article critique 2

Innovative Food Science and Emerging Technologies 27 (2015) 48–56

Contents lists available at ScienceDirect

Innovative Food Science and Emerging Technologies

journal homepage: www.elsevier.com/locate/ifset

The effect of thermal pasteurization and high pressure processing at cold and mild temperatures on the chemical composition, microbial and enzyme activity in strawberry purée

Krystian Marszałek a,⁎, Marta Mitek b, Sylwia Skąpska a a Department of Fruit and Vegetable Product Technology, Prof. Wacław Dąbrowski Institute of Agricultural and Food Biotechnology, 36 Rakowiecka str., 02532 Warsaw, Poland b Division of Fruit and Vegetable Technology, Department of Food Technology, Faculty of Food Science, Warsaw University of Life Science, 161 Nowoursynowska str., 02787 Warsaw, Poland

⁎ Corresponding author. E-mail address: [email protected] (K. Marsz

http://dx.doi.org/10.1016/j.ifset.2014.10.009 1466-8564/© 2014 Elsevier Ltd. All rights reserved.

a b s t r a c t

a r t i c l e i n f o

Article history: Received 15 July 2014 Accepted 21 October 2014 Available online 5 November 2014

Editor Proof Recieve Date 17 November 2014

Keywords: High pressure processing Thermal processing Strawberries Polyphenols Polyphenol oxidase Peroxidase

The impact of high pressure processing (HPP) at 300 or 500 MPa for 1, 5 or 15 min at 0 or 50 °C and thermal pro- cessing (TP) at 90 °C for 15 min on the quality of strawberry purée was studied. TP caused the highest degrada- tion of polyphenols (14%), anthocyanins (43%), vitamin C (61%) and color (dE N 3) but only this method effectively decreased the activity of polyphenol oxidase — PPO (97.7%), peroxidase — POD (99.5%) and microor- ganism count (b1 log cfu/g). The highest decrease of the mentioned nutrients (4%, 14%, 30%, respectively) in HPP-treated samples was noticed at 500 MPa/15 min/50 °C, whereas color changes were unnoticeable (dE b 3) and enzymes were inactivated only in 72% (PPO) and 50% (POD). Counts of yeasts and molds were re- duced to b1 log cfu/g only after TP and HPP at 500 MPa. HPP preservation at 0 °C affects the content of nutrients and color to the least extent. Industrial relevance: This study demonstrated that the nutritional and sensory qualities of strawberry purée after high pressure processing were much better than after thermal pasteurization. Purée treated with HPP at 0 °C did not show significant difference compared to fresh strawberry purée. Greater inactivation of PPO and POD was ob- served after thermal pasteurization, but this treatment caused also slightly more degradation of anthocyanins, vi- tamin C and sensory quality. The results showed that HPP might be a useful method for preservation of strawberry products. However, considering the residual enzyme activity, it will be a very important point to check the stability of the products during storage.

© 2014 Elsevier Ltd. All rights reserved.

1. Introduction

In recent years, there has been a significant increase in consumer in- terest in the quality and safety of foods (Boero, 2011; Wilke, Raab, Breuer, Hamer, & Peterson, 2013). Nowadays consumers demand top- quality food, which is safe to eat and which promotes bodily health and well-being. High quality food is usually associated with, e.g., its nat- uralness and freshness (Bigliardi & Galati, 2013; Farahani, Grunow, & Günther, 2012; Khan, Grigor, Winger, & Win, 2013). Many fruit and veg- etable products available on the market are however, highly-processed, such as clear juices, nectars, jams and preserves. The high temperature used for their processing and preservation (pasteurization, sterilization, blanching) results in undesirable changes in their organoleptic features (flavor, color, texture) and often in considerable losses in their valuable bio-active components, such as vitamin C and polyphenols, including anthocyanin pigments (Kalisz, Oszmiański, Hałdyszowski, & Mitek, 2013; Tiwari, O'Donnell, & Cullen, 2009; Verbeyst, Bogaerts, Plancken,

ałek).

Hendrickx, & Loey, 2013; Verbeyst, Oey, Plancken, Hendrickx, & Loey, 2010).

Therefore, there is a growing interest in developing innovative, non- thermal methods of preserving fruit and vegetable products, such as high pressure processing (HPP), which can ensure product safety, with limited impact on the nutritional and organoleptic quality of the raw material used.

An important factor, which should be taken into consideration when preserving fruit products with HPP, is the process temperature. High pressure coupled with elevated processing temperatures of over 20 °C could have a negative effect on the content of anthocyanin pigments, whereas treatment at less than 20 °C usually has no significant impact on their level (Corrales, Toepfl, Butz, Knorr, & Tauscher, 2008; Garcia-Palazon, Suthanthangjai, Kajda, & Zabetakis, 2004). The color of fruit products preserved using HPP without heating often seems even more intense, and therefore more attractive, due to the extraction of an- thocyanins and flavonols from the tissues to intercellular juice (Marigheto, Vial, Wright, & Hills, 2004; Otero & Prestamo, 2009). It seems interesting that cold high pressure processing (at ca. 0 °C) could be more effective for the inactivation of bacterial spores compared with the same process at room temperature. Generally, lower

49K. Marszałek et al. / Innovative Food Science and Emerging Technologies 27 (2015) 48–56

temperatures raise the costs of the process but cause fewer changes in the chemical composition of foods (Heinz & Buckow, 2009).

Strawberries are considered a fruit with special health-promoting properties, because they contain many valuable antioxidants, e.g., vitamin C and polyphenols (anthocyanins and phenolic acids). The preventive role of polyphenols has already been proved against, e.g., cancer, cardiovascular diseases, arthritis or type 2 diabetes (Blumberg, 2003; Kaur & Kapoor, 2001; Terefe et al., 2013). A particular- ly valuable compound in strawberries, with proven anticancer proper- ties, is ellagic acid (Seeram, Lee, Scheller, & Heber, 2004). Ellagic acid is present both in the flesh and seeds (Klimczak, Rozpara, & Król, 2011), therefore strawberry products, e.g. purée, obtained using waste-free technology, have a full range of the bioactive compounds present in the fruits. Pelargonidin-3-glucoside, the main strawberry an- thocyanin, as well as other phenolics and vitamin C are thermolabile compounds (Terefe, Matthies, Simons, & Versteeg, 2009), so the use of non-thermal methods for preserving strawberry products is particularly reasonable.

The results of studies on the influence of HPP on strawberry poly- phenols reported by different authors are inconsistent. Ferrari, Marcesca, and Ciccarone (2011) and Patras, Brunton, Pieve, and Butler (2009) reported that polyphenol levels in pressure-treated strawberry purée increased significantly, Terefe et al. (2013) observed a significant decrease in these compounds, while Cao et al. (2011) claimed that it showed no significant effect. Our preliminary studies with juices and nectars from ‘Senga Sengana’ strawberries – the popular cultivar in Poland – showed that the commercially used parameters for HPP, 300 and 500 MPa at mild temperature, caused a small decrease in the poly- phenol content and color parameters of the products (Marszałek, Mitek, & Skąpska, 2011).

The inactivation of enzymes is of key significance to the storage sta- bility of HPP-preserved strawberry products. Terefe, Yang, Knoerzer, Buckow, and Versteeg (2010) showed that neither thermal processing nor combined HPP–heat treatment could effectively inactivate polyphe- nol oxidase (PPO) and peroxidase (POD) in strawberry purée, even at 90 °C. Other authors showed that optimal inactivation (25%) of straw- berry POD was achieved using 230 MPa and 43 °C, and the best results in PPO inactivation (60%) were observed at 250 MPa. Some activation was observed for treatment carried out in 250–400 MPa for both en- zymes (Cano, Hernandez, & De Ancos, 1997). Cao et al. (2011) reported a 51.5 and 56.5% reduction in PPO and POD activity respectively in strawberry pulp after 600 MPa and 25 min at room temperature.

The studies presented on the use of HPP as a means of preserving strawberry products were based on a different matrix — different kinds of products, obtained with different fruit varieties, e.g. ‘Festival’, ‘Aroma’, ‘Elsanta’, ‘Pajaro’, ‘Camarosa’ and ‘Rubygem’. Therefore quality indicators are difficult to compare. As can be concluded from this re- view, there is no data available on the preservation of strawberry prod- ucts with HPP at near-zero temperatures and the reported effects of HPP at mild and high temperatures on the quality of strawberry products are ambiguous. Therefore the purpose of this study was to evaluate the im- pact of HPP at low and mild temperatures on the overall quality of strawberry purée, including the inactivation of native microflora and enzymes (PPO and POD), changes in the total and individual phenolic compounds and vitamin C content, as well as color parameters and the sensory quality.

