INTRODUCTION
Blueberries (Vaccinium myrtillus) are the
fourth most economically valuable fruit worldwide due to their antioxidant
content and ability to endure diverse agroclimatic conditions (Faria et al.,
2005). These nutritional benefits make blueberries a highly desirable fruit
(Carpio, 2019). They are low in sodium, rich in fibre, refreshing, tonic,
astringent, diuretic, and contain vitamin C and hippuric acid. Numerous studies
have examined the advantageous effects of consuming berries, due to their
ability to influence cellular metabolism and reduce the impact of free radicals
associated with ageing, heart disease, cancer, Alzheimer's and elevated HDL
levels (Bilawal et al., 2021). In addition, there is a correlation with a lower
incidence of cardiovascular conditions (Habanova et al., 2016).
The climatic diversity of the Andean region
facilitates the growth of many native berries (Parodi & Benavides, 2021).
This potential extends to 7,000 hectares, thereby presenting substantial
commercial opportunities (Sierra and Selva Exportadora, 2016).
On the contrary, coffee production and its processing
result in a significant amount of by-products, including 39.4% of pulp, 21.6%
of mucilage, and 10.4% of exocarp (Pinto et al., 2013). Sadly, these
by-products remain underutilized and are inadequately discarded, thus causing
water and soil contamination (Pinto et al., 2013; Dadi et al., 2018). An
estimated 82,000 tonnes of coffee mucilage are discharged annually into
streams, rivers, or lakes (Pinto et al., 2013; Dadi et al., 2018). This is a
problem as the organic content in the effluent reduces the oxygen levels by up
to 0.25 mg/L (Dadi et al., 2018). The presence of organic matter and nutrient
content poses a significant risk of eutrophication. The primary factors
affecting the pollutant parameters of the water resource are the variations in
soaking time of coffee beans, the fermentation of pulp, and the absence of
suitable treatment facilities (Dadi et al., 2018).
The existence of coffee fermentation by-products has
prompted researchers to seek environment-friendly alternatives and strategies
by using these substances to create a new type of product like edible films. These
films are being put on fruits and vegetables to hinder the proliferation and
dispersion of external pathogens, thereby prolonging their preservation
(V zquez-Briones, 2013; Fern ndez et al., 2017; Aguilar-Duran, 2020). Edible
coatings are a sustainable technology used in many products to control moisture
transfer, gas exchange, and oxidation processes (Dhall, 2013). They add an
extra protective layer to the product and can have the same effect as modified
atmosphere packaging by regulating internal gases (Dhall, 2013; Al-Tayyar et
al., 2020). One of the main benefits of using edible coatings is the ability to
add different active ingredients to the polymeric matrix, which can be safely
consumed along with food. This enhances the overall safety, nutritional, and
sensory qualities (Aguirre-Vargas, 2015; Fern ndez et al., 2017). Coatings
comprising of carbohydrates, proteins, and lipids have demonstrated a high
efficacy in preserving fruits and vegetables (Riva et al., 2020; Al-Tayyar et
al., 2020). Furthermore, these coatings are safe for consumption along with the
produce (Aguirre-Vargas, 2015).
With the goal of utilizing coffee byproducts, this
study aims to evaluate the quality and shelf life of Vaccinium myrtillus
blueberries coated with edible Coffea arabica mucilage. The intention is
also to increase the duration of blueberry storage.
MATERIALS AND METHODS
The experiment implemented a completely randomized
design (CRD) with a 3Ax3B factorial arrangement of three independent variables.
The first factor, A, was the percentage of coffee mucilage (%) at levels 5, 6,
and 7. The second factor, B, was the storage temperature ( C), with levels of
20 2, 4, and -1. There were 9 treatments in total, each with 3 replications
across 27 experimental units.
Obtaining coffee mucilage and edible coating
Pulped, mature coffee beans from the Lonya Chico
district of Luya Province in the Amazonas Region were utilized in this
research. The methodology used by Gonz lez (2011) was followed to acquire
powdered mucilage. Similarly, the edible coating was created by adapting the
methodology described by Gonz lez (2011), using mucilage obtained in the
Agroindustrial Technology laboratory at the National University Toribio
Rodr guez of Mendoza.
