Effect of vacuum and relaxation times on the quality of rice fortified with herbal plant extracts by vacuum impregnation technique

Abstract

Vacuum impregnation is a non-destructive technology, use to introduce external liquid into the structures of food matrices. The aim of this study was to investigate the effect of vacuum and relaxation times on the qualities of roselle (Hibiscus sabdariffa L.) and butterfly pea (Clitoria Ternatea L.) vacuum impregnated rice.  A vacuum pressure of 50 mbar was applied for 10 and 20 min (Vacuum time), following atmospheric pressure restoration for 10 and 20 min (Relaxation time). The result shown that, lightness (L* value) of both herbal plants vacuum impregnated rice reduced with increasing the vacuum and relaxation times. Whereas, the values of water loss, mass fraction of fruit occupied by impregnation liquid (X), sample volume deformation (g) and effective porosity (e_e) were increased as increasing the vacuum and relaxation times. In addition, the impregnated rice treated with 20 min vacuum time and 20 min relaxation time significantly highest antioxidant quality including, total phenolic compounds, total flavonoids, total anthocyanins, DPPH-radical scavenging activity and Ferric reducing antioxidant power (FRAP). The roselle vacuum impregnated rice showed significant higher total flavonoids (483.79 mg Catechin equivalent/100g) and FRAP (55.64 Trolox equivalent/100g) than butterfly pea vacuum impregnated sample (155.09 mg Catechin equivalent/100g and 25.41 Trolox equivalent equivalent/100g, respectively). This study indicated that the longer vacuum and relaxation times were useful for enriching the herbal plant extracts in rice.