2. Materials and methods

2.1. Production of strawberry purée

Strawberries, cv. ‘Senga Sengana’ cultivar, were harvested at the end of June 2010 and pre-treated (washing, destalking, freezing) at “Ulmer” Sp.j. company (Stare Zadybie, Poland). After freezing in a fluidization tunnel (UniDex, Poland), the strawberries were sorted (Niagara Sortex, Bühler, Switzerland) according to color and size (45–55 mm) and stored

at −24 °C. After defrosting (at 4 °C), they were mashed up in a food processor (CL-30, Robot Coupe, France). The resultant semi-liquid strawberry pulp was homogenized (Mz-50, Fryma, Switzerland, Ø ≤ 0.5 mm) and deaerated at 0.06 MPa (LVE, Fryma, Switzerland). The product temperature did not exceed 0 °C throughout the whole processing procedure. This strawberry purée was used as a control sam- ple (CS).

2.2. Preservation of strawberry purée

2.2.1. High hydrostatic pressures (HPP) Samples were preserved in a pressure chamber (ca. 1500 mL in vol-

ume and 110 mm in diameter, Izopress, Moscow, Russia), filled with a water/propylene glycol mixture (50:50, v/v) and equipped with a heating/cooling jacket (operating temperature range of 0–50 °C). Pres- sure inside the chamber was measured directly with a manometer with a pressure transducer (type EBM 6045-700, KGT Kramer). The pressure and temperature parameters were registered using a thermocouple and manometer located in the pressure medium and processed via a data collection computer system (Memory Card MMC, Metronic System MPI-L version 1.11., Kraków, Poland). Strawberry purée was processed in low density polyethylene bottles (PE-LD, 50 mL), without access to air. The process was run using various parameters, i.e., pressure: 300 or 500 MPa; time of sample exposure to pressure: 1, 5 or 15 min; and temperature: 0 or 50 °C (omitting 500 MPa, 5 min at 50 °C). Pressure of up to each 100 MPa was generated in 3 s; the release time was 1 s for each 100 MPa. The temperature increase during pressurization mea- sured in the chamber, was 2 °C for each 100 MPa.

2.2.2. Pasteurization (TP) The purée was pasteurized in 100-mL glass jars in a stainless steel,

gas-heated bath pasteurizer. Process parameters of 90 °C for 15 min as- sured the microbial stability of the purée (Marszałek et al., 2011). The time and temperature data were recorded with a monitoring–measur- ing device (9004, Ellab, Denmark) designed for measuring the temper- ature inside a package and of the heating medium during the course of the process.

2.3. Chemical reagents

The following standards were used in the study: p-hydroxybenzoic acid (p-HBA), ellagic acid (EA), quercetin (Q), kaempferol (K), pelargonidin-3-glucoside (Pg-3-Glc) and cyanidin-3-glucoside (Cy-3- Glc) of HPLC purity (Extrasynthese, France), L-ascorbic acid (AA) of HPLC purity (Supelco, USA), DL-dithiothreitol (DTT) (N99%) and polyvi- nylpyrrolidone (PVPP) (~110 μm) (Fluka, USA), catechol (N99%), gallic acid (GA) (N98%), hydrogen peroxide (30%), Triton X-100, and Trolox (N97%) (Sigma Aldrich, USA). The remaining reagents were purchased from POCh (Warsaw, Poland). Demineralized water used for the analy- ses was purified using a Direct-Q 3 apparatus (Millipore, USA).

2.4. Analyses

2.4.1. Total content of polyphenols (TCP) Strawberry purée (10 g) was extracted for 5 min in an ultrasound

bath (40 kHz, 100 W, 25 °C, ITR, Poland) using 30 g of an extraction mix- ture: methanol/water/hydrochloric acid (80:19.9:0.1; v/v/v) in centri- fuge flasks. Afterwards, the sample was centrifuged in a laboratory centrifuge (MPW-350R, MPW Med. Instruments, Poland) at 3670 g and 4 °C for 5 min. Extraction was repeated five times, supernatants were combined and the methanol was evaporated under vacuum (B- 481, Büchi, Switzerland). The residue was transferred quantitatively to a volumetric flask and filled up to 50 mL with 0.1% (v/v) o-phosphoric acid.

The total content of polyphenols was determined using the Folin– Ciocalteu method modified by Gao, Ohlander, Jeppson, Bjork, and

50 K. Marszałek et al. / Innovative Food Science and Emerging Technologies 27 (2015) 48–56

Trajkovski (2000). The absorbance of the mixture was measured spec- trophotometrically (UV-1650PC, Shimadzu, Japan) at 765 nm. The total content of polyphenols was expressed in milligrams of gallic acid equivalent per 100 g of fresh weight of the purée (mg GAE/100 g FW).

2.4.2. HPLC analysis of anthocyanins The HPLC determination of the anthocyanin content was carried out

using the method described by Goiffon, Mouly, and Gaydou (1999), with modifications consisting of changing the isocratic elution into gra- dient elution, and shortening the analysis time to 22 min. Ten milliliters of the extract (Subsection 2.4.1) was absorbed and purified on Sep-Pak C18 minicolumns (Waters, USA). Anthocyanins were eluted with 5 mL of a methanol/water/hydrochloric acid mixture (75:24.9:0.1; v/v/v), and then filtered on PTFE filters with a pore size of 0.45 μm (Waters, USA). The analysis of the anthocyanins in the HPLC system equipped with a DAD SPD-10Avp detector, thermostat CTD-10AsVp and DEGASEX™ DG-4400 degasser (Shimadzu, Japan) was carried out on a reversed- phase Luna C18 column (250 × 4.6 mm, 5 μm, Phenomenex, USA) at a temperature of 25 °C, flow rate of 1 mL/min and detection at 520 nm. A water/formic acid mixture (89:11, v/v) and acetonitrile were used as eluents (A and B, respectively) in the following program: 9% B (15 min), from 9 to 20% B (1 min), from 20 to 30% B (1 min), from 30 to 9% B (2 min), and 9% B (4 min). Monomers of the anthocyanins were identified by comparing their retention times with those of the standards and with data from literature. Cy-3-Glc and Pg-3-Glc contents were calculated based on their standard calibration curves results. Pg-3- Rut was expressed as Pg-3-Glc. All results were expressed in milligrams per 100 g of fresh weight (mg/100 g FW).

2.4.3. HPLC analysis of phenolic acids and flavonols Phenolic compounds were determined according to a modified

method of Odriozola-Serrano, Soliva-Fortuny, and Martin-Belloso (2008). To determine the contents of p-hydroxybenzoic acid (p-HBA), ellagic acid (EA), quercetin (Q) and kaempferol (K), acidic hydrolysis was conducted with the method used by Da Silva Pinto, Lajolo, and Genovese (2008). Forty milliliters of a methanol/6 M hydrochloric acid/water mixture (56:25:19; v/v/v) was added to 1 mL of the extract (Subsection 2.4.1). The sample was heated at 120 °C for 90 min, then cooled and neutralized with 6 M NaCl to pH ca. 3.5.

Analyses were carried out in a gradient system using the equipment described in Subsection 2.4.2 at 30 °C, flow rate of 1 mL/min and detec- tion at 260 nm (phenolic acids) and 360 nm (flavonols). The water/ formic acid mixture (99:11, v/v) and acetonitrile were used as eluents (eluents A and B, respectively) in the following gradient program: 10% B (10 min), from 10 to 45% B (15 min), from 45 to 70% B (5 min), from 70 to 10% B (3 min), and 10% B (4 min). Selected phenolic com- pounds were quantified using external p-HBA, EA, Q and K calibration curves. The contents of all compounds were expressed in milligrams per 100 g of fresh weight (mg/100 g FW). Peak identities were as recent- ly described by Odriozola-Serrano et al. (2008).

2.4.4. HPLC analysis of AA and DHAA The total vitamin C content, expressed as L-ascorbic acid (AA) and L-

dehydroascorbic acid (DHAA), was determined as described by Odriozola-Serrano, Harnandes-Jover, and Martin-Belloso (2007). Ap- proximately 1 g of purée was transferred to a volumetric flask and filled up to 10 mL with 0.01% of m-phosphoric acid. The extract was then fil- tered through PTFE 0.45-μm filters. In order to assay DHAA, it was re- duced to AA with 0.1% DL-dithiothreitol (DTT) using 1 mL of the following mixture: extract/DTT (50:50; v/v) and leaving it in the dark for 1 h. The content of DHAA was calculated using the formula: DHAA = (AA + DHAA) − AA.

The HPLC analysis (2695, Waters, USA) was carried out using a reversed-phase SunFire C18 column (250 × 4.6 mm, 5 μm, Waters, USA) and a photodiode detector (DAD) (2996, Waters, USA). The anal- ysis was conducted with the isocratic method using 0.01% m-

phosphoric acid at a flow rate of 1 mL/min and column temperature of 25 °C. AA was quantified using external calibration curves. The con- tents of AA and DHAA were expressed in milligrams of AA per 100 g of fresh weight (mg AA/100 g FW). Peak identities were as recently de- scribed by Odriozola-Serrano et al. (2007).

2.4.5. Changes in color parameters The color of the strawberry purée was determined using a CM-

3600d colorimeter (Konica Minolta, Japan), in glass cuvettes with an op- tical path of 10 mm. The measurement was made on the CIEL*a*b* sys- tem, using illuminant D65. Values of L*, a*, and b* parameters enabled calculating the absolute difference of the samples' color after preserva- tion compared to the control sample, using the following equation: ΔE = [(ΔL*)2 + (Δa*)2 + (Δb*)2]1/2, where L* (lightness/darkness), a* (red/green), and b* (yellow/blue).

2.4.6. Determination of PPO and POD activities The activity of selected tissue enzymes was determined as described

by Terefe et al. (2010). The extraction mixture comprised 0.2 M phos- phate buffer (pH = 6.5) containing 4% (w/v) polyvinylpyrrolidone (PVPP), 1% (v/v) Thriton X-100 and 1 M NaCl. The strawberry purée and the mixture (4.5: 4.5 g, w/w) were treated with ultrasound (40 kHz, 100 W, 25 °C, ITR, Poland) for 3 min and centrifuged (MPW- 350R, MPW Med. Instruments, Poland) at 17,700 g for 30 min at 4 °C. The supernatant, after filtration through blotting filter paper, was used to determine PPO and POD activities.

For PPO activity assay, 100 μL of the supernatant was introduced into 3 mL of 0.05 M phosphate buffer (pH 6.5) containing 0.07 M catechol, and the absorbance was measured spectrophotometrically (UV- 1650PC, Shimadzu, Japan) at λ = 420 nm and 25 °C for 10 min. A blank sample was prepared in the same way, by substituting the super- natant with a phosphate buffer. The PPO activity was expressed as a change in absorbance/min/g of fresh weight of the analyzed sample.

For the POD activity assay, 1.5 mL of 0.05 M phosphate buffer (pH = 6.5) was added to 200 μL of the supernatant, 200 μL of 0.05 M phosphate buffer containing 1% p-phenylenediamine (w/v) and 200 μL of 1.5% (v/v) hydrogen peroxide. Mixture absorbance was measured at λ = 485 nm and 25 °C for 10 min. The POD activity was expressed as a change in absorbance/min/g of fresh weight of the analyzed sample.

2.4.7. Microbiological analyses Yeasts and molds were analyzed according to the ISO 21527-1:2008

standard. Purée samples were diluted with sterile normal saline (0.85% sodium chloride), spread plated on sterile nutrient agar plates (PCA) and incubated at 25 °C for 5 to 7 days. The total microbial count (TMC) was determined according to the EN ISO 4833: 2003 standard. Samples diluted with sterile normal saline were plated on DRBC plating medium; plates were incubated at 30 °C for 72 h. All the experiments were conducted in duplicates and mean values of log 10 cfu/g sample have been reported.

2.4.8. Sensory analysis The sensory analysis of strawberry products was conducted as de-

scribed in ISO 4121:1998. A 6-point scale was used to evaluate: color, appearance, consistency, aroma and taste, and an overall quality assess- ment was conducted using a 9-point hedonic scale; assessments were made by a trained sensory panel (eight persons). All samples were eval- uated independently in a test room complying with the requirements of ISO 8589:2007.

2.4.9. Statistical analysis All analyses were conducted using Statistica 10 StatSoft® software.

The significance of differences was computed based on an analysis of the variance with Tukey's test (p-value b 0.05), and the impact of HPP on the quality of strawberry purée was assessed based on a cluster

Ta b le

1 C on

te n ts

of fr ee

p h en

ol ic ac id s an

d fl av

on ol s an

d th ei r to ta lc on

te n t in

co n tr ol

sa m p le

an d in

TP an

d H PP

-p re se rv ed

st ra w b er ry

p u ré e (m

g/ 10

0 g FW

).

T (° C )

P (M

P a)

t (m

in )

B ef o re

h yd

ro ly si s (f re e co

m p o u n d s)

A ft er

h yd

ro ly si s (t o ta l co

n te n t)

TC P

P h en

o li c ac id s

Fl av

o n o ls

P h en

o li c ac id s

Fl av

o n o ls

p -H

B A

E A

Q K

p -H

B A

E A

Q K

C S

0 .1

– n d

2 .1 1 ±

0 1 6 cd

1 .2 6 ±

0 .0 2 f

0 .0 9 ±

0 .0 1 d e

1 .1 9 ±

0 .0 2 b

3 3 .5 4 ±

3 .6 5 d e

6 .2 3 ±

0 .6 8 e f

2 .7 5 ±

0 .1 6 a b c

2 2 1 .0 3 ±

3 .3 3 a b

TP 9 0

0 .1

1 5

n d

5 .1 0 ±

0 .4 8 a

1 .6 4 ±

0 .0 5 a

0 .1 0 ±

0 .0 1 cd

1 .8 5 ±

0 .0 8 a

4 3 .7 7 ±

2 .5 1 a

9 .6 1 ±

0 .4 6 b

3 .0 4 ±

0 .2 5 a

1 9 0 .5 5 ±

3 .5 9 e

H P P

0 3 0 0

1 n d

2 .3 0 ±

0 .1 5 c

1 .3 4 ±

0 .0 7 d e f

0 .1 0 ±

0 .0 1 cd

1 .0 9 ±

0 .0 5 b

3 5 .6 0 ±

3 .3 8 cd

e 7 .8 3 ±

0 .3 7 cd

2 .8 8 ±

0 .0 5 a b

2 2 1 .1 3 ±

3 .9 1 a b

5 n d

2 .0 1 ±

0 .0 5 cd

1 .3 5 ±

0 .0 5 d e f

0 .0 8 ±

0 .0 2 d e

1 .2 6 ±

0 .0 8 b

3 2 .0 8 ±

2 .7 3 e

6 .4 8 ±

0 .4 4 e f

2 .8 7 ±

0 .0 5 a b

2 2 2 .1 3 ±

1 .5 2 a

1 5

n d

2 .1 2 ±

0 .1 1 cd

1 .3 6 ±

0 .0 5 cd

e f

0 .1 0 ±

0 .0 1 cd

1 .2 4 ±

0 .0 8 b

3 4 .4 7 ±

2 .1 5 cd

e 6 .9 1 ±

0 .5 7 d e

2 .8 7 ±

0 .0 4 a b

2 2 1 .3 1 ±

1 .5 2 a b

5 0 0

1 n d

1 .7 8 ±

0 .2 0 d

1 .2 8 ±

0 .1 3 d e f

0 .0 7 ±

0 .0 1 e

1 .2 1 ±

0 .0 2 b

3 2 .0 8 ±

1 .9 7 e

6 .8 3 ±

0 .7 3 d e

2 .5 0 ±

0 .2 2 cd

2 1 8 .4 5 ±

0 .5 6 a b

5 n d

1 .9 7 ±

0 .2 2 cd

1 .4 0 ±

0 .1 0 cd

e f

0 .0 7 ±

0 .0 1 e

1 .1 0 ±

0 .0 9 b

3 4 .5 4 ±

2 .7 7 cd

e 6 .7 8 ±

0 .7 6 d e

2 .7 2 ±

0 .1 4 a b c

2 1 7 .3 5 ±

4 .3 8 b c

1 5

n d

1 .9 0 ±

0 .1 4 cd

1 .2 6 ±

0 .1 8 e f

0 .0 8 ±

0 .0 1 d e

1 .2 3 ±

0 .1 3 b

3 3 .3 4 ±

2 .7 2 d e

5 .2 9 ±

0 .2 3 f

2 .7 1 ±

0 .0 5 a b c

2 2 0 .6 6 ±

0 .8 3 a b

5 0

3 0 0

1 n d

3 .2 4 ±

0 .1 8 b

1 .4 7 ±

0 .1 2 b cd

e 0 .0 9 ±

0 .0 2 cd

1 .8 9 ±

0 .2 3 a

4 3 .0 8 ±

5 .0 8 a b

7 .0 3 ±

1 .2 2 d e

1 .8 5 ±

0 .3 2 e

2 1 9 .9 3 ±

2 .5 1 a b

5 n d

3 .4 1 ±

0 .3 0 b

1 .5 9 ±

0 .1 9 a b

0 .1 1 ±

0 .0 1 b c

2 .0 0 ±

0 .1 7 a

4 1 .7 0 ±

2 .2 8 a b

1 1 .0 7 ±

1 .3 6 a

2 .2 3 ±

0 .1 7 d

2 1 8 .5 5 ±

3 .6 8 a b

1 5

n d

3 .3 5 ±

0 .2 1 b

1 .4 8 ±

0 .1 7 a b cd

0 .1 3 ±

0 .0 2 a

1 .9 2 ±

0 .3 1 a

4 1 .4 7 ±

2 .6 8 a b

9 .3 4 ±

1 .2 2 b

2 .2 1 ±

0 .3 2 d

2 1 2 .1 0 ±

1 .4 4 d

5 0 0

1 n d

3 .3 5 ±

0 .3 6 b

1 .4 7 ±

0 .1 5 a b cd

0 .1 2 ±

0 .0 3 a b

1 .8 9 ±

0 .1 9 a

3 8 .2 9 ±

3 .8 7 b cd

8 .8 5 ±

0 .9 9 b c

2 .6 0 ±

0 .1 6 b c

2 2 1 .4 9 ±

1 .5 4 a b

1 5

n d

3 .4 8 ±

0 .2 9 b

1 .5 6 ±

0 .1 2 a b c

0 .0 9 ±

0 .0 2 cd

1 .8 2 ±

0 .1 1 a

3 9 .4 3 ±

2 .9 4 a b c

9 .2 5 ±

0 .2 8 b

2 .4 4 ±

0 .3 4 cd

2 1 3 .3 9 ±

2 .0 4 cd

D at a re p re se n t m ea

n s ±

SD (n

= 3 );

FW : fr es h w ei gh

t; p -H

B A : p -h yd

ro xy

b en

zo ic ac id ; EA

: el la gi c ac id ; Q : q u er ce ti n ; K : ka

em p fe ro l, TC

P: to ta lc on

te n t of

p ol yp

h en

ol s, n d : n ot

d et ec te d ; C S:

co n tr ol

sa m p le ; TP

: th er m al

p as te u ri za ti on

; H PP

: h ig h

p re ss u re

p ro ce ss in g.

M ea

n va

lu es

d en

ot ed

w it h th e sa m e le tt er s d o n ot

d if fe r si gn

ifi ca n tl y st at is ti ca lly

,p ≤

0. 0 5 .

51K. Marszałek et al. / Innovative Food Science and Emerging Technologies 27 (2015) 48–56

analysis in the form of tree diagrams using weighted average linkage and Euclidean distances.

Three independent samples subjected to simultaneous treatment under the same conditions were analyzed in duplicate.

3. Results and discussion

3.1. Content of phenolic compounds

The TCP in the control sample (CS) was 221 mg GAE/100 g FW (Table 1), which is consistent with the findings of other authors (Oszmiański & Wojdyło, 2009; Oszmiański, Wojdyło, & Matuszewski, 2007). Free p-hydroxybenzoic acid was not identified in any of the sam- ples, which indicates that it occurred only in the bound form. The total content of p-HBA (Table 1) was 1.19 mg/100 g FW and was slightly higher than found by Breitfellner, Solar, and Sontag (2003) and by Odriozola-Serrano et al. (2008), who reported 0.1–0.6 mg/100 g FW of this compound. The contents of free EA, Q and K in CS were 2.11, 1.26 and 0.09 mg/100 g FW, respectively. A similar content of free EA was determined by Amakura, Okada, Tsuji, and Tonogai (2000) and Pallauf, Rivas-Gonzalo, Castillo, Cano, and Pascual-Teresa (2008). As re- ported by Oszmiański and Wojdyło (2009), the contents of flavonol in strawberries may range from 0.5 to 4.0 per 100 g of fruits. Many authors agree that strawberries contain 0.5–7.0 times more quercetin than kaempferol derivatives (Breitfellner et al., 2003; Da Silva Pinto et al., 2008; Oszmiański et al., 2007; Pallauf et al., 2008).

During the production of concentrated strawberry juice, most of the ellagic acid remains in the pomace (Klimczak et al., 2011); hence, straw- berry purée is a very valuable source of this biologically-active compo- nent. Its total content in CS was 33.54 mg EA/100 g FW. Häkkinen and Törrönen (2000) reported that the content of ellagic acid in straw- berries of the ‘Senga Sengana’ variety was 39.66 mg EA/100 g FW. Inter- estingly, in the same strawberry cultivar, Da Silva Pinto et al. (2008) measured from 5.5 to 50.0 mg of ellagic acid per 100 g of strawberries depending on the extraction solution (acetone, methanol), the type and concentration of acid used for hydrolysis, and the time and temper- ature of the hydrolysis process. The contents of quercetin and kaempferol increased 5 and 30 times after hydrolysis, which indicates that they (kaempferol in particular) occur mainly in the bound form.

The predominant phenolic acid in strawberries is ellagic acid, which constitutes from 35 to 50% of the total content of phenolic acids (Da Silva Pinto et al., 2008; Häkkinen, Karenlampi, Mykkanen, Heinonen, & Torronen, 2000; Klimczak et al., 2011). In terms of levels of this con- stituent, strawberries are inferior only to wild strawberries, raspberries and pomegranate fruits (Amakura et al., 2000; Häkkinen et al., 2000; Törrönen, Hakkinen, Karenlampi, & Mykkanen, 1997).

Most of the studied phenolic compounds were present in the bound form. No free p-HBA was detected and the amount of free EA, Q and K was 6, 20 and 3% of their bounded form.

TP significantly increased the contents of free ellagic acid, quercetin, and total contents of phenolic acids and flavonols, as previously report- ed (Cao et al., 2011; Odriozola-Serrano et al., 2008). Purée treated by HPP at 0 °C showed an insignificant difference in its content of phenolic compounds compared to CS. HPP at 50 °C significantly increased the contents of free ellagic acid, quercetin and kaempferol (besides 300 MPa/1 min). The inconsistent effect of temperature on the con- tents of the assayed components is usually linked with the extraction of potentially-antioxidative compounds from fruit tissue (Cao et al., 2011; Patras et al., 2009). Treatment pressure and time had no signifi- cant effect on the levels of free phenolic acids and flavonols.

The sum of free compounds, p-hydroxybenzoic acid, ellagic acid, quercetin and kaempferol constituted only 1.6 to 3.7% of total polyphe- nols in the CS and TP-treated sample, respectively, which is in agree- ment with the data reported by Cao et al. (2011) The contribution of these polyphenols after hydrolysis in TCP was 20 and 27% respectively, for the CS and TP-treated sample; the most abundant compound was

52 K. Marszałek et al. / Innovative Food Science and Emerging Technologies 27 (2015) 48–56

EA, constituting from 15.2 to 20.5% of TCP. The contents of studied poly- phenols in HPP-treated samples were similar to that of CS, especially when treatment at 0 °C was applied.

3.2. Content of anthocyanins

As shown in Table 2, the content of Cy-3-Glc, Pg-3-Glc and Pg-3-Rut in the control sample (CS) was 7.81 (8.4%), 80.79 (87.2%) and 4.03 (4.4%) mg/100 g, respectively. Odriozola-Serrano et al. (2008) reported a similar ratio of these monomers in strawberry juices, ca. 8:88:4. Cao et al. (2011) also found these compounds to be the most abundant an- thocyanins in strawberries, their concentration being as follows: Pg-3- Glc 23.1 mg/100 g, Pg-3-Rut 5.8 mg/100 g and Cy-3-Glc 3.7 mg/100 g, which accounted for 71.3%, 17.9% and 11.4% of total monomeric anthocyanins.

