J Sci Food Agric 1996,72,209-212

Genotypic Variations in Quality Fresh Roots of Philippine Sweet

and Shelf-Life of Potato Grown in _ _

Two Planting Seasons Antonio L Acedo Jr,* Emma S Data and Marcel0 A Quevedo Postharvest Technology Laboratory, Department of Horticulture, Visayas State College of Agriculture, Baybay, Leyte 6521-A, Philippines (Received 2 January 1996; accepted 10 May 1996)

Abstract: Sweet potato breeding in the Philippines has recently integrated root quality and shelf-life attributes in varietal development. In this study, the harvest and post-harvest quality of the fleshy roots of different sweet potato genotypes were determined. These genotypes included the existing recommended varieties and the elite selections from the polycross breeding nursery and were grown during the dry and wet planting seasons. Dry matter, starch, sugar and protein contents of freshly harvested roots were found to differ widely with genotype. During storage at ambient temperatures, starch content decreased, sugar content increased and in some genotypes dry matter increased. Protein content of the stored roots varied only slightly from that of fresh roots. The different genotypes also differed in the degree of weight loss, shrivelling, decay and consequently, shelf-life. Some genotypes had short-lived roots (less than 1 month) while others had roots which were still marketable at the end of the 3-month storage period. Root quality and shelf-life similarly varied with planting season. Some genotypes had increased dry matter, starch and sugar contents and long shelf-life when planted in the dry season while others had these characteristics when produced in the wet months. Protein content generally decreased in wet-season-produced roots. However, a number of genotypes had comparable root quality and shelf- life regardless of planting season.

Key words: sweet potato, Ipornoea batatas (L) Poir, fleshy roots, physico- chemical attributes, sensory quality, shelf-life, genotypic influence, environmental influence.

INTRODUCTION

Sweet potato, Ipomoea batatas (L) Poir, is a crop that produces more food than any of the other major root crops, legumes and cereals (Wolfe 1989). Its fleshy roots provide a good supply of energy and contain potentially high levels of pro-vitamin A and ascorbic acid. Roughly 80% of the world’s sweet potato production occurs in Asia (Horton 1987). The Philippines is the ninth leading world producer. However, Philippine sweet potato pro- duction is highly seasonal and yields remain low (5 tons ha-’) (CRC 1993) in spite of the development of new varieties that can produce 15-20 tons of roots per

include poor eating quality and short shelf-life of the fresh roots.

Only recently, sweet potato breeding work focused not only on the improvement of yield but of quality and shelf-life as well. As part of the varietal development effort, this study investigated the genotypic variations in some chemical, sensory quality and post-harvest charac- teristics of the fresh roots produced from the dry and wet season plantings.

MATERIALS AND METHODS hectare (Villamayor 1988). Disadvantages that restrain farmers’ adoption of the high-yielding varieties (HYVs) Genotypes OPS 37, OPS 56, OPS 99, V15-70 and

V37-151 were used and hereafter referred to as G1, G2, * To whom correspondence should be addressed. G3, G4 and G5, respectively. These genotypes are

209 J Sci Food Agric 0022-5142/96/$09.00 0 1996 SCI. Printed in Great Britain

210 A L Acedo Jr, E S Data, M A Quevedo

potential HYVs which comprised the elite selections from progenies of the polycross breeding nurseries and entered in the seedboard trial-the final phase in vari- etal screening. In addition to the seedboard genotypes, four existing HYVs (VSP1, VSP4, VSPS and VSP6) were evaluated.

The different genotypes were grown during the dry and wet season, each lasting for about 4 months. During the dry season plantings, the average 4-month rainfall and daily temperature and relative humidity were 78.6 & 5.3 cm, 28.0 f 34°C and 73.6 & 8.6%, respectively; while during the wet season plantings, 145.2 14.3 cm, 26.7 f 3.2"C and 77.6 & 11.0%, respectively. Each genotype was planted in three 2 m x 6 m plots, each plot representing a replicate.

From each replicate plot, three to six uniform-sized roots were harvested for dry matter, starch, sugar and protein analysis. Dry matter was determined using a forced draft oven at 70°C. Starch and sugar were analysed by the modified anthrone method (Cagampang and Rodriquez 1981) while protein, by the micro- kjeldahl method (AOA 1980). For sensory quality, the overall flavour of the steamed roots was scored by trained panelists using a nine-point hedonic scale.

For shelf-life evaluation, 10-30 uniform-sized and defect-free roots from each replicate plot were stored for 3 months at ambient (24.2-30.6"C, 66.0-82-2% relative humidity). Weight loss, degree of shriveling and sprout- ing and percentage decayed roots were measured

monthly. Root shriveling was subjectively rated using a scale of 1 (none) to 5 (severe). A scale of 1-5 was also used to rate the degree of sprouting: 1, no sprout; 2, 1-3 sprouts; 3, 4-6 sprouts; 4, 7-10 sprouts and 5, more than 10 sprouts per root. Shelf-life was quantified as less than 1 (< l), 2 (< 2) and 3 (< 3) months if after the first, second and third month of storage, respectively, at least 50% of the stored roots became unmarketable. A shelf- life of more than 3 months (3 +) was given to genotypes with more than 50% of their roots remaining market- able after the third month of storage.

RESULTS AND DISCUSSION

Chemical attributes

Dry matter, starch, sugar and protein contents of the fresh roots varied with genotype (Table 1). Dry matter content (DMC) was highest in G4 and lowest in G2, VSPl and VSP6. The other genotypes had moderately high DMC (30-35%). The starch and sugar contents did not correlate well with DMC. G5 and G3 were the high-starch but low-sugar genotypes while VSP1, the low-starch but high-sugar genotype. The other geno- types had moderately high levels of starch (60-65%) but differed in sugar content, with G2 having the highest sugar content and VSP5, the lowest.

TABLE 1 Chemical and sensory quality attributes of sweet potato roots at harvest"

Genotype . % Dry % Starch YO Sugar YO Protein Overall matter flavour

Dry season G1 G2 G3 G4 GS VSPl VSP4 VSPS VSP6

W e t season G1 G2 G3 G4 G5 VSPl VSP4 VSPS VSP6

32.3 cde

31.9 def 44.1 a 32.7 cde 27.4 fg 29.7 ef 32.0 de

25.6 g

27.5 fg

29.5 ef 25.0 g 33.1 cd

35.5 bc 26.8 fg 31.6 de 27.0 fg 29.2 ef

39.6 ab

62.2 de 61.5 def 62.9 de

72.2 a

62.4 de

62.1 de

66.2 bc

48.2 g

63.9 cd

62.9 de 61.0 def 72.7 a 58.2 f 67- 6b 59.6 ef 63.2 cd 64.1 cd 61.4 def

6.4 c 3.31 abc

4.8 de 3.31 abc 6.6 c 2.95 bcd 3,7 e 3.62 a

12.0 a 3.46 ab 5.8 cd 3.15 abc 3.5 e 3.68 a 8.3 b 2.20 e

12.1 a 3.94 a

3.7 e 3.30 abc 8.0 b 3.15 abc 2.1 f 3.15 abc 6.4 c 2.32 e 3.6 e 3.38 abc

7.6 bc 3.15 abc 3.1 ef 2.20 e 5.4 cd 2.68 de

6.7 c 2.84 cd

7.0 a 6.9 a 6.4 ab 6.9 a 6.8 a 5.4 c 6.8 a 6.9 a 6.3 b

6. 2b 6.6 a 7.0 a 6.9 a 6.6 a

6 4 a 6.0 b

6.1 b 6.1 b

Mean separation by Duncan's Multiple Range test (DMRT), 5%.

Quality and sheljXfe of Philippine sweet potato 21 1

TABLE 2 Shelf-life of sweet potato roots during ambient storage

Genotype Shelf-life Decaf Degree of Weight Degree of (months) shrivelling" loss (%)(I sprout in$

DS W S D S WS DS W S DS WS DS W S

G1 3+ < 1 20 80 2.4 - 27.9 3.1 G2 < 3 <2 67 60 4.0 3.7 33.3 41.1 2.2 1.0 G3 < 1 < 1 67 67 G4 < 2 3 + 60 20 2.2 3.4 31.3 27.7 1.0 1.0 G5 < 3 < 3 73 73 1.8 3.0 30.7 38.7 2.8 1.0

