Nanoparticle protects oil in foods from oxidation, spoilage

December 8, 2009 Brian Wallheimer

WEST LAFAYETTE, Ind. - Using a nanoparticle from corn, a Purdue University scientist has found a way to lengthen the shelf life of many food products and sustain their health benefits.

Yuan Yao, an assistant professor of food science, has successfully modified the phytoglycogen nanoparticle, a starchlike substance that makes up nearly 30 percent of the dry mass of some sweet corn. The modification allows the nanoparticle to attach to oils and emulsify them while also acting as a barrier to oxidation, which causes food to become rancid. His findings were published in the early online version of the Journal of Agricultural and Food Chemistry.

Oxidation destabilizes oil droplets in emulsified food, degrading and changing the chemical structure of the oil and causing it to go bad. This oxidation happens in a wide range of products, shortening their shelf lives.

"This can be widely used in the food industry, cosmetics and nutritional supplements, any system in which the oxidation of lipids is a concern," Yao said. "The shelf life of a product can be low and the quality of the food can become bad because of the oxidation of the lipids."

In fish oils, for example, the lipid oxidation degrades Omega-3 fatty acids, which are essential in infant development and are thought to help with chronic inflammatory and heart diseases in adults.

Yao was able to modify the surface of phytoglycogen nanoparticle to make it behave like an emulsifier, creating phytoglycogen octenyl succinate, or PG-OS. PG-OS is thicker and denser than commonly used emulsifiers, creating a better defense from oxygen, free radical and metal ions, which cause lipid oxidation.

Yao's findings also showed that e-polylysine, a food-grade polypeptide, can be added to the oil droplets to aid in the protection from oxidation. Polylysine is much smaller than the PG-OS nanoparticles, allowing it to fill in the gaps between PG-OS nanoparticles.

According to Yao's study, PG-OS nanoparticles with e-polylysine significantly increased the amount of time it took for oxidation to ruin the oil droplets, in some cases doubling the shelf life of the model product. Shelf life was tested by warming the emulsifiers and checking for chemical reactions that signal oxidation has occurred.

Yao has filed a provisional patent application for the technology. The Whistler Center for Carbohydrate Research in Purdue's Department of Food Science funded the research.

Writer:   Brian Wallheimer, 765-496-2050, bwallhei@purdue.edu

Source: Yuan Yao, 765-494-6317, yao1@purdue.edu

Ag Communications: (765) 494-8415;
Steve Leer, sleer@purdue.edu
Agriculture News Page

ABSTRACT

Phytoglycogen Octenyl Succinate, an Amphiphilic Carbohydrate Nanoparticle, and
ε-Polylysine to Improve Lipid Oxidative Stability of Emulsions

Siqi L. Scheffler, Xue Wang, Lei Huang, Fernanda San-Martin Gonzalez,
and Yuan Yao

Phytoglycogen octenyl succinate (PG-OS) and ε-polylysine (EPL) were used to form oil-in-water emulsions with enhanced lipid oxidative stability. PG-OS is an amphiphilic carbohydrate nanoparticle prepared using octenyl succinate (OS) substitution of phytoglycogen (PG). PG-OS had a dispersed molecular density nearly 20 times that of waxy corn starch octenyl succinate (WCS-OS). Fish oil-in-water emulsions were prepared using PG-OS, WCS-OS, and Tween 20, stored at 55 C for 6 days, and monitored for the accumulation of hydroperoxide and thiobarbituric acid reactive substances (TBARS). The result indicated that PG-OS may lead to high lipid oxidative stability, and that the addition of EPL may further improve the oxidative stability of emulsions. To address the interaction between PG-OS and EPL, zeta-potential was determined for various systems. The results indicated a possible formation of an interfacial complex layer comprising both PG-OS and EPL. This complex layer may provide both physical and electrostatic barriers against pro-oxidative compounds.