Jamun ( L.) pulp-skin paste was dried using four drying methods viz., microwave-convective hot air drying (MCD), freeze drying (FD), vacuum drying (VD), and dehumidified air drying (DAD) at different conditions. Except for FD, the drying temperatures of MCD (1, 2 and 3 W/g power density), VD (60, 160 and 260 mm Hg pressure) and DAD (1, 1.5 and 2 m/s of air velocity; 20% RH) were varied from 40 to 70 °C. The dried pulp-skin flakes were analysed for total phenolics content [TPC, gallic acid equivalent (GAE)], monomeric anthocyanin content [MAC, malvidin-3-glucoside (M3G)] and antioxidant activity [AA, butylated hydroxyanisole (BHA)]. This study aimed on selection of the best drying method based on the retention of the above functionalities. Compared to the fresh sample, TPC and AA of the dried samples increased for all the methods, whereas MAC showed mixed response. With the retention of 31.52 mg GAE, 11.99 mg M3G and 28.63 mg BHA per gram of dried sample (on dry basis), MCD (70 °C, 1 W/g) was selected as the most suitable method based on statistical analyses.
Drying of fruit pulp into powder needs drying aids for achieving desirable powder properties. This article aims to optimize drying aids, such as maltodextrin (MD), tricalcium phosphate (TCP), and glycerol monostearate (GMS) in jamun (Syzygium cumini L.) pulp blend formulation to produce microwave‐convective hot air‐dried jamun pulp powder. Response surface methodology using rotatable central composite design was followed with independent variables MD (1–15), TCP (0–2), and GMS (1–3), % dry basis of pulp, on hygroscopicity (HG), rate of moisture sorption estimated at 60 min (RMS60), flow time (FT), and overall color difference (ΔE*) as responses of the product. The statistically significant factors were: MD for HG; MD, TCP, and GMS for RMS60 and FT; and TCP and GMS for ΔE*. The optimized formulation reduced HG, RMS60, and FT by 29.67, 45.24, and 60%, respectively with respect to the control, with ΔE* being 6.98.
Practical Applications
The antidiabetic and antioxidant properties of jamun (Syzygium cumini L.) fruit are well established. The therapeutic values of jamun pulp and skin are mainly due to the presence of various phytochemicals. However, it is considered as underutilized fruit due to its highly perishable nature. Properly matured fruit can be stored for maximum 2 days at room temperature and 3 weeks at low temperature. Hence, immediate processing and conversion into value‐added products of jamun fruits are needed for better distribution and utilization during off‐season. Processing of fruit pulp into dry powder is a popular practice to obtain shelf‐stable product having wide scope of utilization. However, preparation of fruit powder has many challenges, the main problem being their stickiness due to the presence of low molecular weight sugars and organic acids. Therefore, production of stable free‐flowing jamun pulp powder with selection of suitable drying aids in proper concentration has enough industrial relevance.
The present work aimed to: i) find the suitable proportion, based on sensory evaluation, of microwave-convective hot air dried jamun (Syzygium cumini L.) pulp and seed kernel powder to be mixed for the preparation of jamun powder (JP); ii) generate and model the moisture sorption isotherm (MSI) of JP; and iii) estimate net isosteric heat of sorption (qst), spreading pressure (φ), net integral enthalpy (Qin), and net integral entropy (Sin). To formulate JP, the proportion (w/w, db) comprising 2% kernel and 98% pulp powder was the most desirable. The Peleg model was the best fit to MSI of JP. The qst decreased following linear relationship from 11.02 kJ. mol-1 at 5% equilibrium moisture content (EMC) to 0.27 kJ. mol-1 at 30% EMC. The φ increased with increase in water activity and decreased with increase in temperature from 25 ºC to 35 ºC, and the values of φ at 45 ºC were even higher than at 25 ºC. Net integral enthalpy (Qin) initially decreased till 6% moisture content in JP and displayed an increasing trend with further increase in moisture content. On the contrary, Sin, kept on decreasing continually with increasing moisture content. The moisture zone of 7-11% was considered safe for storage for storage of JP within the temperature range of 45-25 ºC.
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