Extraction of Golden Delicious apple puree: Experimental comparison of three different methods

Journal of Food Engineering 110 (2012) 169–174

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Extraction of Golden Delicious apple puree: Experimental comparison of three different methods L. Guerra b, G. Romagnoli a, G. Vignali a,⇑ a b

University of Parma, Department of Industrial Engineering, v. G.P. Usberti 181/A, 43124 Parma, Italy University of Naples ‘‘Federico II’’, Department of Materials Engineering and Operations Management, P.le Tecchio 80, 80125 Naples, Italy

a r t i c l e

i n f o

Article history: Available online 2 July 2011 Keywords: Puree extraction Enzyme deactivation Golden Delicious apple Color change

a b s t r a c t In this paper, three different processes for puree extraction from Golden Delicious apples and enzyme inactivation are analyzed and compared: (i) hot extraction technique, (ii) cold extraction technique and (iii) a newly developed vacuum puree extraction technology (Zenith ChronoÒ). The analysis was carried out by means of manual laboratory operations reproducing the three processes. The primary objective of this study was the evaluation of the minimum amount of ascorbic acid that must be added to the three fruit purees in order to contain oxidization and color change in the products. Afterwards, the residual enzymatic activity was checked and characteristics of the products were compared (i.e. fraction of dried solids and consistency of the puree). All of the processes achieved complete enzyme deactivation and an imperceptible color change, and the results of this paper support interest in vacuum puree extraction technology. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction In recent years increasing attention has been paid to the role of diet in human health and foods have been recognized as protective agents, alongside with their intrinsic nutritional and sensory properties. The presence of bioactive compounds in fruits and vegetables has been considered of nutritional importance in the prevention of chronic diseases such as cardiovascular disease, diabetes, various cancers and also neurological diseases (Kalt et al., 1999; Nicoli et al., 1999; Willet, 1994). At the same time, consumers have become more critical towards the use of additives to preserve food or enhance characteristics such as color and flavor (Bruhn, 2000), and minimal processing techniques have emerged as an industrial answer to these needs in order to meet the challenge of replacing traditional preservation methods while retaining nutritional and sensory quality (Allende et al., 2006; Ohlsson, 2002). If the attention is focused on commercial fruit juice and jam products, the overall quality of fruit purees is an essential parameter in order to preserve the original features of the post-harvest fruit. Many characteristics are defined as essential, such as chemical and rheological parameters, presence of organic acid, sugar, polyphenolics and anthocyanins (Fügel et al., 2005). For apple in particular, studies have defined the wellness properties and conserving methods during cold storage and industrial treatment, from the post-harvest phase up to the fruit juice packaging (Felicetti and ⇑ Corresponding author. Tel.: +39 0521906061; fax: +39 0521905705. E-mail addresses: [email protected], [email protected] (G. Vignali). 0260-8774/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2011.06.029

Mattheis, 2010; Will et al., 2008). Chemical and microbiological stabilization during the extraction phase is also important in providing the food industry with a suitable fruit puree, and this leads to a series of necessary technological processes (Spanos et al., 1990; Oszmianski et al., 2008). Several industrial methods are currently adopted for fruit puree extraction and enzyme inactivation, such as hot extraction (HE) and cold extraction (CE) (Paciello et al., 2004). However, both these techniques require the addition of antioxidants, such as ascorbic acid (AA), in order to preserve the natural color of the fruit (Miller and Rice-Evans, 1997). This need was generally recognized, together with pasteurization of the product, for the production of apple purees and cloudy juices (Will et al., 2008). The HE method presents a short distance between crusher and cooker inlet and heats the product together with seeds, peels and stems. The open horizontal cooker moves fruit pieces forward by means of a feeding screw, and the heat is exchanged by direct injection of steam. With this method undesirable color, taste, black specks, molds, pesticides and chemicals present on the peels are transferred into the pulp (Paciello et al., 2004), flavor is lost and there may be contamination from chemicals present in the steam generator. The color deterioration of the products can be controlled through the design of tank geometry, which is linked to residence time. This system also gives rise to an increase in the evaporator’s water removal load and a more difficult automated sanitation. The advantage of this technology is supposed to be a quick enzyme inactivation, and consequently higher viscosity of the final product and a moderate consumption of AA (Downing, 1989).

