There was an obvious decrease in caffeic acid derivatives during the boiling of cube-shaped blocks of sweet potatoes. They also decreased in a mixture of freeze-dried sweet-potato powder and water maintained at room temperature. Ascorbic acid prevented the decrease, supporting the occurrence of an enzyme reaction with polyphenol oxidase (PPO). 5-O-Caffeoylquinic acid (5-CQA, "3-O-caffeoylquinic acid" as a trivial name) and 3,5-di-O-caffeoylquinic acid (3,5-CQA), major phenolic compounds of sweet potato, did not change when they were separately heated in boiling water. When the mixture of powdered sweet potato and water was heated at 100 degrees C, there was only a negligible decrease in the total amount of phenolic compounds, and portions of 5-CQA and 3,5-CQA were found to be isomerized to 3-CQA, 4-CQA, 3,4-CQA, and 4,5-CQA. The content and composition of the phenolic compounds in sweet potatoes differed between fresh and long-stored ones, as did their response to heating.

Xanthone compounds in mangosteen (Garcinia mangostana Linn.) fruit have been reported to have biological activities including antioxidative and anti-inflammatory effects, and the major xanthone compounds in mangosteen are α-mangostin and γ-mangostin. The objectives of this research were to quantify and qualify the major xanthones in each part of the mangosteen fruit with and without yellow gum from the point of view of effective utilization of agricultural product. Quantitative evaluation revealed that yellow gum had extremely high amounts of α-mangostin and γ-mangostin (382.2 and 144.9 mg/g on a wet basis, respectively) followed by pericarp and aril. In mangosteen fruit with yellow gum inside, xanthones seemed to have shifted from the pericarp and to have concentrated in a gum on the surface of aril, and there was almost no difference between the amounts of α-mangostin and γ-mangostin in whole fruits with and without yellow gum. Pericarp and yellow gum showed much higher radical-scavenging activity and ferric reducing antioxidant potential than the aril.

Changes in the concentration of major phenolic compounds that occurred during growing, storing and processing of yacon (Smallanthus sonchifolius) were investigated from the viewpoint of e#ective usage of the functional ingredients in yacon.

No abstract

After saut6ing or frying onions as a first procedure in making onion soup, major onion antioxidants (quercetin 4'-glucoside and quercetin 3,4'-diglucoside) remained mostly intact. In the onion soup prepared with saut6ed onions, the quantity of flavonoids remained high, but in the onion soup prepared with fried onions, a part of them was changed during cooking. The heating stability of these flavonoids was investigated through simple boiling and oven heating of these compounds. Major onion antioxidants were quite stable in a simple cooking model of boiling and oven heating at 100'C but considerably degraded in that of oven heating at 200'C. DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activity of saut6ed onions was similar to that of raw onions, and fried onions exhibited much higher activity based on equivalent amounts of raw onion. Fried onions had much higher browning degree than saut6ed onions, and the browning substance was found to contribute to the radical scavenging activity. The onion soup prepared with saut6ed onions had DPPH radical scavenging activity similar to plain saut6ed onions, but the onion soup prepared with fried onions had much lower activity than fried onions alone.