Application of the edible coating
The formulation process involved creating a mucilage
solution combined with distilled water, with varying concentrations of 5%, 6%,
and 7% w/v. This was accomplished through constant stirring over a period of 90
minutes. Additionally, glycerol (20%) and starch (2.5%) were introduced to this
blend. To apply the coating, it was cooled in the refrigerator at 4 C, a
process that was completed by immersing the blueberry berries for 30 seconds.
After drying with the aid of a fan for six hours, the berries were spread out
and coated before being stored in polyethylene (PET) trays to be preserved at a
range of temperatures, including those for refrigeration and freezing [-1, 4,
20 2].
Evaluation of pH and total soluble solids (degrees
Brix)
The juice was obtained by crushing the fruits in a
mortar, and then measured using a digital potentiometer in accordance with AOAC:
Official Methods of Analysis, 2005. The percentage of soluble solids in the
obtained juice was determined using a manual ATC refractometer with temperature
compensation, based on the same standard.
Blueberry Fruit Weight
Loss
The weights of the fruit
were determined using the gravimetry method and were expressed in grams. The
percentage of weight loss was calculated in relation to the initial weight of
the fruits before preservation (100%) using the subsequent equation:
Acidez
titulable
The acidity of the fruit extract was
determined using the titration method. Citric acid was selected as the acidity
indicator due to its prominence according to the AOAC: Official Methods of
Analysis, 2005. To a 50 mL container, 1 mL of fruit extract, 9 mL of ultrapure
water and 3 drops of phenolphthalein were added. The mixture was subsequently
titrated with 0.1 N sodium hydroxide (NaOH) until a change of colour was
observed, and the information was carefully documented.
Determination of ashes
The ash percentage was determined by incinerating
organic matter in the muffle at 500 C to 600 C until weight stabilization was
achieved, using method No. 940.26 and formula specified by the standard (AOAC:
Official Methods of Analysis, 2005).
m2 = The mass in grams of
the capsule containing the ashes.
m1
= The mass of the capsule containing the sample is expressed in grams
m0
= The mass of the empty capsule in grams.
Sensorial
analysis
Twelve
consumer type panelists, partially trained, participated in measuring the
attributes of color, appearance, texture, flavour, aroma, and acceptance using
a 10-point hedonic scale.
Data Analysis
Before
carrying out any analysis of variance, it was confirmed that normality and
homogeneity of variance prerequisites were met. For data with normally
distributed, homogeneous variances, ANOVA and mean comparisons were undertaken
employing Tukey (a = 0.05). In case of data not conforming to normality
assumptions and showing heterogeneous variances, non-parametric analysis of
variance was conducted using the Friedman test.
RESULTS
Physicochemical analysis of mucilage and blueberry
Physical and chemical analyses of both the mucilage
and blueberries show similar low pH with close titratable acidity. However,
blueberries have a significantly higher Brix value (14.05) compared to
mucilage, which only has 4.17 Brix. Moreover, mucilage has a higher ash content
of 4.09%, while blueberries have a high percentage of moisture at 70.53% (Table
1).
Table
1.
Physicochemical analysis for mucilage powder and fresh
blueberry
|
Parameters
|
Mucilage powder
|
Blueberry
|
|
pH
|
3.77
|
3.52
|
|
Titratable acidity (%)
|
1.21
|
1.25
|
|
Brix
|
4.17
|
14.05
|
|
Fiber
|
6
|
1.28
|
|
Ashes (%)
|
4.09
|
0.44
|
|
Humidity (%)
|
9.67
|
70.53
|
Percentage of acidity in blueberry fruits after
applying the coating
During the 28-day storage period at commercial
maturity, the blueberries exhibited an average titratable acidity of 10.3 g
citric acid per 100 g of sample. The percentage of acidity fluctuated between
0.99% and 1.13% of titratable acidity during storage, with T1 (concentration of
5 at -1 C) and T8 (concentration at 4 C) treatments having the highest
percentage of titratable acidity (1.12% and 1.13%, respectively) compared to
the control sample that registered 0.95% (Figure 1).
