Table 2. In vitro gas production characteristics and methane emission of experimental diets incubated in buffered rumen fluid

Items	Treatments				SEM	p-value1)
	No-citric acid		Citric acid
	No-heat (SBM)	Heat (HSBM)	No-heat (CSBM)	Heat (HCSBM)		Heat	CA	H×C
Gas production (mL/g DM)
3 h	55.9bc	51.7c	65.7a	59.0b	1.77	0.007	< 0.001	0.471
6 h	106b	97.9c	118a	97.6c	2.17	< 0.001	0.014	0.011
9 h	148b	136c	160a	128d	2.63	< 0.001	0.568	0.002
12 h	185b	169c	194a	151d	2.90	< 0.001	0.136	< 0.001
24 h	260a	234b	264a	214c	1.84	< 0.001	< 0.001	< 0.001
Methane (%)	11.7a	11.3b	10.8c	10.6c	0.11	0.003	< 0.001	0.793
Methane (mL/g DM)	30.3a	26.5c	28.6b	22.6d	0.28	< 0.001	< 0.001	< 0.001
Fitted parameters of gas2)
Vmax	299a	282b	290a	246c	5.00	< 0.001	< 0.001	< 0.001
Kg	0.076ab	0.071b	0.084a	0.082a	0.0034	0.013	< 0.001	0.492

CA, effect of citric acid addition; H×C, interaction.
V_max, theoretical maximum gas production (mL/g DM); K_g, fractional rate of gas production (h⁻¹)
Values within a row with different superscripts differ significantly at p < 0.05.
SBM, untreated soybean meal; HSBM, heat-treated soybean meal; CSBM, citric acid-treated soybean meal; HCSBM, heat and citric acid-treated soybean meal; DM, dry matter;