Effect of Cooking Methods on Physical and Sensory Properties, Anthocyanins and Polyphenolic Compounds of Pigmented Rice Grains

Abstract

The objective of this research is to study the effect of three methods of rice cooking on four pigmented rice grains for their physical properities, sensory attributes, amylose content, total anthocyanin content (TAC) and polyphenol content (PC). Steaming cooked black rice (Oryza sativa L. indica) was the most darkness with L* value of 39.63. Steamed Egyptian jasmine white rice had the highest L* value (75.03). Red rice exhibited the lowest hardness in all cooking methods as (112.46, 97.65 and 82.19 N), while black rice possessed the best lowest stickiness in all cooking methods as (5.31, 4.18 and 4.08 N) for boiling, steaming and rice cooker, respectively. Black rice (23.76% amylose) which was classified as intermediate amylose rice (20-25%) before cooking kept intermediate after cooking by rice cooker as (21.56%). It could be seen that waxy rice belongs to moist and sticky rices after cooking as (amylose content 7.24%) was best cooked by boiling method. On the other hand, steamed black rice had the most preferred appearance (8.59), black rice which cooked by rice cooker was scored the highest accepted texture (8.04), while boiled black rice was the most accepted taste (9.04). Steamed Egyptian jasmine white rice was the highest accepted regarding aroma (8.69). Black rice contained the highest amount of naturally occurring anthocyanin content (TAC) as (235.68 – 290.78 mg/100 gm) after cooking, These findings indicate that cooking rice by steaming is the preferable cooking method where it caused the lowest losses in anthocyanin content. Polyphenol content (PC) differed significantly among the varieties. It was clear that all the methods of cooking caused a significant decrease in total polyphenols. It was found that cooking rice by steaming also was the best way for decreasing losses of polyphenol content for all rice varieties, Egyptian jasmine white rice, red, black and waxy rice as (25.54, 47.61, 71.22 and 29.34 mg GAE/g), respectively. The present study can guide in using steaming which was found to provide the most quality attributes for rice cooking in terms of physical quality, sensory properties with enhanced antioxidant compounds.