Combination Of Stabilizers And Stabilization Mechanism In Acidified Milk Drinks

Casein precipitation and whey separation under acidified conditions are key issues on the production and research of acidified milk drinks(AMD) that trouble producers very much. It is essential to use stabilizers in production process. Stabilizers have a direct effect on both stability and sensory quality of final products. In addition, the production cost is also a practical problem that must be taken into accounted. The aim of this work is to solve problems about insufficient stabilization of a single stabilizer, unsatisfying taste and high cost of AMD by studying combination of stabilizers. We expect to get excellent combined formulations of stabilizers with good stability, satisfying mouth feel and low cost finally. This work will provide a theoretical basis for further study on the combination of stabilizers.This work mainly investigated the stability behavior of sodium carboxymethyl cellulose(CMC), high methyl pectin(HMP) and soybean soluble polysaccharides(SSPS) when they were used alone and combined(CMC-SSPS, HMP-SSPS) on stability of acidified milk drinks. The main stabilization mechanism was also studied. Stability of AMD systems was evaluated based on the changes of sedimentation ratio, viscosity, Zeta-potential, particle size and size distribution of casein micelles. Sensory analysis and storage stability of products were combined to give a comprehensive assessment.Firstly, we studied the stability effect of CMC, HMP and SSPS concentration 1 g L-1~6 g L-1 on AMD when they were used individually. Results showed that sedimentation ratio and particle size were reduced significantly(P<0.05) with the increasing of the CMC, HMP or SSPS concentration, but viscosity and Zeta-potential increased. There was no significant differences in stability of AMD systems when the concentration of stabilizers was up to 4 g L-1. The stability of AMD was increased in the order of SSPS < CMC< HMP when they were used solely.In order to make respective advantages of stabilizers complement each other, the combined effect of stabilizers on the stability of AMD was then studied. CMC and HMP were combined with SSPS respectively at the total concentration of 4 g L-1. The blending ratios were 4:0, 3:1, 1:1, 1:3, 0:4. Compared to individual stabilizers, the blending stabilizers reduced the sedimentation ratio of AMD significantly(P<0.05), diminished the particle size of casein micelles became smaller, made Zeta-potential absolute value kept above 20 m V and the viscosity more suitable. Sensory scores were also increased. Combination of CMC-SSPS=3:1 and HMP-SSPS=1:3 were better than others.In addition, the stabilization mechanism of combined stabilizers in AMD was studied. In contrast to single stabilizer in control groups, we found that the content of soluble protein in combination stabilizers groups was increased significantly(P<0.05). The surface tension of two optimal combination stabilizers groups was decreased to a minimum value of 47.75 m N/m and 46.17 m N /m, respectively. The amount of large casein micelles in combination groups were observed decreased significantly observed by laser confocal microscopy. The maximum wavelength of fluorescence spectroscopy in combination groups shifted to blue area, indicating that the polarity of micro-environment where tryptophan residues located was decreased. Besides, fluorescence intensity of combination groups was also decreased, indicating that the stability of AMD became better.Finally, the storage experiments of AMD were preformed to study the long-time stability. During the storage, the sedimentation ratios of AMD were kept below 2.5%. There was little change in particle size. The sensory scores were all above 70 points. Results of microbiological observation showed that the colony-forming units of aerobic plate count in AMD during storage were far below the specified value 1×104 CFU/m L. And the coliform bacteria was not found, indicating there was no spoilage phenomenon of AMD products. Combination stabilizers kept good stability, sensory quality and microbiological safety of AMD during shelf- life.All the results above suggested that the stability effect of combination stabilizers in AMD was better than that of individual one. And optimal combinations ratio in two combination groups were CMC :SSPS=3:1 and HMP :SSPS=1:3 respectively. They improved the stability of AMD, sensory properties of final products and reduced the cost of stabilizing agent to a certain extent, which provided ideas and options for the research and development of new AMD products.