Why soymilk powder is hard to dissolve in water?


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  1. Ricebowl Food Expert
    May 27, 2019 at 10:34 am

    Soymilk powder is manufactured from liquid soymilk that is extracted from whole or dehulled soybean, by concentrating and spray-drying (Gupta, 2014). Spray drying is widely used as the commercial method to dry milk due to its short heat contact time and high rate of evaporation that produced high quality product with relatively low cost (Jinapong et al., 2008).

    Solubility is an important feature for powder beverage products and it is a measure of the final condition to which the constituents of the powder can be brought into solution or stable suspension (Sharma et al., 2012).

    Several factors including types of dryer and system of atomization, preheat treatment of the milk, total solids, storage time and temperature have been reported to affect solubility (Ishiwu et al., 2014). Reports have shown that the quality and functionality of the soymilk powder are reliant on factors such as protein concentrations in powder and spray drying conditions. High protein content in a rehydrated soy powder leads to the formation of a precipitate. The more denatured the protein, the poorer its solubility (Syll et al., 2013).

    According to Ishiwu et al. (2014), soy milk spray dried at 204°C had solubility of 48% and 78% when reconstitute at water temperatures of 40°C and 80°C respectively while the soy milk powder spray dried at 260°C exhibited lower solubility of 38.46% at 40°C, greatest at 45.01% at 60°C and decreased to 38% at 80°C. This could be due to adverse effects of high inlet temperature on the carbohydrate and protein present in the sample of soymilk powder. This in agreement with Syll et al. (2013) that the increase in spray drying temperature resulted in higher values of insolubility index mainly due to denaturation of proteins.

    Increase in wettability increases dispersibility and solubility of powdered products. From their findings, soymilk powder samples took longer time to get wet at lower temperature than at higher temperature of reconstituting water. This is in line with the poor wettability of skim milk powder at water temperature below the melting point of fat because the surface of the particles is always covered by fat, forming a water repellent layer around the dry powder particles (Ishiwu et al., 2014).

    Spray-dried products often have a small particle size (<50 µm) that associated with poor handling and reconstitution properties, for example relatively lower insolubility index (Sulieman et al., 2014). Agglomerates are regarded as the result of two flowing particles or droplets coming together which have coarse and open structures that improve the dispersibility of the powder that will be uniformly wetted in both hot and cold water systems.

    Agglomeration is referred to as instantizing because the rehydration and reconstitution of the food powder is improved (Gaiani et al., 2013). It is a necessary step in producing instant powdered products such as coffee, milk, or cocoa that disperses or dissolves quickly in liquids (water/milk) with a good flowability (Barkouti et al., 2013).

    Addition of certain food additives could facilitate the solubility of powdered products (Sulieman et al., 2014). Cano-Chauca et al. (2005) suggested that maltodextrin was mainly used in the process of spray drying due to its high solubility in water. Filler contains a lot of hydroxyl group that can form hydrogen bonds with water therefore higher maltodextrin concentration will gives better solubility of milk powder (Febrianto et al., 2012). According to Jinapong et al. (2008), fluidised bed agglomeration of spray dried soymilk powder with 10% (w/v) maltodextrin as an aqueous binder solution gave the highest particle size of 260µm and turn out to be the best handling and reconstitution properties.  Agglomeration along with addition of natural surfactants (such as soy lecithin) to powders is commonly used to enhance the wettability of milk powders or powder dispersion in water (Sharma et al., 2012; Castejon et al., 2017).





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