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Endo-[beta]-mannanase enzyme activity in the structures of Coffea arabica L. seeds under different types of processing and drying/ Atividade da enzima endo-[beta]-mananase nas estruturas de sementes de Coffea arabica L. submetidas a diferentes tipos de processamentos e secagem.

INTRODUCTION

Enzymes play a fundamental role in various metabolic reactions, both in synthesis and in degradation of molecules during seed germination, development, and deterioration. Thus, they can be used as markers of these processes.

Various factors can affect seed germination. Endosperm is one of the structures that surround the embryo, and it can retard or prevent seed germination, acting as a physical barrier to radicle emergence (SILVA et al., 2005; BISOGNIN et al., 2008; REGO et al., 2011). For the germination process to occur, some enzymes act to degrade the endosperm, increasing the speed and the percentage of seed germination, thus facilitating radicle growth and emergence (NASCIMENTO et al., 2002).

Coffee seeds have a resistant layer, the endosperm, that surrounds the embryo and that can contribute to delay germination. This endosperm must be ruptured because it constitutes a barrier, imposed by the tissues of the endosperm surrounding the embryo (FREITAS et al., 2017). The region where the radicle emerges, called endosperm cap, is composed of high cellulose and hemicellulose polysaccharide content, which confers resistance and protection to the embryo (SILVA et al., 2005; EIRA et al., 2006).

Some authors have affirmed that for seed germination to occur, the endosperm cap must be weakened through the activity of the endo-[beta]-mannanase enzyme, as occurs in seeds of several species, such as Datura ferox (ARANA et al., 2006), peppers (Capsicum spp.) (CAIXETA et al., 2014), coffee (Coffea arabica L.) (SILVA et al., 2004), and lettuce (Lactuca sativa) (ALBUQUERQUE et al., 2010).

Endo-[beta]-mannanase is considered one of the main enzymes responsible for hydrolysis of the mannans present in the endosperm cap during coffee seed germination, acting in hydrolytic degradation of the cell walls and in the process of weakening the structures of the endosperm that surround the embryo, thus allowing primary root emergence (SILVA et al., 2004; SCHRODER et al., 2009).

Loss in quality of coffee seeds is related to the post-harvest treatments of processing and drying. Dry processing consists of drying the whole fruit, i.e., with exocarp (hull), mesocarp (pulp and mucilage), and endocarp (parchment), giving rise to what is known as dry cherry coffee or natural coffee (BOREM, 2008). Furthermore, according to the author, wet processing, which gives rise to parchment coffees, can be carried out in different manners: mechanical removal of the hull or pulp and part of the mucilage gives rise to pulped coffee; mechanical removal of the hull or pulp and removal of the mucilage by biological fermentation gives rise to fully-washed coffee; and mechanical removal of the hull or pulp and of the mucilage gives rise to semi-washed coffee.

Currently, high temperatures are often applied for faster drying of natural coffees, and lower temperatures for fully-washed coffees. This procedure is adopted through the belief that since the natural coffee beans/seeds are still in the fruit, they are more resistant to drying and less exposed to damage than the fully-washed coffee beans/seeds. However, results obtained from some authors confirmed that wet processed (fully-washed) coffees are more tolerant to drying than dry processed (natural) coffees (TAVEIRA et al., 2015).

Nevertheless, these post-harvest treatments affect endo-[beta]-mannanase enzyme activity and the chemical constitution and integrity of the enzyme systems, affecting physiological quality of coffee seeds (SAATH et al., 2014; TAVEIRA et al., 2015).

The aim of this study was to determine endo-[beta]-mannanase enzyme activity in the structures of soaked coffee seeds for the purpose of evaluating the relationship between this activity and the effects of different processes and drying methods of coffee fruit on the physiological quality of coffee seeds.

