Thermal and non-thermal treatments in the processing of cagaita nectar

Abstract

This work aimed to analyze cagaita nectar subjected to different thermal and non-thermal treatments regarding its quality over 30 days of storage (5 °C). Ultra (U) and thermosonication (T) were the techniques used for 30 and 60 minutes of processing samples. These techniques proved to be effective to preserve physicochemical quality, regarding rheology and texture, since ultra and thermosonicated samples had their consistency increased when compared to the pasteurized sample over 30 days, a desirable factor for a fruit nectar. Samples treated more intensely with ultrasound and temperature (Pasteurized, U 25 °C/60 min and T 60 °C/ 30 min) showed higher soluble solids content. The sample U 25 °C/60 min increased its brightness, reduced its firmness and also its consistency after 30 storage days. For all samples there was an increase in carotenoids content and a maintenance of viscosity and cohesiveness (texture) over 30 days, thus indicating that the used treatments can be feasible instead of pasteurization, maintaining the shelf life of cagaita nectar in the time evaluated.

Keywords

beverage storage period bioactives ultrasound thermosonication

INTRODUCTION

The savannas, woodlands and forests of Cerrado, in Brazil, have the growth of native fruits of great economic, nutritional and social potential (Guedes et al., 2017; Siqueira et al., 2018). Among the various native fruits, Eugenia dysenterica DC., from Cerrado, popularly known as cagaita, is a fruit of globular shape, slightly flattened, with thin skin and light yellow color (Martins et al., 2017). Its pulp has significant amounts of phenolic compounds and minerals (Guedes et al., 2017). Because it is a very perishable fruit, cagaita is mostly consumed processed. Its low pH, low titratable acidity, and high humidity favor its use in the production of beverages (Martins et al., 2017), such as nectar, a non-fermented beverage intended for direct consumption (Brasil, 2009), and usually obtained by traditional pasteurization process.

Among the conservation methods most used in the food industry are the heat treatments, one of which is pasteurization. Study by Oliveira et al. (2016), subjected cagaita nectar to slow (65 °C/30min) and fast (72−75 °C/15s) pasteurization, carried out in a water bath and cooling in an ice bath. As well as the study by Bedetti et al. (2013), with cagaita nectar placed in glass jars and pasteurized at 65 ± 1 °C for 30 min. The pasteurization act on the sensory quality, destroying enzymes and pathogenic and/or spoiling microorganisms (Barros et al., 2020). However, they are usually associated with sensory and bioactive compounds content alterations in foods, which should be studied in order to optimize processing.

In this context, considered an emerging technology, sonication has been an excellent substitute for thermal processing in the food industry, since it spends less energy and time and still sufficiently reduces the levels of microorganisms present in fruits and fruit juices (Aadil et al., 2015). Therefore, commercial pasteurization or sterilization options are available with the non-thermal methods of microfiltration and ultrasound, for example, in addition to thermosonication, which uses lower temperatures combined with sonication, avoiding greater energy expenditures in the search for the maintenance of flavor, color, aroma, texture, and nutrients of the food. So, this research is pionner in study the cagaita nectar processing at different temperature and ultrasound condictions.

Given the scarcity of studies on the fruit of cagaita and its insertion in the market in the form of nectar being possible, the objective of this study is to elaborate a nectar of cagaita and evaluate it after thermal and non-thermal treatments.

MATERIALS AND METHODS

Raw materials and nectar preparation

The cagaita pulp used in this study was purchased from Sítio do Bello (Paraibuna, SP, Brazil). The fruits, all from the same batch, are from the 2019 harvest and had their pulp (unprocessed) kept frozen until their use (−18 °C). Besides the pulp, mineral water and sucrose were purchased in the city of Maringá (PR) to formulate the nectar. The other reagents used were of analytical grade (Synth - São Paulo - Brazil).

Cagaita nectar was prepared by mixing 50% pulp (defrost at 5 °C) and 50% water. Sugar was added until the final concentration of 8% (Bedetti et al., 2013). Soon after it was produced, the nectar was stored in glass bottles with a lid and kept under refrigeration (5 °C) until the development of the treatments (performed in replicates) and the analyses.

Thermal and non-thermal treatments

A total of 5 treatments were obtained, being them in the different types of processing, named: P (pasteurized nectar); U30′ (nectar ultrasonicated for 30 min at 25 °C); U60′ (nectar ultrasonicated for 60 min at 25 °C); T40 °C/30′ (nectar thermosonicated for 30 min at 40 °C); T60 °C/30′ (nectar thermosonicated for 30 min at 60 °C). Experiments were done in replication.

