Development of a Process for Clarification and Concentration of Jamun (Syzygium cuminii) Juice using Membrane Filtration

Abstract

Traditional processing of fruit juice is labour, energy and time intensive. It involves heat treatment at various stages of processing. The heat treatment causes losses in natural nutrients, colour and aroma. It also results in typical cooked flavour in the juice. There is a need to develop and adopt non-thermal processing protocols. Enzymatic extraction of juice followed by clarification and concentration through membrane filtration could be a suitable alternative for juice processing. Feasibility of the above-hypothesized process was verified using Jamun (Syzygium cuminii L) as the raw material. Jamun is an underutilised minor fruit grown in plenty. It has several nutritional and therapeutic values. Jamun is an excellent source of antioxidants and anthocyanin that makes it a prospective fruit for value addition and further commercialisation. Various physico-chemical, mechanical and nutritional properties of Jamun fruit were measured which were used in designing and developing the protocol. The Jamun juice was purple in colour (b* value: -0.9) with significant amount of polyphenol (203.76±9.84 mg GAE/g), tannin (94.52±9.19 mg/100g) and anthocyanin (195.58±6.15 mg/100g). Process parameters for enzymatic extraction of Jamun juice were optimised for different variety of Pectinase and Tannase. Pectinase from Aspergillus aculeatus strain gave best results in terms of quality of the juice at 44 oC with an incubation time and enzyme concentration of 80 minute and 0.05% (w/w) respectively. Juice yield could be achieved up to 79% with acceptable turbidity (32.21 NTU), clarity (74.39 %T), polyphenol content (115.31 mg GAE/g), and protein content (102.43 mg/g). The juice so obtained was clarified and concentrated using micro-filtration, ultra-filtration and nano-filtration. Primary clarification of juice by micro-filtration with a pressure of 137.89 kPa and membrane pore size of 0.45 μm had better results in terms of clarity, turbidity, colour and protein concentration, than centrifugation at 7000 rpm and 40 min. There was decline in permeate flux after 130 min of micro-filtration due to the presence of macromolecules and fibre particles in the juice. Fouling of the membrane was also observed due to cake layer resistance (65%). Membranes could be reuse up to 82% after CIP treatment. Secondary clarification of the juice was done by ultra-filtration with optimised membrane pore size (50 kDa) and pressure (137.89 kPa). Juice recovery after ultra-filtration was 60.46% with acceptable turbidity (0.03 NTU), clarity (96.33 %T), polyphenol content (125.74 mg GAE/g) and protein content (109.43 mg/g). Storage stability and quality of the ultra-filtered juice were compared with the juices obtained from enzymatic extraction, centrifugation, and micro-filtration. Ultra-filtered juice had prolonged shelf life (8 weeks) with acceptable qualities. The juice thus obtained from ultra-filtration was further concentrated for bioactive molecules by nanofiltration with a membrane pore size of 300 Da and pressure 2.5 mPa. Protein, polyphenol and antioxidants of the concentrated Jamun juice were quantified by UV-Spectrophotometer. Particle size distribution was measured by zeta-sizer. Anthocyanidins (5.9 mg/10 mg of cyanidine chloride, 20.8 mg/10mg of malvidin chloride and 3.6 mg/10mg of delphinidin chloride) content was determined by RP-HPLC-PDA. Rejection rate of protein, polyphenol and antioxidant for ultra-filtered and nano-filtered permeates were 48%, 22.3%, 51% and 63%, 74%, 40% respectively. The particle size distribution curves for ultra-filtered and nano-filtered juice were parabolic confirming proper membrane filtration. Enzymatic extraction by Pectinase from Aspergillus aculeatus strain (44 oC, 80 min and 0.05%) followed by clarification with micro-filtration (137.89 kPa and 0.45 μm) and ultra-filtration (137.89 kPa and 50 kDa), and concentration through nano-filtration (2.5 mPa and 300 Da) could recover commercial grade clarified Jamun juice (604.6 ml/kg of pulp) and anthocynidins. Total cost for processing Rs. 173.18 /litre. The above processing protocol could be an alternative non-thermal method for fruit juice to concentrate natural colour pigment and bioactive molecules in beverage and pharmaceutical industries.