Table 4 Variance analysis of the established regression equation
| Source of variance | Sum of square of deviations | Degrees of freedom | F | Prob > F |
| X1 | 47,000.08 | 1 | 8.18 | 0.012 6 |
| X2 | 34,347.00 | 1 | 5.98 | 0.028 3 |
| X3 | 16,576.33 | 1 | 2.88 | 0.111 5 |
| X4 | 444.08 | 1 | 0.08 | 0.785 1 |
| X12 | 576.00 | 1 | 0.10 | 0.756 2 |
| X22 | 22,350.25 | 1 | 3.89 | 0.068 7 |
| X32 | 3,249.00 | 1 | 0.57 | 0.464 5 |
| X42 | 9,120.25 | 1 | 1.59 | 0.228 3 |
| X1X2 | 16,002.25 | 1 | 2.79 | 0.117 3 |
| X1X3 | 4,489.00 | 1 | 0.78 | 0.391 7 |
| X1X4 | 188,000.00 | 1 | 32.77 | < 0.000 1 |
| X2X3 | 11,859.08 | 1 | 2.06 | 0.172 8 |
| X2X4 | 5,271.73 | 1 | 0.92 | 0.354 4 |
| X3X4 | 37,105.30 | 1 | 6.46 | 0.023 5 |
| Model | 356,000.00 | 14 | 4.43 | 0.004 4 |
| Error term | 80,440.28 | 14 | | |
| Lack of fit | 71,697.08 | 10 | 3.28 | 0.131 8 |
| Pure error | 8,743.20 | 4 | | |
| Cor total | 437,000.00 | 28 | | |
| r2=0.9157 | radj2 =0.9315 | CV=1.03 | | |
SBH, sheep bone hydrolysate.
X1, X2, X3, and X4 were 4 factors affecting SBH Lactobacillus helveticus fermentation, which represented fermenting temperature, initial pH of SBH, fermenting time and inoculation amount, respectively. X1X2 indicated the interaction between the factor X1 and X2, so were X1X4, X2X3, X2X4, and X3X4.