Aqueous Enzymatic Extraction of Buriti ( Mauritia Flexuosa ) Oil : Yield and Antioxidant Compounds

The study was carried out in two steps. The first assessed the efficiency of different enzymes (cellulase, pectinase, and protease) and the variables of greater influence in the extraction process, being conducted for each enzyme a CCRD design. The second step was carried out with the enzyme that showed the best performance on the extraction yield, changing the experimental bands of the variables that had greater significance in the first step, with the goal of broadening the spectrum of study. Were also evaluated in this step, total carotenoids, total phenolic compounds, and the antioxidant capacity of the oils extracted.


INTRODUCTION
Buriti palm (Mauritia flexuosa Lf) belongs to the family Arecaceae and is widely distributed across the Amazon Forest in Brazil [1,2].It grows in swamps and in seasonally flooded areas along rivers and forests [3].Buriti has great ecological, accounts for the reddish orange color of the oil [5,10,11].
Conventional oil extraction processes for oilseeds or fruit pulp involve mechanical and solvent extraction [12 -15].In face of environmental safety and risks to public health, the food industry is being required to employ alternatives to the organic solvents used in oil extraction, such as enzyme-assisted aqueous extraction, an emerging environmentally friendly technology [14,16].This process has been widely applied to extract oil from a variety of fruits and seeds [14 -27].
Enzymatic aqueous extraction employs enzymes that hydrolyze and break cell walls of the material, making the structure more permeable and further exposing the oil component [28,29].
This study aimed to apply a CCRD to the enzymatic extraction process of buriti oil.The effects of different enzymes (cellulase, pectinase, and protease) and significant variables that impacted oil yield were investigated.In the first step, the enzyme was selected and the most significant variables determined.Next, a second CCRD was carried out with different ranges for the most significant variables to determine the optimal extraction conditions.Besides yield, total carotenoids, total phenolic compounds, and antioxidant capacity (ABTS method) of the oils extracted were assessed.

Raw Material
The raw material used was buriti pulp and skin (mesocarp and epicarp), purchased at the Ver-o-Peso market in the city of Belém, PA, Brazil.The raw material was stored at -10 °C in 1 kg packages until use.

Total Lipid Content
The total amount of buriti oil was determined using solvents [30].Solvent extraction of buriti samples produced 9.4 ± 0.2 g oil.100g -1 (wet basis) of buriti pulp+skin, which was considered 100% yield to bench mark the oil produced by aqueous extraction.

Enzymatic Aqueous Extraction Process
The extraction process used 10 g of pulp+skin added with distilled water at a 1:1 ratio (m/v) in an Erlenmeyer flask.Next, the enzyme was added according to the concentration established in each assay.This mixture was placed in an orbital shaker at 150 rpm under the temperature and time conditions defined for each assay.After incubation, the enzymes were inactivated at 75 °C for 5 min and the mixture was centrifuged for 20 min at 4,000 g to separate the oily phase.
Extraction yield was calculated as percentages according to Equation 1.

(1)
Where: Wo is the mass of buriti oil obtained through enzymatic extraction (g), Wp is the sample mass (g), and Wt is the total mass of oil obtained through solvent extraction.
The study of the enzymatic extraction process of buriti oil was done in two steps: The first assessed the efficiency of the different enzymes in the extraction process through a 2 3 full factorial experimental design with three replicates at the central point using a CCRD, with a total of 17 assays per enzyme studied (cellulase, pectinase, and protease).This aimed to assess the influence of the independent variables (enzyme concentration ([E]), reaction time (t), and reaction temperature (T)) on oil yield.
Table 1 presents the coded and actual values of the variables in the enzymatic treatment of the first step of the extraction process.
After the enzyme that gave the best yield was defined, the second step of the enzymatic extraction process was performed using a CCRD combined with the Response Surface Methodology (RSM).The ranges of the independent variables ([E], t, and T) were changed according to the significance of the first CCRD.In addition, the speed of the orbital shaker was changed to 120 rpm and the sample mass was five times greater.The optimal extraction conditions were assessed based on the yield and concentration of total carotenoids in the oil.Where Y represents the response predicted and βo, βi, βii, and βij are the regression coefficients of the variables for intercept, linear (L), quadratic (Q), and interaction terms, respectively.Xi and Xj are the levels of the coded independent variables. (2)

