Effect of Storage and Processing on Soymilk Flavor

Summary
This study compares five soybean varieties (cultivars) for their chemical and physical characteristics affecting their flavor and appearance as well as the effect of storage. While all varieties give similar yield of soymilk, they vary greatly in their protein and fat content, minerals, volatile compound compositions and their physical attributes. The total amount of volatile substances has a direct correlation with the activity of the enzyme lipoxygenase. A significant finding shows that the color and flavor of soymilk changes with the time of storage of the soybean.

Introduction
Soybean products are popular because of their high nutritional value and low cost.  Soymilk is a dairy substitute for people with lactose intolerance, but many are reluctant to buy it because it retains an unpleasant flavor when produced by traditional processing. Although new techniques have been developed to improve the flavor of soymilk, they adversely affect its protein content. Factors such as the cultivar of soybean and the method of storage together influence the quality of soymilk. Some types of alcohols, aldehydes and ketones are responsible for the unpleasant flavor of soymilk. Also, saponins and isoflavones make it bitter. Solid-phase microextraction (SPME) is used to detect even trace amounts of these compounds. Varieties for better food quality are also being bred. This study compares the physicochemical properties of five such varieties, examines their flavor profile and analyzes the effect of storage on the flavor and appearance of soymilk.

Methodology
* The study selected five varieties of soybean for their high protein and low fat content, making them desirable for production of foods and beverages.
* Samples were processed according to previously published procedures to extract enzymes or produce soymilk for chemical analyses.
* One variety of soybeans was stored for 10 months, and analyzed at regular intervals for changes in chemical composition and appearance.

Results
* If the soybean has high protein, then it reflects in the product.
* Physicochemical analysis shows that “Vinton 81” has optimum fat and protein content, lowest viscosity, highest calcium and magnesium and the second-whitest color among all.
* When lipoxygenase (LOX) enzymes digest certain chemicals in soybean, volatile compounds are released producing an unpleasant flavor in soymilk. The study confirms this correlation between the activity of enzymes and amount of volatile compounds in varieties of soybeans.
* Longer storage of the bean used for soymilk production results in worsening color, decreased enzymatic activity and reduced amounts of volatile substances.

Next steps/ Shortcomings
Other varieties of soybeans need to be analyzed to broaden the range of flavors of soy products. This study uses new techniques to eliminate problems faced by previous researchers. Further advances in techniques will improve the accuracy of the analysis. Studying the effects of environmental conditions should be carried out to develop optimal storage conditions for soybeans.

Conclusions
Soybean varieties differ in their nutritional values and in the taste and appearance of soymilk and tofu. This difference may be due to natural factors like the age of the bean and the quality of soil and environment in which they are grown, or due to the period and method of storage. Certain enzymes in soybean produce volatile compounds causing the unpleasant flavor of soymilk, which reduces its market value. Longer storage of soybeans before production of soymilk causes the color of soymilk to deteriorate, but also reduces the activity of the enzymes, reducing the amount of volatile substances produced, thus improving the flavor.

For More Information:
Soybean Variety and Storage Effects on Soymilk Flavor and Quality
Publication Journal: International Journal of Food Science and Technology, 2008
By Allaoua Achouri; Joyce Irene Boye; Food Research and Development Center, St Hyacinthe, QC, Canada

*FYI Living Lab Reports Are Summaries of the Original Research.