Light Effects on Soy Oil and Soymilk Influence Oxidation, Product Quality, and Packaging Decisions

Abstract

The primary goal of this research was to evaluate the effects of light on soymilk, including the oil component. Soybean oil with added chlorophyll a (0, 1, and 2μg/ml), a photosensitizer, was exposed to light (no light [control], broad-spectrum light) and narrow-band wavelengths (430nm, 450nm, and 660nm] for 4h. Chlorophyll completely degraded under broad-spectrum light and 430nm treatments; 64% degradation occurred at 660nm. Oil with chlorophyll addition resulted in significantly higher peroxide values and malondialdehyde concentrations with light exposure to broad spectrum and 430nm wavelengths. Light at 430 and 660 nm degraded chlorophyll and increased risk of oxidation in soybean oil. Soymilk contains low concentrations of chlorophyll, the photosensitizer riboflavin, as well as highly susceptible oxidizable substrates from the soy oil. Soymilk (1% fat from soybean oil) was packaged under a positive flow hood into 5 high density polyethylene (HDPE) packages and stored for 36 days at 4°C under fluorescent lighting (1122 lux ± 439 lux). Control packaging had no light protective additive (LPA; positive (foil-wrapped) and negative control) and the experimental packaging treatments had three levels of LPA (low, medium, high). Chemical and sensory analyses to measure oxidation changes were completed on the product at days, 1, 4, 8, 15, 22, 29, and 36. HDPE packages with high LPA protected the sensory quality of the product as well as the positive control (foil-wrapped) packages for a minimum of 15 days. High-LPA HDPE protected soymilk for 29 days from degradation of riboflavin and limited development of aldehyde end-products associated with photooxidation. Soymilk was treated with food grade TiO2 at levels of 0, 0.5, and 1.0% by weight. TiO2 significantly whitened the product as demonstrated by L* values. TiO2-treated soymilks resulted in significantly improved hedonic scores for appearance, smell, taste, mouthfeel, and aftertaste compared to control soymilk. However, in a second experiment, overall acceptability of TiO2-treated soymilk, at additions of 0.1%, 0.3%, and 0.5% TiO2, was not higher than control soy milk.