Comparison of Pretreatment Methods for Raspberry Juice Production

Transcription

1 Comparison of Pretreatment Methods for Raspberry Juice Production Réka Juhász, Mónika Stéger-Máté, Beatrix Szabó-Nótin, Judit Monspart-Sényi, József Barta Department of Food Preservation, Corvinus University of Budapest Hungary 1. Introduction Berry fruits are very popular raw materials of juices, jams and confectionery products due to their pleasant flavor, odour and colour. They have also high nutritional value as they are rich in antioxidants especially in phenolic compounds (Häkkinen et al. 1999; Stéger-Máté et al. 2006). Polyphenols and anthocyanins are two characteristic group of phenolic compounds in berry fruits. These molecules are sensitive to several factors such as heat, light, oxidative enzymes, acids. (Wesche-Argaiz 2002) Therefore, development of appropriate processing and preservation technologies is essential. Vacuum drying and vacuum evaporation are effective preservative technologies in fruit processing industry providing exclusion of high temperature and presence of oxygen (Bórquez et al. 2010). Raspberry is mainly processed using vacuum evaporation technology to produce concentrate which is further used for juices, jams, candies etc. Nutritional quality of raspberry concentrate can be influenced by the four main steps of processing technology: pretreatment, pressing, vacuum evaporation and storage. During pretreatment the most important goal is to reach appropriate cell degradation prior to pressing by heating and using pectolytic enzymes. Heat treatment during cell degradation can help increase membrane permeability, increase yield during pressing and inactivate enzymes. However, it can facilitate the degradation of antioxidant components (Stéger-Máté et al. 2006). Pectolytic enzymes help decrease pectin content of fruits which increase yield and can help to liberate antioxidant compounds. Proper pressing technology can help to increase yield and decrease amount of by-products. During vacuum evaporation temperature and pressure affect duration, control non-enzymatic browning and other heatinduced detrimental colour changes. The final dry material content can also be a key parameter in quality of berry concentrates. (Cepeda-Villar 1999) Proper storage conditions such as lightness, temperature and packaging can lengthen the shelf-life of berry concentrates. (Burdurlu 2003; Zegarac 2010) In the present study effect of treatment by different pectolytic enzymes and heating on the quality of raspberry juices were evaluated. 2. Materials and methods Commercially available fast frozen raspberry was used for the experiments. Six different pretreatments were tested: effect of two kinds of commercially available pectolytic enzyme: Fructozym P and Fructozym BE combined with or without heating were tested. As for control, treatment without enzyme addition was also performed (Table 1.). Enzymes were provided by Kerttrade Ltd., Hungary. Fructozym P is a liquid, highly concentrated pectolytic enzyme preparation for fast and complete pectin degradation in juice, precondition for good clarification

2 and filtrability. Fructozym BE is a liquid, highly concentrated pectolytic enzyme preparation for a rapid and complete breakdown of pectin and for degradation of colloids to the largest possible extent in the course of berry processing. Table 1. Summary of raspberry pretreatment methods and sampling 1NN 2N80 3PN 4P80 5BEN 6BE80 sampling 1. raw C - 80 C - 80 C heated C 40 C 40 C 40 C 40 C 40 C FruP FruP FruBE FruBE - 5. pressing pressed 6. FruP FruP Clarification: silica sol and gelatin - 8. Filtration clarified (1NN:treatment without heating or enzyme; 2N80: treatment with heating and without enzyme; 3PN: treatment without heating and with Fructozym P; 4P80: treatment with heating and with Fructozym P; 5BEN treatment without heating and with Fructozym BE; 6BE80 treatment with heating and with Fructozym BE) Samples were heated until 80 C and then cooled until 40 C which is the optimal temperature for pectolytic enzymes. 100 µl enzyme was added to 1 kg raspberry and after 45 minutes pressing was performed using a manual press. In the case of control samples enzyme was added after pressing. Clarification method was the same in all of samples: silica sol (0,5 ml/ kg raspberry) and gelatin (0,1 g/kg raspberry) were used. The final step was vacuum filtration using filtration paper. Samples were taken after each main step (Table 1) in order to follow colour, anthocyanin and polyphenol content changes during pretreatment. Juice yield after pretreatment methods was calculated from the fraction of mass of raw raspberry and clarified juice. Polyphenol content was determined using a Hitachi U-2900 (Hitachi High-Technologies Europe GmbH, Krefeld, Germany) spectrophotometer according to the method described by Singleton - Rossi (1965). Anthocyanin content was determined by spectrophotometric method of Füleki - Francis (1968) reading absorbance at 410 nm (A 410 ) and 530 nm (A 530 ). Based on absorbance at 530 nm total anthocyanin content was calculated. Tone was calculated as follows: A 410 /A 530. Colour values were measured using a digital chroma meter (Konica Minolta CR-410). Lightness, red-green value and yellow-blue value were determined based on C.I.E.lab system. Statistical evaluation of data by factorial analysis of variance at 95% confidence level was performed using Statistica software ver 8.0 (StatSoft Inc., Tulsa, USA).