Total Carotenoids
Total carotenoid content was determined by scanning spectrophotometry according to the methodology described by Rodriguez Amaya [30].The content was calculated based on absorption at the maximum absorption wavelength and absorbance value (A) of 2,592 in petroleum ether.The values were expressed as µg β-carotene per gram of oil (μg β-carotene.g -1 ).

Total Phenolic Compounds
The total concentration of phenolic compounds in the oil (1 g oil in 80% methanol) was quantified using the Folin-Ciocalteu reagent [32] with small changes.A 300 µL aliquot of methanolic extract was mixed with 5 mL Folin-Ciocalteu reagent (10% in distilled water).After 5 min, 4 mL Na 2 CO 3 (7.5% in distilled water) were added.The samples were incubated for 1 h at room temperature protected from light Absorbance was measured at 765 nm.The standard curve was prepared with galic acid.The results were expressed as mg of gallic acid equivalent per g of sample (µg GAE.g -1 ).

Antioxidant Capacity
Antioxidant activity of buriti oil was quantified based on the ABTS radical method as described by Rufino et al. [33] with the modifications of Pellegrini et al. [34].

RESULTS AND DISCUSSION
The most significant effect in the extraction process with cellulase was temperature (L) followed by time (L), whose effects were positive and indicated a directly proportional relation with extraction yield.Oil yield from pumpkin seed (Cucurbita maxima) increased with temperature and the rate of reactions catalyzed by the enzymes [13].According to Jiang et al. [21] and Santos and Ferrari [34], the breakdown of cell wall components can be increased by extending the incubation time, which, consequently, enhances oil extraction yield.
When pectinase was used, the most significant effect for the extraction process was time (L).Temperature (L) had a negative effect, i.e., higher temperatures led to lower yield.The same behavior was observed by Gai et al. [35] for oil extraction from Isatis indigotica seeds.According to those authors, higher temperatures inactivated the enzyme.
The most significant effect in the extraction process with protease was temperature (L), which had a positive effect, as well as time (L) and enzyme concentration (L).
Analysis of variance was applied to all responses Tables 4, 5 and 6 and showed the significance of the regression and nonsignificance of the lack-of-fit at 95% confidence (P < 0.05).The F value calculated for the regression was higher than the F tabulated and p-value was lower than 0.05.That shows the model defined by the regression is appropriate to represent the mechanism of the aqueous enzymatic process of oil extraction in the conditions studied.  1) shows the response surfaces generated through the model proposed for the yield of cellulase, pectinase, and protease, respectively.These surfaces confirm the analysis of effects carried out previously and enable visualizing the variation of the response for each parameter studied.
According to the response surfaces for cellulase, yield increased with increases in temperature and time and the region from 3.7 to 4.68% of enzyme concentration also led to higher yield.  1) for pectinase showed that the parameters with the greatest impact on yield are time and enzyme concentration.Temperature, however, has inverse effect on yield, i.e., the higher the temperature, the lower the yield for the same enzyme concentration.In addition, a decrease in temperature and enzyme conce-ntrations below 1.5% and above 4.4% with a process time of 2.8 h resulted in the highest yield.
The response surfaces for protease showed that the parameter with the greatest impact on yield was temperature.Yields below 60% were obtained at temperatures below 50 °C for any enzyme concentration and times under 2.5 h.The highest yields were obtained at over 52 °C, enzyme concentration over 2.8%, and time over 3.4 h.
Cellulase was chosen for the second step of the extraction process since it obtained the highest oil yield.To allow for the analysis of the antioxidant compounds in the oils extracted, the extraction scale had to be increased for the second step of the CCRD, besides decreasing shaker rotation to prevent the formation of emulsion verified.According to Yang et al. [36], oil extracted by aqueous extraction commonly emulsifies, which can be prevented by adjusting shaking.Table 7 presents the experimental results of the CCRD as a function of yield and total carotenoids of buriti oil.The results showed that the best conditions for oil recovery and highest total carotenoid concentration were found in assay 8 at 76.5% of the total oil content of buriti pulp+skin and concentration of 3,119.5 µg β-carotene.g -1 oil at 55 °C, [E] of 2%, and time of 6 h.
