Sour soup with beef was cooked by boiling veal meat from Qiandongnan, Guizhou in a mixed sour soup (red sour soup + white sour soup). Single factor experiments and orthogonal array design methods were used to optimize the processing parameters including cooking time, the amount of the sour soup added, the amount of the fruit of Litsea pungens Hemsl added, and tumbling time based on sensory evaluation, moisture content and pH. The results showed that the optimal conditions to achieve the highest sensory score (86.33 points) were as follows: tumbling time 50 min, and adding 3.0 g of the fruit of Litsea pungens Hemsl and 110 mL of the mixed sour soup. The moisture content of the product was (72.41±1.77)%. The pH values of the broth and beef were 4.88 and 4.99, respectively. The brightness (L^*), redness (a^*) and yellowness (b^*) values were 58.81, 9.05 and 10.96, respectively. The soluble solids content (SSC) was (2.67 ± 0.09)%. The broth was rich in free amino acids, umami amino acids being the major ones (0.0785 mg/mL), followed by sweet amino acids and bitter amino acids. The microbiological quality of the product complied with the national food safety standards. The optimized sour soup with beef was red in color, and had a tender texture, a rich aroma, and moderate sour and salty tastes.

The effect of cooking beef in sour soup (red sour soup, white sour soup, or their mixture) on the sensory quality, pH, color, moisture content, cooking loss percentage, tenderness and texture properties were studied. The volatile components of beef in sour soup were analyzed by gas chromatography-ion mobility spectrometry (GC-IMS) to evaluate the overall quality. The results showed that compared with the control group (cooked in water), sour soup significantly improved the tenderness and moisture content, reduced the cooking loss percentage, hardness, chewability and viscosity, and improved the color and sensory quality of beef. The cooking loss percentage, hardness, adhesiveness and chewability of beef in white sour soup were the lowest and the moisture content was the highest followed by beef in red sour soup. There was no significant difference in beef tenderness between red sour soup and white sour soup, while red sour soup significantly improved the redness and yellowness of beef. The mixed sour soup was more effective in enhancing beef brightness. The content of lactic acid in red and white sour soup (23.27 and 4.90 mg/mL, respectively) higher than that in their mixture. A total of 55 volatile flavor compounds were detected across the three groups of beef in sour soup and there were significant differences in volatile components among them. Compared with the control group, the relative content of aldehydes was reduced and the relative content of lipids was increased by cooking beef in sour soup. The relative contents of lipids, acids and ketones in beef in red sour soup were relatively high, and the relative content of aldehydes was low. Beef in red sour soup scored highest in sensory evaluation, exhibiting the best taste and flavor. The major characteristic flavor substances of beef in red sour soup were ethyl lactate, butyral, acetic acid, benzaldehyde (dimmer), and 2-methylpropionic acid. The major characteristic flavor substances of beef in white sour soup were propanol, 2-butanone, 3-pentanone and propionic acid. The major characteristic flavor substances of beef in the mixed sour soup were ketones. The content of some flavor substances increased in beef in sour soup compared to the control group, contributing to the characteristic flavor of beef in sour soup. In summary, beef in red sour soup was rich in volatile flavor components, and had a higher sensory score and better overall quality. Red sour soup was a suitable choice for making beef in sour soup.