Retention of Provitamin A Carotenoids in Staple Crops Targeted for Biofortification in Africa: Cassava, Maize and Sweet Potato

Figures & data

Figure 1 Chemical structures of provitamin A carotenoids.

Table 1 Retention of carotenoids in cassava-effect of drying and storage

Reference	Country	Cultivars	Sample size	Methodology	Time	Temp (°C)	Moisture (%)	Average initial carotenoid content	Retention% average (Min/Max)
Drying
Iglesias et al., 1997	Colombia	28 genotypes	28 × 2 replications	Oven dried flour (OVF) and sun dried flour (SUF)	NR	NR	NR	Carotene 18.9 μg/g DW	OVF- AR: 55 (17/99) SUF- AR: 27 (10/55)
Nascimento et al., 2007	Brazil	NR	NR	Oven dried (OVC) and oven dried blanched chips (BLC)	NR	70	NR	trans- beta-carotene 3.57 μg/g FW	OV-TR: 91 BLC-TR: 79
Chavez et al., 2007	Colombia	CM 2772-3, MBRA1324, MCOL2401	9 (3 cultivars × 3 replications)	Coarse chopped oven dried (OV), Shadow dried (SH), and sun dried (SU)	OV: 24 h SH: 6-7 d SU: 2-3 d	OV: 60 SH: NR SU: NR	12	trans- beta-carotene 10.34 μg/g DW	OV-TR: 72 SH-TR: 59 SU- TR: 38
Maziya-Dixon et al., 2008	Nigeria	TMS 01/1371, TMS 01/1412, TMS 01/1663	3 roots per cultivar	Oven dried flour (OVF) and chips (OVC), sun dried flour (SUF) and chips (SUC)	OVF: 3d OVC: 3 d	OVF: 45 OVC: 45	12	total carotenoids 4.61 μg/g DW	OVF- AR: 67 OVC- AR: 178 SUF- AR: 56 SUC: AR: 249
Storage
Nascimento et al., 2007	Brazil	NR	NR	Dried slices of blanched (BL) and unblanched (UB) stored in polyethylene bags	UB: 20 d BL1: 20 d BL2: 110 d	30-35	NR	trans- beta-carotene UB:  8.7 μg/g FW BL:  7.8 μg/g FW	UB- trace BL1- TR: 83 BL2- TR:44
Chavez et al., 2007	Colombia	CM2772-3, MBRA1324, MCOL2401	9 (3 cultivars × 3 replications)	Oven dried flour (OVF) and chips (OVC), sun dried flour (SUF) and chips (SUC)	1: 14 d 2: 30 d	Room temp		trans- beta-carotene 10.34 μg/g DW	OVF1- TR: 41 OVF2- TR: 36 SUF1- TR: 22 SUF2- TR: 18 SUC1- TR: 24 SUC2- TR: 18
Oliveira et al., 2010	Brazil	1757, 1783, 1752, 1740, 1751	5 kg of roots per cultivar	Oven dried flour (OVF)	FL: 19 d	Room temp	ND	total carotenoids 12 μg/g DW	OVF- AR: 4 (2/14)

AR: apparent retention; TR: true retention, OV: oven dried; OVF: oven dried flour; OVC: oven dried chips; SU: sun dried; SUF: sun dried flour; SUC: sun dried chips; SH: shadow dried; BL: blanched; NR: not reported; DW: dry weight; FW: fresh weight.