The yields of the oils obtained through enzymatic extraction are equivalent to or higher than that from the conventional method of pressing, whose maximum yield is around 80% of the total oil in the seed [12].The yield is lower compared to solvent extraction (above 99% oil extraction), however, oil quality decreases when that methodology is used [12,37].That makes enzymatic aqueous extraction a promising alternative since the oils extracted have higher quality than those extracted by traditional methods [18, 27, 38 -40].
The most significant effect for the extraction process was time (L).Liu,Jiang and Li [41] observed that increases in time or temperature increased oil extraction from watermelon seeds.
Analysis of variance, presented in Table 8, shows the model is significant.F calculated for yield (F cal = 93.1 > F tab = 3.4) is approximately 27 higher than F tabulated and P < 0.0196 shows this regression was statistically significant at 95% confidence.In addition, the R 2 value (multiple correlation coefficient) of the regression equation obtained was 0.9558 (value > 0.75 indicates aptitude of the model), which means the model can explain 95.6% of the variation in response.ANOVA for total carotenoids Table 9 showed significance of the regression and non-significance of the lack-of-fit at 95% confidence (P < 0.05), while R  2a), the range with the highest yield is for enzyme concentration between 1.50 and 2.34%, temperature from 47 to 57 °C, and time of 4 h.In Fig. (2b), with temperatures above 45 °C and time over 5.5 h, yields were around 75%.Yields around 80% were obtained with time above 4.7 h, enzyme concentration above 1.2%, and temperature of 50 °C, shown in Fig. (2c).
An increase in enzyme concentration for the same temperature and time resulted in higher yield.Gai et al. [35] extracted oil from Isatis indigotica seeds and observed that higher enzyme concentration favored oil extraction and higher yield.Najafian et al. [19], Teixeira et al. [27], and Santos and Ferrari [34] observed the same behavior in the extraction of oil from olives, palm, and soybean, respectively.
An analysis of Fig. (2), shows the parameters that had the greatest impact on total carotenoids were enzyme concentration and temperature.The highest total carotenoid concentration in buriti oil was obtained using temperature between 52 and 58.41 °C, enzyme conce-ntration between 1.8 and 2.34%, and time between 5 and 7.36 h.
The assays of the enzymatic process obtained higher total carotenoid values than those found in the literature [3, 4, 42 -45].
The mean values of total phenolic compounds for the buriti oil samples are presented in Table 7. Assay 14, with 254 ± 5 µg GAE.g -1 oil, obtained the highest amount of phenolic compounds using temperature of 50 °C, enzyme concentration of 1.5% and time of 7.36 h.Time impacted total phenolic concentration, i.e., the longer the extraction, the higher the phenolic compound concentration.Ribeiro [46] characterized buriti oil and found 303 µg GAE.g -1 oil for phenolic compounds.Jiao et al. [13] used a blend of enzymes (cellulase, pectinase, and proteinase) for enzymatic aqueous extraction of oil from pumpkin seeds and reported that the total phenolic compounds extracted by this method (128.8 µg GAE.g -1 oil) were higher than through soxhlet extraction (73.3 µg GAE.g -1 oil).
The means and standard deviations for antioxidant capacity data through ABTS•+ are presented in Table 7. Assay 17 obtained the highest antioxidant potential with 218.0 ± 0.3 µmol Trolox.g -1 oil at temperature of 50 °C, enzyme concentration of 1.5%, and time of 4 h.
Increasing temperature from 45 °C to 55 °C increased antioxidant capacity, which was also observed when time was extended from 2 to 6 h.Decreasing enzyme conce-ntration from 1 to 2% decreased antioxidant capacity.
Luzia [47] determined the antioxidant capacity of oils from seeds of seven species of the Brazilian Cerrado biome, among which buriti seed oil had an antioxidant potential of 0.9 µmol Trolox.g -1 oil.

