Effects of phenolic compounds on texture of candied guava and its cross-linkage with pectin

• Main Authors: Gia-Long Liu, 劉佳容
• Other Authors: Pijen Tasi
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/47437537100393724162

碩士 === 國立屏東科技大學 === 食品科學系 === 93 === Texture plays an important role in vegetable qualities. Generally, fruit slice become soft after been dried. In order to keep the good texture of candied guava, this study was aimed to improve the cross-linkage chance of the phenolic compounds and pectin of guava by addition of phenolic compounds. It becomes possible to enhance cell adhension and decrease cell wall separation by this procedure. Then, the optimum condition including kinds (ferulic acid, gallic acid, catechin, cinnamic acid, caffeic acid, coumaric acid) and concentration (0.5-2 g/L) of phenolic compounds, immersion pH (3-8), temperature (5-45℃) and time (0-60 hr) which affect the formation of ester phenolic between phenolic compounds and cell walls to gain a better stability of texture were chosen. Further investigation on the effects of binding capacity with phenolic compounds and pectin on the hardness of guava slice, was undertaken through a phenolics-pectin model system. We hope to control the texture of guava preserves by modulating ester phenolic formation. Results showed that, the texture of guava slice can be better enhanced at the following phenolic compounds immersion condition: concentration, 0.5 g/L; pH 5; temperature, 25℃ and time, 24 hours. Ferulic acid, gallic acid, caffeic acid exhibited the better effect on the texture, while catechin was the worse. In the phenolics-pectin model system, cross-linkage formation of guava polyphenol and commercial pectin, alkali was used to destroy their binding and HPLC analysis was performed to determine the contents of ester phenolic. Results showed that, cinnamic acid possessed highest amount of ester phenolic and was the most effective in binding with the pectin, followed by caffeic acid, ferulic acid and coumaric acid. Catechin and epicatechin are incapable of binding with pectin. Furthermore, molecular exclusion chromatography was used to purify the complex formed from guava pectin and commercial phenolic compounds, and their binding capacity were calculated. Ferulic acid was found to exhibit the hightest binding capacity, followed by gallic acid, caffeic acid, cinnamic acid, coumaric acid, and catechin. Apparently, the phenolic compounds that contain carboxylic acid group (-COOH) can be involved in the formation of ester phenolic with the pectin of the cell walls. SEM was further used to observe the completeness of cell wall of guava after cross-linkage. The cell wall was maintained more complete for the samples treated with ferulic acid than those treated with catechin, in which the walls were irregular and tended to collapse. Further autofluorescence reaction revealed cross-linkage located around the cell walls. In the pectin fractionation, addition of phenolic compounds that contain carboxylic acid group (-COOH) which lead to the formation of phenolic compounds cross-linkage with the pectin also increase the hard pectin content. On the antioxidant capacity analysis, the total phenol content, vitamin C remaining, DPPH scavenging ability and FRAP reducing power of dried guava slice by addition phenolic compounds after formation cross-linkage was higher than that of the control. The protection and the effectiveness of the remaining antioxidant capacity at 4℃ was better than 25℃ after 8 weeks storage of the product under vacuum package. In conclusion, the phenolic compounds that contain carboxylic acid group (-COOH) can prevent the separation of cell walls through the cross-linkage with pectin, then improve the texture of candied guava, and the acceptance by sensory evaluation as well.