Table 2 Retention of carotenoids in cassava-effect of cooking

Reference	Country	Cultivars	Sample size	Methodology	Time	Temp (°C)	Average of initial carotenoid content	Retention % average (min/max)
Boiling or blanched
Iglesias et al., 1997	Colombia	28  genotypes	28 × 2 replications	Boiled (B)	30 min	NR	Carotene 8.9 μg/g DW	B-AR: 66 (33/98)
Chavez et al., 2007	Colombia	CM2772-3, MBRA1324, MCOL2401	6 (3 cultivars × 2 replications)	Boiled cuts in closed pot (B)	30 min	NR	trans- beta-carotene 10.34 μg/g DW	B-TR: 56 (16/92)
Nascimento et al., 2006	Brazil	NR	5 roots × 2 replications	Boiled cuts (B)	30 min	NR	trans- beta-carotene 1.5 μg/g FW	B-TR: 81 (79/82)
Nascimento et al., 2007	Brazil	NR	NR	Blanched slices (BL)	1.5 min	NR	trans- beta-carotene 3.57 μg/g FW	BL-TR: 84
Thakkar et al., 2009	Nigeria	TMS 01/1371, TMS 01/1412, TMS 01/1663	3 roots per cultivar	Cubes soaked in water prior to boiling (B)	30 min	95	Total beta-carotene 33.6 μg/g DW	B-AR: >100
Ceballos et al., 2012	Colombia	NR	18 (6 cultivars × 3 replications)	Boiled (B)	30 min	NR	Total carotenoid 32.2 μg/g DW	B-TR:87 (76/97)
Failla et al., 2012	Puerto Rico	3DXS, 20DXS, and 37DXS	3 roots per cultivar	Boiled (B)	30 min	95	trans- beta-carotene 23.6 μg/g DW	B-AR:44 (38/52)
Frying
Nascimento et al., 2006	Brazil	NR	5 roots × 2 replications	Boiled (B) and fried (F)	B: 20 min F: 8 min	NR	trans- beta-carotene 1.3 μg/g FW	B,F-TR: 54 (54/54)
Gari preparation
Chavez et al., 2007	Colombia	CM2772-3, MBRA1324, MCOL2401	9 (3 cultivars × 3 replications)	Fermented (FE) and roasted (R)	FE: 7 d R: NR	NR	trans- beta-carotene 10.34 μg/g DW	FE,R-TR: 34
Maziya-Dixon et al., 2008	Nigeria	TMS 94/0006, TMS 01/1235, TMS01/1371	3 roots per cultivar	Fermented (FE) and roasted (R)	FE: 3 d R: 10 min	NR	total carotenoids 4.94 μg/g DW	FE,R-AR: 187
Thakkar et al., 2009	Nigeria	TMS 01/1371, TMS 01/1412, TMS 01/1663	3 roots per cultivar	Fermented (FE) and roasted (R1 and R2)	FE: 3 d R1: 10 min R2: 20 min	FE: NR R1: 165 R2: 195	total beta-carotene 33.6 μg/g DW	FE,R1-AR: 63 FE,R2-AR: 10*
Failla et al., 2012	Puerto Rico	3DXS, 20DXS, and 37DXS	3 roots per cultivar	Fermented (FE) and roasted (R)	FE: 3 d R2: 20 min	R1: 185 R2: 120	trans- beta-carotene 23.6 μg/g DW	AR: 23(16/30)
Fufu preparation
Thakkar et al., 2009	Nigeria	TMS 01/1371, TMS 01/1412, TMS 01/1663	3 roots per cultivar	Fermented (FE) and roasted (R)	FE: 3 d R: 20 min	FE: NR R: 165	total beta-carotene 33.6 μg/g DW	FE,R-AR: >100
Maziya-Dixon et al., 2008	Nigeria	TMS 01/1371, TMS 01/1412, TMS 01/1663	3 roots per cultivar	Fermented (FE) and cooked with water (B)	FE: 5 d	FE: NR	total carotenoids 4.94 μg/g DW	FE,B-AR: 82
Failla et al., 2012	Puerto Rico	3DXS, 20DXS, and 37DXS	3 roots per cultivar	Fermented (FE) and cooked with water (B)	FE: 5 d B: 10 min	B: 100	trans- beta-carotene 23.6 μg/g DW	FE,B-AR: 44(34/54)
Flour
Oliveira et al., 2010	Brazil	1757, 1783, 1752, 1740, 1751	5 kg of roots per cultivar	Cassava was soaked in water	OVF: 30 min	120–150	total carotenoids 12 μg/g DW	AR: 49 (29/67)
Failla et al., 2012	Puerto Rico	3DXS, 20DXS, and 37DXS	3 roots per cultivar	Non-fermented flour (NFF) and fermented (FE) flour were both dried in oven	FE: 3 d OVF:24 h	37	trans- beta-carotene 23.6 μg/g DW	NFF-AR: 60(35/78) FE-AR: 48(39/56)

*Cultivar TMS 01/1371. AR: apparent retention; TR: true retention, F: fried; FE: fermented; B: boiled; R: roasted; NR: not reported; DW: dry weight; FW: fresh weight.

