Blueberry Pomace, Valorization of An Industry By-Product Source of Fibre With Antioxidant Capacity
Blueberry Pomace, Valorization of An Industry By-Product Source of Fibre With Antioxidant Capacity
Blueberry Pomace, Valorization of An Industry By-Product Source of Fibre With Antioxidant Capacity
DDOI: https://doi.org/10.1590/fst.00318
Abstract
The industrial by-product of blueberry juice, a source of fibre with antioxidant capacity was used to develop cookies. Once
dried and ground the blueberries by-product, its composition and functional properties were analyzed and used to develop fibre
enriched cookies. A central composite design was used to optimize the cookie formulation maximizing antioxidant and total
polyphenol content varying fibre content (3-9 g/100 g), baking temperature (160-180 °C) and dough thickness (0.5-1.0 cm).
Antioxidant capacity and total polyphenol content showed both a similar behaviour, increasing when fibre content increases.
The increasing of dough thickness and baking temperature decreases the antioxidant capacity and total polyphenol content.
Cookie with 9% fibre, 180 °C baking temperature and 0.50 cm dough thickness and cookie with 9% of fibre, 170°C baking
temperature and 0.75 cm dough thickness showed maximum antioxidant capacity and polyphenol content with no significant
differences between them; both cookies can be labelled using a fibre claim.
Keywords: antioxidant fibre; industry waste; blueberry pomace; response surface methodology; functional food.
Practical Application: Processing fruit into juice generates waste with its corresponding environmental impact. Blueberry
by-product could be considered a bioactive-rich ingredient with a prolonged shelf-life, source of dietary fibre and phenols.
The growing interest of consumers for eating healthy products has led the industry to improve the nutritional composition of food.
This improvement may be achieved by adding functional ingredients, like blueberry pomace, to widely consumed food products.
1 Introduction
Industrial and agricultural waste of fruit and vegetable (2009), the most consumed and popular bakery products around
processing are an important source of bioactive compounds the world are cookies for being low-cost, ready-to-eat product
(Ignat, et al., 2011) which is the case of blueberry juice industry. and involving a long shelf life. Consumers are turning to more
The blueberry juice obtention generates waste that may be up health conscious. As a result, it can be seen an increasing need for
to 20% of the initial fruit weight (Šarić et al., 2016). healthy products that led to changes in the cookies’ nutritional
Blueberries, apart from being rich in fibre, minerals and composition, which may be enhaced by adding functional
vitamins, are a relevant source of antioxidants, which have ingredients, such as blueberry pomace.
documented health promoting effects (Šarić et al., 2016). They In order to guarantee that the cookies supplemented with
have a particularly high content of polyphenols, anthocyanins, blueberry pomace are a source of fibre with antioxidant capacity,
phenolic acids, flavanols, flavonols and tannins (Szajdek & efforts should be directed to formulate the product, taking into
Borowska, 2008). Ignat et al. (2011) and Šarić et al. (2016) account formulation and process. Although it may be reasonable
observed that one of the richest sources of phenolic compounds thinking that a rise in fibre content produces an increase in
is the blueberry pomace with an important antioxidant capacity. antioxidant capacity in a direct way, this may be not at all.
There is many literature over dietary fiber and antioxidants Bilgili et al. (2007) assayed the addition of different levels of fibre
but these compounds are investigated independently as from apple in cookies and observed that an increase of fibre content
non‑related compounds, may be for the differences in their decrease the antioxidant capacity. Food fortification with fibre
chemical structures, physicochemical and biological properties, rich in phenolic compounds can result in the loss of absorption
and metabolic pathways (Saura-Calixto, 2011). of these antioxidants by trapping them within the fibre matrix
and forming chemical complexes and colloidal structures that
Blueberry by-product can be processed, to obtain blueberry reduce their bioavailability (Palafox-Carlos et al., 2011). On the
pomace powder. It could be used as ingredient with a prolonged other hand, process conditions can affect functional properties.
shelf-life. This pomace combine the physiological effects of It is known that temperature has a negative effect on bioactive
dietary fiber and antioxidants, in accordance with the concept
compounds, such as antioxidants and phenolics compounds
“antioxidant dietary fiber”, defined by Saura-Calixto (1998).
that are thermolabile in nature. Ross et al. (2011) found that in
Potential uses of blueberry pomace powder include cookies grape pomace heating at temperatures above 180 °C causes a
and cereal-based products, among others. According to Vitali et al. reduction in the antioxidant capacity.