3 3. Results and discussion Juice yield was affected positively by addition of pectolytic enzymes before pressing, while heating did not increase it (Figure 1.). Comparing the two kinds of pectolytic enzyme Fructozym BE the special enzyme mix developed for berries proved to be better than Fructozym P. Best results were observed when Fructozym BE enzyme was used without heating. Figure 1. Raspberry juice yield using different pretreatment methods Yield (%) NN 2N80 3PN 4P80 5BEN 6BE80 Colour values of clarified juices (Table 2.) were compared in order to find out which treatment proved to be the best for keeping the initial colouring power of raspberry. Table 2. Colour values of clarified raspberry juices produced by different pretreatment methods L* a* b* 1NN 22,73 ± 0,01 5,03 ± 0,03 1,51 ± 0,01 2N80 22,22 ± 0,01 3,93 ±0,03 1,26 ± 0,02 3PN 21,96 ± 0,48 5,62 ± 0,13 1,61 ± 0,02 4P80 22,19 ± 0,27 4,23 ± 0,06 1,30 ± 0,01 5BEN 22,32 ± 0,01 7,46 ± 0,05 2,42 ± 0,02 6BE80 22,96 ± 0,01 6,03 ± 0,04 1,98 ± 0,02 (L*: lightness, a* red/green value, b* yellow/blue value, X: average, SD: standard deviation) Pretreatment methods used did not affect the lightness of the samples, there were no significant differences observed. Red / green value was between 4.23 and Heating decreased a* values at each pretreatment, which can be explained by the heat sensitivity of the red colouring compounds (Stéger-Máté et al. 2006). Fructozym P enzyme did not affect the redness of samples compared to the control, while samples treated with Fructozym BE had higher a* values. Yellow / blue value was between 1.26 and Similarly to the red/green values it was lower in the heated samples and showed the highest values in case of pretreatment with Fructozym BE.

4 Tone, polyphenol and anthocyanin content were determined for each step of pretreatment process and results are summarized in Table 3. Table 3. Changes of tone, polyphenol and anthocyanin content of raspberry during different pretreatment processes Pretreatment Sampling Tone PC [mg/l] AC [mg/l] 1NN R 0,13 ± 0, ± ± 46 P 0,18 ± 0, ± 8,5 493 ± 11 C 0,24 ± 0, ± ± 13 2N80 R 0,13 ± 0, ± ± 46 H 0,22 ± 0, ± ± 11 P 0,17 ± 0, ± ± 9,5 C 0,20 ± 0, ± ± 18 3PN R 0,13 ± 0, ± ± 46 P 0,23 ± 0, ± ± 21 C 0,23 ± 0, ± 9,7 720 ± 20 4P80 R 0,13 ± 0, ± ± 46 H 0,15 ± 0, ± ± 33 P 0,19 ± 0, ± ± 18 C 0,31 ± 0, ± 8,1 591 ± 11 5BEN R 0,13 ± 0, ± ± 46 P 0,25 ± 0, ± ± 22 C 0,23 ± 0, ± ± 18 6BE80 R 0,13 ± 0, ± ± 46 H 0,30 ± 0, ± ± 49 P 0,36 ± 0, ± ± 11 C 0,26 ± 0, ± ± 26 (R: raw, P: pressed, H: heated, C: clarified, PC: polyphenol content [mg/l] calculated for 10ref%, AC: anthocyanin content [mg/l] calculated for 10ref%, X: average, SD: standard deviation) Tone or browning value (Table 3.) was calculated using the absorbance data of anthocyanin measurements. The higher tone value refers to the higher level of browning. Results indicated that raspberry juices showed only a slight browning during each pretreatment processes investigated. Lowest tone values were observed in the control samples which can be explained by the shorter duration of process. Changes of polyphenol content of juices increased during each pretreatment process investigated (Table 3.) indicating that polyphenols are concentrated in the clarified juice, not in the solid by-products remained after pressing. Highest polyphenol content in the juices treated with Fructozym BE pectolytic enzyme were observed. Heating did not have detrimental effect on polyphenols which is in accordance with the results of other authors evaluating effect of vacuum drying on polyphenols of apricot (Madrau et al. 2007) and of blueberry (Somsong et al. 2010).