Table 3 Retention of carotenoids in maize-effect of drying and storage

Reference	Country	Cultivars	Sample size	Methodology	Time	Temp (°C)	Moisture (%)	Average initial carotenoid content	Retention %average,% (min/max)
Drying
Burt et al., 2010	Canada	Yellow dent inbred maize lines A619, CG102,  CG60, and high carotenoid lines: HiC-5, HiC-7, HiC-23, and HiC-26	Triplicate from each genotype	Control (C): lyophilized and stored at −80°C Oven-dried (OV) using two methods	OV1: 8 h OV2: 72 h	OV1: 90 OV2: 25	NR	TC: 70–120  μg/g DW	(55/85)
Storage
Weber et al., 1987	US	Maize inbred lines, B84, H51, Oh45, R802A	NR	Storage	6 months	Room temp	NR	27–77 μg/g DW	58 (50/67)
Burt et al., 2010	Canada	Yellow dent inbred maize lines A619, CG102,  CG60, and high carotenoid lines: HiC-5, HiC-7, HiC-23, and HiC-26	Triplicate from each genotype	Control (C): lyophilized and stored at −80°C Oven-dried (OV) at 90°C or 25°C	A) samples of  2 genotypes stored for 18 months; B) 6 genotypes stored for  4 months; All  in the dark	A: 4 B: 25	Relative humidity: 35	TC: 70–120  μg/g DW	A: 39–78 B: 60–65

Table 4 Retention of carotenoids in maize-effect of cooking

						Carotenoid retention (%)
Reference	Maize cultivar	Cooking style	Time	Temp (°C)	Moisture (%)	trans-β-carotene	13-cis-β-carotene	9-cis-β-carotene	β-crypto-xanthin	Lutein	Zeaxanthin	ProA**
Muzhingi et al., 2008***	KUI Synthetic Yellow Maize	Raw*				3.35 ± 0.10	2.08 ± 0.12	0.62 ± 0.04	3.22 ± 0.14	3.96 ± 0.12	32.85 ± 1.17
		Porridge (thick)	30 min	100		123	138	150	101	130	112
		Porridge (thin)				113	105	124	89	113	100
		Boiled	1 h	100		110	119	139	92	115	89
		Muffin (baked)	25 min	232		27	25	31	51	97	78
De La Parra et al., 2007	White	Raw*				0.05			0.01	0.05	0.06
		Dough	33 min		56	ND			117	142	129
		Tortilla (baked)	1 min	280		ND			124	150	125
		Chips (fried)	1 min	175		ND			6.3	14	163
	Yellow	Raw*				0.33			0.19	4.06	3.53	0.43
		Dough	24 min		56	62			16	32	37
		Tortilla (baked)	1 min	280		33			9	27	29
		Chips (fried)	1 min	175		ND			0.6	19	18	0.12
	High carotenoid	Raw*				0.45			0.23	2.45	3.22	0.57
		Dough	53 min		56	57			50	30	35
		Tortilla (baked)	1 min	280		32			54	30	33
		Chips (fried)	1 min	175		18			20	25	29	18.7
Lozano-Alejo et al., 2007	13 genotypes	Raw*										1.38
(0.7–3.05)
		Snacks (fried)	1 min	200–210								64 (18–85)
Li et al., 2007	Kernels resulting from the DeExp x CI.7 cross pollinated with BC Orange	Raw*			14.5 ± 0.5	7.75 ± 0.03	1.20 ± 0.05	1.54 ± 0.10	1.73 ± 0.19	11.71 ± 0.16	9.20 ± 1.08
		Wet milled flour	24 h	30	35.2 ± 2.3	94	93	88	90	94	94
		Wet milled flour, fermented	48 h	30	49.0 ± 1.2	83	84	79	76	76	73
		Wet milled flour fermented, and cooked	9 min	93	61.5 ± 0.4	73	88	79	71	67	64
		Wet milled flour, unfermented and cooked	9 min	93	60.2 ± 0.9	71	98	81	74	71	66

*Uncooked maize is expressed as μg/g DW.

