters, and these datagrams are shown at Figure

4. Good linear correlation was found between the

hyperbolic fitting parameters and the total seedling

elongation for both the 15

and 30

day data, with

> 0.85 in all cases.

4 CONCLUSIONS

The ultra-weak delayed luminescence time profiles

of nine groups of coffee seeds with different

germination capacity were studied in terms of

hyperbolic decay parameters, and good correlations

were found between the DL initial value and the

decay velocity versus the germinating vigour – ie.,

total seedling elongation at the 15

and 30

day after

imbibition.

These preliminary series used old (2 years)

samples, already with their vigour depreciated by the

long storage time in natural condition, and so just

few groups presented significant germination vigour

while four of them are almost dead.

Next series of experiments would replicate this

type of analysis but using fresh seed samples (< 1

year), which may present very high germination

capacity, and also with artificially (thermal) stressed

samples, in order to have also groups with

intermediate vigour.

Although limited in number and range of seed

quality, the preliminary data here presented show

that the DL measurements of coffee seeds may be

used as a fast, non-invasive, non-destructive test to

verify sample’s viability, and so help in improving

post-harvest treatment, storing methods and maybe

GerminationVigourversusDelayedLuminescenceofCoffeeSeeds-PreliminarySeries

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Figure 3: Seedling’s length for viable groups at the 15

and 30

days after imbibition - each group has 200 seeds total.

Figure 4: Seedling’s total length at the 15

and 30

day versus the hyperbolic decay fitting parameters - (left) the b factor

and (right) the c factor; dashed line correspond to linear regression (R

>0.85).

also beverage quality.

ACKNOWLEDGEMENTS

Authors acknowledge Brazilian Coffee Research

Consortium (Embrapa Coffee/UFLA/IAC) for

providing the seed samples, CNPq (Conselho

Nacional de Pesquisa) and FAPESP (Fundação de

Amparo à Pesquisa do Estado de São Paulo,

#04/10146-3) for partial laboratory support.

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