Table 7 .
Retention of carotenoids in sweet potato-effect of cooking
| Reference | Country | Cultivars | Sample size | Methodology | Time | Temp (°C) | Average of initial carotenoid content | Retention % average (min/max) |
|---|---|---|---|---|---|---|---|---|
| Boiling or steaming | ||||||||
| Chandler and Schwartz, 1988 | USA | Jewel variety, cured (30°C, 85% humidity) for 7 d | NR | Steamed: starch gelatinization (SG) Steamed: enzyme inactivation (SE) | SG: 30 min SE: NR | SG: 81 SE: 100 | Total beta-carotene 440 μg/g DW | SG: 113 SE: 104 |
| Hagenimana et al., 1999 | Kenya | 32 cultivars | NR | Boiling (B) | NR | NR | Total carotenoids 49 μg/g DM | B: 80 |
| Van Jaarsveld et al., 2006 | South Africa | Resisto | n = 5 | Boiled covered with water open pot (BO) Boiled, covered with water, closed pot (BC) Boiled, half covered with water, closed pot (BHC) | BO: 30 min BC: 20 min BHC: 20 min | trans-beta-carotene BO: 156 μg/g FW BC: 173 μg/g FW BHC: 155 μg/g FW | BO-TR: 88 BC-TR: 92 BHC-TR: 83 | |
| Nascimento et al., 2006 | Brazil | Purchased locally | n = 5 | Boiled cuts (B) | 20 min | 100 | trans-beta-carotene 4.8 μg/g FW | BC-TR: 88 (87/88) |
| Kidmose at al., 2007 | Kenya | 6 orange and yellow fleshed sweet potato | n = 6 | Boiled, covered with water, closed pot (BC) | 15-39 min | 100 | trans-beta-carotene 12 to 108 μg/g FW | BC-TR: 88 (45/126) |
| Bengtsson et al., 2008 | Uganda | Ejumula and 6 field test varieties | n = 28 | Boiled (B) immersed in water open pot Steamed (S) by wrapping in banana leave an pot with lid on | B: 20 min S: 30 min | B: S: 93 | trans-beta-carotene 108 to 314 μg/g DM | B: 78 S: 77 |
| Wu et al., 2008 | China | Yanshu No. 5 | n = 2 | Sweet potato was covered with water in a electric cooker and boiled with the lid on (BC) *boiling for doneness was about 15 min | 10, 20, 30, 40 and 50 min | 100 | trans-beta-carotene BC: 77 μg/g FW S: 67 μg/g FW | 10/20/30/40/50 min BC: 99/92/87/80/68 S: 95/88/69/57/48 |
| Tumuhimbise et al., 2009 | Uganda | 5 varieties | n = 3 | Slices of sweet potato were boiled (B) and steamed (S) | B: 20 min S: 30 min | B: 92 S: 94 | trans-beta-carotene 67 to 316 μg/g DM | B: 76 (69-84) S: 75 (66-84) |
| Frying | ||||||||
| Hagenimana et al., 1999 | Kenya | Cultivar Zapallo | NR | Fried Mandazis | NR | 65 | Total carotenoids 49 μg/g DM | F: 36 (31-43) |
| Nascimento et al., 2006 | Brazil | Purchased locally | n = 5 | Boiled for 20 minutes (B) then fried for 8 minutes (F) | B:20 min F:8 min | 100 | trans-beta-carotene 3 μg/g FW | B,F-TR: 68 (67/68) |
| Bengtsson et al., 2008 | Uganda | Ejumula and 6 field test varieties | n = 24 | Deep-frying (F) | F:10 min | 160–170 | trans-beta-carotene 108 to 314 μg/g DM | F:78 |
| Wu et al., 2008 | China | Yanshu No. 5 | n = 4 | Sweet potato was steamed (S) for 40 minutes then fried (F) in rapeseed oil for 1 minute | S: 40 min F: 1 min | trans-beta-carotene 68 μg/g FW | S,F-TR: 60 (40 min) S,F-TR: 64 (1 min) | |
| Tumuhimbise et al., 2009 | Uganda | 5 varieties of OFSP | n = 3 | Slices of sweet potato were deep-fried on preheated sunflower cooking oil (F) | F:10 min | 170 | trans-beta-carotene 67 to 316 μg/g DM | F-TR: 75 (62–88) |
| Bechoff et al., 2011c | Uganda | OFSP-Ejumula | n = 3 | Fried chapatis (CP) and mandazis (MD) made of milled OSP chips (30%) and wheat flour (70%) | F: 1.6 min (0.6–3 min) | 143 (116–190) | trans-beta-carotene CP: 30.1 μg/g FW MD: 32.9 μg/g FW | CP:F-TR: 83 (70–97) MD:F-TR: 85 (80–89) |
| Porridge | ||||||||
| Bechoff et al., 2011c | Uganda | Ejumula | n = 2 | Porridge: OSP chips (30%), roasted white-yellow maize (35%) and roasted soybean (35%) | 6.2 min (4.3–10.3) | 84 (81–89) | trans-beta-carotene 56.4 μg/g FW | TR: 78 (69–93) |
| Baking/ Roasting | ||||||||
| Chandler and Schwartz, 1988 | USA | Jewel variety, cured (30°C, 85% humidity) for 7 d | Sweet potatoes were wrapped in aluminum foil and baked (R) | R:80 min | 191 | Total beta-carotene 440 μg/g DW | R:69 | |
| Kidmose et al., 2007 | Kenya | 6 orange and yellow fleshed sweet potato | n = 6 | Roasted until core temperature reached 86°C (R) | R: 30–-90 min | trans-beta-carotene 12 to 108 μg/g FW | R-TR: 85 (49/119) | |
| Tumuhimbise et al., 2009 | Uganda | 5 varieties | n = 3 | Slices of sweet potato were baked on preheated electric oven (R) | R:15 min | 180 | trans-beta-carotene 67 to 316 μg/g DM | R-TR: 65 (54–78) |
| Microwaving | ||||||||
| Chandler and Schwartz, 1988 | USA | Jewel variety, cured (30°C, 85% humidity) for 7d | Sweet potato was micro waved until core temp reached 99°C (M) | M:7 min | 6000 W | Total beta-carotene 440 μg/g DW | M:77 | |
| Wu et al., 2008 | China | Yanshu No. 5 | n = 2 | Portions of sweet potato were put in plastic microwave bowls without covers (M) | M:10 min M:15 min M:20 min | Medium power | trans-beta-carotene 62 μg/g FW | M-TR: 92 (10 min) M-TR: 67 (15 min) M-TR: 34 (20 min) |
B: boiled; BL: blanched; S: steamed; F: fried; BO: boiled, open pot; BC: boiled, closed pot; R: roasted/baked; M: microwaved; S2: blanched strips (2 min); S10: blanched strips (10 min); P: puree; SG: steam, starch, gelatinized; S: steamed; SE: steam, enzyme inactivated; CA: canned; DE: dehydrated, drum-dried; TR: true-retention; NR: not reported; DW: dry weight; FW: fresh weight.