**Provitamin A content was calculated as the sum of all- trans-β-carotene plus (β-cryptoxanthin*0.5).

***Cryptoxanthin values are for total (α + β) cryptoxanthin.

Table 5 Retention of carotenoids in sweet potato- effect of drying

Reference	Country	Cultivars	Sample size	Methodology	Time	Temp (°C)	Moisture (%)	Average initial carotenoid content	Retention % average
Drying
Hagenimana et al., 1999	Kenya	32 cultivars	NR	Oven dried (OV)	12 h	65	6–8	Total carotenoids 49 μg/g DM	OV: 70
Nascimento et al., 2007	Brazil	Purchased in local market	NR	Oven dried (OV) and oven dried of blanched slices (BL)	NR	70	NR	trans- beta-carotene 3.57 μg/g FW	OV-TR: 96 BL-TR: 96
Bengtsoon et al., 2008	Uganda	Ejumula and 6 field test varieties		Oven dried (OV), solar dried (SO) sun dried (SU)	OV: 10 h SO: 6–10 h SU: 6–10 h	OV: 57 SO:45–63 SU: 30–52	OV: 10.8 SO: 6.8 SU: 10	trans- beta-carotene 108 to 314 μg/g DM	OV: 88 SO: 91 SU: 84
Bechoff et al., 2009	France	Imported from USA	n = 5 roots	Hot air (HA) Solar (SO) Sun (SU)	HA: 2 h SO: 8.5 h SU: 8 h	HA: 24–45 SO: 27–50 SU: 24–30	HA: 11 SO: 10 SU: 10	trans- beta-carotene 293 μg/g DW	HA: 84^a SO:77^ab SU: 66^b
Kidmose et al., 2007	Kenya	Variety Zapallo	n = 5 roots	Shade (SH) made into chips (C) and flour from chips (FL)	SH: 5 h		SH: 6	trans- beta-carotene 123 μg/g FW	SH: 79 (chips) SH: 62 (flour)
Mdziniso et al., 2006	USA	Purchased locally		Solar drying (SO)	NR	27–50	8–10	trans- beta-carotene 972 μg/g DW	SO: 94–96
Wu et al., 2008	China	Yanshu No. 5	n = 2	Steamed (S) Oven dried 1 (OV1) Oven dried 2 (OV2)	S: 20 min OV1: 5 h OV2: 11 h	50		trans- beta-carotene 70  μg/g FW	S-TR: 88 OV1-TR: 64 OV2-TR: 59
Bechoff et al., 2010a	Uganda	Ejumula and Kakamega on wet and dry weather		Tent dryers: UV resistant (T1) Red resistant (T2) Not resistant (T3) Tunnel dryer (TU) Sun dried (SU)	wet/dry T1: 13 h/8 h T2: 14 h/10 h T3: 13 h/ 8 h TU: 10 h/6 h SU: 9 h/5 h	wet/dry 27.3/31.2	wet/dry 62.4/32.2	total carotenoids μg/g DW wet/dry 251/306.3 (Ejumula) 75/100.3 (Kakamega)	(kakamega-ejumula) wet dry T1: (81–92) (98–92) T2: (83–96) (91–95) T3: (87–91) (91–95) TU: (90–93) (89–91) SU: (87–93) (90–95)
Bechoff et al., 2011a	Mozam-bique	MGCL01 and Resisto	n = 5 roots in duplicate	Tunnel dryer (TU) Sun dried (SU) Shade dried (SH)	MGCL01/Resisto Thin chips TU : 25.5 h/26.1 h SU: 23.8 h/25.4 h SH: 26.5 h/50.7 h Thick chips SU: 23.9 h/62.3 h	TU: 26 SU: 22 SH: 22	MGCL01/Resisto Thin chips TU: 6.1/8.1 SU: 7.9/8.5 SH: 10.1/10.1 Thick chips SU: 10.4/9	MGCL01  235.6 μg/g DW Resisto 434.4 μg/g DW	MGCL01  Resisto Thin chips TU: 89.2% 85.4% SU: 95.1% 83.5% SH: 101% 92.3% Thick chips SU: 95.3% 75.4%

AR: apparent retention; TR: true retention, OV: oven dried; BL: blanched; UB: unblanched; FL: flour; C: chips; OV: oven dried; SU: sun dried; SO: solar dried; T: tent dried: TU: tunnel dried; SH: shade dried; Z: zipped PE bags; SC: sealed clear bag; SCB: sealed clear PE bag in black PE bag; B: black PE bag; NR: not reported; J: jar; DW: dry weight; FW: fresh weight.