MATERIALS AND METHODS

The study was conducted in the Central Seed Laboratory of the Agriculture Department of the Universidade Federal de Lavras, Lavras, MG, Brazil. Coffea arabica L. fruits were collected in the cherry maturity stage and subjected to three different types of processing: natural (seeds maintained in the fruit itself), fully washed (mechanically pulped fruit and mucilage removed from the seeds through fermentation in water for 24 hours at 25[degrees]C), and semi washed (fruit pulped and mucilage removed both mechanically). Two drying methods were used: one slower drying method in the shade on a suspended screen, and another more rapid drying method in a mechanical dryer at a temperature of 35[degrees]C until the seeds reached moisture content of 11 [+ or -] 1%. Natural coffees were dried in the fruit itself, and the fully-washed and semi-washed coffees were dried in their parchment. After processing and drying, the seeds were evaluated for their physiological quality by the germination test, in which the percentage of normal seedlings was determined, according to the guidelines of the Rules for Seed Analysis (BRASIL, 2009), with germination papers moistened in distilled water, at a 30[degrees]C for 30 days. The percentage of strong normal seedlings was also evaluated (considered as those with a hypocotyl length greater than or equal to 2cm), as well as the percentage of seedlings with expanded cotyledonary leaves at 45 days after sowing.

Evaluation of endo-[beta]-mannanase enzyme activity was determined in whole coffee seeds and in embryos and endosperms separated from the seeds after soaking in distilled water for 10 days under a constant temperature of 30[degrees]C. Whole seeds, embryos, and endosperms were ground up in a mill cooled to 4[degrees]C in the presence of antioxidant polyvinylpyrrolidone (PVP).

In microtubes containing 200mg of ground seeds, 600 [micro]L of extraction buffer was added containing 0.1M Hepes and 0.5M NaCl (pH 8.0) plus ascorbic acid at the rate of 5mg of acid for each ml of buffer. After that, the microtubes were vortexed for 1 minute and centrifuged at 10,000g for 30 minutes at 4 [degrees]C. The supernatant was applied to gel prepared with 6mL of LBG (Locust Bean Gum-Sigma), 0.24g of agarose (Qbiogene), and 24mL of buffer, pH 5.0. Gel casters were covered with Gel Bond[R] Film and gel was applied to them, and after solidification, the gel was stored in a refrigerator for 24 hours and was then pierced with a 2mm diameter punch. The quantity of 2 [micro]L of enzyme extract were applied to each hole, with 3 replications of each sample. For the enzyme present in the extract to act, the gel was kept in a germinator at a 25[degrees]C for 21 hours in the dark in a moist chamber (plastic trays lined with two sheets of paper towel moistened in distilled water and sealed with plastic wrap).

For reading, the gel was first washed in distilled water, then washed in buffer solution (gel buffer) for 30 minutes, and once more washed in distilled water. The gel was covered with 0.5% Congo red dye for 30 minutes and placed in ethanol for 10 minutes to remove the dye. After removing the ethanol with distilled water, a 1M NaCl solution was added until visual observation of white halo formation in the holes containing the samples. At that time, the diameter of the samples was measured with a caliper rule. A standard curve generated by the commercial endo-[beta]-mannanase of Aspergillus niger (Megazyme) was used to calculate endo-[beta]-mannanase enzyme activity, in accordance with DOWNIE et al. (1994).

Results of physiological evaluation were analyzed in a completely randomized design in a 3x2 factorial arrangement, consisting of three methods of processing the fruit (natural, fully-washed, semi-washed) and two methods of drying (slow drying, and rapid drying in a dryer), with four replications. Results of endo-[beta]-mannanase enzyme activity were analyzed in a completely randomized design in a 3x3x2 factorial arrangement, composed of three methods of processing the fruit (natural, fully-washed, semi-washed), three different structures of seeds (whole seed, embryo, and endosperm) and two methods of drying (drying in the shade and in a dryer), with three replications. Data were subjected to analysis of variance and mean values were compared by the Scott-Knott test (p>0.05) through the statistical program SISVAR (FERREIRA, 2011).

