Serum Protein Aggregates in the High-Heated Milk and Their Gelation Properties in Rennet-Induced Milk Gel

Figures & data

FIGURE 1 Effect of heating temperature and time on the protein aggregation in milk serum. The typical elution profiles from 40 to 140 min were used for observation. The heated milk was simplified as temperature/time. Raw milk (RM) in all groups was for comparison. mAU: milli-absorbance units. Upward arrow points to the whey proteins, and downward arrow points to the protein aggregates.

FIGURE 2 SDS-PAGE analysis of the SEC fractions from (A) RM, and from (B) the heated milk. Lane 1, the standard proteins (kDa). Lanes 2–7 were from 53–56, 65–68, 77–80, 85–88, 105–108, and 113–116 min of SEC elution, respectively.

FIGURE 3 The typical profiles of multimodal size distribution of whey proteins and milk protein aggregates in milk serum.

TABLE 1 Effects of heat treatment on the textural variables in the undisturbed gel

Treatment	Textural variable
	Har (g)	Adh (g.s)	Spr	Coh	Gum (g)	Che (g)	Res
RM	170.59^a	197.57^a	0.903^a	0.349^ab	59.47^a	53.67^a	0.037^ab
70/2	118.08^b	160.40^bc	0.814^bcd	0.350^ab	32.83^b	30.79^b	0.044^bc
70/5	96.91^c	158.58^bc	0.817^bc	0.339^a	29.00^bc	24.58^c	0.043^bc
70/8	87.10^d	161.39^bc	0.808^cde	0.336^a	25.90^cd	20.91^cd	0.039^ab
80/2	70.20^e	162.76^b	0.791^ef	0.329^a	23.07^de	18.23^de	0.032^d
80/5	56.60^f	137.58^bcd	0.788^f	0.373^b	21.11^de	16.64^e	0.027^d
80/8	49.92^fg	118.49^d	0.814^bcd	0.406^cd	20.27^e	16.49^e	0.051^c
90/2	49.97^fg	133.82^cd	0.798^def	0.373^b	18.63^e	14.87^e	0.037^ab
90/5	49.03^fg	127.87^d	0.807^cde	0.381^bc	18.67^e	15.06^e	0.041^b
90/8	44.57^g	113.36^d	0.832^b	0.431^d	19.22^e	15.98^e	0.050^c
Effect:
Temperature		***	***	***	***	***	NS
Time	***	***	***	*	***	***	*
Time × temperature	***	***	***	***	***	***	***

The results with the same superscript letters in each column were not significantly different (p > 0.05). ***p < 0.001; *p < 0.05; NS: not significant. The heated milk was simplified as temperature/time. RM: raw milk; Har: hardness; Adh: adhesiveness; Spr: springiness; Coh: cohesiveness; Gum: gumminess; Che: chewiness; and Res: resilience.

TABLE 2 Effects of heat treatment on the textural variables in the stirred gel

Treatment	Textural variable
	Har (g)	Adh (g.s)	Spr	Coh	Gum (g)	Che (g)	Res
RM	22.08^a	104.43^a	0.803^a	0.695^a	15.33^a	12.34^a	0.029^a
70/2	16.52^b	63.50^b	0.851^b	0.777^b	13.19^b	10.91^b	0.190^b
70/5	16.15^bc	59.32^bc	0.854^b	0.781^b	12.65^bc	10.80^bc	0.188^b
70/8	15.21^cd	59.73^bc	0.848^b	0.771^b	11.88^cde	10.03^de	0.222^bc
80/2	16.01^bc	52.63^bcd	0.865^bc	0.793^bc	12.33^bcd	10.50^bcd	0.251^c
80/5	15.08^cd	48.79^cd	0.876^bc	0.828^def	11.96^cde	10.39^cd	0.335^d
80/8	14.19^de	41.17^de	0.876^bc	0.843^f	11.95^cde	10.52^bcd	0.365^de
90/2	14.27^de	41.81^de	0.890^c	0.806^cd	11.50^de	10.22^d	0.325^d
90/5	13.59^e	48.19^cd	0.871^bc	0.813^cde	11.08^e	9.66^e	0.364^de
90/8	13.85^e	30.35^e	0.885^c	0.832^ef	11.62^de	10.30^cd	0.395^e
Effect:
Temperature	***	***	***	***	***	***	***
Time	***	***	*	***	***	***	*
Time×temperature	***	***	***	***	***	***	***

The results with the same superscript letters in each column were not significantly different (p > 0.05). ***p < 0.001; *p < 0.05. The heated milk was simplified as temperature/time; RM: raw milk. Har: hardness; Adh: adhesiveness; Spr: springiness; Coh: cohesiveness; Gum: gumminess; Che: chewiness; and Res: resilience.

FIGURE 4 Biplot of PCA (PC1 and PC2) from the textural variables for the undisturbed gels.

FIGURE 5 Plots of PCA from the textural variables for the stirred gels. (A) Conversion of the textural variables to the principle component; (B) Differences among the heat treatments identified by the principle component.

FIGURE 6 Effect of heating temperature and time on WHC and CCY of rennet gel.

FIGURE 7 Effect of heat treatment (70, 80, and 90ºC for 5 min) on the microstructure of rennet gels from heated milk. The heated milk was simplified as temperature/time.