CONCLUSION
Enzymatic aqueous extraction led to good buriti oil extraction results, with higher or equivalent yields compared to pressing extraction, but less than solvent extraction.Among the studied enzymes, the cellulase presented the best extraction yield.Increasing the temperature, time and concentration of enzyme favored oil yield.The most significant variable for the process was the time.The extracted oils obtained with a high concentration of total carotenoids, total phenolic compounds and antioxidant capacity, presented better nutritional quality than those extracted by traditional methods.This methodology is viable and environmen-tally friendly, does not produce volatile organic compounds as atmospheric pollutants, and its byproducts such as protein and fiber have high quality functional properties free of toxins, thus they can be applied to other processes.

ETHICS
APPROVAL AND CONSENT TO PARTICIPATE Not applicable.

HUMAN AND ANIMAL RIGHTS
No animals/humans were used for studies that are the basis of this research.

Fig. (
Fig. (1) shows the response surfaces generated through the model proposed for the yield of cellulase, pectinase, and protease, respectively.These surfaces confirm the analysis of effects carried out previously and enable visualizing the Fig. (1a) shows that the highest yields were obtained between 53 and 61.82 °C and enzyme concentration of 3.7 to 4.68%.In Fig. (1b), temperature from 50 to 61.82 °C and time from 2.5 to 3.68 h had the highest yields.In Fig. (1c), time from 2.7 to 3.68 h and enzyme concentration from 3.5 to 4.68% produced the best yields.An analysis of Fig. (

Fig. ( 1
Fig. (1).Response surface for effects of (a) enzyme concentration with temperature; (b) time with temperature; and (c) time with enzyme concentration for oil extraction yield using cellulase, pectinase, and protease.
2 was 0.9450, indicating the model explained 94.5% of the variation in experimental data.The response surfaces from the model proposed are presented in Fig. (2a, 2b and 2c) for yield and (2d), (2e), and (2f) for total carotenoids.According to the response surfaces Fig. (2), yield increased with time.In Fig. (

Fig. ( 2 )
Fig. (2).Response surface for effect of (a, d) enzyme concentration with temperature; (b, e) time with temperature; (c, f) time with enzyme concentration for yield and total carotenoids.

Table 2
presents the coded and actual values of the variables in the enzymatic treatment of the second step of the enzymatic extraction process.

Table 1 . Levels of variables for enzymatic treatment of different enzymes: selection of enzymes and most significant variables.
T: extraction temperature (°C); [E]: enzyme concentration in relation to fruit mass (% m/v); t: reaction time (h).

Table 2 . Levels of variables for enzymatic treatment: optimization of the process.
T: extraction temperature (°C); [E]: enzyme concentration in relation to fruit mass (% m/v); t: reaction time (h).

Table 3 . Experimental matrix of the enzymatic aqueous extraction process for different enzymes.
T: extraction temperature (°C); [E]: enzyme concentration in relation to fruit mass (% m/v); t: reaction time (h).

Table 3
presents the results of the CCRD for the different enzymes studied.Assay 8 for cellulase obtained the highest oil extraction yield with 95.9% at 55 °C, [E] of 4%, and time of 3 h.The lowest extraction value was obtained in assay 1 for protease with 41.3% at 35 °C, [E] of 2%, and time of 1 h.

Table 8 . Analysis of variance of yield.
*Significant effects at 5% significance.

Table 9 . Analysis of variance of total carotenoids.
*Significant effects at 5% significance.