RESULTS AND DISCUSSION

According to the results of analysis of variance, in physiological evaluation of Coffea arabica L seeds, a significant effect of interaction was reported on the processing and drying factors on the results of normal seedlings as evaluated in the germination test 30 days after sowing. There was a significant effect of the processing and drying factors separately for strong normal seedlings and expanded cotyledonary leaves.

The physiological performance of naturally processed coffee seeds was lower compared to that of fully-washed and semi-washed seeds, considering the percentage of strong normal seedlings and of seedlings with expanded cotyledonary leaves (Table 1).

In the coffee seeds originating from fully-washed and semi-washed fruit, there was an increase in physiological quality, and this may be related to the effect of these manners of processing on the chemical and enzymatic composition of the seeds (FREITAS et al., 2017). Some authors affirmed that fully-washed coffees have superior beverage characteristics compared to natural coffees (SELMAR et al., 2006; BYTOF et al., 2007). This difference should not be attributed only to the form of processing, but also to the occurrence of undesirable fermentations that are often associated with dry processing, as well as lack of care at the time of harvest and drying of natural coffee (BOREM, 2008). Damage to coffee seeds during the processing and drying steps has been indicated as one of the main causes of loss of physiological quality (ZONTA, 2008).

In this study, the drying method also affected the physiological quality of coffee seeds since there was a significant decline in quality in seeds subjected to rapid drying in a mechanical dryer, as can be observed by the higher percentages of strong normal seedlings and seedlings with expanded cotyledonary leaves after slow drying, compared to rapid drying (Table 2). These results corroborate the results of VIEIRA et al. (2007), who reported that rapid drying decreases the vigor and viability of coffee seeds.

Studies performed on coffee have shown the effect of processing and drying methods on the physiological quality of seeds, as well as physical and biochemical changes that may affect aroma and flavor (BYTOF et al., 2007; BOREM, 2008). During the drying process, seeds undergo physical changes, brought about by temperature and moisture gradations that lead to reduction in the percentage and speed of germination, and also increase the percentage of abnormal seedlings (ZONTA, 2008).

At 30 days after sowing, coffee seeds that underwent slow drying, regardless of the form of processing, had better physiological performance than the seeds that underwent rapid drying and were under the natural and semi-washed processes; the other treatments were not different from each other (Table 3). Coffee seeds under natural processing and rapid drying had lower physiological quality than the other treatments, which were not different from each other in regard to the drying used.

Reduction in the physiological quality of coffee seeds when they are dried within the fruit itself (natural coffee), compared to parchment coffees (fully-washed coffee), has been attributed to undesirable fermentations that may occur during drying (SAATH et al., 2014; TAVEIRA et al., 2015). In addition to undesirable fermentations, natural processing may cause biochemical and physiological changes that hurt the physiological performance of coffee seeds. From these results, it can be inferred that natural coffees are more sensitive to stresses than parchment coffees. A possible explanation for this is the fact that dry processed (natural) coffees are exposed to drying air for longer periods, exposing the endosperm and the embryo to more severe thermal damage and contributing to greater loss of cell membrane activity (SAATH et al., 2014; TAVEIRA et al., 2015).

Regarding the results of endo-[beta]-mannanase enzyme activity, in coffee seeds soaked for 10 days, there was significant triple interaction of the processing x drying x seed structure factors. When seeds were subjected to slow drying, greater endo-[beta]-mannanase enzyme activity was reported in the embryo of the naturally processed seeds (Table 4).

In coffee seeds under rapid drying, greater expression of endo-[beta]-mannanase was observed in the endosperm of seeds that passed through natural processing. In this same manner of processing, lower expression of the enzyme was observed in whole seeds when under rapid drying. In fully-washed and semi-washed seeds, there were no significant differences in the different structures analyzed in regard to rapid or slow drying.

