Effect of drying conditions on properties, pigments and antioxidant activity retentions of pretreated orange and purple-fleshed sweet potato flours

Abstract

Pigmented sweet potatoes (SPs) are outstanding sources of anthocyanin, β-carotene and other color-related phytonutrients. However, fresh SP roots are highly perishable and difficult to store. To reduce losses and extend their uses, fresh SP could be converted into flour. SP cultivars with deep purple (Phichit 65-3) and orange-fleshed (T101) colors newly developed in Thailand were studied. The influence of drying methods on physico-chemical properties, anthocyanin, β-carotene and antioxidant activity retentions of purple and orange-fleshed SP flours (SPFs) was investigated. Peeled purple and orange SPs were pretreated by blanching (100°C, 5 sec) and soaking in 0.5 % (w/v) sodium metabisulphite, then dried in either hot air oven at 50-80°C or steamed for 10 min and placed to the drum dryer at 80-110°C and 3-7 rpm drum speed. The drying processes significantly enhanced anthocyanin contents of SPFs by 1.8 to 3.8 times; however, there was a significant loss of β-carotene occurred during drying processes. Drum drying yielded SPFs with better color, higher total phenolic contents and antioxidant activity than the hot air drying. Pasting temperatures of hot air dried orangefleshed SPFs (84-85°C) were slightly higher than those of purple-fleshed SPFs (80-83°C). Drum drying process produced pre-gelatinized (instant) SPFs as indicated by RVA and DSC results. The optimal conditions for drum dried and hot air dried SPF manufactured were 95°C at 5 rpm and 70°C, respectively, based on anthocyanin, β-carotene, total phenolic, antioxidant activity, color retentions, and pasting properties.

Effect of pre‐treatments on sprouting rate and nutritional quality of green gram ( Vigna radiata L. ) malt

“…The pasting properties of flour depend upon the difference in its components such as protein, fat, sugar, fiber, amylose: amylopectin ratio, etc. (Ruttarattanamongkol, Chittrakorn, Weerawatanakorn, & Dangpium, ). In control and pre‐treated samples, pasting temperature, peak viscosity, breakdown, setback and final viscosity of pulse flours ranged from 72.90 to 75°C, 674.70 to 998.95 cP, 96.8793 to 298.60 cP, 202.10 to 607.05 cP, and 606.25 to 1472 cP, respectively (Table 3 supplementary data).…”

Effect of Incorporating Purple-Fleshed Sweet Potato in Biscuit on Antioxidant Content, Antioxidant Capacity and Colour Characteristics

“…However, sweet potato is highly perishable and difficult to store. Thus, sweet potato can be processed into flour [6][7][8] and paste or puree [9][10][11], which could be incorporated into different appealing products for consumers, such as snacks, pasta, pancake, bread, and cookies.…”

Processing effects on anthocyanins, phenolic acids, antioxidant activity, and physical characteristics of Vietnamese purple-fleshed sweet potato flours

“…Lourenco, Neves, and Silva () reported that the extracted enzyme from sweet potato heated at 90°C for 1 min was completely inactivated, whereas Ma, Silva, Hearnsberker, and Garner () revealed that blanching sweet potato slices for 1 min at 94°C was insufficient for enzyme inactivation but accelerated enzyme activity. Moreover, Ruttarattanamongkol et al () demonstrated that peeled Phichit 65–3 purple sweet potato variety which is soaked in 0.5% (w/v) Na 2 S 2 O 5 and blanched at 100°C for 5 s prior to the hot air drying and drum drying processes had enhanced anthocyanin contents of PFSP by 1.8 to 3.8 times. The current results were in agreement with those previous studies because PFSP slices were pre‐treated by soaking in 0.5% (w/v) Na 2 S 2 O 5 and blanching at 100°C for 2 s before MVD and HA processes that inactivated indigenous enzymes retained anthocyanins in PFSP flours.…”

“…Among treatments, the total phenolic content of PFSP flour produced by DD (724.72 mg GAE/100 g dw) and MVD (464.23 mg GAE/100 g dw) methods was significantly ( p ≤ 0.05) higher than flours produced by other processes. Thermal processing has been reported to increase the phenolic contents of PFSP flours (Ruttarattanamongkol et al, ). Soison et al () also revealed that the increase in total phenolic contents was likely due to the release of phenolic compounds during slurry preparation and drying processes.…”

“…Thermal properties of PFSP flours were determined by differential scanning calorimetry (DSC, model DSC1 Stare Systems, Melter‐Toledo Ltd., Beaumont Leys Leicester, England) according to Ruttarattanamongkol, Chittrakorn, Weerawatanakorn, and Dangpium (). The 5 mg of PFSP flour was made into a paste by mixing it with 10 μL of water in a 40‐μL size aluminum pan and held for 1 hr before analysis.…”