Study of inhibition of browning of clarified banana juice

Transcription

1 Asian J. Dairy & Food Res., 35 (2) 2016 : Print ISSN: / Online ISSN: AGRICULTURAL RESEARCH COMMUNICATION CENTRE Study of inhibition of browning of clarified banana juice A.R. Tapre* and R.K. Jain Department of Food Processing Technology, A.D. Patel Institute of Technology, New V V Nagar, Anand , India. Received: Accepted: DOI: /ajdfr.v35i ABSTRACT Browning is the second largest cause of quality loss in fruits and vegetables. It seems to be the most severe problem during banana pulp processing. Effect of two anti-browning pretreatments viz. addition of ascorbic acid ( ppm) and blanching the peeled fruits (90 0 C for different periods) prior to enzymatic clarification banana juice were studied. Effectiveness of anti-browning pretreatments to the pulp was evaluated by measuring the browning in terms of Browning Index in prepared clarified juices. Clarified banana juice obtained from untreated pulp had dark brown colour with initial browning index value of which continuously increased and reached to at 24 h of storage. Pretreatment of pulp with 1000 ppm of ascorbic acid or heating at 90 0 C for 6 minute was observed to retain the natural colour of prepared clarified juice without marked changes up to 4 h of storage at room temperature. However preheating of banana pulp observed to be caused cooked flavour and altered the original taste of the clarified juices. Key words: Ascorbic acid, Browning, Browning Index, Clarified banana juice, Preheating. INTRODUCTION Banana (Musa sp.) is the fourth most important food crop in the world after rice, wheat and maize with a world production of around MT in 2012 (FAO, 2014). But a large percentage of the crop is typically unsuitable for the fresh market since it is too mature for shipment. Banana could compete in the market either as banana juices or as mixture of other juices because of its widely appreciated flavour and high nutritive value. Banana juice can also be utilized for wine production. However, banana juice is turbid, gray in colour, very viscous, tends to settle during storage and therefore must be clarified prior to commercialization. The problems associated with banana juice processing, a high viscosity and browning seems to be the most severe. The turbidity and viscosity of banana juice are mainly caused by the polysaccharides in the juice such as pectin and starch. Depectinization using pectinase enzyme could effectively clarify fruit juices. Pectinase hydrolyzes pectin and cause pectin-protein complexes to flocculate (Koffi et al., 1991; Yusof and Ibrahim, 1994; Lee et al., 2006). During the preparation of clarified banana juice, banana pulp is highly susceptible to enzymatic browning while pulping. Browning reaction of banana pulp results from the enzymatic oxidation of dopamine (3,4 -dihydroxyphenyl ethylamine) by polyphenoloxidase (Griffiths, 1959, Ranveer et al., 2010) leading to the production of brown pigments. Longer incubation time for enzymatic treated banana pulp will responsible for more oxidation and production of coloured products. Thus, at the end of enzymatic treatment, *Corresponding author s banana pulp becomes dark and the juice released turns brownish with unattractive appearance and also may reduce the nutritive value of the prepared juices (Eskin et al., 1971; Scott, 1975). Several methods such as the addition of browning inhibitors and the exclusion of oxygen as well as thermal processing have been used to inhibit enzymatic browning. A chemical commonly used is sodium metabisulphite. However, one problem with this chemical is that it may induce asthmatic episodes in a segment of the asthmatic population and thus, it need to find alternatives to sulphite (Sapers, 1993). The use of browning inhibitors in food processing is restricted by considerations relevant to toxicity, wholesomeness and effect on taste, flavour, texture and cost. Therefore present study was undertaken in order to to find a suitable method to inhibit the activity of PPO in banana and prevent discoloration during the course of juice clarification. MATERIALS AND METHODS Bananas (Musa sp.) of variety Robusta were procured at the maturity stage 1 (all green) from selected banana orchards near Anand city (India). The procured material was sorted, tagged and kept for ripening as per the method suggested by Kulkarni et al., (2010) up to 7 th stage of maturity. Commercial pectinolytic enzyme i.e. Pectinex Ultra SP-L (with enzymatic activity PG U per ml, optimum ph 3.5 to 6 and temperature below 50 0 C) and cellulase enzyme i.e. Celluclast 1.5L with cellulose activity 158 U per ml were obtained from Novozymes South Asia Pvt. Ltd., Bangalore and other chemicals from local suppliers.