In the pasteurization, 1.2 L of the nectar were stored in two previously sterilized glass bottles (capacity 650 mL), each containing 600 mL of the beverage, to be processed by rapid pasteurization. For this, the bottles were completely immersed in a heating bath (Nova Orgânica Refrigerated Bath) at 85 °C (temperature was controlled manually using a thermometer inside the bottles) for 60 s (Souza et al., 2019). After treatment, the bottles were placed in a refrigerator (5 °C) for further analysis.

Ultrasonication was performed using an ultrasonic bath (40 Hkz - Ultronique, model Q3.0/40A), with aliquots of 500 mL of nectar placed in glass beakers and ultrasonicated for 30 and 60 min (Souza et al., 2019). After the treatments, the nectars were transferred to plastic bottles with lids and cooled to room temperature (25 °C) to perform the analyses.

For the thermosonication an ultrasonic bath was used (40 Hkz - Ultronique, model Q3.0/40A, 88 w power) with maintenance of the nectar temperature (with an automatic thermometer controller) according to tests I and II. In test I, the nectar was kept at 40 °C for 30 min, while in test II, the nectar was kept at 60 °C for 30 min (Souza et al., 2019). After thermosonication and cooling the nectar to room temperature (25 °C) the analyses were performed.

According to previous tests, the time of 30 min was adopted for the thermosonication, since the contents of bioactive compounds did not show significant difference compared to the same treatment for 60 min (with the same temperature).

Characteristics of frozen pulp and nectars

The frozen pulp was evaluated for pH, titratable acidity, color, and soluble solids content. Subsequently, the nectars produced were evaluated for their physicochemical characteristics to better evaluate the processing (at the times right after manufacturing and after 30 days of storage cooled at 5 °C).

Titratable acidity, pH, soluble solids content and color

The titratable acidity was determined according to the recommendations of the Association Official Agricultural Chemists – AOAC (2004). The pH was determined by means of a bench top digital potentiometer model mPA210 (MS Technopon®, Piracicaba, Brazil), by inserting the electrode into the sample, which was previously calibrated with pH 4.0 e 7.0.

The reading of the soluble solids content (SSC) was performed using a digital refractometer (Instruterm®, São Paulo, Brazil) with distilled water as a blank parameter. The results were expressed in °Brix.

The color was quantitative measurement with the help of a previously calibrated colorimeter (Konica Minolta®, model CR- 410, Tokyo, Japan). Measurements of the color parameters L* (brightness), + a* (red-green component) and + b* (yellow-blue) were recorded. The ΔEab values were calculated with equation 1 (Bernat et al., 2014). All mensuriments described in this section were done in triplicate.

Δ E a b = \sqrt (Δ L)^{2} + (Δ a)^{2} + (Δ b)^{2}

(1)

Centesimal composition

The centesimal composition was determined by means of the following procedures: humidity (direct drying in an oven at 105 °C until constant weight), ashes by incineration at 550 °C, lipids by the Bligh Dyer method, proteins by the Micro-Kjeldahl method and carbohydrates by difference, according to the recommendations of the Association Official Agricultural Chemists – AOAC (2004).

Texture Parameters

The texture parameters (firmness, cohesiveness, viscosity and consistency) were determined using a texturometer (TA.XT Express Stable Microsystems Microsystems®, London, England) equipped with a stainless steel probe of 36 stainless steel probe (P 36R) (TextureExponent Lite® software version 6.1.4). The analysis was conducted at 25 °C under the following conditions: compression depth compression depth of 10 mm; test speed of 1 mm/s, pre-test speed of 1 mm/s, post-test speed of 10 mm/s and force of 1 g (Januário et al., 2018).

Rheology

The rheological measurements were performed by means of steady state flow tests (flow curves) in a DV2T model viscometer with coupling for small samples, using SC4-18 rod and constant temperature of 11 °C. To obtain the flow curves, shear stress sweeps were performed: the first with increasing strain rate (0 to 300 s⁻¹) and the second decreasing (300 to 0 s⁻¹). The data from the curve were fitted to the Power Law model by nonlinear regression analysis using Rheocalc T 1.2.19 software.

Analysis of bioactive compounds

After preparing the nectars from different treatments, the samples were centrifuged (Hettich Centrifuge, model Universal 320 R) at 8000/min (15 minutes at 20 °C) to perform the bioactive quantification analyses.

The determination of total phenolic compounds was performed by measuring the absorbance in a spectrophotometer (FEMTO Spectrophotometer, model 700 Plus) at 725 nm after 30 min of incubation (Pierpoint, 2004; Singleton and Rossi, 1965). Gallic acid was used as standard for the calibration curve (R² = 0.9971). The results were expressed as μg of gallic acid equivalent (GAE) mg⁻¹ of product.