5 Anthocyanin content of juices (Table 3.) increased during each pretreatment process investigated. Highest anthocyanin content in the juices treated with Fructozym P pectolytic enzyme was observed. Heated samples had lower anthocyanin content as these compounds are reported to be heat sensitive (Stéger-Máté et al. 2006; Wesche-Argaiz 2002). Effect of heating and pectolytic enzymes on anthocyanin and polyphenol content of clarified raspberry juices was evaluated by analysis of variance at 95 percent confidence level. Results indicated that both of the factors had significant effect on polyphenols and athocyanins. For preserve anthocyanins treatment with Fructozym P and no heating proved to be the best. However, to get the highest polyphenol yield, Fructozym BE enzyme combined with heating is the most effective pretreatment method. 4. Conclusion In summary these experiments showed that pectolytic enzymes are beneficial for increase juice yield, anthocyanin and polyphenol content during pretreatment process. Comparing the pectolytic enzymes used, Fructozym BE proved to be more effective than Fructozym P for producing high quality raspberry juices. However, for preserving anthocyanin compounds Fructozym P seemed to be better. Heating did not help increase juice yield and decreased anthocyanin content, but not decreased polyphenol content. Based on our results pretreatment process using Fructozym BE pectolytic enzyme is suggested to be the best for producing high quality raspberry juice for concentrate production. Further investigations needed to evaluate the effect of vacuum evaporation technologies and then of the storage conditions on the quality of raspberry concentrates. Acknowledgement The authors acknowledge the financial help of the TÁMOP /B-09/1/KMR grant and the technical assistance of D. Jakab and A. Tóbi. References Bórquez, R.M., Canales, E.R., Redon, J.P. (2010) Osmotic dehydration of raspberries with vacuum pretreatment followed by microwave-vacuum drying. Journal of Food Engineering 99: Burdurlu H.S., Karadeniz, F. (2003): Effect of storage on nonenzymatic browning of apple juice concentrates. Food Chemistry 80: Cepeda, E., Villar M.C. (1999): Density and viscosity of Malus oribunda juice as a function ofconcentration and temperature. Journal of Food Engineering 41: Füleki, T., Francis, F.J. (1968): Quantitative methods for anthocyanins 2. Journal of Food Science 33: Häkkinen, S., Heinonen, M., Kärenlampi, S., Mykkänen, H., Ruuskanen, J., Törrönen, R. (1999): Screening of selected flavonoids and phenolic acids in 19 berries. Food Research International 32: Madrau, M., Piscopo, A., Sanguinetti, A., del Caro, A., Poiana, M., Romeo, F.V. & Piga, A. (2007): Effect of drying temperature on polyphenolic content and antioxidant activity of apricots. European Food Research and Technology 228:

6 Robards, K., Prenzler, P.D., Tucker, G., Swatsitang, P., Glover, W. (1999): Phenolic compounds and their role in oxidative processes in fruits. Food Chemistry 66: Singleton, V.L., Rossi, J.A. (1965): Colorimetry of total phenolics with phosphomolybdic phosphotungstic acid reagents. American Journal of Enology and Viticulture 16: Somsong, P., Srzednicki, G., Konszak, I. & Lohachoompol, V. (2010): Effects of preconditioning on quality of dried blueberries. 10th International Working Conference on Stored Product Protection. Archive of Julius-Kühn, 425: Souci, S.W., Fachmann, W., Kraut, H. (2008.): Die Zusammensetzung der Lebensmittel Nährwert-Tabellen. 7. revidierte Auflage, Medpharm Scienctific Publishers, Stuttgart, Deutschland Stéger-Máté, M., Horváth, E., Barta, J. (2006): Investigation of colorant content and stability in elderberry (Sambucus nigra L.). Acta Alimentaria 35: Wesche-Ebeling, P. & Argaiz-Jamet A. (2002): Stabilization mechanisms for anthocyanin: the case for copolymerization reactions. -in: J., Barbosa-Cánovas, G.V., & Aguilera, J.M., Welti- Chanes, Engineering and food for the 21th century. ISBN , CRC Press, Boca Raton, Florida, USA Zegarac J. P., Samec D. (2011): Antioxidant stability of small fruits in postharvest storage at room and refrigerator temperatures. Food Research International 44: