Tastes and volatiles of tropical-type sweet potatoes

Abstract

For fresh market sweet potato [Ipomea batatas (L.) Lam] quality is defined in terms of attractiveness, sweetness, texture, and flavor composed of taste and odor after cooking. There is a scarcity of information regarding taste and volatiles of tropical type sweet potatoes. The first objective of this research was to provide a robust set of data for carbohydrate type and levels, alcohol insoluble solids (AIS) and volatile organic compounds (VOC) from six cultivars of sweet potato, data which will allow us to have a quantitative selection tool besides crop yield, tuber size and appearance. The second objective was to relate VOC differences among sweet potato cultivars that can be attributed to chemical and physical differences of the pulp before and after cooking. A three harvest study was conducted to identify and determine major carbohydrate content, AIS, starch granule diameter and form, and tastes and odors of six cultivars of sweet potato, which were very sweet ('Gem'), sweet ('Miguela' and Travis'), moderately sweet ('Viola' and 'Martina') and non-sweet ('Ninetynine'). The average AIS contents were 81, 77, 79, 85, 66, and 76% for 'Martina', 'Miguela', 'Ninety-nine', 'Viola', 'Gem' and 'Travis', respectively. Scanning electron micrograph (SEM) indicated that the average starch granule diameters were 12.9, 15.3, 16.9 and 25.2 |jm for 'Martina', 'Miguela', 'Ninety-nine' and 'Viola', respectively. In addition, all of the sweet potato starch granules had both spherical and polygonal granules. The cultivars with greatest change in AIS and maltose content (raw vs. baked) were 'Gem', the sweetest, and 'Travis'.  Correlation between sucrose index (SI) and AIS for baked samples was 0.956; for AIS and sweetness, correlation was -0.823. A similar correlation between the AIS and maltose was obtained for the data from the three harvests (-0.8493).  Fifty volatile organic compounds of baked sweet potatoes were trapped in cold methylene chloride. The predominant volátiles were hexanal, 3-pente-2-ol, and isoledene. Other sweet aromas detected were 2,4-decadienal, 2-pentyl furan, benzaldehyde, 4-methyl-4-hydroxy-2-pentanone, and benzene acetaldehyde. The great differences in relative concentrations of volátiles among cultivars seem to be related to the synthesis of maltose and the content of AIS.