Raw materials and chemicals Pink guava puree was obtained from Sime Darby Beverages Sdn Bhd. (Malaysia) and maltodextrin DE 10 from Bronson and Jacobs Pvt. Ltd. (Australia). Acetone, n-hexane, meta-phosphoric acid and butylated hydroxytoluene from Friedemann Schmidt (Australia), ethanol from MerchKGaA (Germany), acetic acid and 2,6- dichlorophenol indophenol from Sigma-Aldrich Chemie GmbH (Germany) and L-ascorbic acid from R and M marketing (U.K) were collected.
Sample preparation and drying The pink guava puree was diluted with distilled water and added sugar at a ratio of 1:2.33:0.27 (v/v/w). The total solid content was maintained at 10.0±0.1°Bx, sieved through a 250 µm sieve and subsequently added maltodextrin to the juice sample at concentrations of 10, 15 and 20% (w/v). Then the samples were homogenized at 5000 rpm for 8 min using Homogenizer (Wise Mix HG-15A, Daihan Scientific, Co. Ltd., Korea) (Carrillo-Navas et al., 2011). A 300 ml sample was subjected to spray drying using a spray dryer (Lab plant SD-05, Lab plant UK Ltd., UK). The spray dryer consists of a drying chamber 215 mm×500 mm long, 0.5 mm diameter pressure nozzle and co-current air flow system. The inlet temperature of 170°C, feed flow rate of 350 ml/hr, compressor air pressure of 2.0 barand feed temperature of 25°C were maintained. During the spray drying, the outlet temperature, drying air flow rate and room temperature were monitored at 96±2ºC of 47±1 m³/hrand 25±1ºC, respectively. In contrast, freeze drying was carried out at -110ºC and 0.001 mbar pressure using Bench-top freeze dryer (Coolsafe 110-4, Labogene APS Industrivej, Denmark). Prior to freeze drying, the sample was placed to deep freezer at -20ºC for 1 day to reduce the temperature of the sample. In order to determine the drying process yield and cost estimation, the drying runs (spray and freeze drying) were replicated twice. The physicochemical analyses were triplicated. After drying, powders were tightly packed in polyethylene bag and kept in desiccator for 24 hours and then stored in refrigerator at 5 ºC for analysis.
Physical properties The moisture content analysis was performed by the method of AOAC (1990). Around two gram of powder was taken to determine the water activity by using electronic water activity meter (FA-ST Lab, GBX Instrumentation Scientifique, France) at approximately 25ºC(Zhang et al., 2015). The particle size was determined by using particle size analyzer (Mastersizer 2000, Malvern Instruments Ltd., U.K.) (Tze et al., 2012). The particle size was expressed as D[4,3], the mean diameter over the volume distribution (Tonon et al., 2008). The glass transition temperature of the powders was determined by using differential scanning calorimeter (DSC 7, Perkin Elmer, USA). The powder (around 5-10 mg) was scanned in a hermetically sealed 20 µl DSC aluminum pan. An empty aluminum pan was used as a reference. The purge gas used was dry nitrogen (20 ml/min). The rate of thermal scanning was carried out in 2 steps such as i) Isothermal at -20ºC for 1 min, and ii) Heat scanning from -20ºC to 250ºC at 10ºC/min(Shrestha et al., 2007). The cost analysis was carried out for the production of 1 kg pink guava powder from the summation of the price of raw material (pink guava puree) and electricity used in aspect of Malaysia and estimated in Malaysian currency (Ringgit).
Chemical properties Lycopene was determined according to the spectrophotometer method developed by Fish et al. (2002)and modified by Kong and Ismail (2011). The pink guava powder of 0.6 g was taken into 50ml conical flask and 5 ml of pure acetone containing 0.05% butylated hydroxytoluene (BHT), 5 ml of 95% ethanol and 10 ml of hexane were added and stirred. The mixture was shaken using WiseCube Shaking Incubator (WIS-20R, Daihan Scientific Co. Ltd., Korea) at 200 rpm for 20 min. Then, 3 ml of distilled water was added and shaken again at 200 rpm for another 5 min. Finally, the mixture was left for 5 min for phase separation, and the hexane layer was read in 1 cm path length quartz cuvette 503 nm using UV-vis spectrophotometer (Ultrospec 3100 pro, Biochrom Ltd., England) with hexane as the blank. The lycopene content was estimated as mg/100g pink guava based on the equation. Molar extinction coefficient for lycopene in hexane is 17.2 x 104 M-1 cm (Kong and Ismail, 2011).
Statistical analysis The data was analyzed by analysis of variance (ANOVA) and Duncan’s multiple range test using SAS 9.3 TS L1M2. All the measurements were conducted in triplicate and evaluated as mean value with standard deviations. The diagrams of mean value and error bars were generated by using Microsoft excel version of 2010.