2 156 ASIAN JOURNAL OF DAIRY AND FOOD RESEARCH Anti-browning pretreatments to pulp: Clarified banana juice were prepared by using the commercial pectinolytic enzyme i.e. Pectinex Ultra SP-L and cellulase enzyme i.e. Celluclast 1.5L as per the process suggested by Tapre and Jain (2014). The banana fruits were washed, peeled manually and cut into small pieces. Pieces were then pulped using a kitchen blender for 2 minute into pulp. After the pulping, 500g pulp was subjected to enzyme treatment i.e. 0.11% Pectinex Ultra SP-L at temperature (40 0 C) for 145 minute and then treated with 0.05% cellulase enzyme i.e. Celluclast 1.5L. At the end of the treatment, the enzymes in the pulp was inactivated by heating at 90 0 C for 5 minute and immediately cooled to room temperature. The enzyme treated pulp was centrifuged at 2900 G/15 minute and the supernatant was filtered through a fine mesh nylon cloth spread on glass funnel and juice was collected. Prior to juice clarification, following anti-browning pretreatments were applied to banana pulp to inhibit the PPO activity and enzymatic browning: a) Addition of ascorbic acid at concentrations of ppm to the peeled fruits during blending and then clarified juices were prepared b) Blanching the peeled fruits in hot water temperature 90 0 C for different periods up to 10 minutes. These heated samples were quickly cooled to room temperature by dipping in cold water then blended and clarified juices were prepared. Browning of the prepared clarified juices obtained was measured immediately after extraction and at intervals of 2, 4, 6 and 24 h. Evaluation of effectiveness of anti-browning pretreatments: Effectiveness of anti-browning pretreatments to the pulp was evaluated by measuring the browning in terms of Browning Index in prepared clarified juices. To measure the enzymatic and non enzymatic browning, 20 ml of the juice was mixed with 30 ml of ethyl alcohol in a glass stoppard flask (Ranganna, 2000). The mixture was shaken thoroughly and filtered through Whatman No.42 filter paper. The absorbance of the filtrate was measured at 420 nm against 60% aqueous alcohol in a using Shimadzu UV VIS spectrophotometer. Browning index (A at 420 nm) was expressed as absorbance value. Statistical analysis: Analysis of variance (ANOVA) was used to detect the effect of pretreatment during different time intervals. Tukey s Multiple Comparison Test was employed for mean separation. The level of significance was at 5%. The analysis was performed using the Daniel s XL Toolbox version Physico-chemical parameters of clarified banana juices: The juice yield was estimated as percentage of the juice obtained based on the initial pulp. The clarity of the juice obtained was determined by measuring % transmittance at a wavelength of 660 nm using UV VIS spectrophotometer (Shimadzu, Model: BL-220-H). Distilled water was used as the reference. Titratable acidity was determined by direct titration of diluted pulp with 0.1N NaOH as described by Ranganna (2000) and TA was expressed as a % of malic acid. TSS was measured as 0 Brix at 200 C with Hand Refractometer. The necessary corrections were made when the measurements were carried out at temperatures other than 200C. Total sugar content were analyzed as per Shaffer - Somogyi method and starch in the alcohol insoluble solids was hydrolyzed using HCL and the resultant reducing sugar was determined by Shaffer -Somogyi method given in Ranganna (2000). RESULTS AND DISCUSSION Ascorbic acid pre-treatment: To evaluate the effectiveness of ascorbic acid, banana pulp was pretreated with different concentrations of ascorbic acid ( ppm) prior to clarification. Pretreated banana pulp was then treated with optimized enzymatic conditions to prepare clarified juices. In the prepared juices, browning in terms of Browning Index was measured immediately after preparation (initial value) and after 2 h interval for the period of 6 h. Also the reading of 24 h storage was recorded. Results depicted in Table 1 indicates that clarified banana juice obtained from untreated pulp had dark brown colour with initial browning index value of which Table 1: Effect of pre-treatment of banana pulp with different concentrations of ascorbic acid in preventing browning in clarified banana juice Ascorbic acid Browning index (A at 420 nm) concentration Initial Value Time intervals (h) (ppm) e d c b a e d c b a d d c b a e d c b a e d c b a d cd c b a d d c b a

3 Volume 35 Issue 2 (2016) 157 continuously increased during holding at ambient temperature and reached to at 24 h of storage. However lower browning index values of clarified juices obtained from ascorbic acid treated pulp indicated that browning reaction suppressed due to action of ascorbic acid. Depending on the concentration of inhibitor, juices obtained had light colour. As the concentration of ascorbic acid increased (200 to 1200 ppm), browning index in clarified juices gradually decreased. Lower concentration of ascorbic acid (200 to 800 ppm) was satisfactory to prevent enzymatic browning during juice extraction and protect the colour of extracted juices only for a short period. However, juices obtained from the pulps pretreated with ppm of ascorbic acid retained their natural light colour without significant change over 4 h at room temperature (as indicated by lower absorbance at 420 nm). The inhibitory action of ascorbic acid is mainly due to its reducing action on enzymatically formed O- quinone back to phenols furnishing fresh substrate to the enzyme resulting in a gradual decrease in its activity (Ponting, 1960). Thus at low concentration, these inhibitor may be quickly consumed in reduction process and the colour formation was delayed for only a limited time but not completely suppressed (Yi and Ding, 2014). At high concentrations, ascorbic acid can also inhibit PPO (Vamos- Vigyazo, 1981, Jang and Moon, 2011). Under the conditions of this investigation, for complete enzymatic clarification of juice, 4 h period was required. Therefore, it is necessary to protect the juice from discolouration during this clarification period. According to the results obtained, on pretreatment of pulp with 1000 ppm of ascorbic acid, the juice obtained retained its natural colour without marked changes up to 4 h at room temperature. Samanta et al, (2010) evaluated the anti-browning (inhibition of polyphenol oxidase activity) effect of different inhibitors in banana, apple and mushroom and also reported ascorbic acid as the most effective PPO inhibitor in all the samples. Heat pretreatment: Blanching is one of the most effectively applied methods of heat treatment for controlling enzymatic browning in fruits and vegetables. Polyphenol oxidase is the endogenous enzyme of most of the fruits and vegetables majorly responsible for their browning (Manohar et al, 2014). Exposure of polyphenol oxidase to temperature in the range of C, results in the destruction of their catalytic activity (Vamos-Vigyazo, 1981). In the present study, peeled banana fruits were blanched in hot water (90 0 C) for different periods up to 10 minutes. These heated samples were quickly cooled to room temperature by dipping in cold water then blended and clarified juices were prepared with optimized enzymatic conditions. Clarified juices obtained from pulps preheated at different periods were measured for browning immediately after preparation (initial value) and after every 2 h of storage over a period of 6 h. Browning index values presented in Table 2 indicates that browning problem was severe in clarified banana juice obtained from pulp without any preheat treatment. However, preheating of banana pulp at 90 0 C was observed to reduce browning reactions in prepared clarified juices, depending on the heating time. Increased in blanching time (2 to 10 minutes) decreased the browning in clarified juices. Blanching at 90 0 C for a short time (2 to 4 minutes) was observed to protect the colour of extracted juices to a less extent and for a short period of time upto 2 h. However juices obtained from the pulps preheated at same temperature for comparatively longer period (6 to 10 minutes) retained their natural light colour without significant change over 4 h. This may be due to the thermal inactivation of endogenous polyphenol oxidase in banana pulp. According to the conditions of the present investigation, anti browning treatment should protect the juice from discolouration for minimum 4 h (clarification period). From Table 2 it is evident that minimum heating of banana pulp for 6 minute was sufficient to retain natural colour for 4 h in prepared clarified juice. The results are in line with observations of Garda et al. (1985) and Sims and Bates (1994) who applied heat treatment to control browning in banana puree. Quality characteristics of clarified banana juices obtained from pre-treated pulp: Pretreatment of pulp with 1000 ppm of ascorbic acid or heating at 90 0 C for 6 minute was observed to retain the natural colour of prepared clarified juice without marked changes up to 4 h of storage at room temperature. To select the most desirable antibrowning Table 2: Effect of pre-heating of banana pulp for different times (At 90 0 C) in preventing browning in clarified banana juice Heating Browning index (A at 420 nm) Time Initial Value Time intervals (h) (minute) e d c b a e d 0.256c b a e d c b a c c c b a c c c b a d cd c b a

4 158 ASIAN JOURNAL OF DAIRY AND FOOD RESEARCH Table 3: Quality characteristics of clarified banana juices obtained from pretreated banana pulp Parameters Pretreatment to Pulp Control Ascorbic acid(1000 ppm) Heating (90 0 C /6 minute) Yield of juice (%) 75.3±1.04 a 74.2±0.32 a 68.0±0.6 b Clarity (%T at 660nm) 94.2±0.2 a 92.26±0.46 b 88.26±0.70 c Titratable Acidity (as % malic acid) 0.51±0.01 b 0.55±0.01 a 0.52±0.00 b TSS ( o Brix) 23.4±0.1 a 23.5±0.1 a 23.1±0.1 b Total sugar (%) 19.06±0.12 a 18.94±0.02 a 18.06±0.12 b Reducing sugar (%) 11.57±0.15 b 12.03±0.06 a 11.47±0.11 b Sensory Qualities Colour Dark Brown Yellow Yellow Flavour Banana Banana Slightly Cooked Taste Typical sweet Typical sweet Cooked Overall Acceptability Good Very Good Fair treatment, juices obtained from these pretreatments were analyzed for their quality characteristics. Juice obtained without any pulp pretreatment was considered as Control. The results depicted in Table 3 indicated that yield, clarity and titratable acidity of juices prepared from ascorbic acid treated pulp were significantly higher than those for preheated pulp. This could be due to thermal inactivation of the endogenous banana pectinases which might have a synergistic effect during pectic enzyme treatment of the pulp. Levi et al. (1980) observed that blanching of banana pulp decreased the activity of pectinesterase of pulp. Total soluble solids and sugar content were found to be decreased in juices prepared with preheated pulp. This may be due to leaching out of water soluble solids during blanching treatment. Considerable variations were recorded in sensory qualities of the clarified juices obtained from both these pretreatments. Undesirable dark brown colour was observed in juices obtained from without pretreated banana pulp. Discoloration of juice may be due browning reaction occurred in the pulp during clarification process. Pretreatment of pulp with 1000 ppm of ascorbic acid was observed to yield banana juices with their natural colour and having typical banana flavour and good sweet taste. Whereas preheating of banana pulp caused cooked flavour and altered the original taste of the clarified juices. CONCLUSION The present study concluded that preheating of banana pulp observed to cause slightly cooked flavour and altered the original taste of the clarified juices. Pretreatment of banana pulp with 1000 ppm of ascorbic acid is the most suitable method to produce clarified juice with natural yellow colour and acceptable flavour. REFERENCES Eskin, N. A. M., Henderson, H. M. and Townsend, R. J. (1971). Browning reactions in Food. In Biochemistry of Foods. Academic Press, New York, (pp ). FAO. Banana Statistics- 2012, Available Source: [Accessed on December 2014] Garda, R., Arriola, M.C., Porres, E. and Rolz, C. (1985) Process for banana puree preservation at rural level. LWT- Food Science and Technology, 18: Griffiths, L. A. (1959). Detection and identification of the polyphenoloxidase substrate of the banana. Nature, 184: Jang, J. H., and Moon, K. D. (2011). Inhibition of polyphenol oxidase and peroxidase activities on fresh-cut apple by simultaneous treatment of ultrasound and ascorbic acid. Food Chemistry, 124: Koffi, E. K, Sims, C. A. and Bates, R. P. (1991). Viscosity reduction and prevention of browning in the preparation of clarified banana juice. Journal of Food Quality, 14: Kulkarni, S.G., Kudachikar, V.B. and Prakash, M.N. (2010). Studies on physico-chemical changes during artificial ripening of banana (Musa spp) variety Robusta. J Food Sci. Technol. (online journal DOI /s y) Lee, W. C., Yusof, S., Hamid, N. S. A., and Baharin, B. S., (2006). Optimizing conditions for enzymatic clarification of banana juice using response surface methodology (RSM). Journal of Food Engineering, 73: Levi, A., Ramirez-Martinez, J.R. and Padua, H. (1980). Influence of heat and sulphur dioxide treatments on some quality characteristics of intermediate moisture banana. J. Food Technol., 15: Manohar,M.P., Harish Nayaka,M.A. and Mahadevaiah (2014). Studies on phenolic content and polyphenol oxidase activity of sugarcane varieties with reference to sugar processing. Sugar Tech, 16: Ponting, J.D. (1960). The control of enzymatic browning of fruits in Food Enzymes H.W. Schultz AVI Publ. Co., INC. Westport, Conn, (pp ).

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