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Fig. 1. Cross-sectional view of Zenith ChronoÒ technology.

In the case of CE the product is heated without seeds, peels and stems, and the crusher is located on the extractor inlet and close to subsequent enzyme inactivation section. The refined pulp is heated in a tube-chest, through an indirect heat exchanger. No undesirable colors, tastes, black specks, molds, pesticides or chemicals are transferred into the pulp, residence time is defined due to the absence of transient heat transfer and sanitation through an automated CIP system is easier. On the other hand, compared to HE, this process presents a few minutes’ delay between fruit crushing and enzyme inactivation and therefore requires a high consumption of AA to reduce the enzymatic browning of the product, which can only reach lower viscosity. This article proposes a new extraction method aimed at reducing the consumption of AA, increasing product consistency by reducing syneresis, preserving color, maintaining aroma and other organoleptic properties, and stabilizing product to achieve longer shelf-life. In order to reach these objectives, a sequence of processing phases was defined: the whole apples are first peeled, stoned and stemmed, then immediately crushed in anaerobic atmosphere (CO2 + other inert gases), where the apples’ temperature is rapidly increased with the injection of culinary steam. After extraction on the horizontal press, the apple puree is maintained at a pasteurization temperature (approximately 95 °C) by means of an indirect heat exchanger in a tube-chest with product recirculation (1:5). As reported in Fig. 1, the industrial system applies this principle by introducing and crushing the product without seeds, peels and stems. The crusher is installed on the cold extractor, in an oxygen-free environment and with the product outlet directly on the enzyme inactivation hot tank. This system was designed to reach immediate enzyme inactivation, by rapidly heating the apples before crushing and dropping the extracted puree directly into the hot mass. It is therefore possible to maintain high viscosity of the final product and avoid early oxidation, even without the use of AA. This equipment also allows a defined residence time and suitable sanitation through automatic

CIP system, and should grant greater protection of flavors, without product contamination and dilution. Aim of this research is also the validation of this new technology (Zenith ChronoÒ (ZC), by CFT S.p.A., Parma (Italy)), with the final goal of merging together the advantages of HE and CE, while limiting the need for AA. This paper provides the comparison of the three methods previously described thanks to the experimental reproduction of the industrial processes for puree extraction and enzyme inactivation of Golden Delicious apples. 2. Materials and methods The experimental analysis was carried out by means of manual laboratory operations reproducing these processes. The choice for the product fell on Golden Delicious apples because of the wide popularity of this particular cultivar, its availability and uniform quality throughout the year, as in Tortoe et al. (2007). Apples were bought in Conad Campus Supermarket and kept refrigerated (T 6 4 °C) up to their utilization (3–5 days). The primary objective of this study was the simulation of three extraction scenarios (HE, CE and ZC) in order to determine the quantity of AA to be added to the purees so as to stabilize their color. The different extraction techniques are shown in Fig. 2. In HE and CE, the apples were crushed and heated by using a Vorwerk Bimby TM 21 food processor in order to attain enzyme deactivation. The enzyme inactivation process was performed according to Oszmianski et al. (2008), at a temperature of 90 °C for 5 min. The fruit puree was refined in two steps, firstly with a common kitchen strainer, then a 1 mm sieve purchased by ENCO Srl (Spinea, Venezia, Italy). AA was purchased from Sigma Aldrich Srl, Italy (SIGMA A-7506 100 g), supplied as a powder and dissolved in distilled water just before its use, and was added to each puree (i.e. HE, CE and ZC) in 100 ppm (w/w) steps, from 0 to 800 ppm. The fruit puree was put into 100 ml glass containers, sealed with screw caps, and pasteurized at 100 °C for 5 min. While

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Fig. 2. Manual operations reproducing HE, CE and ZC.

The influence evaluation of factors AA concentration and time of exposure was performed using the Analysis of Variance (ANOVA) method assessing the relevance of the main effect and the interaction of the two factors analyzed for the three technologies. For each trial sample, 6 measures of L⁄, a⁄, b⁄ were performed, for a total amount of 108 measures for each technology. The secondary goal of this study was the evaluation of certain properties of the apple puree produced with the three techniques, with the added quantities of AA determined at the previous step. The properties which were compared are (i) concentration of the solid fraction (°Brix), (ii) consistency (Bostwick measure), and (iii) residual enzyme activity of per oxidase (PO), poly phenol oxidase (PPO) and pectin esterase (PE). The degrees of Brix were determined by means of an ATAGO RX-5000 CX refractometer, with a threefold repetition. Consistency was measured through a LS 100 Bostwick consistometer (Labo Scientifica, Parma, Italy) at 20 °C for 30 s. This method was adopted in order to evaluate any syneresis effect due to the possible separation between the solid and liquid phase. Furthermore, the Bostwick consistometer is a simple instrument widely used in the food industry to evaluate the consistency of viscous fluid products. This instrument is described by Milczarek and McCarthy (2006), and the outcome of the Bostwick measurement was related to the properties of Newtonian and Non Newtonian foods, respectively by Huppert (1982) and McCarthy and Seymour (1994). The residual activity of PPO was measured according to Nicoli et al. (1991), using a UV–VIS UV 1601 CE-Shimadzu spectrophotometer, at the conditions of

simulating ZC, the apples were vacuum sealed by means of a FoodSaver VAC 550 and kept in FoodSaver – FSR2801I packs (both supplied by Macom Srl, Milan, Italy). Their enzyme deactivation was achieved inside a common kitchen microwave oven at 900 W for 2 min (Inverter NNT 251 W, Panasonic, Germany). The frequency of the microwave oven is equal to 2450 MHz. Nine samples were created for each extraction technology, for a total of 27 samples. Their color was measured with a Minolta CM-2600d colorimeter (Konica Minolta, Germany) and expressed in L⁄, a⁄ and b⁄ coordinates. For each sample, color measuring was carried out after production and after a 30-min exposure to atmospheric air, allowing the color of apple puree to achieve its stabilization (De Poix et al., 1980). Each sample of fruit puree was placed on a Petri plate (25  100 mm) and color measurements were carried out through the bottom of the plate itself. Every trial sample underwent a 6fold repetition of the color measurement, i.e. one at the centre of the plate, 4 in the outer part and a random one, performed immediately after the process and after 30 min; for each method a series of 108 measures were also performed. Colors were expressed in CIE L⁄ a⁄ b⁄ coordinates and the total color difference (TCD) was calculated according to Tiwari et al. (2008), Eq. (1), with reference to a benchmark puree sample (subscript s) obtained with total enzyme deactivation through methyl alcohol and no heating or browning effects.

TCD ¼

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi   ðL  Ls Þ2 þ ða  as Þ2 þ ðb  bs Þ2

ð1Þ

Table 1 Average values of L, a⁄ and b⁄ related to the concentration of AA added and to the extraction technology at 0 and 30 min of open air exposure. Hot extraction

Cold extraction

0 min

AA added (ppm)

0 100 200 300 400 500 600 700 800

30 min

Zenith Chrono

0 min

30 min

0 min

30 min

L⁄

a⁄

b⁄

L⁄

a⁄

b⁄

L⁄

a⁄

b⁄

L⁄

a⁄

b⁄

L⁄

a⁄

b⁄

L⁄

a⁄

b⁄

44.36 44.13 44.06 43.64 43.82 41.95 40.90 39.90 40.09

1.15 1.73 1.74 1.91 1.42 1.54 1.84 1.45 1.50

13.99 13.73 13.34 11.73 11.07 9.47 10.02 8.57 8.66

43.98 44.46 43.93 44.10 42.97 41.65 40.57 40.58 40.63

1.25 1.70 1.88 1.72 1.49 1.62 1.69 1.46 1.46

13.65 13.16 13.27 11.98 9.95 8.80 9.73 8.55 8.57

39.74 41.88 41.56 40.86 40.87 39.86 39.68 40.75 39.89

0.02 0.08 1.33 1.90 2.29 2.18 2.27 1.85 1.98

10.06 10.94 9.56 8.77 8.87 7.63 7.85 9.97 8.44

41.07 40.88 39.99 40.32 41.70 41.57 40.23 40.54 40.22

0.24 0.39 0.06 1.97 1.92 2.13 2.05 1.78 2.07

11.37 10.42 9.55 7.96 9.86 9.57 9.32 9.75 8.05

41.95 41.22 40.64 41.62 41.22 40.28 40.12 41.34 39.37

1.23 1.22 1.26 1.24 1.75 1.79 1.45 1.24 1.36

9.53 8.64 8.02 9.10 7.92 7.08 7.68 8.54 7.50

42.04 40.42 40.88 41.35 39.46 40.54 40.30 40.75 39.88

1.19 1.49 1.09 1.24 1.84 1.82 1.60 1.28 1.42

8.91 7.65 8.10 8.72 9.05 7.21 7.47 7.93 7.49

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Table 2 ANOVA for TCD of ZC, CE and HE. Source

Sum of square

df

Mean square

F value

p-Value

Model – ZC A-concentration of AA B-time AB Pure error Cor total

4.9962 4.5729 0.0673 0.3560 5.6640 10.6602

17 8 1 8 90 107

0.2939 0.5716 0.0673 0.0445 0.0629

4.6700 9.0829 1.0696 0.7071

<0.0001 <0.0001 0.3038 0.6845

Model – CE A-concentration of AA B-time AB Pure error Cor total

110.2592 100.6960 1.5664 7.9968 19.0273 129.2864

17 8 1 8 90 107

6.4858 12.5870 1.5664 0.9996 0.2114

30.6783 59.5371 7.4091 4.7282

<0.0001 <0.0001 0.0078 <0.0001

Model – HE A-concentration of AA B-time AB Pure error Cor total

483.6823 476.0597 2.3616 5.2610 39.7949 523.4772

17 8 1 8 90 107

28.4519 59.5075 2.3616 0.6576 0.4422

64.3467 134.5819 5.3410 1.4873

<0.0001 <0.0001 0.0231 0.1729

25 °C, pH = 6.5, with the wavelength of 480 nm and a width of the cuvette of 10 mm. This method uses the following reagents: L-3,4dihydroxyphenylalanina (L-DOPA), sodium phosphate, monobasic (NaH2PO4) 0.2 mol/dm3, sodium phosphate, dibasic (Na2HPO4) 0.2 mol/dm3, NaOH 0.1 mol/dm3, NaOH 1 mol/dm3 and a PPO solution (2 mg in 0.2 dm3 of simulant solution). Similarly, the residual activity of PO was measured according to Chance and Maheli (1955), using the same spectrophotometer and a ALC (Milan, Italy) 4239 R centrifuge. The reaction conditions are as follows: 25 °C, pH = 5.0, with the wavelength of 405 nm and a width of the cuvette of 10 mm. The reagents adopted are: potassium phosphate 0.1 mol/dm3 (pH 5 at 25 °C), 2,20 -azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) 0.0091 mol/dm3, hydroperoxide solution at 0.3% (w/w), potassium phosphate 0.04 mol/dm3 with 0.25% (w/v) of bovine serum albumin and 0.5% (v/v) di Triton X1002 (pH 6.8 at 25 °C). Finally, the evaluation of PE activity was performed as in Vas et al. (1967) measuring the carboxyl groups liberated after the reaction of PE with pectin at 30 °C and pH = 7.5. For this test an automatic titrator 718 Stat, Metrohm Titrino (Herisau, Switzer-

land) was used, as well as the following reagents: pectin with a degree of esterification of about 62%, sucrose, ethanol 95%, NaCl 0.15 mol/dm3, NaOH 0.1 mol/dm3 and NaOH 1 mol/dm3. All the data obtained were processed with Design ExpertÒ 7.1 and MS Excel.

