The effect of induced yellowing on the physicochemical properties of specialty rice.
BACKGROUND
Postharvest yellowing (PHY) of rice kernels can be a major problem in the rice industry. This is especially true with high-valued specialty rice, because profit loss will be greater. The objective of this work was to determine whether a significant change occurs in the physicochemical properties (apparent amylose and protein concentrations, viscosity profile and gelatinisation temperature) as a result of induced PHY.


RESULTS
In this study, four specialty rices (Basmati, Jasmine, Arborio and Sushi) were yellowed using a laboratory method. PHY increased apparent amylose concentration. It also significantly increased onset and peak gelatinisation temperatures. However, peak, breakdown and setback Rapid ViscoAnalyzer viscosities were decreased by PHY. Trough viscosity for Basmati and Jasmine decreased, whereas it increased for Arborio. Moisture and protein concentrations were unchanged by the yellowing process. Attempts to rehydrate the kernels after induced PHY caused them to fracture, thus making them unsuitable for their intended purpose.


CONCLUSIONS
This study indicates that rice that has been subjected to PHY shows a reduction not only in appearance but also in cooking and processing quality, decreasing its value. However, the changes differed for each rice type, with Jasmine being affected the least.
USDA-ARS, Dale Bumpers National Rice Research Center, 2890 Highway 130 E, Stuttgart, AR 72160, USA. rolfe.bryant@ars.usda.gov
Rolfe J
RJ
Bryant
Kathleen M
KM
Yeater
Helen
H
Belefant-Miller
D000688:Amylose / Q000032:analysis; D002152:Calorimetry, Differential Scanning; D055598:Chemical Phenomena; D003116:Color; D004044:Dietary Proteins / Q000032:analysis; D005511:Food Handling; D063427:Food Quality; D005782:Gels; D055595:Mechanical Phenomena; D012275:Oryza / Q000737:chemistry*; D010940:Plant Proteins / Q000032:analysis; D012639:Seeds / Q000737:chemistry*; D013045:Species Specificity; D044366:Transition Temperature; D014481:United States; D014783:Viscosity; D014867:Water / Q000032:analysis
D004044:Dietary Proteins; D005782:Gels; D010940:Plant Proteins; D014867:Water; D000688:Amylose