The study showed a statistically significant (p-value ≤ 0.05) effect of the preservation temperature on the contents of all investigated antho- cyanin monomers (Table 2); however, the treatment pressure and pro- cessing time had no significant effect on their levels compared to CS. The content of anthocyanin monomers in TP and HPP treated samples was similar to the CS and reached on average ca. 8:88:4% (w/w) for Cy-3- Glc:Pg-3-Glc:Pg-3-Rut, respectively. The analysis of anthocyanins dem- onstrated losses of a total level of the analyzed pigments compared to CS reaching ~43, 7 and 14% in the samples treated with TP, HPP at 0 °C and HPP at 50 °C, respectively. In other studies on the effect of thermal pro- cessing on anthocyanin levels in juices and strawberry purée, the losses ranged from 3 to 30% (Cao et al., 2011; Hartmann, Patz, Andlauert, Dietrich, & Ludwig, 2010; Marszałek et al., 2011; Odriozola-Serrano et al., 2008; Patras et al., 2009). These differences may be caused by an- other type of device (flow system) used by some authors, or mild con- ditions of the process. Pg-3-Rut appeared slightly more susceptible to preservation conditions than the other anthocyanins. After TP its losses were ca. 6% higher compared to the remaining monomers. Losses of Pg- 3-Rut in HPP-treated strawberry purée at 50 and 0 °C were higher com- pared to other anthocyanin monomers by 18 and 9%, respectively. Most authors demonstrated, however, that Pg-3-Glc was the most sensitive anthocyanin in strawberries (Tiwari et al., 2009; Verbeyst, Hendrickx, & Loey, 2012; Verbeyst et al., 2010). The thermal stability of anthocya- nins also depends on the equilibrium between the three main forms in which they occur in the natural environment, i.e., flavylium cations, pseudo-bases and chalcones. Increasing the heating temperatures dis- turbs this equilibrium and induces the formation of colorless chalcones, which is accompanied by decreasing the contents of the quinoid bases and flavylium cations. During long-term exposure to increased temper- atures, the resultant chalcones are easily transformed into color (brownish) polymers, which results in the browning of strawberry

Table 2 Content of anthocyanins and vitamin C in control sample and TP and HPP-preserved strawber

T (°C) P (MPa) t (min) Anthocyanins

Cy-3-Glc Pg-3-Glc Pg-3-Rut

CS – 0.1 – 7.81 ± 0.01a 80.79 ± 4.81a 4.03 ± 0. TP 90 0.1 15 4.36 ± 0.11e 45.97 ± 1.68g 2.04 ± 0. HPP 0 300 1 7.46 ± 0.07b 76.70 ± 2.28ab 3.23 ± 0.

5 7.74 ± 0.04a 73.69 ± 5.69bcde 3.28 ± 0. 15 7.23 ± 0.19b 76.28 ± 1.75b 3.35 ± 0.

500 1 7.25 ± 0.15b 73.85 ± 1.34bcde 3.57 ± 0. 5 7.37 ± 0.13b 75.04 ± 3.31bcd 3.60 ± 0. 15 7.35 ± 0.22b 75.17 ± 0.19bc 3.46 ± 0.

50 300 1 6.49 ± 0.11d 68.41 ± 0.54f 2.73 ± 0. 5 6.74 ± 0.34cd 71.43 ± 2.46cdef 3.03 ± 0. 15 6.84 ± 0.17c 69.79 ± 1.27ef 2.57 ± 0.

500 1 6.83 ± 0.09c 70.70 ± 0.44def 2.70 ± 0. 15 6.86 ± 0.08c 70.13 ± 1.52ef 2.80 ± 0.

Data represent means ± SD (n = 3); FW: fresh weight; Cy-3-Glc: cyanidin-3-glucoside; Pg-3- anthocyanins; AA: ascorbic acid; DHAA: dehydroascorbic acid; CS: control sample; TP: therma Mean values denoted with the same letters are not statistically significantly different, p ≤ 0.05

products during processing and storage (Odriozola-Serrano et al., 2008; Özkan, 2002).

3.3. Contents of AA and DHAA

As shown in Table 2, the content of AA and DHAA in the control sample was 37.49 (70.2%) and 15.89 (29.8%) mg/100 g, respectively. These values are in the range of those previously reported by other authors (Hakala et al. 2003). They reported from 32.4 to 84.7 mg vi- tamin C in six strawberry cultivars. TP significantly degraded vitamin C (Table 2), reducing its content by 62% compared to CS. The level of vita- min C (AA + DHAA) also decreased significantly in HPP-preserved purée, but losses reached only 15% (at 0 °C) and 16% (at 50 °C). The AA to DHAA ratio in CS did not change significantly after TP. However, an increase was noted in L-dehydroascorbic acid, and a simultaneous decrease in L-ascorbic acid, in the HPP-preserved samples. In strawberry purée preserved with HPP at 50 °C, DHAA constituted 55% of the total vitamin C content, and in that preserved at 0 °C ~36%. Significant differ- ences were also determined in the contents of both forms of vitamin C depending on the treatment pressure and exposure time. Considering that DHAA is less stable and more rapidly degraded than AA, faster ox- idation of AA during HPP at higher temperatures may seem undesirable. When analyzing the quality of strawberry purée preserved with HPP (400–600 MPa, 15 min, 10–30 °C) and by pasteurization (70 °C, 2 min), Patras et al. (2009) reported losses of AA at 5–10% depending on the HPP process parameters and 22% for pasteurized purée. Hartmann et al. (2010) showed a decrease (of 37%) in the content of vi- tamin C in pasteurized products (85 °C, 2 min).

3.4. Activity of PPO and POD

Enzyme activities in CS showed that POD activity (A0 POD = 1.59 OD/ min/g FW) was three times greater than PPO activity (A0 of PPO = 0.43 OD/min/g FW). In different strawberry cultivars (‘Pajaro’, ‘Camarosa’, ‘Festival’, ‘Rubygem’, ‘Aroma’) other authors reported from 0.27 to 2.31 OD/min/g FW and from 0.04 to 2.24 OD/min/g FW for POD and PPO activity, respectively (Cano et al., 1997; Terefe et al., 2010, 2013).

Only TP led to effective inactivation of both analyzed enzymes (Fig. 1). A significant decrease (45% on average) in PPO activity in the HPP-preserved strawberry purée was determined at a processing tem- perature of 50 °C. The higher process temperature (50 °C) coupled with higher pressure (500 MPa) and the longer time of its action (15 min) were more effective in inhibiting PPO activity, with only 28% of its initial activity remaining. POD turned out to be more resistant to higher pressures than PPO. In turn, the higher temperature of HPP pres- ervation caused a significant decrease in POD activity of 16 to 37%.

ry purée (mg/100 g FW).

TCA Vitamin C Sum AA + DHAA

AA DHAA

71a 92.60 ± 5.49a 37.49 ± 0.77a 15.89 ± 0.72f 53.38 ± 0.95a

08f 52.36 ± 1.86g 14.93 ± 0.16j 5.55 ± 0.39h 20.48 ± 0.33i

16bcd 87.39 ± 2.19b 29.16 ± 0.19c 12.92 ± 0.74g 42.08 ± 0.65g

64bcd 84.71 ± 6.36bcd 27.09 ± 0.14d 16.36 ± 0.28f 43.45 ± 0.35f

71bc 86.86 ± 1.28b 29.36 ± 0.91c 17.63 ± 0.37e 46.99 ± 0.55cd

32ab 84.67 ± 1.70bcde 26.24 ± 0.20e 19.66 ± 0.59d 45.91 ± 0.48d

36ab 86.01 ± 3.68bc 30.91 ± 0.47b 15.34 ± 1.04f 46.26 ± 0.67d

13ab 85.98 ± 0.28bc 31.45 ± 0.62b 16.31 ± 1.48f 47.76 ± 1.94c

05de 77.63 ± 0.49f 17.49 ± 0.67i 23.96 ± 0.81c 41.45 ± 0.58g

02bcde 81.21 ± 2.82cdef 22.57 ± 0.32f 26.35 ± 0.69b 48.92 ± 0.72b

04ef 79.19 ± 1.44f 19.27 ± 0.55h 25.32 ± 1.00b 44.60 ± 0.48e

09de 80.23 ± 0.36def 17.68 ± 0.17i 32.14 ± 0.57a 49.82 ± 0.41b

07cde 79.79 ± 1.61ef 21.60 ± 0.22g 16.28 ± 0.28f 37.88 ± 0.18h

Glc: pelargonidin-3-glucoside; Pg-3-Rut: pelargonidin-3-rutinoside; TCA: total content of l pasteurization; HPP: high pressure processing. .

a

g

a a a,b a,b a,b a,b

c c,d

e

c

f

0

20

40

60

80

100

120

1 min 5 min 15 min 1 min 5 min 15 min

CS TP HPP 300 MPa HPP 500 MPa

% re

si du

al a

ct iv

ity

PPO activity0°C 50°C

a

d

a a a a a a,bb b

b b,c

c

1 min 5 min 15 min 1 min 5 min 15 min

CS TP HPP 300 MPa HPP 500 MPa

POD activity0°C 50°C

Fig. 1. Activity of enzymes in the control sample and in TP and HPP-preserved strawberry purée. Data: mean ± SD (n = 3); FW: fresh weight; CS: control sample; TP: thermal pasteur- ization. The % residual activities ((A/A0) · 100) are presented where A0 represents the activity of enzymes in the fresh strawberries (A0 of PPO = 0.43 OD/min/g FW; A0 of POD = 1.59 OD/ min/g FW). Mean values denoted with the same letter do not differ significantly statistically, p ≤ 0.05.

53K. Marszałek et al. / Innovative Food Science and Emerging Technologies 27 (2015) 48–56

Terefe et al. (2009) obtained only a 30% reduction in PPO activity and as much as an 85% lower POD activity in HPP-preserved strawberries (600 MPa, 60 °C, 10 min). The resistance of strawberry PPO to pressure was also reported by Garcia-Palazon et al. (2004), who achieved com- plete inactivation of PPO upon pressure treatment at 800 MPa for 10 min. These conditions were, however, insufficient to inactivate POD. In contrast, in the study conducted by Terefe et al. (2010), the PPOs in strawberry purée from two cultivars ‘Aroma’ and ‘Festival’ were found to be highly resistant to thermal inactivation at temperature as high as 100 °C with a maximum inactivation of 28% after a 30-min treatment.

3.5. Changes in color

The major color of strawberry juice is a mix of red and yellow. Thus, Hunter a* and b* values or some combination of a* and b* should be considered as the physical parameters to describe the visual color deg- radation. But in fact, any change in a* and b* values is associated with a simultaneous change in the L* value, therefore representation of qual- ity in terms of total color may be more relevant (Rodrigo, Loey, & Hendrickx, 2007). Changes in food product color are best described by two color coefficients L* · a*/b* and ΔE. These coefficients have already been used by many authors studying strawberry color changes during processing (Rodrigo et al., 2007; Terefe et al., 2009) (Fig. 2). The L* · a*/b* coefficient in the control sample was 77.28 at pH 3.2. Rodrigo et al. (2007) reported ca. 59.0 at pH 3.7 but they also proved a highly dependent L* · a*/b* coefficient from pH.

The L* · a*/b* coefficient increased significantly (by 4.5 units) after TP compared to CS. Significant changes in the L* · a*/b* coefficient were also determined in HPP purée at 50 °C (omitting 300 MPa at 50 °C), but in this

e,f

a

e,f e,f d d,e

f f

c c

d,e,f

c b

75

77

79

81

83

1 min 5 min 15 min 1 min 5 min 15 min

CS TP HPP 300 MPa HPP 500 MPa

L*·a*/b*0°C 50°C

Fig. 2. Color changes in TP and HPP-preserved strawberry puree. Data: mean ± SD (n = 3); FW the same letter do not differ significantly, p ≤ 0.05.

case these were mainly due to the increased value of the a* parameter from +24.12 to ca. +26, which probably resulted from the mechanical extraction of anthocyanin pigments from the tissue to intercellular juice. By contrast the a* parameter decreased to +21.77 after TP. Similar, but less significant changes were observed in the L* and b* parameters. This phenomenon was earlier described by Rodrigo et al. (2007) and Terefe et al. (2009) also determined increased values of color parameters during high pressure treatment (up to 600 MPa).

The highest value of ΔE was noted in purée after TP (ΔE = 3.0). Slightly lesser, but statistically significant, color changes were observed in the samples preserved with HPP at 50 °C (ΔE = 2.3), and the lowest in the samples preserved at 0 °C (ΔE = 1.6). It has been shown that, if ΔE is lower than 1.5, changes in the sample color are unnoticeable by in- experienced observers (Barba, Esteve, & Frigola, 2013). Cao et al. (2011) reported that the ΔE was ≥5 at 400 MPa and ≤3 at 500 and 600 MPa, and it reduced (to 1.79) with increasing pressures. By contrast they re- ported ΔE = 10.18 after thermal processing. Much lower changes in strawberry purée were noticed by Patras et al. (2009). They reported ΔE 5.67 and 2.44 after TP and HPP (500 MPa, 15 min, room tempera- ture) treatment, respectively. The changes in the color parameters could also be related to the higher residual activity of PPO and POD at TP.

3.6. Microbiological quality

Yeast and mold counts and the total microbial count indicated a sig- nificant effect of HPP and TP on the microbiological quality of the prod- uct (Table 3). TP and preservation by HPP at 500 MPa (at both temperatures) reduced the colony-forming units of yeasts and molds from 4.6 log cfu/g and 3.8 log cfu/g to b1 log cfu/g, respectively. The lower pressure allowed a significant reduction in microorganism

a

e e d d

e d

b

e

b

c c

0

1

2

3

4

1 min 5 min 15 min 1 min 5 min 15 min

TP HPP 300 MPa HPP 500 MPa

ΔE0°C 50°C

: fresh weight; CS: control sample; TP: thermal pasteurization. Mean values denoted with

Table 3 Count of yeast and molds and total microbial count in fresh strawberries and strawberry purée pasteurized and preserved with the HPP method (log cfu/g FW).

T (°C)

P (MPa)

t (min)

Yeast Molds TMC

CS – 0.1 – 4.60 ± 0.06a 3.82 ± 0.08a 4.86 ± 0.12a

TP 90 0.1 15 b1 ± 0.05c b1 ± 0.07e b1 ± 0.06c

HPP 0 300 1 1.60 ± 0.15b 3.32 ± 0.06b 4.30 ± 0.10a

5 1 ± 0.09c 1.70 ± 0.12d 4.26 ± 0.07a

15 b1 ± 0.08c b1 ± 0.06e 4.28 ± 0.09a

500 1 b1 ± 0.07c b1 ± 0.07e 4.26 ± 0.11a

5 b1 ± 0.06c b1 ± 0.09e 4.26 ± 0.10a

15 b1 ± 0.07c b1 ± 0.06e 4.36 ± 0.08a

50 300 1 1.95 ± 0.14b 2.74 ± 0.04c 3.54 ± 0.12b

5 1.84 ± 0.12b 1.48 ± 0.12d 3.26 ± 0.14b

15 1 ± 0.07c 1 ± 0.08e 3.20 ± 0.11b

500 1 b1 ± 0.06c b1 ± 0.06e 3.40 ± 0.12b

15 b1 ± 0.07c b1 ± 0.03e 3.41 ± 0.15b

Data represent means (n = 3); FW: fresh weight; TMC: total microbial count; CS: control sample; TP: thermal pasteurization; HPP: high pressure processing. TMC — DRBC plating medium, incubation at 30 °C for 72 h; yeasts and molds — PCA plating medium, incuba- tion at 25 °C for 5 to 7 days. Mean values denoted with the same letter are not statistically significantly different, p ≤ 0.05.

54 K. Marszałek et al. / Innovative Food Science and Emerging Technologies 27 (2015) 48–56

counts, minimum 2.6 and 0.5 log cfu/g for yeast and molds, respectively. HPP treated at 0 °C was ineffective to reduce TMC, compared to HPP at 50 °C and TP treated where TMC was reduced by 1.5 and 4.8 log cfu/g, respectively.

3.7. Sensory quality

The sensory assessment conducted after preservation demonstrated that the greatest changes, compared to the control sample, occurred in purée after TP (Table 4). The color, taste and aroma of pasteurized purée were scored from 0.5 to 1.0 pts lower than CS. Only the purée con- sistency remained unaffected. In the overall quality assessment with a hedonic scale, pasteurized purée was scored as 7.8. In turn, no signifi- cant changes were noted in the color and consistency of HPP- preserved purée at 0 °C, and the statistical analysis revealed a small de- crease in the scores given for aroma and taste. According to Table 4, the color, taste, aroma and consistency of all samples treated with HPP at 50 °C, either at 300 or 500 MPa, show no significant differences com- pared to the fresh samples. The overall acceptability of the products pre- served using this method was significantly lower than that of the unprocessed material, but still at a high level (8.5 on average). However, some examples showed an adverse effect of the HPP method on taste and smell. As a result of high pressure a rancid smell appears in

Table 4 Sensory quality of fresh strawberries and strawberry purée TP and preserved with the HPP me -point hedonic scale).

