Effects of Some Soy Products on Rheological, Functional and Sensory Propertıes of Milk Chocolate

Abstract

Today, different types of diets and food products are of great interest. Soy chocolate, which is one of these products, is produced in various countries and there is not much research on the effect of the soy products on chocolate rheology and functionality. Rheology defines the flow properties of molten chocolate which is important parameter for producers and antioxidant capacity attracts the interest of consumer. In this study, two different soy products (soy milk powder and soy protein isolate) and two different milk products (whole and skimmed milk powder) were used to produce laboratory-scale milk chocolates with different conching times (2, 4, 6 hours). Rheological and functional properties of chocolates were investigated. Soymilk powder was produced as laboratory-scale and proximate and chemical analysis was performed. Physical properties of powder ingredients used in chocolate production were determined and functional properties of soy products were defined. Soymilk powder was found to have 44.43 % protein, 18.14 % fat and 6.06 % ash content. According to the chemical analysis, inactivation of 99.1 % for LOX-1, 100 % for LOX-3 and 98.5 % for trypsin inhibitors was achieved by heat treatment of 98 °C for 20 minutes. Casson, Herschel-Bulkley and Bingham models were used to define the rheology of molten chocolates. According to the results, rheological behaviors of the chocolates were compatible with all models (R2> 0.99). Apparent viscosities of chocolates were determined at constant shear rate (50 s-1) and SoMC and WMC samples had lower viscosity values due to their fat content other than cocoa butter. According to the Casson model, these samples were found to have apparent viscosity values of 2.199 and 2.174 Pa.s respectively, after 6 hours of conching. The highest apparent viscosity value (4.430 Pa.s) was obtained by Herschel-Bulkley model in SPC2 samples, while the lowest apparent viscosity (1.854 Pa.s) was obtained by Casson model in WMC4 samples. According to the particle size distribution analysis, the 2 hour conched chocolates had a larger particle size than the 6 hour conched samples. All chocolates had a lower particle size at the end of the conching process, even though no linear decrease was observed with the increase of the conching time. This reduction in size is thought to occur in powder products added to chocolates. D90 values were obtained as 35.70 µm for SMC6 samples, 25.55 µm for WMC6 samples, 24.30 µm for SoMC6 samples and 60.35 µm SPC6 samples. Although SMC and SPC samples showed a significant reduction in particle size by concing, the desired particle size (<30 µm) was not obtained by 6 hours conching process. For this reason, it is recommended to extend the conching times for SMC and SPC chocolates in terms of particle size. The specific surface area data increased with increasing time of the conching. WMC6 samples had 1401 m2/kg specific surface area, which was the highest value among the samples, while SPC2 samples had the lowest value with 746 m2/kg. The yield stress, particle size and texture of chocolates are known to be related. It was observed that the chocolates snap more easily and texture becomes mellow with decreasing particle size.

Polymorphic structure was determined by X-ray diffractometer and sensory analysis was performed in order to evaluate the quality of chocolates. The analysis results showed that the polymorphic structure of all chocolates were in the desired β crystal form. Sensory analyzes showed that there was no statistically significant difference (P>0.05) in terms of after taste, appearance, flavour, odor and texture of the chocolates. This shows that soy chocolates are as much appreciated as milk chocolates. Functionality of chocolates was evaluated in terms of total phenolic content and total antioxidant capacity. The antioxidant capacities were determined by ABTS, DPPH and CUPRAC methods. These methods were carried out by the QUENCHER procedure, which did not require any extraction step. The results were significantly higher than the literature data. According to Total Phenolic Content (TPC) analysis, SPC4 had the lowest value with 80.10 mg GAE/g dry sample and, and SoMC2 had the highest value with 129.33 mg GAE/g dry sample. Among the antioxidant capacity methods, the highest results were obtained by ABTS method as 6.79 mM Trolox/g dry sample for SoMC4 samples while the lowest results were obtained by DPPH method as 4.96 mM Trolox/g dry sample for SPC2 samples. It was observed that SoMC samples had the highest antioxidant capacity and SMC samples had the highest total phenolic content. This shows that soy-ingredients has an increasing effect on the amount of total phenolics and antioxidant capacity but the phenolics in soy are sensitive to the process. It is thought that high antioxidant content is caused by isoflovans in soy. SPC samples showed the lowest antioxidant activity and total phenolic content. This may be due to the fact that the proteins in soy mask the phenolic substances and antioxidant character.

In conclusion, although soy protein isolate provides high protein contribution in soy-chocolate, soymilk powder is recommended to be used in chocolate in terms of rheology and functionality of the product.