With focus in the development of a new product source Ash was determined following ISO 5984-2002 (International
of antioxidants and dietary fibre and revalorize the blueberry Organization for Standardization, 2002). Total carbohydrates
juice waste, the aim of this work was to optimize antioxidant content was obtained by difference.
capacity and polyphenol content in the formulation of cookies
supplemented with blueberry pomace. 2.5 Phenolic compounds
Ethanol:water (50:50) solution was used to dilute the ABTS (76.5 g/100 g dwb, U.S Department of Agriculture, 2016) because
stock solution to an absorbance of 0.7 (±0.02) at 734 nm. Then, all of the non‑structural carbohydrates remain in the juice.
3 mL of this solution were added to to 30 µL of extract or Trolox
Both blueberry and derived products present low lipids
standard solution, which were left standing during 30 minutes
content. However, the blueberry pomace powder presented
in the dark.
higher lipids content than the fresh fruit (2.7 g/100 g dwb, U.S
Absorbance was read in a Shimadzu 1800 UV-Visible Department of Agriculture, 2016). The difference is mainly
spectrophotometer at 734 nm. attributed to pomace high content of seeds rich in fatty acids
resulting in an increase of the amount of lipids.
3 Statistical analysis The amount of dietary fibre is high compared to fresh
All analyses were performed in triplicate, data reported fruit (15 g/100 g dwb U.S Department of Agriculture, 2016)
as mean ±SD. One way analysis of variance (ANOVA) was due to the pomace composition, being rich in skins and seeds.
performed on each assay, and differences between samples were The main component in dried pomace is dietary fibre from cell
determined with the Tukey test (α≤0.05). wall components, which are approximately 68% (Struck et al.,
2016). The seeds are also rich in dietary fibre, especially lignin
Analyses were performed using InfoStat software (InfoStat, and hemicellulose (Moldes et al., 2003). Moreover, these
2014). components are concentrated in the pomace, since it was dried.
In the optimization study, the results were analyzed using Because of the high content of dietary fibre, pomace powder
Response Surface Methodology (RSM) (Gacula, 1993). Both may be a useful ingredient in the development of functional
Antioxidant capacity and Polyphenol content, in related with food. Functional properties of blueberry pomace powder are
independent variables (fibre content, baking temperature and shown in Table 2. The antioxidant capacity of blueberries has
dough thickness) were submitted to a multivariate regression been highly correlated to their anthocyanin and total phenolic
analysis and fitted to a second-order model equation (Equation 1) contents (Prior et al., 1998; Struck et al., 2016). Antioxidant
provided in the design: capacity was calculated as the sum of ABTS extractable and
hydrolysable fraction of the blueberry pomace powder. Results
Y =B0 + B1 X 1 + B2 X 2 + B3 X 3 + B11 X 12 + B22 X 2 2 + shown by the ABTS radical scavenging activity concluded that
(1)
B33 X 3 2 + B12 X 12 + B13 X 13 + B23 X 23 + Error 69% of the antioxidant capacity was due to the hydrolysable
fraction, related to antioxidant fibre compounds. Only 31%
where, Y is the dependent variable (Y1 is the antioxidant capacity, of the antioxidant capacity was from the extractable fraction.
Y2 is the polyphenol content), B0 is the intercept (constant), Different types of berry pomaces exhibit higher antioxidant
B1, B2, B3 the linear, B11, B22, B33 the quadratic and B12, B13, B23 capacity and total phenolic content than the fresh fruits as
the interaction effects, X1, X2 and X3 the independent variables: reported by Struck et al. (2016). This can be explained by the
fibre content, baking temperature, dough thickness. fact that antioxidants associated to wall compounds located in
the skins and seeds remain in the pomace after juice production
Software Statgraphics (Centurion XVI Version 16.1.03, (White et al., 2011).
Virginia, USA) was used.