When whole seeds were used for determination of endo-[beta]-mannanase activity there were no significant differences, regardless of the type of processing and the drying method. The enzyme activity determined in the endosperms of seeds under slow drying also did not differ in regard to the manners of processing used. However, greater activity of the endo-[beta]-mannanase enzyme was reported in seeds under natural processing, in the endosperm and in the embryo of seeds under rapid drying, and in the embryos of seeds that were under slow drying (Table 4).

This result may be related to greater loss of quality in seeds kept in the fruit (natural processing) during drying, which was also observed in other studies. These seeds remain in the fruit for a longer time during drying, accelerating the deterioration process and thus increasing the activity of the enzyme that is directly linked with deterioration, or, otherwise, the longer drying time of seeds under natural processing may lead to denaturation of some enzymes (SAATH et al., 2014). The activity of the endo-[beta]-mannanase enzyme also occurs in coffee seeds during storage, showing evidence of its relationship to an advancing deterioration process (VEIGA et al., 2007).

In contrast, different results have been observed, in which there was reduction in endo-[beta]-mannanase enzyme activity during the storage of lettuce seeds; i.e., the greater the deterioration, the lower the activity of this enzyme (PIMENTEL et al., 2012).

Although, significant differences were not reported, a tendency of reduction in endo-[beta]-mannanase enzyme activity is observed in seeds that passed through the mucilage removal process, in all the seed structures (Table 4).

According to table 5, rapid drying led to reduction in endo-[beta]-mannanase activity in whole seeds and in the embryos of coffee seeds under natural processing; however, lower enzyme activity was reported in endosperms when slow drying and natural processing were used. The other treatments did not differ from each other, regardless of the drying, processing, or structure used.

These results corroborate those reported by DUSSERT et al. (2006), who affirmed that during processing and drying of seeds and grains, changes may occur in the relative composition of phospholipids of membranes in the synthesis of heat resistant proteins and in the ability of seeds to prevent, tolerate, or repair damage from free radicals.

Seeds under natural processing remain within the fruit, under the action of compounds present in the exocarp, in the mesocarp, and in the endocarp, favoring the oxidation process, leading to deterioration of coffee seeds. These structures make for greater moisture transfer to the seeds within them, which may favor the beginning of the process of weakening the structures of the endosperm that surround the embryo. This promotes an increase in activity of the cellulase enzyme, followed by an increase in endo-[beta]-mannanase activity (SCHRODER et al., 2009).

Furthermore, the pericarp imposes a certain restriction on gas exchanges, increasing seed respiration and, consequently, deterioration, increasing the activity of enzymes directly connected with deterioration, as is the case of endo-[beta]-mannanase, as reported in this study.

CONCLUSION

Coffee seeds submitted to natural processing have lower physiological performance, as well as greater deterioration and greater activity of the endo-[beta]-mannanase enzyme. Removal of mucilage during fully washed and semi-washed processing of coffee seeds reduces the activity of the endo-[beta]-mannanase enzyme and lowers deterioration, especially after faster drying. The enzyme endo-[beta]-mannanase is efficient in studying of the effects of processing and drying on coffee seeds, and can be evaluated in whole seeds, endosperms or embryos.

http://dx.doi.org/10.1590/0103-8478cr20170839

ACKNOWLEDGMENTS

Our thanks to the Empresa Brasileira de Pesquisa Agropecuaria (EMBRAPA), to the Fundacao de Amparo a Pesquisa do Estado de Minas Gerais (FAPEMIG), and to the Instituto Nacional de Ciencia e Tecnologia do Cafe (INCT Cafe) for the resources and scholarships provided.

DECLARATION OF CONFLICTING INTERESTS

The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

AUTHORS' CONTRIBUTIONS

All authors contributed equally for the conception and writing of the manuscript. All authors critically revised the manuscript and approved of the final version.

