Beneficial Oxidation Reactions in Foods

1. Beneficial Oxidation Reactions in Foods Zeynep Sevimli Yurttas 4/10/2014

2. Oxidation • Oxidation reactions occur when food is exposed to oxygen in the air. • Oxidation of food is a detrimental process causing loss of quality and nutritional value as well as changes in chemical composition. • Oxidation of fats and oils causes rancidity, in fruits and vegetables, it causes the formation of compounds which discolor the fruit or vegetable. http://www.understandingfoodadditives.org/pages/ch2p8-1.htm

3. Polyphenol oxidase (PPO) is a generic term for the group of enzymes that catalyze the oxidation of phenolic compounds to yield brown color on cut surfaces of fruits and vegetables. • Controlled browning is often used to develop desirable color, flavor, and odor properties in foods. • PPO activity is desirable in processing of prunes , black raisins, black figs, zapote, tea, coffee, and cocoa. • Maillard products are desirable in the color and flavor development of coffee and bread. Whitaker, J.R., and Lee, C. Y.1995. Recent Advances in Chemistry of Enzymatic Browning An Overview Friedman, M. 1996. Food Browning and Its Prevention: An Overview.

4. Tea • Withering-an artificial atmosphere with controlled humidity is maintained for leaf senescence to take place. • Maceration/rolling- to undertake cell rupture carried out in a rolling machine where progressive disintegration of cellular organelles takes place.  • Oxidation-the main step in the tea production since color and flavor development take place in this step. Fermentation term is mostly used instead of oxidation. • Drying (firing)- enzymatic activities are stopped. http://tea.health-tips-diseases.com/2008/11/tea-withering.html

5. Color and flavor development • Degradation of carotenoids during withering and fermentation yields to important flavor in high quality tea compounds. • Conversion of chlorophylls to pheophytins during fermentation and firing contributes to black tea appearance. • Total catechin content decrease during withering. Tomlins, K.I., and Mashingaidze, A. 1997. Influence of withering, including leaf handling, on the manufacturing and quality of black teas-a review.

6. Catechin+PPO-theaflavin (TF) and low molecular weight thearubigins (TR). • Catechin+PO-high molecular weight TRs • TF-high at the beginning of the oxidation but decreases by time • TR-low at the beginning of the oxidation but increases by time • TF- bright, brisk, thin • TR-less brightness and briskness but improved body Tomlins, K.I., and Mashingaidze, A. 1997. Influence of withering, including leaf handling, on the manufacturing and quality of black teas-a review. TC Ministry of Education. Food Technology. Oxidation in Tea. 2010. (Turkish)

7. http://www.teavana.com/tea-info/how-tea-is-made

8. Raisins • Browning occurs because of enzymatic and non-enzymatic browning reactions initiated cell breakdown from cell dehydration. • When cell integrity is lost, PPO reacts with the phenolic compound (caftaric acid). • Most of the PPO activity is found in plastid in the skin and in the seeds or seed traces. That’s why browning starts at the periphery and the center of the berry. • High temperatures and slower drying increase browning while rapid drying at cooler temperatures concentrates sugars that inhibit PPO activity and tends to maintain cellular integrity. Christensen, L.P., and Peacock W.L. The Raisin Drying Process.

9. In order to accelerate drying of the raisins, fruit dipping mixtures are used. Food grade potassium carbonate and ethyl esters of fatty acids are combined in unheated water (cold dip). • Light coloration is optimized by cold dip and rack drying at ambient temperatures. • Low-maturity grapes that ripen in a shaded part of the canopy retain more chlorophyll. When this type of grape is dried in the shade, the raisin has green color. If it dried in the dark, even more green and lighter color remains. Christensen, L.P., and Peacock W.L. The Raisin Drying Process.

10. Coffee • Picking-Processing-Milling-Roasting-Grinding-Brewing • Only during roasting (210°C- 240°C) complex aroma of coffee is formed by pyrolysis, Stecker degradation, and Maillard reaction. • In the initial phase- free water evaporates. • @130°C, sucrose caramelizes, and the seeds begin to brown and swell. • >160°C the seeds become light brown and aroma formation begins. Farah, A. Coffee Constituents. IFT Press Book.

11. Non volatile compounds: • Water, carbohydrates and fiber, proteins and free amino acids, lipids, minerals, organic acids, chlorogenic acids, trigonelline, and caffeine. • Volatile compounds: • Appx~100 different volatile compounds • Most abundantly alcohols, esters, hydrocarbons, and aldehydes. Farah, A. Coffee Constituents. IFT Press Book.

12. http://en.wikipedia.org/wiki/Coffee_roasting

13. http://en.wikipedia.org/wiki/Coffee_roasting

14. Bread • Bread flavor and appearance is a key factor that affects consumer acceptance. • Crust coloring during baking results from results from caramelization of sugars, and from the Maillard reactions between reducing sugars and amino acids. • Baking evaporates the moisture from the surface of the bread, causing caramelization and Mailard reactions to occur. • Baking at lower temperatures for longer times and adding steam at the start of the process enhance crust development. • Steam changes the crust color from yellow-brown to dark brown-reddish by gelatinizing more of the starch so that it becomes dextrinizedlater in baking and is available for Maillard reactions. Lallemand Baking Update. Bread Flavor

15. Questions?