VSPl <1 < 1 100 100 VSP4 <1 < 3 100 72 1.5 27.3 1.5 VSP5 <1 <1 100 60 VSP6 < 1 < 3 67 43 4.3 36.7 2.1

~~~ ~

(I Data taken on the first, second and third month of storage for genotypes with shelf-lives of < 1, <2 and < 3 to 3+ months, respectively (DS, dry season; WS, wet season). Data not taken for genotypes with < 1 month shelf-life.

The environmental condition during growth of the crop had contrasting influence on starch content. While it did not affect the starch content of five genotypes, wet season growing increased the starch content of G3 and VSP 1 but decreased that of G4 and G5. On the other hand, the sugar content consistently decreased in wet- season-produced roots of G1, G2, G3, VSPl and VSP6. These changes in starch and sugar content did not effect corresponding changes in DMC. The DMC did not vary with planting season except for VSPS whose wet season-produced roots had lower DMC than the dry season-produced ones implying increased root water content.

Protein content was low and ranged from 2.20- 3.94% (Table 1). G4 and VSP6 had much lower protein content than the other genotypes. Wet season planting reduced the protein level of G4 roots as well as that of VSPl and VSPS roots. The protein content of the other genotypes did not vary with growing season.

Sensory quality

The overall flavour of the steamed roots of most geno- types from the dry season plantings was rated compara- bly desirable (6.4-7-0) (Table 1). Only the VSPl and VSP6 roots had markedly lower ratings due to their wet texture. When grown during the wet season, flavour ratings decreased for G1 and VSPS roots which became wet-textured and less sweet. This seemed to reflect the decrease in DMC and sugar content of these two geno- types. In contrast, the wet-season-produced roots of G3 and VSPl had better flavour than the dry-season-pro- duced ones. This was due to improved mealiness, a pos- sible result of the increase in starch content of the roots.

Shelf-life and post-harvest characteristics

The fresh roots of some genotypes (G3, VSPl and VSPS) had short shelf-lives ( < 1 month) while others

TABLE 3 Chemical and sensory quality attributes of sweet potato roots after 3 months

of ambient storage" ~~~~~~~~~~ ~ ~

Genotype % Dry % Starch % Sugar % Protein Overall matter flavour

Dry season G1 32.4 b 51.4 9.4 b 3.78 b 7.2 a G2 32.4 b 57.5 12.4 a 3.15 bc 6.8 a

Wet season G4 43.7 a 55.0 9.1 b 4.72 a 6.9 a VSP6 30.0 b 54.4 9.8 b 2.84 c 6.3 b

a Mean separation by DMRT, 5%.

212 A L Acedo Jr, E S Data, M A Quevedo

(G5) had long shelf-lives ( < 3 months) regardless of growing season (Table 2). The other genotypes (G2, VSP4, VSP6) showed season-dependent root shelf-life. Only two genotypes had a root shelf-life of more than 3 months ( 3 + ) but this was dependent again on the growing season. These were the G1 roots produced from the dry season plantings and the G4 roots from the wet season plantings. Root quality deterioration was due mainly to decay and partly to shrivelling, weight loss and sprouting (Table 2). Shriveling appeared to be favored in wet-season-produced roots while sprouting, in dry-season-produced ones.

After 3 months of storage, sound roots of some geno- types were subjected to chemical and sensory quality analysis. Table 3 shows that the root DMC and overall flavour were unaffected by storage as these compared well with that of unstored roots (Table 1). However, starch content decreased while sugar content increased indicating starch breakdown to sugars during storage. No adverse changes in protein content were obtained. It even increased in G4 roots after 3 months of storage.

Most of the seedboard genotypes outperformed the existing HYVs in terms of root quality and shelf-life.

Furthermore, the results demonstrate the high possi- bility of developing varieties of good root quality and long root shelf-life for a particular growing season (eg G1) or for all seasons (eg G5).

REFERENCES

AOAC 1980 Methods of Analysis. Association of Official Analytical Chemists, Washington, DC, USA.

Cagampang G B, Rodriquez F M 1981 Methods of Analysis for Screening Crops of Appropriate Qualities. Institute of Plant Breeding, College, Laguna, Philippines.

CRC 1993 Philippine Agribusiness Factbook and Directory. Center for Research and Communication, Manila, Philip- pines.

Horton D E 1987 World patterns and trends in sweet potato production and use. In : Maintenance and Utilization of Sweet Potato Genetic Resources. International Potato Center, Peru, p. 17.

Villarnayor F G 1988 Recommended sweet potato varieties in the Philippines. Root Crops Dig 3 1-4.

Wolfe J A 1989 Nutritional aspects of sweet potato roots and leaves. In: Improvement of Sweet Potato in Asia. Interna- tional Potato Center, Peru, p. 167.