The analysis for the determination of carotenoids was performed according to Rodriguez-Amaya (2001). The absorbance of the samples was read in a spectrophotometer (FEMTO Spectrophotometer, model 700 Plus) at 450 nm.

Antioxidant activity by the method DPPH• and ABTS • + radical method

The determination of the antioxidant activity by the DPPH- method was performed according to the methodology described by Thaipong et al. (2006). After 1 h of reaction, the absorbance (515 nm) was read in a spectrophotometer (FEMTO Spectrophotometer, model 700 Plus). The antioxidant capacity of the samples was given in μmol of Trolox equivalent per mL of sample, calculated from a Trolox standard curve (R² = 0.994).

The determination of the ABTS- + radical inhibition activity was performed according to Rufino et al. (2007). After the reaction, the absorbance reading was at 734 nm in a spectrophotometer (FEMTO Spectrophotometer, model 700 Plus). The antioxidant capacity of the samples was given in μmol of Trolox equivalent per mg of sample, calculated from a standard curve of Trolox (R² = 0.9944).

Microbiological characterization

According to the RDC n°. 12 of 2001 and 331/2019 from the National Health Surveillance Agency, from serial dilutions were evaluated: presence of coliforms at 35 °C for 48 h and molds and yeasts were evaluated using the Spread-plate technique in Potato Dextrose Agar acidified in 10% Tartaric Acid incubated at 25 °C during 5 days, the microbiological of the samples was according to the APHA methodology, Compendium of Methods for the Microbiological of Methods for the Microbiological Examination of Foods, 5th Ed.

Data analysis

Data were subjected to analysis of variance and Tukey's test (p < 0.05) for the least significant difference between means (for both difference between processed samples and storage time) using the statistical program SISVAR version 5.6.

Results and discussions

Physicochemical characterization

Characterization of frozen cagaita pulp

Table 1 shows the results of physicochemical analysis and centesimal composition performed on the frozen cagaita pulp used to prepare the nectar.

Table 1.

Mean values for physical-chemical analysis of the frozen cagaita (Eugenia dysenterica) pulp.

Analysis	Result
pH	3.80 ± 0.08
Soluble Solids Content	5.47 ± 0.02 °Brix
Titratable Acidity	4.31 ± 0.22g citric acid/ 100g
Color – L	41.87 ± 0.4
a*	−1.48 ± 0.21
b*	12.72 ± 0.38
Humidity	94.39 ± 0.05%
Ashes	0.19 ± 0.04%
Proteins	Not significant
Lipids	Not significant
Carbohydrates	5.41%

Based on the data obtained and according to the work of Alvarenga et al. (2019), who studied physicochemical parameters of cagaita pulp at different stages of maturity, the results presented in Table 1 show that the pulp used in this study was probably prepared with fruits at stage 1 of maturity (fruits with greenish to yellowish peels), with low soluble solids content and high pH values and citric acid content compared to a ripe fruit (3.10 and 0.65 g/100 g, respectively), besides low carbohydrate content (5.41%).

In the centesimal composition, finally, the pulp showed no lipid content and was low in ash, protein and carbohydrate, but high in humidity. According to Silva et al. (2015) the cagaita pulp produced with fully ripe fruits presents low percentage of ash (0.28%), probably due to the high content of water present in the fruits (approximately 90%), of lipids (1.02%) and carbohydrates (5.94%). Being a pulp produced from unripe fruits in the case of the study presented here, it is observed that there is a higher content of humidity and lower contents of lipids and carbohydrates, when compared to the author cited above.

Characterization of the nectars

The freshly prepared nectars showed no significant difference between them (p > 0.05) for pH values (day 1) and remained at acceptable levels for the to the food industry, since pH values below 4 restrict the growth of microorganisms (Vera et al., 2003). After 30 days of storage under refrigeration, only the sample U 60 min differed (p < 0.05) from the others and had its pH value reduced (approximately 1.6%), as did the samples thermosonicated throughout the storage. This same behavior was observed for the camu-camu nectar without thermal treatment studied by Maeda et al. (2007), in which there was a reduction (by 3.5%) of the pH at the end of 30 days of refrigerated storage and absence of light.

For titratable acidity, none of the samples it had significant differences from each other (p > 0.05) both on day 1, as the results observed by Abid et al. (2013) for apple juice, and on day 30. According to Lima et al. (2008), when there is no significant decrease in the titratable acidity value or increase in pH, it is observed that the organic acids that are present in cagaita nectar did not oxidize throughout the storage of the product.