The sum of extractable and hydrolysable fractions antioxidant
4 Results and Discussion capacity was 339.09 ± 2.69µM TE/g dwb, which is significantly
higher when compared to other berry pomaces, such as strawberry
4.1 Proximate composition and functional properties of (71.71 µM TE/g dwb), raspberry (30.89 µM TE/g dwb) and
blueberry pomace powder blackberry pomaces (12.36 µM TE/g dwb), as reported by
Blueberry pomace powder proximate composition is presented Struck et al. (2016). This difference is explained by the aggressive
in Table 1. The high protein content of blueberry pomace, extraction method used in this work for the hydrolysable
compared to the fresh fruit (4,7 g/100 g, U.S Department of phenolic fraction, which remained with the extraction
Agriculture, 2016) is related to the fact that pomace is constituted solution for 20 hours. This procedure released the antioxidants
in a 19% by skins (Lee & Wrolstad, 2004), where 5-10% of its
composition are structural proteins (Blaker & Olmstead, 2015).
The value of total carbohydrates is lower than the fresh fruit Table 2. Functional properties of blueberry pomace powder (BPP).
BPP
ABTS Extractable fraction1 104.74 ± 1.16
Table 1. Proximate composition of blueberry pomace powder (BPP). ABTS Hydrolysable fraction1 234.35 ± 2.43
Total antioxidant capacity 1,4 339.09 ± 2.69
BPP (g/100 g dwb)
Extractable phenols 2 102.34 ± 2.44
Protein 6.64 ± 0.08
Hydrolysable phenols 2 182.80 ± 3.76
Lipids 4.05 ± 0.01
Total phenols 2,4 285.14 ± 4.48
Ash 2.06 ± 0.01
Total anthocyanins 3 125.82 ± 5.89
Dietary fibre 26.15 ± 0.23 1
– in µM TE/g dry weight basis (dwb); 2– in mg gallic acid/gdwb; 3– in mg cyanidin-3-
Carbohydrates 60.941 glucoside/100g dwb; 4–Total fraction refers to the sum of extractable and hydrolysable
1
– Carbohydrates content obtained by difference. fraction.
compounds from the cell wall. A higher number of hydrolysable present that can also transfer electrons but are not phenolics
polyphenols extracted may result in a higher antioxidant capacity. (Karadag et al., 2009).
Blueberry powder antioxidant capacity was also higher than
Total anthocyanin content of the blueberry pomace dried
the result obtained by Reque et al. (2014) for blueberry flour
powder was 125.82 ± 5.89 mg cyanidin-3-glucoside/100g dwb.
(41.93 ± 0.36 µM TE/g dwb). Difference may be attributed,
Results are similar to the ones reported by Khanal et al. (2009)
neglecting the extraction method, to the processing conditions
where the anthocyanin content was 102.3 to 175.7 mg/100 g dwb.
during drying (time, temperature and drying method) since
Differences in anthocyanins content with blueberry flour reported
bioactive compounds including phenols and anthocyanins are
by Reque et al. (2014) could be attributed to the juice mashing
easily degraded (Skrede et al., 2000). Moreover, antioxidant
steps as anthocyanins are susceptible to degradative reactions
capacity is mainly due to phenolic compounds. Apart from the during various processing unit operations (Khanal et al., 2009;
skins’ compounds with antioxidant capacity, seeds are also an Skrede et al., 2000). The drying conditions of the pomace could
important source of valuable compounds. Residues of berry also affect the content of anthocyanins given their susceptibility
seeds have shown to exhibit high levels of antioxidant capacity, to degradation when exposed to heat.
being comparable to the level in herbs (Struck et al., 2016).
Anthocyanin content of blueberry pomace is generally higher
The fraction of hydrolysable polyphenol is significantly higher than in fresh fruits (Lee et al. 2002; Reque et al., 2014; Struck et al.,
compared to the extractable fraction. The sum of extractable and 2016). This is mainly related to the fact that anthocyanins exist
hydrolysable polyphenolic fraction was used to calculate total almost in the skin (Lee & Wrolstad, 2004). While disposal of
phenolic content as done by Vitali et al. (2009) and suggested blueberry waste is an important cost to the juice processing
by Saura-Calixto et al. (2007). The TPC results showed that industry, it also represents a significant loss of a rich source of
the content of soluble polyphenols was 102.34 ± 2.44 mg gallic bioactive compounds with potential health benefits. Therefore,
acid/g dwb. Phenols content concerning the hydrolysable fraction using this rich source as an ingredient is of utmost importance.
was 182.80 ± 3.76 mg gallic acid/g dwb; that is, 64% of the total
phenols are in the hydrolysable fraction, bound to dietary fibre.