T (°C)

P (MPa)

t (min)

Color

CS – 0.1 – 6.0 ± 0.0a

TP 90 0.1 15 5.5 ± 0.4b

HPP 0 300 1 6.0 ± 0.0a

5 6.0 ± 0.0a

15 6.0 ± 0.0a

500 1 5.9 ± 0.2a

5 6.0 ± 0.0a

15 6.0 ± 0.0a

50 300 1 5.8 ± 0.4a

5 5.8 ± 0.4a

15 5.8 ± 0.4a

500 1 5.8 ± 0.4a

15 5.8 ± 0.4a

Data represent means ± SD (n = 8); CS: control sample; TP: thermal pasteurization; HPP: hig Mean values denoted with the same letter are not statistically different, p ≤ 0.05.

tomatoes (Poretta, Birzi, Ghizzoni, & Vicini, 1995). On the other hand, the smell of HPP-treated onions (350 MPa, 30 min, 25 and 40 °C) was less intense and was like frozen onions (Butz, Koller, Tauscher, & Wolf, 1994). Pressure above 100 MPa damages cell structures such as mem- branes and provokes a massive release of enzymes leading to numerous enzymatic reactions that influence flavor and product stability. UHP processing (30 min/300 MPa/25 and 40 °C) changes the odor of fresh onions towards that of braised or fried onions. The excess increase in the content of n-hexane in tomatoes is what gives them an unpleasant smell. During HPP, very high n-hexanal and cis-3-hexenal concentra- tions were formed from free fatty acid oxidation. In the case of onions, the authors noted two reasons: a reduction in dipropyl sulfides and an increase in trans-propylene disulfide and 3.4-dimethylthiophene.

3.8. Statistical analysis

The cluster analysis conducted using the method of weighted aver- age linkage and Euclidean distance for analyzing the contents of pheno- lic acids, flavonols, anthocyanins, vitamin C, color, enzymatic activity and sensory assessment (Fig. 3) showed explicitly the greatest changes in the quality of strawberry purée upon thermal pasteurization (TP). The HPP-treated sample, especially at 0 °C, showed the lowest differ- ences compared to the control sample. The analysis of variance conduct- ed for results concerning the chemical composition of purée did not show any significant effect of the pressure value and duration of the time of treatment on phenolic acids, flavonols, the total content of poly- phenols, anthocyanins and the total microbial count.

4. Conclusions

The study showed the effects of high pressure and thermal pasteur- ization on the chemical compounds, color, sensorial quality and micro- bial count in strawberry (‘Senga Sengana’ cv.) purée. The level of phenolic acids, flavonols, total polyphenols, anthocyanins, vitamin C, color and taste depended on the temperature, whereas pressure and time were not significant factors. Pressure, temperature and time influ- enced the PPO and POD activity and the microbial count. The measure- ment of the activities of PPO and POD demonstrated, however, greatest inactivation at the longest exposure time (15 min). Although the senso- ry quality of all strawberry purée samples preserved with the HPP method was very high compared to TP, taking into account the results of microbiological analyses and tissue enzyme activity, the recommend- ed pressure treatment is that applied at 500 MPa and 50 °C. Milder con- ditions of the process may result in the product being equally valuable in terms of its chemical quality, but with a shorter shelf-life due to mi- crobiological quality and enzymatic activity. Further studies are,

thod (color, taste, aroma, consistency in a 6-point scale, overall quality assessment in a 9-

Taste Aroma Consistency Overall quality

6.0 ± 0.0a 6.0 ± 0.0a 6.0 ± 0.0a 9.0 ± 0.0a

5.0 ± 0.0c 5.3 ± 0.4b 6.0 ± 0.0a 7.8 ± 0.4b

5.6 ± 0.4ab 5.4 ± 0.4b 5.8 ± 0.4a 8.5 ± 0.4ab

5.4 ± 0.4bc 5.4 ± 0.4b 5.8 ± 0.4a 8.5 ± 0.4ab

5.5 ± 0.4abc 5.6 ± 0.4ab 5.8 ± 0.4a 8.3 ± 0.4ab

5.5 ± 0.4abc 5.4 ± 0.4b 5.8 ± 0.4a 8.5 ± 0.4ab

5.8 ± 0.4ab 5.6 ± 0.4ab 5.8 ± 0.4a 8.5 ± 0.4ab

5.6 ± 0.4ab 5.5 ± 0.4ab 5.8 ± 0.4a 8.5 ± 0.4ab

6.0 ± 0.0a 5.8 ± 0.4ab 5.8 ± 0.4a 8.5 ± 0.4ab

6.0 ± 0.0a 5.8 ± 0.4ab 6.0 ± 0.0a 8.5 ± 0.4ab

6.0 ± 0.0a 6.0 ± 0.4a 5.8 ± 0.4a 8.3 ± 0.4ab

6.0 ± 0.0a 6.0 ± 0.4a 5.8 ± 0.4a 8.5 ± 0.4ab

6.0 ± 0.0a 5.8 ± 0.4ab 6.0 ± 0.0a 8.5 ± 0.4ab

h pressure processing.

Fig. 3. Cluster analysis conducted with the method of weighted average linkage using the Euclidean distance for analyzing the contents of polyphenols, anthocyanins, vitamin C, color, enzymatic activity and sensory assessment. Data: CS: control sample; TP: thermal pasteurization; HPP/pressure/time/temperature.

55K. Marszałek et al. / Innovative Food Science and Emerging Technologies 27 (2015) 48–56

therefore, recommended to evaluate the quality of strawberry purée preserved with HPP at 500 MPa, 50 °C, and 15 min during storage. The most distinct advantage of the HPP method was the good preservation of the sensory attributes, which were similar to the control sample and much better than after thermal pasteurization.

Acknowledgments

The Project was financed from funds of the National Research Center (grant No. NN 312 252540) and co-financed from funds of the European Union within the European Social Fund (contract No. 78/ES/ZS-II/W- 2151.1/11). Authors would like to thank Prof. Monika Fonberg- Broczek (Institute of High Pressures PAS UNIPRESS, Poland) for the pos- sibility of using the pressure chamber. We are also grateful to Prof. Alan Kelly (UCC, Cork, Ireland) for his valuable remarks during manuscript preparation.

References

Amakura, Y., Okada, M., Tsuji, S., & Tonogai, Y. (2000). High-performance liquid chro- matographic determination with photodiode array detection of ellagic acid in fresh and processed fruits. Journal of Chromatography A, 896, 87–93.

Barba, F.J., Esteve, M.J., & Frigola, A. (2013). Physicochemical and nutritional characteris- tics of blueberry juice after high pressure processing. Food Research International, 50, 545–549.

Bigliardi, B., & Galati, F. (2013). Innovation trends in the food industry: The case of func- tional foods. Trends in Food Science and Technology, 31, 118–129.

Blumberg, J. (2003). Dietary antioxidants of fruits and vegetable in prevention of chronic diseases. Horticultural Science, 38(5), 771.

Boero, R. (2011). Food quality as a public good: Cooperation dynamics and economic de- velopment in a rural community. Mind & Society, 10, 203–215.

Breitfellner, F., Solar, S., & Sontag, G. (2003). Radiation induced chemical changes of phe- nolic compounds in strawberries. Radiation Physics and Chemistry, 67, 497–499.

Butz, P., Koller, W.D., Tauscher, B., & Wolf, S. (1994). Ultra-high pressure processing of on- ions: Chemical and sensory changes. Food Science and Technology, 27, 463–467.

Cao, X., Zhang, Y., Zhang, F., Wang, Y., Yi, J., & Liao, X. (2011). Effects of high hydrostatic pressure on enzymes, phenolic compounds, anthocyanins, polymeric color and color of strawberry pulps. Journal of the Science and Food Agriculture, 91, 877–885.

Cano, M.P., Hernandez, A., & De Ancos, B. (1997). High pressure and temperature effects on enzyme inactivation in strawberry and orange products. Journal of Food Science, 62(1), 85–88.

Corrales, M., Toepfl, S., Butz, P., Knorr, D., & Tauscher, B. (2008). Extraction of anthocya- nins from grape by-products assisted by ultrasonic, high hydrostatic pressure or pulsed electric fields: A comparison. Innovative Food Science & Emerging Technologies, 9, 85–91.

Da Silva Pinto, M., Lajolo, F.M., & Genovese, M.I. (2008). Bioactive compounds and quan- tification of total ellagic acid in strawberries (Fragaria × ananassa Duch.). Food Chemistry, 107, 1629–1635.