Table 2. Titratable
acidity was measured in the various treatments.
|
Treatments
|
Acid percentage
|
|
T1 (C5 X 20 C), 5% coffee
mucilage + 20 C Storage temperature.
|
1.12
|
|
T2 (C5 X 4 C), 5% coffee
mucilage + 4 C Storage temperature.
|
1.06
|
|
T3 (C5 X -1 C), 5% coffee
mucilage + -1 C Storage temperature.
|
99
|
|
T4 (C6 X 20 C), 6% coffee
mucilage + 20 C Storage temperature.
|
1.06
|
|
T5 (C6 X 4 C), 6% coffee
mucilage + 4 C Storage temperature
|
1.01
|
|
T6 (C6 X -1 C), 6% coffee
mucilage + -1 C Storage temperature
|
1.01
|
|
T7 (C7 X 20 C), 7% coffee
mucilage + 20 C Storage temperature
|
1.08
|
|
T8 (C7 X 4 C), 7% coffee
mucilage + 4 C Storage temperature
|
1.13
|
|
T9 (C7 X -1 C), 7% coffee
mucilage + -1 C Storage temperature
|
1.03
|
|
T0 (Control) without
coverage to 20 C Storage temperature
|
0.95
|
C5: Formulated with 50 grams of coffee
mucilage, 25 grams of starch, and 200 grams of glycerol.
C6: Formulated with 60 grams of coffee
mucilage, 25 grams of starch, and 200 grams of glycerol.
C7: Formulated with 50 grams of coffee
mucilage, 25 grams of starch, and 200 grams of glycerol.
Total soluble solids content
Our analysis indicates
that blueberries coated with an edible coating and stored at temperatures of 4
C and -1 C have a higher sugar content as compared to those stored at room
temperature (20 2 C). Among all the treatments, T2 (C5 x4 C) showed the
highest concentration of Brix, measuring 14.1. This suggests a significant
difference among storage temperatures when concentration and temperature
interact. However, the other treatments did not show any significant difference
between them (Figure 1).
Figure 1.
Interaction between
concentration and temperature on soluble solids content in blueberries coated
with an outer layer.
pH analysis
The pH of blueberries decreases when applying the
coffee mucilage coating, resulting in a pH of 1.8. In comparison, the control
group had a higher level of 3.7. The group with the lowest pH value was T1 with a concentration of 7 at 20 C,
registering a value of 1.8 (Figure 2).
Figure 2.
pH variation in coated blueberry.
Weight loss percentage
The weight change
percentage during the 28-day storage period is presented. Treatments at room
temperature underwent the greatest weight loss during storage. The control
treatment (S/R without coating) experienced the highest weight loss percentage
at 22.9%, while the best treatment T1 (C5x-1 C) had the lowest weight loss
percentage at 6.1% when treated with the coating (Figure 3).
Figure 3.
Percentage of weight loss in cranberry-coated berries at different storage
temperatures.
Sensorial analysis
Figure
4 shows the results of the Friedman non-parametric test, which reveals a
significant difference among treatments with a p-value of less than 0.05
(0.0039). T3, with a 5% concentration and storage at -1 C, and T2, with a 5%
concentration and storage at 4 C, performed the best in terms of the organoleptic
characteristic "Appearance" (Figure 4-A). The treatments T3, T6, and
T9, stored at -1 C with concentrations of 5%, 6%, and 7% respectively, were
found to be the most effective for preserving the blueberry fruit's color,
according to the organoleptic criterion (Figure 4-B). Therefore, these
treatments are expected to yield better results at the given concentrations. On
the other hand, T1 (5% concentration) stored at -1 C was found to be the most
successful treatment for preserving the blueberry fruit's aroma, according to
the same criterion (Figure 4-C). Finally, the optimal treatments for the
sensory attribute "Texture" were T1 with a 5% concentration,
maintained at -1 C, and T2 with a 5% concentration, stored at 4 C (Figure 4-D).
Figure
4. Sensory analysis of blueberry berries treated with edible
blueberry coating.
DISCUSSIONS
Blueberries have a high perishability
rate, necessitating proper handling for delivering a superior product to
consumers (Forney et al. 2022). Although blueberry fruits can endure high
levels of CO2, prolonged exposure can result in fruit softening and discoloration
of the pulp (Alsmairat et al., 2011). Recently, blueberries and other fruits
have gained attention from the food industry and consumers due to their highly
effective antioxidant properties, which may protect against cancer and aging
(Feng et al., 2022). However, transporting these fruits over long distances
can decrease their moisture content, rendering current conservation methods
inefficient (Feng et al., 2022). Looking for solutions that are
product-friendly or easy to use is a common response to such problems. For
instance, one possible solution is storing the product in controlled
atmospheres (Forney et al. 2022), even though this may result in a considerable
increase in acidity (Forney et al. 2022). However, when employing alternative techniques
like edible coatings, as utilized in this study, the level of titratable
acidity decreases, providing a beneficial characteristic for fruit preservation
and enhancing nutritional quality when treated with this natural coating.
Regarding soluble solids ( Brix), it has been
determined that there is an increase in sugars, which is a function of mucilage
concentrations and storage temperatures. This increase is due to the conversion
of organic acids into reserve carbohydrates and subsequently into simple
saccharides, driven by the low photosynthetic capacity (Ayala et al., 2012).
Technical terms such as Brix will be explained since ripe fruits rely on this
type of sugar for the formation of organic compounds that determine their color,
flavor, and quality (Liu et al. 2016; Li et al. 2022). Therefore, while fruits
treated with RC and stored at low temperatures maintain their sugar content,
their sugar content increases as the temperature rises (20 C), despite the
coating treatment. This effect also corresponds to weight loss. Blueberries
treated with coatings and stored at three different temperatures (-1, 5, and 20
C) exhibited significant differences in weight loss after 28 days of storage
in comparison to untreated berries, which experienced greater weight loss at
all three storage temperatures. This indicates that dehydration occurs in
untreated fruit due to the transpiration process, while treated fruit retain
their weight better. (Triunfo et al. 2023): The edible coating (RC), such as
coffee mucilage, produces a semi-permeable effect that acts as a barrier for
the passage of CO2 and RH (Relative Humidity). This effect bestows the fruits
with the desired marketable and consumer-oriented characteristics.
As storage time increases, the pH decreases due to
accelerated degradation of cellulosic substances, resulting in loss of firmness
and an increase in soluble sugars (Lupano, 2013). The study revealed pH
variations and increases (from 3.4 to 3.7) among different treatments compared
to the initial measurement of 3.52. This could possibly be due to the ripening
of the fruits, since as time passes the soluble solids increase and the pH also
increases. It is not unusual, since the shelf life of blackberry fruits can be
extended for 15 days at 4 C of storage, preserving the physicochemical and
physiological properties by using a coating based on hydroxypropyl
methylcelluloseH (PMC) with the inclusion of bee era (CA). (Villegas &
Albarrac n, 2016). These ways of preserving fruits or vegetables guarantee food
security and quality food for consumption or for agricultural export.
This study emphasizes the significance of
employing natural coatings like coffee pulp mucilage as an alternative to
extend the shelf life of Andean fruits like blueberries. Additionally, aloe
vera gels present themselves as another conservation option (Vieira et al.,
2016; Ates et al., 2022). Therefore, this study provides support and
reliability to the demonstrated results regarding the utilization of coffee
mucilage as an alternative solution to address dehydration problems. The
proliferation of fungi and bacteria due to dehydration results in degradation
and subsequent economic losses for the producers and other stakeholders in the
Andean fruit production chain.
CONCLUSIONS
The
coffee mucilage and plasticizer in the coating significantly reduce blueberry
fruit weight loss, potentially extending their shelf life. Concentrations of
the three coating components - coffee mucilage, cassava starch, and glycerol-cause
rapid changes in weight, texture, appearance, color, aroma, and flavor. Thus,
the optimal mixture for the coating consisted of 5% coffee mucilage, 2.5%
starch, and 20% glycerol, resulting in decreased weight loss at temperatures of
-1, 4, and 20 C. Thus, the optimal mixture for the coating consisted of 5%
coffee mucilage, 2.5% starch, and 20% glycerol, resulting in decreased weight
loss at temperatures of -1, 4, and 20 C. This lays the foundation for
potential future utilization on diverse Andean fruits.
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