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Valquiria Fatima Ferreira (1) (ID) Marcela Andreotti Ricaldoni (1) (ID) Sttela Dellyzete Veiga Franco da Rosa (2) * Madeleine Alves de Figueiredo (1) (ID) Stefania Vilas Boas Coelho (1) (ID) Tatiana Botelho Fantazzini (1) (ID)

(1) Departamento de Agricultura, Universidade Federal de Lavras (UFLA), Campus da UFLA, Lavras, MG, Brasil. (2) Empresa Brasileira de Pesquisa Agropecuaria, Embrapa Cafe, Parque Estacao Biologica (PqEB), 70770-901, Brasilia, DF, Brasil.

E-mail: sttela.rosa@embrapa.br. 'Corresponding author.

Received 11.18.17 Approved 10.13.18 Returned by the author 11.02.18 CR-2017-0839.R2
Table 1--Percentage of strong normal seedlings and seedlings with
expanded cotyledonary leaves originating from coffee seeds under
different manners of processing.

Processing     Strong normal       Seedlings with
                 seedlings      expanded cotyledonary
                                        leaves

Fully washed        71a                  30a
Semi washed         70a                  38a
Natural             25b                  16b
CV(%)              20.31                41.02

Mean values followed by the same letter in the column do not differ
from each other by the Scott-Knott test at 5% probability.

Table 2--Percentage of strong normal seedlings and seedlings with
expanded cotyledonary leaves originating from coffee seeds under
different drying methods.

Drying method   Strong normal    Seedlings with expanded
                  seedlings        cotyledonary leaves

Rapid                41b                   17b
Slow                 64a                   36a
CV (%)              20.31                 41.02

* Mean values followed by the same letter in the column do not differ
from each other by the Scott-Knott test at 5% probability.

Table 3--Normal seedlings at 30 days originated from coffee seeds
under different types of processing and drying methods.

Processing     Drying method

               Slow                  Rapid

Fully washed   88Aa                  82Aa
Semi-washed    93Aa                  83Ab
Natural        85Aa                  27Bb
CV (%)                         655

* Mean values followed by the same lowercase letter in the line and
uppercase letter in the column do not differ from each other by the
Scott-Knott test at 5% probability.

Table 4--Endo-[beta]-mannanase enzyme activity in whole seeds and in
different structures of coffee seeds under different types of
processing and drying methods.

Processing     Rapid drying                          Slow drying

               Whole seeds    Endosperms   Embryos   Whole seeds

Natural           2.01Ac       11.29Aa     6.27Ab      6.13Ab
Fully washed      3.07Aa        3.68Ba     2.49Ba      4.75Aa
Semi-washed       2.06Aa        1.82Ba     2.27Ba      2.15Aa

Processing     Slow drying

               Endosperms   Embryos

Natural          6.12Ab     32.72Aa
Fully washed     4.73Aa     3.27Ba
Semi-washed      3.48Aa     3.27Ba

* Mean values followed by the same lowercase letter in the line and
uppercase letter in the column do not differ from each other by the

Scott-Knott test at 5% probability.

Table 5--Endo-[beta]-mannanase enzyme activity in whole seeds and in
different structures of coffee seeds under different types of
processing and drying methods.

Processing     Whole            Endosperms           Embryos
               seeds
                                Drying
                                methods

               Rapid    Slow      Rapid      Slow     Rapid     Slow

Natural        2.01B    6.13A     11.29A     6.12B    6.27B    32.72A
Fully washed   3.07A    4.75A     3.68A      4.73A    2.49A    3.27A
Semi-washed    2.06A    2.15A     1.82A      3.48A    2.27A    3.27A

* Mean values followed by the same uppercase letter in the line do
not differ from each other by the Scott-Knott test at 5% probability.
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Title Annotation:CROP PRODUCTION
Author:Ferreira, Valquiria Fatima; Ricaldoni, Marcela Andreotti; da Rosa, Sttela Dellyzete Veiga Franco; de
Publication:Ciencia Rural
Date:Dec 1, 2018
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