Soymilk flavor

Feng, Y.-W. and Acree, T.E. 2001. Processing modulation of soymilk flavor chemistry. In Aroma Active Compounds in Foods (G.R. Takeoka, M. Guntert, and K.-H. Engel, eds.) pp. 251-264. American Chemical Society, Washington, D.C. 

Matsuura, M., Obata, A., and Fukushima, D. 1989. Objectionable flavor of soymilk developed during the soaking of soybeans and its control. J. Food Sci. 54 602-605... 

Soymilk. In the traditional process, soybeans are soaked in water, ground into a slurry, cooked, and filtered to remove the insoluble cell wall and hull fractions. A number of modifications have been made in the process since the 1960s, including heat treatment before or during grinding to inactivate the enzyme lipoxygenase and thus prevent formation of grassy and beany flavors. The soymilks are available in plain and flavored, eg, vanilla and chocolate, forms (90,91). 

In addition to the products of lipid oxidation, methanethiol and dimethyl trisulfide were shown to contribute to the complex odor characteristic of soy protein products such as SPI and soy protein concentrates (Boatright Lei, 2000 Lei Boatright, 2001) and soymilk (Lozano et al., 2007) at concentrations comparable to hexanal. Since the threshold in water for methanethiol was reported at 0.02 ppb compared to hexanal at 4.5 ppb (MacLeod C Ames, 1988), these sulfur compounds are intense flavor notes in soy protein products. Lei and Boatright (2007) provided evidence that methanethiol is generated in aqueous slurries of SPI or defatted soy flake from methionine by a free radical mechanism involving manganese, sulfite, and... 

In contrast, modern soymilk, sometimes referred to as soy beverage or soy drink, is produced by using modern technology and equipment. Known as dou ru or dou nai in Chinese, these products have a relatively bland taste with their own commercial identity and standards. In most cases, they are flavored, sweetened and/or fortified for better taste and better nutrition, and packed for longer shelf-life, when compared with traditional soymilk. Sold as a milk substitute or a healthful soft drink, soymilk is particularly important to infants who suffer from malnutrition due to absence of dairy milk supply in certain regions of the world or who suffer from allergies and diseases associated with dairy milk consumption. Thus, for the past several decades. 

A steam-infusion cooking process, known as hydrothermal cooking (HTC), was developed to produce soymilk continuously from ground full-fat soy flour (Johnson et al., 1981). It was claimed that soymilk processed by the HTC process had less beany flavors because of the much shorter time for lipoxygenase to be active and because steam flashing stripped volatiles. The process also increased recovery of dry matter and protein in the soymilk. 

Recently, a high-pressure procedure was found to inactivate lipoxygenase in soymilk. The beany flavor of the final product was not evaluated in the study (Wang et al., 2008). 

Since lipoxygenase activity is a major cause of beany flavor formation during processing of soy products, an alternative strategy to control beany flavor in soymilk... 

Once off-flavors are formed, the only way to eliminate them is to strip off the responsible volatile compounds. To accomplish this task, a deodorization process is available for soymilk production. The process involves passing cooked soymilk through a vacuum pan at high temperature and high vacuum. The method is fairly complex and expensive, and is used in conjunction with other techniques by a number of large soymilk manufacturers. 

During yuba production, protein and lipid contents in the film successively formed decrease, while the carbohydrate and ash contents gradually increase. Therefore, the first several pieces of yuba to be lifted off the heated soymilk are considered premium products. They have creamy white color, mild flavor, and less sweet taste. They stay relatively soft and flexible even when dried. The later formed products are regarded as second rate, because they become sweeter with a faintly reddish tinge, lack internal cohesiveness, tear more easily, and become brittle upon drying. 

Soymilk resembles dairy milk in composition, so it can also be fermented by lactic acid producing bacteria to produce such products as sour soymilk and soy yogurt. Fermentation of soymilk offers not only a means of preserving soymilk but also a possibility for modifying or improving its flavor and texture so that it becomes more acceptable to Westerners. It also leads to new types of soy products, which resemble cultured dairy products but are at a low cost. 

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