STUDIES ON PROCESSING AND STORAGE OF TENDER COCONUT WATER
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Date
2016
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Acharya N.G. Ranga Agricultural University, Guntur
Abstract
Coconut water (Cocos nucifera L.) is an ancient tropical beverage whose original properties have drawn the attention of manufacturers as a natural functional drink. The tender coconut water (TCW) technically the liquid endosperm, is the most nutritious wholesome beverage that the nature has provided for the people of the tropics. TCW is rich in essential minerals such as potassium, sodium and natural nutrients like polyphenols. The water inside the nut is sterile but when it is extracted and exposed to air it becomes vulnerable to oxidation besides microbial contamination. Thermal treatments combined with chemical additives are used by the industry but other technologies such as micro and ultrafiltration are yet to be used on an industrial scale. In thermal and chemical processes, taste, aroma and colour are difficult to control and maintain to achieve fresh like taste in the product.
The membrane separation processes such as Microfiltration (MF), Ultrafiltration (UF), Nanofiltration (NF) and Reverse osmosis (RO) are promising novel alternative non-thermal and non-chemical methods that are relatively less energy intensive and retain heat labile components. MF and UF offer excellent potential in food industry for clarification and pasteurization of liquid foods to replace conventional processing techniques. Therefore a study was conducted to develop process technology for bottling TCW using membrane filtration, pasteurization and chemical additive and suggest a suitable method.
A continuous cross flow flat sheet membrane module was used in the study to process by MF and UF. Initially the permeate fluxes were established using pure water on 0.2μm pore size and 40 kDa and 500 Da molecular weight cut off (MWCO) membranes at various transmembrane pressures (TMPs). The experiments revealed that permeate flux increases with an increase in TMP and membrane pore size or MWCO. The steady state fluxes were relatively higher with MF in comparison to UF and NF at the given TMP. The permeate flux of microfiltered TCW declined from 189.98 L /m2h and reached a steady flux at 88.51L/m2h at a TMP of 5.06 kg/cm2. The flux also
declined from 107.54 to 82.07 L/m2 h in UF. The flux decline during MF and UF is perhaps due to concentration polarization and consequent fouling.
Five different treatments were investigated to develop process technology and extend shelf life during storage of TCW. In the first treatment, the coconut water was passed through a microfiltration membrane of 0.2 µm pore size at a pressure of 5.06 kg/cm2 to remove microbes and suspended particles. In the second treatment, coconut water was passed through ultrafiltration membranes of 40 kDa MWCO at pressures about 5.06 kg/cm2 to remove enzymes such as polyphenoloxidase (PPO) and peroxidase (POD). In the third treatment, the coconut water was bottled and pasteurized at 85 oC for 10 min. In the fourth and fifth treatments, the coconut water was filtered through a MF membrane and chemical preservative nisin was added in two concentrations of 5000 I.U. and 2500 I.U. The TCW filtered through muslin cloth was taken as control sample. The control as well as all the treated samples were bottled and stored at 4 °C. The samples were taken at four days interval and their physico-chemical, microbiological and sensory characteristics were determined upto 20 days of storage.
The TSS of TCW generally decreased during storage except for pasteurized samples. Pasteurized TCW did not show any change in TSS compared to all other treatments. The pH generally decreased in all the treatments during storage up to 20 days. The percentage reducing sugars increased for all the samples during storage. However, pasteurized samples recorded lower increase in reducing sugars. The turbidity of the TCW increased during storage as indicated by decrease in the light transmittance values. Turbidity was observed to be relatively low for microfiltered and ultrafiltered TCW suggesting that membranes processes are useful for clarification of TCW. E.coli, Fungal and bacterial count were observed to be less in pasteurized samples. Overall based on different quality attributes, pasteurized treatment, MF and UF have been found to give a better quality bottled TCW in that order, the first treatment being the best. It can be concluded that membrane processing of TCW is one of the alternate methods along with thermal processing for producing quality product.
Keywords: Membrane processing, Microfiltration, Ultrafiltration, Permeate flux
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D5354
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