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Effect of additives on the quality of tender coconut water processed by nonthermal two stage microfiltration technique
LWT - Food Science and Technology 59 (2014) 1191e1195
Contents lists available at ScienceDirect
LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt
Research note
Effect of additives on the quality of tender coconut water processed by nonthermal two stage microfiltration technique* Nikhil Kumar Mahnot a, Dipankar Kalita a, Charu Lata Mahanta a, Mihir Kanti Chaudhuri b, * a b
Department of Food Engineering and Technology, School of Engineering, Tezpur University, Assam, India Tezpur University, Assam, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 July 2013 Received in revised form 10 June 2014 Accepted 16 June 2014 Available online 24 June 2014
Non-thermal two-stage microfiltration technique in aseptic conditions was used to preserve coconut water. Concentrations of citric acid (0.02 g/100 mL), ascorbic acid (0.18 g/100 mL) and L-cysteine (0.009 g/ 100 mL) were standardized according to taste and added to coconut water as natural additives. The coconut water was packed in glass and plastic bottles after flushing the headspace with nitrogen and stored under refrigeration (4 C). The microfiltered water was studied for microbial, sensory and physicochemical properties for a period of 46 days. The quality of the water packed in glass bottles was better in all respects. The total soluble solids changed from 5.4 to 6 Brix. The pH changed from 5.7 to 5.8. The soluble sugar concentration increased from 1.9 g/100 mL to 3.1 g/100 mL, free fatty acid content increased from 0.064 mg KOH/g to 2.8 mg KOH/g at the end of 46 days, which was much lower than the changes in control. The protein content decreased in all the samples. Two way ANOVA showed that the storage time had more impact on the sensory properties of the product than the packaging material. The glass bottled product was acceptable on sensory basis till 46 days of storage. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Tender coconut water Non-thermal sterilization Microfiltration Additives Storage
1. Introduction Coconut (Cocos nucifera L.) is an important fruit in the tropical regions. Tender coconut water is consumed as a refreshing drink because of its nutritional and therapeutic properties. The electrolyte and mineral balance makes tender coconut water suitable as a sports drink. However, it is very sensitive to deterioration and the water is unsuitable for drinking after a day or so due to external contamination by microorganisms and oxidation because of which it loses most of its sensory and nutritional characteristics (Haseena, Kasturi, & Padmanabhan, 2010; Reddy, Das, & Das, 2005). Commercially available canned coconut water is given a hightemperature/short-time thermal treatment. Although the shelf life of thermally processed tender coconut water is long, thermal processing tends to decrease the nutrient content and completely destroys its natural flavor (Haseena et al., 2010) unlike non-thermal techniques. This severely limits the marketability of the product (Jayanti, Rai, Dasgupta, & De, 2008). Today's consumers are looking
*
Patent applied for. * Corresponding author. Tel.: þ91 3712 267008x5702; fax: þ91 3712 267005. E-mail addresses: [email protected], [email protected] (C.L. Mahanta), [email protected] (M.K. Chaudhuri). http://dx.doi.org/10.1016/j.lwt.2014.06.040 0023-6438/© 2014 Elsevier Ltd. All rights reserved.
for natural products which are not adversely modified while providing targeted benefits. Selecting technological processes to preserve the natural wholesome properties of the coconut water still remains a challenge. Various workers have studied effects of thermal and non-thermal technologies including pasteurization, (Chowdhuri, Rahman, Islam, & Islam, 2009; Chowdhury, Aziz, & Uddin, 2005), ohmic pasteurization (Somboonsilp, Tia, & Yoovidhya, 2011) and cold pasteurization (Rolle, 2007), dense phase carbon dioxide technology (Damar, Balaban, & Sims, 2009), filtration (Das Purkayastha, Kalita, Das, et al., 2012; Das Purkayastha, Kalita, Mahnot, et al., 2012; Reddy et al., 2005; Reddy, Das, & Das, 2007), etc. These techniques alone or in combination with preservatives were studied to increase the shelf life of tender coconut water. Das Purkayastha, Kalita, Das, et al. (2012) and Das Purkayastha, Kalita, Mahnot, et al. (2012) using microfiltration technique and adding ascorbic acid were able to preserve tender coconut water for 21 days in refrigerated condition. In this study we used the microfiltration technique and added citric acid, ascorbic acid and cysteine to the filtered water and monitored its shelf life in glass and plastic packaging material. The additives were added based on their properties including metal chelating, microbial growth inactivating ability, anti-oxidant activity, anti-browning property and ability to delay the increase of titratable acidity as reported by various researchers (Brul & Coote,
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1999; Darkwa, Mundoma, & Simoti, 1988; Iyidogan & Bayındirli, 2004; Lawrence, Botting, Antrobus, & Coote, 2004; Lisbeth, Hawken, & Talcott, 2007; Mao, Xu, & Que, 2007). 2. Materials and methods Tender coconuts were obtained from surrounding area of Tezpur University, Assam. Chemicals were obtained from Merck and HIMEDIA and glass wares were of Borosil. The filtration setup consisted of filter funnel with clamps, bacterial filtration units, heavy duty vacuum flasks, and autoclavable pipes that were from Tarsons. Cellulose nitrate bacterial filter membranes of 0.8 mm and 0.45 mm pore size were obtained from Sartorius and Merck Millipore, respectively. 2.1. Methods 2.1.1. Sanitization of tender coconuts and materials The whole processing area was cleaned carefully and fumigated with formaldehyde and potassium chromate two days before processing. On the day of filtration the tender coconuts were washed with tap water to remove the surface dust and dipped in 300 mg/L sodium hypochlorite solution to sanitize. All the processing equipments used were sterilized in an autoclave at 103.42 KPa for 15 min. 2.1.2. Addition of ascorbic acid, citric acid and L-cysteine and fuzzy logic Different concentrations of citric acid ranging from 0.005 to 0.02 g/100 mL and ascorbic acid ranging from 0.01 to 0.2 g/100 mL were added to coconut water and evaluated on a 9 point Hedonic scale by 15 member semi-trained panelists. The panelists had preferred the combination of 0.02 g/100 mL citric acid and 0.01 g/ 100 mL ascorbic acid added to tender coconut water. To this selected combination of citric acid and ascorbic acid, five different concentrations of L-cysteine was added. Coconut water samples were marked as S1 (no L-cysteine), S2 (0.007 g/100 mL L-cysteine), S3 (0.008 g/100 mL L-cysteine), S4 (0.009 g/100 mL L-cysteine) and S5 (0.010 g/100 mL L-cysteine). These samples were evaluated for sensory attributes of taste, aroma, mouthfeel and overall acceptability by 15 semi-trained panelists. Fuzzy logic (Das, 2005) was applied to get the best combination from the scores obtained. 2.1.3. Processing of tender coconut water The tender coconuts were cut open with a sanitized stainless steel knife and its water was strained into a beaker inside the laminar air flow. The microfiltration process was also carried out inside the laminar flow. The collected water was first filtered in a filter and clamp connection through a Whatman No. 4 filter paper. The filtered water was transferred through the Teflon pipe to a bacterial filtration unit with a 0.8 mm membrane filter which was attached to a vacuum pump. The filtrate was collected and the process was repeated to filter through a second filtration unit with a 0.45 mm filter. Any spillage of coconut water inside the laminar air flow was cleaned with cotton dipped in alcohol. The final filtered coconut water was transferred slowly to a heavy duty vacuum flask. Following this accurately weighed and calculated amount of citric acid, ascorbic acid and L-cysteine were added to the heavy duty vacuum flask and mixed slowly. The processed tender coconut water was then filled into sterilized plastic (Tarsons) and glass bottles of 50 mL each. The headspace was flushed with nitrogen gas inside a laminar hood. The lids were closed tightly and the samples were stored under refrigerated condition at 4 C. 2.1.4. Storage study The tender coconut water of both plastic and glass bottles were analyzed at 7 days, 22 days and 46 days. The samples were initially
Table 1 Similarity values of samples S1eS5. Scale factors
S1
S2
S3
S4
S5
Not satisfactory, F1 Fair, F2 Satisfactory, F3 Good, F4 Very good, F5 Excellent, F6
0.0073 0.107 0.311 0.525 0.653 0.332
0.0073 0.109 0.315 0.531 0.652 0.3254
0.010 0.122 0.325 0.529 0.630 0.312
0.004 0.097 0.304 0.523 0.675 0.349
0.012 0.135 0.347 0.555 0.618 0.290
S1eS5 denotes the samples under study. F1eF6 indicates membership function of standard fuzzy scale.
checked for microbial load and then given for sensory evaluation on a 9 point hedonic scale by semi-trained panelists. Various parameters like pH, Brix, total titratable acidity, simple sugars, protein and free fatty acid were analyzed for all the samples. Untreated coconut water (original) was stored in glass bottle and was analyzed on 0 day and 46th day. The analysis of bottled coconut water was based on its sensory properties. The analysis was stopped after 46th day because bottled coconut water lost its flavor and its characteristic taste except for microbial load.
2.1.5. Microbial load Nutrient broth agar and Rapid HiColiform media was used to count the number of microbes and number of coliforms present in the sample, respectively.
2.1.6. Measurement of physicochemical properties The pH and total soluble solids were measured using a pH meter (Eutech) and a hand refractometer (Erma, Japan) respectively (Ranganna, 1986). Total titratable acidity and free fatty acid (Acid value) were estimated according to the method given in Sadasivam and Manickam (2007). The total titratable acidity was calculated with respect to citric acid.
TTA ¼ Titre volume 0:1 67:05 100=Sample volume 1000 Acid value ðmg KOH=gmÞ ¼ Titre value 0:1N KOH 56:1=Amount of sample Protein estimation was done according to Lowry, Rosebrough, Farr, and Randall (1951). A modified anthrone method of total carbohydrate determination was followed for simple sugar estimation (Sadasivam & Manickam, 2007). In the modified method, 0.1 mL of the coconut water was taken and the volume was made up to 1 mL with distilled water and anthrone reagent (200 mg anthrone in 100 mL of 95 g/L sulphuric acid) was added. Absorbance for sugar and protein was observed at 630 nm and 660 nm respectively in a spectrophotometer (Cecil Aquarius 7400, England).
Table 2 Similarity for quality attributes of tender coconut water of sample S4. Scale factors
Taste
Aroma
Mouthfeel
Overall acceptability
Not satisfactory, F1 Fair, F2 Satisfactory, F3 Good, F4 Very good, F5 Excellent, F6
0 0 0.149 0.583 0.979 0.545
0 0.024 0.237 0.572 0.756 0.371
0 0.025 0.242 0.584 0.764 0.371
0 0.025 0.242 0.584 0.764 0.371
F1eF6 indicates membership function of standard fuzzy scale.
N.K. Mahnot et al. / LWT - Food Science and Technology 59 (2014) 1191e1195
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Table 3 Microbial count (cfu/mL) during storage.
Media Nutrient media Rapid Hicoliform
0th day
7th day
Original 140 ± 13 0
Glass 0 0
22nd day Plastic 0 0
Glass 0 0
46th day Plastic 70 ± 10 100 ± 8
Original UC UC
Glass 0 0
Plastic 920 ± 23 760 ± 31
UC e Uncountable.
Fig. 1. Comparative changes in (a) pH, (b) Brix, (c) Total titratable acidity, (d) Simple sugar concentration, (e) Total soluble protein, and (f) Free fatty acid during storage.
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3. Results and discussion 3.1. Selection of microfiltered sample based on fuzzy logic for packaging and storage studies Sample S4 containing 0.018 g/100 mL ascorbic acid, 0.20 g/ 100 mL citric acid and 0.009 g/100 mL L-cysteine was selected to be used for the study purpose based on the similarity values (Table 1) obtained from Fuzzy Logic. Based on the similarity values the order of ranking of samples was S4 (Very good) > S1 (Very good) > S2 (Very good) > S3 (Very good) > S5 (Very good). According to the similarity values for quality attributes of sample S4, as seen in Table 2, the influence of the different sensory attributes was judged. The order of influence was Taste (very good) > Mouthfeel (very good) ¼ Overall acceptability (very good) > Aroma (very good). S4 was further taken for packaging and storage studies. 3.2. Microbial load Table 3 shows the microbial load during the storage study. The microbial load of fresh tender coconut (not microfiltered and no additives added) water was 140 cfu/mL. Microfiltered coconut water stored in glass bottles showed no microbial growth during the storage period that indicated its effectiveness in filtering out the microbes completely. However, microfiltered coconut water bottled in plastic bottles that was sterile for 7 days showed microbial growth on 22nd and 46th day of study. The cause of microbial growth in plastic bottles may be due to certain defects and contamination in the plastic bottles. According to Anonymous (2007) recommendation good quality tender coconut water should have a microbial load of less than 5000 cfu/mL and less than 10 cfu/mL of coliforms. The microbial load was also calculated on 51st day of study. The microbial load of coconut water in plastic bottles exceeded the recommended value while the glass bottled coconut water showed no microbial growth even on 180 days of storage. The other analyses were not carried out as the packaged coconut water lost its flavor and characteristic taste. 3.3. pH and total titratable acidity The unfiltered coconut water (control with no additives added) showed a reduction in pH from 6.5 to 6.3 as analyzed on the 0th day and 46th day. The pH in glass and plastic bottle samples did not change much (Fig. 1a). The pH of microfiltered coconut water was lower than that of the control. Titratable acidity showed a gradual increase in all the samples during storage (Fig. 1c). The acidity of samples in plastic bottle increased to a greater extent. The effect on pH and titratable acidity may be attributed to the addition of preservatives. Studies on water chestnut slices treated with citric acid also showed an increase in total titratable acidity on storage (Jiang, Pen, & Li, 2004). The probable reason of decrease in pH and titratable acidity in control sample may be because of microbial growth. 3.4. Simple sugar concentration and total soluble solids The concentration of simple sugars showed an increasing trend in control and glass stored sample (Fig. 1d). The increasing trend may be due to the breakdown of carbohydrate like sucrose into simple sugars. This is also supported by the fact that total soluble solids also showed a similar increase during storage (Fig 1b). Increase might also be due to hydrolysis or inversion of non-reducing sugars to reducing sugars because of the biochemical processes (Yadav, Yadav, & Kalia, 2010). The coconut water in plastic bottles showed an initial increase in total soluble solids and a drop in the
later period. This can be explained to be due to the microbial growth as they probably utilized the sugars for their growth. Similar results were also reported by Das Purkayastha, Kalita, Mahnot, et al. (2012). Increase in the simple sugars has made the coconut water taste sweeter and also increased its soluble solids during storage. 3.5. Changes in soluble protein concentration The microfiltered samples contained more soluble protein than the control because of the presence of the added L-cysteine which interferes with the copper ions during color development and enhances the color intensity. The protein concentration showed a gradual decrease in all the samples Fig. 1e. The decrease may be due to formation of complexes with other compounds like phenols forming phenoleprotein complex (Cheynier, 2005) and also due to break down of proteins, which occurs normally in beverages during storage as reported by Kulkarni and Aradhya (2005). 3.6. Changes in free fatty acid In all the samples there was an increase in free fatty acids Fig. 1f. The increase in free fatty acid in coconut water on storage is inevitable because of the high fat and mineral content (Das Purkayastha, Kalita, Mahnot, et al., 2012; Reddy et al., 2007). The control showed higher increase in free fatty acid content, while in the treated sample the increase in free fatty acid content was more in plastic bottle than glass bottle. However, the level got stabilized thereafter in both type of packaging materials probably due to antioxidant activity of ascorbic acid and L-cysteine that reduced fat degradation. 3.7. Statistical analysis of sensory data The hedonic rating test on a 9 point scale was also done during the storage study. The significance of storage and packaging material on the product was studied by applying two way ANOVA at 5% significance level (Table 4). It was seen that days of storage and bottle material did not significantly change taste although storage had more effect on taste. Other parameters changed significantly due to storage period but not due to bottle material. 4. Conclusion The study has shown that coconut water can be sterilized by non thermal microfiltration technique and can be stored for 46 days in glass and plastic bottles in refrigerated condition with acceptable sensory results on addition of L-ascorbic acid, citric acid and Lcysteine. While the tender coconut water remained sterile for 180 days in glass bottles, the sensory qualities were found to remain stable up to 46 days. The pH and total soluble solids did not change significantly but there was an increase in total titratable acidity and simple sugars. Statistical analysis has shown that the changes in the sensory parameters depended significantly upon the storage period rather than the packaging material used. It can
Table 4 F values of two-way ANOVA at 5% significance level.
Taste Aroma Mouthfeel Overall acceptability
F value (storage)
F value (packaging materials)
F tabulated
6.12 18.75 16.60 10.8
2.06 1.74 2.25 1.60
6.94
N.K. Mahnot et al. / LWT - Food Science and Technology 59 (2014) 1191e1195
therefore be concluded that the additives used helped to lessen deterioration of processed coconut water. Acknowledgement Nikhil Kumar Mahnot is thankful to Department of Science and Technology, Ministry of Science and technology, New Delhi for grant of DST/INSPIRE Fellowship/2013/482. References Anonymous. (2007). How to bottle coconut water. Spotlight. http://www.fao.org/ag/ magazine/0701sp1.htm Accessed 16.08.11. Brul, S., & Coote, P. (1999). Preservative agents in foodsdmode of action and microbial resistance mechanisms. International Journal of Food Microbiology, 50(1e2), 1e17. Cheynier, V. (2005). Poplyphenols in food are more complex than often thought. American Journal of Clinical Nutrition, 81, 223Se229S. Chowdhuri, M. G. F., Rahman, M. M., Islam, A. F. M. T., & Islam, M. S. (2009). Processing and preservation of green coconut water. Journal of Innovation and Development Strategy, 2(3), 01e05. Chowdhury, M., Aziz, M. G., & Uddin, M. B. (2005). Development of shelf stable and ready to serve green coconut water. Biotechnology, 4(2), 121e125. Damar, S., Balaban, M. O., & Sims, C. A. (2009). Continuous dense-phase CO2 processing of a coconut water beverage. International Journal of Food Science & Technology, 44(4), 666e673. Darkwa, J., Mundoma, C., & Simoti, R. H. (1988). Antioxidant chemistry reactivity and oxidation of L-cysteine by some common oxidants. Journal of the Chemical Society Faraday Transactions, 94(14), 1971e1978. Das, H. (2005). Food processing operation analysis (1st ed.). New Delhi: Asian Books Private Limited. Das Purkayastha, M., Kalita, D., Das, K. V., Mahanta, C. L., Thakur, A. J., & Chaudhuri, M. K. (2012). Effect of L-ascorbic acid addition on micro-filtered coconut water: preliminary quality prediction study using H-NMR, FTIR and GCeMS. Innovative Food Science and Emerging Technologies, 13, 184e199. Das Purakayastha, M., Kalita, D., Mahnot, N. K., Mahanta, C. L., Mandal, M., & Chaudhuri, M. K. (2012). Effect of L-ascorbic acid addition on the quality attributes of micro-filtered coconut water stored at 4 C. Innovative Food Science & Emerging Technologies, 16, 69e79. Haseena, M., Kasturi, K. V., & Padmanabhan, S. (2010). Post-harvest quality and shelf-life of tender coconut. Journal of Food Science and Technology, 47(6), 686e689.
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Iyidogan, N. F., & Bayındirli, A. (2004). Effect of L-cysteine, kojic acid and 4-hexylresorcinol combination on inhibition of enzymatic browning in Amasya apple juice. Journal of Food Engineering, 62(3), 299e304. Jayanti, V. K., Rai, P., Dasgupta, S., & De, S. (2008). Quantification of flux decline and design of ultra filtration system for clarification of tender coconut water. Journal of Food Process Engineering, 10, 1e16. Jiang, Y., Pen, L., & Li, J. (2004). Use of citric acid for shelf life and quality maintenance of fresh-cut Chinese water chestnut. Journal of Food Engineering, 63(3), 325e328. Kulkarni, A. P., & Aradhya, S. M. (2005). Chemical changes and antioxidant activity in fruit arils during fruit development. Food Chemistry, 93(2), 319e324. Lawrence, C. L., Botting, C. H., Antrobus, R., & Coote, P. J. (2004). Evidence of a new role for the high-osmolarity glycerol nitogen-activated protein kinase pathway in yeast: regulating adaptation to citric acid stress. Molecular Cell Biology, 24(8), 3307e3323. Lisbeth, A., Hawken, P., & Talcott, S. T. (2007). Juice matrix composition and ascorbic acid fortification effects on the phytochemical, antioxidant and pigment stability of acacia (Euterpe oleracea Mart.). Food Chemistry, 105(1), 28e35. Lowry, O. H., Rosebrough, N. J., Farr, A. L., & Randall, R. J. (1951). Protein measurement with the folin phenol reagent. Journal of Biological Chemistry, 193(1), 265e275. Mao, L. C., Xu, Y., & Que, F. (2007). Maintaining the quality of sugarcane juice with blanching and ascorbic acid. Food Chemistry, 104(2), 740e745. Ranganna, S. (1986). Hand book of analysis and quality control for fruits and vegetable products (2nd ed.). New Delhi: Tata McGraw Hill. Reddy, K. V., Das, M., & Das, S. K. (2005). Filtration resistances in non-thermal sterilization of green coconut water. Journal of Food Engineering, 69(3), 381e385. Reddy, K. V., Das, M., & Das, S. K. (2007). Non thermal sterilization of green coconut water for packaging. Journal of Food Quality, 30(4), 466e480. Rolle, R. (2007). Good practice for small scale-production of bottled coconut water. Agricultural and Food Engineering Training and Resource Material. ISSN: 19962738. http://www.coconutresearchcenter.org/Good%20Practice%20for% 20Coconut%20Water.pdf Accessed 16.08.11. Sadasivam, S., & Manickam, A. (2007). Biochemical methods (3rd ed.). New Delhi: New Age International Publishers. Somboonsilp, P., Tia, S., & Yoovidhya, T. (2011). Development of a small-scale Ohmic pasteurization system for flavor retention in fruit juice production in the 12th ASEAN Food Conference. Bangkok: Thailand. Yadav, R. B., Yadav, B. S., & Kalia, N. (2010). Development and storage studies on whey-based banana herbal (Mentha arvensis) beverage. American Journal of Food Technology, 5(2), 121e129.
Contents lists available at ScienceDirect
LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt
Research note
Effect of additives on the quality of tender coconut water processed by nonthermal two stage microfiltration technique* Nikhil Kumar Mahnot a, Dipankar Kalita a, Charu Lata Mahanta a, Mihir Kanti Chaudhuri b, * a b
Department of Food Engineering and Technology, School of Engineering, Tezpur University, Assam, India Tezpur University, Assam, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 July 2013 Received in revised form 10 June 2014 Accepted 16 June 2014 Available online 24 June 2014
Non-thermal two-stage microfiltration technique in aseptic conditions was used to preserve coconut water. Concentrations of citric acid (0.02 g/100 mL), ascorbic acid (0.18 g/100 mL) and L-cysteine (0.009 g/ 100 mL) were standardized according to taste and added to coconut water as natural additives. The coconut water was packed in glass and plastic bottles after flushing the headspace with nitrogen and stored under refrigeration (4 C). The microfiltered water was studied for microbial, sensory and physicochemical properties for a period of 46 days. The quality of the water packed in glass bottles was better in all respects. The total soluble solids changed from 5.4 to 6 Brix. The pH changed from 5.7 to 5.8. The soluble sugar concentration increased from 1.9 g/100 mL to 3.1 g/100 mL, free fatty acid content increased from 0.064 mg KOH/g to 2.8 mg KOH/g at the end of 46 days, which was much lower than the changes in control. The protein content decreased in all the samples. Two way ANOVA showed that the storage time had more impact on the sensory properties of the product than the packaging material. The glass bottled product was acceptable on sensory basis till 46 days of storage. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Tender coconut water Non-thermal sterilization Microfiltration Additives Storage
1. Introduction Coconut (Cocos nucifera L.) is an important fruit in the tropical regions. Tender coconut water is consumed as a refreshing drink because of its nutritional and therapeutic properties. The electrolyte and mineral balance makes tender coconut water suitable as a sports drink. However, it is very sensitive to deterioration and the water is unsuitable for drinking after a day or so due to external contamination by microorganisms and oxidation because of which it loses most of its sensory and nutritional characteristics (Haseena, Kasturi, & Padmanabhan, 2010; Reddy, Das, & Das, 2005). Commercially available canned coconut water is given a hightemperature/short-time thermal treatment. Although the shelf life of thermally processed tender coconut water is long, thermal processing tends to decrease the nutrient content and completely destroys its natural flavor (Haseena et al., 2010) unlike non-thermal techniques. This severely limits the marketability of the product (Jayanti, Rai, Dasgupta, & De, 2008). Today's consumers are looking
*
Patent applied for. * Corresponding author. Tel.: þ91 3712 267008x5702; fax: þ91 3712 267005. E-mail addresses: [email protected], [email protected] (C.L. Mahanta), [email protected] (M.K. Chaudhuri). http://dx.doi.org/10.1016/j.lwt.2014.06.040 0023-6438/© 2014 Elsevier Ltd. All rights reserved.
for natural products which are not adversely modified while providing targeted benefits. Selecting technological processes to preserve the natural wholesome properties of the coconut water still remains a challenge. Various workers have studied effects of thermal and non-thermal technologies including pasteurization, (Chowdhuri, Rahman, Islam, & Islam, 2009; Chowdhury, Aziz, & Uddin, 2005), ohmic pasteurization (Somboonsilp, Tia, & Yoovidhya, 2011) and cold pasteurization (Rolle, 2007), dense phase carbon dioxide technology (Damar, Balaban, & Sims, 2009), filtration (Das Purkayastha, Kalita, Das, et al., 2012; Das Purkayastha, Kalita, Mahnot, et al., 2012; Reddy et al., 2005; Reddy, Das, & Das, 2007), etc. These techniques alone or in combination with preservatives were studied to increase the shelf life of tender coconut water. Das Purkayastha, Kalita, Das, et al. (2012) and Das Purkayastha, Kalita, Mahnot, et al. (2012) using microfiltration technique and adding ascorbic acid were able to preserve tender coconut water for 21 days in refrigerated condition. In this study we used the microfiltration technique and added citric acid, ascorbic acid and cysteine to the filtered water and monitored its shelf life in glass and plastic packaging material. The additives were added based on their properties including metal chelating, microbial growth inactivating ability, anti-oxidant activity, anti-browning property and ability to delay the increase of titratable acidity as reported by various researchers (Brul & Coote,
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N.K. Mahnot et al. / LWT - Food Science and Technology 59 (2014) 1191e1195
1999; Darkwa, Mundoma, & Simoti, 1988; Iyidogan & Bayındirli, 2004; Lawrence, Botting, Antrobus, & Coote, 2004; Lisbeth, Hawken, & Talcott, 2007; Mao, Xu, & Que, 2007). 2. Materials and methods Tender coconuts were obtained from surrounding area of Tezpur University, Assam. Chemicals were obtained from Merck and HIMEDIA and glass wares were of Borosil. The filtration setup consisted of filter funnel with clamps, bacterial filtration units, heavy duty vacuum flasks, and autoclavable pipes that were from Tarsons. Cellulose nitrate bacterial filter membranes of 0.8 mm and 0.45 mm pore size were obtained from Sartorius and Merck Millipore, respectively. 2.1. Methods 2.1.1. Sanitization of tender coconuts and materials The whole processing area was cleaned carefully and fumigated with formaldehyde and potassium chromate two days before processing. On the day of filtration the tender coconuts were washed with tap water to remove the surface dust and dipped in 300 mg/L sodium hypochlorite solution to sanitize. All the processing equipments used were sterilized in an autoclave at 103.42 KPa for 15 min. 2.1.2. Addition of ascorbic acid, citric acid and L-cysteine and fuzzy logic Different concentrations of citric acid ranging from 0.005 to 0.02 g/100 mL and ascorbic acid ranging from 0.01 to 0.2 g/100 mL were added to coconut water and evaluated on a 9 point Hedonic scale by 15 member semi-trained panelists. The panelists had preferred the combination of 0.02 g/100 mL citric acid and 0.01 g/ 100 mL ascorbic acid added to tender coconut water. To this selected combination of citric acid and ascorbic acid, five different concentrations of L-cysteine was added. Coconut water samples were marked as S1 (no L-cysteine), S2 (0.007 g/100 mL L-cysteine), S3 (0.008 g/100 mL L-cysteine), S4 (0.009 g/100 mL L-cysteine) and S5 (0.010 g/100 mL L-cysteine). These samples were evaluated for sensory attributes of taste, aroma, mouthfeel and overall acceptability by 15 semi-trained panelists. Fuzzy logic (Das, 2005) was applied to get the best combination from the scores obtained. 2.1.3. Processing of tender coconut water The tender coconuts were cut open with a sanitized stainless steel knife and its water was strained into a beaker inside the laminar air flow. The microfiltration process was also carried out inside the laminar flow. The collected water was first filtered in a filter and clamp connection through a Whatman No. 4 filter paper. The filtered water was transferred through the Teflon pipe to a bacterial filtration unit with a 0.8 mm membrane filter which was attached to a vacuum pump. The filtrate was collected and the process was repeated to filter through a second filtration unit with a 0.45 mm filter. Any spillage of coconut water inside the laminar air flow was cleaned with cotton dipped in alcohol. The final filtered coconut water was transferred slowly to a heavy duty vacuum flask. Following this accurately weighed and calculated amount of citric acid, ascorbic acid and L-cysteine were added to the heavy duty vacuum flask and mixed slowly. The processed tender coconut water was then filled into sterilized plastic (Tarsons) and glass bottles of 50 mL each. The headspace was flushed with nitrogen gas inside a laminar hood. The lids were closed tightly and the samples were stored under refrigerated condition at 4 C. 2.1.4. Storage study The tender coconut water of both plastic and glass bottles were analyzed at 7 days, 22 days and 46 days. The samples were initially
Table 1 Similarity values of samples S1eS5. Scale factors
S1
S2
S3
S4
S5
Not satisfactory, F1 Fair, F2 Satisfactory, F3 Good, F4 Very good, F5 Excellent, F6
0.0073 0.107 0.311 0.525 0.653 0.332
0.0073 0.109 0.315 0.531 0.652 0.3254
0.010 0.122 0.325 0.529 0.630 0.312
0.004 0.097 0.304 0.523 0.675 0.349
0.012 0.135 0.347 0.555 0.618 0.290
S1eS5 denotes the samples under study. F1eF6 indicates membership function of standard fuzzy scale.
checked for microbial load and then given for sensory evaluation on a 9 point hedonic scale by semi-trained panelists. Various parameters like pH, Brix, total titratable acidity, simple sugars, protein and free fatty acid were analyzed for all the samples. Untreated coconut water (original) was stored in glass bottle and was analyzed on 0 day and 46th day. The analysis of bottled coconut water was based on its sensory properties. The analysis was stopped after 46th day because bottled coconut water lost its flavor and its characteristic taste except for microbial load.
2.1.5. Microbial load Nutrient broth agar and Rapid HiColiform media was used to count the number of microbes and number of coliforms present in the sample, respectively.
2.1.6. Measurement of physicochemical properties The pH and total soluble solids were measured using a pH meter (Eutech) and a hand refractometer (Erma, Japan) respectively (Ranganna, 1986). Total titratable acidity and free fatty acid (Acid value) were estimated according to the method given in Sadasivam and Manickam (2007). The total titratable acidity was calculated with respect to citric acid.
TTA ¼ Titre volume 0:1 67:05 100=Sample volume 1000 Acid value ðmg KOH=gmÞ ¼ Titre value 0:1N KOH 56:1=Amount of sample Protein estimation was done according to Lowry, Rosebrough, Farr, and Randall (1951). A modified anthrone method of total carbohydrate determination was followed for simple sugar estimation (Sadasivam & Manickam, 2007). In the modified method, 0.1 mL of the coconut water was taken and the volume was made up to 1 mL with distilled water and anthrone reagent (200 mg anthrone in 100 mL of 95 g/L sulphuric acid) was added. Absorbance for sugar and protein was observed at 630 nm and 660 nm respectively in a spectrophotometer (Cecil Aquarius 7400, England).
Table 2 Similarity for quality attributes of tender coconut water of sample S4. Scale factors
Taste
Aroma
Mouthfeel
Overall acceptability
Not satisfactory, F1 Fair, F2 Satisfactory, F3 Good, F4 Very good, F5 Excellent, F6
0 0 0.149 0.583 0.979 0.545
0 0.024 0.237 0.572 0.756 0.371
0 0.025 0.242 0.584 0.764 0.371
0 0.025 0.242 0.584 0.764 0.371
F1eF6 indicates membership function of standard fuzzy scale.
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Table 3 Microbial count (cfu/mL) during storage.
Media Nutrient media Rapid Hicoliform
0th day
7th day
Original 140 ± 13 0
Glass 0 0
22nd day Plastic 0 0
Glass 0 0
46th day Plastic 70 ± 10 100 ± 8
Original UC UC
Glass 0 0
Plastic 920 ± 23 760 ± 31
UC e Uncountable.
Fig. 1. Comparative changes in (a) pH, (b) Brix, (c) Total titratable acidity, (d) Simple sugar concentration, (e) Total soluble protein, and (f) Free fatty acid during storage.
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3. Results and discussion 3.1. Selection of microfiltered sample based on fuzzy logic for packaging and storage studies Sample S4 containing 0.018 g/100 mL ascorbic acid, 0.20 g/ 100 mL citric acid and 0.009 g/100 mL L-cysteine was selected to be used for the study purpose based on the similarity values (Table 1) obtained from Fuzzy Logic. Based on the similarity values the order of ranking of samples was S4 (Very good) > S1 (Very good) > S2 (Very good) > S3 (Very good) > S5 (Very good). According to the similarity values for quality attributes of sample S4, as seen in Table 2, the influence of the different sensory attributes was judged. The order of influence was Taste (very good) > Mouthfeel (very good) ¼ Overall acceptability (very good) > Aroma (very good). S4 was further taken for packaging and storage studies. 3.2. Microbial load Table 3 shows the microbial load during the storage study. The microbial load of fresh tender coconut (not microfiltered and no additives added) water was 140 cfu/mL. Microfiltered coconut water stored in glass bottles showed no microbial growth during the storage period that indicated its effectiveness in filtering out the microbes completely. However, microfiltered coconut water bottled in plastic bottles that was sterile for 7 days showed microbial growth on 22nd and 46th day of study. The cause of microbial growth in plastic bottles may be due to certain defects and contamination in the plastic bottles. According to Anonymous (2007) recommendation good quality tender coconut water should have a microbial load of less than 5000 cfu/mL and less than 10 cfu/mL of coliforms. The microbial load was also calculated on 51st day of study. The microbial load of coconut water in plastic bottles exceeded the recommended value while the glass bottled coconut water showed no microbial growth even on 180 days of storage. The other analyses were not carried out as the packaged coconut water lost its flavor and characteristic taste. 3.3. pH and total titratable acidity The unfiltered coconut water (control with no additives added) showed a reduction in pH from 6.5 to 6.3 as analyzed on the 0th day and 46th day. The pH in glass and plastic bottle samples did not change much (Fig. 1a). The pH of microfiltered coconut water was lower than that of the control. Titratable acidity showed a gradual increase in all the samples during storage (Fig. 1c). The acidity of samples in plastic bottle increased to a greater extent. The effect on pH and titratable acidity may be attributed to the addition of preservatives. Studies on water chestnut slices treated with citric acid also showed an increase in total titratable acidity on storage (Jiang, Pen, & Li, 2004). The probable reason of decrease in pH and titratable acidity in control sample may be because of microbial growth. 3.4. Simple sugar concentration and total soluble solids The concentration of simple sugars showed an increasing trend in control and glass stored sample (Fig. 1d). The increasing trend may be due to the breakdown of carbohydrate like sucrose into simple sugars. This is also supported by the fact that total soluble solids also showed a similar increase during storage (Fig 1b). Increase might also be due to hydrolysis or inversion of non-reducing sugars to reducing sugars because of the biochemical processes (Yadav, Yadav, & Kalia, 2010). The coconut water in plastic bottles showed an initial increase in total soluble solids and a drop in the
later period. This can be explained to be due to the microbial growth as they probably utilized the sugars for their growth. Similar results were also reported by Das Purkayastha, Kalita, Mahnot, et al. (2012). Increase in the simple sugars has made the coconut water taste sweeter and also increased its soluble solids during storage. 3.5. Changes in soluble protein concentration The microfiltered samples contained more soluble protein than the control because of the presence of the added L-cysteine which interferes with the copper ions during color development and enhances the color intensity. The protein concentration showed a gradual decrease in all the samples Fig. 1e. The decrease may be due to formation of complexes with other compounds like phenols forming phenoleprotein complex (Cheynier, 2005) and also due to break down of proteins, which occurs normally in beverages during storage as reported by Kulkarni and Aradhya (2005). 3.6. Changes in free fatty acid In all the samples there was an increase in free fatty acids Fig. 1f. The increase in free fatty acid in coconut water on storage is inevitable because of the high fat and mineral content (Das Purkayastha, Kalita, Mahnot, et al., 2012; Reddy et al., 2007). The control showed higher increase in free fatty acid content, while in the treated sample the increase in free fatty acid content was more in plastic bottle than glass bottle. However, the level got stabilized thereafter in both type of packaging materials probably due to antioxidant activity of ascorbic acid and L-cysteine that reduced fat degradation. 3.7. Statistical analysis of sensory data The hedonic rating test on a 9 point scale was also done during the storage study. The significance of storage and packaging material on the product was studied by applying two way ANOVA at 5% significance level (Table 4). It was seen that days of storage and bottle material did not significantly change taste although storage had more effect on taste. Other parameters changed significantly due to storage period but not due to bottle material. 4. Conclusion The study has shown that coconut water can be sterilized by non thermal microfiltration technique and can be stored for 46 days in glass and plastic bottles in refrigerated condition with acceptable sensory results on addition of L-ascorbic acid, citric acid and Lcysteine. While the tender coconut water remained sterile for 180 days in glass bottles, the sensory qualities were found to remain stable up to 46 days. The pH and total soluble solids did not change significantly but there was an increase in total titratable acidity and simple sugars. Statistical analysis has shown that the changes in the sensory parameters depended significantly upon the storage period rather than the packaging material used. It can
Table 4 F values of two-way ANOVA at 5% significance level.
Taste Aroma Mouthfeel Overall acceptability
F value (storage)
F value (packaging materials)
F tabulated
6.12 18.75 16.60 10.8
2.06 1.74 2.25 1.60
6.94
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