Table 6 Retention of Carotenoids in Sweet Potato-Effect of Storage

Reference	Country	Cultivars	Sample size	Methodology	Time	Temp (°C)	Moisture (%)	Average initial carotenoid content	Retention % average
Storage
Hagenimana et al., 1999	Kenya	25 cultivars	NR	Stored OFSP dried chips	11 months	Room temp	NR	Total carotenoids 49 μg/g DW	AR: 57
Nascimento et al., 2007	Brazil	Purchased locally	Triplicate analysis	Dried slices of blanched (BL) and unblanched (UB) stored in polyethylene bags	UB: 20 d BL1: 20 d BL2: 70 d	30–35	NR	trans- beta-carotene UB:  463 μg/g FW BL:  513 μg/g FW	UB- 45 BL1- TR: 80 BL2- TR:49
Bechoff et al., 2010a	Uganda	6 cultivars		OFSP chips stored: Zipped PE bag (Z) Sealed clear PE bag (SC) Sealed clear PE bag in black PE bag (SCB) Black PE bag (B)	4 months	Room temp		Total carotenoids Ejumula: 199.8 μg/g DW Kakamega: 52.4 μg/g DW	(Kakamega-Ejumula) Z: (23–23) SC: (35–35) SCB: (34–32) B: (36–29)
Bechoff et al 2010b	United Kingdom	Ejumula	N = 3	Laboratory storage kinetics of carotene in dried chips Experimental data: Stored in Jar in dark (J)-UK Stored in LPDE bags (LPDE)-Uganda	J: 88 d LPED: 125 d	Room temp	NR	trans- beta-carotene J: 181.2 μg/g DW LPDE: 219.6 μg/g DW	J: 41 LPED: 23
Bechoff et al., 2011a	Mozambique	MGCL01 and Resisto	n = 5 roots in duplicate	Stored in traditional bags made of jute and hung inside a house made of mud	31 d 62 d 125 d	25 (20/31)	NA	MGCL01 223.6 μg/g Resisto 366.2 μg/g	(MGCL01-Resisto) 31 d: (61–73) 62 d : (37–52) 125 d: (12–21)
Bechoff et al., 2011b	Uganda	Ejumula	N = 4 roots in duplicate	Pre-treatments Deionized water (W) 0.5% citric acid (CA) 1% ascorbic acid (AA) 1% salt (S) Unsoaked (U) 1% AA, 1% salt (AA&S) 0.5% sodium metabisulfite (SM) 0.5% sodium metabisulfite, 0.5% citric acid (SM&CA) 0.5% citric acid, 1% salt (CA&S)	1 month 2 months 4 months 6 months	−20	NA	Total carotenoid W: 237.7 μg/g CA: 232.2 μg/g CA&S: 254.7 μg/g S: 251.4 μg/g AA&S: 260.4 μg/g U: 269.4 μg/g SM: 250 μg/g AA: 260.8 μg/g SM&CA: 259.6 μg/g	Storage:(1m/2m/4m/6m) W: (52/38/31/17) CA: (57/40/23/16) CA&S: (50/39/25/17) S: (54/47/30/17) AA&S: (53/47/32/18) U: (53/47/39/18) SM: (55/50/37/20) AA: (59/38/37/20) SM&CA: (63/49/32/21)

AR: apparent retention; TR: true retention, OV: oven dried; BL: blanched; UB: unblanched; FL: flour; C: chips; OV: oven dried; SU: sun dried; SO: solar dried; T: tent dried: TU: tunnel dried; SH: shade dried; Z: zipped PE bags; SC: sealed clear bag; SCB: sealed clear PE bag in black PE bag; B: black PE bag; NR: not reported; J: jar; DW: dry weight; FW: fresh weight.

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.

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