As for the soluble solids content, the highest contents for day 1 were found in samples P, U 60 min and T 60 °C/30 min, differing from the other samples (p < 0.05), results that suggest that more intense treatments in temperature and ultrasound (generation of high pressure gradients created by cavitation) possibly cause colloidal disintegration, dispersion and lysis of macromolecules into into smaller particles (Abid et al., 2013) to be accounted for as soluble solids in the medium. The samples U 60 min and T 40 °C/30 min were the only ones that maintained their initial soluble solids contents after 30 days. Mattietto et al. (2007) verified that the soluble solids content of mixed nectar of cajá and umbu remained constant until the first 30 days of storage, followed by a decline and then remained unchanged until 90 days.

The color parameters indicate that the sample U 30 min presented the highest value for brightness, differing (p < 0.05) only from sample P for day 1. On day 30, the L parameter became equal at all samples, without differing significantly significantly (p > 0.05). At the end of storage, the samples P (2.48% increase) and U 60 min (2.15% increase) were clearer. Cândido Filho and Bergamasco (2014) observed an increase (approximately 6%) in luminosity in passion fruit nectar enriched with β-cyclodextrin after 30 days of storage.

Regarding the parameters a* and b*, there were significant differences (p < 0.05) among the samples. It is observed that with the passage of time there was an increase in color intensity as indicated by the significant increase in the a* factor, except for sample U 60 min that did not change significantly (p > 0.05). Ordóñez-Santos et al. (2017) state that the effect of ultrasound can intensify the color of juices (variations from yellow to red), justified by the formation of hydroxyls from the hydroxylation of aromatic rings of phenols.

Moreover, the samples P and T 60 °C/ 30 min presented intensification of the yellow tone (b* factor) when analyzed separately with the passing of 30 days of storage differing significantly from the other samples (p < 0.05), although the ultrasonicated samples kept their initial yellowish tone and the sample T 40 °C/30 min presented reduction. In terms of the b* parameter, finally, samples P and T 60 °C/30 min differed from all the others on day 1, with significantly lower results, suggesting that the treatments made the colors of the products less intense in yellow possibly due to the action of temperature on the pigments present.

The ΔE values obtained ranged from 0.40 to 2.20 (Table 2). According to Bernat et al. (2014), ΔE* values less than 3 cannot be easily detected by human eyes and values greater than 12 imply absolutely different color spaces. Therefore, changes in the color of cagaita nectar would likely be sensory imperceptible, given the results obtained in this study.

Table 2.

Parameters of pH, soluble solids content, titratable acidity and color for the nectars of different treatments and storage times.

Parameters	Storage time (days)	P	Formulations*
Parameters	Storage time (days)	P	U 30 min	U 60 min	T 40 °C/ 30 min	T 60 °C/ 30 min
pH	1	3.23 ^aa ± 0.01	3.22^aA ± 0.01	3.21^aA ± 0.02	3.21^aA ± 0.01	3.22^aA ± 0.01
	30	3.21^aA ± 0.04	3.19 ^abA ± 0.04	3.16^dB ± 0.04	3.17 ^bcB ± 0.02	3.17 ^bcB ± 0.02
SSC (°brix)	1	10.60 ^abb ± 0.00	10.50^bB ± 0.00	10.60^abA ± 0.00	10.53^bA ± 0.00	10.70^aA ± 0.00
	30	10.70^aA ± 0.00	10.60^abA ± 0.00	10.63^abA ± 0.00	10.50^bA ± 0.00	10.60^abB ± 0.00
Titratable acidity (g	1	1.91^aa ± 0.00	1.93^aA ± 0.04	2.02^aA ± 0.04	1.91^aA ± 0.00	1.91^aA ± 0.00
citric acid /100 g)	30	1.91^aA ± 0.11	1.91^aA ± 0.01	2.03^aA ± 0.02	1.98^aA ± 0.07	1.99^aA ± 0.10
Color - L	1	39.77^bb ± 0.19	41.30^aA ± 0.41	40.09^abB ± 0.12	40.77^abA ± 0.50	40.56^abA ± 1.18
	30	40.78^aA ± 0.19	41.44^aA ± 0.32	40.97^aA ± 0.32	41.34^abA ± 0.57	41.19^aA ± 0.64
A*	1	−1.85^abB ± 0.06	−2.06^bB ± 0.02	−1.73^aA ± 0.01	−1.97^bB ± 0.01	−1.86^abB ± 0.16
	30	−1.67^abA ± 0.04	−1.82^bA ± 0.06	−1.70^abA ± 0.10	−1.63^abA ± 0.11	−1.57^aA ± 0.10
b*	1	10.80^bB ± 0.19	12.37^aA ± 0.14	11.82^aA ± 0.13	12.20^aA ± 0.07	9.66^cB ± 0.92
	30	11.86^aA ± 0.24	12.05^aA ± 0.11	11.52^abA ± 0.50	11.21^abB ± 0.50	10.83^cA ± 0.34
ΔE	1	-	2.20	1.08	1.72	1.39
	30	-	0.70	0.40	0.86	1.11

** Means ± standard deviation in the same row accompanied by lower case letters indicate significant difference (p ≤ 0.05) among the nectar formulations for the same day of storage. Means ± standard deviation in the same column accompanied by distinct capital letters indicate significant difference (p ≤0.05) for each formulation affected by storage time. *Formulations: P (pasteurized nectar); U 30 min (nectar ultrasonicated for 30 min); U 60 min (nectar ultrasonicated for 60 min); T 40 °C/ 30 min (nectar thermosonicated for 30 min at 40 °C); T 60 °C/ 30 min (nectar thermosonicated for 30 min at 60 °C). ΔE = $\sqrt[2]{Δ L *^{2} + Δ a *^{2} + Δ b *^{2}}$ .

For the texture parameters (Table 3), in the case of firmness, there was no significant difference among the samples (p > 0.05) analyzed on day 1, although on day 30 the sample U 60 min differed from the others (p < 0.05), having its value reduced (2.98%) over the 30 days. This may have been caused by the inactivation of enzymes involved in the breakdown of plant cell structures (Ketsa; Daengkanit, 1999).

Table 3.

Mean values of rheology and instrumental texture for the nectars of different treatments and storage times.

Parameters	Storage time (days)	P	Formulations*
Parameters	Storage time (days)	P	U 30 min	U 60 min	T 40 °C/ 30 min	T 60 °C/ 30 min
Texture -	1	27.73^aA ± 0.28	27.26^aA ± 0.19	27.15^aA ± 0.48	27.33^aB ± 0.28	27.81^aA ± 0.22
Firmness (g)	30	27.62^aA ± 0.39	27.92^aA ± 0.51	26.34^bB ± 0.67	28.40^aA ± 0.61	27.92^aA ± 0.80
Texture -	1	155.11^aA ± 1.28	152.94^aB ± 1.60	151.84^aA ± 3.70	151.54^aB ± 1.24	155.83^aA ± 1.87
Consistency (g.s)	30	157.92^aA ± 2.00	158.64^aA ± 1.42	148.33^bA ± 3.32	160.57^aA ± 3.11	157.23^aA ± 3.08
Texture -	1	−6.00^aA ± 0.23	−5.70^aA ± 0.28	−5.89^aA ± 0.06	−6.00^aA ± 0.23	−5.96^aA ± 0.11
Cohesiveness (g)	30	−6.03^aA ± 0.23	−6.03^aA ± 0.17	−5.77^aA ± 0.13	−7.76^aA ± 3.03	−6.14^aA ± 0.17
Texture -	1	−0.96^aA ± 0.05	−0.75^aA ± 0.11	−0.85^aA ± 0.11	−0.92^aA ± 0.01	−0.96^aA ± 0.08
Viscosity (g.s)	30	−0.85^aA ± 0.18	−0.84^aA ± 0.06	−0.83^aA ± 0.06	−1.38^aA ± 0.81	−0.87^aA ± 0.18
Rheology –	1	70.57^aA ± 2.12	60.83^aA ± 7.78	64.83^aA ± 4.88	56.80^aA ± 7.22	62.20^aA ± 9.55
Confidence of fit (%)	30	79.27^aA ± 3.01	66.27^abA ± 3.06	66.63^abA ± 5.39	59.67^bA ± 9.68	63.20^abA ± 10.05
Rheology -	1	0.59^aA ± 0.13	0.80^aB ± 0.20	0.71^aB ± 0.05	1.16^aA ± 0.13	0.80^aA ± 0.17
Consistency (Pa.s)	30	0.40^cA ± 0.13	2.17^aA ± 0.58	1.96^abA ± 0.90	1.26 ^abcA ± 0.38	1.10^bcA ± 0.20
Rheology - Flow Behavior Index	1	0.17^aA ± 0.05	0.12^aA ± 0.07	0.12^aA ± 0.04	0.05^aA ± 0.01	0.17^aA ± 0.04
Rheology - Flow Behavior Index	30	0.20^aA ± 0.07	0.14^abA ± 0.04	0.12^abA ± 0.11	0.04^bA ± 0.02	0.07^abA ± 0.03

**Means ± standard deviation in the same row accompanied by lower case letters indicate significant difference (p ≤ 0.05) among the nectar formulations for the same day of storage. Means ± standard deviation in the same column accompanied by distinct capital letters indicate significant difference (p ≤0.05) for each formulation affected by storage time. *Formulations: P (pasteurized nectar); U 30 min (nectar ultrasonicated for 30 min); U 60 min (nectar ultrasonicated for 60 min); T 40 °C/ 30 min (nectar thermosonicated for 30 min at 40 °C); T 60 °C/ 30 min (nectar thermosonicated for 30 min at 60 °C).

For consistency (referring to texture), also the sample U 60 min presented significantly (p < 0.05) lower than the others after 30 days of storage, and the samples U 30 min and T 40 °C/ 30 min increased their consistency throughout the time studied. The cohesiveness and viscosity data, finally, show that there was no significant difference among the samples (p > 0.05), even after the storage time.

According to Oliveira et al. (2016), who studied the rheological behavior of cagaita nectar after slow and fast pasteurizations, it was observed that the variations in thermal processing did not bring significant influence on the rheological behavior according to the Power Law. In the study presented here, this can also be observed by comparing the results of all samples, heat treated or not heat treated, with each other on day 1, which did not differ significantly (p > 0.05) for confidence of fit, consistency, or flow behavior index. Flow behavior indices with values less than 1 indicate that cagaita nectar is a pseudoplastic fluid, i.e., it loses apparent viscosity as a function of the applied strain rate (Oliveira et al., 2016), a fact observed in the study presented here, with flow index values ranging from 0.04 to 0.20.

The analyses performed on the 30th day show that the storage time did not interfere in the confidence of fit and flow behavior index factors of any of the samples analyzed separately, unlike the consistency factor (rheology), being that the ultrasonicated samples had their values increased significantly with time by an mean of 5.15 times and the thermosonified ones by 2.95 times when compared to the pasteurized sample (p < 0.05). According to Aadil et al. (2015), the quality parameters of homogeneity and consistency are desirable for fruit and vegetable juices. Such parameters have a direct link with product turbidity, which can be increased by the association of the chemical and physical effects of ultrasound, in addition to the application of heat (as in the case of thermosonication). The increase in turbidity is attributed to cavitation, since the pressure applied during the collapse promotes the breakdown of particles into smaller structures, increasing the number of particles suspended in the medium as cellulose, hemicellulose and pectin.

It is also mentioned that the rheological properties of the juice, finally, can be attributed to its processing conditions. When treating this type of product with ultrasound, its consistency can be changed permanently or temporarily, increasing or decreasing the consistency, depending on the ultrasound energy used (Soria and Villamiel, 2010).

Analysis of bioactive compounds

The data of the analyzes (Table 4), in relation to the results of the bioactive compounds of the samples from the same storage time did not differ from each other (p > 0.05), except in the case of the thermosonication at 40 °C for 30 min, which presented lower amount of phenolics after 30 days of storage compared to the other samples (p < 0.05). In the study by Dutra et al. (2012), it was observed that for mandarin myrtle juice the variations in the binomial time/temperature in its processing did not bring changes to the content of phenolic compounds, as well as observed in the study presented here (analysis of day 1).

Table 4.

Mean values of bioactive compounds for nectars from different treatments and storage times.

Parameters	Storage time (days)	P	Formulations*
Parameters	Storage time (days)	P	U 30 min	U 60 min	T 40 °C/ 30 min	T 60 °C/ 30 min
Total phenolics	1	0.151^aB ± 0.00	0.160^aB ± 0.00	0.155^aB ± 0.00	0.156^aB ± 0.00	0.157^aB ± 0.00
(ug EAG/mg)	30	0.364^aA ± 0.00	0.361^aA ± 0.00	0.359^aA ± 0.00	0.269^bA ± 0.06	0.367^aA ± 0.01
DPPH	1	1.58^aA ± 0.01	1.58^aA ± 0.00	1.59^aA ± 0.01	1.58^aA ± 0.00	1.58^aA ± 0.01
(uM ET/mg)	30	1.57^aB ± 0.00	1.56^abB ± 0.01	1.56^abB ± 0.00	1.57^aB ± 0.01	1.54^bB ± 0.02
ABTS	1	1.80^dB ± 0.22	2.24^cB ± 0.08	2.19^cB ± 0.09	2.49^bB ± 0.15	3.20^aB ± 0.10
(uM ET/mg)	30	4.38^aA ± 0.01	4.38^aA ± 0.00	4.36^aA ± 0.02	4.29^aA ± 0.10	4.30^aA ± 0.02
Carotenoids	1	59.03^bB ± 1.71	45.13^cB ± 3.29	44.19^cB ± 0.56	36.96^dB ± 1.24	124.14^aB ± 5.27
(mg/100g)	30	131.70^bA ± 4.65	124.97^cA ± 1.58	125.94^cA ± 2.41	158.62^aA ± 4.42	159.51^aA ± 4.62

**Means ± standard deviation in the same row accompanied by lower case letters indicate significant difference (p ≤ 0.05) among the nectar formulations for the same day of storage. Means ± standard deviation in the same column accompanied by distinct capital letters indicate significant difference (p ≤0.05) for each formulation affected by storage time. *Formulations: P (pasteurized nectar); U 30 min (nectar ultrasonicated for 30 min); U 60 min (nectar ultrasonicated for 60 min); T 40 °C/ 30 min (nectar thermosonicated for 30 min at 40 °C); T 60 °C/ 30 min (nectar thermosonicated for 30 min at 60 °C).

When comparing the amounts of total phenolics on days 1 and 30 in each case, it was observed that all had a significant difference (p < 0.05) and that their content increased, with the highest percentages of increase in the samples P and T 60 °C/30 min (approximately 58%), showing the increased bioavailability of these compounds for their quantification with the passing of the days of storage of refrigerated nectars.

Some authors have previously observed the increase in phenolic content over the storage period of juices and associate this event to the possibility of microbial growth or reactions between oxidized phenolics and formation of new antioxidant compounds (Kallithraka et al., 2009; Martinez-Flores et al., 2015). In addition, according to Castro-López et al. (2016), one should consider the possibility that some compounds may have formed during storage and reacted with the Folin-Ciocalteu reagent, significantly increasing the phenolic content; according to these authors, the Folin-Ciocalteu method can be affected by the presence of reducing sugars, aromatic amines, ascorbic acid, organic acids and other compounds present in fruit juices, making the result often unstable.

For the antioxidant profile analysis by DPPH, the samples on day 1 did there were no significant differences (p > 0.05), although on day 30 the antioxidant profile of the P sample was statistically equal to the ultrasonicated samples and the T 40 °C/30 min sample, differing only from the T 60 °C/30 min sample. When comparing the antioxidant profiles from days 1 and 30, it is observed that for all cases there was a significant difference (p < 0.05), with a decrease in the levels in this time interval: the ultrasonicated samples reduced, on mean, 1.58%; the P and T 40 °C/30 min samples reduced 0.63% since day 1; and the T 60 °C/30 min sample obtained the greatest reduction (2.53%). These values indicate that the DPPH profile for cagaita nectar may be impaired by the 30 days storage time.

As already observed by other authors, according to Zielinski et al. (2014), the decrease in the antioxidant profile (DPPH) may occur due to antioxidant antagonism linked to the presence of different bioactive compounds and their interactions. This scenario indicates that the nectars treated in this study should be considered as products with a short shelf life, and should be consumed within a few days of production for the benefits of bioactives to be harnessed.

In the study conducted by Souza et al. (2019), thermosonication was used in the processing of camu-camu nectar and the authors concluded that this treatment at 60 °C for 30 min increased DPPH concentrations compared to pasteurized nectar (matching the control nectar), and matched the control and pasteurized nectars regarding the contents of phenolic compounds for analyses performed soon after its production. These results suggest that the use of ultrasound can increase or maintain the bioavailability levels of bioactive compounds, helping to maintain the antioxidant capacity of camu-camu nectar, as shown by Abid et al. (2013) and Aadil et al. (2015) for apple and grapefruit juices for antioxidant capacity DPPH and phenolic compounds. In the case of the cagaita nectar of the study presented here, the antioxidant compounds (DPPH) had their contents maintained without significant difference (p > 0.05) regardless of the type of treatment for day 1.

The highest value for antioxidant profile by the ABTS method for day 1 was in the treatment of the nectar thermosonicated at 60 °C for 30 min, which differed from the other samples (p < 0.05), with the pasteurized nectar having the lowest result. Thus, as Abid et al. (2013) explained that the use of ultrasound can increase the bioavailability of bioactive compounds for apple and grapefruit (increasing their antioxidant capacity), the better result of thermosonication for this antioxidant profile of cagaita nectar can be justified. After 30 days, there was an increase of approximately 50% of the values for ABTS antioxidant profile in which the samples reached the same level of values with no significant difference between them (p > 0.05).

Sattar et al. (2020), who studied the beverage stability of peach treated by ultrasonic, pasteurization and microwave observed that antioxidant activity (ABTS) tends to increase at the end of storage for all types of treatments. This increase may be caused by several factors, such as the tendency of polyphenols to undergo polymerization reactions.

As for the carotenoids, it was observed that in the analyses on day 1, the sample thermosonicated at 60 °C for 30 min it had significant differences in relation to all the others (p < 0.05), showing a higher amount of these compounds. Although food processing can cause oxidation of the carotenoid molecules, their availability for quantification can also be improved due to dissociation or weakening of their bonds with the plant cell matrix (Saunders et al., 2000). According to Van Het Hof et al. (2000), thermal processing by heating the food, for example, can increase the bioavailability of the carotenoids present by up to 6 times. Thus, the type of processing of sample T 60 °C/ 30 min, which combines ultrasound and temperature, may have its higher carotenoid content justified. On day 30, the two thermosonicated samples showed better results, differing statistically from the others (p < 0.05).

The content of carotenoids is related to the presence of pigments that vary from yellow to red. Thus, when the instrumental color results of the nectars are resumed (Table 2), and although only the samples P and T 60 °C/ 30 min presented intensification of the yellow tone (b* factor) with the passage of time, it is observed that throughout the 30 days the carotenoid compounds became more available and were observed in larger quantities in all samples.

Considered a source of vitamin C, cagaita presents contents that can vary from 34.11 mg/ 100 g to 64 mg/ 100 g (Silva et al., 2016). In this context, the presence of ascorbic acid in juices can cause a protective effect to carotenoid compounds, which can be a direct oxidative protection or through isomerization reactions (Talcott et al., 2003), which, as indicate by the results, may be the case of the nectar studied here. The oxidation of the ascorbic acid present, still, can cause reductions in the brightness of the sample, as indicate by the results of Cândido Filho and Bergamasco (2014).

In the case of other products, such as the apple juice studied by Abid et al. (2013), the ultrasonic treatment significantly increased the antioxidant profile, phenolic compounds and among other bioactives, without affecting the physicochemical parameters.

Microbiological characterization

The results of the microbiological analyses indicated that all treatments were effective in inactivation microorganisms, culminating in insignificant growth of Coliforms incubated at 35 °C in 50 mL of nectar and <10 UFC/g of molds and yeasts for all treatments performed both on day 1 and day 30. Thus, it can be observed that there was no initial contamination in the nectar production and also no microbial growth over the 30 days.

Thus, it is possible to indicate the treatments evaluated here for microbiological control. It has been shown that microbial degradation by ultrasound action is due to the thinning of cell membranes, production of free radicals and localized heating, as well as the generation of intracellular cavitation (mechanical shocks start to break structures up to cell lysis), confirming the effectiveness of ultrasonication and thermosonication processes as commercial sterilization methods (Verruck and Prudencio, 2018).

CONCLUSION

In general, the evaluated treatments showed effectiveness regarding the physicochemical parameters. All nectars obtained were characterized by rheology as pseudoplastic fluid. The ultra and thermosonic samples had higher consistency (rheology) when compared to the pasteurized sample over 30 days, which is desirable for fruit nectars.

The thermal and non-thermal treatments, in general were feasible to process cagaita nectar. Being the treatment T 60 °C/ 30 min showed a less intense yellow color than the others (days 1 and 30), besides showing higher values for antioxidant profile (ABTS) and carotenoids (days 1 and 30) and one of the highest increases in phenolic compounds over the 30 days, showing no changes in its color brightness.

Finally, it is noted that the use of the emerging technology of ultrasound, alone or combined with temperature, has the potential to replace the traditional pasteurization process bringing benefits to processed foods, as is the case of cagaita nectar.

Footnotes

DECLARATION OF CONFLICTING INTERESTS

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

FUNDING

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iDs

Ana Paula Stafussa

Carlos Eduardo Barão

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Thermal and non-thermal treatments in the processing of cagaita nectar - Eugenia dysenterica

Abstract

Keywords

INTRODUCTION

MATERIALS AND METHODS

Raw materials and nectar preparation

Thermal and non-thermal treatments

Characteristics of frozen pulp and nectars

Titratable acidity, pH, soluble solids content and color

Centesimal composition

Texture Parameters

Rheology

Analysis of bioactive compounds

Antioxidant activity by the method DPPH• and ABTS • + radical method

Microbiological characterization

Data analysis

Results and discussions

Physicochemical characterization

Characterization of frozen cagaita pulp

Characterization of the nectars

Analysis of bioactive compounds

Microbiological characterization

CONCLUSION

Footnotes

DECLARATION OF CONFLICTING INTERESTS

FUNDING

ORCID iDs

References