Farahani, P., Grunow, M., & Günther, H.O. (2012). Integrated production and distribution planning for perishable food products. Flexible Services and Manufacturing Journal, 24, 28–51.

Ferrari, G., Marcesca, P., & Ciccarone, R. (2011). The effects of high hydrostatic pressure on the polyphenols and anthocyanins in red fruit products. Procedia Food Science, 1, 847–853.

Gao, X., Ohlander, M., Jeppson, N., Bjork, L., & Trajkovski, V. (2000). Changes in antioxidant effect and their relationship to phytonutrients in fruit of sea buckthorn (Hippophae rhamnoides L.) during maturation. Journal of Agriculture and Food Chemistry, 48, 1845–1890.

Garcia-Palazon, A., Suthanthangjai, W., Kajda, P., & Zabetakis, I. (2004). The effects of high pressure on β-glucosidase, peroxidase and polyphenoloxidase in red raspberry (Rubus idaeus) and strawberry (Fragaria × ananassa). Food Chemistry, 88, 7–10.

Goiffon, J.P., Mouly, P.P., & Gaydou, E.M. (1999). Anthocyanic pigment determination in red fruit juices, concentrated juices and syrups using liquid chromatography. Analytica Chimica Acta, 382, 39–50.

Hakala, M., Lapveteläinen, A., Huopalahti, R., Kallio, H., & Tahovonen, R. (2003). Effects of varieties and cultivation conditions on the composition of strawberries. Journal of Food Composition and Analysis, 16, 67–80.

Hartmann, A., Patz, C., Andlauert, H., Dietrich, H., & Ludwig, M. (2010). Change of ascorbic acid and phenolic compounds during the processing of strawberry purée and juice. Fruit Processing, 4–6, 102–109.

Häkkinen, S.H., Karenlampi, S.O., Mykkanen, H.M., Heinonen, I.M., & Torronen, A.R. (2000). Ellagic acid content in berries: Influence of domestic processing and storage. European Food Research and Technology, 212, 75–80.

Häkkinen, S.H., & Törrönen, A.R. (2000). Content of flavonols and selected phenolic acids in strawberries and Vaccinium species: Influence of cultivar, cultivation site and tech- nique. Food Research International, 33, 517–524.

Heinz, V., & Buckow, R. (2009). Food preservation by high pressure. Journal für Verbraucherschutz und Lebensmittelsicherheit, 10(1007), 3–9.

Kaur, C., & Kapoor, H.C. (2001). Antioxidants in fruits and vegetables. The millennium's health. International Journal of Food Science and Technology, 33, 703–725.

Kalisz, S., Oszmiański, J., Hałdyszowski, J., & Mitek, M. (2013). Stabilization of anthocyanin and skullcap flavones complexes — Investigations with computer simulation and ex- perimental methods. Food Chemistry, 138, 491–500.

Khan, R.S., Grigor, J., Winger, R., & Win, A. (2013). Functional food product development — Opportunities and challenges for food manufacturers. Trends in Food Science and Technology, 30, 27–37.

Klimczak, E., Rozpara, E., & Król, B. (2011). Distribution of ellagitannins in juice, flesh, and achenes as additional criterion for optimal utilization of strawberries. Food. Science Technology. Quality, 6(79), 142–154.

Marigheto, N., Vial, A., Wright, K., & Hills, B. (2004). A combined NMR and microstructural study of the effect of high-pressure processing on strawberries. Applied Magnetic Resonance, 26, 521–531.

Marszałek, K., Mitek, M., & Skąpska, S. (2011). Application of high hydrostatic pressure to stabilize juices and nectars. Food. Science Technology. Quality, 1(74), 113–123.

Odriozola-Serrano, I., Harnandes-Jover, T., & Martin-Belloso, O. (2007). Comparative eval- uation of UV–HPLC methods and reducing agents to determine vitamin C in fruits. Food Chemistry, 105, 1151–1158.

Odriozola-Serrano, I., Soliva-Fortuny, R., & Martin-Belloso, O. (2008). Phenolic acids, fla- vonoids, vitamin C and antioxidant capacity of strawberry juices processed by high- intensity pulsed electric fields or heat treatments. European Food Research and Tech- nology, 228, 239–248.

Oszmiański, J., & Wojdyło, A. (2009). Comparative study of phenolic content and antiox- idant activity of strawberry purée, clear, and cloudy juices. European Food Research and Technology, 228, 623–631.

Oszmiański, J., Wojdyło, A., & Matuszewski, P. (2007). In polyphenols compounds changes In the industrial production process of concentrated strawberry juice. Food. Science Technology. Quality, 1(50), 94–104.

Otero, L., & Prestamo, G. (2009). Effects of pressure processing on strawberry studied by nuclear magnetic resonance. Innovative Food Science & Emerging Technologies, 10, 434–440.

Özkan, M. (2002). Degradation of anthocyanins in sour cherry and pomegranate juices by hydrogen peroxide in the presence of added ascorbic acid. Food Chemistry, 78, 499–504.

Pallauf, K., Rivas-Gonzalo, J.C., Castillo, M.D., Cano, M.P., & Pascual-Teresa, S. (2008). Char- acterization of the antioxidant composition of strawberry tree (Arbutus unedo L.) fruits. Journal of Food Composition and Analysis, 21, 273–281.

Patras, A., Brunton, N.P., Pieve, S., & Butler, F. (2009). Impact of high pressure processing on total antioxidant activity, phenolic, ascorbic acid, anthocyanin content and colour of strawberry and blackberry purées. Innovative Food Science and Emerging Technology, 10, 308–313.

Poretta, S., Birzi, A., Ghizzoni, C., & Vicini, E. (1995). Effects of ultrahigh hydrostatic pres- sure treatment on the quality of tomato juice. Food Chemistry, 52, 35–41.

Rodrigo, D., Loey, A., & Hendrickx, M. (2007). Combined thermal and high pressure colour degradation of tomato purée and strawberry juice. Journal of Food Engineering, 79, 553–560.

Seeram, N.P., Lee, R., Scheller, S., & Heber, D. (2004). Bioavailability of ellagic acid in human plasma after consumption of ellagitannins from pomegranate (Punica granatum L.). Clinica Chimica Acta, 348, 63–68.

Terefe, N.S., Kleintschek, T., Gamage, T., Fanning, K.J., Netzel, G., Versteeg, C., et al. (2013). Comparative effects of thermal and high pressure processing on phenolic phyto- chemicals in different strawberry cultivars. Innovative Food Science & Emerging Technologies, 19, 57–65.

Terefe, N.S., Matthies, K., Simons, L., & Versteeg, C. (2009). Combined high pressure-mild temperature processing for optimal retention of physical and nutritional quality of strawberries (Fragaria × ananassa). Innovative Food Science and Emerging Technology, 10, 297–307.

Terefe, N.S., Yang, Y.H., Knoerzer, K., Buckow, R., & Versteeg, C. (2010). High pressure and thermal inactivation kinetics of polyphenol oxidase and peroxidase in strawberry purée. Innovative Food Science and Emerging Technology, 11, 52–60.

56 K. Marszałek et al. / Innovative Food Science and Emerging Technologies 27 (2015) 48–56

Tiwari, B.K., O'Donnell, C.P., & Cullen, P.J. (2009). Effect of non-thermal processing tech- nologies on the anthocyanin content of fruit juices. Trends in Food Science and Technology, 20, 137–145.

Törrönen, R., Hakkinen, S., Karenlampi, S., & Mykkanen, H. (1997). Flavonoids and pheno- lic acid in selected berries. Cancer Letters, 114, 191–192.

Verbeyst, L., Oey, I., Plancken, V.I., Hendrickx, M., & Loey, A. (2010). Kinetic study on the thermal and pressure degradation of anthocyanins in strawberries. Food Chemistry, 123, 269–274.

Verbeyst, L., Bogaerts, R., Plancken, I., Hendrickx, M., & Loey, A. (2013). Modeling of vita- min C degradation during thermal and high-pressure treatments of red fruit. Food and Bioprocess Technology, 6(4), 1015–1023.

Verbeyst, L., Hendrickx, M., & Loey, A. (2012). Characterisation and screening of the pro- cess stability of bioactive compounds in red fruit paste and red fruit juice. European Food Research and Technology, 234, 593–605.

Wilke, T., Raab, V., Breuer, O., Hamer, M., & Peterson, B. (2013). Lebensmittelsicherheit und die Entwicklung von Public-Private-Partnership-Strukturen. Die Zeitschrift für Außen- und Sicherheitspolitik, 6, 23–33.