4.2 Optimization of cookies’ formulation
The hydrolysable fraction along with the antioxidant capacity
would be lost as the skins of berries are not part of the juice, The antioxidant capacity and total polyphenol content of
demonstrating the high nutritional content and functional cookies are shown in Table 3. The equation that represents the
properties of the blueberry by-product and its potential use in relationship between antioxidant capacity (Y1) and total polyphenol
functional foods. Contents of total phenols are higher than berry content (Y2) with fibre content (X1), baking temperature (X2)
pomace data from Struck et al. (2016). Difference is mainly due and dough thickness (X3) are (Equation 2 and 3).
to the fact that pomace has a moisture content of approximately
3422.5 + 27.898 X 1 – 40.990 X 2 +
Y1 =
50% whereas blueberry pomace powder was dried and the (2)
compounds are highly concentrated. Besides, Folin–Ciocalteu 235.78 X 3 + 0.11856 X 2 2 – 176.70 X 3 2
assay may overestimate the content of polyphenols in cases
in which there are other compounds with reducing groups − 4432.9 + 27.900 X 1 + 51.771X 2 – 44.224 X 3 – 0.1522 X 2 2 (3)
Y2 =
Table 3. Experimental matrix design for the three factors: X1(fibre content in percentage); X2 (baking temperature in Celsius degree) and X3
(dough thickness in centimeter) and results for total polyphenol content and antioxidant capacity of cookies.
Formulation X1 X2 X3 Total polyphenol content 1 Antioxidant capacity 2
1 9 160 0.5 205.46 ± 2.30 e, f
105.23 ± 4.88 g, h
2 9 180 0.5 210.88 ± 0.73 f, g 107.97 ± 1.41 h
3 3 180 1 45.23 ± 0.81 a 16.88 ± 1.14 a
4 6 180 0.75 145.96 ± 0.06 b, c 87.89 ± 0.10 e, f
5 6 170 0.75 132.00 ± 3.47 b 90.54 ± 5.67 f, g
6 3 160 0.5 68.20 ± 2.11 a 62.73 ± 6.63 c, d
7 9 180 1 202.78 ± 0.20 e, f, g 90.03 ± 9.10 e, f, g
8 6 170 1 120.67 ± 0.15 b, c 57.30 ± 4.35 c
9 6 170 0.5 173.00 ± 0.42 d, e 74.39 ± 8.57 d, e
10 3 160 1 51.84 ± 0.28 a 34.95 ± 4.10 b
11 3 170 0.75 65.60 ± 0.13 a 13.24 ± 3.67 a
12 9 160 1 201.31 ± 0.89 e, f 104.55 ± 1.70 g, h
13 9 170 0.75 232.32 ± 1.28 g 117.22 ± 1.78 h
14 3 180 0.5 74.85 ± 0.14 a 26.57 ± 1.29 a, b
15 6 170 0.75 160.96 ± 1.51 c, d 75.58 ± 0.08 d, e, f
16 6 160 0.75 115.96 ± 2.70 b 89.60 ± 2.34 e, f, g
For each parameter, values not shearing letters differ significantly (p>0.05). 1– mg gallic acid/g wwb; 2–µM TE/g Wet weight basis (wwb).
Table 4. Estimated regression coefficients of the fitted equations obtained for Antioxidant capacity and Total polyphenol content of cookies
depending on fibre content (A), baking temperature (B) and dough thickness (C).
p-value Coefficients
Item
Antioxidant capacity Total polyphenol content Antioxidant capacity Total polyphenol content
Constant 3422.52 -4369.40
A 0.0000 0.0000 27.8984 24.9007
B 0.0082 0.1884 -40.9907 51.7717
C 0.0042 0.0006 235.785 -44.2242
AA 0.0175 0.7031 -1.29535 ns1
AB 0.0535 0.7834 ns1
ns1
AC 0.374 0.1848 ns1
ns1
BB 0.0159 0.0066 0.118569 -0.15227
BC 0.9686 0.4916 ns1 ns1
CC 0.0235 0.9912 -176.705 ns1
R2 0.9138 0.9678
Standard error 108.054 119.458
Lack-of-fit 0.6260 0.6914
1
– Terms not significantly different from zero (p>0.05).
The estimated model for antioxidant capacity was adequate effect on the antioxidant capacity (Figure 1). Zilic et al. (2016)
to describe the antioxidant capacity of cookies in a 91.83% of the found that the baking process increased the content of total
variation of the response variable (R2=0.9183) and the model phenolic compounds by affecting the solubility of bound forms
had not significant lack-of-fit (P>0.05). of phenolic acids in anthocyanin-rich corn flour cookies. They
Results of ANOVA for the model, the regression coefficients also observed that the content of phenolic compounds in the
and the coefficient of determination R2 are shown in Table 4. cookies was significantly affected by baking temperature and
baking time decreasing with the temperature and increasing
For total polyphenol content the model was able to explain with the time.
96.78% of the response variable (R2=0.9678) and the ANOVA
showed that there was no significant lack of fit (P>0.05), showing ANOVA shows that cross-products terms are not significantly
that the selected model is adequate to describe the effect of the different from zero (P>0.05) which indicates that interactions did
three independent variables on the response variables. For all not have any influence on the response variable. The correlation
of the terms in the model, a large regression coefficient and a coefficient between antioxidant capacity and total polyphenols
small p-value indicate a more significant effect on the response was 0.89, suggesting that the strong antioxidant capacity exhibited
variables (Wani et al., 2015). by the cookies is explained by the fibre added with blueberry
pomace as an ingredient.
In both models, the goodness of fit was evaluated by coefficient
of determination R2, standard error and the lack-of-fit from the Since the final goal of RSM was to optimize the cookies
analysis of variance (ANOVA). formulation (fibre, baking temperature and dough thickness), an
optimization was conducted specifying the criteria of maximum
According to the models and as it can be seen from the
response surface plots (Figure 1 and 2), antioxidant capacity antioxidant capacity and total polyphenol content. Optimum
and total polyphenol content are mainly influenced by fibre conditions for antioxidant capacity (124.174 µM TE/g wwb) were
content, having a positive effect in the studied range (3-9%). found to be 9% fibre, 160 °C baking temperature and 0.668 cm
Fibre content is provided by the blueberry pomace powder added of dough thickness. The maximum total polyphenol content was
which exhibits high values of antioxidant capacity. These results achieved at 233.185 ± 11.9460 mg gallic acid/g wwb whereas
agree with investigations in other antioxidant enriched cookies the combination of factor levels maximizing were found to be
formulations. Mir et al. (2017) studied the effect of incorporating 9% at fibre content, baking temperature 170 °C and 0.5 cm
3%, 6% and 9% apple pomace in gluten free crackers. They dough thickness.
reported that the increased amount of apple pomace in the According to results, the maximum antioxidant capacity
cookie formulation resulted in higher antioxidant properties, and polyphenol content were obtained in cookie with 9% fibre,
total dietary fibre and minerals in the final product. 180 °C baking temperature and 0.5 cm dough thickness and
For antioxidant capacity, according to the model, both cookie with 9% of fibre, 170 °C baking temperature and 0.75 cm
linear and quadratic parameters of fibre, baking temperature dough thickness, showing no significant differences between
and dough thickness were highly significant (P<0.001 or P<0.05) them. These two formulations of cookies can be labeled using
with baking temperature and dough thickness having a negative a fibre claim.
Figure 1. Effect of (a) Baking temperature and Fibre; (b) Dough Figure 2. Effect of (a) Dough thickness and Baking temperature; (b)
thickness and Baking temperature; (c) Dough thickness and Fibre on Dough thickness and Fibre; (c) Baking temperature and Fibre on Total
the Antioxidant capacity. polyphenol content.
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