3. Results and discussion The color changes of apple purees for HE, CE and ZC were measured through TCD, and related to the quantity of AA added and to the time of exposure. The average results of L⁄, a⁄ and b⁄, related to the concentration of AA and to the extraction technology, are reported in Table 1, which shows how the addition of AA drives the values of L⁄, a⁄ and b⁄ towards the reference level of non treated apples (which is equal to L⁄ = 40.55, a⁄ = 2.47 and b⁄ = 8.72), as in Oszmianski et al. (2008). The ANOVA results for every extraction process are reported in Table 2, where the TCD is related to the concentration of AA and to the time of exposure to open air (0 or 30 min) for each of the three extraction models.

Fig. 3. TCD results for cold, hot and ZC extraction lab technologies after 30 min of product exposure to open air.

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Fig. 4. TCD of HE, CE and ZC after 0 min (a) and 30 min (b) of product exposure to open air.

Table 3 Product comparison results. AA quantity

P – 0 ppm

HE – 500 ppm

CE – 300 ppm

ZC – 0 ppm

Average °Brix Bostwick consistency (cm)

12.20 Pulp Liquid 335 0.024

12.35 3.3 4.0 0 0

14.68 2.8 3.5 0 0

12.86 2.7 2.7 0 0

1.07

0

0

0

PPO residual activity (U/ml) PO residual activity (U/ml) PE residual activity (U/ml)

The statistical analysis for HE, CE and ZC technologies confirms the validity of the hypothesis that the color of the apple purees is significantly influenced by the concentration of AA. The time of exposure to open air, i.e. the interaction between this factor and the amount of AA, does not appear to be significant (with a = 0.01) for the laboratory simulation of ZC and HE methods. CE instead exhibits a major influence of the time of exposure. A suitable residual analysis was performed in order to check model adequacy and validate all the ANOVA results (Montgomery, 2005). By comparing the F values of the AA concentration factor on the three technologies it is possible to see that the influence of this factor is extremely higher for CE and HE. For these two methods it is necessary to add a certain amount of AA to stabilize the color of the fruit puree. Since a TCD between 2 and 3 is perceptible to human beings (Francis and Clydesdale, 1975), a color change is defined perceptible if TCD > 2.5. On these premises, Fig. 3 shows the TCD value reached by the tree extraction technologies after a 30-min exposure of the product to open air, in function of the quantity of AA added. Fig. 4 indicates the average value of TCD for every condition, allowing to compare the different performance of the extraction systems. The amounts of AA needed to keep TCD below 2.5 are (i) 500 ppm, (ii) 300 ppm and (iii) 0 ppm for HE, CE and ZC, respectively. The analyses were performed with such quantities of AA as in Table 3, where P stands for non treated product (raw apples). It emerges that HE allows a small increase in solid concentration (from 12.20° to 12.35° Brix), but lower consistency (according to Bostwick method, the HE treated pulp reaches a value of 3.3 cm, while the liquid reaches 4.0 cm), while CE retains consistency

(with Bostwick value of 2.8 cm for the pulp and 3.5 for the liquid) but increases the Brix (14.68° Brix). ZC shows a slightly higher solid concentration (12.86° Brix) but retains the consistency at its highest level, especially avoiding syneresis (the pulp and the liquid show the same consistency with a Bostwick value equal to 2.7 cm). All of the products achieved complete enzyme deactivation due to the thermal treatment. As indicated in Section 2, the enzymatic residual activity was measured by monitoring PO, PPO and PE. 4. Conclusions This paper compares three different puree extraction methods, with the experimental simulation of the processes and analyses of the most recognized parameters of quality, i.e. Brix degree, color, consistency and the ability to reach a PPO, PO, PE enzyme inactivation. The comparison shows that ZC is the only technology capable of preserving the natural color of Golden Delicious apples without any need for AA as a source of antioxidant and can therefore achieve a consistent economic saving. In order to achieve the same result, CE needs 300 ppm of AA and HE 500 ppm. The comparison of these samples shows how all the technologies achieve complete enzyme deactivation. However, CE delivers a product with higher concentration of solid fraction (which is not desirable from the producer’s point of view), and HE fails to meet the customers’ needs, delivering an end product with lower consistency. ZC meets both of these needs and therefore appears to be the best choice. Further developments of this work may lead to the evaluation of the stability of the products during their shelf life, comparison of

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